A.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 296-12:
B.
SWM site plans approved by the Township, in accordance with § 296-34, shall be on site throughout the duration of the regulated activity.
C.
The Township 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.
D.
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 requirements under Title 25 of the Pennsylvania Code 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]), No. 363-2134-008, as amended and updated.
E.
Impervious areas:
(1)
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages.
(2)
For development taking place in stages, the entire development plan
must be used in determining conformance with this chapter.
(3)
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 296-27 and the peak rate controls of § 296-28 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
F.
Stormwater flows onto adjacent property shall not be created, increased,
or otherwise altered without written notification to the adjacent
property owner(s). Such stormwater flows shall be subject to the requirements
of this chapter. Areas of existing diffused drainage discharge onto
adjacent property shall be managed such that, at minimum, the peak
diffused flow does not increase in the general direction of discharge,
except as otherwise provided in this chapter. If diffused flow is
proposed to be concentrated and discharged onto adjacent property
(including flows from detention basin emergency spillways), the developer's
engineer must document and certify that there are adequate downstream
conveyance facilities to safely transport the concentrated discharge
to the point of predevelopment flow concentration, to the stream reach,
or otherwise prove that no harm will result from the concentrated
discharge. It is recommended the developer obtain written permission
from the downstream property owner(s) for the proposed discharges.
Areas of existing diffused drainage discharge shall be subject to
any applicable release rate criteria in the general direction of existing
discharge where they are proposed to be concentrated or maintained
as diffused drainage areas.
G.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property.
(2)
Meet the water quality goals of this chapter by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
H.
The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
I.
Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter.
J.
Normally dry, open top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
K.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the latest version of the Precipitation-Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 14[3] can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
L.
N.
Storm drainage system shall be designed to preserve natural watercourses
except as modified by stormwater detention facilities, recharge facilities,
water quality facilities, pipe systems or open channels consistent
with this chapter.
O.
Where a site is traversed by watercourses, swales, ditches, etc., there shall be provided drainage easements conforming substantially with the line of such watercourses, swales, ditches, etc. The width of any easement shall be adequate to provide for unimpeded flow of post-development storm runoff based on either calculations completed by the developer in conformance with § 296-18 for the 100-year return period runoff, the Little Lehigh Creek, Coplay Creek or Jordan Creek Act 167 100-year return period flows, or Federal Emergency Management Agency (FEMA) 100-year frequency flood flows and to provide a freeboard allowance of 0.5 foot above the design water surface level. In all areas, the flow rate to be utilized shall be the maximum rate identified through either developer's calculations, the Little Lehigh Creek, Coplay Creek or Jordan Creek Act 167 or (if applicable) FEMA study flows. In areas where the Act 167 flow rate is the maximum rate, this rate shall be used unless a reduced flow rate is determined by the Lehigh Valley Planning Commission to take precedence over the Act 167 flow rate. This maximum flow rate shall be used to determine the 100-year water surface elevations based on HEC-RAS modeling (or other modeling method as approved by the Township). The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement in the post-development condition. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the 100-year floodplain is formally defined by FEMA studies are subject to the applicable municipal floodplain regulations. All proposed buildings within or adjacent to a floodplain as defined by FEMA studies shall have first floor elevations at least 1.5 feet above the 100-year frequency flood elevation. The 100-year flood elevation to be used to establish the first-floor elevation shall be determined using the greater of the maximum flow rate referenced in FEMA study flows, Act 167 flows, or calculated flows as set forth above.
P.
Any drainage facilities or structures required by this chapter that
are located on state highway rights-of-way shall be subject to approval
by the Pennsylvania Department of Transportation and the Township.
Q.
When it can be shown that, due to topographic conditions, natural
drainage swales on the site cannot adequately provide for drainage,
open channels may be constructed conforming substantially to the line
and grade of such natural drainage swales. Capacities of open channels
shall be calculated using the Manning Equation.
R.
Storm drainage facilities and appurtenances shall be so designed
and provided as to minimize erosion in watercourse channels and at
all points of discharge.
S.
Consideration should be given to the design and use of volume controls
for stormwater management, where geology and soils permit. Areas of
suitable geology for volume controls shall be determined by the Township.
Documentation of the suitability of the soil for volume controls shall
be provided by the applicant. Volume controls shall be acceptable
in areas of suitable geology where the soils are designated as well
drained in the County Soil Survey. Other soils may be acceptable for
use of volume controls based on site-specific soils evaluations provided
by the applicant.
T.
Within areas containing soils identified by the Soils Conservation
Service to be sinkhole prone, detention basins shall be lined with
a material which, after installation, attains a permeability rate
of less than or equal to 1 x 10-7 cm/sec.
U.
Parking lot ponding depth may not exceed two inches in areas of anticipated
pedestrian traffic and six inches in all areas for a twenty-five-year
frequency storm.
V.
Post-construction BMPs shall be designed, installed, operated, and
maintained to meet the requirements of the Clean Streams Law[7] and implementing regulations, including the established
practices in 25 Pa. Code Chapter 102 and the specifications of this
chapter as to prevent accelerated erosion in watercourse channels
and at all points of discharge.
[7]
Editor's Note: See 35 P.S. § 691.1 et seq.
W.
No earth disturbance activities associated with any regulated activities
shall commence until approval by the Township of a plan which demonstrates
compliance with the requirements of this chapter.
X.
Techniques described in Appendix F (low-impact development) of this
chapter are encouraged because they reduce the costs of complying
with the requirements of this chapter and the state water quality
requirements.
Y.
Infiltration for stormwater management is encouraged where soils
and geology permit, consistent with the provisions of this chapter
and, where appropriate, the Recommendation Chart for Infiltration
Stormwater Management BMPs in Carbonate Bedrock in Appendix D.[8] Infiltration is encouraged for capturing and treating the water quality volume (as calculated in § 296-15), any part of the water quality volume or for otherwise meeting the purposes of this chapter.
[8]
Editor's Note: Said appendix is included as an attachment to this chapter.
B.
Agricultural activity is exempt from the SWM Site Plan preparation
requirements of this chapter, provided the activities are performed
according to the requirements of 25 Pa. Code Chapter 102.
C.
Forest management and timber operations are exempt from the SWM Site
Plan preparation requirements of this chapter, provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
E.
The Township may deny or revoke any exemption pursuant to this section
at any time for any project that the Township believes may pose a
threat to public health and safety or the environment.
