[Ord. 2011-12-10, 12/12/2011]
1.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 23-302:
2.
SWM site plans approved by the Borough, in accordance with § 23-406, shall be on site throughout the duration of the regulated activity.
3.
The Borough may, after consultation with DEP, approve measures for
meeting the state water quality requirements other than those in this
chapter, provided that they meet the minimum requirements of, and
do not conflict with, state law, including, but not limited to, the
Clean Streams Law.[1] The Borough shall maintain a record of consultations with
DEP pursuant to this subsection.
A.
DEP is not required to be consulted for waiver of the requirements
within:
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
4.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities, i.e., during construction,
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual) 2, No. 363-2134-008 (April 15, 2000), as amended and updated.
6.
Impervious Areas:
A.
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in phases.
B.
For development taking place in phases, the entire development plan
must be used in determining conformance with this chapter.
C.
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 23-304 and the peak rate controls of § 23-305 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
7.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
of the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this chapter.
8.
All regulated activities shall include such measures as necessary
to:
A.
Protect health, safety, and property;
B.
Meet the water quality goals of this chapter, as stated in § 23-103, Purpose, by implementing measures to:
(1)
Minimize disturbance to floodplains, wetlands, wooded areas,
and existing vegetation.
(2)
Maintain or extend riparian buffers.
(3)
Avoid erosive flow conditions in natural flow pathways.
(4)
Minimize thermal impacts to waters of this commonwealth.
(5)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(6)
Minimize soil disturbance and compaction. Topsoil, if removed,
shall be replaced to a minimum depth equal to its depth prior to removal
or four inches, whichever is greater. (Additional topsoil may be needed
for vegetation other than sod.)
C.
To the maximum extent practicable, incorporate the techniques for
low-impact development practices described in the Pennsylvania Stormwater
Best Management Practices Manual (BMP Manual).
9.
The design of all facilities in areas of carbonate geology or karst
topography shall include an evaluation of measures to minimize adverse
effects, including hydrogeologic studies if required by the Borough.
10.
Infiltration BMPs shall be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter. In addition,
infiltration BMPs shall include pretreatment BMPs where appropriate.
11.
All natural streams, channels, swales, drainage systems and/or areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by the Borough. All encroachment activities shall comply with the requirements of PADEP, 25 Pa. Code, Chapter 105 (Water Obstructions and Encroachments), Rules and Regulations of PADEP. Any approvals or permits issued do not relieve compliance as referenced in § 23-108, Compatibility With Other Requirements.
12.
All stormwater management facilities (excluding individual residential
underground infiltration facilities) are considered structures and
must comply with building setback requirements. The outside toe of
slope of the embankment in a fill condition or the top of embankment
in a cut condition shall be considered as the point that must meet
the setback requirements. Individual residential underground infiltration
facilities shall be a minimum of 10 feet from the property line. Discharge
of controlled flows can be no closer to an adjacent property than
two times the length of the required discharge riprap apron. This
requirement applies to discharge aprons that do not outlet to a defined
waterway or an existing storm sewer. Minimum distance is 10 feet.
13.
All storage facilities shall completely drain both the volume control
and rate control capacities over a period of time not less than 24
hours and not more than 72 hours from the end of the design storm.
However, any designed infiltration at such facilities is exempt from
the minimum twenty-four-hour standard, i.e., may infiltrate in a shorter
period of time, so long as none of the stormwater flowing into the
infiltration facility is discharged directly into the surface waters
of the commonwealth. (Inordinately rapid infiltration rates may indicate
the presence of large fractures or other conditions for which an additional
soil buffer may be required.)
14.
The design storm volumes and precipitation intensities to be used
in the analysis of discharge or runoff shall be obtained from the
Precipitation-Frequency Atlas of the United States, Atlas 14, Volume
2, Version 3.0, United States Department of Commerce, National Oceanic
and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas
14 can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
15.
For all regulated activities, SWM BMPs shall be designed, implemented,
operated, and maintained to meet the purposes and requirements of
this chapter and to meet all requirements under Title 25 of the Pennsylvania
Code, the Clean Streams Law, and the Storm Water Management Act.
16.
Various BMPs and their design standards are listed in the BMP Manual.
17.
All work shall be in accordance with the Borough's Construction
and Material Specifications.
18.
