A.
Applicants proposing regulated activities in Schuylkill River Watershed which do not fall under the exemption criteria shown in § 398-21 shall submit a drainage plan consistent with the Schuylkill River Watershed Stormwater Management Plan to the municipality for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
For all regulated activities, unless preparation of an SWM site plan
is specifically exempted by this chapter:
C.
SWM site plans approved by the municipality in accordance with this
chapter shall be on site throughout the duration of the regulated
activity.
D.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this chapter, provided that they meet the minimum requirements
of, and do not conflict with, state law, including but not limited
to the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
E.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this chapter and to meet
all the requirements under the Pennsylvania Code Title 25 and the
Clean Streams Law. Various BMPs and their design standards are listed
in the Erosion and Sediment Pollution Control Program Manual (E&S
Manual) 2, Commonwealth of Pennsylvania, Department of Environmental
Protection, No. 363-2134- 008, as amended and updated.
F.
For all regulated activities, implementation of the volume controls
in accordance with the chapter is required.
G.
The applicant is required to evaluate practicable alternatives to
the surface discharge of stormwater, the creation of impervious surfaces
and the degradation of waters of the commonwealth, and must maintain
as much as possible the natural hydrologic regime.
H.
The drainage plan must be designed consistent with the sequencing provisions of § 398-12 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article III of this chapter.
I.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
J.
Existing points of concentrated drainage that discharge onto adjacent
property shall not be altered in any manner which could cause property
damage without permission of the affected property owner(s) and shall
be subject to any applicable discharge criteria specified in this
chapter.
K.
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If diffused
drainage discharge is proposed to be concentrated and discharged onto
adjacent property, the applicant must document that adequate downstream
conveyance facilities exist to safely transport the concentrated discharge,
or otherwise prove that no erosion, sedimentation, flooding or other
impacts will result from the concentrated discharge.
L.
Where a development site is traversed by existing watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall conform to the stream buffer requirements contained in § 398-14E of this chapter.
M.
Any stormwater management facilities regulated by this chapter that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by PaDEP through the joint permit application
process, or, where deemed appropriate by PaDEP, the general permit
process. When there is a question whether wetlands may be involved,
it is the responsibility of the applicant or his agent to show that
the land in question cannot be classified as wetlands, otherwise approval
to work in the area must be obtained from PaDEP.
N.
Any stormwater management facilities regulated by this chapter that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
O.
Minimization of impervious surfaces and infiltration of runoff through
seepage beds, infiltration trenches, etc. are encouraged, where soil
conditions permit, to reduce the size or eliminate the need for detention
facilities or other structural BMPs.
P.
Roof drains shall not be connected to streets, sanitary or storm
sewers or roadside ditches in order to promote overland flow and infiltration/percolation
of stormwater where advantageous to do so. When it is more advantageous
to connect directly to streets or storm sewers, then it shall be permitted
on a case by case basis by the municipality.
Q.
All stormwater runoff shall be pretreated for water quality prior
to discharge to surface or groundwater.
R.
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Article VII.
S.
In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high water table.
(5)
Proximity to building foundations and wellheads.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream bank erosion.
(10)
Efficiency of the BMPs to mitigate potential water quality problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
(15)
Recreational value.
T.
Transference of runoff from one DEP designated Act 167 watershed
to another shall be prohibited.
The following permit requirements may apply to certain regulated
earth disturbance activities, and must be met prior to commencement
of regulated earth disturbance activities, as applicable:
A.
All regulated earth disturbance activities subject to permit requirements
by DEP under regulations at 25 Pa. Code Chapter 102.
B.
Work within natural drainageways subject to permit by DEP under 25
Pa. Code Chapter 105.
C.
Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by DEP under 25 Pa. Code Chapter 105.
D.
Any stormwater management facility that would be located on a state
highway right-of-way, or require access from a state highway, shall
be subject to approval by the Pennsylvania Department of Transportation
(PENNDOT).
E.
