Easements and rights-of-way for sanitary sewer facilities, stormwater
drainage facilities, public utilities or pedestrian access shall meet
the following standards:
A. To the fullest extent possible, easements shall be adjacent to property
lines.
B. Nothing shall be placed, planted, set or put within the area of an
easement that would adversely affect the function of the easement
or conflict with the easement agreement. This requirement shall be
noted on the final plan and shall be included in all deeds for lots
which contain an easement.
C. Pedestrian walkways shall have a minimum right-of-way width of 10 feet and contain sidewalk in accordance with §
265-40B of this article.
D. Utility easements shall have a minimum width of 20 feet and all utility
companies are encouraged to use common easements. Plans shall include,
by reference or detailed description, provisions to ensure compliance
with all authority or utility company restrictions.
E. The applicant shall reserve easements where stormwater or surface
water drainage facilities are existing or proposed, whether located
within or beyond the boundaries of the property. Easements shall have
a minimum width of 20 feet and shall be adequately designed to provide
area for: 1) the collection and discharge of water; 2) the maintenance,
repair and reconstruction of the drainage facilities; and 3) the passage
of machinery for such work. The easements shall clearly identify who
has the right-of-access and responsibility of maintenance. This requirement
shall be noted on the final plan and shall be included in all deeds
for lots which contain an easement.
F. Where any petroleum or petroleum product transmission line traverses
a subdivision or land development, the applicant shall confer with
the applicable transmission or distribution company to determine the
minimum distance which shall be required between each structure and
the center line of such petroleum or petroleum product transmission
line. Additionally, the Borough will require, with the final plan
application, a letter from the owner of the transmission line stating
any conditions on the use of the tract which shall contain the above.
G. Where a subdivision or land development is adjacent to or traversed
by a watercourse, drainageway, channel or stream, there shall be provided
a drainage easement conforming substantially with the line of such
watercourse, drainageway, channel or stream of such width as will
be adequate to preserve the unimpeded flow from a one-hundred-year
design rainfall.
H. When a subdivision proposes multifamily attached dwellings, such
as townhouses, the plans shall include an access easement along the
front and rear property lines of all units and the side property lines
of the end units, to allow all lot owners within the unit access to
front and rear yards. The access easement shall have a minimum width
of six feet. This requirement shall be noted on the final plan and
shall be included in all deeds for lots which contain the easement.
All stormwater management, collection, conveyance, erosion control,
and floodplain considerations shall be accomplished in accordance
with the following provisions:
A. General requirements.
(1) In the interest of: a) reducing the total area of impervious surface;
b) preserving existing features which are critical to stormwater management;
and c) reducing the concentration of stormwater flow, the design should
consider alternate design concepts and the flexibility provided by
the waiver process.
(2) Maximum use should be made of the existing on-site natural and man-made
stormwater management facilities.
(3) At the discretion of the Borough Engineer, the applicant shall submit
all stormwater design and analysis calculations on a computer diskette
for verification of those calculations by the Borough.
(4) Innovative stormwater management and recharge facilities shall be
used whenever and wherever feasible or necessary to protect adjoining
properties, to control the volume of water leaving the site, to remove
pollutants from runoff leaving the site or to provide for recharge
of groundwater supplies. Such facilities may include rooftop storage,
dry wells, cisterns, diversion structures, aeration of lawns, holding
tanks, infiltration systems, stream channel storage, in-line storage
in storm sewers, and grading patterns. Applications including such
facilities shall be accompanied by detailed engineering plans and
performance capabilities for review by the Borough.
(5) Post-development rates of runoff from any regulated activity shall not exceed 50% of the peak rates of runoff prior to development for all design storms (two-, five-, ten-, twenty-five-, fifty- and one-hundred-year storm events) unless the preexisting hydrograph is not exceeded at all points in time [see §
265-45H(1)].
[Amended 11-4-2003 by Ord. No. 310; 8-1-2006 by Ord. No. 329]
B. General design requirements.
(1) All stormwater management plans shall be designed and certified by
individuals registered in the Commonwealth of Pennsylvania and qualified
to perform such duties.
(2) All stormwater runoff flowing over the project site shall be considered
in the design of the stormwater management facilities.
(3) Stormwater management facilities located within or affecting the floodplain of any watercourse shall also be subject to the requirements of the Adamstown Borough Zoning Ordinance (Chapter
320), as amended or any future ordinances, regulating construction and development within areas of the Borough subject to flooding.
(4) Stormwater runoff from a project site shall flow directly into a
natural watercourse or into an existing storm sewer system. If neither
of these is available, the applicant shall obtain an easement from
the downstream landowner to allow the runoff discharge from the ten-year
storm to be properly conveyed to a natural watercourse or existing
storm sewer system. Where the downstream owner will not grant such
an easement, the runoff from the applicant's site shall flow
onto the adjacent property in a manner similar to the runoff characteristics
of the predevelopment flow. Where such an easement is granted, the
twenty-five- through one-hundred-year discharge from the basin shall
flow onto the adjacent property in a manner similar to the runoff
characteristics of the predevelopment flow.
(5) Stormwater management facilities shall be provided so that the peak rates of runoff for stormwater originating on the project site must meet the following conditions for all watersheds [as defined by §
265-45B(10)] within the site:
(a)
The two-, ten-, twenty-five-, fifty- and one-hundred-year post-development
peak flow must be less than or equal to the calculated two-, ten-,
twenty-five-, fifty- and one-hundred-year predevelopment peak flow,
respectively.
