ORDINANCE NO. 122
AN ORDINANCE AMENDING ZONING ORDINANCE NO. 50, AS AMENDED, ESTABLISHING REGULATIONS GOVERNING STORMWATER MANAGEMENT FACILITIES THAT MAY BE INCLUDED IN THE MINIMUM REQUIRED OPEN SPACE FOR CLUSTER AND LOT AVERAGING DEVELOPMENTS.
The Board of
Supervisors of Kennett Township hereby enacts and ordains that the Zoning
Ordinance of Kennett Township, Ordinance No. 50, as amended, be amended further
as follows:
SECTION 1.
Amend Article XV, Section 1504 E.3 by adding the following:
Except, at the discretion of the Board of Supervisors, upon recommendation by the Planning Commission, areas devoted to stormwater management facilities may be included within the minimum required open space where the Applicant can demonstrate to the satisfaction of the Board that such facilities are designed to a) promote recharge of groundwater systems; or b) be available and appropriate for active or passive recreational or scenic enjoyment.
The area that may be
included within the minimum required open space shall be calculated as follows:
a.
Calculate the total
stormwater volume to be managed within the tract.
b.
For all areas
satisfying either a) or b) above, calculate the volume of stormwater managed
within that area
c.
The area, which can
be included as part of the minimum required open space, is the total Defined
Area (below) times the ratio of calculation #2, divided by calculation #1.
The Defined Area is
calculated by including all areas within the perimeter embankments or berms.
The measurements will include all areas within the contour line
established by the top elevation of the stormwater retention embankment on the
outlet or downhill side of the basin.
This contour will be continued around the basin until it closes back on
itself. The area thus enclosed is
the “Defined Area.”
The Applicant
recognizes that any area considered as applicable for inclusion with the minimum
required open space would then be subject to management as described by the Open
Space Management Plan that will be required by the Township.
ORDINANCE NO. 122
Page 2
The stormwater
management facility must meet the following minimum requirements to be
considered for inclusion in the minimum open space requirements:
1.
Recharge to the
groundwater system can be accomplished by either of the following methods:
installation of subsurface infiltration methods, such as stone seepage
beds, pits or trenches, and perforated pipes or cisterns, or by direct
infiltration into the soil where infiltration rates assure that the system will
meet all design requirements.
2.
Infiltration rates
shall be established by soils testing.
Soils testing shall be conducted to a depth no less than 3 feet below the
bottom of the infiltration facility to be considered.
In no case shall the bottom of the infiltration system be less than 4
feet below the finished ground elevation.
The tests will conform to the procedures for infiltration beds
established by the Chester County Health Department.
75% of the tested percolation rate shall be used to determine the storage
volume required.
3.
Infiltration shall
be sized to store the next increase in stormwater volume from a 2-year frequency
rainfall (3.3 inches in 24 hours) event without consideration of infiltration.
4.
The bottom elevation
of the infiltration system shall be at least 2 feet above bedrock or the
seasonal high water table.
5.
Filtering devices
will be incorporated in piping or structures distributing runoff to the
infiltration systems in order to collect and prevent sediment from entering the
system.
6.
This stormwater
management system shall be no closer than 50 feet of any sewage bed, stream or
water supply well. Also, they will
be situated downgrade from structures on adjacent lots or be isolated at least
100 feet from them.
7.
Overflow facilities
that direct overflow from infrequent storms exceeding design capability will be
installed. Acceptable points to
accept the overflow would be inlets or piping of downstream storm sewer systems,
wetland areas, flood plain fringe areas or other stormwater management
facilities.
8.
The system shall be
designed to empty the total design storm volume within 24 hours or less
following the storm event.
9.
All subsurface
infiltration systems shall use a permeable geotextile fabric to separate
aggregate within the facility from soil on the sides and top to prevent loss of
bed capacity.
ORDINANCE NO. 122
Page 3
10.
The design of the
stormwater facility shall, when not storing water runoff, accommodate active or
passive recreation and/or improve the aesthetic quality of the proposed
development or Township.
11.
Perimeter
embankments or berms shall have side slopes of 4 to 1 and flatter.
They will also blend into the existing topography.
12.
The detention area
shall be designed to be a shallow holding area with a storage depth no greater
than 3-1/2 feet.
13.
If designed for
active recreational use, the soils of the basin shall be such that they will
quickly drain to allow a usable playing surface.
If necessary, an underground drain system shall be installed to
facilitate the drainage.
14.
Outlet works of
stormwater management facilities shall be constructed to prevent entry by
children or animals.
15.
If designed for
active recreational use, any fixtures required for the approved type of athletic
field or court shall be permanently anchored to prevent floatation.
16.
Any plantings or
vegetation placed in the impoundment area must be able to withstand the expected
frequency and depth of inundation.
Further, the Open Space Management Plan should include specific recommendations
of plant species and instructions for the appropriate care and maintenance of
the facility.
ENACTED AND ORDAINED
this 15th
day of February
1999.
BOARD OF SUPERVISORS
_________________________________
Attest: Michael E. Elling
______________________________ _________________________________
Secretary-Treasurer James C. Henderson
_________________________________
Charles G. Shoemaker