The technical standards provided within this chapter are considered
the baseline for the design and layout of an SWM site plan. Use of
other alternative and innovative designs for controlling stormwater
runoff may be permitted when approved by the Borough Engineer.
[Ord. 2011-12-10, 12/12/2011]
1.
Any regulated activity that meets the following exemption criteria
is exempt from the part(s) of this chapter as specified herein. However,
the requirements of the chapter shall otherwise remain in effect.
The criteria for exemption in this section apply to the total development
proposed, including instances in which the development is proposed
to take place in phases. The date of enactment of this chapter shall
be the starting point from which future development and the respective
proposed impervious surface computations shall be cumulatively considered
and regulated. Exemption shall not relieve an applicant from implementing
such measures as necessary to meet the intent of this chapter or compliance
with any NPDES permit requirements.
A.
Regulated activities that create DIAs equal to or less than 1,000
square feet are exempt from the peak rate control and the SWM site
plan preparation requirements of this chapter, and, therefore, no
formal application to the Borough is required.
B.
Regulated activities that create DIAs greater than 1,000 square feet
and equal to or less than 5,000 square feet are exempt only from the
peak rate control requirement of this chapter.
C.
Agricultural activity is exempt from the rate control and SWM site
plan preparation requirements of this chapter, provided the activities
are performed according to the requirements of 25 Pa. Code, Chapter
102. For regulated activities that meet this exemption criteria, no
formal application to the Borough is required.
D.
Forest management and timber operations are exempt from the rate
control and SWM site plan preparation requirements of this chapter,
provided the activities are performed according to the requirements
of 25 Pa. Code, Chapter 102. For regulated activities that meet this
exemption criteria, no formal application to the Borough is required.
E.
Domestic gardening and landscaping are exempt from specific approval
and permitting under this chapter so long as those activities are
associated with one, and only one, dwelling unit and the activities
comply with all other applicable ordinances and statutes.
G.
The Borough may deny or revoke any exemption pursuant to this section
at any time for any project that the Borough determines poses a threat
to public health, safety, property or the environment.
[Ord. 2011-12-10, 12/12/2011]
2.
Description of Stormwater Management Districts. Two types of stormwater
management districts may be applicable to Red Lion Borough, namely
the release rate districts and provisional no-detention districts
as described below:
A.
Release Rate Districts. Rate districts differ in the extent to which
post-development runoff must be controlled. Within a given district,
the post-development peak rate of storm runoff must be controlled
to the stated percentage of the predevelopment peak rate of storm
runoff in order to protect downstream watershed areas.
B.
Provisional No-Detention Districts. These watershed areas may discharge post-development peak runoff without detention without adversely affecting the total watershed peak flow. In certain instances, however, the "local" runoff conveyance facilities, which transport runoff from the site to the main channel, may not have adequate capacity to safely transport increased peak flows associated with no detention for a proposed development. In those instances, the developer shall either use a one-hundred-percent release rate control or provide increased capacity of downstream drainage elements to convey increased peak flows consistent with § 23-309. In determining if adequate capacity exists in the local watershed drainage network, the developer must assume that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified in this chapter. Similarly, any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvements consistent with the capacity criteria specified in § 23-309.
3.
When a project or land disturbance activity is located in more than one stormwater management district, stormwater may not be transferred from a district with stricter stormwater management criteria to a district with less-strict criteria, unless the need for such a transfer is identified in the Regional Water Quality Management Plan Act 167 Study. In any district, infiltration and volume regulations dictated in § 23-304 will be required.
|
Codorus - District 1
East Branch Codorus - District 2
Susquehanna - District 3
Muddy - District 4
| |||
|---|---|---|---|
|
District ID
|
Regulated Storm Frequency
(years)
|
Percentage of Predeveloped Peak Flow Rate to Determine
Allowable Post-Developed Release Rate
| |
|
All districts
|
2
|
100% 2-year
| |
|
All districts
|
5
|
100% 5-year
| |
|
All districts
|
10
|
100% 10-year
| |
|
All districts
|
25
|
100% 25-year
| |
|
All districts
|
50
|
100% 50-year
| |
|
All districts
|
100
|
100% 100-year
| |
|
NOTES:
| ||
|---|---|---|
|
*
|
The intention of this table is to reduce the runoff rate.
| |
[Ord. 2011-12-10, 12/12/2011]
1.
