A.
For all regulated activities, unless preparation of a SWM site plan is specifically exempted in § 180-15:
B.
All SWM site plans for regulated activities shall include such measures
as necessary to:
(1)
Protect health, safety, and property.
(2)
Meet the water quality goals of this chapter:
(a)
Minimize disturbance to floodplains, wetlands, wooded areas,
and existing vegetation.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of the commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas.
(f)
Minimize soil disturbance and compaction.
(3)
Incorporate the techniques for low-impact development practices described
in the Pennsylvania Stormwater Best Management Practices Manual (BMP
Manual).
C.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without the written notification
of the adjacent property owner(s) by the developer. Copies of all
such notifications shall be included in the SWM site plan submission.
D.
For all regulated activities where erosion and sediment control is
required in accordance with Title 25 of the Pennsylvania Code and
the Clean Streams Law, the SWM site plan shall include the required
erosion and sedimentation control measures. Necessary E&S BMPs
shall be designed in accordance with the Erosion and Sediment Pollution
Control Program Manual (E&S Manual), No. 363-2134-008 (March 2012),
as amended and updated. Approval of the SWM site plan by Abbottstown
Borough shall be conditioned on the applicant obtaining erosion and
sedimentation control approval from the appropriate agency(ies), when
applicable.
E.
For all regulated activities where NPDES permitting is required in
accordance with the Clean Water Act (33 U.S.C. § 1251 et
seq. [1972], as amended), the SWM site plan shall include the information
required in the applicant's NPDES permit application. Approval of
the SWM site plan by Abbottstown Borough shall be conditioned on the
applicant obtaining NPDES permit approval from the appropriate agency(ies),
when applicable.
G.
Special management areas. SWM site plans involving regulated activities
within special management areas shall be prepared in a manner consistent
with the guidance provided in Chapter 7 of the BMP Manual. The SWM
site plan submission shall include design details for Stormwater BMPs
within said special management area.
H.
A SWM site plan may propose that stormwater related to the proposed
regulated activities be accommodated by existing stormwater management
facilities on adjoining or nearby properties provided that the SWM
site plan documents the following.
(1)
The use of the stormwater BMPs located on said adjoining or nearby
property is approved in writing by the owner of the property.
(2)
The stormwater BMPs located on said adjoining or nearby property
are designed in a manner that can accommodate the stormwater management
needs of the regulated activity in a manner consistent with all requirements
of this chapter. The SWM site plan shall include all documentation
necessary for Abbottstown Borough to confirm such compliance.
I.
SWM site plans, once approved by Abbottstown Borough, shall remain
on site throughout the duration of the regulated activity and be available
for review as may be necessary by representatives of Abbottstown Borough.
J.
The design of all stormwater BMPs over karst geology shall include
an evaluation of measures necessary to minimize adverse effects including
hydrogeologic studies if required by the Borough.
K.
Abbottstown Borough may, after consultation with and approval by
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. Abbottstown Borough shall maintain
a record of consultations with DEP pursuant to this subsection.
L.
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 PA DEP 25 Pa. Code Chapter 105 (Water Obstructions and Encroachments), Rules and Regulations of PA DEP. Any approvals or permits issued do not relieve compliance as referenced in § 180-8, Compatibility with other requirements.
M.
The technical standards provided within this chapter are considered
the baseline for design and layout of an SWM plan. Use of other alternative
and innovate designs for controlling stormwater runoff may be permitted
when approved by the Borough Engineer.
N.
All existing stormwater management facilities and agreements shall
continue to be maintained with the intended functionality as designed
and approved.
O.
All work shall be in accordance with the Borough's Construction and
Material Specifications.
A.
A property owner or developer of any regulated activity that meets
the following exemption criteria may be, upon approval from Abbottstown
Borough, exempt from certain stormwater management requirements of
this chapter. However, the property owner or developer shall be subject
to all other requirements of this chapter other than related requirements
for which an exemption or exemptions have been authorized. 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 exemption criteria
shall be cumulatively considered and regulated.
(1)
Regulated activities that involve less than 800 square feet of impervious surface, where the total cumulative impervious added since the adoption date of this chapter is less than 800 square feet, may be exempted from portions of Article III including volume control (§ 180-16) and peak rate control (§ 180-17), and all of Article IV and V of the Abbottstown Borough SWM Ordinance. The applicant shall complete requirements as defined by the simplified approach (see Appendix D).[1]
[1]
Editor's Note: Said appendix is on file in the Borough offices.