The following permit requirements apply to certain regulated
and earth disturbance activities and must be met prior to commencement
of regulated and earth disturbance activities, as applicable:
A.
All regulated and 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 102.
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 Township shall
commence until approval by the Township of an erosion and sediment
control plan for construction activities. Written approval by DEP
or a delegated County Conservation District shall satisfy this requirement.
B.
An erosion and sediment control plan is required by DEP regulations
for any earth disturbance activity of 5,000 square feet or more under
Pa. Code § 102.4(b) and must be approved by the Conservation
District per memo of understanding.
C.
A DEP NPDES stormwater discharges associated with construction activities permit is required for regulated earth disturbance activities under Pa. Code Chapter 92.
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 Township before the commencement
of earth disturbance activity.
E.
A copy of the erosion and sediment control plan and any permit, as
required by DEP regulations, shall be available at the project site
at all times.
A.
No regulated earth disturbance activities within the Township shall
commence until approval by the Township of a drainage plan which demonstrates
compliance with this chapter. This chapter provides standards to meet
NPDES permit requirements associated with construction activities
and MS4 permit requirements.
B.
The water quality volume (WQv) shall be captured and treated. The
WQv shall be calculated two ways.
(1)
First, WQv shall be calculated using the following formula:
|
WQv
|
=
|
(c)(P)(A)
12
|
|
Where:
| ||
|
WQv
|
=
|
Water quality volume in acre-feet
|
|
c
|
=
|
Rational method post-development runoff coefficient for the
two-year storm
|
|
P
|
=
|
1.25 inches
|
|
A
|
=
|
Area in acres of proposed regulated activity
|
(2)
Second, the WQv shall be calculated as the difference in runoff volume
from predevelopment to post-development for the two-year return period
storm. The effect of closed depressions on the site shall be considered
in this calculation. The larger of these two calculated volumes shall
be used as the WQv to be captured and treated. This standard does
not limit the volume of infiltration an applicant may propose for
purposes of water quantity/peak rate control.
C.
The WQv shall be calculated for each post-development drainage direction
on a site for sizing BMPs. Site areas having no impervious cover and
no proposed disturbance during development may be excluded from the
WQv calculations and do not require treatment.
D.
If an applicant is proposing to use a dry extended detention basin,
wet pond, constructed wetland or other BMP that ponds water on the
land surface and may receive direct sunlight, the discharge from that
BMP must be treated by infiltration, a vegetated buffer, filter strip,
bioretention, vegetated swale or other BMP that provides a thermal
benefit to protect the high-quality waters of the Little Lehigh Creek
from thermal impacts.
E.
The WQv for a site as a result of the regulated activities must either be treated with infiltration or two acceptable BMPs such as those listed in Subsection O, except for minor areas on the periphery of the site that cannot reasonably be drained to an infiltration facility or other BMP.
F.
Infiltration BMPs shall not be constructed on fill unless the applicant
demonstrates that the fill is stable and otherwise meets the infiltration
BMP standards of this chapter.
G.
The applicant shall document the bedrock type(s) present on the site
from published sources. Any apparent boundaries between carbonate
and noncarbonate bedrock shall be verified through more detailed site
evaluations by a qualified geotechnical professional.
H.
For each proposed regulated activity in the watershed where an applicant
intends to use infiltration BMP's, the applicant shall conduct
a preliminary site investigation, including gathering data from published
sources, a field inspection of the site, a minimum of one test pit
and a minimum of two percolation tests, as outlined in Appendix G.
This investigation will determine depth to bedrock, depth to the seasonal
high-water table, soil permeability and location of special geologic
features, if applicable. This investigation may be done by a certified
Sewage Enforcement Officer (SEO) except that the location(s) of special
geologic features shall be verified by a qualified geotechnical professional.
Additionally, the Township Geotechnical Consultant or its authorized
representative shall be notified of the soil testing in order to observe
any such testing as determined to be necessary.
I.
Sites where applicants intend to use infiltration BMPs must meet
the following criteria:
(1)
Depth to bedrock below the invert of the BMP greater than or equal
to two feet.
(2)
Depth to seasonal high-water table below the invert of the BMP greater
than or equal to three feet; except for infiltration of residential
roof runoff where the seasonal high-water table must be below the
invert of the BMP. (If the depth to bedrock is between two and three
feet and the evidence of the seasonal high-water table is not found
in the soil, no further testing to locate the depth to seasonal high-water
table is required.)
(3)
Soil permeability (as measured by the adapted 25 PA Code § 73.15.
percolation test in Appendix G) greater than or equal to 0.5 inches/hour
and less than or equal to 12 inches per hour.
(4)
Setback distances or buffers as follows:
(a)
One hundred feet from water supply wells.
(b)
Fifteen feet down gradient or 100 feet upgradient from building
foundations; except for residential development where the required
setback is 15 feet downgradient or 40 feet upgradient from building
foundations.
(c)
Fifty feet from septic system drainfields; except for residential
development where the required setback is 25 feet from septic system
drainfields.
(d)
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.
(e)
One hundred feet from the property line unless documentation
is provided to show that all setbacks from existing or potential future
wells, foundations and drainfields on neighboring properties will
be met; except for one- and two-family residential dwellings where
the required setback is 40 feet unless documentation is provided to
show that all setbacks from existing or potential future wells, foundations
and drainfields on neighboring properties will be met.
J.
For entirely noncarbonate sites, the recharge volume (REv) shall be infiltrated unless the applicant demonstrates that it is infeasible to infiltrate the REv for reasons of seasonal high- water table, permeability rate, soil depth or setback distances; or except as provided in Subsection U.
(1)
The REv shall be calculated as follows:
|
REv = (0.25)*(I)/12
|
|
Where:
| ||
|
REv
|
=
|
Recharge volume in acre-feet
|
|
I
|
=
|
Impervious area in acres
|
(2)
The preliminary site investigation described in Subsection H is required and shall continue on different areas of the site until a potentially suitable infiltration location is found or the entire site is determined to be infeasible for infiltration. For infiltration areas that appear to be feasible based on the preliminary site investigation, the additional site investigation and testing as outlined in Appendix G shall be completed.
(3)
If an applicant proposes infiltration, the Township may determine
infiltration to be infeasible if there are known existing conditions
or problems that may be worsened by the use of infiltration.