The low-impact development practices provided in the BMP Manual shall
be utilized for all regulated activities to the maximum extent practicable.
Water volume controls shall be implemented using the Design Storm
Method in Subsection 1A or the Simplified Method in Subsection 1B
below. For regulated activity areas equal or less than one acre that
do not require hydrologic routing to design the stormwater facilities,
this chapter establishes no preference for either methodology; therefore,
the applicant may select either methodology on the basis of economic
considerations, the intrinsic limitations on applicability of the
analytical procedures associated with each methodology, and other
factors.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
Do not increase the post-development total runoff volume for
all storms equal to or less than the two-year, twenty-four-hour duration
precipitation.
B.
The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and should be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities greater than one acre or for projects that require design
of stormwater storage facilities. For new impervious surfaces:
(1)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options for the first one inch of runoff include reuse, evaporation,
transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities should be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed stormwater runoff shall be infiltrated.
[Ord. 2011-12-10, 12/12/2011]
1.
For computation of predevelopment peak discharge rates, 20% of the
existing impervious area of a project site, when present, shall be
considered meadow.
2.
Post-development discharge rates shall not exceed the predevelopment discharge rates provided in § 23-303, Subsection 3, for the one-, two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour storms. If it is shown that the peak rates of discharge indicated by the post-development analysis are less than or equal to the peak rates of discharge indicated by the predevelopment analysis for one-, two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year, twenty-four-hour storms, then the requirements of this section have been met. Otherwise, the applicant shall provide additional controls as necessary to satisfy the peak rate of discharge requirement.
[Ord. 2011-12-10, 12/12/2011]
1.
For the purposes of the Act 167 stormwater management (plan) elements, contained within the York County Integrated Water Resources Plan, and this chapter, design policy pertaining to stormwater management facilities for Pennsylvania Department of Transportation (PennDOT) and Pennsylvania Turnpike Commission (PTC) roadways and associated facilities is provided in Section 13.7 (Antidegradation and Post Construction Stormwater Management Policy) of PennDOT Publication No. 13M, Design Manual Part 2 (August 2009), as developed, updated, and amended in consultation with the Pennsylvania Department of Environmental Protection (DEP). As stated in DM-2.13.7.D (Act 167 and Municipal Ordinances), PennDOT and PTC roadways and associated facilities shall be consistent with Act 167 Plans. DM-2.13.7.B (Policy on Antidegradation and Post Construction Stormwater Management) was developed as a cooperative effort between PennDOT and DEP. DM-2.13.7.C (Project Categories) discusses the anticipated impact on the quality, volume, and rate of stormwater runoff.
2.
Where standards in the Act 167 elements of the IWRP and this chapter
are impractical, PennDOT or the PTC may request assistance from DEP,
in consultation with the Borough and county, to develop an alternative
strategy for meeting state water quality requirements and the goals
and objectives of the Act 167 elements within the IWRP.
3.
For the purposes of the Act 167 elements in the IWRP and this chapter,
road maintenance activities are regulated under 25 Pa. Code, Chapter
102.
[Ord. 2011-12-10, 12/12/2011]
1.
Off-Site Areas. Off-site areas which drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
2.
On-Site Areas. On-site areas proposed to remain undisturbed as part
of the regulated activity, including previously developed areas, that
are not within the drainage area of any proposed BMPs shall be considered
as existing conditions, without considering any reductions in cover
type.
3.
"Downstream Hydraulic Capacity Analysis." Any existing downstream
hydraulic capacity analysis shall be conducted in accordance with
this chapter.
A.
All downstream facilities impacted by the total site area of the
regulated activity shall be studied to determine if the facility has
adequate capacity to handle existing and proposed flows. An impacted
downstream facility is one to which the runoff from the total site
area of the regulated activity comprises more than 50% of the total
flow to such a facility. The study shall end at a perennial stream.
Downstream facilities include, but are not limited to, man-made or
natural swales and open channels, pipes, inlets, culverts, bridges
and roadways.
B.
If any private facility is found to be undersized, the applicant
shall be responsible for updating the facility in coordination with
the regulated activity.
C.
If any public facility is found to be undersized or inadequate, the
applicant shall work with the Borough on upgrading the facility in
coordination with the regulated activity.
4.
