Charles County, MD Article VIII Design Criteria

§ 291-61 General.

This section is to offer appropriate guidance to the public for basic water and sewer design criteria and reference to current construction specifications, which shall include those contained within this chapter, the Charles County Standard Specifications for Construction Manual, the Charles County Water and Sewer Detail Manual, the Charles County Plan Preparation Package, the Maryland State Plumbing Code, the Maryland Department of the Environment, the Code of Maryland Regulations (COMAR), Pipeline Design for Water and Wastewater, Recommended Standards for Wastewater Facilities (commonly known as the "Ten States Standards"), Recommended Standards for Water Works (commonly known as the "Ten States Standards") and any other local, state or federal agency governing water and sewer design and/or construction.

§ 291-62 Water mains.

A. General requirements.

(1) Water plans submitted for review and approval to the County will not be required to include the standard details on the plans. The plans, however, must include a table, on the cover sheet, listing by detail number and name all water details which are applicable to the project. In cases where the County has no adopted standard detail for a specific construction method, the engineer must submit a special detail to the County Water and Sewer Engineer for review and approval. Once approved, the special detail shall be placed within the plans with notes in plan and profile on all applicable sheets referring to the special detail.

(2) Lines that serve two or more properties will be dedicated to the County.

B. Demands. The design engineer who is responsible for the extensions of the distribution mains shall follow the guidelines in this manual for the derivation of design flows. The calculation of water demands will usually require extension of the average daily rate for the facility, application of a peaking factor to derive the maximum daily rate, then addition of the fire flow requirement. System losses have been accounted for in the peaking factors. (See Appendix O.[1])

[1] Editor's Note: Said appendix is included as an attachment to this chapter.

C. Hydraulic computations.

(1) General. The hydraulic design of water mains shall be in accordance with Pipeline Design for Water and Wastewater, ASCE, 1992 (or latest edition), and the additional guidelines and criteria in this chapter. Computations shall be submitted for all water designs and shall include average and peak demands, fire demand, and future requirements. Design computations for all components of the water system shall be submitted.

(2) Design flows and residual pressures.

(a) Service connections, distribution mains and transmission mains shall be sized based on the following design flow rates and residual pressures:

[1] Maintain a minimum residual pressure of 20 psi for peak hourly flow and maximum daily flow plus fire flow at ground level anywhere in the system; and

[2] Maintain a minimum residual pressure of 65 psi for average daily flow at the service connection.

(b) In some locations, the main size will be determined by the flow rate required to refill a storage facility which may be more critical than the above requirements or by main sizes shown in the Comprehensive Water and Sewer Plan. (See Appendix O.[2])

[2] Editor's Note: Said appendix is included as an attachment to this chapter.

(3) Flow velocities. Although the flow velocities and direction may vary considerably in distribution mains, there are upper and lower velocity bounds that indicate to the design engineer that design weaknesses may exist.

(a) The following is a useful guideline. Peak flow velocities shall not be greater than seven feet per second.

(4) Hazen-Williams "C" and minor losses.

(a) The total head loss at the point of discharge for design flows shall be the sum of both frictional and minor losses. The elevation difference between the source and discharge point shall be algebraically added to the total head losses.

(b) Head losses for new pipes shall be computed using the nomograph in Appendix P[3] and the following coefficients:

	Type		Pipe Diameter (inches)	Hazen-Williams "C"
	Service Connections
		Copper	3/4 – 3	130
		PVC	3/4 – 4	130
		DIP	3	100
	Distribution Mains
		PVC	4 – 8	120
		PVC	8 – 12	130
		DIP	4 – 8	100
		DIP	10 – 12	110
		DIP	16 – 24	120
	Transmission Mains
		All material	16 – 20	120
		All material	24 and larger	130

[3] Editor's Note: Said appendix is included as an attachment to this chapter.

(c) Minor losses due to fittings and valves shall be included as equivalent lengths of pipe as shown in Appendix Q[4] or as fractional losses in velocity head as described in Pipeline Design for Water and Wastewater, ASCE, 1992 (or latest edition) or other hydraulics texts.

[4] Editor's Note: Said appendix is included as an attachment to this chapter.

D. Distribution mains.

(1) General.

(a) Extensions to distribution mains will normally be on a grid basis with interconnecting nodes at street intersections. Lines are to be "looped" to the maximum extent possible to provide redundancy and to avoid dead ends in the system. If looping cannot be provided in accordance with the County request, then written justification shall be provided to the County for review and approval. Approval of the justification shall be determined on a case-by-case basis.

(b) Ductile iron pipe and restrained joints, in accordance with the County Standard Specifications for Construction Manual and Standard Detail Manual, shall be used for jack and bore carrier pipe.

(c) Water mains terminated for future extension shall have a fire hydrant and valve provided as specified in § 291-62D(8)(b)[3] such valves must be anchored to allow removal of the fire hydrant for extension upon closing.

(d) Flag lot water utilities.

[1] For a two flag lot maximum, service laterals will be provided off of the main and include a curb stop and box or meter vault at the right-of-way or easement line. Water service for each lot shall be located on each side of the driveway. Adequate easements are to be provided on both sides of the water service and must extend outside of the common access easement if necessary. The water service must be constructed in conjunction with the main from the curb stop and box to the building lot and capped closed for future connection. The end of the service should be marked in accordance with the County Standard Detail Manual. Extension of the service as indicated above will prevent problems associated with the construction of the driveway prior to the construction of all water services.

[2] For three or more flag lots, provide an extension of the water main to the last lot and terminate with a valve and fire hydrant. Provide service connections to all adjacent lots, with curb stop and boxes or meter vault located at the easement line. Adequate easements are to be provided on both sides of the water main and services and must extend outside of the common access easement if necessary.

(e) Where water distribution mains are extended to accommodate future development, they shall be extended across the full frontage of the property being served or constructed to the property line of all adjacent properties for future looping or extension.

(2) Residential subdivision (new and existing). The water distribution system for residential areas where fire protection is to be provided shall meet the following criteria:

(a) Maximum length of dead end eight-inch main shall be 1,500 feet.

(b) Dead ends shall be minimized by providing looping wherever practical.

(3) Commercial and industrial. The water distribution mains for commercial and industrial areas where fire protection is to be provided shall meet the following criteria:

(a) Minimum size shall be eight-inch, except for fire hydrant leads of less than 200 feet and service connections.

(b) Maximum length of dead end eight-inch main shall be 800 feet.

(c) Maximum length of dead end ten-inch main shall be 1,200 feet or as approved by County Engineer.

(d) Dead ends shall be minimized by providing looping wherever practical.

(e) Where design flow rates exceed 1,500 gpm, hydraulic computations shall be provided for dead end mains.

(4) Location.

(a) New subdivisions. In new subdivisions, distribution mains shall be located five feet from the centerline of the street right-of-way, generally on the side of the street toward high ground. Distribution mains shall be located within the pavement area wherever possible, no less than two feet from the edge of the existing or proposed gutter pan.

(b) Existing developments (closed section roads). In existing developments with curbs, distribution main location shall generally be the same as in new subdivisions. The location of other existing and proposed utilities shall be fully considered.

(c) Existing developments (open section roads). In existing developments without curbs, distribution mains shall generally be located four feet outside of the edge of pavement, except that the distribution main shall not be located under a future curb. The location of other existing and proposed utilities shall be considered.

(d) Parks and public rights-of-way. Where location of distribution mains would require the removal of or damage to trees within parks or public rights-of-way, design engineers shall obtain approval from the appropriate state or federal agencies for distribution main alignment and trees to be removed.

(e) Easements. All distribution main utility easements widths shall be in accordance with latest plan preparation package. No other utilities or structures will be allowed in the distribution main utility easement without written County approval.

(f) Distribution mains may be designed on a curved alignment to reduce the number of bends. Along curves, the water main may be deflected at each joint within 1/2 the limits established by the manufacturer.

(5) Sizing.

(a) Distribution mains shall be sized to provide the required design flow rate and residual pressures as detailed in § 291-62B and C.

(b) Mains serving fire hydrants and services shall be a minimum of eight inches, except where a six-inch reduction is needed for a terminal hydrant. Place a six-inch-by-eight-inch reducer before the hydrant valve for permanent settings and after the valve for lines to be extended in the future.

(6) Cover.

(a) Normal cover over distribution mains shall be three feet six inches, except at crossings over utilities where a minimum cover of three feet zero inches or a maximum cover of nine feet zero inches, may be allowed.

(b) In new subdivisions, cover shall be measured from the final grade of the street.

(c) In existing roads or unpaved streets, a future profile grade shall be obtained from the County. If such a profile grade is not available, the design engineer shall submit a proposed profile grade for approval by the County. If the future profile grade is at or below the existing grade, cover shall be measured from the future profile grade; if the future profile grade is above the existing grade, cover shall be measured from the existing grade.

(d) In areas outside of existing or planned streets, cover shall be measured from existing grade. The design engineer shall thoroughly investigate, and make suitable allowances for likely changes to existing topography. Such changes include future erosion of stream beds or grading of lots.

(7) Clearance. Clearances between water mains and other utilities shall be measured from outside of pipe to outside of pipe.

(a) General. The following design factors must be considered in providing adequate separation:

[1] Materials and types of joints for water and sewer pipe.

[2] Soil conditions.

[3] Service and branch connection into the water main and sewer line.

[4] Compensating variations in horizontal and vertical separations.

[5] Space for repair and alterations of water and sewer pipes.

[6] Location of manholes.

[7] Disturbance of the bedding of the water mains or other utilities.

(b) Parallel installation. A horizontal distance of at least 10 feet shall separate water mains and sewers mains. The distance shall be measured outside of pipe to outside of pipe. In cases where a ten-foot separation is not practical, deviation may be allowed on a case-by-case basis subject to County and/or state approval, if supported by data from the design engineer. Such deviation may allow a horizontal separation of a minimum of five feet with at least a six-foot vertical clearance or closer installation provided that the sewer main be encased in concrete 10 feet each side of the water main. If horizontal separation is less than 10 feet, then compaction requirements shall conform to the same as with the road right-of-way. This is to protect the interest of the other utility's bedding.

(c) Crossings. Where water mains and sanitary sewers must cross, there shall be a vertical separation of 18 inches between the bottom of the water main and the top of the sanitary sewer. This vertical separation must be maintained horizontally for a distance of 10 feet. The ten-foot distance is to be measured as a perpendicular distance from the sewer to the water line.

(d) Exceptions. When it is impossible to obtain the proper horizontal or vertical separation as stipulated above, both the water and sewer mains shall be constructed of ductile iron pipe. Other types of pipe with equal or greater integrity may be used at the discretion of the County. These installations shall be pressure tested to assure water tightness before backfilling. Where a water main must cross under a sewer pipe, additional protection of the water main shall be provided. The County shall be consulted to discuss the use of double casing or concrete encasement of the sewer and/or water main.

(e) Utilities other than Sanitary Sewer. Water mains shall have a minimum clearance of one foot where crossing utilities other than sanitary sewers.

(8) Appurtenances. Where it is not feasible for distribution mains to be located within the pavements, they shall be located wholly within the grass plot or wholly within the grass plot between the curb and sidewalk. On private roads and parking areas valve boxes are to be located outside of parking areas. Valves boxes will not be allowed in sidewalk.

(a) Valves and vaults. Mains of four inches to 16 inches shall have valves of the same size as the main. All valves larger than 16 inches shall have bevel gears and enclosed gear case and be constructed within a valve vault. The valve vault or valve road box type and size to be used with any size or type of valve shall be as shown in the standard detail manual.

(b) Provide valves for isolation at:

[1] Two-thousand-foot intervals (maximum) on straight/non-intersecting runs. Valves shall be provided on water mains between intersecting runs for isolation purposes.

[2] A maximum of 75 services/dwellings units isolated at once.

[3] After the last service. Also prior to the terminus of the line excludes permanent settings allowing future extension without service disruption to users.

[4] Provide valves on all sides of tees and crosses, with the exception of hydrant tees which will require one.

[5] On water mains at any arterial and major collector road crossings, creek crossings, railroad crossings, and transmission pressure gas mains, valves to be on each side of the crossing.

[6] Existing water mains where there are no isolation valves between two proposed extensions. The isolation valve is needed on the water main between the extensions to allow for maintenance on the main while providing water supply to the development.

(c) Fire hydrants.

[1] General.

[a] Fire hydrants on private property (example: shopping centers, industrial complexes, commercial sites, townhouse or apartment complexes) shall be dedicated to the County with the water lines serving the fire hydrants and the water system being dedicated to the County.

[b] Fire hydrants shall be installed as shown in the Standard Detail Manual. Hydrants shall not be located within 10 feet of sanitary sewers or storm drains.

[c] All hydrants not meeting substantial completion acceptance will have an "out of service" disk placed on one or more of the nozzles most visible to traffic.

[2] Hydrant spacing.

[a] Commercial and industrial areas.

[i] Spacing 300 feet as supply hose is laid from motorized fire apparatus.

[b] Multifamily residential areas including but not be limited to townhouses, duplexes and other multiplex dwellings, condominiums, apartments, etc.

[i] Maximum spacing: 300 feet as supply hose is laid from motorized fire apparatus.

[c] Single-family detached residential and flag lots:

[i] Maximum hydrant spacing shall be 400 feet as measured along an improved roadway.

[d] Fire hydrants on roadways divided by an island separator shall alternate from side to side and meet the spacing requirements described in section § 291-62D(8)(C)[2][c].

[e] General locations.

[i] In all areas not specified in § 291-62D(8)(c)[2][a], [b] and [c] above, the maximum fire hydrant spacing shall be 800 feet. For divided highways every other hydrant shall be located on opposite sides of the divided highway and maintain 800 feet on each side of the highways. If divided highways are abut to commercial or residential buildings, the spacing must comply with the above § 291-62D(8)(c)[2][a], [b] and [c].

[3] Hydrant location.

[a] Commercial and industrial areas.

[i] Building sprinkler/standpipe connections must be shown on plans and not more than 100 feet from the nearest hydrant as hose is laid from a motorized fire apparatus. The route to the hydrant shall not be obstructed by fencing, trees and shrubs, significant elevation changes, or other obstacles that would delay fire department operations.

[ii] The sprinkler/standpipe connection for use by the fire department shall be located within 20 feet of the primary entrance to the building or a location approved by the first due fire department. Should a building have multiple entrances on the primary entrance side (e.g., a one-story building with multiple business entrances), the connection shall be centered on the primary entrance side of the building. The primary entrance of a building is defined as that entrance used by the majority of a building's occupants and/or the public.

[iii] The fire department sprinkler/standpipe connection will be labeled with a white reflective sign. The reflective sign will have eight-inch red reflective letters reading "FDC." Below the "FDC" lettering, a reflective six-inch icon of a siamese connection (Y) for sprinklered building, or a six-inch reflective hose reel icon for buildings with a standpipe system shall be placed. Buildings with both sprinklers and a standpipe system will have both icons on the reflective sign. The sign shall be located directly above the FDC and be clearly visible as the building is approached from the street. It should be located at least eight feet above the ground and clear of all vegetation and other obstructions.

[iv] Locate pumper connections outside of fenced areas.

[v] No portion of the building shall be more than 300 feet away from the nearest hydrant, or as approved by the County in cooperation with the local fire department.

[vi] No portion of a commercial building shall be located further than 300 feet from a hydrant unless a variance is granted by the County engineer. One consideration for the variance approval will be the support of the local fire chief for this request.

[vii] Building "Fire Department Connection" (FDC) must be shown on plans and not more than 100 feet from the nearest hydrant. The location of the FDC shall be on the front of the building within 50 feet of the main entrance. If the building has several entrances (i.e., strip business malls) the FDC shall be in the middle of the building. Also, the FDC shall be labeled with a reflective sign with the letters "FDC" and an icon of a Siamese Connection (Y). This sign shall be located directly above the FDC and be clearly visible as the building is approached from the street. It should be at least eight feet above the ground and clear of all vegetation and other obstructions.

[viii] When water mains and hydrants are installed prior to the buildings being designed it may require additional fire hydrants and main upsizing to meet the required spacing, flow, or pressure requirements.

[b] Multifamily residential areas including but not be limited to townhouses, duplexes and other multiplex dwellings, condominiums, apartments, etc.

[i] No portion of the building shall be more than 300 feet away from the nearest hydrant.