(5)
If it is not feasible to infiltrate the full REv, the applicant shall infiltrate that portion of the REv that is feasible based on the site characteristics. If none of the REv can be infiltrated, REv shall be considered as part of the WQv and shall be captured and treated as described in Subsection O.
(6)
If REv is infiltrated, it may be subtracted from the WQv required
to be captured and treated.
K.
In entirely carbonate areas, where the applicant intends to us infiltration BMPs, the preliminary site investigation described in Subsection H shall be conducted. For infiltration areas that appear feasible based on the preliminary site investigation, the applicant shall conduct the additional site investigation and testing as outlined in Appendix G. The soil depth, percolation rate and proposed loading rate, each weighted as described in § 296-18, along with the buffer from special geologic features shall be compared to the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in Subsection I are required for infiltration in carbonate areas. Applicants are encouraged to infiltrate the REv, as calculated in Subsection J, but are not required to use infiltration BMPs on a carbonate site even if the site falls in the "Recommended" range on the chart in Appendix D. Any amount of volume infiltrated can be subtracted from the WQv to be treated by non-infiltration BMPs. If infiltration is not proposed, the full WQv shall be treated by two acceptable BMPs, as specified in Subsection O.
L.
If a site has both carbonate and noncarbonate areas, the applicant shall investigate the ability of the noncarbonate portion of the site to fully meet this chapter to meet the requirements for REv for the whole site through infiltration. If that proves infeasible, infiltration in the carbonate area as described in Subsection K or two other non-infiltration BMPs as described in Subsection O must be used. No infiltration structure in the noncarbonate area shall be located within 50 feet of a boundary with carbonate bedrock, except when a preliminary site investigation has been done showing the absence of special geologic features within 50 feet of the proposed infiltration area.
M.
If infiltration BMPs are proposed in carbonate areas, the post-development
two-year runoff volume leaving the site shall be 80% or more of the
predevelopment runoff volume for the carbonate portion of the site
to prevent infiltration of volumes far in excess of the predevelopment
infiltration volume unless otherwise approved by Township Geotechnical
Consultant and the Township Engineer.
N.
Site areas proposed for infiltration shall be protected from disturbance
and compaction except as necessary for construction of infiltration
BMPs.
O.
If infiltration of the entire WQv is not proposed, the remainder
of the WQv shall be treated by two acceptable BMPs in series for each
discharge location. Sheet flow draining across a pervious area can
be considered as one BMP. Sheet flow across impervious areas and concentrated
flow shall flow through two BMPs. If sheet flow from an impervious
area is to be drained across a pervious area as one BMP, the length
of the pervious area must be equal to or greater than the length of
impervious area. In no case may the same BMP be employed consecutively
to meet the requirement of this section. Acceptable BMPs are listed
below along with the recommended reference for design.
|
Best Management Practice
|
Design Reference NumberC
|
|---|---|
|
BioretentionA
|
4, 5, 11, 16
|
|
Capture/reuseB
|
4, 14
|
|
Constructed wetlands
|
4, 5, 8, 10, 16
|
|
Dry extended detention ponds
|
4, 5, 8, 12, 18
|
|
Minimum disturbance/minimum maintenance practices
|
1, 9
|
|
Significant reduction of existing impervious cover
|
N/A
|
|
Stormwater filtersA (sand, peat,
compost, etc.)
|
4, 5, 10, 16
|
|
Vegetated buffers/filter strips
|
2, 3, 5, 11, 16, 17
|
|
Vegetated roofs
|
4, 13
|
|
Vegetated swalesA
|
2, 3, 5, 11, 16, 17
|
|
Water quality inletsD
|
4, 7, 15, 16, 19
|
|
Wet detention ponds
|
4, 5, 6, 8
|
|
NOTES:
| |
|
A
|
This BMP could be designed with or without an infiltration component.
If infiltration is proposed, the site and BMP will be subject to the
testing and other infiltration requirements in this chapter.
|
|
B
|
If this BMP is used to treat the entire WQv, then it is the
only BMP required because of this BMPs superior water quality performance.
|
|
C
|
See table below.
|
|
D
|
Water quality inlets include such BMPs as oil/water separators,
sediment traps/catch basin sumps, and trash/debris collectors in catch
basins.
|
|
Design Reference Title
| |
|
1
|
"Conservation Design For Stormwater Management — A Design
Approach to Reduce Stormwater Impacts From Land Development and Achieve
Multiple Objectives Related to Land Use," Delaware Department of Natural
Resources and Environmental Control, The Environmental Management
Center of the Brandywine Conservancy, September 1997.
|
|
2
|
"A Current Assessment of Urban Best Management Practices: Techniques
for Reducing Nonpoint Source Pollution in the Coastal Zone," Schueler,
T. R., Kumble, P. and Heraty, M., Metropolitan Washington Council
of Governments, 1992.
|
|
3
|
"Design of Roadside Channels with Flexible Linings," Federal
Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic Engineering
Circular 15, FHWA-IP-87-7, McLean Virginia, 1988.
|
|
4
|
"Draft Stormwater Best Management Practices Manual," Pennsylvania
Department of Environmental Protection, January 2005.
|
|
5
|
"Evaluation and Management of Highway Runoff Water Quality,"
Federal Highway Administration, FHWA-PD-96-032, Washington, D.C.,
1996.
|
|
6
|
"Evaporation Maps of the United States," U.S. Weather Bureau
(now NOAA/National Weather Service) Technical Paper 37, Published
by Department of Commerce, Washington D.C., 1959.
|
|
7
|
"Georgia Stormwater Manual," AMEC Earth and Environmental, Center
for Watershed Protection, Debo and Associates, Jordan Jones and Goulding,
Atlanta Regional Commission, Atlanta, Georgia, 2001.
|
|
8
|
"Hydraulic Design of Highway Culverts," Federal Highway Administration,
FHWA HDS 5, Washington, D.C., 1985 (revised May 2005).
|
|
9
|
"Low Impact Development Design Strategies An Integrated Design
Approach," Prince Georges County, Maryland Department of Environmental
Resources, June 1999.
|
|
10
|
"Maryland Stormwater Design Manual," Maryland Department of
the Environment, Baltimore, Maryland, 2000.
|
|
11
|
"Pennsylvania Handbook of Best Management Practices for Developing
Areas," Pennsylvania Department of Environmental Protection, 1998.
