A.
Applicants proposing regulated activities in the Brodhead/Tobyhanna Creek Watershed which do not fall under the exemption criteria shown in § 179-20 shall submit a drainage plan consistent with the Brodhead/Tobyhanna Creek Watershed Stormwater Management Plan to the municipality for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
The applicant is required to perform an alternative
analysis to find 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.
(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.
(2)
All practicable alternatives to the discharge of stormwater
are presumed to have less adverse impact on quantity and quality of
waters of the commonwealth unless otherwise demonstrated.
C.
The drainage plan must be designed through an alternative analysis consistent with the sequencing provisions of § 179-11 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.
Stormwater drainage systems shall be provided in order
to permit unimpeded flow along natural watercourses, except as modified
by stormwater management facilities or open channels consistent with
this chapter.
E.
The 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 applicant(s) and shall be subject to any applicable discharge
criteria specified in this chapter.
F.
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.
G.
Where a development site is traversed by existing
watercourses, drainage easements shall be provided conforming to the
top-of-bank of such watercourses. The terms of the easement shall
prohibit any alterations which may adversely affect the flow of stormwater
within any portion of the easement.
H.
Any stormwater management facilities regulated by
this chapter that would be located in the floodway or waters of the
commonwealth or wetlands shall be subject to approval by PA DEP through
the joint permit application process or, where deemed appropriate
by PA DEP, the general permit process. When there is a question whether
wetlands may be involved, it is the responsibility of the applicant
to show that the land in question cannot be classified as wetlands,
otherwise approval to work in the area must be obtained from PA DEP.
I.
Any stormwater management facilities regulated by
this chapter that would be located on state highway rights-of-way
shall be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
J.
Infiltration of runoff through seepage beds, infiltration
trenches, etc., where soil conditions permit, and minimization of
impervious surfaces to the extent permitted by the municipality's
Zoning Ordinance[1] are required to reduce the size or eliminate the need
for detention facilities or other structural BMPs.
K.
In order to promote overland flow and infiltration,
roof drains shall not be connected to streets or storm sewers or roadside
ditches. Direct connection of roof drains to storm sewers or roadside
ditches shall only be permitted by the Borough on a case-by-case basis
when it is demonstrated that it is more advantageous to do so from
an environmental standpoint. It is recommended that roof runoff be
directed to infiltration BMPs. Considering potential pollutant loading,
roof drain runoff in most cases will not require pretreatment.
L.
All stormwater runoff other than rooftop runoff shall
be treated for water quality prior to discharge to surface water or
groundwater.
The applicant shall demonstrate that it designed
the regulated activities in the following sequence to minimize the
increases in stormwater runoff and impacts to water quality:
A.
Prepare an existing resource and site analysis map
(ERSAM) showing environmentally sensitive areas, including but not
limited to slopes in excess of 15%, ponds, lakes, streams, wetlands,
hydric soils, vernal ponds, floodplains, buffer areas, hydrologic
soil groups A and B (areas conducive to infiltration), any existing
recharge areas and any other requirements outlined in the municipal
Subdivision and Land Development Ordinance.[1]
B.
Establish buffers according to the Zoning Ordinance.
C.
Prepare a draft project layout avoiding earth disturbance in sensitive areas identified in § 179-11A and minimizing total site earth disturbance as much as possible. The ratio of the disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included on the ERSAM.
D.
Identify site-specific predevelopment drainage areas,
discharge points, recharge areas to be preserved and hydrologic soil
groups A and B to be utilized for recharge.
G.
Satisfy groundwater recharge (infiltration) objective § 179-13 and provide for stormwater treatment prior to infiltration.
I.
Prepare final project design to maintain predevelopment
drainage areas and discharge points, to minimize earth disturbance
and impervious surfaces, and to reduce runoff to the maximum extent
possible.
J.
Conduct a post-development runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (§ 179-14).
K.
Manage any remaining runoff through treatment prior
to discharge, as part of detention, bioretention, direct discharge
or other structural control. All stormwater runoff, other than rooftop
runoff, shall be treated for water quality prior to discharge to surface
water or groundwater.