Regional Detention Alternatives. For certain areas within the study
area, it may be more cost-effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by-case
basis using the hydrologic model of the watershed consistent with
protection of the downstream watershed areas. "Hydrologic model" refers
to the calibrated model as developed for the stormwater management
plan.
5.
Capacity Improvements of Local Drainage Networks. In certain instances, primarily within the provisional no-detention areas, local drainage conditions may dictate more-stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Any capacity improvements would be designed based upon development of all areas tributary to the proposed improvement and the capacity criteria specified in § 23-308. In addition, all new development upstream of a proposed capacity improvement shall be assumed to implement the applicable runoff controls consistent with this chapter, except that all new development within the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control, if any.
6.
Capacity improvements may also be provided as necessary to implement
any regional or subregional detention alternatives.
7.
Where the potential for groundwater and/or surface water contamination
exists, based on the proposed use of the regulated activity, safeguards
shall be incorporated into the site.
A.
For industrial or commercial sites where it is possible that toxic
or hazardous substances may come into contact with stormwater runoff,
pretreatment of the first-flush (first 1/2 inch) runoff over areas
where industrial and commercial operations take place shall be provided.
Pretreatment shall include means for separating light and heavy toxic
and hazardous substances from the stormwater before the stormwater
is conveyed to the general stormwater management facility(ies).
B.
Infiltration systems may be used to handle runoff from commercial
or industrial working or parking areas only after the first-flush
stormwater from these areas has been pretreated for removal of toxic
and hazardous substances.
8.
Roof drains and sump pumps shall discharge to infiltration or vegetative
BMPs and, to the maximum extent practicable, satisfy the criteria
for DIAs.
[Ord. 2011-12-10, 12/12/2011]
1.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
2.
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 PADEP through the joint permit application
process or, where deemed appropriate by PADEP, the general permit
process. When there is a question whether wetlands may be involved,
it is the responsibility of the developer 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 PADEP.
3.
Any stormwater management facility located within the vicinity of
a floodplain shall be subject to approval in accordance with PADEP,
25 Pa. Code, Chapter 106 (Floodplain Management), of PADEP's
Rules and Regulations.
4.
All earthmoving activities must be reviewed and approved by the York
County Conservation District prior to commencing work.
5.
The design of all stormwater management facilities shall incorporate
good engineering principles and practices. The Borough shall reserve
the right to disapprove any design that would result in the occupancy
or continuation of adverse hydrologic or hydraulic conditions within
the watershed.
6.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered without permission of the adjacent
property owner(s) and shall be subject to any applicable discharge
criteria specified in this chapter.
7.
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
flow is proposed to be concentrated and discharged onto adjacent property,
the developer must document that adequate downstream conveyance facilities
exist to safely transport the concentrated discharge, or otherwise
prove that no erosion, sedimentation, flooding or other harm will
result from the concentrated discharge.
8.
Where a development site is traversed by watercourses, drainage easements
shall be provided conforming to the line of such watercourses. The
terms of the easement shall prohibit excavation, the placing of fill
or structures, and any alterations that may adversely affect the flow
of stormwater within any portion of the easement. Also, maintaining
of vegetation in a natural state within the easement shall be required,
except as approved by the appropriate governing authority.
9.
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by PADEP through the joint permit application
process or, where deemed appropriate by PADEP, through the general
permit process.
10.
Roof drains must not be connected to streets, sanitary or storm sewers
or roadside ditches to promote overland flow and infiltration/percolation
of stormwater where advantageous to do so. When it is more advantageous
to connect directly to streets or storm sewers, then it shall be permitted
on a case-by-case basis by the Borough.
11.
Special Requirements for Areas Falling Within Defined Exceptional-Value
and High-Quality Subwatersheds. The temperature and quality of water
and streams that have been declared as exceptional value and high
quality is to be maintained as defined in Chapter 93, Water Quality
Standards, Title 25, of the Pennsylvania Department of Environmental
Protection Rules and Regulations. Temperature-sensitive BMPs and stormwater
conveyance systems are to be used and designed with storage pool areas
and supply outflow channels and should be shaded with trees. This
will require modification of berms for permanent ponds and the relaxation
of restrictions on planting vegetation within the facilities, provided
that capacity for volumes and rate control is maintained. At a minimum,
the southern half on pond shorelines shall be planted with shade or
canopy trees within 10 feet of the pond shoreline. In conjunction
with this requirement, the maximum slope allowed on the berm area
to be planted is 10:1. This will lessen the destabilization of berm
soils due to root growth. A long-term maintenance schedule and management
plan for the thermal control BMPs is to be established and recorded
for all development sites within defined exceptional-value and/or
high-quality subwatersheds.