|
|
12
|
"Recommended Procedures for Act 167 Drainage Plan Design," LVPC,
Revised 1997.
|
|
13
|
"Roof Gardens History, Design, and Construction," Osmundson,
Theodore. New York: W.W. Norton and Company, 1999.
|
|
14
|
"The Texas Manual on Rainwater Harvesting," Texas Water Development
Board, Austin, Texas, Third Edition, 2005.
|
|
15
|
"VDOT Manual of Practice for Stormwater Management," Virginia
Transportation Research Council, Charlottesville, Virginia, 2004.
|
|
16
|
"Virginia Stormwater Management Handbook," Virginia Department
of Conservation and Recreation, Richmond, Virginia, 1999.
|
|
17
|
"Water Resources Engineering," Mays, L. W., John Wiley and Sons,
Inc., 2005.
|
|
18
|
"Urban Hydrology for Small Watersheds," Technical Report 55,
US Department of Agriculture, Natural Resources Conservation Service,
1986.
|
|
19
|
US EPA, Region 1 New England web site (as of August 2005) http://www.epa.gov/NE/assistance/ceitts/stormwater/techs/html.
|
P.
Stormwater runoff from hot spot land uses shall be pretreated. In no case may the same BMP be employed consecutively to meet this requirement and the requirement in Subsection O. Acceptable methods of pretreatment are listed below.
|
Hot Spot Land Use
|
Pretreatment Method(s)
|
|---|---|
|
Vehicle maintenance and repair facilities, including auto parts
stores
|
Water quality inlets
|
|
Use of drip pans and/or dry sweep material under vehicles/equipment
| |
|
Use of absorbent devices to reduce liquid releases
| |
|
Spill prevention and response program
| |
|
Vehicle fueling stations
|
Water quality inlets
|
|
Spill prevention and response program
| |
|
Storage areas for public works
|
Water quality inlets
|
|
Use of drip pans and/or dry sweep material under vehicles/equipment
| |
|
Use of absorbent devices to reduce liquid releases
| |
|
Spill prevention and response program
| |
|
Diversion of stormwater away from potential contamination areas
| |
|
Outdoor storage of liquids
|
Spill prevention and response program
|
|
Commercial nursery operations
|
Vegetated swales/filter strips
|
|
Constructed wetlands
| |
|
Stormwater collection and reuse
| |
|
Salvage yards and recycling facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
Fleet storage yards and vehicle cleaning facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
Facilities that store or generate regulated substances*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
Marinas*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
Certain industrial uses (listed under NPDES)*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
NOTES:
| |
|
*
|
Regulated under the NPDES Stormwater Program
|
(1)
Design
references for the pretreatment methods, as necessary, are listed
below. If the applicant can demonstrate to the satisfaction of the
municipality that the proposed land use is not a hot spot, then the
pretreatment requirement would not apply.
|
Pretreatment Method
|
Design ReferenceA
|
|---|---|
|
Constructed wetlands
|
4, 5, 8, 10, 16
|
|
Diversion of stormwater away from potential contamination areas
|
4, 11
|
|
Stormwater collection and reuse (especially for irrigation)
|
4, 14
|
|
Stormwater filters (sand, peat, compost, etc.)
|
4, 5, 10, 16
|
|
Vegetated swales
|
2, 3, 5, 11, 16, 17
|
|
Water quality inlets
|
4, 7, 15, 16, 19
|
|
NOTES:
| |
|
A
|
These numbers refer to the Design Reference Title Chart in Subsection O, above.
|
Q.
The use of infiltration BMPs is prohibited on hot spot land use areas
unless otherwise approved by Township Geotechnical Consultant and
the Township Engineer.
R.
Stormwater infiltration BMPs shall not be placed in or on a special
geologic feature(s). Additionally, stormwater runoff shall not be
discharged into existing on-site sinkholes.
S.
Applicants shall request, in writing, public water suppliers to provide the Zone I Wellhead Protection radius, as calculated by the method outlined in the Pennsylvania Department of Environmental Protection Wellhead Protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsection I, infiltration is prohibited in the Zone I radius as defined and substantiated by the public water supplier in writing. If the applicant does not receive a response from the public water supplier, the Zone I radius is assumed to be 100 feet.
T.
The volume and rate of the net increase in stormwater runoff from
the regulated activities must be managed to prevent the physical degradation
of receiving waters from such effects as scour and stream bank destabilization,
to satisfy state water quality requirements, by controlling the two-year
post-development runoff to a 30% release rate.
U.
The Township may, after consultation with DEP, approve alternative
methods for meeting the state water quality requirements other than
those in this section, 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.
A.
Mapping of stormwater management districts. To implement the provisions
of the Little Lehigh Creek Watershed, Coplay Creek Watershed and Jordan
Creek Watershed stormwater management plan, the Township is hereby
divided into stormwater management districts consistent with the Little
Lehigh Creek, Coplay Creek and Jordan Creek release rate maps presented
in the plan. The boundaries of the stormwater management districts
are shown on an official map which is available for inspection at
the Township Community Development Department office. A copy of the
official map at a reduced scale is included in Appendix A for general
reference.
B.
Description of stormwater management districts. Two types of stormwater
management districts may be applicable to the Township, namely conditional/provisional
no detention districts and dual release rate districts as described
below:
(1)
Conditional/provisional no detention districts. Within these districts, the capacity of the "local" runoff conveyance facilities (as defined in Article II) must be calculated to determine if adequate capacity exists. For this determination, the developer must calculate peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition. The developer must also calculate peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this chapter. The larger of the two peak flows calculated will be used in determining if adequate capacity exists. If adequate capacity exists to safely transport runoff from the site to the main channel these watershed areas may discharge post-development peak runoff without detention facilities. If the capacity calculations show that the local runoff conveyance facilities lack adequate capacity, the developer shall either use a 100% release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with § 296-17P. Any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 296-17D. By definition, a storm drainage problem area associated with the local runoff conveyance facilities indicates that adequate capacity does not exist. Sites in these districts are still required to meet all of the water quality requirements in § 296-15.
(2)
Dual release rate districts. Within these districts, the two-year
post-development peak discharge must be controlled to 30% of the predevelopment
two-year runoff peak. Further, the ten-, twenty-five- and 100-year
post-development peak runoff must be controlled to the stated percentage
of the predevelopment peak. Release rates associated with the ten-
through 100-year events vary from 50% to 100% depending upon location
in the watershed.
