A.
Regulated activities are subject to the following permitting requirements:
(1)
Regulated activities that propose up to 2,000 square feet of
new impervious area qualify for utilization of the small projects
guide contained within this chapter. See Appendix D.[1]
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
(2)
Regulated activities that propose greater than 2,000 square feet of new impervious area shall be required to submit a stormwater management plan that meets the requirements set forth in § 173-401.
(3)
No regulated activities shall commence until the Borough issues
written approval of an SWM site plan or other applicable authorization
which demonstrates compliance with the requirements of this chapter.
B.
SWM site plans approved by the Borough, in accordance with § 173-406, shall be on site throughout the duration of the regulated activity.
C.
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.[2] The Borough shall maintain a record of consultations with
DEP pursuant to this subsection. Where the Borough identifies a potential
water quality issue raised by an application or project, the application
or project information will be forwarded to DEP for consultation,
along with the proposed Borough decision on the application or project.
If the Borough does not receive a response from DEP within 15 days
from DEP's receipt of such information, the Borough will issue its
decision to the application noting that the DEP has not responded
to the request. DEP is not required to be consulted for waiver of
the within requirements: stormwater management districts; design criteria;
regulations governing stormwater management facilities; calculation
methodology; carbonate geology; erosion and sedimentation control
requirements; municipal stormwater maintenance fund; and stormwater
service fees.
[2]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
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.[3] Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual),[4] No. 363-2134-008 (April 15, 2000), as amended and updated.
F.
Impervious areas:
(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 entire development
plan 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 § 173-304 and the peak rate controls of § 173-305 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity. An existing impervious area is considered to be altered when it is physically changed by the proposed regulated activity except that maintenance work of an existing impervious surface (i.e., repaving, reroofing, etc.) shall not be considered alteration.
G.
Stormwater flow(s) 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.
H.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this chapter, as stated in § 173-103, Purpose, by implementing measures to:
(a)
Minimize disturbance to floodplains, wetlands, wooded areas,
and existing vegetation.
(b)
Maintain, enhance, expand, or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(f)
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.)
(3)
To the maximum extent practicable, incorporate the techniques
for low-impact development practices (LIDP) described in the Pennsylvania
Stormwater Best Management Practices Manual (BMP Manual). If methods
other than green infrastructure and LIDP are proposed to achieve the
volume and rate controls required under this chapter, the stormwater
site plan must include a detailed justification demonstrating the
use of the LIDP and green infrastructure is not practicable.
I.
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.
J.
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.
K.
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 25 Pa. Code, Chapter 105 (Water Obstructions and Encroachments). Any approvals or permits issued do not relieve compliance as referenced in § 173-108, Compatibility with other requirements.
L.
All stormwater management facilities (excluding individual residential
underground infiltration facilities) are considered "structures" under
local ordinances and must comply with applicable 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 compliance point applied to meet the setback requirements.
Individual residential underground infiltration facilities shall be
a minimum of 10 feet from the nearest property line. Discharge of
controlled flows can be no closer to an adjacent property than two
times the length of the required discharge rip-rap apron. This requirement
applies to discharge aprons that do not outlet to a defined waterway
or an existing storm sewer.
M.
Normally dry, open-top storage facilities, designed as such, 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.)
N.
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, U.S. 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/.
O.
P.
Various BMPs and their design standards are listed in the BMP Manual.
Q.
All work performed under this chapter shall also comply with the
Borough's construction and material specifications.
R.
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.
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 propose less than 500 square feet of additional
impervious area ("small project") may be fully exempt from the requirements
of this chapter and a fee paid in lieu thereof to the Borough. Refer
to Appendix D,[1] hereto to determine the requirements for exempt small
projects.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
B.
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.
C.
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.
D.
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.
E.
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.
F.
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 all the activities
comply with all other applicable ordinances and statutes.
H.
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.
B.