(6) Stormwater management facilities shall be supplemented by BMPs as outlined in the Adamstown Borough BMP Design Standards, §
265-45G. Required storage volume shall be provided to minimize the impacts to water quality of receiving waters.
(7) Runoff calculations for the predevelopment and post-development comparison
shall consider five different storm frequencies (two-, ten-, twenty-five-,
fifty- and one-hundred-year storm events).
(8) When plan applications are submitted in sections, and if temporary
facilities are required for construction of a section, such facilities
shall be included in the submitted plans. In the event temporary measures
cannot adequately handle the stormwater runoff, the main outfall line
shall be included as part of the construction of the proposed section.
(9) Consideration shall be given to the relationship of the subject property
to the drainage pattern of the watershed.
(10)
Stormwater shall not be transferred from one watershed to another,
unless: a) the watersheds are subwatersheds of a common watershed
which join together within the perimeter of the property; or b) the
effect of the transfer does not alter the peak discharge onto adjacent
lands.
(11)
A concentrated discharge of stormwater to an adjacent property
shall be within an existing watercourse or enclosed in an easement.
(12)
If the parent tract is located in areas of carbonate geology,
a registered professional geologist shall certify the following:
[Added 11-4-2003 by Ord.
No. 310; amended 8-1-2006 by Ord. No. 329]
(a)
No stormwater facilities shall be placed in, over or immediately
adjacent to the following features: sinkholes, closed depressions,
lineaments in carbonate areas, fracture traces, caverns, intermittent
streams, ephemeral streams, bedrock pinnacles (surface or subsurface).
It shall be the developer's responsibility to verify if the development
site is underlain by carbonate geology. Whenever a stormwater facility
will be located in an area underlain by carbonate geology, a geological
evaluation of the proposed location by a registered professional geologist
shall be conducted to determine susceptibility to sinkhole formation.
The developer shall include the following note on the stormwater management
plans which shall be signed and sealed by the developer's professional
geologist: "I, ____________________, certify that the proposed detention
basin (circle one) is/is not underlain by carbonate geology."
(b)
Stormwater management basins shall not be located closer than
100 feet from the rim of sinkholes or closed depressions, nor within
100 feet from disappearing streams; nor shall these basins be located
closer than 50 feet from lineaments or fracture traces; nor shall
these basins be located closer than 25 feet from surface or identified
subsurface pinnacles.
(c)
Stormwater resulting from land development activities shall
not be discharged into sinkholes.
C. Methods for calculation of runoff.
(1) Runoff calculations for on-site stormwater facilities shall be based
upon the following methods:
(a)
Rational Method. This method is recommended and preferred for
design of all collection, conveyance and retention facilities when
drainage areas are less than 1.5 square miles or where times of concentration
are less than 60 minutes.
(b)
SCS TR-55 tabular hydrograph method (1986, or latest revision).
This method is recommended and preferred for design of conveyance
and retention facilities when drainage areas are greater than 1.5
square miles.
(c)
Any other method must be approved by the Borough.
(2) Criteria and assumptions to be used in the determination of stormwater
runoff and design of stormwater management facilities are as follows:
[Amended 11-4-2003 by Ord. No. 310]
(a)
Runoff coefficients shall be based on the land use coefficients
listed in Appendixes No. 27 and 28 of this chapter and in conjunction with the criteria outlined by §
265-45C(3) of this chapter.
(b)
Times of concentration shall be based on the following design
parameters:
[1]
Overland flow. The maximum length of overland flow before shallow
concentrated swale and/or channel flow develops is 150 feet. The nomograph
in Appendix No. 29 shall be used for determination of the times of
concentration. Sheet flow may be determined using the nomograph in
Appendix No. 29 or the Manning's kinematic solution shown in
the sheet flow section of Worksheet No. 1 in Appendix No. 37.
[2]
Concentrated flows. At points where shallow concentrated flows
concentrate in field depressions, swales, gutters, curbs or pipe collection
systems, the time of concentration between these design points shall
be based upon Manning's Equation and/or acceptable engineering
design standards as determined by the Borough Engineer. Manning "n"
values used for design of pipes and culverts shall be in accordance
with Appendix No. 39. Travel time for shallow concentrated flow shall
be determined using Figure 3-1 from TR-55, Urban Hydrology for Small
Watersheds, as shown in Appendix No. 38.
(c)
If the Rational Method is used, the Rainfall Intensity Duration-Frequency
Chart shown in Appendix No. 26 shall be used to compute the rainfall intensities.
(d)
If the Soil-Cover-Complex Method is used, stormwater runoff
shall be based on the following twenty-four-hour storm events:
|
Storm Event
|
Inches of Rainfall
|
---|
|
2 years
|
3.1
|
|
5 years
|
4.1
|
|
10 years
|
5.0
|
|
25 years
|
5.5
|
|
50 years
|
6.2
|
|
100 years
|
7.0
|
(e)
Use of other criteria, assumptions, references, calculation
methods, and/or computer modeling may be utilized, provided detailed
design information and programming with references are submitted and
approved by the Borough.
(f)
Runoff calculations shall include a hydrologic and hydraulic
analysis indicating volume and velocities of flow and the grades,
sizes and capacities of water-carrying structures, sediment basins,
retention and detention structures and sufficient design information
to construct such facilities. Runoff calculations shall also indicate
both predevelopment and post-development rates for peak discharge
of stormwater runoff from the development site.
