A.
Applicants proposing regulated activities in tributaries to the Schuylkill River in Berks County which do not fall under the exemption criteria shown in § 165-28 shall submit a drainage plan consistent with the Tributaries to the Schuylkill River in Berks County Stormwater Management Plan to Union Township for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
The applicant is required to evaluate practicable
alternatives to the surface discharge of stormwater, the creation
of impervious surfaces and the degradation of waters of the commonwealth
and must maintain as much as possible the natural hydrologic regime.
C.
The drainage plan must be designed consistent with the sequencing provisions of § 165-13 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article III of this chapter.
D.
Existing points of concentrated drainage that discharge
onto adjacent property shall not be altered in any manner which could
cause property damage without permission of the affected property
owner(s) and shall be subject to any applicable discharge criteria
specified in this chapter.
E.
Areas of existing diffused drainage discharge shall
be subject to any applicable discharge criteria in the general direction
of existing discharge, whether proposed to be concentrated or maintained
as diffused drainage areas, except as otherwise provided by this chapter.
If diffused drainage discharge is proposed to be concentrated and
discharged onto adjacent property, the applicant must document that
adequate downstream conveyance facilities exist to safely transport
the concentrated discharge or otherwise prove that no erosion, sedimentation,
flooding or other impacts will result from the concentrated discharge.
F.
Where a development site is traversed by existing watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall conform to the stream buffer requirements contained in § 165-15D of this chapter.
G.
Any stormwater management facilities regulated by
this chapter that would be located in or adjacent to waters of the
commonwealth or wetlands shall be subject to approval by the PADEP
through the joint permit application process or, where deemed appropriate
by the PADEP, the general permit process. When there is a question
whether wetlands may be involved, it is the responsibility of the
applicant or his agent to show that the land in question cannot be
classified as wetlands; otherwise approval to work in the area must
be obtained from the PADEP.
H.
Any alteration that affects stormwater flow directly
or indirectly toward a PennDOT facility shall be subject to PennDOT
regulations.
I.
Minimization of impervious surfaces and infiltration
of runoff through seepage beds, infiltration trenches, etc., are encouraged,
where soil conditions permit, to reduce the size or eliminate the
need for detention facilities or other structural BMPs.
J.
Roof drains shall not be connected to impervious surfaces
in order to promote overland flow and infiltration/percolation of
stormwater where advantageous to do so. When site conditions preclude
infiltration/percolation, then it shall be permitted on a case-by-case
basis by Union Township.
K.
All stormwater runoff shall be treated for water quality.
L.
Transference of runoff to or from an EV/HQ watershed
is prohibited unless otherwise authorized by the DEP, DRBC or SRBC.
Permits must be obtained for all relevant regulated
activities in compliance with any and all applicable local, county,
state and federal regulations.
A.
No regulated earth-disturbance activities within Union
Township shall commence until Union Township receives an approval
from the Berks County Conservation District of an erosion and sediment
control plan for construction activities.
B.
The DEP has regulations that require an erosion and
sediment control plan for any earth-disturbance activity of 5,000
square feet or more, under 25 Pa. Code § 102.4(b).
C.
In addition, under 25 Pa. Code, Chapter 92, a DEP
NPDES construction activities permit is required for regulated earth-disturbance
activities.
D.
Evidence of any necessary permit(s) for regulated earth-disturbance activities from the appropriate DEP regional office or Berks County Conservation District must be provided to Union Township. The issuance of an NPDES construction permit [or permit coverage under the statewide general permit (PAG-2)] satisfies the requirements of § 165-11A.
E.
A copy of the erosion and sediment control plan and
any required permit, as required by DEP regulations, shall be available
at the project site at all times.
F.
Additional erosion and sediment control design standards
and criteria that are recommended to be applied where infiltration
BMPs are proposed shall include the following:
(1)
Areas proposed for infiltration BMPs shall be protected
from sedimentation and compaction during the construction phase to
maintain maximum infiltration capacity.
(2)
Infiltration BMPs shall not be constructed nor receive
runoff until the entire contributory drainage area to the infiltration
BMP has achieved final stabilization.
A.
Any regulated activity that meets the impervious area exemption criteria in Table 1 shall not be required to implement the stormwater quantity controls specified in § 165-17A of this chapter. These criteria shall apply to the total development even if development is to take place in phases. The date of the adoption of this chapter shall be the starting point from which to consider tracts as "parent tracts" in which future subdivisions and respective impervious area computations shall be cumulatively considered. Impervious areas existing on the parent tract prior to adoption of this chapter shall not be considered in cumulative impervious area calculations for exemption purposes.
|
Table 1
Impervious Area Exemption Criteria
| ||
|---|---|---|
|
Total Parcel Size
(acres)
|
Impervious Area Exemption
(square feet)
| |
|
0 to 0.125
|
1,000
| |
|
0.125 to 0.5
|
2,500
| |
|
0.5 to 1
|
5,000
| |
|
1 to 2
|
7,500
| |
|
2 to 3
|
10,000
| |
|
3 to 4
|
12,500
| |
|
4 or more
|
15,000
| |
B.