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by DEP under 25 Pa. Code Chapter
105.
A.
No regulated earth disturbance activities within the municipality
shall commence until the municipality receives an approval from the
Conservation District of an erosion and sediment control plan for
construction activities.
B.
DEP has regulations that require an erosion and sediment control
plan for any earth disturbance activity of 5,000 square feet or more,
under 25 Pa. Code § 102.4(b).
D.
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the municipality. The issuance of an NPDES construction permit [or permit coverage under the statewide General Permit (PAG-2)] satisfies the requirements Subsection A of this section.
E.
A copy of the erosion and sediment control plan and any required
permit, as required by DEP regulations, shall be available at the
project site at all times.
F.
Additional erosion and sediment control design standards and criteria
are recommended to be applied where infiltration BMPs are proposed.
They shall include the following:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity.
(2)
Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
achieved final stabilization.
A.
The design of all regulated activities shall include the following
steps in sequence to minimize stormwater impacts:
(1)
The applicant is required to evaluate practicable alternatives to
the surface discharge of stormwater, the creation of impervious surfaces
and the degradation of waters of the commonwealth, and must maintain
as much as possible the natural hydrologic regime of the site.
(2)
An alternative is practicable if it is available and capable of being
done after taking into consideration cost, existing technology and
logistics in light of overall project purposes, and other municipal
requirements.
(3)
All practicable alternatives to the discharge of stormwater are presumed
to have less adverse impact on quantity and quality of waters of the
commonwealth unless otherwise demonstrated.
B.
The applicant shall demonstrate that they designed the regulated
activities in the following sequence to minimize the increases in
stormwater runoff and impacts to water quality:
(1)
Prepare an Existing Resource and Site Analysis Map (ERSAM), showing environmentally sensitive areas, including but not limited to steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools, floodplains, stream buffer zones, hydrologic soil groups A and B (areas conducive to infiltration), special geologic features, any existing recharge areas and any other requirements outlined in Chapter 410, Subdivision and Land Development.
(3)
Prepare a draft project layout avoiding sensitive areas identified in § 398-12B(1).
(4)
Identify site specific existing conditions drainage areas, discharge
points, recharge areas and hydrologic soil groups A and B.
(6)
Satisfy infiltration objective (§ 398-13) and provide for stormwater pretreatment prior to infiltration. Pretreatment may not be necessary for rooftop runoff which enters the infiltration facility directly from a roof leader.
(9)
Prepare final project design to maintain existing conditions drainage
areas and discharge points, to minimize earth disturbance and impervious
surfaces, and to the maximum extent possible, to ensure the remaining
site development has no surface or point discharge.
(10)
Conduct a proposed conditions runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (§ 398-16).
(11)
Manage any remaining runoff through treatment prior to discharge,
as part of detention, bioretention, direct discharge or other structural
control.
Maximizing the groundwater recharge capacity of the area being developed is required. Design of the infiltration stormwater management facilities shall give consideration to providing groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs which can be over-designed to compensate for the infiltration losses due to parking areas. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with § 398-3, and take advantage of utilizing any existing recharge areas. Infiltration may not be feasible on every site due to site-specific limitations such as soil type. If it cannot be physically accomplished due to seasonal high water table, soil permeability rate, soil depth or setback distances from special geologic features, then the design professional shall be responsible to show that this cannot be physically accomplished. If it can be physically accomplished, then the volume of runoff to be infiltrated shall be determined from § 398-13A(3) depending on demonstrated site conditions and shall be the greater of the two volumes.
A.
Infiltration BMPs shall meet the following minimum requirements:
(1)
Infiltration requirements.
(a)
Regulated activities will be required to infiltrate, where site conditions permit, a portion of the runoff created by the development as part of an overall stormwater management plan designed for the site. The volume of runoff to be infiltrated shall be determined from § 398-13A(3)(a) or (b), depending upon demonstrated site conditions.