In addition to the performance standards and
design criteria requirements of this chapter, the applicant shall
comply with the following water quality requirements of this article:
A.
For water quality and stream bank erosion, the objective
is to design a water quality BMP to detain the proposed conditions
two-year, twenty-four-hour design storm to the existing conditions
one-year flow using the SCS Type II distribution. Additionally, provisions
shall be made (such as adding a small orifice at the bottom of the
outlet structure) so that the proposed conditions one-year storm takes
a minimum of 24 hours to drain from the facility from a point where
the maximum volume of water from the one-year storm is captured. (i.e.,
the maximum water surface elevation is achieved in the facility.)
At the same time, the objective is not to attenuate the larger storms
in "no detention" areas (District C) only. This can be accomplished
by configuration of the outlet structure not to control the larger
storms, or by a bypass or channel to divert only the two-year flood
into the basin or divert flows in excess of the two-year storm away
from the basin. Where practicable, wet basins shall be utilized for
water quality control and shall meet the requirements found in the
Pennsylvania BMP Manual. 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 consider
and minimize the chances of clogging and sedimentation. Orifices smaller
than three inches' diameter are not recommended. However, if the design
professional can provide proof that the smaller orifices are protected
from clogging by use of trash racks, etc., smaller orifices may be
permitted.
B.
In selecting the appropriate BMPs or combinations
thereof, the applicant shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high-water table.
(5)
Proximity to building foundations and wellheads.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream bank erosion.
(10)
Efficiency of the BMPs to mitigate potential
water quality problems.
(11)
The volume of runoff that will be effectively
treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife
habitat.
(15)
Recreational value.
C.
For areas within defined special protection subwatersheds
which includes exceptional value (EV) and high quality (HQ) waters,
the temperature and quality of water and streams shall be maintained
through the use of temperature-sensitive BMPs and stormwater conveyance
systems.
F.
Stream bank restoration projects shall include the
following:
(1)
No restoration or stabilization projects may be undertaken
without examining the fluvial geomorphology of stable reaches above
and below the unstable reach.
(2)
Restoration project design must then consider maintenance
of stability in the adjacent stable reaches of the stream channel.
(3)
An erosion and sediment control plan approved by the
conservation district must be provided by the applicant.
(4)
All applicable state and federal permits must be obtained.
H.
To accomplish the above, the applicant shall submit
original and innovative designs to the municipality for review and
approval. Such designs may achieve the water quality objectives through
a combination of BMPs (best management practices).
Maximizing the groundwater recharge capacity of the area being developed is required. The design shall incorporate the measures listed in § 179-2 and take advantage of utilizing any existing recharge areas.
A.
Regulated activities will be required to recharge (infiltrate), where practicable based on suitability of soils and site conditions, a portion of the runoff created by the development, except as provided in Subsection B. The following criteria shall apply to recharge facilities:
(1)
Infiltration BMPs shall be selected based on suitability
of soils and site conditions. A detailed soils evaluation of the project
site performed by a qualified design professional shall be performed
to determine general areas of suitability for infiltration practices.
The evaluation shall include, at a minimum, the following:
(a)
An analysis of the hydrologic soil groups as
well as material and man-made features within the watershed to determine
general areas of suitability for infiltration practices.
(b)
Depth to limiting zone, bedrock and water table
and subgrade stability.
(c)
Site-specific infiltration test results. The
tests shall be run at the level of the proposed infiltration surface
and shall be in accordance with ASTM Guide No. D5126 to determine
the appropriate hydraulic conductivity rate.
(d)
Infiltration rates to be used on the design
based on the site specific testing.
(2)
A minimum depth of 24 inches shall be maintained between
the bottom of the infiltration BMP and the limiting zone of the soil.
(3)
The infiltration rate of the soils as determined by
field tests must be sufficient to accept the additional stormwater
load and drain completely.