Submissions for projects that utilize the exemption under § 165-12A shall still be required to meet the groundwater recharge (§ 165-14), water quality (§ 165-15), and stream bank erosion (§ 165-16) controls of this chapter. Drainage plans in accordance with § 165-29A(2), B(7), (8), (11), (15) and (22), and D(2) must still be submitted. Any exemption must first be approved by Union Township.
C.
Additional exemption requirements.
(1)
Exemption responsibilities. An exemption shall not
relieve the applicant from implementing such measures as are necessary
to protect the public health, safety, and property. An exemption shall
not relieve the applicant from providing adequate stormwater management
for regulated activities to meet the requirements of this chapter.
(2)
HQ and EV streams. This exemption shall not relieve the applicant from meeting the special requirements for watersheds draining to high-quality (HQ) or exceptional-value (EV) waters, identified and source water protection areas (SWPA), and requirements for nonstructural project design sequencing (§ 165-13), groundwater recharge (§ 165-14), water quality (§ 165-15), and stream bank erosion (§ 165-16).
(3)
Drainage problems.
(a)
If a drainage problem is documented or known
to exist downstream of or expected from the proposed activity, then
Union Township may require a drainage plan submittal.
(b)
All regulated activities occurring in drainage areas tributary to waters designated HQ/EV pursuant to 25 Pa. Code, Chapter 93, shall not change any biological, chemical, or physical characteristics, including volume, rate, velocity, course, current, cross section, or temperature of the waters, unless the activity is specifically permitted in accordance with the environmental laws of the commonwealth.
A.
For projects disturbing one acre or more, the design
of all regulated activities shall include evaluation of practicable
alternatives to the surface discharge of stormwater, the creation
of impervious surfaces, and the degradation of waters of the commonwealth
and must maintain as much as possible the natural hydrologic regime
of the site.
(1)
An alternative is practicable if it is available and
capable of being done after taking into consideration cost, existing
technology and logistics in light of overall project purposes and
other municipal requirements.
(2)
All practicable alternatives to the discharge of stormwater
are presumed to have a less-adverse impact on quantity and quality
of waters of the commonwealth unless otherwise demonstrated.
B.
The applicant shall demonstrate that he/she designed
the regulated activities that disturb one acre or more to include
consideration of the following issues:
(1)
Prepare an existing resource and site analysis map (ERSAM) showing environmentally sensitive areas, including but not limited to steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools, floodplains, stream buffer zones, Hydrologic Soil Groups A and B (areas conducive to infiltration), special geologic features, any existing recharge areas and any other requirements outlined in Chapter 172, Subdivision and Land Development.
(2)
Establish appropriate buffers for each of the delineated environmentally sensitive areas per Chapter 200, Zoning. (See § 165-15D for stream buffers and § 165-14B(11) for special geologic feature buffers.)
(3)
Prepare a draft project layout, avoiding sensitive areas identified in § 165-13B(1).
(4)
Identify site-specific existing conditions drainage
areas, discharge points, recharge areas and Hydrologic Soil Groups
A and B.
(6)
Satisfy infiltration objectives (§ 165-14) and provide for stormwater pretreatment prior to infiltration. Pretreatment may not be necessary for rooftop runoff which enters the infiltration facility directly from a roof leader.
(8)
Determine what management district the site falls
into (Appendix D[1]) and conduct an existing conditions runoff analysis.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
(9)
Prepare the final project design to maintain existing
conditions drainage areas and discharge points, to minimize earth
disturbance and impervious surfaces, and, to the maximum extent possible,
to ensure the remaining site development has no surface or point discharge.
(10)
Conduct a proposed conditions runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (§ 165-17).
(11)
Manage any remaining runoff through treatment
prior to discharge, as part of detention, bioretention, direct discharge
or other structural control.
A.
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 overdesigned to compensate for the infiltration losses due to parking areas. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with § 165-3 and take advantage of utilizing any existing recharge areas.
B.
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 § 165-14B(3), depending on demonstrated site conditions, and shall be the greater of the two volumes.
(1)
Infiltration BMPs shall meet the following minimum
requirements:
(a)
Infiltration requirements.
[1]
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 § 165-14B(3)(a) or (b), depending upon demonstrated site conditions.