A.
No watersheds within the Borough are listed as exceptional-value
and/or high-quality watersheds.
[Ord. 2011-12-10, 12/12/2011]
1.
Stormwater runoff from all development sites shall be calculated
using the Rational Method, Modified Rational Method, or a Soil-Cover-Complex
Methodology.
A.
Any stormwater runoff calculations involving drainage areas greater
than 200 acres, including on- and off-site areas, shall use a generally
accepted calculation technique that is based on the NRCS Soil-Cover-Complex
Method. It is assumed that all methods will be selected by the design
professional based on the individual limitations and suitability of
each method for a particular site.
B.
The Borough may allow the use of the Rational Method or Modified
Rational Method to estimate peak discharges from drainage areas that
contain less than 200 acres.
C.
All calculations consistent with this chapter using the Soil-Cover-Complex
Method shall use the appropriate design rainfall depths. If a hydrologic
computer model such as PSRM or HEC-RAS is used for stormwater runoff
calculations, then the duration of rainfall shall be 24 hours. The
SCS Rainfall Type II curve shall be used for the rainfall distribution.
D.
For the purposes of predevelopment flow rate determination, undeveloped
land, including areas to be disturbed as part of the regulated activity,
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 Tables 1 and 2, respectively.
E.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times-of-concentration for overland flow
and return periods. 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). Time-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 1.
G.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table 2.
H.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations such as the capacity of open channels,
pipes, and storm sewers. Values for Manning's roughness coefficient
(n) shall be consistent with Table 3.
I.
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 either
manual methods or computerized routing. Routing shall be based upon
the Modified PULS Method; other routing methodologies shall be subject
to the approval of the Borough Engineer.
J.
The stormwater collection system shall be designed using the peak
discharge computed using the Rational Formula.
2.
Design Standards - Water-Carrying Facilities.
A.
All storm sewer pipes, streets, and inlets (excluding detention and
retention basin outfall structures) shall be designed for a ten-year
storm event. Sole-access structures (culverts and bridges) shall be
designed to convey the twenty-five-year flood without overtopping
the roadway.
(1)
When a pipe or culvert is intended to convey the discharge from
a stormwater management facility, its required capacity shall be computed
by the Rational Method and compared to the peak outflow from the stormwater
facility for the one-hundred-year storm. The greater flow shall govern
the design of the pipe or culvert.
(2)
When a pipe is part of a storm sewer system and crosses the
roadway, it shall be designed as a storm sewer with the same design
storm as the remainder of the drainage system.
(3)
Greater design frequencies may be justified on individual projects.
(4)
A one-hundred-year storm frequency may be required for design
of the stormwater collection system to ensure that the resultant stormwater
runoff from the post-development storm is directed into the management
facility.
B.
In general, inlets shall be spaced such that, based upon the Rational
Method, tc = 5 min. and ten-year rainfall intensity, the area contributing
to the inlet shall not produce a peak runoff of greater than 4 cfs.
Also, inlets shall be spaced so that their efficiency, based upon
efficiency curves published by the Pennsylvania Department of Transportation,
is not less than 65%.
C.
Inlets shall be placed on both sides of the street at low spots and
at the upper side of street intersections to prevent stormwater from
crossing an intersection. Other devices such as high-efficiency grates
or perforated pipe may be required if conditions warrant. All inlets
at low points along the roadway shall have a ten-inch curb reveal
and shall be equipped with pavement base drain extending 50 feet in
either direction, parallel to the center line of the roadway.
D.
In all cases where drainage is picked up by means of a headwall,
the pipe shall be designed as a culvert. Inlet and outlet conditions
shall be analyzed. The minimum diameter of culvert shall be 18 inches.
The procedure contained in Hydraulic Engineer Circulars No. 5 and
No. 13, as prepared by the United States Department of Transportation,
Federal Highway Administration, Washington, D.C., shall be used for
the design of culverts. All culverts shall include concrete headwalls
and endwalls.
E.
Guards shall be provided on all intake and outfall structures as
well as outlet structures. The guard bars shall be one-half-inch-diameter
galvanized bars on six-inch centers attached to the structure with
three-eighths-inch-diameter stainless steel anchors. Guards shall
also be provided for any pipe opening 18 inches in diameter or larger.