(4)
The volume of runoff to be recharged shall be determined
based on the following equation:
|
Equation 304.1
| ||
|
Re (cubic feet = I inch x Impervious area (square
feet x (1 foot/12 inch)
| ||
|
Where:
|
Re is the required recharge volume
| |
|
I is the infiltration requirement
| ||
(5)
The infiltration requirement (I) shall be determined
based upon the following:
(a)
NRCS Curve Number Equation — Equation
304.2.
|
I (inch = (200/CN) - 2
| ||
|
Where:
|
I is the infiltration requirement
| |
|
CN is the NRCS curve number for the area contributing
to the recharge facility based on existing conditions.
| ||
|
Equation 304.2 is displayed graphically in Figure
304.1
| ||
|
Figure 304.1. Infiltration requirement based
upon NRCS Curve Number
|
 |
(b)
Annual recharge, water budget approach. It has been determined that infiltrating 0.6 inches of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of § 179-13A(1)(a) cannot be achieved due to soils limitations and/or site conditions, then the infiltration requirement (I) may be reduced to 0.6 when existing conditions curve numbers (CN) are less than 77.
(6)
The recharge facility shall be capable of completely
infiltrating the recharge volume within four days.
(8)
If individual on-lot infiltration structures are proposed,
it must be demonstrated that the soils are conducive to infiltration
on those lots.
B.
Stormwater hotspots. A stormwater hotspot is defined
as a land use activity that generates higher concentrations of hydrocarbons,
trace metals or toxicants than are found in typical stormwater runoff,
based on monitoring studies. The table below provides samples 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 cannot be allowed to infiltrate into groundwater
where it may contaminate water supplies. Therefore, the Rev requirement is not applied to development sites that
fit into the hotspot category (the entire WQv must still be treated). Second, a greater level of stormwater treatment
may be needed at hotspot sites to prevent pollutant washoff after
construction. EPA's NPDES stormwater program requires some industrial
sites to prepare and implement a stormwater pollution prevention plan.
|
Classification of Stormwater Hotspots
|
|---|
|
The following land uses and activities are samples
of stormwater hotspots:
|
|
Salvage yards and recycling facilities
|
|
Fleet storage areas (bus, truck, etc.)
|
|
Public works storage areas
|
|
Facilities that generate or store hazardous
materials
|
|
Commercial gasoline and fuel oil sales
|
|
Vehicle fluid replacement facilities
|
|
Vehicle service stations, repair facilities
and body repair and painting facilities
|
|
Dry-cleaning and dyeing establishments and laundries
that utilize cleaning solvents
|
|
Printing and photo-processing establishments
|
|
Furniture and finish-stripping establishments
|
(1)
Extreme caution shall be exercised where salt or chloride
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/recharge facility and perform a hydrogeologic
justification study if necessary. The infiltration requirement in
high quality/exceptional value waters shall be subject to the Department's
Chapter 93 Antidegradation Regulations. The municipality may require
the installation of an impermeable liner in detention basins where
the possibility of groundwater contamination exists. A detailed hydrogeologic
investigation may be required by the municipality.
C.
Extreme caution shall be exercised where infiltration
is proposed in source water protection areas or that may affect a
wellhead or surface water intake.
D.
Recharge/infiltration facilities shall be used in
conjunction with other innovative or traditional BMPs, stormwater
control facilities, and nonstructural stormwater management alternatives.
A.
The Brodhead and Tobyhanna Watersheds have been divided
into stormwater management districts as shown on the Watershed Maps
in Appendix D.[1]
(1)
Standards for managing runoff from each subarea in
the Brodhead and Tobyhanna Watersheds located in the Borough for design
storms are shown in Table 305.1. Development sites must control proposed
conditions runoff rates to existing conditions runoff rates for the
design storms in accord with the table.