Description of stormwater management districts. Two types of stormwater
management districts may be applicable to Dallastown Borough, namely
the "release rate districts" and "provisional no detention districts,"
as described below:
(1)
Release rate districts. Release rate districts ("district")
differ in the extent to which postdevelopment runoff must be controlled.
Within a given district, the postdevelopment 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 properties
and watershed areas.
(2)
Provisional no detention districts. These watershed areas may discharge postdevelopment peak runoff without detention and 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 100% release rate control or provide increased capacity of downstream drainage elements to convey increased peak flows consistent with § 173-307D. 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 § 173-307F.
(3)
When a regulated activity 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 § 173-304 will be required.
|
Codorus - District 1
| ||
|---|---|---|
|
District ID
|
Regulated Storm Frequency
|
Percentage of Predeveloped Peak Flow Rate to Determine Allowable
Postdeveloped Release Rate
|
|
District 1
|
2
|
100% 2-year
|
|
District 1
|
5
|
100% 5-year
|
|
District 1
|
10
|
100% 10-year
|
|
District 1
|
25
|
100% 25-year
|
|
District 1
|
50
|
100% 50-year
|
|
District 1
|
100
|
100% 100-year
|
|
East Branch - District 2
| ||
|---|---|---|
|
District ID
|
Regulated Storm Frequency
|
Percentage of Predeveloped Peak Flow Rate to Determine Allowable
Postdeveloped Release Rate
|
|
District 2
|
2
|
100% 2-year
|
|
District 2
|
5
|
100% 5-year
|
|
District 2
|
10
|
100% 10-year
|
|
District 2
|
25
|
100% 25-year
|
|
District 2
|
50
|
100% 50-year
|
|
District 2
|
100
|
100% 100-year
|
|
*
|
The intention of this table is to reduce the runoff rate.
|
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 A or the Simplified Method in Subsection
B 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 postdevelopment 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.
A.
For computation of predevelopment peak discharge rates, 20% of the
existing impervious area of a project site, when present, shall be
considered meadow.
B.
Postdevelopment discharge rates shall not exceed the predevelopment
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 postdevelopment 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 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.
A.
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 Resources
(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.
B.
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 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.
C.
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.
A.
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.
B.
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.
C.
Downstream hydraulic capacity analysis. Any existing downstream hydraulic
capacity analysis shall be conducted in accordance with this chapter.
(1)
All downstream stormwater management facilities impacted by
the regulated activity shall be studied to determine if the stormwater
management facility has adequate capacity to handle existing and proposed
flows. An impacted downstream stormwater management facility is one
to which the runoff from the regulated activity comprises more than
50% of the total flow to such a stormwater management facility. The
study shall end at a perennial stream. Downstream stormwater management
facilities include, but are not limited to, man-made or natural swales
and open channels, pipes, inlets, culverts, bridges and roadways.
(2)
If any private stormwater management facility is found to be
undersized, the applicant shall be responsible for upgrading the stormwater
management facility concurrent with the regulated activity, if approved
by the private SMF owner.
(3)
If any publically owned stormwater management facility is found
to be undersized or inadequate, the applicant shall work with the
Borough to upgrade the stormwater management facility concurrent with
the regulated activity, if approved by the Borough.
D.
Regional detention alternatives. For certain areas within the study
area, it may be more cost-effective to provide one stormwater management
facility for more than one development site than to provide an individual
stormwater management facility for each development site. The initiative
and funding for any regional runoff control alternatives is the responsibility
of the applicant. The design of any regional control facilities 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.
E.
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 § 173-308. 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.
F.
Capacity improvements may also 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 design of the regulated activity, safeguards
shall be incorporated into the site design.
(1)
For industrial or commercial sites where it is possible that
toxic or hazardous substances may come into contact with runoff, pretreatment
of the first-flush (first 1/2 inch) volume 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 public stormwater management facility(ies).
(2)
Infiltration systems may be used to handle runoff from commercial
or industrial storage, working or parking areas only after the first-flush
stormwater from these areas has been pretreatedi for removal of hazardous
substances.
H.
