Permits must comply with any and all applicable local, county,
state and federal regulations.
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 requirements of the parking areas. However, the runoff from the parking lot would still be required to meet the water quality provisions of this chapter, §
182-14. These measures are required to be consistent with §
182-3 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 Subsection A(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 Subsection
A(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 24 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. The NRCS runoff equation shall be
utilized to calculate infiltration requirements (I) in inches.
Equation No. 1 of 182-13A(3)(a)
I (Infiltration requirement, in inches) = (200/CN) - 2
Where:
CN = SCS (NRCS) curve number of existing conditions contributing
to the infiltration facility.
This equation is displayed graphically in, and the infiltration
requirement can be determined from Figure 182-13A(3)(a).
Figure 182-13A(3)(a)
Infiltration Requirement Based Upon NRCS Curve Number
|
Equation No. 2 of 182-13A(3)(a)
The retention (infiltration) volume (Rev) required to meet the infiltration requirement would therefore be
computed as:
Rev (Cubic Feet) = I* impervious area
(square feet)/(12 in/feet)
Where:
I = infiltration requirements (in inches)
(b)
Annual recharge - Water budget approach. It has been determined that infiltrating 0.46 inch of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of Subsection
A(2)(a) cannot be achieved, then 0.46 inch 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 No. 1 of 182-13A(3)(a) or the curve in Figure 182-13A(3)(a) should be used to determine the infiltration requirement.
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 Township of Maidencreek
that the soils are conducive to infiltrate on the lots identified.
C. Carbonate areas.
(1) The applicant shall investigate noncarbonate areas of the site for the suitability of infiltration and, if feasible, proceed to undertake infiltration pursuant to §
182-13A. If infiltration in noncarbonate areas is not feasible, the applicant shall investigate areas of the site underlain by carbonate bedrock for infiltration purposes. If a suitable area is identified that meets the requirements of this provision and Table B-5, infiltration shall be conducted in accordance with the requirements of this chapter. Only if infiltration proves infeasible in both carbonate and noncarbonate areas of the site may the applicant be granted a waiver from the infiltration requirements of this chapter without structural BMPs.
(2) Infiltration BMP loading rate percentages in Table B-5 in Appendix
B of this chapter shall be calculated as follows:
(3) 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%
|
(4) Soil thickness is to be measured from the bottom of any proposed
infiltration BMP. The effective soil thickness in Table B-5 in Appendix
B is the measured soil thickness multiplied by the thickness
factor based on soil permeability, as follows:
Permeability Range
(inches per 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
|
(5) The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
D. Stormwater hotspots. Following is a list of examples of designated
hotspots. If a site is designated 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 be 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.
EPAs NPDES stormwater program requires some industrial sites as well
as 923 municipalities and other entities 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:
(a)
Residential streets and rural highways.
(c)
Institutional development.
(f)
Pervious areas, except golf courses and nurseries [which may
need an integrated pest management (IPM) plan].
(3) While large highways [average daily traffic volume (ADT) greater
than 30,000] are not designated as a stormwater hotspot, it is important
to ensure that highway stormwater management plans adequately protect
groundwater.
E. Caution shall be exercised where infiltration is proposed in source
water protection areas as defined by the local municipality or water
authority.
F. Infiltration facilities shall be used in conjunction with other innovative
or traditional stormwater control facilities that are found within
the PADEP State BMP Manual.
G. Caution shall be exercised where salt or chloride (municipal salt
storage) would be a pollutant since soils do little to filter this
pollutant and it may contaminate the groundwater. The qualified design
professional shall evaluate the possibility of groundwater contamination
from the proposed infiltration facility and perform a hydrogeologic
justification study if necessary. A hydrogeologic justification study
would entail: field reconnaissance, in which local geology, topographic
features, local wall characteristics, surface water flows, potential
contamination, and nature of impermeable areas are determined; data
review of collected pertinent information such as geologic information,
hydrologic data concerning both surface water and groundwater, and
geophysical data. With the collected data, a hydrologic model may
be developed to determine the extent to which salt or chloride affects
the groundwater.
H. The infiltration requirement in high quality or exceptional value waters shall be subject to the Department's Chapter
93 antidegradation regulations.
I. Dependent upon certain land use or hotspots an impermeable liner
will be required in detention basins where the possibility of groundwater
contamination exists. A detailed hydrogeologic investigation may be
required by the Township of Maidencreek.
J. The Township of Maidencreek shall 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. For projects that disturb one acre or more, unless otherwise specified
in the Zoning Ordinance, 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.
A. Developed areas shall provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. The infiltration volume computed under §
182-13 may be a component of the water quality volume if the applicant chooses to manage both components in a single facility. If the infiltration volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than infiltration BMPs. The required water quality volume (WQ
v) is the storage capacity
needed to capture and treat a portion of stormwater runoff from the
developed areas of the site. To achieve this goal, the following criterion
is established:
(1) The following calculation formula is to be used to determine the
water quality storage volume, (WQv), in acre-feet
of storage for the Maiden Creek watershed:
Equation No. 1 of 182-14A(1)
|
WQv=[(P)(Rv)(A)]/12
|
Where:
|
WQv
|
=
|
Water quality volume (acre-feet)
|
P
|
=
|
1 inch
|
A
|
=
|
Total contributing drainage area to the water quality BMP (acres)
|
Rv
|
=
|
0.05 + 0.009(I) where I is the percent of the area that is impervious
surface [(impervious area/A)*100)
|
(2) This volume requirement can be accomplished by the permanent volume
of a wet basin or the detained volume from other BMPs.
(3) 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). The
design of the facility shall provide for protection from clogging
and unwanted sedimentation.
B. For areas within defined special protection subwatersheds which include
exceptional value (EV) and high quality (HQ) waters, cold water fishery
(CWF) the temperature and quality of water and streams shall be maintained.
C. To accomplish the above, the applicant shall use innovative or traditional
stormwater control facilities that are found within the PADEP State
BMP Manual.
D. 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 appropriate native vegetation referenced
in Appendix F of this chapter, (See 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.
This does not include lakes or wetlands.
E. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the Township of Maidencreek. The issuance of an NPDES construction permit (or permit coverage under the statewide general permit) satisfies the requirements of Subsection
A.