(b)
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:
[1]
A minimum depth of 24 inches between the bottom
of the BMP and the limiting zone shall be provided.
[2]
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,
shall be provided.
[3]
The infiltration facility shall be capable of
completely infiltrating the required retention (infiltration) volume
within four days (96 hours).
[4]
Pretreatment shall be provided prior to infiltration.
(c)
The size of the infiltration facility shall
be based upon the following volume criteria:
[1]
NRCS curve number equation.
[a]
The NRCS runoff equation shall
be utilized to calculate infiltration requirements (I) in inches.
|
Equation 1
| |
|---|---|
|
I (infiltration requirement, in inches) = (200
/ CN) – 2
| |
|
Where:
| |
|
CN = SCS (NRCS) curve number of existing conditions
contributing to the infiltration facility.
|
[b]
This equation is displayed graphically
in and the infiltration requirement can be determined from Figure
1.
[c]
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 1 - Infiltration Requirement Based
Upon NRCS Curve Number
|
[d]
The retention (infiltration) volume
(Rev) required to meet the infiltration requirement would therefore
be computed as:
|
Equation 2
| |
|---|---|
|
Rev = (0.5 or I, whichever
is greater) * impervious area (square feet) / (12 inches per foot)
= cubic feet
| |
|
Where:
| |
|
I = Infiltration requirements (in inches).
|
[2]
Annual recharge — water budget approach.
[a]
If the goals of § 165-14B(3)(a) 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 3 or the curve in Figure 1 should be used to determine the infiltration requirement.
[b]
The retention (infiltration) volume
(Rev) required again would therefore be computed as:
|
Equation 3
| |
|---|---|
|
Rev = (0.5 or I, whichever
is greater) * impervious area (square feet) / (12 inches per foot)
= cubic feet
|
(d)
Only double-washed, clean aggregate, free of
fines, shall be allowed. A stone slip is required to document washing;
and the Township Engineer may reject any stone deemed unsuitable for
infiltration/recharge facilities.
(2)
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:
(a)
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.
(b)
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.
(c)
Design the infiltration structure for the required
retention (Rev) volume based on field-determined
capacity at the level of the proposed infiltration surface.
(d)
If on-lot infiltration structures are proposed
by the applicant's design professional, it must be demonstrated to
Union Township that the soils are conducive to infiltrate on the lots
identified.
(3)
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 § 165-14B. If this investigation proves infeasible, infiltration can occur on areas underlain by carbonate rock by following the recommended procedure below in conjunction with Figure B-1 in Appendix B.[1] However, the applicant is not required to use infiltration in carbonate areas even if the site falls into the "recommended" range on Figure B-1 in Appendix B. If infiltration is not proposed, the calculated infiltration volume (§ 165-14B) shall be treated by an acceptable BMP.
(a)
Infiltration BMP loading rate percentages in
Figure B-1 in Appendix B shall be calculated as follows:
 |
(b)
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%
|
(c)
Soil thickness is to be measured from the bottom
of any proposed infiltration BMP. The effective soil thickness in
Figure B-1 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
|
(d)
The design of all facilities over karst shall
include an evaluation of measures to minimize adverse effects.
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
(4)
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. The EPA's NPDES stormwater program requires some industrial
sites to prepare and implement a stormwater pollution prevention plan.
(a)
Examples of hotspots:
[1]
Vehicle salvage yards and recycling facilities.
[2]
Vehicle fueling stations.
[3]
Vehicle service and maintenance facilities.
[4]
Vehicle and equipment cleaning facilities.
[5]
Fleet storage areas (bus, truck, etc.).
[6]
Industrial sites (based on Standard Industrial
Codes).
[7]
Marinas (service and maintenance).
[8]
Outdoor liquid container storage.
[9]
Outdoor loading/unloading facilities.
[10]
Public works storage areas.
[11]
Facilities that generate or store
hazardous materials.
[12]
Commercial container nursery.
[13]
Other land uses and activities
as designated by an appropriate review authority.
(b)
The following land uses and activities are not
normally considered hotspots:
(c)
While large highways [average daily traffic
volume (ADT) greater than 30,000] are not designated as stormwater
hotspots, it is important to ensure that highway stormwater management
plans adequately protect groundwater.
(5)
Caution shall be exercised where infiltration is proposed
in source water protection areas, as defined by Union Township or
the Union Township Municipal Authority.
(6)
Infiltration facilities shall be used in conjunction
with other innovative or traditional stormwater control facilities
that are found within the PADEP State BMP Manual.
(7)
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.
(8)
The infiltration requirement in high-quality or exceptional-value waters shall be subject to the Department's Chapter 93 Antidegradation Regulations.
(9)
Dependant 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 Union Township.
(10)
Union Township 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.