[c] General locations:

[i] Locate hydrants at all intersections to provide easier access and fire fighting capabilities for the fire department.

[ii] Locate hydrants adjacent to property lines (where applicable) to avoid conflicts with driveways.

[iii] Locate hydrants at the terminus of all lines.

[iv] Hydrants shall be located so that parking is not allowed within 15 feet on either side of the hydrant.

[v] Locate hydrant such that the 4.5 inch connection to face the roadway or drive aisle.

[vi] Locate hydrants no further than 10 feet from a roadway curb line or shoulder edge.

[vii] The location of additional hydrants utilized to meet the fire flow requirement cannot be such that hose will be laid across a minor arterial or higher classification roadway.

[viii] Locating the hydrant in pinch point where roadways will be blocked by a pumper connection to the hydrant shall be avoided.

[ix] Fire hydrants located within public parking lot areas shall be placed on island outcrops that separate parking spaces so that they are fully visible to approaching fire apparatus.

[x] Fire hydrants located on roadways and within parking lots shall be accessible by an allweather road surface capable of supporting the weight of fire apparatus.

[d] Single-family flag lots detached residential. All flag lots of single-family residents shall be within 400 feet of a hydrant.

[4] Hydrant color coding.

[a] The following color designations are based on National Fire Protection Association (NFPA) Standard 291 as well as a local amendment to NFPA standard. These color designations shall be based on the available fire flow measured at 20 psi residual pressure under normal conditions.

	Fire Flow (gpm)	Color	Reflective tape on
	1,500 or greater	Blue	Around bonnet flange
	1,000 to 1,499	Green	Around bonnet flange
	500 to 999	Orange	Around bonnet flange
	All hydrant barrels shall be painted yellow

[b] When the fire flow is less than 500 gpm, the hydrant bonnet and all nozzle caps shall be painted red.

[c] At the time the system becomes substantially completed, the developer/contractor shall install white reflective tape on around bonnet flange.

[d] During inventory process, the Department of Public Works will test the fire flow and color code the hydrant according to the above table. Note that it is not County responsibility for the painting of all hydrant barrels. Also the County is not responsible for painting all bonnet and nozzle caps for hydrant fire flow less than 500 gpm.

(d) Tapping sleeve and valves. Tapping sleeves and valves on ductile iron pipe mains to serve as line valves shall be used for all connections eight inches and larger in size to any existing main where more than 10 domestic services would be shut off during installation of a standard tee. The main being tapped may be the same size as the proposed main or tapping valve, but the tapping cutter shall be 1/4 inch or more undersized. Use of mechanical joint sleeves may be permitted only upon written consent of the County and will be considered only where the pipe being tapped is ductile iron pipe. Valve boxes or vaults for tapping sleeves shall be sized in accordance with the County Standard Detail Manual.

(e) Blow-offs and air release valves. A blow-off shall be installed at the low point of mains in accordance with the Standard Detail Manual. Hydrants will serve as blow-offs at the end of mains. Hydrants shall be installed at the end of mains to be extended in the future. Air release valves shall be installed at prominent peaks on long distribution mains where there are no service connections. Air release valves will generally not be required for distribution mains. Where required, air release valves shall be installed in accordance with the Standard Detail Manual.

(9) Materials. All distribution mains and fittings shall be in accordance with the Standard Specifications for Construction Manual.

(10) Installation. Installation of all distribution mains and appurtenances shall be in accordance with the Standard Specifications for Construction Manual. Such requirements shall be noted in the specifications and on the drawings.

(11) Existing hydrant relocation and reuse will only be allowed if the hydrant is less than seven years old. If hydrant is greater than seven years old, the hydrant shall be replaced and the existing hydrant conveyed to the County.

E. Transmission mains.

(1) Location. The approximate location of transmission mains shall be based on a computerized network analysis by the design engineer, which meets with County approval. This analysis shall indicate the beginning and ending points of the main and the major distribution system intersecting nodes. The design engineer shall select an alignment which satisfies the approximate location as determined in the analysis while taking into consideration length of pipe, number and type of fittings, public or private property, construction and maintenance access, future road widening, horizontal and vertical alignment changes, flood prone areas, subsurface conditions, and existing and future utility interferences. All water utility easements shall be 20 feet minimum width. No other utilities or structures will be allowed in the water easement without the County's written approval.

(2) Sizing. The sizing of transmission mains shall be based on the computerized network analysis by the design engineer or any previously approved studies, as to be determined by the County.

(3) Cover. Normal cover for transmission mains shall be 3.5 feet, except where existing utilities are crossed, where the minimum will be three feet. Maximum cover will be nine feet, except where authorized by the County.

(4) Clearances. See distribution mains in § 291-62D(7).

(5) Hydraulics. System hydraulic gradient, static and residual pressures, velocities, and flow direction will be provided by the County if established. If not established the design engineer shall submit a proposal to the County for review and approval. The design engineer will analyze transient pressures in transmission mains and provide written results to the County for review. In most cases, the transient pressure analysis will be limited to pipelines of finite length for line rupture and sudden valve closure. The computation methodology is detailed in Pipeline Design for Water and Wastewater, ASCE, 1992 or later edition; see also Pumping Station Design, 3rd Edition (or later), 2006, by Garr M. Jones.

(6) Appurtenances.

(a) Valves and vaults. All valves larger than 16 inches shall be placed in a standard concrete vault in accordance with the Standard Detail Manual and Standard Specifications for Construction Manual.

(b) Air and vacuum release valves. The proper ventilation of transmission mains is very important. Trapped air pockets can significantly reduce the capacity of the mains as well as cause increased pumping heads and corresponding higher pumping costs. Valve sizing and location shall be evaluated during design and coordinated with valve manufacturer. The following guidelines shall be used to locate air and vacuum release valves:

[1] Peaks in profiles.

[2] Abrupt increase in downward slope.

[3] Abrupt decrease in upward slope.

[4] Long ascents: 1,500 foot to 3,000 foot intervals.

[5] Long descents: 1,500 foot to 3,000 foot intervals.

[6] Long horizontals: 1,500 foot to 3,000 foot intervals.

[7] Pumps: On the discharge pipe as close as possible to the check valve.

[8] System side of the check valve.

[9] Valves: high point of large valves or bypass piping and downstream of large pressure reducing valves.

[10] Shop drawings of manufacturer shall be provided to County for acceptance prior to installation.

(7) Materials. The pipe material class of transmission mains shall be selected based on its corrosion resistance, strength against internal and external pressures, hydraulic characteristics, installation conditions, and economics and be in accordance with the Standard Specifications for Construction Manual.

(8) Installation. Installation of all service connections and appurtenances shall be in accordance with the Standard Specifications for Construction Manual. Such requirement shall be noted in the specifications and on the drawings.

F. Service connections.

(1) Location.

(a) Water house or building connections shall be constructed with a curb stop and/or meter vault box to the right-of-way/property/easement line for all lots within a proposed development unless otherwise approved by the County Engineer. All adjacent lots which are not part of the proposed development, but are to be served by the water line shall be shown on the plans. Water service laterals, including curb stops and boxes or meter vault, are to be provided to the right-of-way/property/easement lines for all existing dwellings fronting a new water main. Twin services may be placed on the property line separating the two houses in single-family, detached house subdivisions.

(b) All piping shall be arranged in accordance with the County Standard Detail Manual.

(2) Sizing.

(a) The minimum sizing for any service connections shall be one inch. For larger homes and other buildings, larger connections are required. Provide water meter sizing computations for meter sizing per Appendix R.[5]

[5] Editor's Note: Said appendix is included as an attachment to this chapter.

(b) Sizing for commercial, industrial and institutional meters shall be based on Appendix R.[6]

[6] Editor's Note: Said appendix is included as an attachment to this chapter.

(3) Cover. Cover over service lines shall be as indicated in the Standard Details Manual and measured from finished grade.

(4) Clearances.

(a) Parallel to sewer house connections. Water house services shall ordinarily be placed 10 feet horizontally and one foot vertically over and from the sewer house connections. In cases where this is not achievable, deviation may be allowed on a case-by-case basis subject to County and/or state approval. Such deviation may allow a horizontal separation of 1.5 feet with at least a six-foot vertical clearance (sewer being placed on the bottom). If schedule 40 PVC solvent weld pipe is utilized for the sewer house connection a 1.5 foot horizontal separation with at least a one-foot vertical clearance (sewer being placed on the bottom) may be allowed if a passing pressure test with 10 feet of head of water or equivalent taken in the presence of a County representative is achieved.

(b) Crossing storm drains or other utilities. Water house and building connections crossing storm drains and other utilities (existing or future) shall have a minimum clearance of 12 inches from these utilities.

(5) Cross-connections. Cross-connections shall not be permitted or allowed to continue. No cooling water or condensate may be returned to the potable water supply line. All interconnections shall be approved by the County and other appropriate reviewing authorities. On-site private wells must be properly abandoned (per MDE guidelines) prior to public service activation.

(6) Appurtenances. Backflow prevention devices shall be located in accordance with § 291-29 and Res. No. 2005-20 and the Standard Detail Manual.

(7) Installation. Installation of all service connections and appurtenances shall be in accordance with the latest County Standard Specifications for Construction and Detail Manuals. Such requirement shall be noted in the specifications on the drawings.

(8) Booster pumps. Booster pumps are not permitted for any individual service, without prior County approval. If a booster pump is installed on any individual service, the service will require protection with a reduced pressure principle backflow preventer.

(9) PRVS. When pressure in the water main exceeds 80 psi, an approved pressure reducing valve at the customer's expense, complying with ANSI/ASSE 1003, shall be installed to limit pressures on fixtures to less than 80 psi. Pressure reducing valves may cause a closed system requiring thermal expansion devices. Where pressure reducing valves are installed and the downstream piping is not rated for the maximum upstream pressure, a pressure relief valve shall be installed downstream of the pressure reducing valve at the customer's expense.

G. Structural considerations.

(1) Buttresses and anchors.

(a) At all fittings which achieve a change in pipeline direction, such as tees, fire hydrants, valves (as needed) bends and dead ends, thrust restraint is necessary. Restrained joints and/or anchorage blocks are two means of achieving thrust restraint. The design engineer shall decide what is appropriate for each particular situation based on an analysis of such factors as soil conditions, clearance requirements, constructability, future expansion and cost.

(b) Under normal soil conditions, fittings up to thirty-six-inch diameter shall be buttressed or anchored as provided for in the Standard Details Manual. In the event the soils will not bear 3,000 pounds per square foot, the design engineer shall design buttresses or anchorages appropriate to the situation.

(2) Restrained joints. If the soils at the project site are unusually poor, or other factors such as cost, space limitations, or future construction so indicate, restrained pipe joints shall be designed. The joint restraint may be either Field Lock Gaskets harnesses or mechanical joints with retainer glands for mains and valves up to sixteen-inch diameter. Restrained joint types for larger mains and valves shall be approved by the County prior to proceeding with design. The design shall account for test pressures, surge from sudden valve closures, poly encasement (wrap) soil frictional resistance and effect of groundwater as a minimum.

(3) Jacking and tunneling.

(a) Where mains are being designed to cross railroads, state highways, County roads, or other roads on which service cannot be interrupted, the water main shall be installed in a sleeve, tunneled or jacked under the road. The sleeve size, material, and method of tunneling or jacking shall be approved by the owner of the road or the railroad being crossed.

(b) The sleeve diameter shall be sufficient to permit the proper positioning of the water main within the sleeve. Water mains installed in sleeves shall have restrained joints throughout the length of the sleeve. The annular void between the main and the sleeve shall be completely filled with grout or County-approved casing spacers with end caps at the ends of the casing.

(c) Water mains installed in sleeves shall be equipped with sufficient valves to isolate the sleeved section. A valve at each end is required.

(4) Design loads and piping design.

(a) The design engineer shall submit calculations necessary to support the selection of the type and class of pipe indicated on the drawings.

(b) The calculations may account for the following:

[1] Vehicle or railroad loads (h-20, e-80, etc.).

[2] Pipe loading factors (dead, live, impact).

[3] Internal pressure (static, dynamic, surge).

[4] Installation trench configuration.

(5) Corrosion protection. If soil tests or inspection of existing utilities in the project area reveals evidence of, or potential for, corrosion, the County shall be notified of the condition. Should the County deem it necessary, the design engineer shall design suitable galvanic and/or cathodic corrosion protection measures using AWWA Controlling Corrosion within Water Systems, 1978 or latest edition.

(6) Curves and deflections. Gradual changes in pipeline direction may be achieved by joint deflection in accordance with the manufacturer's recommendations. Curvature shall only be allowed for lines constructed of ductile iron pipe. The joint deflection for DIP sizes three inches through 12 inches shall not exceed 3.5°. The joint deflection for DIP size 14 inches through 20 inches shall not exceed 1.5°. The joint deflection for DIP sizes 24 inches through 48 inches shall not exceed 1.0°.

H. Testing and disinfection. The contract documents shall provide for hydrostatic testing of newly laid mains as described in the County's Standard Specifications for Construction Manual. Hydrostatic tests shall be performed for pressure retention and leakage. Disinfection shall be done in accordance with the Standard Specification for Construction Manual.

I. Abandonment procedures. Abandoned service connections shall be cut and plugged at the service main, and the meters removed and provided (delivered) to the County to salvage, if their condition permits reuse. Distribution mains that are to be abandoned shall be plugged at the point of abandonment and on each side of any existing valves, and the valves and hydrants removed and salvaged if their reuse appears practical. Any necessary buttresses or anchorage required shall be designed in accordance with the Standard Detail Manual and this chapter.

J. Water pumping, treatment and storage. A detailed presentation of design criteria for pumping, treatment, and storage facilities shall be in accordance with the requirements of § 291-63, the needs of the County, and the recommendations in Pumping Station Design, 3rd edition (or latest), 2006, by Garr M. Jones. The sizing of water pumping and storage facilities will be in accordance with Appendix O.[7]

[7] Editor's Note: Said appendix is included as an attachment to this chapter.

§ 291-63 Minimum design guidelines and requirements for water facilities.

A. General.

(1) In addition to the criterion contained herein, the design of water pumping facilities, well houses, and water towers shall meet the requirements of all relevant guidelines issued by the Maryland Department of the Environment (MDE) or shall be exceeded where specified by the County. The following additional manuals shall be consulted and applied to the design with the approval of the County:

(a) American Water Works Association (AWWA) Standards.

(b) Recommended Standards for Water Works, also known as the "Ten State Standards," latest edition.

(c) "Pumping Station Design," 3rd Edition (or later), 2006, by Garr M. Jones.

(2) All aspects of the facility shall maximize operator safety. The facility shall be designed to operate reliably and efficiently with a minimum of attention and have provisions for easy access and maintenance. Equipment shall be selected on the basis of durability, availability of replacement parts, standardization, efficiency, and ease of maintenance and repair.

(3) The pumping/storage facility shall be designed for the maximum build out conditions of the service area as approved by the County using flows approved by the County.

B. Design.

(1) Planning period. Water pumping/storage facility design conditions shall, at minimum, accommodate twenty-year planning horizon. For all pumping/storage facilities, consideration shall be given to future upgrade flexibility necessary to accommodate design conditions beyond the normal planning horizon. This is especially important for larger facilities.

(2) Hydraulic analysis.

(a) Refer to § 291-62 and Appendix O[1] for water pumping/storage facility sizing requirements. A service area map and tabulation of the design flow shall appear on the plans. The map and tabulations shall show initial and ultimate service areas.

[1] Editor's Note: Said appendix is included as an attachment to this chapter.

(b) Water facilities must satisfy the hydraulic conditions of the system. A complete hydraulic analysis of each water pumping and storage facility is required. During the study phase, the designer shall consult with the County for the requirements of the hydraulic analysis. At a minimum, the designer shall perform twenty-four- and forty-eight-hour extended period computer simulations using average day demand, maximum day demand and peak hour demand for both current and full development conditions. Fire flows shall be analyzed during maximum day rate for both initial and full development conditions.

(c) The hydraulic analysis shall be presented in a clear, logical and easy to understand format and shall relate to the proposed construction drawings. If construction drawings are not available at the time of the analysis then scale drawings shall be prepared with street names to locate the proposed system.

(3) Pump and system curves.