(2)
Infiltration BMPs intended to receive runoff from developed areas
shall be selected based on suitability of soils and site conditions
and shall be constructed on soils that have the following characteristics:
(a)
A minimum depth of 36 inches between the bottom of the BMP and
the limiting zone.
(b)
An infiltration and/or percolation rate sufficient to accept
the additional stormwater load and drain completely as determined
by field tests conducted by the applicant's design professional.
(c)
The infiltration facility shall be capable of completely infiltrating
the required retention (infiltration) volume within four days (96
hours).
(d)
Pretreatment shall be provided prior to infiltration.
(3)
The size of the infiltration facility shall be based upon the following
volume criteria:
(a)
NRCS Curve Number equation.
[1]
The NRCS runoff equation shall be utilized to calculate infiltration
requirements (I) in inches.
|
Equation 398-13.1
| |
|---|---|
|
I (Infiltration requirement, in inches) = (200/CN) - 2
|
|
Where:
| ||||
|---|---|---|---|---|
|
CN
|
=
|
SCS (NRCS) curve number of existing conditions contributing
to the infiltration facility
| ||
[2]
This equation is displayed graphically in, and the infiltration
requirement can be determined from Figure 398-13.1.
 |
|---|
|
Figure 398-13.1. Infiltration requirement based upon NRCS
Curve Number
|
[3]
The retention (infiltration) volume (Rev) required to meet the infiltration requirement would therefore be
computed as:
|
Equation 305.2
| |
|---|---|
|
Rev = I * impervious area (square feet)/(12
in/ft) = cubic feet
|
|
Where:
| ||||
|---|---|---|---|---|
|
I
|
=
|
infiltration requirements (in inches)
| ||
(b)
Annual recharge water budget approach.
[1]
It has been determined that infiltrating 0.46 inches of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of § 398-13A(3)(a) cannot be achieved, then 0.46 inches of rainfall shall be infiltrated from all impervious areas, up to an existing site conditions curve number of 81. Above a curve number of 81, Equation 398-13.1 or the curve in Figure 398-13.1 should be used to determine the infiltration requirement.
[2]
The retention (infiltration) volume (Rev) required again would therefore be computed as:
|
Rev = (0.46 or I, whichever is less)
* impervious area (sq.ft.)/(12in/ft) = cubic feet
|
B.
Soils. A detailed soils evaluation of the project site shall be required
where practicable to determine the suitability of infiltration facilities.
The evaluation shall be performed by a qualified design professional,
and at a minimum, address soil permeability, depth to bedrock and
subgrade stability. The general process for designing the infiltration
BMP shall be:
(1)
Analyze hydrologic soil groups as well as natural and man-made features
within the site to determine general areas of suitability for infiltration
practices. In areas where development on fill material is under consideration,
conduct geotechnical investigations of subgrade stability; infiltration
is not permitted to be ruled out without conducting these tests.
(2)
Provide field tests such as double-ring infiltrometer or hydraulic
conductivity tests (at the level of the proposed infiltration surface)
to determine the appropriate hydraulic conductivity rate. Percolation
tests are not recommended for design purposes.
(3)
Design the infiltration structure for the required retention (Rev) volume based on field determined capacity at the level
of the proposed infiltration surface.
(4)
If on-lot infiltration structures are proposed by the applicant's
design professional, it must be demonstrated to the municipality that
the soils are conducive to infiltrate on the lots identified.
C.
Carbonate areas. The applicant is required to investigate the ability of all areas on the site which are not underlain by carbonate rock to meet the infiltration requirements of § 398-13A. If this investigation proves infeasible, infiltration can occur on areas underlain by carbonate rock by following the recommended procedure below in conjunction with Figure B-4 in Appendix B.[1] However, the applicant is not required to use infiltration in carbonate areas even if the site falls into the "Recommended" range on Figure B-4 in Appendix B. If infiltration is not proposed, the calculated infiltration volume (§ 398-13A) shall be treated by an acceptable BMP.