(3) For the purpose of determining predevelopment and post-development
runoff coefficients, the following criteria shall be used:
(a)
Predevelopment runoff coefficients for all areas within the
site boundaries shall be based on a good grass cover unless portions
of the site contain wooded areas. When the site contains wooded areas,
runoff coefficients shall be based on forest/woodland cover.
(b)
Off-site land use conditions used to determine storm flows for
the predevelopment and post-development comparison shall be based
on existing land uses assuming summer or good conditions.
(c)
Off-site land use conditions used to determine storm flows for
collection and conveyance facilities shall be based on existing land
uses assuming winter or poor conditions.
D. Design standards; detention facilities.
(1) Detention basins shall be designed to safely discharge the peak discharge
of a post-development one-hundred-year frequency storm event through
an emergency spillway in a manner which will not damage the integrity
of the basin. Where applicable, the emergency spillway shall be constructed
in undisturbed ground and not upon the embankment fill material. An
easement shall be provided from the spillway outfall to a natural
or artificial watercourse. Stormwater management control facilities
(i.e., detention and retention basins) shall be provided so that the
peak discharge of the calculated post-development runoff to an adjacent
property does not exceed 50% of the predevelopment peak discharge
for all design storms (two-, five-, ten-, twenty-five-, fifty- and
one-hundred-year storm events).
[Amended 11-4-2003 by Ord. No. 310; 8-1-2006 by Ord. No. 329]
(2) Detention basins and water-carrying facilities shall be stabilized
in accordance with current engineering and United States Natural Resources
Conservation Service practices and the Adamstown Borough BMP Design
Standards.
(3) Detention basins shall be designed and maintained to ensure the design
capacity after sedimentation has taken place.
(4) Basins which are not designed to release stormwater (i.e., retention
basins) shall not be permitted except for basins designed for groundwater
recharge and/or water quality storage. All basins (other than groundwater
recharge and/or water quality storage basins) shall have provisions
for dewatering, particularly the bottom. Low-flow channels and tile
fields may be used to dewater the bottom of a basin. Discharge structures
shall be designed to eliminate the possibility of blockage during
operation. Retention or permanent bond basins shall be allowed only
for groundwater recharge and/or water quality storage purposes or
only when permitted by a waiver granted by Borough Council.
[Amended 11-4-2003 by Ord. No. 310; 8-1-2006 by Ord. No. 329]
(5) Detention basins which are designed with earth-fill dams shall be
structurally sound and shall be constructed of sound and durable materials
and shall incorporate the following minimum standards:
[Amended 11-4-2003 by Ord. No. 310]
(a)
The maximum water depth shall not exceed five feet, unless approved
by waiver from Borough Council.
(b)
The minimum top width of all dams shall be five feet.
(c)
The side slopes of earth-fill dams shall not be less than three
horizontal to one vertical on the downstream side of the embankment.
(d)
Basins without restricted access shall have impoundment areas
with side slopes no greater than five horizontal to one vertical.
Basins with steeper side slopes shall be protected by fencing that
will discourage access.
(e)
A cutoff trench of impervious material shall be provided under
all dams.
(f)
All pipes and culverts through dams shall have properly spaced
concrete cutoff collars or factory-welded anti-seep collars.
(g)
A minimum one foot of freeboard above the maximum design water
surface elevation at the emergency spillway shall be provided. Where
practical, the emergency spillway shall be constructed in undisturbed
ground.
(h)
Minimum floor elevations for all structures that would be affected
by a basin, other temporary impoundments, or open conveyance systems
where ponding may occur shall be two feet above the one-hundred-year
water surface. If basement or underground facilities are proposed,
detailed calculations addressing the effects of stormwater ponding
on the structure and waterproofing and/or floodproofing design information
shall be submitted for approval.
(i)
Soils used for the construction of basins shall have low erodibility
factors.
(6) The effect on downstream areas if the basin embankment fails shall
be considered in the design of all basins. Where possible, the basin
shall be designed to minimize the potential damage caused by such
failure of the embankment.
(7) All groundwater recharge facilities shall be designed to empty in
48 hours subsequent to any storm event. All water quality facilities
shall be designed so that water is released slowly for a minimum of
24 hours subsequent to any storm event. All infiltration, detention
or retention facilities used for stormwater management (pre vs. post)
shall be designed to empty within 24 hours subsequent to any storm
event.
(8) All outlet structures and emergency spillways shall include a satisfactory
means of dissipating the energy of flow at its outlet to ensure conveyance
of flow without endangering the safety and integrity of the basin
and the downslope drainage area.
(9) No outflow from a detention basin shall discharge directly onto or
be conveyed onto a public road but shall discharge into a culvert
under or storm sewer along a public road.
(10)
Appropriate easements to enclose and permit access to all detention
and retention facilities shall be provided.
E. Design standards –collection and conveyance facilities.
(1) All storm sewer pipes, culverts and bridges (excluding detention
and retention basin outfall structures), gutters and swales conveying
water originating only from within the boundaries of the development
site shall be designed for a twenty-five-year storm event. All storm
sewer pipes, culverts and bridges (excluding detention and retention
basin outfall structures) conveying water originating from off site
shall be designed for a fifty-year storm event. Drainage easements
shall be provided to contain and convey the one-hundred-year frequency
flood throughout the development site. Easements shall begin at the
furthest upstream property line of the proposed development site in
a watershed.
[Amended 8-1-2006 by Ord.