(a) The designer shall show pump and system curves on the plans to scale. System curve characteristics for each design condition shall be determined by the Hazen Williams formula for piping head loss in conjunction with the County water model.

(b) The pump selection shall be reviewed for both the initial and maximum design year conditions.

(c) The following pump and system curves shall be shown on the plans:

[1] System curve for peak hour demand for the design year.

[2] System curve for maximum day demand plus fire flow for the design year.

[3] System curve for average day demand for the design year.

[4] System curve for average day demand for the initial year of station operation.

[5] Pump curve for single pump operation and multiple pump operation where station has three or more pumps.

(d) In addition, the designer shall list next to the curves the pump design criteria including pump motor horsepower, efficiency, npsh at design points and rpm. Pump and system curves shall be shown for new water main conditions. Hazen-Williams "C" factors used in evaluating pump and system curves shall be in accordance with the guidelines given in § 291-62 regarding hydraulic calculations.

(4) Number of pumps. Water pumping facilities shall be capable of pumping the maximum day demand with the largest single pump out of service.

(5) Pump selection criteria. Avoid applications where pumps must operate in an adverse area of their performance curve. Design for maximum efficiency at the operating point. Examples would be pumps operating at very low flows and high heads, near shutoff heads or "runout" conditions. These conditions can result in excessive hydraulic loading or cavitation damage to impellers, casings and shafts, rapid bearing and mechanical seal wear and high vibration. Under no circumstances shall a pump be specified operating outside of its recommended range.

(6) Variable frequency drives (VFDs). The use of VFDs or other methods to achieve minimum flow conditions below the full speed operating range of the pumps shall be approved by the County. If VFDs are used, multiple speed performance curves shall be shown.

(7) Water hammer. The potential impact of water hammer under usual and unusual circumstances (power outages, etc.) shall be evaluated. If the combined effects of static head and water hammer (using a safety factor of 1.1) do not exceed the weakest piping system component working pressure, no special provisions need to be included to control water hammer. Where the maximum water hammer pressure (using a safety factor of 1.1) exceeds the weakest piping system component working pressure, the designer shall strengthen those elements affected, reevaluate pipe size and velocities or select an appropriate device to control water hammer. No pressure vessel/surge tank type devices will be acceptable.

C. Design criteria for water facilities.

(1) Site design.

(a) Location. Water facilities shall be located near the areas to be served. Natural screening and remoteness of the site shall be primary elements of site selection wherever possible. Where pump stations are sited in proximity to developed areas, the architecture shall be compatible with the surrounding area. Building aspects such as generator exhaust and ventilation fan noises shall be considered. Similarly, building setbacks shall be considered to provide minimal impact to neighboring properties.

(b) Land acquisition. Land required for facilities, including necessary vehicular access routes to an existing or proposed public roadway shall be owned in fee simple by the County. As part of this process, a boundary survey of the property is required together with a record plat and a metes and bounds description of the parcel unless otherwise approved by the County Attorney. In determining the space requirements for the facility, particular attention should be given to the width provided for the access road to insure adequate space for grading and drainage within the access road right-of-way. Sufficient room shall be provided for future maintenance of wells, tanks, towers, and generators. Vehicle access shall be provided with adequate turning radii for well rigs, truck-mounted cranes and other large equipment that might be expected to be on site.

(c) Topography. Adjacent areas potentially served by the water facility must also be considered. Water facility site selection shall also be compatible with suitable site access and soil capability with respect to land grading in conjunction with site development. Existing contours and other topography shall be shown for the entire site including a one-hundred-foot minimum width outside of the proposed property boundary on all sides. Contour interval shall be two-foot, unless otherwise approved by the County engineer.

(d) Floodplain. Water facilities shall be sited to remain operational and permit access during a one-hundred-year return frequency flood. Building top slab elevation shall be set a minimum of two feet above the one-hundred-year floodplain elevation. The access road shall be above the one-hundred-year floodplain elevation.

(e) Wetlands. Avoid direct impacts wherever possible and minimize impacts to wetland buffer areas. Buffer areas include 25 feet beyond non-tidal wetlands.

(f) Grading. Water facility grades shall prevent local ponding and provide positive drainage away from all structures and site. The site shall be a minimum of one foot above the surrounding area. Slopes on site shall be generally limited to no less than 1% and no greater than 4%. Stone surfaces around paved areas shall provide proper site drainage at slopes 10% or less. Land grading outside of the water facility perimeter fence shall not exceed three to one slopes; four to one slope maximums are desirable. Lesser slopes wherever possible are preferred. Site grading design shall be compatible with slope stability for the soils encountered. Slope stabilization shall be appropriate for the degree of slope and soil conditions. The use of retaining walls on or immediately adjacent to the water facility site is not permitted. Provide for adequate drainage and conveyance for the discharges of the control valves, blow-offs, roof drains, and condensers as well. There shall never be a situation where roof drains flow across walkways, roadways, or parking areas.

(g) Site security. Water facility sites shall be fenced with black vinyl coated chainlink fencing eight feet tall, black vinyl coated post and black hardware, and a sixteen-foot wide locking gate for vehicle access. The fence is to include three strands of barbed wire around the top. Additional property line fencing may be required as determined by the County Engineer. Buildings shall have exterior lighting controlled by motion detectors and provided with an entry alarm connected to the station SCADA.

(h) The area within the fencing, and two feet beyond the fence is to be covered with a minimum of six inches of No. 57 crushed stone over a weed barrier film. No proposed grassed areas are allowed.

(i) Paving. Water facility sites shall have P-4 paving section in accordance with Table 2.07 of the road ordinance[2] and include a minimum of two parking spaces. The site shall have sufficient room to allow AASHTO WB-40 access to equipment by maintenance trucks. An access road to the water facility site shall have P-2 paving section in accordance with Table 2.07 of the road ordinance.[3] The width of the pavement shall be 20 feet wide with two-foot gravel shoulders. The maximum grade for the access road shall not exceed 5%. The cross slope shall be in accordance with standard detail R/2.16.

[1] The access road and site shall support a minimum AASHTO WB-40 turning radius. The site shall also include a WB-40 turn-around area. Access roads shall be used exclusively for facility maintenance and access.

[2] Editor's Note: See Ch. 276, Attachment L.

[3] Editor's Note: See Ch. 276, Attachment L.

(j) Sidewalks. Four feet wide, in accordance with the road ordinance/detail manual, are to be provided between buildings and/or structures and from paved areas to buildings and structures for access of equipment, dollies, etc.

(k) Sediment control, a sediment control plan shall be provided and approval obtained from the Charles Soil Conservation District (SCD).

(l) At least two test borings shall be taken at the building location to determine soil types, rock, water table elevations, soil bearing values, etc., standard penetration tests shall be taken at intervals not to exceed five feet. Borings shall be taken to a depth of not less than 15 feet below the bottom of the proposed structure. Borings shall be taken deeper as necessary, depending on soil conditions.

(m) Station sign. A permanent sign shall be provided at each facility stating the station name, street address and emergency telephone number. The sign must meet Charles County 911 addressing system.

(n) Yard hydrants and hose bibs shall be provided for wash down, maintenance, and sanitation purposes.

(2) Structures.

(a) Design/architectural standards. Water facilities shall be architecturally compatible with surrounding structures and shall not have slate roofs. Water facility buildings shall be precast concrete and shall be designed to be vandal-proof. Roof shall be precast concrete gable type. There shall be no exposed woodwork on the outside of the building. All exterior woodwork shall have a vinyl or aluminum coating. The facility shall have a lightning protection system. Provisions shall be made in the structure for traversing bridge cranes of adequate capacity to facilitate the removal of pumps, motors, valves and all other related heavy equipment. Doors shall be sixteen-guage steel with deadbolts and locks keyed to the County standard. Doors shall be located and/or situated so that they are not affected by rain runoff from the roof. Exterior lights shall be vandal proof, wall-mounted, energy-efficient, controlled by motion detectors and an on-off switch. Facilities shall be provided with outside non-freeze hose bibbs. Ventilation openings shall be protected with aluminum louvers with birdscreens. The building shall conform to all Charles County building codes and zoning regulations.

[1] Pump room. Pumps and piping shall be located above pump room floor at a height sufficient to connect to suction/discharge piping. Parallel suction and discharge headers shall be provided. Pumps shall be of the horizontal style placed on individual concrete bases. Floors shall be sloped to floor drains piped to a sump. The minimum floor slope toward the sump shall be 1/4 inch per foot. Water shall not pool in any areas of the floor. Each water pump shall have a floor drain located next to it. Pump baseplate drains shall be piped to adjacent floor drains. A building sump with sump pump and piping shall be provided. The pump room shall be furnished with a service sink with both hot and cold water, and inside hose bibb.

[a] Adequate room is required for working around and above equipment. A minimum of three feet of clearance between equipment and walls shall be provided.

[b] All electrical and control equipment shall be located at least three feet above the floor.

[c] Locate all auxiliary equipment above ground in an appropriate building which allows safe and efficient all-weather, all-hour, electrical and mechanical maintenance, including but not limited to motor controls, blowers, meters, etc.

[d] A restroom shall be provided with toilet, lavatory, on-demand hot water heater, towel dispenser, soap dispenser and mirror onsite as determined on a case-by-case basis based on the anticipated number of man-hours of operation and the remoteness of the site.

[2] Water service. A minimum of one-inch-diameter metered potable water source shall be provided for wash down, maintenance, and sanitation purposes. The service shall include a backflow preventer. The water service line shall provide a minimum of 30 gallons per minute to the emergency shower with a minimum residual pressure of 35 psi.

[3] Control room. Electrical equipment shall be located above grade in a control room that is designed with adequate space to accommodate future upgrades.

[4] Generator area.

[a] A separate generator area shall be provided for housing the emergency generator and fuel tank. The generator slab/floor shall be located a minimum of two feet above the one-hundred-year flood elevation. If the generator is in a room, it shall have a roll-up metal garage door for access and shall be equipped with a floor drain located outside the fuel spillage containment area, piped to the building sump. The generator area shall be supplied with hose bibb, hose rack and 50 feet of rubber hose.

[b] Alternatively, the generator may be installed outdoors in a separate, self-contained, sound attenuated enclosure on a concrete pad of sufficient size for the generator and maintenance access.

[5] Heating and ventilation.

[a] The building shall be heated by electric unit heaters with integral thermostats sized to maintain a minimum inside temperature of 40° F. Provide cooling as necessary to maintain air temperatures below 95° F. inside electrical devices. Ventilation shall be by means of wall-mounted exhaust fans with backdraft dampers operated by thermostats and freezestats and intake louvers with motor operated dampers.

[b] Ventilation shall be designed for a minimum of six air changes per hour. Each room shall have a dedicated exhaust fan(s). Ventilation shall be sufficient to remove heat generated by the pump motors and controls. Provisions shall be made to ensure against condensation forming on controls and other major items of equipment.

(3) Equipment.

(a) Yard valves. Yard valves shall be buried resilient seat gate valves complying with the standard specifications with operating nut and roadway valve box at grade.

(b) Station bypass. Water facilities shall be provided with bypass connections in the form of two fire hydrants, one on each side of the suction and discharge lines of the station. Hydrants shall be labeled "suction" and "discharge," respectively. The hydrants shall be located adjacent to the parking area and shall be no more than 50 feet apart for easy setup of temporary pumps for pump around capability.

(c) Interior piping. All interior water piping shall be DIP, Class 53, with flanged fittings. Flanges shall be integrally cast on pipe or factory assembled screwed-on with proper bonding compound. Manifolds shall include flexible couplings for make-up and for expansion and contraction of the piping system. Flexible couplings shall be provided on the suction and discharge of each pump. Arrangement of piping and equipment within the station shall be made with adequate space for maintenance, repair, removal or replacement of equipment, as well as to safeguard personnel working in the station. A minimum of three feet of clearance between equipment and walls shall be provided. Depending on the size of the equipment and piping, greater clearances may be needed. Piping shall be adequately supported. Control and instrumentation piping shall be copper or stainless steel. Chemical feed piping shall be clear PVC. Provide color coding for piping in accordance with the standard specifications for construction manual.

(d) Interior valves. Each water pump shall have isolation valves to permit the removal or maintenance of the pumps without affecting the operation of the remaining pumps. Isolation valves shall be resilient seated gate valves. Valves larger than sixteen-inch shall have geared operators with handwheels. Handwheels shall be marked with an open arrow. Each pump shall have a hydraulically operated, time adjustable pump check service valve to prevent backflow through inoperative pumps. In accordance with the criteria for water hammer control, pump check service valves shall be of the type and strength required to eliminate water hammer damage. Surge relief valves shall also be provided on the suction and discharge headers of the station and piped to the nearest storm drain system.

(e) Pressure gauges. Pressure gauges for direct reading of line conditions shall be placed on both the suction and discharge of each pump, on the main discharge header piping after the last pump, and on the suction header as it enters the building. Pressure gauges shall be oil-filled type, have a minimum 3 1/2-inch diameter face and be equipped with snubbers. Pressure gauges shall be installed and configured such that the gauge can be isolated and the gauge piping be drained. Accuracy shall be to within 0.5% of pressure. Pressure gauges shall have a range such that the normal operating pressure is near the middle of the gauge.

(f) Flow metering. All water pumping facilities shall have a County approved water meter. A seven-day chart recorder and 4-20 MA output to the SCADA system, with totalizer, and indicator recorder in units of gpm shall also be provided.

(g) Transfer pumping units.

[1] All water pumps shall rotate clockwise as viewed from the motor end. Pump bearings shall have a minimum 100,000 hours abma-10 bearing life. Pump motors shall operate on three-phase, sixty-cycle electrical service and at a speed no higher than 1,780 rpm. Pump discharge velocities shall be between five and 15 feet per second. Pump inlet pressure shall be maintained at a sufficient level to avoid cavitation. Pump motor horsepower shall be sufficient to prevent motor overload under all possible conditions. Water pumps and motors shall be suitable for continuous duty. All pumps shall be factory witness tested and approved prior to shipment. Water pumps shall meet the requirements of the hydraulic institute for vibration. Pumps shall be one of the following types:

[a] In-line split case (horizontal).

[b] End suction (horizontal).

[2] The pump casing/volute, impeller, seal housing and motor housing shall be of cast iron construction. Impeller shall be cast iron or bronze. The pump's casing and impeller shall be fitted with replaceable hardened bronze or stainless steel wear rings to maintain sealing efficiency between the volute and the impeller. At the County's option, other pump materials may be required to suit a particular application.

[3] Pumps shall have the following additional features:

[a] Stainless steel shaft.

[b] NSF approved fusion bonded epoxy coating (interior).

[c] Flexible shaft coupling and removable OSHA-compliant shaft guard.

[d] Mechanical shaft seals cooled and lubricated by the pumped fluid.

[e] Premium efficiency motors shall be specified (where commercially available) for all three-phase pump motors.

(4) Electrical and controls.

(a) Electrical design. All electrical designs and components shall be in strict accordance with all applicable national and County Code requirements. Electrical design shall be such that phase out protection shall be provided so that the power will automatically switch off in the event of a loss of any one phase. Incoming electrical service shall be underground with electric meters installed outside the building. The electrical plans shall include, but not be limited to, the following:

[1] Design report shall provide the correspondence with the Charles County local power company showing the consultant's load breakdown along with the local power company's assessment of the voltage available, their ability to serve the project, and the availability of a second independent source of power. Specific local power company permission to use across-the-line starters or requirement for reduced voltage starters is required.

[2] In addition to the proposed wiring diagrams, provide a narrative of the control sequence scenario which clearly explains the operational intent.

[3] Complete plan layout indicating all conduit, wire sizes and equipment locations including lighting and other appurtenances. Incoming electrical service on the site shall be underground and within concrete-encased conduits.

[4] Installation details of equipment that are wall-mounted, or suspended from the ceiling or otherwise required for clarity.

[5] Single line diagrams incorporating all electrical components required for operation of the facility.

[6] Complete lighting schedule noting model, size, location and installation data as well as appurtenances. Vandal proof exterior lighting shall be provided. Interior and exterior quartz lighting, separately switched, for maintenance purposes including auxiliary dc safety lighting is to be provided. Minimum lighting levels shall be 15 footcandles for stairways, 50 footcandles for operation, and 100 footcandles for electrical and mechanical maintenance.

[7] Complete control and SCADA diagrams.