(1)
Infiltration BMP loading rate percentages in Figure B-4 in Appendix
B shall be calculated as follows:
 |
(2)
The area tributary to the infiltration BMP shall be weighted as follows:
|
Area Description
|
Weighting
| |
|---|---|---|
|
All disturbed area to be made impervious
|
100%
| |
|
All disturbed areas to be made pervious
|
50%
| |
|
All undisturbed impervious areas
|
100%
| |
|
All undisturbed pervious areas
|
0%
|
(3)
Soil thickness is to be measured from the bottom of any proposed
infiltration BMP. The effective soil thickness in Figure B-4 in Appendix
B[2] is the measured soil thickness multiplied by the thickness
factor based on soil permeability, as follows:
|
Permeability Range
|
Thickness Factor
| |
|---|---|---|
|
6.0 to 12.0 inches/hour
|
0.8
| |
|
2.0 to 6.0 inches/hour
|
1.0
| |
|
1.0 to 2.0 inches/hour
|
1.4
| |
|
0.75 to 1.0 inches/hour
|
1.2
| |
|
0.5 to 0.75 inches/hour
|
1.0
|
[2]
Editor's Note: Appendix B is included as an attachment to
this chapter.
(4)
No infiltration structure in non-carbonate areas shall be within
50 feet of a boundary with carbonate rock, except when a preliminary
site investigation has been done showing the absence of special geologic
features within 50 feet of the proposed infiltration area.
[1]
Editor's Note: Appendix B is included as an attachment to
this chapter.
D.
Stormwater hotspots. Following is a list of examples of designated
hotspots. If a municipality designates a site or use as a hotspot,
it has important implications for how stormwater is managed. First
and foremost, untreated stormwater runoff from hotspots shall not
be allowed to recharge into groundwater where it may contaminate water
supplies. Therefore, the Rev requirement shall
not applied to development sites that fit into the hotspot category
(the entire WQv must still be treated). Second, a greater level of
stormwater treatment shall be considered at hotspot sites to prevent
pollutant washoff after construction. EPA's NPDES stormwater
program requires some industrial sites to prepare and implement a
stormwater pollution prevention plan.
(1)
Examples of hotspots:
(a)
Vehicle salvage yards and recycling facilities.
(b)
Vehicle fueling stations.
(c)
Vehicle service and maintenance facilities.
(d)
Vehicle and equipment cleaning facilities.
(e)
Fleet storage areas (bus, truck, etc.).
(f)
Industrial sites (based on Standard Industrial Codes).
(g)
Marinas (service and maintenance).
(h)
Outdoor liquid container storage.
(i)
Outdoor loading/unloading facilities.
(j)
Public works storage areas.
(k)
Facilities that generate or store hazardous materials.
(l)
Commercial container nursery.
(m)
Other land uses and activities as designated by an appropriate
review authority.
(2)
The following land uses and activities are not normally considered
hotspots:
(3)
While large highways [average daily traffic volume (ADT) greater
than 30,000] are not designated as a stormwater hotspot; however,
it is important to ensure that highway stormwater management plans
adequately protect groundwater.
E.
Where infiltration is proposed in source water protection areas as
defined by the local municipality or water authority, the applicant
shall work with the appropriate entity to ensure protection of the
water supply.
F.
Infiltration facilities shall be used in conjunction with other innovative
or traditional BMPs, stormwater control facilities, and nonstructural
stormwater management alternatives.
G.
Where salt or chloride (salt storage) would be a pollutant, since
soils do little to filter this pollutant and it may contaminate the
groundwater, a qualified design professional shall evaluate the possibility
of groundwater contamination from the proposed infiltration facility
and perform a hydrogeologic justification study if necessary.
H.
The infiltration requirement in high quality or exceptional value
waters shall be subject to the Department's Chapter 93 Antidegradation
Regulations.
I.
An impermeable liner will be required in detention basins where the
possibility of groundwater contamination exists. A hydrogeologic study
may be required by the municipality.