(2)
In addition to the requirements specified in Table 305.1 below, the water quality and stream bank erosion (§ 179-12), groundwater recharge (§ 179-13), and erosion control (§ 179-17) requirements shall be implemented.
|
TABLE 305.1 — Runoff Rate Requirements
| |||
|---|---|---|---|
|
District
|
Proposed Conditions
|
(reduce to)
|
Existing Conditions
|
|
Tobyhanna
| |||
|
A
|
2.33-year
|
2.33-year
| |
|
10-year
|
10-year
| ||
|
50-year
|
50-year
| ||
|
Brodhead
| |||
|
B-1
|
2-year
|
1-year
| |
|
5-year
|
2-year
| ||
|
10-year
|
5-year
| ||
|
25-year
|
10-year
| ||
|
50-year
|
25-year
| ||
|
100-year
|
100-year
| ||
|
Brodhead
| |||
|
B-2
|
2-year
|
1-year
| |
|
5-year
|
2-year
| ||
|
25-year
|
5-year
| ||
|
50-year
|
10-year
| ||
|
100-year
|
50-year
| ||
[1]
Editor's Note: Appendix D is an attachment
to this chapter.
B.
General. Proposed conditions 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 (Ordinance Appendix
D[2]) and § 179-14, of this chapter.
[2]
Editor's Note: Appendix D is an attachment
to this chapter.
C.
District boundaries. The boundaries of the stormwater
management districts are shown on an official map that is available
for inspection at the municipal office. A copy of the official map
at a reduced scale is included in the Ordinance Appendix D.[3] The exact location of the stormwater management district
boundaries as they apply to a given development site shall be determined
by mapping the boundaries using the two-foot topographic contours
(or most accurate data required) provided as part of the drainage
plan.
[3]
Editor's Note: Appendix D is an attachment
to this chapter.
D.
Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the existing conditions peak discharge for that subarea as indicated in § 179-11. 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 by the municipalities if discharges from multiple subareas recombine in proximity to the site. In this case, peak discharge in any direction may be a one-hundred-percent release rate, provided that the overall site discharge meets the weighted average release rate.
E.
Off-site areas. Off-site areas that drain through
a proposed development site are not subject to release rate criteria
when determining allowable peak runoff rates. However, on-site drainage
facilities shall be designed to safely convey off-site flows through
the development site.
F.
Site areas. Where the site area to be impacted by
a proposed development activity differs significantly from the total
site area, only the proposed impact area utilizing stormwater management
measures shall be subject to the management district criteria. In
other words, unimpacted areas bypassing the stormwater management
facilities would not be subject to the management district criteria.
G.
"No-harm" option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that no-harm would be caused by discharging at a higher runoff rate than that specified by the stormwater management plan. The no harm option is used when an applicant can prove that the proposed hydrographs can match existing hydrographs, or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of no harm must be shown based upon the following downstream impact evaluation which shall include a downstream hydraulic capacity analysis consistent with Subsection H to determine if adequate hydraulic capacity exists. The applicant shall submit to the municipality this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
(1)
The hydrologic regime of the site must be maintained.
(2)
The downstream impact evaluation shall include hydrologic
and hydraulic calculations necessary to determine the impact of hydrograph
timing modifications due to the proposed development upon a dam, highway,
structure, natural point of restricted stream flow or any stream channel
section established with the concurrence of the municipality.
(3)
The evaluation shall continue downstream until the
increase in flow diminishes due to additional flow from tributaries
and/or stream attenuation.
(4)
The peak flow values to be used for downstream areas
for the design return period storms (two-, five-, ten-, twenty-five-,
fifty-, and one-hundred-year) shall be the values from the calibrated
model for the Brodhead/McMichaels Watershed. These flow values can
be obtained from the original Act 167 watershed stormwater management
plans.
(5)
Applicant-proposed conditions 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 H.
(6)
A financial distress shall not constitute grounds
for the municipality to approve the use of the no-harm option.
(7)
Downstream capacity improvements may be provided as
necessary to achieve the no-harm option.
H.
Downstream hydraulic capacity analysis. Any downstream
hydraulic capacity analysis conducted in accordance with this chapter
shall use the following criteria for determining adequacy for accepting
increased peak flow rates:
(1)
Existing natural or man-made channels or swales must
be able to convey the increased runoff associated with a two-year
return period event within their banks at velocities consistent with
protection of the channels from erosion. Acceptable velocities shall
be based upon criteria included in the DEP Erosion and Sediment Pollution
Control Program Manual.
(2)
Existing natural or man-made channels or swales must
be able to convey increased twenty-five-year return period runoff
without creating any hazard to persons or property.