[8] Elevation of control panels with equipment and mounting dimensions and notes identifying each component.

[9] Complete circuit breaker schedule indicating size and identifying each circuit.

[10] Ventilation schedule noting fan size, operating conditions, location, model, installation data, etc. The ventilation schedule shall also outline louver data including size, material, fixed or motorized.

[11] Secondary power facilities and alarm equipment shall be designed so that they may be manually activated for periodic maintenance checks to ensure proper operation.

[12] Provide a legend of all symbols used for the above.

[13] Power for the station shall be 480 volts, three-phase.

[14] IEC electrical components shall not be utilized. For replacement compatibility and availability, only full-sized NEMA UL listed electrical devices shall be used regardless of any equivalent UL ratings of IEC devices.

[15] Lockable safety disconnect switches are to be provided for all rotating equipment. Use lockable knife-switches rather than remote lockable start/stop button stations.

[16] Provide "push-to-test" type indicator lamps with screw-in type bulbs. Use of 120 mb type bulbs is prohibited.

[17] Permanent, in-place, volt/amp meters are required for each pump or major piece of equipment.

[18] Due to compatibility and standardization needs, provide only "Square-D," "Furnas," or "Cutler-Hammer" electrical equipment; no alternatives allowed.

[19] Use "Square-D," or County-approved equal, Class 8501 Type "K" plug-in style relays to the maximum extent possible where appropriate. Provide integral power indicating lamps in the relays. The only exception to this should be where current requirements exceed contact ratings. Use plug-in style relays for timers, alternators, and latching as well. Octal or square relays are equally acceptable, although eight-pin octal relays are preferred. Use "Square-D" Type KP12P14 or KP13P14 or County-approved for DPDT or 3PDT respectively.

[20] Provide non-resettable elapsed time meters for all rotating equipment. Meters are to be in hours and tenths of an hour, not minutes. Provide an elapsed time meter for parallel operation of main pumps; e.g., a meter for Pump No. 1, Pump No. 2, and Pump Nos. 1 and 2 together.

[21] A weatherproof red exterior "trouble light" for visual indication of equipment failures/problems is to be provided. A horn is not to be provided.

(b) Lightning and surge protection: the designer shall provide lightning and surge protection at the water facility. The lightning and surge protection shall comply with the latest editions of all applicable codes and standards. Provide phase failure and phase reversal protection for all equipment. A single phase condition shall not destroy motors, transformers, relays, etc., should the second source of power fail to take over.

(c) Backup power. All water pumping facilities shall be provided with emergency generators with automatic transfer switches as described in MDE guidelines. Emergency generators shall be sized to maintain full station operation. Emergency generators shall be diesel driven with fuel storage on the underside of the generator in a belly tank or outside the building in an aboveground storage tank. Fuel spillage protection shall be provided. Tank size shall be suitable for a minimum of 24 hours of generator operation at full load. Generators shall be mounted on vibration spring isolators. When emergency generators are located inside a building, they shall be mounted with a fuel tank fill connection to the outside. Generator engine exhaust shall be provided with a critical grade silencer and piped to the outside of the control building. Generator exhaust shall face away from nearby neighbors. If this is not possible, a baffle wall shall be constructed in front of the generator exhaust to deflect the noise.

(d) Control/SCADA system: a complete and operable control/SCADA system shall be provided per County standard specifications for construction.

(5) Painting and coating. All exposed piping, pump equipment and appurtenances, including all structures, shall be painted per County standard specifications for construction.

(6) Disinfection. All piping, pumps and appurtenances shall be disinfected prior to placing in service in accordance with applicable AWWA standards.

(7) Safety.

(a) Appropriate emergency eyewash facilities shall be provided whenever chemical handling is proposed. The need for emergency fountains and showers, the design/configuration thereof, and their locations shall be in accordance with the most current edition of the 10 states standards and the applicable requirements of MOSH and the County Safety Officer. As a minimum, the eyewash fountains shall be supplied with water of moderate temperature, 50° F. to 90° F., suitable to provide 15 to 30 minutes of continuous irrigation to the eyes. As a minimum, the emergency showers shall be capable of discharging 30 gallons per minute of water at moderate temperature and at a minimum pressure of 35 psi.

(b) Appropriately designed dielectric rubber floor mats are to be provided for insulation at all motor controls for personnel safety. If water on the floor is a possibility, the design must eliminate such water. A situation of motor control maintenance in wet or unsafe conditions is unacceptable.

D. Production wells.

(1) General. The design professional is directed to Section 02555, Production wells, of Charles County's Standard Specifications for Construction, and the following:

(a) General well appurtenances. The following well appurtenances are required:

[1] A pitless adapter shall be provided.

[2] A sampling tap shall be provided for raw water sampling within the well house piping.

[3] Adequate control switches, etc., for the pumping equipment shall be provided.

[4] A water meter is required to determine water production for each well and the meter shall be located upstream of the well blow-off.

[5] The well casing shall extend at least 12 inches above the concrete floor or apron surrounding the well and above the one-hundred-year floodplain elevation.

[6] Adequate support for the well pump and drop pipe shall be provided.

[7] Each well casing shall be equipped with a drawdown gauge, airline, and appurtenances for measuring the change in the elevation of the water level in the well and a conduit for level transducer from the well to the well house.

[8] Wellhead protection shall be provided.

(b) Submersible pumps. Where a submersible pump is used, the top of the casing shall be effectively sealed against entrance of water under all conditions of vibration or movement of conductors or cables.

(c) Discharge piping. The discharge piping shall be provided with separate means to pump (blowoff) water of unsatisfactory quality to a point away from the groundwater source and toward the stormwater management system, but shall not be directly connected to a sewer. The discharge line shall:

[1] Have control valves located above the pump well house floor.

[2] Be protected against freezing.

[3] Be valved to permit testing and control of each well.

[4] Have watertight joints.

[5] Have all exposed valves protected.

[6] Have erosion protection at the point of waste discharge.

(d) Well apron surrounding the well shall meet the following requirements:

[1] Be minimum 3,500 psi concrete with adequate reinforcement meeting standard specs for construction.

[2] Be a minimum of six inches in thickness.

[3] Extend a minimum of three feet in all directions from the well.

[4] Slope at least 1/4 inch per foot towards a screened four-inch floor drain to atmosphere.

E. Potable water storage facilities.

(1) General. The materials and designs used for finished water storage structures shall provide stability and durability as well as protect the quality of the stored water. Steel and concrete structures shall follow the most current available American Water Works Association (AWWA) standards concerning steel and concrete tanks, standpipes, reservoirs, and elevated tanks except as may be modified herein.

(a) Location of finished water storage facilities.

[1] The bottom of ground-level reservoirs, storage tanks and standpipes should be placed a minimum of two feet above the one-hundred-year flood elevation.

[2] Buried tanks are not permitted.

[3] The site shall be large enough to permit construction of the facility, maintenance for painting and have a right-of-way to the nearest public road.

[4] All sites shall have electrical service providing a minimum of 480 volts/three-phase power.

(b) Obstructions to air navigation.

[1] For structures within a four-nautical-mile radius of a public-use airport, the design professional shall be governed by the latest revision of COMAR; shall contact the Maryland Aviation Administration (MAA) office of regional aviation assistance; and shall complete the appropriate Federal Aviation Administration (FAA) form as required by the Federal air regulations and deliver the completed form to the MAA.

[2] For structures within a four-nautical-mile radius of a military airport, submit to the FAA.

(c) Safety. The safety of employees shall be considered in the design of the storage structure. As a minimum, such matters shall conform to pertinent building codes, laws, and regulations of the area where the storage structure is constructed.

[1] Ladders, ladder guards, balcony railings, and safe location of entrance hatches shall be provided.

[2] Elevated tanks with riser pipes over eight inches in diameter shall have protective bars over the riser opening inside the tank.

[3] Ladders must meet the minimum requirements of OSHA, 29 CFR 1910.

[4] Requirements for safety belts and harnesses shall be included in the specifications.

[5] Lighting, pumps and cathodic protection system equipment shall meet the requirements of the national electric code. Lights shall be LED.

(d) Drains.

[1] No drain on a water storage structure shall have a direct connection to a sewer or storm drain.

[2] All finished water storage structures shall be equipped with separate drains discharging to the atmosphere. Drainage of finished water storage structures to the distribution system through inlet/outlet piping shall not be allowed.

(e) Freezing. All finished water storage structures and their appurtenances, especially the riser pipes, overflows, and vents, shall be designed to prevent freezing which will interfere with proper functioning.

(f) Internal catwalk. Every catwalk over finished water in a storage structure shall have a solid floor with raised edges so designed that shoe scrapings and dirt will not fall into the water.

(2) Storage tanks.

(a) Types of tanks permitted.

[1] Ground level shall be glass-lined steel bolted tanks.

[2] Welded steel, single pedestal spheroid elevated tanks shall be used for up to 1,000,000 gallons.

[3] Composite concrete/steel tanks shall be used for any tank 1,000,000 gallons and greater.

[4] All tanks must meet the latest AWWA standards.

[5] All tanks shall provide a mounting system for cellular antennas and County SCADA equipment.

[6] Exceptions to the above must be given in writing by the County Engineer.

(b) Welded steel tanks. Design shall follow the provisions of AWWA Standard D100, "Welded Steel Tanks for Water Storage," modified as follows:

[1] Tanks should be designed for Seismic Zone Zero.

[2] All permanent attachments to the tank shall be made prior to the hydrotest.

[3] The alternative design basis presented in AWWA D100 will not be used unless approved by the County Engineer.

[4] Aluminum dome roofs shall be used only by approval of the County Engineer.

[5] Tanks shall be provided with remote level sensing and recording equipment with telemetry to the Mattawoman WRF control building.

[6] The design professional will specify that the contractor will furnish at a minimum, the information listed in AWWA D100, forward, Paragraph iii.b.1 or iii.b.2, as appropriate.

[7] Silt stops are not required for welded steel tanks.

[8] Disinfection shall be performed by the contractor in accordance with § 291-63E(5)(a) of this chapter.

(c) Factory-coated bolted steel tanks. Design shall follow the provisions of AWWA Standard D103, "Factory-Coated Bolted Steel Tanks," modified as follows:

[1] Tanks shall be designed for Seismic Zone Zero.

[2] Coatings for bolted tanks are usually proprietary, and each tank manufacturer is different. The coating shall, therefore, be a consideration in the selection of a manufacturer.

[3] Foundations shall be installed by the contractor.

[4] Foundation selection in AWWA D103, Section 11.4, shall be based on site soil conditions.

[5] Aluminum dome roofs shall be used only by approval of the County Engineer.

[6] Silt stops are not required for factory-coated bolted steel tanks.

[7] Tanks shall be provided with remote level sensing and recording equipment with telemetry to the Mattawoman WRF control building.

[8] Disinfection will be performed by the contractor in accordance with § 291-63E(5)(a) of this chapter.

[9] The design professional will specify that the contractor will furnish, at a minimum, the information listed in AWWA D103, forward, Paragraph iv.

(3) Coatings and linings for steel tanks. Selection of coating and lining systems for steel tanks shall follow the provisions of AWWA Standard D102, "Coating Steel Water Storage Tanks," modified as follows:

(a) Use Outside Coating System No. 6 except the Dry Film Thickness (DFT) of the system selected should be a minimum of nine mils.

(b) Use Inside Coating System No. 2, Paint 2, except the dry film thickness (DFT) of the system selected should be a minimum of 13 mils.

(c) Roller application is the preferred method of application.

(d) Dry film thickness (DFT) is the preferred method to determine acceptability.

(e) The design professional shall specify that the contractor submit an affidavit of compliance that all materials and work comply with the applicable requirements of AWWA Standard D102.

(f) The design professional shall list in the project specifications all federal, state and local regulations regarding environmental issues.

(g) The design professional shall specify that the contractor will furnish for approval submittals for the coatings manufacturer to include, but not be limited to, application method, materials, and material safety data sheets.

(4) Cleaning. All finished water storage facilities shall be cleaned to remove all dirt and loose materials prior to disinfection of the structure. Only potable water shall be used to clean and rinse the water storage facilities. All equipment including brooms, brushes, spray equipment, and workmen's boots shall be disinfected before they are used to clean the storage facilities.

(5) Disinfecting and testing.

(a) Disinfection. All potable water storage facilities shall be satisfactorily disinfected in accordance with AWWA Standard C652, Chlorination Method 1, using calcium hypochlorite, prior to being placed in operation. The disinfection of the storage facilities shall be repeated until it is determined, by bacteriological testing, that the water is free of coliform bacteria.

(b) Testing. Testing of the water following disinfection shall be performed in accordance with AWWA Standard C652.

(6) Cathodic protection. If, at the direction of the County Engineer, cathodic protection is required the design shall follow the provisions of AWWA Standard D104, "Automatically controlled, impressed current cathodic protection for the interior of steel water tanks," modified as follows:

(a) The design professional shall retain the services of a NACE International (National Association of Corrosion Engineers) certified corrosion engineer to design the cathodic protection system.

(b) The design professional shall specify that the contractor shall furnish an affidavit of compliance for all applicable provisions of AWWA D104.

(c) The design professional shall use the Type A - IR drop-free potential measurement system.

(d) Long life anodes with a minimum life of 20 years shall be specified.

(e) The anode suspension system shall be a buoyant spider-type rope system with a design life of 20 years, minimum.

(7) Flexible membrane lining and floating cover materials.

(a) Design shall follow the provisions of AWWA Standard D130, "Flexible-membrane-lining and floating-cover materials for potable water storage," modified as follows:

(b) The design professional shall specify that the contractor furnish an affidavit of compliance for all installed materials.

(8) Distribution storage.

(a) Pressure variation. The maximum variation between high and low water levels in finished water storage structures which float on a distribution system should not exceed 30 feet or as approved by County Engineer. Large diameter, shallow depth reservoirs are preferable over small diameter, deep depth reservoirs.

(b) Level controls. Adequate controls shall be provided to maintain levels in distribution system storage structures at all times.

(c) A telemetering system and recording equipment shall be provided, to Mattawoman WRF control building, for the transmission and recording of storage levels in the distribution system.

[1] Altitude valves or equivalent controls may be required for subsequent structures on the system.

[2] Overflow, low level and pump malfunction warnings or alarms shall be transmitted to the Mattawoman WRF control building.

(d) Pressure tanks. Pressure tanks shall not be used for distribution storage systems. Pressure tanks may be used for small community systems if approved by the County.

§ 291-64 Sewer mains.

A. General.

(1) Sewer plans submitted for review and approval to the County will not be required to include the standard detail on the plan. The plans however must include a table, on the cover sheet, listing by detail number and name all sewer details which are applicable to the project. In cases where the County has no adopted standard detail for a specific construction method, the engineer must submit a special detail to the County Water and Sewer Engineer for review and approval. Once approved, the special detail shall be placed within the plans with notes in plan and profile on all applicable sheets referring to the special detail.

(2) Lines that serve two or more properties will be dedicated to the County.

(3) Lines terminated for future shall end with a manhole and a one-foot temporary capped stub.

(4) Computations shall be shown on the plans in accordance with Chapter 2, Subsection 1.J, Technical Bulletin: M-DHMH-EHA-S-001 Edition "Design Guidelines for Sewer Facilities," State of Maryland.

(5) Provide concrete encasement for protection of sewer mains per State Health Standards/Maryland Department of the Environment requirements as they relate to the vicinity of other utilities. Concrete encasement is also to be provided where SDR-PVC mains have less than a two-foot clearance under storm drains, C-900-PVC and ductile iron mains have less than a one-foot clearance under storm drains, under stream crossings, and on a case-by-case basis as determined by the County.

(6) Ductile iron pipe and restrained joints, in accordance with the County Standard Specifications for Construction Manual and Standard Detail Manual, shall be used for jack and bore carrier pipe.

(7) Ductile iron pipe with VITON or NBR rubber gaskets is required if gasoline storage is within 100 feet of the lines or if there is the presence of petroleum products within the soil.

(8) Sewer mains are to be constructed to the property line of all adjacent properties for future extension. If the adjacent property is designated as commercial, industrial or subdivided, the main extension should be sized appropriately.

(9) The repaving of roads shall be in accordance with the County Standard Specifications for Construction Manual and Standard Detail Manual.