(11)
For projects that disturb one acre or more, unless otherwise specified in Chapter 200, Zoning, the following setbacks for infiltration facilities shall apply:
(a)
One hundred feet from water supply wells.
(b)
Ten feet downslope or 100 feet upslope from
building foundations.
(c)
Fifty 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 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 § 165-14 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.
(1)
The following calculation formula is to be used to
determine the water quality storage volume (WQv), in acre-feet of
storage, for the tributaries to the Schuylkill River in Berks County:
|
Equation 4
| |
|
WQv = [(P)(Rv)(A)]/12
| |
|
Where:
| |
|
WQv = Water quality volume (acre-feet).
| |
|
P = One 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
and cold water fisheries (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. (Refer
to Appendix H 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. 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.
E.
Evidence of any necessary permit(s) for regulated earth-disturbance activities from the appropriate DEP regional office must be provided to Union Township. The issuance of an NPDES construction permit (or permit coverage under the statewide general permit) satisfies the requirements of § 165-15A.
A.
In addition to control of the water quality volume,
in order to minimize the impact of stormwater runoff on downstream
stream bank erosion, the primary requirement is to design a BMP to
detain the proposed conditions two-year, twenty-four-hour design storm
to the existing conditions one-year peak flow using the SCS Type II
distribution. Additionally, provisions shall be made (such as adding
a small orifice at the bottom of the outlet structure) so that the
proposed conditions one-year storm takes a minimum of 24 hours to
drain from the facility from a point where the maximum volume of water
from the one-year storm is captured (i.e., the maximum water surface
elevation is achieved in the facility). Release of water can begin
at the start of the storm (i.e., the invert of the water quality orifice
is at the invert of the facility).
B.
The minimum orifice size in the outlet structure to
the BMP shall be a three-inch-diameter orifice, and a trash rack shall
be installed to prevent clogging. On sites with small contributing
drainage areas to this BMP that do not provide enough runoff volume
to allow a twenty-four-hour attenuation with the three-inch orifice,
the calculations shall be submitted showing this condition. Orifice
sizes less than three inches can be utilized, provided that the design
will prevent clogging of the intake.
A.
The tributaries to the Schuylkill River in Berks County
have been divided into stormwater management districts as shown on
the Management District Maps in Appendix D.[1]
(2)
Standards for managing runoff from each subarea in
the tributaries to the Schuylkill River in Berks County for the two-year
through one-hundred-year design storms are shown in Table 2. Development
sites located in each of the districts must control proposed conditions
runoff rates to existing conditions runoff rates for the design storms
in accord with Table 2.
|
Table 2
Water Quantity Requirements
| |||||
|---|---|---|---|---|---|
|
Management District
|
Proposed Condition Design Storm
|
Existing Condition Design Storm
| |||
|
A
|
2-year
|
Reduce to
|
1-year
| ||
|
5- year
|
5-year
| ||||
|
10-year
|
10-year
| ||||
|
25-year
|
25-year
| ||||
|
50-year
|
50-year
| ||||
|
100-year
|
100-year
| ||||
|
B
|
2-year
|
Reduce to
|
1-year
| ||
|
5-year
|
2-year
| ||||
|
10-year
|
5-year
| ||||
|
25-year
|
10-year
| ||||
|
50-year
|
25-year
| ||||
|
100-year
|
50-year
| ||||
|
Equivalent Release Rate
| |||||
|
C
|
2-year
|
Reduce to
|
1-year
|
100%
| |
|
5-year
|
5-year
|
100%
| |||
|
10-year
|
10-year
|
100%
| |||
|
25-year
|
25-year
|
100%
| |||
|
50-year
|
50-year
|
100%
| |||
|
100-year
|
100-year
|
100%
| |||
|
NOTE: The minimum performance standard for development
sites in District C is that stormwater management controls must be
provided to limit the postdevelopment peak rate of stormwater runoff
to a rate that is equal to or less than the existing peak rate of
stormwater runoff. This minimum performance criteria was set through
a policy directive of the Pennsylvania Department of Environmental
Protection. However, in the previous development of the Act 167 Plan,
this district was originally established as a conditional no-detention
district, such that development sites which could discharge directly
to the main channel of the Schuylkill River and its major tributaries,
or indirectly to the main channel through an existing stormwater drainage
system (i.e., storm sewer or open channel), could do so without control
of the postdevelopment peak rate of runoff.
|
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
B.
General. Proposed condition rates of runoff from any
regulated activity shall not exceed the peak release rates of runoff
prior to development for the design storms specified on the Stormwater
Management District Watershed Maps (Appendix D[2]) and § 165-17 of this chapter.
[2]
Editor's Note: Appendix D is included as an attachment to this chapter.