J.
The municipality may, upon its sole discretion, require the applicant
to provide safeguards against groundwater contamination for land uses
that may cause groundwater contamination should there be a mishap
or spill.
K.
Unless otherwise specified in Chapter 475, Zoning, the following setbacks for infiltration facilities shall apply:
(1)
One hundred feet from water supply wells.
(2)
Ten feet downslope or 100 feet upslope from building foundations.
(3)
Fifty feet from septic system drainfields.
(4)
Fifty feet from a geologic contact with carbonate bedrock, unless
a preliminary site investigation is done in the carbonate bedrock
to show the absence of special geologic features within 50 feet of
the proposed infiltration area.
(5)
One hundred feet from the property line unless documentation is provided
to show all setbacks from wells, foundations and drainfields on the
neighboring property will be met.
The applicant shall comply with the following water quality
requirements of this article. No regulated earth disturbance activities
within the municipality shall commence until approval by the municipality
of a plan which demonstrates compliance with state water quality requirements
postconstruction is complete.
A.
The BMPs shall be designed, implemented and maintained to meet state
water quality requirements, and any other more stringent requirements
as determined by the municipality.
B.
To control postconstruction stormwater impacts from regulated earth
disturbance activities, state
water quality requirements can be met by BMPs, including site design,
which provide for replication of preconstruction stormwater infiltration
and runoff conditions, so that postconstruction stormwater discharges
do not degrade the physical, chemical or biological characteristics
of the receiving waters. As described in the DEP Comprehensive Stormwater
Management Policy (#392-0300-002, September 28, 2002), this may be
achieved by the following:
(1)
Infiltration. Replication of preconstruction stormwater infiltration
conditions;
(2)
Treatment. Use of water quality treatment BMPs to ensure filtering
out of the chemical and physical pollutants from the stormwater runoff;
and
(3)
Stream bank and streambed protection. Management of volume and rate
of postconstruction stormwater discharges to prevent physical degradation
of receiving waters (e.g., from scouring).
C.
For areas within defined special protection subwatersheds which include
exceptional value (EV) and high quality (HQ) waters, the temperature
and quality of water and streams shall be maintained through the use
of temperature-sensitive BMPs and stormwater conveyance systems.
D.
To accomplish the above, the applicant shall submit original and
innovative designs to the Municipal Engineer for review and approval.
Such designs may achieve the water quality objectives through a combination
of BMPs (best management practices).
E.
If a perennial or intermittent stream passes through the site, the
applicant shall create a stream buffer extending a minimum of 50 feet
to either side of the top of bank of the channel. The buffer area
shall be maintained with and encouraged to use appropriate native
vegetation (reference to Appendix H of Pennsylvania Handbook of Best
Management Practices for Developing Area for plant lists). If the
applicable rear or side yard setback is less than 50 feet, the buffer
width may be reduced to 25% of the setback to a minimum of 10 feet.
If an existing buffer is legally prescribed (i.e., deed, covenant,
easement, etc.) and it exceeds the requirements of this chapter, the
existing buffer shall be maintained. [The municipality may select
a smaller or larger buffer width if desired, but the selected buffer
may not be less than 10 feet.] This does not include lakes or wetlands.
F.
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the municipality. The issuance of an NPDES Construction Permit [or permit coverage under the statewide General Permit (PAG-2)] satisfies the requirements of Subsection A of this section.
A.
In addition to control of the water quality volume, in order to minimize
the impact of stormwater runoff on downstream stream bank erosion,
the primary requirement is to design a BMP to detain the proposed
conditions two-year, twenty-four-hour design storm to the existing
conditions one-year flow using the SCS Type II distribution. Additionally,
provisions shall be made (such as adding a small orifice at the bottom
of the outlet structure) so that the proposed conditions one-year
storm takes a minimum of 24 hours to drain from the facility from
a point where the maximum volume of water from the one-year storm
is captured. (i.e., the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the water quality orifice is at the invert of
the facility).