B. Collector sewers.

(1) Design basis. A sewage collection system shall be designed, to service the potential development of the sewerage service area at full build out based on the Zoning Ordinance permitted densities and current design criteria.[1] Systems shall also be designed to connect with existing trunk lines or sub-interceptors at existing stub-outs wherever feasible. Whenever cost-effectiveness permits, the construction may be programmed in stages to accommodate both present and future needs. Special attention shall be paid to the depth of sewers adjacent to drainage ways such that the sewer is deep enough to accept flow from both sides of the drainage way. Sufficient cover over the sewer is required to prevent adverse affect on the drainage way.

[1] Editor's Note: See Ch. 297, Zoning Regulations.

(2) Existing development. In developed areas, the basis for the flow projection shall be the actual number of single or multifamily homes, apartments units, various types of businesses, etc., present in the drainage area as determined by field count. An allowance shall be made for undeveloped areas as described below. Unless field investigations give reason to choose a different number, it shall be assumed that 2.83 persons reside in each dwelling unit. If there is strong evidence from field investigations that sufficiently less than 2.83 persons reside in each dwelling unit in the drainage area and that this condition will persist throughout the design period, the County will consider using a smaller number for design.

(3) Future development.

(a) In small undeveloped areas, the basis for flow projection shall be the maximum number of residential units per acre according to current zoning regulations. This applies to residential or mixed residential/commercial zones. It shall be assumed that 2.74 persons will reside in each dwelling unit. In the case of small undeveloped portions of commercial or industrial zones, design flows shall be based on the land use consistent with current zoning regulations which would provide the most likely maximum sewage flow.

(b) In large, undeveloped areas, the average daily flow for a given zoning classification shall be as given in Appendix S, regarding flow generation rates by zoning classification.[2]

[2] Editor's Note: Said appendix is included as an attachment to this chapter.

(4) Average daily flow.

(a) The average daily flow for collector sewers is based on the population and land use inventories and projections described above. Appendices T and U are compilations of average daily flow generation rates for various types of establishments.[3] The flow from each existing establishment shall be based on Appendix T when the number of persons using the facility can be determined or on Appendix U when only the gross area of the facility can be determined. The average daily flow shall be the sum of the flows projected for the existing or ultimate land use of each lot or parcel in the service area. In the case of largely undeveloped service areas, the average daily flow shall be based on Appendix S, as described in § 291-64B(3).

[3] Editor's Note: Said appendixes are included as attachments to this chapter.

(b) Average daily flows given in the appendices for industrial facilities are for domestic-type flows only. Flows generated by industrial processes must be determined on a case-by-case basis.

(5) Peak domestic flow.

(a) The peak domestic flow is the average daily domestic flow peaked in accordance with the curve entitled "Diagram for Converting Average Daily Domestic Flow to Peak Flow" (Appendix V).[4]

[4] Editor's Note: Said appendix is included as an attachment to this chapter.

(b) Peak commercial or industrial flow is the average daily commercial or industrial flow peaked in accordance with a factor determined by evaluation of historical data for the commercial or industrial facilities and the periods in which these flows are generated. If historic peaking data for these facilities is unavailable, the average daily domestic flow, average daily commercial flow, and average daily industrial flow may be combined and then peaked using the curve in Appendix V.[5]

[5] Editor's Note: Said appendix is included as an attachment to this chapter.

(c) When evaluating and designing sewers that convey flow discharged from pump stations, the peak flow calculation for each downstream sewer section from the point of discharge, shall include the design pumping rate of the pump station within the calculation.

(6) Infiltration and inflow.

(a) In the evaluation and design of sewers both future and existing, a minimum infiltration rate of 400 gallons/acre of service area per day shall be used. A higher rate of infiltration may be justified if there is evidence of poor soil conditions, high groundwater table, or deteriorated SHCs.

(b) New nonsanitary connections to sanitary sewers are strictly prohibited.

(7) Design hydraulic flow. The design hydraulic flow shall be the sum of the peak flows determined as described in § 291-64B(5), the infiltration rate determined as described in § 291-64B(6), and any industrial flows.

C. Interceptor sewers. Determination of design hydraulic flows for interceptor sewers shall be generally as outlined for collector sewers. Interceptors which carry flows from a significant number of older collectors may have infiltration rates far in excess of 400 gallons/acre/day. ASCE manuals on Engineering Practice No. 37 (WPCF MOP-9) and No. 60 (WPCF MOP FD-5) should be consulted for further information on computation of design flows for interceptor sewers. In all cases, the design hydraulic flows shall be approved by the County prior to proceeding with sewer design.

D. Hydraulic criteria.

(1) Collector sewers.

(a) Size. The size of the sewer shall be sufficient to carry the previously discussed design hydraulic flow with the hydraulic gradient coincident with or slightly below the crown of pipe. Size shall be determined by the relationship Q = VA, where:

	Q	=	Quantity of sewage in cubic feet per second (design flow). All flow calculations shall be expressed in GPM, GPD, MGD and CFS.
	V	=	Velocity in feet per second
	A	=	Required cross section area of conduit in square feet

(b) Velocity.

[1] Velocity shall be determined by the manning formula:

	V	=	1.486 R2/3S1/2
			n
	n	=	Coefficient of roughness as indicated in Appendix W[6]
	S	=	Slope in feet per foot
	R	=	Hydraulic radius-area divided by wetted perimeter

[6] Editor's Note: Said appendix is included as an attachment to this chapter.

[2] Minimum velocities of 2.5 feet per second shall be provided. Minimum velocities shall be determined based upon present average sewage flow. Appendix X (Mannings Formula Solutions) shows required slopes for various velocities with pipes flowing full. Appendix Y (Hydraulic Elements of Circular Section) indicates hydraulic elements of pipes flowing partially full.[7]

[7] Editor's Note: Said appendixes are included as attachments to this chapter.

[3] Where velocities greater than 15 feet per second are attained, provisions shall be made to protect against erosion and displacement by shock. If practical, suitable drop manholes shall be provided to reduce steep slopes so as to thereby limit the velocities in pipes and manholes. When drop manholes are impractical for reduction of velocities, the sewer shall be ductile iron or other abrasion resistant material as approved by the County.

(2) Interceptor sewers.

(a) Size. Interceptor sewers shall be sized to carry the design hydraulic flow when two-thirds full (i.e., the maximum hydraulic grade line will be at [D/d -] d/D = 0.67 per Appendix Y.

(b) Velocity. Velocities in interceptor sewers shall be as presented in § 291-64D(1)(b).

(3) Force mains.

(a) General.

[1] The design of a wastewater force main must be coordinated with the design of the wastewater pumping station. The proposed alignment and profile of the force main shall depict the changes in force main elevations and strive to achieve a vertical profile that rises continuously from the pumping station toward the transition manhole. The need for air and vacuum relief valves shall be evaluated and minimized as much as possible by adjusting the force main profile to minimize high points. The system curve for the force main, showing the total energy losses associated with the range of possible pumping rates, shall be developed and provided on the plans.

[2] HGL profiles shall be developed for the various flow scenarios planned for the pumping station using the system curve for the force main. All HGL profiles shall be provided on the plans separately from the standard force main design profiles and shall indicate hydraulic gradients, flows, force main velocities, design friction coefficients, existing ground, proposed pipe invert elevations and all other pertinent data.

(b) Size.

[1] Force main size shall be based on the required pipe's maximum carrying capacity to convey the design flow rate within the required velocities per § 291-64D(3)(c), while minimizing life cycle, construction, maintenance, and operational costs. The minimum force main size shall be four inches.

[2] The Hazen-Williams (HW) equation shall be used for calculating friction losses in force mains. Minor losses at transitions and bends shall also be added in the determination of the total energy losses, the hw coefficient of roughness ("C" factors) for force mains shall be as follows:

	Material	"C" factor
	DIP (new)	140
	DIP (design)	120
	DIP (old)	100

[a] The Hazen-Williams factors indicated are representative of long-term design values for the system. The designer shall check all pump station and force main selections for the anticipated lower headlosses (higher C value representing new conditions) and higher headlosses (lower C value representing old conditions) to ensure the satisfactory operation throughout the design life of the system.

[3] The static head shall be based on the difference in vertical elevations between the lowest "normal pump stop" level in the wet well and the point the force main discharges to the gravity sewer or at the highest point along the system, whichever is higher.

(c) Velocity. Forcemain design velocities shall be a minimum of 2.5 feet per second and a maximum of 5.0 feet per second.

(d) Water hammer. The design professional shall prepare a complete study of each force main design in conjunction with the related pumping station. A written detailed analysis along with supporting plans and calculations shall be submitted to the County for approval prior to completion of the design and the contract drawings. This analysis shall include, but is not necessarily limited to the following:

[1] Transient pressures due to water hammer and the effect of these pressures on the entire system.

[2] Investigation of the pipeline profile to determine the possibility of water column separation.

[3] Reverse rotation characteristics of the pumps.

[4] Shut-off characteristics of the proposed pump control valves.

[5] A graphic solution of the transient pressures combined with the total system characteristics.

[6] Substantiation for the use of surge valves, when necessary, listing recommended size and computed discharge pressures. The maximum transient pressure plus the static head shall not be greater than the working pressure strength of the pipe and associated appurtenances.

(e) Hydrogen sulfide control. The design at a minimum, shall address hydrogen sulfide control as follows:

[1] In areas where hydrogen sulfide is a concern the designer shall minimize the number of drop manholes to the maximum extent possible (i.e., drops downstream of force main discharge).

[2] All interior surfaces and inverts of sanitary sewer manholes including the transition manhole shall be coated with a hydrogen sulfide resistant material per County specifications. The coverage of protection shall be from either a force main or grinder pump discharge to the first downstream manhole or within 400 feet, whichever is greater. In addition, hydrogen sulfide protection shall be provided where turbulence may be caused due to a drop manhole, severe pipeline slopes or any other sources of turbulence within a sewer system. Protection must be provided to all surfaces exposed to the sulfides. All applications of specialized coatings and liners are subject to the review and approval of the County engineer. See the standard specifications for all coating and lining material requirements.

[3] The design shall also address odor control and may warrant additional corrosion control measures if high concentrations of hydrogen sulfide are expected. The designer shall provide an evaluation of the system and indicate the measures proposed to address odor and corrosion control.

E. System layout criteria.

(1) Collector sewers.

(a) Horizontal layout.

[1] General. Collector sewers shall be laid on tangents only. All changes of direction and connections to other collector sewers shall be accomplished at manholes. In laying out the sewer, the design engineer shall take into full account such factors as environmental impact, maintenance of traffic, maintenance of existing utility services, constructability, and system maintenance, and shall produce the overall most cost-effective design.

[2] New subdivisions. In new subdivisions, collector sewers shall be located five feet from the centerline of the street right-of-way, generally on the side of the street toward low ground. Collector sewers shall be located within the pavement area wherever possible, no less than five feet from the face of existing or proposed curb. Where it is not feasible for manholes to be located within the pavements, they shall be located wholly within the grass plot or wholly within the grass plot between the curb and sidewalk. On private roads and parking areas manholes are to be located outside of parking areas. Manholes will not be allowed in sidewalk.

[3] Existing developments (closed section roads). In existing developments with curbs, sewer location shall generally be the same as in new subdivisions. The location of other existing and proposed utilities shall be fully considered.

[4] Existing developments (open section roads). In existing developments without curbs, collector sewers shall generally be located four feet outside of the edge of pavement, except that the sewer shall not be located under a future curb. The location of other existing and proposed utilities shall be considered.

[5] Parks and public rights-of-way. Where location of sewer would require the removal of or damage to trees within parks or public rights-of-way, design engineers shall obtain approval of the state department of forestry for sewer alignment and trees to be removed.

[6] Easements. All sewer utility easement widths shall be in accordance with latest plan preparation package. No other utilities or structures will be allowed in the sewer utility easement without written County approval.

(b) Profile layout.

[1] Grades. Grades shall be such as to require the least excavation while satisfying minimum and maximum velocity requirements, clearances, and depth requirements discussed hereinafter. All collector sewers shall be on tangent grades with required breaks in grade accomplished in manholes.

[2] Depth. In developed areas, sewer inverts shall be a minimum of [two feet + H] below the basement elevations, where H = length of house lateral connection between the sewer and the point of connection to the existing house sewage system, or stack, multiplied by the required house connection slope. For houses without basements, sewers shall be a minimum of [two feet + H] below the first floor elevations. In all cases, sewer depth shall be sufficient to meet criteria established for house connection, depth, grade, and clearance.

[a] Sewers at stream crossings shall be constructed with a minimum of three feet of cover between the pipe and stream invert. At all stream crossings, the design engineer shall consider such items as flotation, stream meandering and scouring, and infiltration; and shall include protective measures for such in the design.

[3] Upstream of pumping stations.

[a] Protection of private property from collection system surcharges where a plumbing drainage system is subject to backflow of sewage from the public sewer or private disposal system, suitable provision shall be made to prevent overflow in the building.

[b] In order to insure that surcharges in the collection system and/or pumping station failures will not result in sewage backing up into basement and first floor plumbing fixtures of nearby residences, the design of all pumping station collection systems shall:

[i] Determine the rim elevation of the next upstream manhole in the public sewer from the building.

[ii] For projects having basement service, all basement elevations lower than the manhole frame and cover established in § 291-64E(1)(b)[3][a][i] above shall be identified, fixtures and/or drain inlets subject to backflow and flooding from blocked or restricted public sewers shall be protected by a backwater valve. Such situations include those where fixtures and/or drains are located above the crown level of the public sewer at the point of connection thereto but are below the overflow level of the public sewer.

[iii] For projects or portions of projects having first floor service only, first floor elevations lower than the manhole frame and cover established in § 291-64E(1)(b)[3][a][i] above shall be identified and protected by a backwater valve.

[iv] All vacant lots having a ground elevation lower than the manhole frame and cover established in § 291-64E(1)(b)[3][a][i] above shall be identified.

[4] Gravity service not to be provided. Sewer project plans shall clearly label any improved lots for which gravity service is not to be provided. Any recommendation for not providing gravity service is to be documented, with the reasons therefore, by the design engineer to the County for approval. For lots where it is determined that gravity service is not available, a note shall be placed on the drawings as follows:

"A grinder pump is required for sewer service to this lot. The grinder pump and associated low pressure sewer system shall be owned, operated, maintained, and replaced by the property owner."

(c) Clearances of other utilities.

[1] Interactive considerations. In general, existing utilities have prior right to maintain their location. The existence and location of such utilities must be considered when designing new sewers. Clearance shall be measured between outside of pipes. Design engineers shall investigate clearance between sewer and other utilities, both existing and future.

[a] General. The following design factors must be considered in providing adequate separation:

[i] Materials and type of joints for water and sewer pipes.

[ii] Soil conditions.

[iii] Service and branch connection into the water main and sewer line.

[iv] Compensating variations in horizontal and vertical separations.

[v] Space for repair and alterations of water and sewer pipes.

[vi] Location of manholes.

[b] Parallel installation. A horizontal distance of at least 10 feet shall separate water mains and sewers. The distance shall be measured edge to edge. In cases where a ten-foot separation is not practical, deviation may be allowed on a case-by-case basis subject to County and state approval if supported by data from the design engineer. Such deviation may allow closer installation provided that the water main is laid in a separate trench or on an undisturbed earth shelf located on one side of the sewer at such an elevation that the bottom of the water main is at least 18 inches above the top of the sewer.

[c] Crossings. Where water mains must cross sanitary sewers, building drains or storm drains cross, there shall be a vertical separation of 18 inches between the bottom of the water main and the top of the sanitary sewer, building or storm drain. This vertical separation must be maintained horizontally for a distance of 10 feet. The ten-foot distance is to be measured as a perpendicular distance from the sewer, building or storm drain to the water line.

[d] Exceptions. When it is impossible to obtain the proper horizontal or vertical separation as stipulated above, both the water and sewer lines shall be constructed of ductile iron with mechanical joints. Other types of pipe and joints with equal or greater integrity may be used at the discretion of the County. Thermoplastic pipe may be used with mechanical or solvent weld joints. These installations shall be pressure tested to assure water tightness before backfilling. Where a water main must cross under a sewer, additional protection of the water main shall be provided. The County shall be consulted to discuss the use of double casing or concrete encasement of the sewer and/or water main.

[2] Separation of utilities and sewer manholes. No utilities shall pass through any part of a sewer manhole.