(3)
Culverts, bridges, storm sewers or any other facilities
which must pass or convey flows from the tributary area must be designed
in accordance with DEP Chapter 105 regulations (if applicable) and,
at minimum, pass the increased twenty-five-year return period runoff.
I.
Hardship option. The stormwater management plan and
its standards and criteria are designed to maintain existing conditions
peak flows and volumes throughout the Brodhead/McMichaels watershed
as the watershed becomes developed. There may be certain instances,
however, where the standards and criteria established are too restrictive
for a particular applicant. The existing drainage network in some
areas may be capable of safely transporting slight increases in flows
without causing a problem or increasing flows elsewhere. If an applicant
cannot meet the stormwater standards due to lot conditions or if conformance
would become a hardship to an applicant, the hardship option may be
applied. A financial distress shall not constitute grounds for the
municipality to approve the use of the hardship option. The applicant
would have to plead his/her case to the governing body with the final
determination made by the municipality. Any applicant pleading the
hardship option will assume all liabilities that may arise due to
exercising this option. A financial distress shall not constitute
grounds for the municipality to approve the use of the no-harm option.
A.
Stormwater runoff from all development sites shall
be calculated using a generally accepted calculation technique that
is based on the NRCS Soil-Cover-Complex Method. Table 306-1 summarizes
acceptable computation methods, and the method selected by the design
professional shall be based on the individual limitations and suitability
of each method for a particular site. The municipality may allow the
use of the Rational Method to estimate peak discharges from drainage
areas that contain less than 200 acres. The Soil-Cover-Complex Method
shall be used for drainage areas greater than 200 acres.
|
TABLE 306-1
| ||
|---|---|---|
|
Acceptable Computation Methodologies for
Stormwater Management Plans
| ||
|
Method
|
Method Developed By
|
Applicability
|
|
TR-20 (or commercial computer package based
on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer
model is desirable or necessary
|
|
TR-55 (or commercial computer package based
on TR-55)
|
USDA NRCS
|
Applicable for land development plans within
limitations described in TR-55
|
|
HEC-1/HEC-HMS
|
US 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, or as approved
by the municipality and/or Municipal Engineer
|
|
Other methods
|
Varies
|
Other computation methodologies approved by
the municipality and/or Municipal Engineer
|
B.
All calculations consistent with this chapter using the Soil-Cover-Complex
Method shall use the appropriate design rainfall depths for the various
return period storms according to NOAA (National Oceanic and Atmospheric
Administration) Atlas 14 Point Precipitation Frequency Estimates,
which is available online at http://hdsc.nws.noaa.gov/hdsc/pfds/.
If a hydrologic computer model such as PSRM or HEC-1 is used for stormwater
runoff calculations, then the duration of rainfall shall be 24 hours.
Rainfall distribution can be developed from the NRCS (SCS) Type II
Rainfall Distribution 'S' Curve shown in Figure B-1, Appendix
B of this chapter[1] or can be developed directly from the Atlas 14 rainfall
information according to the instructions available from the NRCS
(National Resources Conservation Service), which are available online
at www.nrcs.usda.gov/.
[Added 10-5-2015 by Ord.
No. 4-2015]
[1]
Editor's Note: Original Appendix B was repealed 10-5-2015
by Ord. No. 4-2015. The Appendix B which replaced it is an attachment
to this chapter and contains a reference to NOAA Atlas 14 Point Precipitation
Frequency Estimates.
C.
Times-of-concentration for overland flow shall be
calculated using the methodology presented in Chapter 3 of Urban Hydrology
for Small Watersheds, NRCS, TR-55 (as amended or replaced from time
to time by NRCS). Times-of-concentration for channel and pipe flow
shall be computed using Manning's equation.
D.
All calculations using the Rational Method shall use
rainfall intensities consistent with appropriate times-of-concentration
for overland flow and return periods from the Design Storm Curves
from Pennsylvania Department of Transportation Design Rainfall Curves
(1986) (Figures B-2 to B-4).
E.