C.
District boundaries. The boundaries of the stormwater
management districts are shown on an official map that is available
for inspection at the municipal office. A copy of the official map
at a reduced scale is included in Appendix D. The exact location of
the stormwater management district boundaries as they apply to a given
development site shall be determined by mapping the boundaries using
the two-foot topographic contours (or most accurate data required)
provided as part of the drainage plan.
D.
Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall meet the management district criteria for which the discharge is located, as indicated in § 165-17. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea. An exception to the above may be granted if discharges from multiple subareas recombine in proximity to the discharge site. In this case, peak discharge in any direction shall follow Management District A criteria, provided that the overall site discharge meets the management district criteria for the district in which the discharge is located.
E.
Off-site areas. Off-site areas that drain through
a proposed development site are not subject to release-rate criteria
when determining allowable peak runoff rates. However, on-site drainage
facilities shall be designed to safely convey off-site flows through
the development site.
F.
Site areas. Where the site area to be impacted by
a proposed development activity differs significantly from the total
site area, only the proposed impact area utilizing stormwater management
measures shall be subject to the management district criteria. In
other words, unimpacted areas bypassing the stormwater management
facilities would not be subject to the management district criteria.
A.
Applicants may select a combination of runoff control
techniques that are most suitable to control stormwater runoff from
the site. All controls shall be subject to the approval of Union Township.
The Municipal Engineer may request specific information on design
and/or operating features of the proposed stormwater controls in order
to determine their suitability and adequacy in terms of the standards
of this section.
B.
The applicant shall consider the effect of the proposed
stormwater management techniques on any special soil conditions or
geological hazards that may exist on the development site. In the
event such conditions are identified on the site, the Municipal Engineer
may require in-depth studies by a geotechnical engineer.
C.
Basins and impoundments. Any BMP that is a dam, as
defined in 25 Pa. Code, Chapter 105, shall be designed according to
the requirements in those regulations. Any stormwater BMP that does
not constitute a dam under 25 Pa. Code, Chapter 105, but is designed
to store runoff and requires a berm or earthen embankment (i.e., detention
basin), shall be designed to comply with the following:
(1)
Basins with earthen embankments shall be designed
with an emergency spillway that has the capacity and stability to
accommodate the one-hundred-year postdevelopment hydrograph in a manner
that will not damage the integrity of the facility and will not create
a downstream hazard. Emergency spillway design shall assume that all
other basin outlets are nonfunctional. Where practical, the emergency
spillway shall be constructed in undisturbed ground, and locations
in fill should be avoided. Regardless of location, appropriate stabilization
measures shall be provided.
(2)
The height of the embankment shall be designed to
provide a minimum 1.0 foot of freeboard above the maximum elevation,
computed when the one-hundred-year peak postdevelopment flow passes
through the emergency spillway. Embankment heights shall not exceed
15 feet, unless approved by Union Township.
(3)
The minimum top width of earthen embankments shall
be equal to 3/4 of the embankment height, but in no case shall the
top width be less than eight feet.
(4)
Interior and exterior embankment side slopes shall
not be greater than three horizontal to one vertical.
(5)
All pipes, conduits, etc., passing through basin embankments
shall have properly spaced anti-seepage collars. Minimum collar projection
beyond the pipe shall be two feet, and maximum collar spacing is 14
times the projection. The joint between the collar and pipe shall
be watertight.
(6)
A key trench of relatively impervious material shall
be provided within all basin embankments. The key trench shall be
at least two feet deep or extend down to stable subgrade, whichever
is deeper. The minimum bottom width for a key trench shall be four
feet. The maximum side slopes for the key trench shall be one horizontal
to one vertical. A compacted impervious core at least three feet wide
at the top, having maximum side slopes of one horizontal to one vertical,
shall extend for the full length of the embankment, and the top elevation
shall be set at the ten-year design water surface elevation.
(7)
All basins shall be structurally sound and shall be
constructed of durable materials. The completed structure and the
foundation of all basins shall be stable under all probable conditions
of operation. Embankments shall be placed in maximum eight-inch lifts
to a minimum of 95% of maximum dry density, as established by ASTM
D-1557. Compaction test results shall be provided to Union Township
upon request. Embankments shall be constructed six inches above design
elevations to allow for settlement.
(8)
All basins not including groundwater recharge and/or
water quality storage shall include an outlet structure to permit
draining the basin to a completely dry condition within 24 hours following
the end of the design rainfall.
(9)
All discharge control devices with appurtenances (except
discharge pipes) shall be made of reinforced concrete and stainless
or hot-dip galvanized steel. Bolts/fasteners and any orifice plates
are to be stainless or galvanized steel. Outlet barrels/pipes shall
have a minimum diameter of 15 inches and shall be made of reinforced
concrete pipe with watertight joints, or approved equivalent. Where
installation conditions merit, structural calculations that address
the actual design requirements will be required.