[3] Clearances at other utilities. Sewers shall have a minimum of 12 inches of clearance from drains, gas mains, and other unspecified utilities. If 12 inches cannot be maintained at crossings, provide encasement of sewer for the width of the utility trench.

(d) Appurtenances.

[1] Manholes.

[a] Details are shown in the Standard Details Manual. The designer shall use these standards as required to meet the design situation and shall designate the type of each manhole on the drawings.

[b] Manholes and vaults are to be constructed two feet above finished grade in flood plains and nonmaintained areas.

[c] Maximum spacing for manholes on sewers less than 18 inches in diameter shall be 400 feet; 500 feet for sewers 18 inches to 27 inches in diameter; and 600 feet for sewers larger than 27 inches.

[d] Line manholes shall be used at all changes of pipe size, grade, alignment, or connections of two or more sewers. A minimum drop of 0.10 feet between influent and effluent inverts shall be used at line manholes.

[e] Interior coating of manholes shall be as specified in the Charles County Standard Specifications for Construction Manual.

[2] Frames and covers.

[a] Provide a bolt-down frame and cover for all manholes in flood plains and nonmaintained areas in accordance with the County Standard Detail Manual.

[b] Watertight frames and covers are to be provided for manholes within flood plains, ditches or other areas of collecting or passing water.

[c] All manhole frames and covers that are not bolt-downs shall be fitted with manhole cover inserts/liners to minimize the amount of inflow and sediment that enters the sewer system. The inserts shall be installed upon "substantial completion."

(e) Structural considerations.

[1] Soil conditions/foundations. Where extremely poor soil conditions, such as running sand, material with high organic content, etc., are anticipated, design engineers shall secure soil samples and discuss the analysis of the samples with the County. In all cases, a proper foundation shall be provided for pipes. Where pipes are to be placed on fill, ductile iron pipe shall be placed on timber pile bents unless special measures satisfactory to the County are taken to consolidate the fill.

[2] Grades/anchors. Sewers designed on slopes of 20% or greater shall have anchorages in accordance with the Standard Details Manual as follows:

[a] Twenty percent to 34%: 36 feet center maximum.

[b] Thirty-five percent to 50%: 24 feet center to center (maximum).

[c] Greater than 50% [+] - 16 feet center to center (maximum).

[3] Under drains. Where there is evidence of spring heads or a high groundwater table in the area of the proposed sewer, under drains shall be provided and shown on the drawings.

[4] Depth and loading. Minimum and maximum permissible depths and loadings for pipes of the various types and classes shall be in accordance with the Standard Specifications for Construction Manual and the manufacturers' recommendations and bedding requirements. Manufacturers' data shall be submitted as part of the plan submittal.

(f) Venting. The design engineer shall indicate the method of proposed ventilation of gravity sewers if other than manhole top openings.

(2) Interceptor sewers. There shall be no service connections made directly to interceptor sewers. All service connections shall be made at manholes. Once the interceptor has been installed, no new manholes may be constructed over interceptor sewers.

(a) Horizontal layout.

[1] Interceptor sewers generally follow streams or the valley of a drainage area. They shall be located so as to best serve the drainage area. Special caution is required to insure the proper location of manholes for future connection of collecting sewers.

[2] All sewers, especially interceptor sewers shall be laid with straight horizontal and vertical alignment between manholes. Horizontal and/or vertical curves shall not be employed on gravity sewer mains.

(b) Profile layout.

[1] Grade requirements shall generally be as described for collector sewers in § 291-64E(1)(b)[1]. The depth of interceptor sewers is not directly controlled by lot and house elevations. The depth of interceptor sewers shall be sufficient to allow connection of all existing and foreseeable future collector sewers within the service area served. In general, the top of the sewer elevation should be a minimum 3 1/2 feet (42 inches) lower than the stream bed and have six feet of cover where possible.

[2] Sewers at stream crossings shall be constructed with a minimum of 3 1/2 feet (42 inches) of cover between the pipe and stream invert. At all stream crossings, the design engineer shall consider such items as flotation, stream meandering and scouring, and infiltration; and shall include protective measures for such in the design.

(c) Clearances at other utilities. The requirements for horizontal and vertical clearances between interceptor sewers and other utilities shall be the same as those for collector sewers. See § 291-64E(1)(c).

(d) Appurtenances.

[1] Manholes. Manhole requirements for interceptor sewers shall be the same as those for collector sewers, § 291-64E(1)(d)[1], with the following modifications:

[a] Manholes will be required where collector sewers join the interceptor.

[b] Precast concrete manholes constructed in these areas shall meet the standard ASTM C478 criteria.

[2] Frames and covers. Frame and cover requirements for interceptor sewers shall be the same as those for collector sewers, § 291-64E(1)(d)[2].

(e) Structural considerations. Structural considerations shall be the same as for collector sewers. See § 291-64E(1)(e).

(3) Force mains.

(a) Layout. Force mains shall be located within public rights-of-way or easements.

(b) Material. Force main material shall be ductile iron.

(c) Profile.

[1] Ideally, the force main shall be designed without intermediate high points and with the top of the force main being below the hydraulic grade line at the minimum pumping rate so that air release valves will not be needed. If the elimination of high points is not feasible or if the design requires long, relatively flat vertical alignments, the design may require air release and air and vacuum valves.

[2] Blowoffs along four-inch and larger force mains are required where the force main contains a depressed section between two high points.

[3] Continuous uphill pumping is preferred for a force main, where the force main discharge point to the gravity sewer is at a higher elevation than the rest of the system, so as to keep the force main full.

[4] Force mains with intermediate high points above the gravity sewer discharge point can create partial vacuum conditions in the force main under circumstances such as draining conditions that occur due to intermittent pumping or when the HGL profile drops below the pipeline profile. The designer shall provide appropriate air release and air vacuum valves to protect the force main against damage under these conditions.

[5] Downhill pumping is prohibited.

[6] All force mains shall have a minimum 3.5-foot depth of cover. In street rights-of-way cover shall be measured from the top of the force main to the proposed grade, or in cases when the proposed grade is above the existing ground surface, the depth of cover shall be measured from the existing ground line. In easements across private property, future development in the area shall be given consideration when developing the force main profile and possible future development grades shall be evaluated to ensure that the minimum depth of cover is met.

[7] The top of the force main and its appurtenances shall generally be designed to be lower than the HGL. If the top of the force main is above the HGL, then the fm should be lined with Protecto 401 or better for a sufficient distance to eliminate H₂S corrosion.

(d) Clearance.

[1] Sanitary force mains paralleling water mains shall have a minimum clearance of 10 feet horizontally and shall be a minimum of 1.5 feet below water main.

[2] Sanitary force mains shall have a minimum of one foot vertical clearance when parallel to or crossing other utilities.

[3] Clearance shall be measured from the outside diameter of the pipes.

(e) Appurtenances.

[1] Pipe deflections. Force mains may be curved by deflecting the alignment at the joints. Deflection at the joints shall not exceed 1/2 the maximum as set forth by the manufacturer of the pipe used.

[2] Air release and air/vacuum release valves.

[a] Valves shall be constructed per County specifications and details. The following guidelines shall be used to locate air and vacuum release valves:

[i] Peaks in profile.

[ii] Abrupt increases in downward slopes.

[iii] Abrupt decreases in upward slopes.

[iv] Long ascents: 1,500 feet to 3,000 feet intervals.

[v] Long horizontal: 1,500 feet to 3,000 feet intervals.

[vi] At pumps: on the discharge pipe as close as possible to the check valve.

[vii] At large valves or bypass piping.

[b] The air and vacuum release valve vault will be vented above ground as shown on the standard details. Odor control measures, such as soil odor filters, may be required by the department if air release valves are located near populated areas. Air release valve bypasses may be required at the County's option. Intakes for vacuum valves shall be above the one-hundred-year flood elevation to allow proper operation of the valve during flood conditions.

[3] Blowoff valves shall be located at all low points along the force main per County standard details manual.

[4] Isolation valves shall be located at intervals and crossings as stated under section § 291-62D(8)(b)[1] and [5] and at air/vacuum/blowoff valve locations.

(f) Structural considerations.

[1] Pipe loading. Minimum and maximum permissible depths and loadings for pipes of the various types and classes shall be in accordance with County standard details and the manufacturers' recommendations and bedding requirements. Manufacturers' data shall be submitted as part of the plan submittal.

[2] Anchorages. Force main design shall have anchorages in accordance with the standard details manual.

(g) Test. Leakage tests shall be in accordance with the procedures outlined in the latest County specifications.

F. Grinder pumps/pressure sewer systems/step systems. Alternative wastewater systems will be reviewed on a case-by-case basis, but will not be considered as a method of providing sewer service that could otherwise be furnished by conventional gravity systems (including pumping stations). Unless otherwise agreed to, grinder pumps are to be privately operated and maintained and must adhere to the County Standard Specifications for Construction Manual.

G. Sewer house connections.

(1) Location. The County-owned portion of house connections shall be built to the right-of-way/property/easement line for all lots within proposed developments. All adjacent improved lots which are not a part of the proposed development, but which front and may be served by the service line, shall have the sewer service laterals, including cleanouts, constructed to the right-of-way/property/easement lines. Twin sewer house connections shall be allowed and encouraged. Service lines for house connections shall not be connected directly to interceptor sewers.

(2) Size. Connections to large buildings such as apartments or factories shall be designed and sized in accordance with the criteria previously presented for collector sewers. The minimum connection size for buildings shall be six-inch diameter from the main to the clean-out and four-inch from the clean-out to the building.

(3) Materials. House and building connections shall be in accordance with the latest County Standard Specifications for Construction Manual.

(4) Appurtenances. Clean-outs shall be provided on all house and building connections at the right-of-way/property/easement line. Clean-outs shall be shown and constructed in accordance with the latest County Standard Specifications for Construction Manual and Standard Detail Manual.

(5) Grades. House and building connections shall be designed such that service is provided for all lots to the mid-point of the lot at a two-percent minimum grade, unless otherwise approved by the County. The maximum grade shall be 6%. House and building connections may have a one-percent minimum grade as determined by the County on a case-by-case basis. Minimum cover at the right-of-way/property/easement line shall be 42 inches. Where storm drains have been designed, or have not been installed, house connections shall have a minimum cover within the street right-of-way of 6.5 feet.

(6) Clearance.

(a) Parallel to water house service. Sewer house services shall ordinarily be placed 10 feet horizontally and one foot vertically under and from the water house connections. In cases where this is not achievable, deviation may be allowed on a case-by-case basis subject to County and/or state approval. Such deviation may allow a horizontal separation of 1.5 feet with at least a six-foot vertical clearance (sewer being placed on the bottom). If schedule 40 PVC solvent weld pipe is utilized for the sewer house connection a 1.5 foot horizontal separation with at least a one-foot vertical clearance (sewer being placed on the bottom) may be allowed if a passing pressure test with 10 feet of head of water or equivalent taken in the presence of a County representative is achieved.

(b) Crossing storm drains or other utilities. Sewer house and building connections crossing storm drains and other utilities (existing or future) shall have a minimum clearance of 12 inches from these utilities.

(7) Structural considerations. Structural considerations shall be the same as for collector sewers. See § 291-64E(1)(e).

H. Grease interceptors.

(1) Are required for all food preparation facilities.

(2) To be located outside the building and constructed in accordance with the County Standard Detail Manual.

(3) Shall be sized for a minimum capacity of 2,000 gallons.

(4) To be shown in plan and profile with inverts and elevations.

I. Oil and flammable liquids separators. Oil and flammable liquids separators are required in accordance with COMAR requirements.

J. Flag lot sewer utilities.

(1) For a two flag lot maximum, service laterals will be provided off of the main and include a clean-out at the right-of-way or easement line. Sewer service for each lot shall be located on each side of the driveway. Adequate easements are to be provided outside of the common access easement if necessary. The sewer service must be constructed in conjunction with the main from the clean-out to the building lot and capped for future connection. The end of the service should be marked in accordance with the County Standard Detail Manual. Clean-outs are to be provided every 75 feet and at the end of the lateral. Extension of the service as indicated above will prevent problems associated with the construction of the driveway prior to the construction of all sewer services.

(2) For three or more flag lots, provide an extension of the sewer main to the last lot and terminate with a manhole. Provide service connections to all adjacent lots, with clean-outs located at the easement line. Adequate easements are to be provided on both sides of the sewer main and services and must extend outside of the common access easement if necessary.

§ 291-65 Minimum design guidelines and requirements for wastewater pumping stations and related facilities.

A. General.

(1) In addition to the criterion contained herein, the design of wastewater pumping stations and related facilities shall meet the requirements of the 1978 edition of the State of Maryland "Design Guidelines for Sewage Facilities" or shall be exceeded where specified by the County. The following additional manuals shall be consulted and applied to the design with the approval of the County:

(a) Water Environment Federation Manuals of Practice.

(b) Recommended Standards for Sewage Works, (latest edition) also known as the "Ten State Standards."

(c) "Pumping Station Design," 3rd Edition (or latest), 2006, by Garr M. Jones.

(d) "Design and Construction of Sanitary and Storm Sewers," 1969 by ASCE (MOP NO. 37) and WPCF (MOP NO. 9).

(e) "Odor Control in Wastewater Treatment Plants," 1995, WEF (MOP NO. 22) AND ASCE (MOP NO. 82).

(2) All aspects of the facility shall maximize operator safety. The facility shall be designed to operate reliably and efficiently with a minimum of attention and have provisions for easy access and maintenance. Equipment shall be selected on the basis of durability, availability of replacement parts, standardization, efficiency, and ease of maintenance and repair.

(3) The pumping station shall be designed for the maximum build out conditions of the wastewater pumping station service area as approved by the County using flows approved by the County.

B. Hydraulic computations.

(1) Design hydraulic flow rate.

(a) Wastewater pumping stations shall satisfy the design hydraulic flow rate. Refer to § 291-64B and C.

(b) A drainage area map and tabulation of the design flow shall appear on the plans. The map and tabulations shall show initial and ultimate drainage areas and wastewater flows.

(2) Wastewater composition. Wastewater composition can vary widely depending upon the proportion of design flow generated by nondomestic users. Nondomestic user wastewater composition shall be investigated and the results included in the Engineering Report provided to the County Engineer. Adequate consideration and all necessary provisions shall be taken to ensure that wastewater pumping station equipment and materials are suitable for the anticipated composition of the wastewater. Consultation with the County Engineer is required in the event that the wastewater composition affects standard material and equipment requirements.

(3) Number of pumps. Wastewater pumping stations shall be capable of pumping the design hydraulic flow rate with the largest single pump out of service.

(4) Wetwell sizing. A minimum cycle time of 15 minutes is to be provided. Wet well capacity (in gallons) from pump on to pump off shall be of four times the capacity of the largest pump (in gallons per minute) for pumping stations with a three-pump arrangement or greater, the minimum cycle time of 15 minutes shall be provided for each pump. Larger pumps may require cycle times greater than 15 minutes to satisfy motor manufacturer requirements.

(5) Hydraulic analysis.

(a) Wastewater pumping stations must satisfy the hydraulic conditions of the system. The designer shall perform a complete hydraulic analysis of each wastewater pumping station, the hydraulic analysis shall consider potential impacts on existing force mains, gravity sewers and pumping stations when the new pumping station is added to the system. See § 291-64, Sewer mains, for force main design requirements and analyses that must be performed in conjunction with the pumping station design.

(b) Wastewater pumping stations shall be designed to operate at the appropriate discharge head and flow rate without the need for throttling valves or flow restriction devices.

(6) Pump and system curves.

(a) System curve (head versus flow) characteristics shall be determined by the Hazen-Williams formula for piping head loss. The pump/system curve shall be shown on the plans to scale. The pump/system curve shall show the following information at a minimum:

[1] Static head.

[2] System curves for both new, design, and existing system conditions.

[3] Pump curve: include single and multiple pump performance curves. If VFDS are used, multiple speed performance curves shall be shown.

[4] Pump horsepower, efficiency and rpm.

[5] Pump manufacturer's published recommended range of operation.

(b) Pump/system curves shall be shown for single pump operation, as well as for multiple pump operation in stations having three or more pumps. Hazen-Williams "C" factors used in evaluating pump and system curves shall be in accordance with the guidelines given in § 291-64, regarding hydraulic calculations, of this chapter for various pipe materials.