No. 329]
(2) All developments must also include design provisions that allow for
the overland conveyance of the post-one-hundred-year-storm flows through
the site without damage to any private or public property.
(3) When the design of the overall stormwater management plan requires a transfer of watershed, as outlined by §
265-45B(10) of this article, the design shall illustrate that the facilities utilized to accomplish the transfer can safely convey the one-hundred-year storm event.
(4) The capacities of the pipes, gutters, inlets, culverts, outlet structures
and swales shall consider all possible hydraulic conditions. The following
minimum design standards have been established by the Borough:
(a)
For grass swales and roadside gutters two design considerations
shall be met: the first shall consider channel velocity and stability
based upon a low degree of retardance ("n" of 0.03); the second shall
consider channel capacity based upon a high degree of retardance ("n"
of 0.05).
(b)
The "n" factors to be used for paved or riprap swales or gutters
shall be based on accepted engineering design practices.
(c)
The following chart shall be used to determine the "n" factors
for corrugated metal pipe:
|
"n" Factors
|
---|
|
|
Helical
|
Annular
|
---|
|
Pipe Diameter
(inches)
|
Capacity
|
Velocity
|
Capacity
|
Velocity
|
---|
|
Up to 18
|
0.017
|
0.014
|
0.026
|
0.024
|
|
21 through 30
|
0.021
|
0.017
|
0.026
|
0.021
|
|
Larger than 30
|
0.026
|
0.019
|
0.026
|
0.019
|
(d)
The "n" factor for concrete or any other smooth pipe shall be
0.010 for velocity and 0.013 for capacity.
(e)
The velocity to be used in the design of any piped stormwater
conveyance system shall be based on the maximum velocity obtainable.
The capacity shall be based upon full flow conditions.
(f)
Inlets, culverts and basin discharge systems shall be designed
for the worst case condition. Inlet capacity shall be based on design
data provided by the manufacturers and accepted by the Borough Engineer.
If acceptable information is not available, inlets in nonponding areas
shall be designed for a maximum capacity of four cubic feet per second
(cfs). Where ponding occurs, inlet capacity shall be based on accepted
engineering design practices. Culvert design shall consider either
inlet/outlet control or a combination of hydraulic losses through
the system, whichever is greater. Basin discharge systems shall be
designed to the same standards as culverts. If it cannot be readily
determined which hydraulic condition controls, the basin discharge
rate shall be based on the highest possible discharge rating curve
with the basin capacity sized to store the excessive storm runoff
based on the lowest possible discharge rating curve.
(5) Inlets shall be along the curbline and are not permitted along the
curb radius at an intersection. For the purpose of inlet placement,
curb, gutter or roadside swale depths shall not exceed three inches
along the roadway and 1.5 inches across streets and all other access
drives.
(6) Manholes and inlets, when proposed, shall not be spaced more than
400 feet apart. Additionally, manholes shall be placed at points of
abrupt changes in the horizontal or vertical direction of storm sewers.
Inlets shall be substituted for manholes where they will serve a useful
purpose.
(7) Curves in pipes or box culverts without an inlet or manhole are prohibited.
Tee joints, elbows and wyes are also prohibited.
(8) Stormwater management pipe collection and conveyance systems shall
have a minimum diameter of 15 inches and shall be made of reinforced
concrete pipe, corrugated galvanized metal pipe, corrugated polyethylene
smooth-lined pipe (SLCPP) or approved equivalent. Where installation
conditions merit, structural calculations that address the actual
design requirements shall be required.
[Amended 11-4-2003 by Ord. No. 310]
(9) All storm sewer pipe and culverts shall be laid to a minimum depth
of one foot from finished subgrade to the crown of pipe in paved areas
and one foot from finished grade to the crown of pipe in grassed areas.
(10)
All storm sewer pipes, culverts, manholes, inlets, endwalls
and end sections shall be constructed in accordance with Pennsylvania
Department of Transportation, Form 408, as amended.
(11)
Storm sewer pipes, culverts, manholes, inlets, endwalls and
end sections shall conform to the requirements of the Pennsylvania
Department of Transportation, Bureau of Design, Standards for Roadway
Construction, Publication No. 72, in effect at the time the design
is submitted, as modified by the adopted Borough construction standards.
(12)
All inlets used along existing and proposed curbed streets shall
include PennDOT Type "C" top units or approved equivalent.
(13)
Inlets shall be depressed two inches below the grade of the
street gutter or shoulder surface. Inlets used in grassed areas will
have their tops installed level. Inlets used along curbed streets
shall have their tops installed at a grade equal to the street or
curb grade.
(14)
Where storm sewers exceed fifteen-percent slope, properly spaced
concrete anchors will be used.
(15)
Stormwater roof drains, sump pumps and pipes, wherever possible,
shall discharge water into a stormwater runoff dispersion and infiltration
control device and not into storm sewers or street gutters.
(16)
All storm sewer crossings of streets shall be perpendicular
to the street center line unless otherwise approved by the Borough
Engineer.
(17)
All storm pipe, other than culverts for existing channels, which
discharge from residential lots to a street or from a street to residential
lots, shall extend from the street right-of-way a minimum distance
of 2/3 the length of the longest lot dimension adjacent to the street.
(18)
The proposed stormwater discharge at the perimeter of the site
shall not be beyond the capacity of any existing, immediately contiguous,
stormwater management facility into which it flows.
(19)
Storm pipes which discharge to a detention or retention basin
shall be located as to outlet directly to the basin floor.