(3)
Agricultural activities shall be exempt from the rate control, volume control and SWM site plan preparation and submission requirements of this chapter provided the agricultural activities are performed in accordance with the requirements of 25 Pa. Code 102. Further, such activities shall not be subject to the exemption approval process of § 180-15B of this chapter.
(4)
Forest management and timber operations shall be exempted from the rate control, volume control and SWM site plan preparation and submission requirements of this chapter provided the forest management and timber operations are performed in accordance with the requirements of 25 Pa. Code 102. Further, such activities shall not be subject to the exemption approval process of § 180-15B of this chapter.
(5)
Regulated activities involving domestic gardening for single-family consumption shall be exempted from volume control, rate control, and SWM site plan preparation and submission requirements of this chapter. Further, such activities shall not be subject to the exemption approval process of § 180-15B of this chapter.
(6)
In-kind repair, in-kind replacement, and maintenance of existing surfaces, and structures shall be exempted from volume control, rate control, and SWM site plan preparation and submission requirements of this chapter. Further, such activities shall not be subject to the exemption approval process of § 180-15B of this chapter.
(7)
An area of up to 800 square feet of permeable pavers, permeable pavement, and/or green roofs may be considered as pervious area and may be accounted for as such, when considering exemptions provided in § 180-15A(2) of this chapter. At a minimum, the submittal of a minor stormwater management plan in accordance with Appendix D which is attached hereto and made a part of this chapter[2] will be required for any such projects.
[2]
Editor's Note: Said appendix is on file in the Borough offices.
B.
Authorization of exemptions. Abbottstown Borough shall determine, in accordance with the following requirements and process, whether the proposed regulated activity qualifies for exemption under the requirements as defined by § 180-15A(1).
(1)
The property owner or developer proposing the regulated activity shall submit necessary plans and documents per ordinance requirements based on exemption criteria in § 180-15A(1).
(2)
Upon receipt of the plans and documents required, the Abbottstown
Borough Council or its designee shall either approve or deny the exemption
request. If the exemption request is denied, the Abbottstown Borough
Council or its designee shall direct the property owner or developer
to submit the information required to demonstrate that the proposed
regulated activity complies with the requirements of this chapter
or meets the exemption criteria.
(3)
Exemption request approval shall be at the discretion of the Abbottstown
Borough Council or its designee, and shall be subject to the following:
(a)
Abbottstown Borough may deny any exemption request or suspend
or revoke any approved exemption request at any time for any project
where Abbottstown Borough believes that the proposed regulated activity
poses a threat to public health, safety, property, or the environment.
(b)
Approval of an exemption request does not relieve the property
owner or developer from other applicable requirements of this chapter
or of other Abbottstown Borough ordinance or regulations.
(c)
Abbottstown Borough reserves the right to deny an exemption
request if a drainage problem is known or identified by Abbottstown
Borough to exist or is expected to exist downstream from the proposed
regulated activity.
The low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities. Water volume controls shall be implemented using the Design Storm Method in § 180-16A.
A.
The Design Storm Method (CG-1 in the BMP Manual) may be used for
any size of regulated activity. This method requires detailed modeling
to achieve the following standards.
(1)
The post-development total runoff volume shall not increase for all
storms equal to or less than the two-year twenty-four-hour duration
precipitation.
(2)
For modeling purposes:
(a)
Existing (pre-development), non-forested, pervious areas must
be considered meadow within the regulated activity area unless the
existing land use dictates a lower runoff condition.
(b)
Twenty percent of existing impervious area within the regulated
activity area, when present, shall be considered meadow in the model
for existing conditions.
B.
Infiltration alternative. Where infiltration is not possible due to soil characteristics or is not desirable given other characteristics, water quality control may be proposed as an alternative to strict adherence to the volume control standards of § 180-16 of this chapter. Where water quality control is proposed, the following standards shall be achieved.
(1)
At a minimum, the following documentation shall be provided to justify
the proposal to reduce the infiltration requirements:
(a)
Description of and justification for field infiltration/permeability
testing with respect to the type of test and test locations.