Roof drains and sump pumps shall discharge to infiltration or vegetative
BMPs and to the maximum extent practicable satisfy the criteria for
DIAs.
I.
Design standards, water-carrying facilities.
(1)
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.
(a)
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
management facility for the 100-year storm. The greater flow shall
govern the design of the pipe or culvert.
(b)
When a pipe is part of a storm drain 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.
(c)
Greater design frequencies may be justified on individual projects.
(d)
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 stormwater
management facility.
(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 PennDOT, is
not less than 65%.
(3)
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.
(4)
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 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.
(5)
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-fourth-inch diameter stainless steel anchors. Guards shall
also be provided for any pipe opening, 18 inches in diameter or larger.
(6)
Manholes, inlets, headwalls, and endwalls shall conform to the
requirements of the PennDOT Publication 408, as modified by the adopted
Borough standards.
(7)
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 DEP Erosion and Sediment Pollution Control Program Manual.
(8)
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, public safety, or property.
(9)
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."
J.
Design standards, detention and retention basins.
(1)
Permanent detention and retention basins shall be designed to
meet the following standards:
(a)
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.
(b)
The minimum top width of all basin embankments shall be eight
feet.
(c)
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.
(d)
Minimum bottom slope. All detention basins shall have a minimum
bottom slope of 2% unless infiltration facilities are provided.
(e)
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.
(f)
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).
(g)
Any stormwater management facility (i.e., detention basin) designed
to store runoff and requiring a berm or earthen embankment shall be
designed to provide an emergency spillway to handle flow up to and
including the 100-year, twenty-four-hour design storm at postdevelopment
conditions, assuming the principal outlet structure to be clogged.
The height of the 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 permit under 25 Pa. Code Chapter 105, the facility shall comply
with 25 Pa. Code Chapter 105, which may require the structure to handle
storms larger than 100-year event.
(h)
A cutoff trench of impervious material shall be provided within
all detention basin embankments.
(i)
Where a detention basin embankment is constructed using fill
on an existing 15% or greater slope, the basin must be keyed into
the existing grade.
(j)
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:
[1]
The stormwater management 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.
[2]
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.
(k)
All outlet structures and emergency spillways shall include
a satisfactory means of energy dissipation at the outlet to assure
conveyance and flow without endangering the safety and integrity of
the basin and the downstream drainage area.
(l)
A concentrated discharge of stormwater to an adjacent property
shall be within a natural drainageway or watercourse, or an easement
shall be required.
(m)
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 DEP-required 10 feet. Infiltration rates shall be
based upon perc and probe tests conducted at the location of the proposed
facility.
A.
Any stormwater management 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 a water of the commonwealth or
wetlands shall be subject to approval by DEP where required by 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 DEP.
C.
Any stormwater management facility located within the vicinity of
a floodplain shall be subject to approval in accordance with 25 Pa.
Code Chapter 106 (Floodplain Management).
D.
All earth disturbance activities must be reviewed and approved by
the York County Conservation District prior to commencing work.
E.
The design of all stormwater management facilities shall incorporate
good engineering principles and practices. The Borough reserves 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 stormwater 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
drainageways on the project 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 DEP through the joint permit application
process, or, where deemed appropriate by DEP, through the general
permit process.
J.
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 Dallastown Borough.
K.
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 or high quality shall be maintained as defined in 25 Pa. Code Chapter 93 (Water Quality Standards). BMPs and stormwater conveyance systems are to be used and designed to address and control temperature 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 of pond shorelines shall be planted with shade or canopy trees within 10 feet of a pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is 10 to 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.
Stormwater runoff from a development site shall be calculated using
the Rational Method, Modified Rational Method, or a Soil Cover Complex
Method.
B.
Any stormwater runoff calculations involving drainage areas greater
than 200 acres, including on- and off-site areas, shall use 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 development site.
C.
Dallastown 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.
D.
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.
E.
For the purposes of the 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 it Tables 1 and 2, respectively.[1]
[1]
Editor's Note: Said tables are included as attachments to this chapter.