A.
Applicants shall provide a comparative pre- and post-construction
stormwater management hydrograph analysis for each direction of discharge
and for the site overall to demonstrate compliance with the provisions
of this chapter.
B.
Any stormwater management controls required by this chapter and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, ten-, twenty-five- and 100-year return period runoff events consistent with the calculation methodology specified in § 296-18.
C.
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 provided as
part of the drainage plan. The district boundaries as originally drawn
coincide with topographic divides or, in certain instances, are drawn
from the intersection of the watercourse and a physical feature such
as the confluence with another watercourse or a potential flow obstruction
(e.g., road, culvert, bridge, etc.). The physical feature is the downstream
limit of the subarea and the subarea boundary is drawn from that point
up slope to each topographic divide along the path perpendicular to
the contour lines.
D.
Any downstream capacity 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.
(2)
Natural or man-made channels or swales must be able to convey the
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.
E.
For a proposed development site located within one release rate category
subarea, the total runoff from the site shall meet the applicable
release rate criteria. For development sites with multiple directions
of runoff discharge, individual drainage directions may be designed
for up to a 100% release rate so long as the total runoff from the
site is controlled to the applicable release rate.
F.
For a proposed development site located within two or more release
category subareas, the peak discharge rate from any subarea shall
be the predevelopment peak discharge for that subarea multiplied by
the applicable release rate. 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 site. In this
case, peak discharge in any direction may be a 100% release rate provided
that the overall site discharge meets the weighted average release
rate.
G.
For a proposed development site located partially within a release
rate category subarea and partially within a conditional/provisional
no detention subarea, the size of the predevelopment drainage area
on a site may not be changed post-development to create potentially
adverse conditions on downstream properties except as part of a no
harm or hardship waiver procedure.
H.
No portion of a site may be regraded to redirect runoff onto adjacent
property except as part of a no harm or hardship waiver procedure,
or unless runoff peak flow rate and volume controls are proposed and
implemented which limit post-development peak flow rate and volume
discharges to predevelopment levels, or all affected downstream property
owners have granted express permission in the form of recorded easements.
I.
Within a release rate category area, for a proposed development site which has areas which drain to a closed depression(s), the design release from the site will be the lesser of 1) the applicable release rate flow assuming no closed depression(s) or 2) the existing peak flow actually leaving the site. In cases where 2) would result in an unreasonably small design release, the design discharge of less than or equal to the release rate will be determined by the available downstream conveyance capacity to the main channel calculated using Subsection D and the minimum orifice criteria.
J.
Off-site areas which 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 using the capacity criteria in Subsection D and the detention criteria in § 296-18.
K.
For development sites proposed to take place in phases, all detention
ponds shall be designed to meet the applicable release rate(s) applied
to all site areas tributary to the proposed pond discharge direction.
All site tributary areas will be assumed as developed, regardless
of whether all site tributary acres are proposed for development at
that time. An exception shall be sites with multiple detention ponds
in series where only the downstream pond must be designed to the stated
release rate.
L.
Where the site area to be impacted by a proposed development activity
differs significantly from the total site area, only the proposed
impact area shall be subject to the release rate criteria. The impact
area includes any proposed cover or grading changes.
M.
Development proposals which, through groundwater recharge or other
means, do not increase either the rate or volume of runoff discharged
from the site compared to predevelopment are not subject to the release
rate provisions of this chapter.
N.
"No harm" water quantity option. For any proposed development site not located in a conditional/provisional no detention district, the developer has the option of using a less restrictive runoff control (including no detention) if the developer can prove that special circumstances exist for the proposed development site and that no harm would be caused by discharging at a higher runoff rate than that specified by the plan. Special circumstances are defined as any hydrologic or hydraulic aspects of the development itself not specifically considered in the development of the plan runoff control strategy. Proof of no harm would have to be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Delaware or Lehigh River. Proof of no harm must be shown using the capacity criteria specified in Subsection D if downstream capacity analysis is a part of the no harm justification. Attempts to prove no harm based upon downstream peak flow versus capacity analysis shall be governed by the following provisions:
(1)
The peak flow values to be used for downstream areas for the design
return period storms (two-, ten-, twenty-five- and 100-year) shall
be the values from the calibrated PSRM Model for the Little Lehigh
Creek, Coplay Creek or Jordan Creek or as calculated by an applicant
using an alternate method acceptable to the municipality. The flow
values from the PSRM Model would be supplied to the developer by the
Lehigh Valley Planning Commission upon request.
(2)
Any available capacity in the downstream conveyance system as documented
by a developer may be used by the developer only in proportion to
his development site acreage relative to the total upstream undeveloped
acreage from the identified capacity (i.e., if his site is 10% of
the upstream undeveloped acreage, he may use up to 10% of the documented
downstream available capacity).
(3)
Developer-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 Subsection P.
O.
Regional detention alternatives. For certain areas within the study
area, it may be more cost-effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined based on
the required release rate at the point of discharge.
P.
Capacity improvements. In certain instances, primarily within the conditional/provisional no detention areas, local drainage conditions may dictate more stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Peak flow calculations shall be done assuming that the local watershed is in the existing condition and then assuming that the local watershed is developed per current zoning and using the specified runoff controls. Any capacity improvements would be designed using the larger of the above peak flows and the capacity criteria specified in Subsection D. All new development in the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control, if any. Capacity improvements may also be provided as necessary to implement any regional detention alternatives or to implement a modified no harm option which proposes specific capacity improvements to provide that a less stringent discharge control would not create any harm downstream.
Q.
Compatibility with NPDES requirements. Any proposed regulated activity
for which a permanent stormwater quality control detention basin is
required under the NPDES regulations shall use the more stringent
runoff control criteria between this chapter and the NPDES requirements.
R.
In any stormwater management district, the Township reserves the
right to require a more stringent design release rate for a development
site or other amendments to a drainage plan to address problems in
the local runoff conveyance system downstream of the site. Such problems
include existing flooding and erosion problems, inadequate conveyance
capacity, poorly defined or poorly stabilized downstream conveyance
systems or other factors; or for other good cause shown; and supported
by engineering data of the kind and type commonly accepted by the
civil engineering profession in the evaluation and management of stormwater
runoff.
S.