(7) Water hammer. The potential impact of water hammer under usual and unusual circumstances (power outages, etc.) shall be evaluated. If the combined effects of static head and water hammer (using a safety factor of 1.1) do not exceed the weakest piping system component working pressure, no special provisions need to be included to control water hammer. Where the maximum water hammer pressure (using a safety factor of 1.1) exceeds the weakest piping system component (all piping, fittings, thrust blocks, and other appurtenances) working pressure, strengthen those elements affected, reevaluate pipe size and velocities or select an appropriate device to control water hammer. No pressure vessel/surge tank type devices will be acceptable.

(8) Pump selection criteria.

(a) Provide proper wet well design and suction line design per hydraulic institute standards to avoid cavitations. The designer shall perform a Net Positive Suction Head Available (NPSHA) analysis and include this information in the pump specification.

(b) The NPSHA shall be calculated for the expected design flows and shall exceed the pump manufacturer's requirements by an added margin of safety of not less than five feet. Pumps shall be selected to have their maximum efficiency at the operating design point. Under no circumstances shall a pump be specified to operate outside of its published recommended range under new through old system operating conditions. Examples would be pumps operating at very low flows and high heads, near shutoff heads, or "runout" conditions (maximum possible flow rate of the pump). These conditions can result in excessive hydraulic loading or cavitation damage to impellers, casings and shafts, rapid bearing and mechanical seal wear, and high vibration. The designer shall avoid the selection of pumps whose curves are flat (i.e., small changes in head resulting in large changes in flow rate).

C. Types of wastewater pumping stations and selection. Charles County wastewater pumping stations are divided into two categories, large (500 gpm and greater) and small (less than 500 gpm). The types of stations allowed are described below along with acceptable selection criteria. Station selection shall be determined by the County.

(1) Large pumping stations. Conventional: This type of pumping station is defined here as pumping stations in which the wet well and dry well structures are assembled or constructed on site and are typically used for flows 500 gpm and greater. The preferred method of construction is for the contractor to use precast concrete sections. However, if the configuration or sizes would make this unfeasible then cast-in-place concrete sections will be permitted with the approval of the County. To help prevent overflows and maintain continuous operation during maintenance procedures, pumping stations shall have divided wetwells. Dry wells, including their superstructure, shall be completely separated from the wet wells. To facilitate differential settling or unforeseen movement, flexible joints shall be placed in the piping between all structures. All of the piping, valves, wiring and controls are assembled on-site by the contractor. Conventional wastewater pumping stations shall be engineered to meet the requirements of these guidelines, as well as any supplemental guidelines imposed by the County Engineer on a case-by-case basis. These stations will have a wet well/dry well configuration and be of precast or cast-in-place concrete construction. Conventional pumping stations shall be designed as long-term (greater than 30 years) facilities. The design of conventional stations shall include room for anticipated expansion. The following guidelines and features shall be incorporated in the design of these stations:

(a) Site design.

[1] Location: wastewater pumping stations shall be located as far as possible from populated areas. Natural screening and remoteness of the site shall be primary elements of site selection wherever possible. Where pumping stations are sited in proximity to developed areas, the architecture of the station shall be compatible with the surrounding area. Predominant wind direction for potential odor dispersion and building aspects such as generator exhaust and ventilation fan noises shall be considered. Similarly, building setbacks shall be considered to provide minimal impact to neighboring properties.

[2] Land acquisition: land required for pumping stations, including necessary vehicular access routes to an existing or proposed public roadway shall be owned in fee simple by the County. As part of this process, a boundary survey of the property is required together with a record plat and a metes and bounds description of the parcel. In determining the space requirements for the facility, particular attention shall be given to the width provided for the access road to ensure adequate space for grading and drainage within the access road right-of-way and easy access for maintenance and delivery trucks.

[3] Topography: sewers tributary to wastewater pumping stations commonly dominate site selection. Adjacent drainage areas potentially served by the wastewater pumping station must also be considered. Wastewater pumping station site selection shall also be compatible with suitable site access, drainage, and soil capability with respect to land grading in conjunction with site development. Existing contours and other topography shall be shown for the entire site including a one-hundred-foot minimum width outside of the proposed property boundary on all sides.

[a] Contour interval shall be two-foot, unless otherwise approved by the County Engineer.

[4] Floodplain: wastewater pumping stations shall be sited to remain operational and permit access during a one-hundred-year return frequency flood. All top slab elevations of structures shall be set a minimum of two feet above the one-hundred-year floodplain elevation. The access road shall be above the one-hundred-year floodplain elevation.

[5] Wetlands: avoid direct impacts wherever possible and minimize impacts to wetland buffer areas. Buffer areas include the first 25 feet beyond non-tidal wetlands.

[6] Grading: wastewater pumping station site grades shall prevent local ponding and provide positive drainage away from all structures and site. The site shall be a minimum of one foot above the surrounding area. Slopes on site shall be generally limited to no less than 1% and no greater than 4%. Stone surfaces around paved areas shall provide proper site drainage at slopes 10% or less. Land grading outside of the wastewater pumping station perimeter fence shall not exceed three to one slopes; four to one slope maximums are desirable. Lesser slopes wherever possible are preferred. Site grading design shall be compatible with slope stability for the soils encountered. Slope stabilization shall be appropriate for the degree of slope and soil conditions, the use of retaining walls on or immediately adjacent to the wastewater pumping station site is not permitted. There shall never be a situation where roof drains flow across walkways, roadways, or parking areas.

[7] Pump-around connection: a pump-around configuration shall be provided for the use of portable pumps to prevent overflows during maintenance or repair of the pumping station. A manhole shall be provided within the fenced area of the station immediately upstream of the wet well. A device for isolation purposes (stainless steel sluice gate) shall be provided in the upstream manhole or on the influent sewer within the wet well. The force main will be provided with a connection on the outside of the pumping station for portable pumping from the upstream manhole directly to the force main. As an alternative, a partitioned wet well can be utilized such that the wastewater can be directed to either of the pump intakes while allowing safe maintenance of the opposite side of the wet well or intake. Enough room shall be provided on the pump site to park the portable pump while allowing vehicle access to the wet well and dry well. The pump-around connection shall provide the capability to launch PIGS pipe cleaning devices, which shall require the pump-around diameter to be the same size as the force main and with an "increaser" to the next nominal size of pipe and a spool-piece whose length is two times the diameter of the force main. (Example: a six-inch force main needs a six-inch pump-around line with a six-by-eight increaser and a twelve-inch long spool-piece.).

[8] Pumping stations shall not be located directly downstream of any stormwater management facility discharge. Grading shall direct stormwater away and around the access road and site to an area downstream for treatment and/or further conveyance.

[9] Sediment control: A sediment control plan shall be provided and approval obtained from the Charles Soil Conservation District (SCD).

[10] At least two test borings shall be taken, one at the proposed wetwell location and one at the proposed drywell/building structure to determine soil types, rock, water table elevations, soil bearing values, etc. Standard penetration tests shall be taken at intervals not to exceed five feet. Borings shall be taken to a depth of not less than 15 feet below the bottom of the proposed structure. Borings shall be taken deeper as necessary, depending on soil conditions.

[11] Site security: Pumping station sites shall be fenced with black vinyl coated chainlink fencing eight feet tall, black vinyl coated post and black hardware, and a sixteen-foot wide locking gate for vehicle access. The fence is to include three strands of barbed wire around the top. Additional property line fencing may be required as determined by the County Engineer. The pumping station building shall have exterior lighting controlled by motion detectors. The building shall be provided with an entry alarm connected to the station SCADA.

[12] Paving: Pumping station sites shall have P-4 paving section in accordance with Table 2.07 of the road ordinance[1] and include a minimum of two parking spaces. The site shall have sufficient room to allow AASHTO WB-40 access to equipment by maintenance trucks (boom and vacuum trucks). An access road to the pumping station site shall have P-2 paving section in accordance with Table 2.07 of the road ordinance. The width of the pavement shall be 20 feet wide with two-foot gravel shoulders. The maximum grade for the access road shall not exceed 5%. The cross slope shall be in accordance with Standard Detail R/2.16.

[a] The access road and site shall support a minimum AASHTO WB-40 turning radius. The site shall also include a WB-40 turn-around area. Pumping station access roads shall be used exclusively for pumping station maintenance and access.

[1] Editor's Note: See Ch. 276, Streets, Roads and Sidewalks.

[13] Sidewalks, four feet wide in accordance with the road ordinance/detail manual, are to be provided between buildings and/or structures and from paved areas to buildings and structures for access of equipment, dollies, etc.

[14] Station sign: A permanent sign shall be provided at each pumping station stating the station name, street address and emergency telephone number. The sign must meet Charles County 911 addressing system.

[15] Yard hydrants and hose bibs shall be provided for wash down, maintenance, and sanitation purposes.

(b) Structures. All structures shall be set such that the top slab elevation is a minimum of one foot above finished grade.

[1] Wet well design: wet wells shall be considered a hazardous environment, classified as NEC Class I, Division I for explosive gases. Wet wells shall be designed and constructed to be as hazard free as possible, and corrosion resistant materials shall be used throughout. All materials and equipment used in wet wells shall meet NEC Class I, Division I standards, with the exception of control floats. Wet wells shall not exceed 25 feet in depth.

[a] Structure: Wastewater pumping station wet wells shall be constructed of precast concrete. Wastewater pumping station wet wells shall consist of reinforced concrete base slabs, riser sections/walls and top slabs. Wet wells shall have an interior epoxy coating and exterior elastomeric membrane waterproofing. The bottom of the wet well shall be grouted to a minimum slope of one to one to the hopper bottom and pump suction inlet. The horizontal area of the hopper bottom shall not be greater than necessary for proper installation and function of the inlet. Slope the hopper bottom between the inlets if necessary to prevent deposition of material between the inlets. Wet wells for pumping stations greater than 1.5 MGD design hydraulic flow shall be of the self-cleaning trench type design. Wet wells shall be adequately designed to prevent flotation. The wet well size and depth shall be as required to accommodate the influent sewer, as well as pump suction submergence as recommended by hydraulic institute standards and manufacturer requirements. The required working volume and preferred intervals between influent sewer and control elevations shall be determined as follows:

[i] Wet wells shall be designed for a minimum pump cycle time of 15 minutes as defined by the following formula:

	T = 4V/Q
	Where:
		T	=	pump cycle time (time between pump starts) in minutes
		V	=	volume of wet well between the lead pump start and pump stop elevations, in gallons
		Q	=	pump rate of the lead pump, in gallons per minute

[ii] The detention period for wastewater in the wet well shall not exceed 30 minutes at the average flow rate for the initial, intermediate and ultimate design years. When initial average flows are insufficient to actuate the pumps within a thirty-minute period, temporary removable appurtenances shall be placed in the wet well or the adjustable floats for pump start shall be lowered. Wet wells shall be deep enough to accommodate the control elevation points.

[b] Access: Wet well access shall be through a top slab opening with aluminum hatch cover and frame. Hatch shall be sized to utilize the top slab area to the maximum extent possible to facilitate removal of equipment and cleaning/maintenance of wetwell. The hatch shall also be designed to the same loading as the top slab. In no instance, shall the access hatch be less than thirty-six-inch by thirty-six-inch.

[c] Ventilation: wet wells shall be provided with a separate ventilation system and shall be sized to provide a minimum of 30 complete air changes per hour. In addition to manual control, time clock operation of fans shall be provided to allow a minimum of two complete air changes per hour.

[i] Ventilation shall be accomplished by the introduction of fresh air into the wet well under positive pressure. The fan shall be installed outdoors. The fan assembly and housing shall be corrosion-resistant and weatherproofed. The entrance hatch to the wet well shall be provided with a limit switch to energize the fan whenever the hatch is open. The fan shall be direct drive.

[2] Dry well design: Dry wells shall consist of precast concrete construction. Dry wells shall have exterior elastomeric membrane waterproofing. The dry well floor shall be sloped to a sump. A sump pump with piping to the wet well shall be provided and sump pump alarms are required. Sump pump piping shall contain a check valve to prevent siphoning from the wet well. The pump suction isolation valve shall have a hand wheel with an operating stem extending up to the control room. The hand wheels shall be marked with an open arrow, a surge relief valve, if required, shall be placed on the discharge header before the pipe leaves the station. Surge relief piping shall be piped to the wet well.

[a] Access: dry well access shall be via a staircase with all necessary landings and handrails per OSHA requirements. Stairs are to be provided with appropriate landings in lieu of ladders with cages. Hatch and ladder access and circular stairs are prohibited. Equipment hatches for the pumps shall be located in the top slab and directly above the pumps. Traversing monorails with cranes of adequate capacity shall be provided above the dry well to facilitate removal of the pumps, motors, valves and all other related equipment. Grating (catwalks) shall be provided in the dry well to facilitate access to all piping without climbing over pipes, equipment, etc. Grating, where used shall be structurally sound for the loads to be applied during maintenance and removal of equipment.

[b] Ventilation: Dry wells shall be provided with a separate ventilating system and shall be sized to provide a minimum of 10 complete air changes per hour. In addition to manual control, time clock operation of fans shall be provided to allow a minimum of four complete air changes per hour.

[i] Ventilation shall be accomplished by the introduction of fresh air into the dry well under positive pressure. The dry well ventilation system shall under no circumstances be connected to the wet well ventilation system and shall be away from any source of contamination.

[ii] Ventilation shall be automatically activated whenever the dry well lighting is energized and/or the access door is opened and the station is occupied by personnel.

[c] Dual sump pumps shall be provided for redundancy. Alternation shall be accomplished by means of a manual H-O-A selector switch rather than electrical alternators.

[d] To facilitate pump draining without flooding the building, pump intakes shall be drainable directly to the sump through piping or a channel drain.

[3] Influent manhole: One influent manhole collecting all of the gravity sewers that flow to the pumping station shall be provided. The influent manhole shall be located on the pumping station site. A gravity sewer shall carry wastewater from the influent manhole to the wet well. The influent manhole shall be capable of being isolated from the pumping station wet well by a sluice gate as required in § 291-65C(1)(a)[7].

[4] Pumping station design.

[a] Pumping station building design/architectural standards: pumping stations shall be architecturally compatible with surrounding structures and shall not have slate roofs. Pumping station buildings shall be of precast concrete and shall be designed to be vandal-proof. Roof shall be precast concrete gable type. Wood or asphalt shingles are not permitted. There shall be no exposed woodwork on the outside of the building. All exterior woodwork shall have a vinyl or aluminum coating. The pumping station shall have a lightning protection system. Provisions shall be made in the structure for traversing bridge cranes of adequate capacity to facilitate the removal of pumps, motors, valves and all other related heavy equipment. The pumping station doors shall be sixteen-gauge steel with deadbolts and locks keyed to the County standard. Doors shall be located and/or situated so that they are not affected by rain runoff from the roof.

[b] The building shall be a minimum of 10 feet by 12 feet and shall include a work bench and wall cabinets for storage.

[c] The finished floor and all electrical equipment shall be located at least two feet above the one-hundred-year flood elevation. Ventilation openings shall be protected with aluminum louvers with bird screens. Floors shall be sloped (minimum slope shall be 1/4 inch per foot) to floor drains piped to the influent manhole or wet well. The building floor shall be higher than the top elevation of the wet well. The building shall be furnished with a service sink with both hot and cold water, on-demand hot water heater, outside non-freeze hose bibb, and small desk with chair, a restroom shall be provided onsite as determined on a case-by-case basis based on the anticipated number of man-hours of operation and the remoteness of the site. The building shall conform to all Charles County building codes and zoning regulations.

[i] Control room. Electrical equipment shall be located above grade in a control room above the dry well. The control room shall be designed with adequate space to accommodate future upgrades.

[ii] Toilet room. In some instances, a toilet room shall be provided with toilet, lavatory, on-demand hot water heater, towel dispenser, soap dispenser and mirror.

[iii] Water service. A one-inch diameter metered potable water source shall be provided for wash down, maintenance, and sanitation purposes. The service shall include a backflow preventer. The water service line shall provide a minimum of 30 gallons per minute to the emergency shower with a minimum residual pressure of 35 psi.