F.
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.
G.
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.[2]
[2]
Editor's Note: Said table is included as an attachment to this chapter.
H.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table 2.[3]
[3]
Editor's Note: Said table is included as an attachment to this chapter.
I.
Where uniform flow is anticipated, Manning's 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.[4]
[4]
Editor's Note: Said table is included as an attachment to this chapter.
J.
The design of any stormwater detention facility 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.
K.
The stormwater collection system shall be designed using the peak
discharge computed using the rational formula.
A.
In areas of carbonate geology, a geologist shall certify to the following:
(1)
No stormwater management facility will be placed in, over, or
immediately adjacent to the following features:
(a)
Closer than 100 feet from sinkholes.
(b)
Closer than 100 feet from closed depressions.
(c)
Closer than 100 feet from caverns, intermittent lakes, or ephemeral
streams.
(d)
Closer than 50 feet from lineaments in carbonate areas.
(e)
Closer than 50 feet from fracture traces.
(f)
Closer than 25 feet from bedrock pinnacles (surface or subsurface).
(2)
Stormwater resulting from regulated activities shall not be
discharged into sinkholes.
(3)
If a 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 § 173-304, Volume control. However, the project site shall still be required to meet all other standards contained in this chapter.
(4)
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."
(5)
Whenever a stormwater management facility will be located in
an area underlain by carbonate geology, a technical 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 technical 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.
(6)
A detailed soils evaluation of the project site shall be performed
to determine the suitability of infiltration structures. 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:
(a)
Site evaluation to determine general areas of suitability for
infiltration structures.
(b)
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.
(c)
Design the infiltration structure(s) for required storm volume
based on all available data.
(7)
Extreme caution shall be exercised where infiltration is proposed in areas prone to undermining 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 sinkholes. The design of all stormwater facilities over carbonate formations shall include measures to prevent groundwater contamination and, where necessary, sinkhole formation. Infiltration in the high quality and exceptional value waters are subject to the requirements of 25 Pa. Code Chapter 93, and antidegradation regulations. A detailed hydrogeologic investigation may be required by Dallastown Borough and, where appropriate, the Borough may require the installation of an impermeable liner in detention basins.
A.
As required in § 173-301D, whenever the vegetation and topography are to be disturbed, such activity must be in conformance with 25 Pa. Code Chapter 105, Part I, Subpart C (Protection of Natural Resources), and 25 Pa. Code Chapter 102 ("Erosion Control"), which may require review and/or approval of erosion and sedimentation control plans by the York County Conservation District.
B.
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 structure BMPs are proposed, specifically
including areas proposed for infiltration BMPs. These areas shall
be protected from sedimentation and compaction during the construction
phase, so as to maintain their maximum infiltration capacity.
C.
Fencing for sedimentation basins or traps must comply with § 173-307J(1)(j).
D.
The developer shall demonstrate that the postdevelopment hydrograph flows during the construction phase are less than or equal to the predevelopment hydrograph flows to assure the rate and volume of runoff leaving the project site is controlled for the two-, five-, and ten-year frequency storms. All calculation methodology shall be in accordance with §§ 173-303 through 173-310 of this chapter.
A.
In order to protect and improve water quality, a riparian buffer
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian buffer.
C.
Minimum management requirements for riparian buffers.
(1)
Existing native vegetation shall be protected and maintained
within the riparian buffer easement.
(2)
Whenever practicable invasive vegetation shall be actively removed,
and the riparian buffer easement shall be planted with native trees,
shrubs, and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
D.
The riparian buffer easement shall be enforceable by the municipality
and shall be recorded in the Office of the Recorder of Deeds in and
for York County, Pennsylvania, so that it shall run with the land
and shall limit the use of the property located therein. The easement
shall allow for the continued private ownership and shall count toward
the minimum lot area required by zoning unless otherwise specified
in the municipal Zoning Ordinance.[2]
E.
Any permitted use within the riparian buffer easement shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
G.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