(10)
All basins employing small orifices (i.e., less
than six inches in diameter or equivalent area) shall be provided
with an apron of concrete or similar durable material which abuts
the orifice invert and extends a minimum of 18 inches in all directions
from the orifice, to prevent potential blockage by vegetative growth
or debris and to allow for easy cleaning of the area approaching the
orifice. Appropriate trash racks are required for all orifice openings.
(11)
The minimum slope within a basin that does not
include groundwater recharge and/or water quality storage shall be
2% positive grade to the low-flow channel.
(12)
Design storms for the computation of retention
basin volumes shall be based upon a twenty-four-hour storm with a
one-hundred-year return period (SCS Type II storm).
(13)
The effect on downstream areas if the basin
embankment fails shall be considered in the design of all basins.
The basin shall be designed to minimize the potential damage caused
by such failure of the embankment.
(14)
All structures (detention basins, cisterns,
etc.) other than those used for groundwater recharge volume and water
quality volume must completely drain within 24 hours after the end
of the design storm.
(15)
Soils used for the construction of basins shall
have low erodibility factors (K factors).
(16)
Minimum floor elevations for all structures
that would be affected by a basin, other temporary impoundments, or
open conveyance systems where ponding may occur shall be two feet
above the one-hundred-year water surface. If basement or underground
facilities are proposed, detailed calculations addressing the effects
of stormwater ponding on the structure and waterproofing and/or floodproofing
design information shall be submitted for approval.
D.
Stormwater collection and conveyance systems. Gutters,
inlets, pipes, conduits, swales, ditches and any other means for collecting
and/or conveying stormwater shall be designed to comply with the following:
(1)
All storm sewer pipes, culverts and bridges (excluding
detention and retention basin outfall structures), gutters and swales
conveying water originating only from within the boundaries of the
development site shall be designed for a twenty-five-year storm event.
All storm sewer pipes, culverts and bridges (excluding detention and
retention basin outfall structures) conveying water originating from
off site shall be designed for a fifty-year storm event. Facilities
that convey runoff to stormwater management facilities (e.g., detention
basins, etc.) shall be designed for the one-hundred-year storm event,
unless adequate alternate means for conveying the one-hundred-year
flow to the facilities are provided. Drainage easements having widths
no less than 20 feet shall be provided to contain and convey the one-hundred-year
frequency flood throughout the development site. Easements shall begin
at the furthest upstream property line of the proposed development
site in a watershed.
(2)
Water obstructions shall convey runoff from the twenty-five-year
design storm with a minimum of 2.0 feet of freeboard, measured below
the lowest point along the top of the roadway, without damage to the
drainage structure or the roadway, unless more restrictive local,
state and/or federal regulations apply. A concentrated discharge of
stormwater to an adjacent property shall be within an existing watercourse
or otherwise an easement and appropriate agreements shall be required.
(3)
Storm sewer pipes other than those used as roof drains,
detention basin underdrains, and street subbase underdrains shall
have a minimum diameter of 15 inches and be either Class III reinforced
concrete pipe (RCP) or smooth-lined corrugated high-density polyethylene
pipe (HDPE). Corrugated metal pipe is not permitted. HDPE pipe joints
shall be silt-tight at a minimum (e.g., ADS N-12 ST/IB or equal),
and RCP joints shall have prelubed O-ring gaskets. Watertight specification
is required in areas of carbonate geology and elsewhere as may be
specified by the municipality. Where installation conditions merit
(e.g., deep fills), structural calculations that address the actual
design requirements will be required.
(4)
Storm sewer pipes and culverts shall be installed
on sufficient slopes to provide a minimum velocity of three feet per
second when flowing full.
(5)
Storm sewers shall be placed within the cartway of
curbed streets and parallel to the road shoulders of streets without
curbs. At curbed street intersections, inlets shall be placed on the
tangent and not on the curved portion of the curbing. Storm sewer
crossings of streets shall be perpendicular to the street center line
to the maximum extent practicable.
(6)
Storm facilities not located within a public right-of-way
shall be contained in and centered within an easement not less than
20 feet wide. Easements shall follow property boundaries where possible.
(7)
Manning "n" values used for design of pipes and culverts
shall be in accordance with generally accepted engineering practice.
Adequate documentation shall be provided in support of the chosen
values.
