[Ord. 338, 12/21/2015]
All activities regulated by this chapter must comply with any
and all applicable local, county, state and federal regulations.
[Ord. 338, 12/21/2015]
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 runoff from, and infiltration
losses due to, parking areas. These measures are required to be consistent
with § 103, 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 § 305(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. 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 § 305(a)(3)(i) or (ii), 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:
(i)
A minimum depth of 24 inches between the bottom of the BMP and
the limiting zone.
(ii)
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.
(iii) The infiltration facility shall be capable of
completely infiltrating the required retention (infiltration) volume
within four days (96 hours).
(iv)
Pretreatment shall be provided prior to infiltration. The pretreatment
shall be designed to protect the infiltration system from clogging
prior to scheduled maintenance and to protect groundwater quality.
(3)
The size of the infiltration facility shall be based upon the
following volume criteria:
(i)
NRCS Curve Number equation. The
NRCS Runoff Equation shall be utilized to calculate infiltration requirements
(I) in inches.
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I(Infiltration requirement, in inches) = (200/CN) - 2
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Eqn: 305.1
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Where:
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CN = SCS (NRCS) curve number of existing conditions contributing
to the infiltration facility.
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1.
This equation is displayed graphically in and the infiltration
requirement can be determined from Figure 305-1.
2.
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. However, the rounded number 0.5 inch will be used.
Figure 305-1. Infiltration requirement based upon NRCS
curve number.
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3.
The retention (infiltration) volume (Rev) required to meet the infiltration requirement would therefore be
computed as:
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Where:
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I = Infiltration requirements (in inches).
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(ii)
Annual Recharge: Water Budget Approach.
1.
If the goals of § 305(a)(3)(i) cannot be achieved,
then 0.5 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 305.1 or the curve in Figure 305.1
should be used to determine the infiltration requirement.
2.
The retention (infiltration) volume (Rev) required again would therefore be computed as:
(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, presence
of special geologic features 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 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 § 305(a). If this
investigation proves infeasible, infiltration may occur on areas underlain
by carbonate rock. Nevertheless, extreme caution shall be exercised
where infiltration is proposed in geologically susceptible areas.
Design of such infiltration facilities shall follow the recommended
procedure below in conjunction with Figure A-1 in ordinance Appendix
A; however, the applicant is not required to use infiltration in carbonate
areas even if the site falls into the "recommended" range on Figure
A-1 in ordinance Appendix A. If infiltration is not proposed, the calculated infiltration
volume [§ 305(a)] shall be treated by an acceptable BMP.
(1)
Infiltration BMP loading rate percentages in Figure A-1 in ordinance
Appendix A shall be calculated as follows:
(2)
The area tributary to the infiltration BMP shall be weighted
as follows:
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Area Description
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Weighting
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All disturbed area to be made impervious
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100%
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All disturbed areas to be made pervious
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50%
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All undisturbed impervious areas
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100%
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All undisturbed pervious areas
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0%
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(3)
Soil thickness is to be measured from the bottom of any proposed
infiltration BMP. The effective soil thickness in Figure A-1 in ordinance
Appendix A is the measured soil thickness multiplied by the thickness
factor based on soil permeability, as follows:
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Permeability Range
(inches/hour)
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Thickness Factor
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6.0 to 12.0
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0.8
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2.0 to 6.0
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1.0
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1.0 to 2.0
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1.4
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0.75 to 1.0
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1.2
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0.5 to 0.75
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1.0
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(4)
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 the Township 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 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. The EPA's
NPDES stormwater program requires some industrial sites to prepare
and implement a stormwater pollution prevention plan.
(1)
Examples of hotspots:
(i)
Vehicle salvage yards and recycling facilities.
(ii)
Vehicle fueling stations.
(iii) Vehicle service and maintenance facilities.
(iv)
Vehicle and equipment cleaning facilities.
(v)
Fleet storage areas (bus, truck, etc.).
(vi)
Industrial sites (based on standard industrial codes).
(vii) Marinas (service and maintenance).
(viii) Outdoor liquid container storage.
(ix)
Outdoor loading/unloading facilities.
(x)
Public works storage areas.
(xi)
Facilities that generate or store hazardous materials.
(xii) Commercial container nursery.
(xiii) Other land uses and activities as designated
by an appropriate review authority.
(2)
The following land uses and activities are not normally considered
hotspots:
(i)
Residential streets and rural highways.
(iii) Institutional development.
(vi)
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) Where infiltration is proposed in source protection areas as defined
by the Township, municipal authority or other local water provider,
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 stormwater control facilities that are found within
the PaDEP State BMP Manual.
(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) Dependant upon certain land uses or hotspots, an impermeable liner
will be required in detention basins where the possibility of groundwater
contamination exists. A detailed hydrogeologic study may be required
by the Township.
(j) The Township 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) For projects that disturb one acre or more, unless greater setbacks
are specified in the Zoning Ordinance, the following setbacks for infiltration facilities shall
apply:
(1)
From water supply wells: 100 feet.
(2)
From building foundations: 10 feet downslope or 100 feet upslope.
(3)
From septic system drainfields: 50 feet.
(4)
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 100 feet of the proposed infiltration
area: 100 feet.
(5)
From the property line, unless documentation is provided to
show all setbacks from wells, foundations and drainfields on the neighboring
property will be met: 100 feet.
[Ord. 338, 12/21/2015]
The applicant shall comply with the following water quality
requirements of this Part:
(a) Developed areas shall provide adequate storage and treatment facilities
necessary to capture and treat stormwater runoff. The infiltration
volume computed under § 305 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 (WQv) 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 any watershed within Lower Heidelberg Township:
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WQv = [(P)(Rv)(A)]/12
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Eqn: 306.1
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Where:
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WQv = Water quality volume (acre-feet).
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P = 1 inch.
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A = Total contributing drainage area to the water quality BMP
(acres).
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Rv = 0.05 + 0.009(I), where I is the
percent of the area that is impervious surface [(impervious area/A)*100].
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(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 (reference
Appendix G of the 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. However, in no case
shall such buffer be less in width than that specified for a riparian
buffer in the Township Zoning Ordinance. 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 PaDEP regional office must be provided
to the Township. The issuance of an NPDES construction permit [or
permit coverage under the statewide general permit (PAG-2)] satisfies
the requirements of § 306(a).
(f) In selecting the appropriate BMPs or combinations thereof, the land
developer shall consider the following:
(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.
(7)
Land availability and configuration of the topography.
(g) The following additional factors should be considered when evaluating
the suitability of BMPs used to control water quality at a given development
site:
(1)
Peak discharge and required volume control.
(3)
Efficiency of the BMPs to mitigate potential water quality problems.
(4)
The volume of runoff that will be effectively treated.
(5)
The nature of the pollutant being removed.
(6)
Maintenance requirements.
(7)
Creation/protection of aquatic and wildlife habitat.
(9)
Enhancement of aesthetic and property value.