A. BMP's shall be provided to retain all runoff generated by the groundwater recharge design storm (seventy-five-hundredths-inch, twenty-four-hour rainfall event) for infiltration.
B. BMP's shall be designed to infiltrate retained runoff within a forty-eight-hour period. Infiltration rates shall be based on field measurements using a method approved by the Township Engineer. Tests shall be conducted at the proposed depth of the bottom of the infiltration device. A factor of safety of 3, or greater. shall be used when computing infiltration potential of a BNP from field measurements of infiltration rate.
C. Compliance by lot owners; exceptions.
(1) Lot owners must comply, individually, with the groundwater recharge requirement. However, groundwater recharge BMP's will not be required on properties where:
(a) Average slopes for the property exceed 10%.
(b) Seasonal high water table is shallower than four feet below final grade.
(c) Soil or bedrock conditions will not permit efficient percolation (nominal infiltration rate of less than 0.2 inches/hour).
(d) Site configuration will require that runoff must be infiltrated within:
[1] One hundred feet of a known or suspected sinkhole.
[2] Fifty feet of a water supply well.
[3] Fifty feet of a perennial stream.
[4] Twenty feet of a basement wall.
[5] Fifty feet of a septic system.
(2) The groundwater recharge objective can be obtained through a variety of approved BMP's or combinations thereof, including bioretention areas, dry wells, french drains, infiltration trenches, porous pavement and some types of sand filters. Community (multilot) groundwater recharge BMP's may be approved by the Township Engineer. However, the total upgradient drainage areas served by any groundwater recharge BMP may not exceed five acres.
D. The storage volume of detention basins or retention basins may not be used to satisfy the required retention volume for groundwater recharge.
E. Potentially contaminated runoff may not be infiltrated without appropriate pretreatment. The Township Engineer will determine whether contaminated runoff can be satisfactorily treated to permit infiltration. Sites which generate contaminated runoff must segregate uncontaminated runoff (e.g., roof runoff). Measures shall be introduced to infiltrate uncontaminated runoff generated by a property during the groundwater recharge design storm (e.g., roof runoff).
F. Above-grade groundwater recharge BMP's which incorporate biofiltration are required for the infiltration of untreated runoff from public, commercial or industrial parking lots. Runoff from private or institutional parking lots may utilize below-grade devices (e.g., infiltration trenches, porous pavement).
G. Direct runoff from public roads is exempt from the groundwater recharge requirement. However, privately owned and maintained roads must comply with this requirement.
H. Procedures used to predict runoff must use standard and accepted calculation methodology and be satisfactory to the Township Engineer.
I. Groundwater recharge BMP's shall be designed to provide storage equal to 100% of the required retention volume.