F.
Manholes, inlets, headwalls, and endwalls shall conform to the requirements
of PennDOT Publication 408, as modified by the adopted Borough standards.
G.
Proposed channels or swales must be able to convey the increased
runoff associated with a proposed one-hundred-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 PADEP Erosion and Sediment Pollution Control Program
Manual.
H.
Existing natural or man-made channels or swales must be able to convey
proposed one-hundred-year return period runoff without creating any
hazard to persons or property.
I.
Stormwater runoff on roadways (i.e., gutter spread, lane encroachment,
etc.) shall be controlled in accordance with PennDOT Publications
13M, "Design Manual, Part 2," and 584, "Drainage Manual."
3.
Design Standards - Detention and Retention Basins.
A.
Permanent detention and retention basins shall be designed to meet
the following standards:
(1)
The maximum permitted depth for detention or retention basins
shall be six feet, measured from the bottom of the emergency spillway
to the lowest point in the basin.
(2)
The minimum top width of all basin embankments shall be eight
feet.
(3)
The maximum permitted side slopes for detention or retention
basins shall be 4 horizontal to 1 vertical. In order to obtain a waiver
for slopes steeper than 4:1, the plan must include a planting schedule
to stabilize the embankments. The proposed vegetation shall be low-maintenance
varieties.
(4)
Minimum Bottom Slope. All detention basins shall have a minimum
bottom slope of 2% unless infiltration facilities are provided.
(5)
Outlet Control Structures. Outlet control shall be accomplished
utilizing (six-inch diameter or six-inch width maximum) perforations
arranged vertically to provide for positive control of stormwater
runoff. Outlet controls shall also provide for modification of the
orifice to a smaller diameter through the use of removable plates.
(6)
Discharge Dispersion. Discharges from piping outlets of stormwater
management facilities shall be provided with a concrete "level spreader"
to convert point discharge back to simulated sheet flow. The length
of the spreader shall be equal to 10 times the outlet pipe diameter
(e.g., an eighteen-inch discharge pipe would require a fifteen-foot-wide
level spreader).
(7)
Any stormwater management facility (i.e., 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, twenty-four-hour design storm at post-development conditions, assuming the principal outlet structure to be clogged. The height of embankment must be set as to provide a minimum one foot of freeboard above the maximum elevation computed for the clogged orifice condition. Should any stormwater management facility require a dam safety permit under PADEP 25 Pa. Code, Chapter 105, the facility shall be designed in accordance with PADEP 25 Pa. Code, Chapter 105, and meet the regulations of PADEP 25 Pa. Code, Chapter 105, concerning dam safety which may be required to pass storms larger than a one-hundred-year event.
(8)
A cutoff trench of impervious material shall be provided within
all basin embankments.
(9)
Where a basin embankment is constructed using fill on an existing
15% or greater slope, the basin must be keyed into the existing grade.
(10)
Fencing. Any aboveground stormwater management detention/retention
facility, that is designed to store at least a two-foot depth of runoff,
shall be subject to the following fencing requirements:
(a)
The stormwater facility must be completely surrounded by a chain-link
fence of not less than four feet in height. Alternative fences and
barriers may be permitted upon request to and approval by the Borough.
(b)
All gates or doors opening through such enclosure shall be equipped
with a self-closing and self-latching device for keeping the gate
or door securely closed at all times, when not in actual use.
(11)
All outlet structures and emergency spillways shall include
a satisfactory means of energy dissipation at its outlet to assure
conveyance and flow without endangering the safety and integrity of
the basin and the downstream drainage area.
(12)
A concentrated discharge of stormwater to an adjacent property
shall be within a natural drainageway or watercourse, or an easement
shall be required.
(13)
Plans for infiltration must show the locations of existing and
proposed septic tank infiltration areas and wells. A minimum twenty-five-foot
separation from on-lot disposal systems (OLDS) infiltration areas,
including replacement areas, is desired and will be evaluated by the
Borough on a case-by-case basis. However, the separation shall not
be less than the PADEP required 10 feet. Infiltration rates shall
be based upon perk and probe tests conducted at the site of the proposed
facility.
[Ord. 2011-12-10, 12/12/2011]
1.