B.
The minimum orifice size in the outlet structure to the BMP shall
be a three-inch diameter orifice and a trash rack shall be installed
to prevent clogging. On sites with small contributing drainage areas
to this BMP that do not provide enough runoff volume to allow a twenty-four-hour
attenuation with the three-inch orifice, the calculations shall be
submitted showing this condition. Orifice sizes less than three inches
can be utilized provided that the design will prevent clogging of
the intake.
C.
In "no detention" areas (District C) only (see § 398-16), the objective is not to attenuate the storms greater than the two-year recurrence interval. This can be accomplished by configuring the outlet structure not to control the larger storms, or by a bypass channel that diverts only the two-year stormwater runoff into the basin, or conversely, diverts flows in excess of the two-year storm away from the basin.
A.
The Schuylkill River Watershed has been divided into stormwater management
districts as shown on the Management District Map in Appendix D.[1]
(2)
Development sites located in each of the districts must control proposed
conditions runoff rates to existing conditions runoff rates for the
design storms in accordance with the table located on the Map.
(3)
For any site which proposes direct discharge, the site may only utilize
any available capacity in the downstream conveyance system which is
equivalent to the ratio of the proposed development site acreage to
the total watershed acreage to the downstream conveyance system. Therefore,
if the proposed development site is 10% of the total watershed area,
the increase in runoff may only use up 10% of the documented available
downstream, capacity at peak flow.
[1]
Editor's Note: Appendix D is included as an attachment to
this chapter.
B.
General. Proposed condition rates of runoff from any regulated activity
shall not exceed the peak release rates of runoff prior to development
for the design storms specified on the Stormwater Management District
Watershed Map (Appendix D[2]) and in this section.
[2]
Editor's Note: Appendix D is included as an attachment to
this chapter.
C.
District boundaries. The boundaries of the Stormwater Management
Districts are shown on an Official Map that is available for inspection
at the municipal office. A copy of the Official Map at a reduced scale
is included in the Appendix D.[3] The exact location of the Stormwater Management District
boundaries as they apply to a given development site shall be determined
by mapping the boundaries using the two-foot topographic contours
(or most accurate data required) provided as part of the drainage
plan.
[3]
Editor's Note: Appendix D is included as an attachment to
this chapter.
D.
Sites located in more than one district. For a proposed development
site located within two or more stormwater management district category
subareas, the peak discharge rate from any subarea shall meet the
Management District Criteria for which the discharge is located, as
indicated in this section. The calculated peak discharges shall apply
regardless of whether the grading plan changes the drainage area by
subarea. An exception to the above may be granted if discharges from
multiple subareas recombine in proximity to the discharge site. In
this case, peak discharge in any direction shall follow Management
District A criteria provided that the overall site discharge meets
the Management District Criteria for which the discharge is located.
E.
Off-site areas. Off-site areas that drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
F.
Site areas. Where the site area to be impacted by a proposed development
activity differs significantly from the total site area, only the
proposed impact area utilizing stormwater management measures shall
be subject to the Management District Criteria. In other words, unimpacted
areas bypassing the stormwater management facilities would not be
subject to the Management District Criteria.
G.
"No harm" option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that "no harm" would be caused by discharging at a higher runoff rate than that specified by the stormwater management plan. The "no harm" option is used when an applicant can prove that the proposed condition hydrographs can match existing conditions hydrographs, or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of "no harm" must be shown based upon the following downstream impact evaluation, which shall include a downstream hydraulic capacity analysis consistent with § 398-16H to determine if adequate hydraulic capacity exists. The applicant shall submit to the municipality this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
(1)
The hydrologic regime of the site must be maintained.
(2)
The downstream impact evaluation shall include hydrologic and hydraulic
calculations necessary to determine the impact of hydrograph timing
modifications due to the proposed development upon a dam, highway,
structure, natural point of restricted stream flow or any stream channel
section, established with the concurrence of the municipality.