(20)
Endwalls and end sections shall be used where stormwater runoff
enters or leaves the storm sewer horizontally from a natural or man-made
channel.
(21)
Storm facilities not located within a public right-of-way shall
be centered within an easement.
F. Design standards – erosion and sedimentation control.
(1) The applicant must comply with the erosion control rules and regulations
of Pa. Code Title 25, Rules and Regulations, Part I. Department of
Environmental Protection, Subpart C. Protection of Natural Resources,
Part 2. Water Resources, Chapter 102, Erosion Control, as amended
from time to time.
(2) The design plan and construction schedule shall incorporate measures
to minimize soil erosion and sedimentation.
(3) The following principles shall be applied to the design plan and
construction schedule to minimize soil erosion and sedimentation:
(a)
Erosion and sedimentation controls designed in conformance with
the Department of Environmental Protection Erosion and Sedimentation
Pollution Control Program Manual shall be implemented during the construction
and post-construction periods to prevent soil erosion, sedimentation
and other pollutants from entering streams, lakes, etc.
(b)
Whenever feasible, natural vegetation shall be retained and
protected.
(c)
The extent of the disturbed area and the duration of its exposure
shall be kept to a minimum. Stockpiles to remain in place longer than
20 days shall be seeded.
(d)
It shall be the contractor's responsibility during construction
to prevent soil pollution to neighboring property, public streets
and streams. Soil dropped from construction equipment and sedimentation
shall be immediately removed from roads, public and private property,
and streams.
(e)
Drainage provisions shall accommodate the stormwater runoff
both during and after construction.
(f)
Soil erosion and sedimentation facilities shall be installed
prior to any on-site earth disturbance.
(4) The maximum swale, gutter or curb velocity of stormwater runoff shall
be maintained at levels which result in a stable condition both during
and after construction. The following are considered characteristics
of a stable condition:
(a)
It neither aggrades or degrades beyond tolerable limits.
(b)
The channel banks do not erode to the extent that the channel
cross section is changed appreciably.
(c)
Sediment bars do not develop.
(d)
Erosion does not occur around culverts and bridges or elsewhere.
(e)
Gullies do not form or enlarge due to the entry of uncontrolled
stormwater runoff.
(5) Grass-lined channels shall be considered stable if the calculated
velocity does not exceed the allowable velocities shown below:
(a)
Three feet per second where only sparse vegetation can be established
and maintained because of shade or soil condition.
(b)
Four feet per second where normal growing conditions exist and
vegetation is to be established by seeding.
(c)
Five feet per second where a dense, vigorous sod can be quickly
established or where water can be temporarily diverted during establishment
of vegetation. Netting and mulch or other equivalent methods for establishing
vegetation shall be used.
(d)
Six feet per second where there exists a well-established sod
of good quality.
(6) Swale bends.
(a)
Where swale bends occur, the allowable velocities listed above
shall be divided by the following factors:
[1]
Swale bends: 0° to 30° - 1.50.
[2]
Swale bends: 30° to 60° - 1.75.
[3]
Swale bends: 60° to 90° - 2.00.
[4]
Swale bends: 90° and over - 2.50.
(b)
These calculated grass-lined channel flows may be exceeded if
the designer can provide acceptable supportive design criteria as
proof of erosion prevention. Where the velocity of stormwater runoff
exceeds the allowable velocity, erosion protection must be provided.
The method of erosion protection proposed must be supported by the
appropriate design information and/or references.
(7) Flow velocities from any storm sewer may not result in a deflection
of the receiving channel.
(8) Energy dissipators shall be placed at the outlets of all storm sewer
pipes, culverts and bridges where flow velocities exceed maximum permitted
channel velocities.
G. Best management practices (BMPs).
(1) Best management practices (BMPs) should be implemented in Adamstown
Borough in order to protect the Borough's water quality. BMPs
should be applied to all subdivision and land development plans and
other activities regulated by the stormwater provisions of this chapter.
(See Appendix No. 34.)
(2) The purpose of these design standards is to provide designers with
guidance to meet (BMP) requirements. This field is in its infancy
and modifications will be necessary as new methods become available.
Innovations are strongly encouraged in order to meet the objectives
at a reasonable cost.
(3) The strategy employed avoids the use of performance standards related
to effluent standards. Instead, it establishes a suggested long-term
storage volume to be provided with any proposed land use. Other design
methods are available and may be utilized, provided documentation
is furnished and the Borough approves the design. Other measures of
control, including the use of natural open space, may be substituted
for structural measures. The use of nonstorage-related measures must
be carefully evaluated to ensure the water quality goals are being
met.
(4) General conditions.
(a)
Minimize on-site impervious area.
[1]
Preserve natural wooded cover and drainageways on site.
[2]
Pervious surfaces such as porous pavement and gravel are considered
BMPs.
(b)
Maximize the amount of on-site drainage areas that are directed
to BMPs. Minimum accepted area is 70% of the site. Impervious areas
shall be directed to BMPs.
(c)
Minimize directly connected impervious area. Promote natural
removal of pollutants using vegetation and soil. Direct impervious
area runoff to pervious area. For example:
[1]
Roof downspouts to lawns.
[3]
Parking areas to lawns or grassed swales.
(d)
Minimize mixing of off-site and on-site runoff, unless the upstream
drainage area is insignificant in size.
(e)
Delay construction of BMPs until all other land-disturbing activities
are complete to minimize the potential for clogging and maintenance
or remedial action.