(8)
All storm sewer pipe and culverts shall have a minimum
cover of 18 inches. Embedment for all storm sewer pipe and culverts
shall consist of AASHTO No. 8 (1B) aggregate from a minimum of six
inches of bedding beneath the pipe to a minimum of 12 inches over
the pipe. Aggregate requirements for street construction shall take
precedence over the 1B specification, but in no case shall total aggregate
cover over the pipe be less than 12 inches. Compaction shall be in
conformance with manufacturer's specifications. Select backfill shall
complete the trench to pavement subgrade or topsoil layer in grassed
areas. Properly spaced trench plugs are required in areas of high
groundwater.
(9)
Curves, tees, elbows and wyes are not permitted in
pipes other than those used as roof drains, detention basin underdrains,
and street subbase underdrains. Manholes or inlets are required to
facilitate such configurations.
(10)
Manholes and inlets shall not be spaced more
than 400 feet apart for pipes with diameters of 24 inches and less
and not more than 500 feet apart for pipes of greater diameter. Ladder
rungs shall be placed in manholes and inlets with depths exceeding
five feet.
(11)
When there is a change in the pipe size in a
manhole or inlet, the elevations of the top of the pipes shall be
the same, or the smaller pipe(s) higher. A minimum drop of one-tenth
foot shall be provided from the inlet invert elevation(s) to the outlet
invert elevation. Nonsumped inlets shall have flow channels.
(12)
Inlets in grassed areas or BMPs are to be sealed
at all joints and pipe penetrations.
(13)
Manholes, inlets, headwalls, endwalls and end
sections proposed for dedication or located along streets or subject
to vehicular traffic shall conform to the requirements of PennDOT
or to specifications as otherwise modified by Union Township. Manhole
covers shall have the word "STORM" cast clearly on the lid.
(14)
Inlets along curbed streets shall be spaced
to limit depth along the curb to a maximum of three inches during
a ten-year storm. Inlet capacities and bypass calculations shall be
determined by PennDOT design techniques.
(15)
Pipe underdrains and/or pavement base drains
shall be provided in areas known or otherwise documented to have a
seasonal high-water table and as directed by the Union Township Engineer.
(16)
Appropriate headwalls, endwalls or end sections
shall be used where stormwater runoff enters or leaves the storm sewer
horizontally from a natural or man-made channel. Such facilities shall
conform to the requirements of PennDOT or to specifications as otherwise
modified by Union Township.
(17)
Adequate erosion and sediment control protection
shall be provided along all open channels and at all points of discharge.
(18)
Stormwater roof drains, sump pumps, and pipes
shall not directly discharge water into a street right-of-way or discharge
into a sanitary sewer or storm sewer.
(19)
All existing and natural watercourses, channels,
drainage systems, wetlands and areas of surface water concentration
shall be maintained in their existing condition, unless an alteration
is approved by Union Township and any other necessary approving body.
(20)
Flow velocities from any storm sewer may not
result in erosion of the receiving channel.
(21)
Energy dissipaters shall be placed at the outlets
of all storm sewer pipes, culverts, and bridges where flow velocities
exceed maximum permitted channel velocities as specified in the PADEP
Erosion and Sediment Pollution Control Manual, as amended.
(22)
The following conditions shall be met for all
swales:
(a)
Capacities and velocities shall be computed
using the Manning equation.
(b)
Stabilization (i.e., linings, etc.) shall be
as specified in the PADEP Erosion and Sediment Pollution Control Manual,
as amended.
(c)
All vegetated swales shall have a minimum slope
of 1%, unless approved by the municipality.
(d)
"n" factors shall be based upon accepted engineering
design practices, as approved by the municipality.
(e)
All swales shall be designed to concentrate
low flows to minimize siltation and meandering.
(f)
All roadside swales along Township streets,
or streets to be dedicated to the Township, are to be lined with appropriate
erosion-control blanket or turf reinforcement mats for permanent stabilization.
(g)
V-shaped (triangular) swale sections are not
permitted.
A.
Stormwater runoff from all development sites with
a drainage area of greater than 200 acres shall be calculated using
a generally accepted calculation technique that is based on the NRCS
Soil Cover Complex Method. Table 3 summarizes acceptable computation
methods, and the method selected by the design professional shall
be based on the individual limitations and suitability of each method
for a particular site. Union Township may allow the use of the Rational
Method to estimate peak discharges from drainage areas that contain
less than 200 acres. The Soil Cover Complex Method shall be used for
drainage areas greater than 200 acres.
|
Table 3
Acceptable Computation Methodologies For
Stormwater Management Plans
| |||
|---|---|---|---|
|
Method
|
Method Developed by
|
Applicability
| |
|
TR-20(or commercial computer package based on
TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer
model is desirable or necessary
| |
|
TR-55(or commercial computer package based on
TR-55)
|
USDA NRCS
|
Applicable for land development plans within
limitations described in TR-55
| |
|
HEC-1 / HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer
model is desirable or necessary
| |
|
PSRM
|
Penn State University
|
Applicable where use of a hydrologic computer
model is desirable or necessary; simpler than TR-20 or HEC-1
| |
|
Rational Method(or commercial computer package
based on Rational Method)
|
Emil Kuichling (1889)
|
For sites less than 200 acres and with time
of concentration less than 60 minutes (tc < 60 min) or as approved
by the municipality
| |
|
Other methods
|
Varies
|
Other computation methodologies approved by
the municipality
| |
|
NOTE: Successors to the above methods are also
acceptable. These successors include WINNTR55 for TR55 and WINTR20
for TR20 and SWMM.
|
B.