(3)
The evaluation shall continue downstream until the increase in flow
diminishes due to additional flow from tributaries and/or stream attenuation.
(4)
The peak flow values to be used for downstream areas for the design
return period storms (two-, five-, ten-, twenty-five-, fifty-, and
one-hundred-year) shall be the values from the calibrated model for
the Schuylkill River Watershed. These flow values can be obtained
from the original Act 167 watershed stormwater management plans.
(5)
Applicant-proposed runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove "no harm," except in conjunction with proposed capacity improvements for the problem areas consistent with § 398-16H.
(6)
A financial distress shall not constitute grounds for the municipality
to approve the use of the "no-harm" option.
(7)
Capacity improvements may be provided as necessary to implement the
"no-harm" option which proposes specific capacity improvements to
provide that a less stringent discharge control would not create any
harm downstream.
H.
Downstream hydraulic capacity analysis. Any downstream capacity hydraulic
analysis conducted in accordance with this chapter shall use the following
criteria for determining adequacy for accepting increased peak flow
rates:
(1)
Natural or man-made channels or swales must be able to convey the
increased runoff associated with a two-year return period event within
their banks at velocities consistent with protection of the channels
from erosion. Acceptable velocities shall be based upon criteria included
in the DEP Erosion and Sediment Pollution Control Program Manual.
(2)
Natural or man-made channels or swales must be able to convey increased
twenty-five-year return period runoff without creating any hazard
to persons or property.
(3)
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased twenty-five-year return period runoff.
I.
Hardship option.
(1)
The municipality may hear requests for waivers where it is alleged
that the provisions of this (Act 167) ordinance inflict unnecessary
hardship upon the applicant. The waiver request shall be in writing
and accompanied by the requisite fee based upon a fee schedule adopted
by the municipality. A copy of the waiver request shall be provided
to each of the following: municipality, municipal engineer, municipal
solicitor and Berks County Planning Commission. The request shall
fully document the nature of the alleged hardship.
(2)
The municipality may grant a waiver, provided that all of the following
findings are made in a given case:
(a)
That there are unique physical circumstances or conditions,
including irregularity of lot size or shape, or exceptional topographical
or other physical conditions peculiar to the particular property,
and that the unnecessary hardship is due to such conditions, and not
the circumstances or conditions generally created by the provisions
of this chapter in the Stormwater Management District in which the
property is located;
(b)
That because of such physical circumstances or conditions, there
is no possibility that the property can be developed in strict conformity
with the provisions of this chapter, including the "no harm" provisions,
and that the authorization of a waiver is therefore necessary to enable
the reasonable use of the property;[4]
(c)
That such unnecessary hardship has not been created by the applicant;
(d)
That the waiver, if authorized, will represent the minimum waiver
that will afford relief and will represent the least modification
possible of the regulation in issue; and
(e)
That financial hardship is not the criteria for granting of
a hardship waiver.
(3)
In granting any waiver, the municipality may attach such conditions
and safeguards as it may deem necessary to implement the purposes
of Act 167 and this chapter. If a hardship waiver is granted, the
applicant must still manage the quantity, velocity, direction and
quality of resulting storm runoff as is necessary to prevent injury
to health, safety or other property.
A.
Stormwater runoff from all development sites with a drainage area
of greater than 200 acres shall be calculated using a generally accepted
calculation technique that is based on the NRCS Soil Cover Complex
Method. Table 398-17.1 summarizes acceptable computation methods and
the method selected by the design professional shall be based on the
individual limitations and suitability of each method for a particular
site. The municipality may allow the use of the Rational Method to
estimate peak discharges from drainage areas that contain less than
200 acres. The Soil Complex Method shall be used for drainage areas
greater than 200 acres.
|
Table 398-17.1
Acceptable Computation Methodologies for Stormwater Management
Plans
| |||
|---|---|---|---|
|
Method
|
Method Developed by
|
Applicability
| |
|
TR-20
(or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary.