(f)
Incorporate the site's soil conditions to ensure the maximum
life of facility.
(g)
Use water-tolerant vegetation (orchard and bermuda grass, perennial
rye, fescue and reed canary grass,) in swales with slopes of 2% or
less and where swale dikes are utilized.
(h)
Provide a length-to-width ratio in basins/ponds of at least
2:1 and avoid short-circuiting. Maximize the distance between inflow
and outflow.
(i)
Provide proper erosion protection at all pipe outlets.
(j)
Utilize underdrains for all ponds; may be used as BMP outlet
if properly sized.
(k)
Size BMP outlets to release water at a rate producing approximately
a thirty-six-hour drawdown time. Orifices should be sized to accomplish
this (minimum one-half-inch-diameter holes). To prevent clogging around
a vertical riser, use a cone of gravel or a noncorrosive fine-mesh
screen.
(l)
Infiltration trenches provided for stormwater management do
not require additional storage volume calculations for BMP.
(m)
Minimize disturbed project area.
(5) System of controls.
(a)
The Adamstown Borough approach to protect water quality is to
minimize the impact of pollutants in stormwater runoff through a system
of controls. These controls can be at the source, in the lot, at the
site or at some regional facility. Examples are listed below:
(b)
Source controls. Eliminate the opportunity for pollutants to
mix with stormwater runoff.
[2]
Cover chemical storage areas.
[3]
Dike potential spill areas.
[4]
Regular sediment removal from drainage system.
(c)
Lot controls. Minimize the potential for concentrating pollutants
and concentrating stormwater runoff.
[1]
Minimize directly connected impervious areas.
[2]
Minimize impervious areas.
[3]
Utilize grass swales and filter strips.
[4]
Utilize infiltration trenches, where applicable.
(d)
Site controls. Structural methods required to meet storage volume
requirements and water quality objectives.
(e)
Regional controls (development area > 100 acres) – off-site
structural measures for large projects.
H. Groundwater recharge, water quality and stormwater management performance standards. Developers shall meet all of the standards set forth in this subsection in addition to all other requirements of this §
265-45. To the extent that a requirement of this subsection is more restrictive than a requirement of another subsection of this §
265-45 concerning the same item, the requirements of this subsection shall apply.
[Added 11-4-2003 by Ord.
No. 310; amended 8-1-2006 by Ord. No. 329]
(1) Match preexisting hydrograph. Developers and/or landowners are encouraged
to provide infiltration facilities or utilize other techniques which
will allow the post-development hydrograph to match the preexisting
hydrograph along all parts of the hydrograph for the development site.
This option is most feasible for small subdivisions in areas of noncarbonate
geology. "Groundwater recharge" and "water quality" volumes as given
in this subsection below can be used as part of this option.
(2) Groundwater recharge.
(a)
Developed areas shall maintain groundwater recharge consistent with predevelopment conditions, dependent on hydrologic soil groups and impervious cover, unless the developer can prove the inability of the development site to achieve recharge based on existing development site conditions. This volume of runoff is termed the "recharge volume" and is calculated in accordance with §
265-45H(4). The recharge volume must be infiltrated within 48 hours after the end of the design storm. Development sites where the post-developed impervious area is equal to or less than the predeveloped impervious area shall not be required to provide groundwater recharge volume.
(b)
Design of the stormwater management facilities shall provide
for groundwater recharge to compensate for the reduction in the percolation
that occurs when the ground surface runoff characteristics have been
altered. A detailed geologic evaluation of the development site shall
be performed to determine the suitability of recharge facilities.
The evaluation shall be performed by a registered professional geologist
and shall, at a minimum, address soil permeability, depth to bedrock,
susceptibility to sinkhole formation, and subgrade stability. Where
pervious pavement is permitted for parking lots, recreational facilities,
nondedicated streets or other areas, pavement construction specifications
shall be noted on the plan.
(c)
If the developer can prove through analysis by a professional
geologist that the development site is in an area underlain by carbonate
geology, and such geologic conditions may result in sinkhole formations,
then the development site is exempt from recharge requirements. The
development site shall still be required to meet all other hydrologic
and water quality management standards as found in this chapter.
(3) Water quality. Developed areas will provide adequate storage and treatment facilities necessary to capture and treat a minimum of the runoff from the first 1.2 inches of rainfall. This volume of storage is the "water quality volume" and is calculated in accordance with §
265-45H(5). The recharge volume may be a component of the water quality volume. If the recharge volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than recharge/infiltration BMPs. The water quality volume must take a minimum of 24 hours to be discharged. Development sites where the post-developed impervious area is equal to or less than the predeveloped impervious area shall not be required to provide water quality volume unless required by NPDES Part II.
(4) Groundwater recharge requirements. The groundwater recharge volume
(Rev) is the volume of stormwater runoff from
a developed site which shall be required to maintain existing predevelopment
groundwater recharge at the development site. It may be part of the
water quality volume and is calculated on the basis of treatment and
recharge by structural stormwater management practices, as follows:
|
Where:
|
|
|
Rev
|
=
|
Recharge volume in acre-feet
|
|
|
A
|
=
|
Area of watershed in acres
|
|
|
Rv
|
=
|
0.05 + 0.9(I) where I = net increase in impervious area/Area
of watershed (A)
|
|
S is the soil-specific recharge factor and varies according
to soil type, as follows:
|
|
Hydrologic Soil Group
|
Soil-Specific Recharge Factor(s)
|
---|
|
A
|
0.32
|
|
B
|
0.22
|
|
C
|
0.10
|
|
D
|
0.05
|
(a)
If more than one hydrologic soil group (HSG) is present at a
development site, a composite recharge volume shall be computed based
upon the proportion of total development site area within each HSG.