In any stormwater management district, storm sewer piping, swales and inlet systems shall be designed for a twenty-five-year return period storm, or a 100-year return period storm where the system is designed to convey 100-year storm flows to a detention facility. Bridges and culverts along roadways shall be designed to convey the 100-year return period storm. Flows from off-site upstream areas shall be determined in accordance with the procedure identified in § 296-11O.
A.
Stormwater runoff from all development sites shall be calculated
using either the rational method or the soil-cover-complex methodology.
B.
Infiltration BMP loading rate percentages in the Recommendation Chart
for Infiltration Stormwater Management BMPs in Carbonate Bedrock in
Appendix D shall be calculated as follows:
|
Area Tributary to infiltration BMP
| |
|
*100%
| |
|
Base area of infiltration BMP
| |
|
The area tributary to the infiltration BMP shall be weighted
as follows:
| |
|
All disturbed areas to be made impervious:
|
weight at 100%
|
|
All disturbed areas to be made pervious:
|
weight at 50%
|
|
All undisturbed pervious areas:
|
weight at 0%
|
|
All existing impervious areas:
|
weight at 100%
|
C.
Soil thickness is to be measured from the bottom of any proposed
infiltration system. The effective soil thickness in the Recommendation
Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock
in Appendix D is the measured soil thickness multiplied by the thickness
factor based on soil permeability (as measured by the adapted 25 PA
Code § 73.15 percolation test in Appendix G), as follows:
|
Permeability Range*
inches/hour
|
Thickness Factor
|
|---|---|
|
6.0 to 12.0
|
0.8
|
|
2.0 to 6.0
|
1.0
|
|
1.0 to 2.0
|
1.4
|
|
0.75 to 1.0
|
1.2
|
|
0.5 to 0.75
|
1.0
|
|
NOTES:
| |
|
*
|
If the permeability rate (as measured by the adapted 25 PA Code
§ 73.15 percolation test in Appendix G) falls on a break
between two thickness factors, the smaller thickness factor shall
be used.
|
|
Sites with soil permeability greater than 12.0 in/hr or less
than 0.5 in/hr, as measured by the adapted 25 PA Code § 73.15
percolation test in Appendix G, are not recommended for infiltration.
| |
D.
The design of any detention basin intended to meet the requirements
of this chapter shall be verified by routing the design storm hydrograph
through the proposed basin using the storage indication method or
other methodology demonstrated to be more appropriate. For basins
designed using the rational method technique, the design hydrograph
for routing shall be the Universal Rational Hydrograph unless another
methodology is approved by the Township.
E.
BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the storage indication method.
F.
BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall provide storage volume for the full WQv
below the lowest outlet invert.
G.
Wet detention ponds designed to have a permanent pool for the WQv
shall assume that the permanent pool volume below the primary outlet
is full at the beginning of design event routing for the purposes
of evaluating peak outflows. All wet detention ponds shall be subject
to review by the Township geotechnical consultant.
H.
All stormwater detention facilities shall provide a minimum one-foot
freeboard above the maximum pool elevation associated with the two-
through twenty-five-year runoff events. A 0.5-foot freeboard shall
be provided above the maximum pool elevation of the 100-year runoff
event. The freeboard shall be measured from the maximum pool elevation
to the invert of the emergency spillway. The two- through 100-year
storm events shall be controlled by the primary outlet structure.
An emergency spillway for each basin shall be designed to pass the
100-year return frequency storm peak basin inflow rate with a minimum
0.5 foot freeboard measured to the top of basin. The freeboard criteria
shall be met considering any off-site areas tributary to the basin
as developed, as applicable. If this detention facility is considered
to be a dam as per DEP Chapter 105, the design of the facility must
be consistent with the Chapter 105 regulations and may be required
to pass a storm greater than the 100-year event.
I.
The minimum circular orifice diameter for controlling discharge rates
from detention facilities shall be three inches. Designs where a lesser
size orifice would be required to fully meet release rates shall be
acceptable, provided that as much of the site runoff as practical
is directed to the detention facilities.
J.
Runoff calculations using the soil-cover-complex method shall use
the Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution. The twenty-four-hour rainfall depths for the
various return periods to be used consistent with this chapter may
be taken from the latest version of the field manual for Pennsylvania
Design Rainfall Intensity Charts from NOAA Atlas 14.
|
Return Period
|
24 Hour Rainfall Depth
|
|---|---|
|
1 year
|
2.40 inches
|
|
2 year
|
3.00 inches
|
|
5 year
|
3.60 inches
|
|
10 year
|
4.56 inches
|
|
25 year
|
5.52 inches
|
|
50 year
|
6.48 inches
|
|
100 year
|
7.44 inches
|
|
NOTES:
|
|
A graphical and tabular presentation of the Type II twenty-four-hour
distribution is included in Appendix C.
|
K.
Runoff calculations using the rational method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and NOAA Atlas 14 and the Atlas of the United States
Precipitation and Precipitation Frequency Charts, current version.
L.
Runoff Curve Numbers (CN's) to be used in the soil-cover-complex
method shall be based upon the matrix presented in Appendix C.
M.
Runoff coefficients for use in the rational method shall be based
upon the table presented in Appendix C.
N.
All time of concentration calculations shall use a segmental approach
which may include on or all of the flow types below:
(1)
Sheet flow (overland flow) calculations shall use either the NRCS
average velocity chart (Figure 3-1, Technical Release-55, 1975) or
the modified kinematic wave travel time equation (equation 3-3, NRCS
TR-55, June 1986). If using the modified kinematic wave travel time
equation, the sheet flow length shall be limited to 50 feet for designs
using the rational method and limited to 150 feet for designs using
the soil-cover-complex method.
(2)
Shallow concentrated flow travel times shall be determined from the
watercourse slope, type of surface and the velocity from Figure 3-1
of TR-55, June 1986.
(3)
Open channel flow travel times shall be determined from velocities
calculated by the Manning Equation. Bankfull flows shall be used for
determining velocities. Manning 'n' values shall be based
on the table presented in Appendix C.
(4)
Pipe flow travel times shall be determined from velocities calculated
using the Manning Equation assuming full flow and the Manning 'n'
values from Appendix C.
O.
If using the rational method, all predevelopment calculations for
a given discharge direction shall be based on a common time of concentration
considering both on-site and off-site drainage areas. All post-development
calculations for a given discharge direction shall be based on a common
time of concentration considering both on-site and any off-site drainage
areas.
P.