| |
|
TR-55
(or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55.
| |
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary.
| |
|
PSRM
|
Penn State University
|
Applicable where use of a hydrologic computer model is desirable
or necessary; simpler than TR-20 or HEC-1.
| |
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites less than 200 acres and with time of concentration
less than 60 minutes (tc< 60 min), or as approved by the municipality
and/or Municipal Engineer.
| |
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer.
| |
B.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms according to the region in which
they are located as presented in Table B-1 in Appendix B of this chapter.[1] If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS
is used for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours. The SCS "S" curve shown in Figure B-1, Appendix
B, of this chapter shall be used for the rainfall distribution.
[1]
Editor's Note: Appendix B is included as an attachment to
this chapter.
C.
For the purposes of existing conditions flow rate determination,
undeveloped land shall be considered as "meadow" in good condition,
unless the natural ground cover generates a lower curve number or
Rational "C" value (i.e., forest), as listed in Table B-2 or B-3 in
Appendix B of this chapter.
D.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the Design Storm Curves from Pennsylvania Department of Transportation Design Rainfall Curves (1986) (Figures B-2 to B-4). Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's equation.
F.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table B-3 in
Appendix B of this chapter.
G.
Where uniform flow is anticipated, the Manning equation shall be
used for hydraulic computations, and to determine the capacity of
open channels, pipes, and storm sewers. Values for Manning's
roughness coefficient (n) shall be consistent with Table B-4 in Appendix
B of this chapter.
H.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
I.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities using the Storage
Indication Method. For drainage areas greater than 200 acres in size,
the design storm hydrograph shall be computed using a calculation
method that produces a full hydrograph (i.e., TR-20, TR-55, HEC-1,
PSRM). The municipality may approve the use of any generally accepted
full hydrograph approximation technique that shall use a total runoff
volume that is consistent with the volume from a method that produces
a full hydrograph.
A.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
B.
Pretreatment shall be provided prior to infiltration.
D.
Any other drainage conveyance facility that does not fall under Chapter
105 regulations must be able to convey, without damage to the drainage
structure or roadway, runoff from the twenty-five-year design storm
with a minimum 1.0 foot of freeboard measured below the lowest point
along the top of the roadway. Any facility that constitutes a dam
as defined in PaDEP Chapter 105 regulations may require a permit under
dam safety regulations. Any facility located within a PennDOT right-of-way
must meet PennDOT minimum design standards and permit submission requirements.
E.
The design of any proposed roadway drainage facilities shall be consistent
with the PennDOT Design Manual Part 2, Publication 13M.
F.
Storm sewers must be able to convey proposed conditions runoff from
a one-hundred-year design storm without surcharging inlets, where
appropriate.
G.
Adequate erosion protection shall be provided along all open channels,
and at all points of discharge.
H.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The municipality reserves
the right to disapprove any design that would result in the construction
in or continuation of a stormwater problem area.
I.
No stormwater detention facility shall be placed within 50 feet of
a special geologic feature. No stormwater conveyance facility shall
be constructed within 50 feet of a special geologic feature, unless
it is constructed of concrete pipe utilizing watertight joints, or
an approved equal.
Federal regulations approved October 1999 require operators
of small municipal separate storm sewer systems (MS4s) to obtain NPDES
Phase II permits from DEP by March 2003. (NPDES II is an acronym for
the National Pollutant Discharge Elimination System Phase II Stormwater
Permitting Regulations.) This program affects all municipalities in
"urbanized areas" of the state. This definition applies to all Schuylkill
River watershed municipalities identified in Table III-1 of the Schuylkill
River Stormwater Management Plan Volume II as NPDES Phase II municipalities.
Therefore, these identified municipalities will be subject to the
NPDES Phase II requirements mandated by the Federal Clean Water Act[1] as administered by DEP. For more information on NPDES
II requirements, contact the DEP Regional Office.
[1]
Editor's Note: See 33 U.S.C. § 1251 et seq.