In areas of carbonate geology, a geologist shall certify to the following:
A.
No stormwater management facility will be placed in, over, or immediately
adjacent to the following features:
(1)
Closer than 100 feet from sinkholes.
(2)
Closer than 100 feet from closed depressions.
(3)
Closer than 100 feet from caverns, intermittent lakes, or ephemeral
streams.
(4)
Closer than 50 feet from lineaments in carbonate areas.
(5)
Closer than 50 feet from fracture traces.
(6)
Closer than 25 feet from bedrock pinnacles (surface or subsurface).
B.
Stormwater resulting from regulated activities shall not be discharged
into sinkholes.
C.
If the developer can prove through analysis that the project site is an area underlain by carbonate geology, and such geologic conditions may result in sinkhole formations, then the project site is exempt from recharge requirements as described in § 23-304, Volume Control. However, the project site shall still be required to meet all other standards found in this chapter.
D.
It shall be the developer's responsibility to verify if the
project site is underlain by carbonate geology. The following note
shall be attached to all stormwater management plans and signed and
sealed by the developer's geologist: "I, __________, certify
that the proposed stormwater management facility (circle one) is/is
not underlain by carbonate geology."
E.
Whenever a stormwater management facility will be located in an area
underlain by carbonate geology, a geological evaluation of the proposed
location by a geologist shall be conducted to determine susceptibility
to sinkhole formation. The evaluation may include the use of impermeable
liners to reduce or eliminate the separation distances listed in the
BMP Manual. Additionally, the evaluation shall, at a minimum, address
soil permeability, depth to bedrock, seasonally high groundwater table,
susceptibility for sinkhole formation, suitability of stormwater management
facilities, subgrade stability and maximum infiltration capacity in
depth of water per unit area.
F.
A detailed soils evaluation of the project site shall be performed
to determine the suitability of recharge facilities. The evaluation
shall be performed by a qualified professional and, at a minimum,
address soil permeability, depth to bedrock, susceptibility to sinkhole
formation, and subgrade stability. The general process for designing
the infiltration BMP shall be:
(1)
Site evaluation to determine general areas of suitability for
infiltration practices.
(2)
Provide field test throughout the area proposed for development
to determine appropriate percolation rate and/or hydraulic conductivity.
At least one infiltration test must be included in each soil group,
and at least one infiltration test must be conducted for each five
lots proposed for development. Infiltration tests must be taken at
the location and depth of all proposed infiltration structures.
(3)
Design infiltration structure for required storm volume based
on all available data.
G.
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas such as strip mine or limestone
areas. It is also extremely important that the design professional
evaluate the possibility of groundwater contamination from the proposed
infiltration/recharge facility and recommend a hydrogeologic justification
study be performed if necessary. Whenever a basin will be located
in an area underlain by limestone, a geological evaluation of the
proposed location shall be conducted to determine susceptibility to
sinkhole formations. The design of all facilities over carbonate formations
shall include measures to prevent groundwater contamination and, where
necessary, sinkhole formation. The infiltration requirement in the
high-quality/exceptional-value waters shall be subject to the Department's
Chapter 93 and Antidegradation Regulations. A detailed hydrogeologic
investigation may be required by the Borough, and, where appropriate,
the Borough may require the installation of an impermeable liner in
detention basins.
[Ord. 2011-12-10, 12/12/2011]
1.
As required in § 23-301, Subsection 4, whenever the vegetation and topography are to be disturbed, such activity must be in conformance with PADEP 25 Pa. Code, Chapter 105, Rules and Regulations, Part I, Subpart C, Protection of Natural Resources, Article II, Water Resources, Chapter 102, "Erosion Control," and in accordance with the York County Conservation District.
2.
It is extremely important that strict erosion and sedimentation control
measures be applied surrounding infiltration structures during installation
to prevent the infiltrative surfaces from becoming clogged. Additional
erosion and sedimentation control design standards and criteria must
be applied where infiltration BMPs are proposed and shall include
the following:
A.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase, so as to maintain their
maximum infiltration capacity.
4.
The developer shall demonstrate that the post-development hydrograph flows during the erosion and sedimentation control phase are less than or equal to the predevelopment hydrograph flows to assure the rate and volume of runoff leaving the site is controlled for the two-, five-, and ten-year frequency storms. All calculation methodology shall be in accordance with §§ 23-303 through 23-310.