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-2 in Appendix B of this chapter, except as noted in Subsections G and H below.[2]
[2]
Editor's Note: Original Appendix B was repealed 10-5-2015
by Ord. No. 4-2015. The Appendix B which replaced it is an attachment
to this chapter.
F.
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from Table B-3 in Appendix B of this chapter, except as noted in Subsections G and H below.[3]
[3]
Editor's Note: Original Appendix B was repealed 10-5-2015
by Ord. No. 4-2015. The Appendix B which replaced it is an attachment
to this chapter.
G.
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, as listed in Table B-2 or B-3
in Appendix B of this chapter.[4]
[4]
Editor's Note: Original Appendix B was repealed 10-5-2015
by Ord. No. 4-2015. The Appendix B which replaced it is an attachment
to this chapter.
H.
The designer shall consider that the runoff from proposed
sites graded to the subsoil will not have the same runoff conditions
as the site under existing conditions, even after topsoiling or seeding.
The designer may increase his proposed condition "CN" or "c" to better
reflect proposed soil conditions.
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-4 in Appendix B of
the chapter.[5]
[5]
Editor's Note: Original Appendix B was repealed 10-5-2015
by Ord. No. 4-2015. The Appendix B which replaced it is an attachment
to this chapter.
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. The municipality
may approve the use of any generally accepted full hydrograph approximation
technique that shall use a total runoff volume that is consistent
with the volume from a method that produces a full hydrograph.
A.
Any stormwater management facility (i.e., BMP, detention
basin) designed to store runoff and requiring a berm or earthen embankment
required or regulated by this chapter shall be designed to provide
an emergency spillway to handle flow up to and including the one-hundred-year
proposed conditions. Emergency spillways shall be constructed on undisturbed
ground and shall not be constructed on embankment fill. The height
of embankment must provide a minimum 1.0 foot of freeboard above the
maximum pool elevation, computed when the facility functions for the
one-hundred-year proposed conditions inflow. Should any stormwater
management facility require a dam safety permit under PA DEP Chapter
105, the facility shall be designed in accordance with Chapter 105,
which may require facilities to pass storms larger than the one-hundred-year
event.
B.
Any other drainage conveyance facility (e.g., culverts,
bridges, outfalls of stream enclosure) that does not fall under PA
DEP Chapter 105 regulations must be able to convey, without damage
to the drainage structure or roadway, runoff from the twenty-five-year
design storm with a minimum 1.0 foot of freeboard measured below the
lowest point along the top of the roadway.
C.
Any drainage conveyance facility and/or channel not
governed by PA DEP Chapter 105 regulations must be able to convey,
without damage to the drainage structure or roadway, runoff from the
twenty-five-year design storm. Conveyance facilities to or exiting
from stormwater management facilities (i.e., detention basins) shall
be designed to convey the design flow to or from that structure. Roadway
crossings located within designated floodplain areas must be able
to convey runoff from a one-hundred-year design storm.
D.
Storm sewers must be able to convey proposed conditions
runoff from a twenty-five-year design storm without surcharging inlets,
where appropriate.
E.
The design of all stormwater management facilities
shall incorporate sound engineering principles and practices. The
municipality reserves the right to disapprove any design that would
result in the creation of or continuation of a stormwater problem
area.
F.
A fifteen-foot-wide access easement to and around
all stormwater management facilities is required to provide ingress
and egress from a public right-of-way.
A.
Any earth disturbance must be conducted in conformance
with Title 25 Pa. Code Chapter 102, Erosion and Sediment Control.
B.
Additional erosion and sediment control design standards
and criteria that must be or 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.
All regulated activities shall submit a "consumptive
use tracking report" (CUTR), which shall be developed in accordance
with Appendix F as follows:[1]
A.
Residential development or redevelopment. The CUTR
shall be submitted to the Monroe County Conservation District along
with the erosion and sedimentation control plan.
B.
Commercial/industrial development or redevelopment.
The CUTR shall be submitted to the Monroe County Conservation District
during the land development plan approval process.
[1]
Editor's Note: Appendix F, Consumptive Use Tracking, is an
attachment to this chapter.