(b)
Infiltration BMPs intended to receive runoff from developed
areas shall be selected based on suitability of soils and development
site conditions and shall be constructed on soils that have the following
characteristics:
[1]
A minimum depth of 48 inches between the bottom of the facility
and the seasonal high-water table and/or bedrock (limiting zones).
[2]
An infiltration and/or percolation rate sufficient to accept
the additional stormwater load and drain completely as determined
by field tests conducted by the developer's professional designer.
(c)
Infiltration BMPs receiving only roof runoff may be placed in
soils having a minimum depth of 24 inches between the bottom of the
facility and the limiting zone.
(d)
The recharge volume provided at the development site shall be
directed to the most permeable HSG available.
(e)
Structural stormwater management facilities which provide treatment
and recharge of the required recharge volume will be designed as part
of a stormwater management facility which incorporates groundwater
recharge BMPs as a primary benefit of using that facility, in accordance
with design specifications contained in "Pennsylvania Handbook of
Best Management Practices for Developing Areas," 1998.
(f)
The groundwater recharge volume shall be infiltrated within
48 hours after the end of the design storm.
(g)
Development sites where the post-developed impervious area is
equal to or less than the predeveloped impervious area shall not be
required to provide groundwater recharge volume.
(5) Calculation of water quality volume. The water quality volume (WQv) is the storage capacity needed to treat stormwater
runoff equivalent to a minimum of the first 1.2 inches of runoff from
the developed areas of the development site. The following calculation
is used to determine the storage volume, WQv, in acre-feet of storage:
|
Where:
|
|
|
WQv
|
=
|
Water quality volume in acre-feet
|
|
|
A
|
=
|
Area of watershed in acres
|
|
|
Rv
|
=
|
0.05 + 0.9(I) where I = net increase in impervious area/Area
of watershed (A)
|
|
If the recharge volume is less than the water quality volume,
the remaining water quality volume may be captured and treated by
other than recharge/infiltration BMPs.
|
|
WQv shall be designed as part of a stormwater
management facility which incorporates water quality BMPs as a primary
benefit of using that facility, in accordance with design specifications
contained in "Pennsylvania Handbook of Best Management Practices for
Developing Areas," 1998. The water quality volume shall take a minimum
of 24 hours to be discharged from the basin. Development sites where
the post-developed impervious area is equal to or less than the predeveloped
impervious area shall not be required to provide water quality volume,
unless required by NPDES Part II.
|
(6) Subregional (combined development site) storage. Runoff can be managed regionally by one or more developers, either on site or off site. The design and release rate shall be consistent with the applicable Act 167 plan. Groundwater recharge and water quality volumes as described in §
265-45H(4) and
(5) will be a part of this option.
(7) The "no harm" option does not apply to the water quality requirement described in §
265-45H(3) and
(5) above. The no harm option does not apply to the groundwater recharge requirement described in §§
265-45H(2) and
(4) above, unless it can be shown that the development site is underlain by carbonate geology and infiltration cannot be safely accomplished.
(a)
For any proposed development, the developer has the option of using a less-restrictive runoff control if the developer can prove that no harm would be caused by discharging at a higher runoff rate than that specified by the applicable Act 167 plan. Proof of no harm would have to be shown from the development site through the remainder of the downstream drainage network until there is no additional flow increase. Proof of no harm must be shown using the capacity criteria specified in §
265-45E(1) if downstream capacity analysis is a part of the no harm justification.
(b)
Attempts to prove no harm, based upon downstream peak flow versus
capacity analysis, shall be governed by the following provisions:
[1]
The peak flow values to be used for downstream areas for the
design return period storms (two-, five-, ten-, twenty-five-, fifty-
and one-hundred-year) shall be the values from the calibrated TR-20
Model for the applicable Act 167 plan. These flow values are available
from the Lancaster County Engineer's office.
[2]
At peak flow, any available capacity in the downstream conveyance
system (as documented by a developer) may be used only in proportion
to the proposed development site acreage relative to the total upstream
undeveloped acreage (i.e., if the development site is 10% of the upstream
undeveloped acreage, the developer may use up to 10% of the documented
downstream available capacity at peak flow).
[3]
Developer-proposed runoff controls which would generate increased
peak flow rates at documented storm drainage problem areas would,
by definition, be precluded from successful attempts to prove no harm,
except in conjunction with proposed capacity improvements for the
problem areas consistent with this section.
(c)
Any no harm justifications shall be submitted by the developer
as part of the application.
I. Stormwater management districts.
(1) The Borough shall comply with the applicable provisions of the Lancaster
County Stormwater Management Plan upon adoption of said plan. If the
provisions of this chapter are sufficient to regulate development
within the Borough in a manner consistent with the Lancaster County
Stormwater Management Plan, this chapter shall be deemed to satisfy
the requirements of Section 11(b) of Act 167 without the necessity of reenactment.
J. Floodplains.
(1) Floodplain areas shall be established and preserved as provided by Chapter
320, Zoning.