(b)
An interpretive narrative describing existing soils of the site
and their structure as these relate to the interaction between soils
and water characteristics of the site. In addition to providing soil
and soil profile descriptions, this narrative shall identify depth
to seasonal water tables and depth to bedrock and provide a description
of all subsurface elements (restrictive layers, geology, etc.) that
influence the direction and rate of subsurface water movement.
(c)
A qualitative assessment of the site's contribution to annual
aquifer recharge shall be made, along with the identification of any
restrictions or limitations associated with the use of designed infiltration
facilities.
(d)
The provided documentation must be signed and sealed by a qualified
professional.
(2)
Water quality BMPs shall be implemented on all permanent stormwater
discharges from the proposed project site to achieve pollutant removal
efficiencies in accordance with the following table. (Efficiency removal
rating shall be based on a testing specification for particle size
distribution as required per TARP Tier 1 and 2 Protocol Testing. The
minimum design flow shall be based on the peak flow produced from
one inch of rain as calculated.)
|
Required Pollutant Removal Efficiencies for Infiltration Alternatives
| ||
|---|---|---|
|
Pollutant Load
|
Units
|
Required Removal Efficiency
|
|
Total suspended solids (TSS)
|
Pounds
|
85%
|
|
Total phosphorus (TP)
|
Pounds
|
85%
|
|
Total nitrate (NO3)
|
Pounds
|
50%
|
(3)
Design guidance from the most current version of the BMP Manual,
or equivalent resource as pre-coordinated with Abbottstown Borough,
shall be consulted when choosing design criteria for water quality
BMPs.
A.
Post-development discharge rates shall not exceed the pre-development
discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-,
and 100-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
pre-development analysis for one-, two-, five-, ten-, twenty-five-,
fifty-, and 100-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.
B.
For computation of pre-development peak discharge rates:
(1)
Existing (pre-development) pervious areas must be considered meadow
within the regulated activity area, unless the existing land use dictates
a lower runoff condition.
(2)
Twenty percent of existing impervious area within the regulated activity
area, when present, shall be considered meadow in the model for existing
conditions.
C.
The developer shall demonstrate that the flows for the one-, two-,
five-, and ten-year frequency storms peak rates are less than or equal
to pre-development rates during the construction phase.
A.
For the purposes of the Act 167 Stormwater Management (Plan) elements
and this chapter, design policy pertaining to stormwater management
facilities for Pennsylvania Department of Transportation (PennDOT)
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
Resources (DEP). As stated in DM-2.13.7.D (Act 167 and Municipal Ordinances),
PennDOT 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.
B.
Where standards in the Act 167 Ordinance are impractical, PennDOT
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 Plan
elements.
C.
For the purposes of the Act 167 Ordinance, road maintenance activities
are regulated under 25 Pa. Code Chapter 102.
A.
Off-site areas. Off-site areas proposed to 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. When conditions as described above are encountered, separate
analysis for developed and off-site areas shall be made for comparison
purposes.
B.
On-site areas. On-site areas proposed to remain outside a regulated
activity area shall be considered as existing conditions, without
considering any reductions in cover type. When conditions as described
above are encountered, separate analysis for these areas shall be
made for comparison purposes.
C.
Downstream hydraulic capacity analysis. Any existing downstream hydraulic
capacity analysis shall be conducted in accordance with this chapter.
(1)
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, manmade or
natural swales and open channels, pipes, inlets, culverts, bridges
and roadways.
(2)
If any private facility is found to be undersized, the applicant
shall be responsible for updating the facility in coordination with
the regulated activity and appropriate municipal representation.
D.
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.
E.
Capacity improvements of local drainage networks. In certain instances,
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 can 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 this chapter. 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.
F.
Capacity improvements may be provided as necessary to implement any
regional or subregional detention alternatives.
G.
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.
(1)
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).
(2)
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.
H.
Roof drains and sump pumps shall discharge to lawns, infiltration
or vegetative BMPs, or pervious areas wherever/whenever possible.
If the above discharge criteria cannot be met or when it is more advantageous
to connect directly to streets, storm sewers or other stabilized conveyance
designations, then the discharge will be permitted on a case by case
basis by Oxford Township. All discharges shall be conveyed in a manner
as to not cause water problems on adjoining property owners.
I.