All calculations consistent with this chapter using
the Soil Cover Complex Method shall use the appropriate design rainfall
depths for the various return-period storms according to NOAA's National
Weather Service Precipitation Frequency Data Server (PFDS) or NOAA
Atlas 14. If a hydrologic computer model such as PSRM or HEC-1 / HEC-HMS
is used for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours.
C.
For the purposes of existing conditions flow rate
determination, undeveloped land shall be considered as "meadow" in
good condition, unless the natural ground cover generates a lower
Curve Number or Rational C value (i.e., forest), as listed in Table
B-1 or B-2 in Appendix B of this chapter.
D.
All calculations using the Rational Method shall use
rainfall intensities consistent with appropriate times-of-concentration
for overland flow and return periods from NOAA's National Weather
Service Precipitation Frequency Data Server (PFDS) or NOAA Atlas 14.
E.
Times-of-concentration shall be calculated using the
methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds,
NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times-of-concentration
for channel and pipe flow shall be computed using Manning's equation.
F.
Runoff Curve Numbers (CN) for both existing and proposed
conditions to be used in the Soil Cover Complex Method shall be obtained
from Table B-1 in Appendix B of this chapter.
G.
Runoff coefficients (C) for both existing and proposed
conditions for use in the Rational Method shall be obtained from Table
B-2 in Appendix B of this chapter.
H.
For residential land development and subdivisions,
anticipated impervious cover per lot shall be increased by a factor
to account for future impervious surfaces attributable to building
additions, sheds, patios, swimming pools, etc. These factors shall
be as follows: for lot size up to and including 1/2 acre, multiply
anticipated impervious cover by 1.2; for lot size greater than 1/2
acre, multiply anticipated impervious cover by 1.3. Impervious assumptions
relative to stormwater management shall be identified on the record
plan for subdivisions and land developments to be recorded and on
the stormwater management plan for individually permitted proposals.
I.
Where uniform flow is anticipated, the Manning equation
shall be used for hydraulic computations and to determine the capacity
of open channels, pipes, and storm sewers. Values for Manning's roughness
coefficient (n) shall be consistent with Table B-3 in Appendix B of
this chapter. Full flow shall be assumed for closed conduits.
J.
Outlet structures for stormwater management facilities
shall be designed to meet the performance standards of this chapter
using any generally accepted hydraulic analysis technique or method.
K.
The design of any stormwater detention facilities
intended to meet the performance standards of this chapter shall be
verified by routing the design storm hydrograph through these facilities
using the Storage-Indication Method. For drainage areas greater than
200 acres in size, the design storm hydrograph shall be computed using
a calculation method that produces a full hydrograph (i.e., TR-20,
TR-55, HEC-1, PSRM). Union Township may approve the use of any generally
accepted full hydrograph approximation technique that shall use a
total runoff volume that is consistent with the volume from a method
that produces a full hydrograph.
A.
All wet basin designs shall incorporate biologic minimization
controls consistent with the West Nile Guidance found in Appendix
F.[1]
[1]
Editor's Note: Appendix F is included as an attachment to this chapter.
B.
Any facilities that constitute water obstructions
(e.g., culverts, bridges, outfalls, or stream enclosures), water encroachments,
and any work involving wetlands governed by PADEP Chapter 105 regulations
(as amended or replaced from time to time by PADEP) are subject to
PADEP Chapter 105 regulations.
C.
Adequate erosion protection shall be provided along
all open channels and at all points of discharge (DEP Erosion, Sediment
and Pollution Control Manual).
D.
Union Township reserves the right to disapprove any
design that would result in the construction in or continuation of
a stormwater problem area.
E.
No stormwater detention facility shall be placed within
50 feet of a special geologic feature. No stormwater conveyance facility
shall be constructed within 50 feet of a special geologic feature,
unless it is constructed of durable pipe utilizing watertight joints.
F.
Stormwater controls, conveyance facilities and BMPs
are subject to additional design and construction criteria as may
be included in a separate stormwater specifications document.