[iv] Heating and ventilation. The building shall be heated by electric unit heaters with integral thermostats sized to maintain a minimum inside temperature of 40° F. Provide cooling as necessary to maintain air temperatures below 95° F. inside electrical devices. Ventilation shall be by means of wall mounted exhaust fans with backdraft dampers operated by thermostats and freezestats and intake louvers with motor-operated dampers. Ventilation shall be designed for a minimum of six air changes per hour. Provisions shall also be made, if applicable, to ensure against condensation forming on controls and other major items of equipment.

(c) Equipment.

[1] Screening and grit removal: Coarse bar screens are to be provided ahead of the pumps to protect equipment from rags, cans, bottles, sticks, etc. Grit removal will be required in areas where the County has experienced or expects a collection of grit and debris as determined by the County Engineer. The pumping station shall include provisions for the installation of a grinder/macerator that may be installed at a later time by the County. This includes determining the correct size unit, and ensuring that sufficient electric service is provided to operate the grinder/macerator. This shall also include the furnishing and installation of lifting hoist, access hatch, sliding guide rails, and associated mounting hardware.

[2] Provide built-in lifting equipment rated for the expected loads. The equipment should be capable of transporting the equipment to the exterior of the building for loading onto service trucks.

[3] Yard valves: Yard valves shall be buried gate valves complying with the County's standard specifications and details for construction with operating nut and roadway valve box at grade.

[4] Interior piping: All interior wastewater piping shall be DIP, Class 53, with flanged fittings. Flanges shall be integrally cast on pipe or factory assembled screwed-on with proper bonding compound. Manifolds shall include flexible couplings for make-up and for expansion and contraction of the piping system.

[a] Flexible couplings shall be provided on the suction and discharge of each pump.

[5] Arrangement of piping and equipment within the station shall be made with adequate space for maintenance, repair, removal or replacement of equipment, as well as to safeguard personnel working in the station. A minimum of three feet of clearance between equipment and walls shall be provided. Depending on the size of the equipment and piping, greater clearances may be needed. Piping shall be adequately supported. Control and instrumentation piping shall be copper or stainless steel.

[a] Provide color coding for piping in accordance with the Standard Specifications for Construction Manual.

[6] Valves: each wastewater pump shall have isolation valves on the suction and discharge to permit the removal or maintenance of the pumps without affecting the operation of the remaining pumps. Valves shall be gate type per County standard specifications for construction. To prevent valve fouling, locate the suction gate valve a minimum three feet ahead of the reducers. In addition to the valving normally utilized within the pumping station provide an additional exterior isolation valve on each pump suction line between the wet well and dry well. The pumping station isolation valve shall be provided with a handwheel, extension stem and operating nut to allow access from the control room floor. The handwheel shall be marked with an open arrow. Each pump shall have a hydraulically operated, time adjustable pump check service valve or a swing check valve to prevent backflow through inoperative pumps. In accordance with the criteria for water hammer control, pump check service valves shall be of the type and strength required to eliminate water hammer damage. Pump isolation or check valves shall not be located in the wet well. Spring type, oil cushioned surge relief valves, when required, shall be provided on the discharge header of the station and be piped to the wet well.

[7] Pressure gauges: Pressure gauges for direct reading of line conditions shall be placed on both the suction and discharge of each pump and on the main discharge header piping after the last pump. Pressure gauges shall be oil-filled type, have a minimum 3 1/2-inch diameter face and be equipped with snubbers and diaphragms. Pressure gauges shall be installed and configured such that the gauge can be isolated and the gauge piping be drained.

[a] Accuracy shall be to within 0.5% of pressure. Pressure gauges shall have a range such that the normal operating pressure is near the middle of the gauge.

[8] Flow metering: all wastewater pumping stations shall have polyurethane lined magnetic type flow meters with a replacement spool piece or bypass line provided to enable the pumping station to operate when the meter is being serviced.

[a] Magnetic flow meters shall be provided with grounding rings and isolation valves. Accuracy shall be to within 1% of flow. All flow meters shall have an adequate straight run of pipe both upstream and downstream of the meter in accordance with the manufacturer's recommendations. A seven-day circular chart recorder with totalizer and indicator recorder in units of gpm shall also be provided.

[9] Pumping units: wastewater pump suction and discharge shall be four-inch minimum diameter. All wastewater pumps shall rotate clockwise as viewed from the motor end. Wastewater pumps shall be centrifugal non-clog solids handling pumps capable of passing a hard three-inch sphere as well as stringy material and meet all requirements of MDE.

[a] The pump bearings shall have a minimum 100,000 hours ABMA-10 bearing life. The pump motors shall operate on 480 volt, three-phase, 60 cycle electrical service and at a speed no higher than 1,780 rpm. The pump motor horsepower shall be sufficient to prevent motor overload under all possible conditions. The pumps shall meet the vibration performance specifications of the Hydraulic Institute (HI). All wastewater pumps shall be factory witness tested and approved prior to shipment. All wastewater pumps must pass an on-site vibration test performed by an independent vibration testing company prior to acceptance. Wastewater pumps and motors shall be suitable for continuous duty, pumps shall be of the types listed below.

[i] Dry well wastewater pumps (conventional and package stations only): pumps shall be of the dry pit submersible design. The pump casing/volute, impeller, support base, suction elbow, seal housing/motor adapter and motor housing shall be of cast iron construction. The pump's casing and impeller shall be fitted with replaceable hardened stainless steel wear rings to maintain sealing efficiency between the volute and the impeller. At the option of the County Engineer, other pump materials may be required to suit a particular application. Each pump discharge volute casing and suction elbow shall be provided with an inspection and clean out opening.

[ii] Dry pit submersible wastewater pumps shall have the following additional features:

[A] One piece backhead and motor adapter with impeller adjustment cap screws.

[B] Solid full diameter stainless steel shaft with no shaft sleeve or solid large diameter high strength alloy steel shaft with stainless steel shaft sleeve having a tapered end with a keyway to receive the impeller.

[C] Double mechanical shaft seals cooled and lubricated by potable water through a cleanable seal filter assembly and provided with a mechanical seal vent with petcock. Oil cooled may be provided with the approval of the County Engineer.

[D] Premium efficiency motors shall be specified (where commercially available) for all three-phase pump motors dry pit submersible wastewater pumps shall be designed for continuous operation in air for application in a dry well. The motors for dry pit applications shall be capable of a minimum of eight starts per hour in air.

[iii] The pumps/motors shall also be designed to function continuously in a submerged condition should the dry well become flooded. Motor cooling shall be via cooling water jacket, submersible-rated air-over motor cooling fan or positively forced oil cooling. Variable drive units shall be provided when feasible.

(d) Electrical and controls.

[1] Electrical design: All electrical designs and components shall be in strict accordance with all applicable national and County code requirements. Electrical design shall be such that phase out protection shall be provided so that the power will automatically switch off in the event of a loss of any one phase. Incoming electrical service shall be underground with electric meters installed outside the pumping station building. The electrical plans shall include, but not be limited to, the following:

[a] Design report shall provide the correspondence with the Charles County local power company showing the consultant's load breakdown along with the local power company's assessment of the voltage available, their ability to serve the project, and the availability of a second independent source of power. Specific local power company permission to use across-the-line starters or requirement for reduced voltage starters is required.

[b] In addition to the proposed wiring diagrams, provide a narrative of the control sequence scenario which clearly explains the operational intent.

[c] Complete plan layout indicating all conduit, wire sizes and equipment locations including lighting and other appurtenances. Incoming electrical service on the pumping station site shall be underground and within concrete encased conduits.

[d] Installation details of equipment that are wall mounted, or suspended from the ceiling or otherwise required for clarity.

[e] Single line diagrams incorporating all electrical components required for operation of the facility.

[f] Complete lighting schedule noting model, size, location and installation data as well as appurtenances. Vandalproof exterior lighting shall be provided. Interior and exterior quartz lighting, separately switched, for maintenance purposes including auxiliary DC safety lighting is to be provided. Minimum lighting levels shall be 15 footcandles for stairways, and 100 footcandles for operations and maintenance.

[g] Complete control and SCADA diagrams, including panel and instrument diagrams.

[h] Elevation of control panels with equipment and mounting dimensions and notes identifying each component.

[i] Complete circuit breaker schedule indicating size and identifying each circuit.

[j] Ventilation schedule noting fan size, operating conditions, location, model, installation data, etc. The ventilation schedule shall also outline louver data including size, material, fixed or motorized.

[k] Secondary power facilities and alarm equipment shall be designed so that they may be manually activated for periodic maintenance checks to ensure proper operation.

[l] Provide a legend of all symbols used for the above.

[m] Power for the station shall be 480 volts, three-phase.

[n] IEC electrical components shall not be utilized. For replacement compatibility and availability, only full-sized NEMA UL listed electrical devices shall be used regardless of any equivalent UL ratings of IEC devices.

[o] Lockable safety disconnect switches are to be provided for all rotating equipment. Use lockable knife-switches rather than remote lockable start/stop button stations.

[p] Provide "push-to-test" type indicator lamps with screw-in type bulbs. Use of 120 mb type bulbs is prohibited.

[q] Permanent, in-place, volt/amp meters are required for each pump or major piece of equipment.

[r] Due to compatibility and standardization needs, provide only "Square-D," "Furnas," or "Cutler-Hammer" electrical equipment; no alternatives allowed.

[s] Use "Square-D," or County-approved equal, Class 8501 Type "K" plug-in style relays to the maximum extent possible where appropriate. Provide integral power indicating lamps in the relays. The only exception to this should be where current requirements exceed contact ratings. Use plug-in style relays for timers, alternators, and latching as well. Octal or square relays are equally acceptable, although eight-pin octal relays are preferred. Use "Square-D" Type KP12P14 or KP13P14 or County-approved for DPDT or 3PDT respectively.

[t] Provide non-resettable elapsed time meters for all rotating equipment. Meters are to be in hours and tenths of an hour, not minutes. Provide an elapsed time meter for parallel operation of main wastewater pumps; e.g., a meter for Pump No. 1, Pump No. 2, and Pump Nos. 1 and 2 together.

[u] A weatherproof red exterior "trouble light" for visual indication of equipment failures/problems is to be provided. A horn is not to be provided.

[v] Provide a junction pedestal(s) near, but outside, the wet well for power, lighting, and control cables leading to the wet well. Provide gas tight connections. No junction boxes are allowed inside the wet well. Gas tight lighting is to be provided inside the wet well.

[2] Lightning and surge protection: The designer shall provide lightning and surge protection at the wastewater pumping station. The lightning and surge protection shall comply with the latest editions of all applicable codes and standards. Provide phase failure and phase reversal protection for all equipment. A single phase condition shall not destroy motors, transformers, relays, etc. should the second source of power fail to take over.

[3] Backup power: All pumping stations shall be provided with emergency generators with automatic transfer switches as described in MDE guidelines. At the discretion of the County, a diesel driven permanent standby pumping system may be required in lieu of an emergency generator. The generator area shall be located a minimum of two feet above the one-hundred-year flood elevation. Emergency generators shall be sized to maintain full station operation. Emergency generators shall be diesel driven with fuel storage on the underside of the generator in a belly tank or outside the building in an aboveground storage tank. Fuel spillage protection shall be provided. Tank size shall be suitable for a minimum of 24 hours of generator operation at full load. Generators shall be mounted on vibration spring isolators. When emergency generators are located inside the pumping station building, they shall be mounted with a fuel tank fill connection to the outside. Generator engine exhaust shall be provided with a critical grade silencer and piped to the outside of the control building. Generator exhaust shall face away from nearby neighbors. If this is not possible, a baffle wall shall be constructed in front of the generator exhaust to deflect the noise. If the generator is located outside, its enclosure shall be acoustically lined.

[4] Control/SCADA: A complete and operable control/SCADA system shall be provided per County standard specifications for construction.

(e) Painting and coating. All exposed piping, pump equipment and appurtenances including all structures shall be painted per County standard specifications for construction.

(f) Miscellaneous.

[1] Odor control.

[a] An odor-control system shall be provided when required by the County Engineer. The type of odor-control system to be used at a particular station must be approved by the County Engineer prior to design. Odor-control systems shall be designed to mitigate odors from the wet well and influent manhole.

[b] Acceptable methods include, but are not limited to: Carbon adsorption (air scrubbing), chemical addition at the wet well or influent manhole, and soil odor filters.

[c] Wastewater pumping stations should be designed to minimize the possible formation of odors by limiting wet well detention times and avoiding turbulence in manholes and wet wells which cause odors to be released.

[2] Hydrogen sulfide control: See § 291-64D(3)(e).

(g) Safety.

[1] Gas detection and annunciation shall be provided for the dry well in the form of low explosive levels, and oxygen level as a minimum.

[2] Appropriate emergency eye wash facilities shall be provided whenever chemical handling is proposed for the pumping station. The need for emergency fountains and showers, the design/configuration thereof, and their locations shall be in accordance with Section 57.29 of the most current edition of the Ten States Standards for wastewater facilities and the applicable requirements of MOSH and the County Safety Officer. As a minimum, the eyewash fountains shall be supplied with water of moderate temperature, 50° F. to 90° F., suitable to provide 15 to 30 minutes of continuous irrigation to the eyes. As a minimum, the emergency showers shall be capable of discharging 30 gallons per minute of water at moderate temperature and at a minimum pressure of 35 psi.

[3] Appropriately designed dielectric rubber floor mats are to be provided for insulation at all motor controls for personnel safety. If water on the floor is a possibility, the design must eliminate such water. A situation of motor control maintenance in wet or unsafe conditions is unacceptable.

(2) Small pumping stations. Design criteria for small wastewater pumping stations shall be the same as for conventional stations described above except where specifically stated otherwise.

(a) Submersible: Submersible stations are defined as stations where the pumps are "submerged" in the wet well. Because the pumps operate under water in the wet well, there is no need for a separate pump room. Guide rails enable the pump to be raised and lowered into place without requiring entry by personnel under normal circumstances. Submersible stations shall not be used for wet well depths greater than 25 feet.

[1] Pumping station configuration: submersible pumping stations shall be designed with an equipment hatch in the top slab for pump removal, nonsparking guide rails and manway hatch. Pumps shall be of the wet pit submersible type. The pumping station building shall contain all mechanical, electrical, and control equipment and a toilet room as described in the preceding sections of this chapter. The wet well and pumps shall be located adjacent to the pumping station building. The emergency generator shall be located outside of the pumping station building in a weatherproof, sound insulated enclosure.

[2] Wet well design: submersible pumping station wet wells shall be designed for precast concrete construction. Wet well coating and design features shall be the same as described for conventional pumping stations.

[3] Wet pit submersible wastewater pumps: Pump volute, impeller and motor housing shall be of cast iron construction. Pumps shall be centrifugal non-clog solids handling pumps capable of passing a hard three-inch sphere as well as stringy material and meet all requirements of MDE. The pump volute casing and impeller shall be fitted with replaceable stainless steel wear rings to maintain sealing efficiency between the pump volute and impeller. At the County Engineer's option, other special pump materials may be required for a particular application. The motor shaft shall be a single piece heat-treated high strength alloy steel or high strength stainless steel having a tapered end with keyway to receive the impeller. All nuts, bolts and screws shall be stainless steel. The motor shall be Class F insulated (minimum) and sealed from the pump by independent double mechanical seals.

[a] The upper and lower mechanical seal shall run in an oil chamber. The upper seal shall be a stationary tungsten-carbide seal with rotating carbon ring. The lower seal shall be one stationary and one positively driven rotating tungsten-carbide ring. All mating surfaces where watertight sealing is required shall be machined and fitted with a rubber o-ring. The machining of mating surfaces shall provide metal to metal bearing on sealing surfaces without crushing the o-ring.

[4] Influent grinder/macerator: The wetwell or influent manhole shall be designed to accommodate an influent wastewater grinder/macerator (grinder) along with a bypass screening mechanism. The influent grinder shall be of the vertical twin rotor type and be located in either the influent manhole or in the wet well. The influent grinder shall be capable of being lifted out of the wet well or manhole by means of stainless steel guide rails without entering through an adequately sized access hatch. The pumping station shall include provisions for the installation of a grinder/macerator that may be installed at a later time by the County. This includes determining the correct size unit, and ensuring that sufficient electric service is provided to operate the grinder/macerator. This shall also include the furnishing and installation of lifting hoist, access hatch, sliding guide rails, and associated mounting hardware.

[5] Electrical and controls: Shall meet the same requirements for conventional pumping stations.