Subsurface detention facilities shall provide adequately designed
pretreatment for removal of pollutants, oil, trash and debris. Appropriate
supporting information shall be provided for all proposed devices.
All subsurface facilities shall be designed such that access for inspection
and cleaning of the facility can occur.
J.
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 centerline of the roadway.
K.
Manholes, inlets, headwalls, and endwalls shall conform to the requirements
of the PennDOT Publication 408, as modified by the adopted Borough
Standards.
L.
Design standards. Permanent detention and retention facilities shall
be designed to meet the following standards:
(1)
The maximum permitted depth for dry 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 four horizontal to one 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)
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 100-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 PA DEP 25 Pa.
Code Chapter 105, the facility shall be designed in accordance with
PA DEP 25 Pa. Code Chapter 105 and meet the regulations of PA DEP
25 Pa. Code Chapter 105 concerning dam safety which may be required
to pass storms larger than 100-year event.
(6)
A cutoff trench of impervious material shall be provided within all
basin embankments.
(7)
Where a basin embankment is constructed using fill on an existing
15% or greater slope, the basin must be keyed into the existing grade.
(8)
Fencing. Any above-ground 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)
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.
(9)
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.
(10)
A concentrated discharge of stormwater to an adjacent property
shall be within a natural drainage way or watercourse, or an easement
shall be required.
(11)
All facilities shall be provided with an access slope at no
more than 5:1 along with an access easement.
(12)
Plans for infiltration must show the locations of existing and
proposed septic tank infiltration areas and wells. A minimum ten-foot
separation from on-lot disposal systems (OLDS) infiltration areas,
including replacement areas, is required; however, 25 feet is desirable.
Infiltration rates shall be based upon perc and probe tests conducted
at the site of the proposed facility.
(13)
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.
M.
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.) Where extended detention facilities
are utilized to mitigate increased volume, the increased volume is
required to be detained not less than 24 hours from the end of the
twenty-four-hour design storm (assuming the peak rate occurs at approximately
the twelve-hour time period in the storm).
N.
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 Stormwater Management Act.
O.
Design for BMPs shall be in accordance with design standards as listed
in the BMP Manual or other legitimate source.
P.
Existing (pre-development) pervious areas must be considered meadow
within the regulated area, unless the existing land use dictates a
lower runoff condition.
Q.
Infiltration BMPs shall be spread out such that impervious to BMP
loading ratios are less than or equal to 5:1, 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.
R.
Impervious area.
(1)
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.
(2)
For development taking place in phases, the total proposed impervious
for all phases must be used in determining conformance with this chapter.
(3)
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 § 180-16 and the peak rate controls of § 180-17 do not need to be considered for existing impervious areas that are not being altered by the proposed regulated activity.
(4)
Twenty percent of existing impervious area within the regulated area,
when present, shall be considered meadow in the model for existing
conditions.
S.
Infiltration BMPs shall be designed in the following manner. 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, seasonally high groundwater table, suitability of stormwater
management facilities and maximum infiltration capacity in depth of
water per unit area. 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 facility for required storm volume based on all
available data.
(4)
The infiltration requirement in the high quality/exceptional waters
shall be subject to the Department's Chapter 93 and anti-degradation
regulations.
(5)
A double ring infiltrometer test shall be used for all infiltration
tests in accordance with the current edition of the BMP Manual.
T.
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
municipality on a case-by-case basis. However, the separation shall
not be less than the PADEP-required 10 feet.
A.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
B.
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 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 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 PA DEP.
C.
Any stormwater management facility located within the vicinity of
a floodplain shall be subject to approval in accordance with PA DEP
25 Pa. Code Chapter 106 (Floodplain Management) of PA DEP's Rules
and Regulations.
D.
All earthmoving activities must be reviewed and approved by the Adams
County Conservation District prior to commencing work.
E.
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.
F.
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.
G.
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.
H.
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.
I.
When it can be shown that, due to topographic conditions, natural
conveyance facilities 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 conveyance
facilities shall be subject to approval by PA DEP through the joint
permit application process, or, where deemed appropriate by PA DEP,
through the general permit process.
J.
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 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 to one. 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.