The Manning Equation shall be used to calculate the capacity of watercourses.
Manning 'n' values used in the calculations shall be consistent
with the table presented in Appendix C or other appropriate standard
engineering 'n' value resources. Pipe capacities shall be
determined by methods acceptable to the Township Engineer.
Q.
The Pennsylvania DEP, Chapter 105, Rules and Regulations, applies
to the construction, modification, operation or maintenance of both
existing and proposed dams, water obstructions and encroachments throughout
the watershed. Criteria for design and construction of stormwater
management facilities according to this chapter may differ from the
criteria that are used in the permitting of dams under the Dam Safety
Program.
R.
Storm drainage.
(1)
General requirements. Stormwater management facilities shall be provided
where necessary to adequately control storm runoff in accordance with
all applicable state and local laws and to protect the general public
and prevent undue damage to public and private property. To the extent
that the provisions of this section conflict with any stormwater management
plan adopted by the Township, the more stringent criteria shall prevail.
(a)
Any proposed storm drainage plans which affect the drainage
basin of any river or stream shall be approved by the Pennsylvania
Department of Environmental Protection if the drainage basin so affected
has an area of at least 0.5 square mile.
(b)
Storm sewers, culverts, and related installations shall be provided to permit the unimpeded flow of natural watercourses, to ensure the drainage of all low points on the reasonably related to the extent and grade of the area drained. The system shall also be designed in accordance with § 296-17S.
[1]
Developers shall dedicate easements, pipe collection systems
and structures for storm drainage to the Township.
(c)
No stormwater runoff or natural drainage water shall be so diverted
as to overload existing drainage systems or create flooding or the
need for additional drainage structures on other private or public
lands, without proper and approved provisions being made for taking
care of these conditions.
[1]
The Township Board of Commissioners with the advice of the Township Engineer shall decide what provisions, including but not limited to suitable detention basins shall be made to implement § 312-39A(3). Where stormwater management facilities are permitted, adequate assurances of maintenance, indemnification, liability insurance and security shall be provided by agreement with the Township, which agreement shall be approved by the Township Solicitor.
(d)
In areas in which street curbs are not required by the Township
Board of Commissioners or Township Engineer, drainage may be accomplished
by natural or artificial swales and culverts. Special structures such
as check dams, drop-outlets, permanent detention basins or other energy
dissipating structures or riprap may be required to prevent scour
or erosion in locations with large runoff quantities or high velocities.
[1]
Developers shall dedicate easements and/or structures for storm drainage to the Township pursuant to § 312-39A(4) where swales and/or culverts traverse or enter onto private property.
[2]
The Township Board of Commissioners may require a fixed pipe
collection system with catch basins.
(e)
A subsurface collection system with catch basins shall be used
in all areas in which street curbs and gutters are required.
[1]
Underdrain pipe systems shall be required where soil conditions
warrant their installation.
(f)
Developer shall grade and install all necessary drainage facilities
to ensure the drainage of all low points on subdivided lots or within
the subdivision.
(2)
Collection system. The collection system shall be designed by the
rational method of design in accordance with American Society of Civil
Engineers Manual No. 37 except as noted using the formula Q = CiA,
as amplified by the following sections.
(a)
"Q" is the required capacity in cubic feet per second for the
collection system at the point of design.
(b)
"C" is the run-off coefficient applicable to the entire drainage area. It shall be based on consideration of soil conditions, average slope of the drainage area and the ultimate development of the entire drainage area according to comprehensive plans. For various types of ultimate development, the run-off coefficient shall be within the ranges specified in accordance with § 296-18M.
(c)
"i" is the rainfall intensity in inches per hour and shall be determined from a calculated time of concentration and specified, storm frequency. Time of concentration shall be computed in accordance with the requirements contained in § 296-18K. Design storm frequencies shall be twenty-five-year for residential and all other developments. Rainfall intensities shall be in accordance with § 296-18K. Any conveyance system designed to transport runoff from a tributary area of greater than 100 acres shall be designed for the 100-year frequency design storm.
(d)
"A" is the drainage area, in acres, tributary to the point of
design, and shall include tributary from outside sources as well as
from within the subdivision itself. All calculations shall be accompanied
by a drainage area map showing all areas tributary to each structure
or discharge point.
(e)
Pipes and conduits shall be designed on the basis of Manning's
formula and the continuity equation.
|
v = 1.486/n*r2/3*s1/2
|
|
"v" is the mean velocity of flow in feet per second.
|
|
"n" is the coefficient of roughness.
|
|
n equals 0.013 for concrete pipe.
|
|
n equals 0.021 for asphalt coated corrugated metal
pipe, 25% paved.
|
|
"r" is the hydraulic radius in feet.
|
|
"s" is the slope of the energy grade line.
|
|
"Q" equals VA where "A" equals cross-sectional area in square
feet.
|
|
Q = V * A
|
(f)
Culverts shall be designed on the basis of inlet or outlet control
as appropriate, except where a more detailed backwater analysis is
deemed warranted by the Township Engineer.
(g)
Manholes shall be spaced at intervals not exceeding 400 feet
and shall be located wherever branches are connected or sizes are
changed and wherever there is a change in alignment or grade.
(h)
For sewer lines of at least 36 inches diameter, manholes may
be spaced at intervals greater than 400 feet with the approval of
the Township Engineer.
(i)
Sewer lines shall be located between the centerline of the street
and the curb line and shall parallel the centerline of the street
as far as practical. Sufficient number of structures shall be provided
such that unnecessary crossings of other utility lines and passage
beneath curbs are eliminated.
(j)
Culvert and/or hydraulic grade analysis, and inlet grate capacity
calculations, shall be provided with storm sewerage system design
calculations.
(3)
Swales. Swales used for outlets shall be designed on the basis of
Manning's formula with the following considerations:
(a)
The roughness coefficient shall be: 0.040 for earth swales,
and 0.015 for paved swales.
(b)
Design velocity in earth swales shall not exceed four feet per
second.
(c)
A swale right-of-way of sufficient minimum width to include
a ten-foot access strip in addition to the width of the swale from
bank top, shall be offered for dedication to the Township for drainage
purposes. The Township Engineer may, under unusual conditions, require
a wider swale right-of-way.
(d)
Side or rear yard swales upstream or downstream of pipe culverts
will be permitted only under the following conditions. If any one
of these conditions cannot be met the stormwater shall be piped in
an underground system.