(2) Whenever a floodplain is located within or along a lot, the plan
shall include the boundary of the floodplain and the elevation or
locational dimensions from the center line of the watercourse; a plan
note that the floodplain shall be kept free of structures, fill and
other encroachments; and a plan note that floor elevations for all
structures adjacent to the floodplain shall be two feet above the
one-hundred-year flood elevation.
All residential subdivisions and land developments shall provide
park and open space land which shall be dedicated to the Borough.
The developer may request that the Borough not require the dedication
of land, and any such request should be accompanied by an offer to
pay a fee in lieu of dedication of the land, computed in accordance
with the guidelines provided herein, an offer to construct recreational
facilities, and/or an offer to privately reserve land for park or
recreation purposes.
A. The land reserved for park and open space usage shall be a single lot which shall comply with applicable requirements of this chapter, Chapter
320, Zoning, and the following requirements:
(1) The park and open space land shall be reasonably located so as to
serve all the residents of the subdivision or land development.
(2) No stormwater management facilities designed to retain or detain
water from other portions of the development shall be permitted on
such land reserved for park and open space.
(3) In the event that the tract contains natural features which are worthy
of preservation, the developer may request that the Borough Council
permit the provision of recreational land configured in such a manner
as to best preserve natural features.
(4) The park and open space land shall be accessible from a public street
or shall adjoin and become part of an already existing public park
or open space area which is accessible from a public street.
(5) The park and open space land shall be accessible to utilities such
as sewer, water and power that are provided with the subdivision,
and if so requested by the municipality that will accept dedication
of the land, the developer shall extend such utilities to the park
and open space land.
(6) If the adjoining property has previously been developed and recreational
land has been provided at the boundary of that previously developed
property, the Borough Council shall require that the park and open
space land required of the development be located adjoining the previously
provided recreational land.
(7) If the adjoining property is undeveloped land, the Borough Council
shall require that such land be provided at the property boundary
of the development in order that it may be added to land provided
for park and open space purposes on the adjoining tract at such time
that the adjoining property is developed.
B. Consistent with the standards of the National Recreation and Park
Association (NRPA) and the Cocalico Region Recreation, Parks and Open
Space Plan, the amount of park and open space land required to be
dedicated shall equal at least one acre per 100 projected residents
or fraction thereof. The developer shall provide the Borough with
information concerning the estimated population density based upon
the number and type of dwelling units proposed. In the event of a
dispute as to the estimated population of the proposed residential
subdivision or land development, the determination of Borough Council
shall control.
C. The developer may request that the Borough Council permit the provision
of park and open space land other than through public dedication of
land as set forth above. The developer shall set forth, in writing,
the means by which he will fulfill this requirement, which may include
the payment of a fee in lieu of dedication of all or a portion of
the amount of land required to be dedicated, construction of recreational
facilities, the private reservation of land or any combination of
dedication, fees, construction of recreational facilities, or private
reservation.
(1) In-lieu fees.
(a)
If a fee in lieu of dedication is proposed by the developer
and approved by Borough Council, said fee shall be equal to the average
fair market value of the land otherwise required to be dedicated under
this section. The formula to be used in computing the fee based upon
fair market value shall be as follows:
|
N x (average FMV of 1 acre) = fee
|
|
Where:
|
---|
|
|
N
|
=
|
the number of acres required to be dedicated for park and open space purposes, calculated in accordance with § 265-48B; and
|
---|
|
|
FMV
|
=
|
fair market value
|
(b)
The applicant shall provide the Borough Council with all information
necessary to determine the fair market value of the land, including,
but not limited to, the following:
[1]
If the applicant is the equitable owner or purchased the land
in fee simple less than two years prior to the preliminary or final
plan submission, a copy of the agreement of sale or real estate transfer
tax affidavit of value.
[2]
If the applicant is the equitable owner or purchased the land
in fee simple more than two years prior to the preliminary or final
plan submission, an opinion of value of the property by a state-certified
appraiser acceptable to Borough Council.
(c)
Any applicant aggrieved by the fee established shall have the
right to secure a second opinion of value of the property by a state-certified
appraiser acceptable to Borough Council. The two estimated values
shall be averaged, with the result being the amount upon which the
fee will be based.
(d)
Such fee shall be payable to the Borough prior to the recording
of each final phase of the plan and shall be in an amount equal to
the percentage of the total number of dwelling units in the phase.
(e)
All fees shall be held and used by the Borough in accordance with the requirements of Article
V of the Municipalities Planning Code.
(2) If the developer proposes to construct recreational facilities, the
developer shall present a sketch plan of such facilities and an engineer's
estimate of the cost of construction.
(3) If the developer proposes the private reservation of land, the developer shall provide for the maintenance of such land through either the inclusion of such land as common elements of a condominium or the creation of a homeowners' association which shall meet the requirements for a unit owners' association contained in the Pennsylvania Uniform Condominium Act, 68 Pa.C.S.A. § 3101 et seq. Such documentation shall be recorded, shall provide that the land cannot be further developed, and shall give the Borough the rights to maintain the land as set forth in Article
VII of the Municipalities Planning Code dealing with the maintenance of common open space in planned residential developments. Notwithstanding the foregoing, the developer may request that the Borough Council approve transfer of the land to an organization dedicated to the conservation of natural resources with deed restrictions preventing further development acceptable to the Borough Solicitor.
(4) The developer shall enter into an agreement with the Borough setting
forth the fees to be paid, the facilities to be constructed or the
land to be privately reserved, and the method of its maintenance.
All such agreements shall be in a form satisfactory to the Borough
Solicitor and shall be provided prior to final plan approval.