Stormwater runoff hydrographs/peak rates shall be calculated in the
following manner:
(1)
For the purpose of considering peak flows with a fully developed
runoff hydrograph, the Soil Cover Complex Method-TR-20 or TR-55 and
a twenty-four-hour rainfall event shall be used with the appropriate
design rainfall depths. A dynamic or interconnected model is required
for modeling of multiple drainage or sub-areas. The SCS Rainfall Type
II curve or local precipitation frequency data shall be used for the
rainfall distribution. The Borough may allow the use of other methodologies
on a case-by-case basis as approved prior to design submittal.
(2)
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).
(3)
The design storm volumes to be used in the analysis of peak rates
of discharge shall be obtained from the Precipitation-Frequency Atlas
of the United States, Atlas 14, Volume 2, Version 3.0, as amended
and updated, U.S. Department of Commerce, National Oceanic and Atmospheric
Administration (NOAA), National Weather Service, Hydro meteorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 can
be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
(5)
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.
B.
Conveyance facilities shall be designed in the following manner:
(1)
All storm drain systems, 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.
(a)
When a pipe or culvert is intended to convey to or pass the
discharge from a stormwater management facility, its required capacity
shall be computed using the methodology considered for the stormwater
management facility design as part of a dynamic model.
(b)
Greater design frequencies may be justified on individual projects.
(c)
A 100-year storm frequency may be required for design of the
stormwater collection system to insure that the resultant stormwater
runoff from the postdevelopment storm is directed into the management
facility.
(d)
If the Rational Method is used for calculating peak flows, conveyance
facilities 30 inches diameter or less shall use a time of concentration
of five minutes for the contributing drainage area shall be considered
for the design.
(2)
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 four
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%.
(3)
The Rational Method may be used for stormwater collection and conveyance
facilities provided the facilities are part of an integrated SWM facility
requiring modeling using SCS Modeling. Rainfall intensities shall
be consistent with appropriate times-of-concentration and return periods.
(5)
Existing and proposed channels or swales must be able to convey the
increased runoff associated with a proposed 100-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 PA DEP Erosion and Sediment Pollution
Control Program Manual.
(6)
Existing natural or man-made channels or swales must be able to convey
proposed 100-year return period runoff without creating any hazard
to persons or property.
(7)
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.
(8)
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 a culvert shall be 18 inches.
The procedure contained in Hydraulic Engineer Circulars No. 5 and
No. 13, as prepared by the U. S. 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.
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 § 180-16, Volume controls. 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 qualified licensed professional shall be conducted to
determine susceptibility to sinkhole formation and the possibility
of groundwater contamination from the facility.
Where an applicant proposes to utilize riparian buffers as the
means to meet the requirements of this chapter, said riparian buffers
shall be established and/or maintained in accordance with the BMP
Manual or the publication Riparian Forest Buffer Guidance, published
November 2010 by the Pennsylvania Department of Environmental Protection,
and as may be amended or updated.
A.
Any drain or conveyance, whether on the surface or subsurface, that
allows any non-stormwater discharge including sewage, process wastewater,
and wash water to enter the waters of the commonwealth is prohibited.
B.
No person shall allow, or cause to allow, discharges into surface waters of the commonwealth which are not composed entirely of stormwater, except (1) as provided in Subsection C below and (2) discharges allowed under a state or federal permit.
C.
The following discharges are authorized unless they are determined
to be significant contributors to pollution to the waters of the commonwealth:
(1)
Discharges from firefighting activities.
(2)
Potable water sources including water line flushing.
(3)
Irrigation drainage.
(4)
Air conditioning condensate.
(5)
Springs.
(6)
Water from crawl space pumps.
(7)
Pavement wash waters where spills or leaks of toxic or hazardous
materials have not occurred (unless all spill material has been removed)
and where detergents are not used.
(8)
Diverted stream flows.
(9)
Flows from riparian habitats and wetlands.
(10)
Uncontaminated water from foundations or from footing drains.
(11)
Lawn watering.
(12)
De-chlorinated swimming pool discharges.
(13)
Uncontaminated groundwater.
(14)
Water from individual residential car washing.
(15)
Routine external building wash-down (which does not use detergents
or other compounds).
(16)
Water discharged in well testing for potable water supplies.
No person shall modify, remove, fill, landscape, or alter any
stormwater BMPs, facilities, areas, or structures in a manner, without
the written approval of Abbottstown Borough, with the exception of
necessary maintenance activities such as mowing.