[1]
The diameter of the pipe culvert does not exceed 18 inches and
the depth of flow in the swale for a twenty-five-year frequency storm
is less than one foot;
[2]
The side slopes of the swale are not steeper than four horizontal
to one vertical (4:1). An easement of sufficient width to encompasses
the design full flow cross section plus one foot of freeboard at the
design cross slope shall be offered for dedication to the Township;
[3]
A note shall be added to the plan to be recorded that the ground
surface elevations in any such drainage easements may not be altered
by the property owner without the express, advance, written permission
of the Township Board of Commissioners;
[4]
Flared end sections shall be provided on the open pipe ends
in lieu of headwalls. The pipe shall be extended as far as is necessary
to achieve a maximum 4:1 slope on the roadway embankment commencing
at the edge of right-of-way in the case of a curbed roadway or at
the edge of shoulder in the case of a non-curbed roadway.
(4)
Detention basins.
(a)
Permanent detention basins may be required by the Township Engineer
or Township Board of Commissioners as part of a stormwater drainage
plan when the rate of runoff after development will exceed the pre-development
condition.
(b)
Detention basins shall be designed to drain completely after
every storm in order to avoid problems associated with stagnant water
unless as otherwise approved by the Board of Commissioners upon recommendation
of the Township Geotechnical Consultant. Basins located in residential
areas should have very flat slopes (less than four horizontal to one
vertical) and shallow water depths (less than 30 inches). A minimum
longitudinal slope of 2% shall be provided across the basin floor.
Detention basin designs shall be in accordance with Township Standard
Construction Documents (latest revision).
(c)
Fencing shall be required around detention basins in the following
cases:
[1]
The maximum depth of water in the basin for a ten-year or a
storm of greater intensity design storm is greater than 30 inches;
[2]
The side slopes of the basin are steeper than four horizontal
to one vertical;
[3]
The time to empty the basin is longer than three hours;
[4]
The detention basin is to be dedicated to South Whitehall Township,
and fencing is requested by the Township; or
[5]
The Board of Commissioners determines that the public safety
would be endangered if the basin is not fenced.
(d)
Fencing and associated warning signs shall be in accordance
with the Township Standard Construction Documents (latest revision).
(e)
Outflow pipes shall be provided with child-proof screening.
(f)
Detention basin design shall be based upon the general design
requirements of Township stormwater management plan which provides
for stormwater management.
(g)
The rate of outflow from the basin shall be restricted in accordance
with the current provisions of the Act 167 Stormwater Management Regulations.
(h)
A minimum twelve-foot-wide ramp at a maximum 10% slope shall
be constructed near the basin access fence to permit access to the
bottom of basins for maintenance.
(i)
Anti-seep collars shall be provided along basin discharge pipes.
(5)
Soil erosion and sedimentation control.
(a)
No changes shall be made in the contour of the land, no grading,
excavation, removal or destruction of the topsoil, trees, or other
vegetative cover of the land shall be commenced until such time that
a plan for minimizing erosion and sedimentation has been reviewed
and approved by the representative for the Lehigh County Conservation
District, South Whitehall Township and the Board of Commissioners.
(b)
No subdivision plan shall be approved unless there has been
a plan approved by the representative for the Lehigh County Conservation
District and the South Whitehall Township Board of Commissioners that
provides in the opinion of the South Whitehall Township Board of Commissioners
for minimizing erosion and sedimentation and acceptable securities
are deposited with the Township in the form of an escrow guarantee
which will ensure installation and completion of the required improvements;
or there has been a determination by the representative for the Lehigh
County Conservation District and the South Whitehall Township Board
of Commissioners that a plan for minimizing erosion and sedimentation
is not necessary.
(c)
Measures used to control erosion and reduce sedimentation shall
comply with the standards and specifications of the Lehigh County
Conservation District and receive the approval of the District. Once
the subdivision plans have been finally approved, the District shall
ensure compliance with the appropriate specifications and plans.
(d)
Whenever sedimentation is caused by stripping vegetation, regrading,
or other development, it shall be the responsibility of the person,
corporation, or other entity causing such sedimentation to remove
it from all adjoining surfaces, drainage systems, watercourses, roads,
and rights-of-way, and to repair any damage at this expense within
24 hours of the occurrence.
(e)
Each person, corporation or other entity which makes any surface
changes shall be required to:
[1]
Collect on-site surface runoff and dispose of it to the point
of discharge into the common natural watercourse of the drainage area.
[2]
Handle existing and potential off-site runoff through his development
by designing to adequately handle storm runoff from a fully developed
area upstream.
[3]
Provide and install at his expense, in accordance with Township
requirement, all drainage and erosion control improvements (temporary
and permanent) as required by the erosion and sediment control plan.
(6)
General design standards.
(a)
Curb inlets shall be located at curb tangents on the uphill
side of street intersections. The Township Engineer shall approve
design and location of curb inlets.
(b)
Drainage structures that are located on state highway rights-of-way
shall be approved by the Pennsylvania Department of Transportation,
and a letter from that office indicating such approval shall be directed
to the Township Planning Commission.
(c)
The design of the storm sewerage system shall be in accordance
with the Township Standard Construction Documents (latest revision).
(7)
Construction specifications. Township Standard Construction Documents
(latest revision) as adopted by the Township will govern. Copies are
available at the Township Building upon request and payment of cost
of reproduction.
(8)
The following statements shall be provided on the plans to be recorded:
"Notwithstanding any provisions of the Township stormwater management
plan, including exemption and waiver provisions, any landowner and
any person engaged in the alteration or development of land which
may affect stormwater runoff characteristics shall implement such
measures as are reasonably necessary to prevent injury to health,
safety or other property. Such measures shall include such actions
as are required to manage the rate volume, direction and quality of
resulting stormwater runoff in a manner which otherwise adequately
protects health and property from injury and damage."
"Township review and approval of the drainage plan or the subsequent
observation and approval of stormwater management facilities, shall
not constitute land development on behalf of or by the Township or
otherwise cause the Township to be engaged in the alteration or development
of land. By submitting an application under the Township stormwater
management plan, the developer hereby agrees to indemnify, defend,
and hold harmless the Township and all its representatives, servants,
employees, officials and consultants of and from any and all claims
demands, causes of action or suits which arise out of or relate to
the review, approval, construction or observation of the developer's
drainage plan and stormwater management facilities."
