Section 250-RICR-150-10-8.8 - Minimum Standard 2: Groundwater RechargeA. Stormwater must be recharged within the same subwatershed to maintain baseflow at pre-development recharge levels to the maximum extent practicable in accordance with the requirements described in §§ 8.8(D) through (H) of this Part. Applicants may be required to provide a water budget analysis for proposed groundwater dewatering. Recharge volume is determined as a function of annual pre-development recharge for site-specific soils or surficial materials, average annual rainfall volume, and amount of impervious cover on a site. Recharge must occur in a manner that protects groundwater quality.B. Stormwater runoff from a LUHPPL is not allowed to infiltrate into groundwater. The stormwater recharge requirement may be specifically waived if an applicant can demonstrate a physical limitation that would make implementation impracticable or where unusual geological or soil features may exist such as significant clay deposits or ledge, where recharge does not currently occur; fill soils; or areas of documented slope failure.C. Maintaining pre-development groundwater recharge conditions may also be used to reduce the volume requirements dictated by other sizing criteria (water quality, channel protection, and overbank flood control) and the overall size and cost of stormwater treatment practices.D. The recharge criterion (Rev) requires that the following volume of stormwater be recharged based on the amount of impervious area. The groundwater recharge requirement may be waived or reduced by applying the LID Stormwater Credit outlined in § 8.18 of this Part. Recharge requirements are based on hydrologic soil group (HSG) as follows: Rev = (1 inch) (F) (I)/12
Where:
Rev = groundwater recharge volume (acre feet)
F = recharge factor, see table below in § 8.8(F) of this Part
I = impervious area (acres)
E. Recharge Factors Based on Hydrologic Soil Group (HSG) HSG | Recharge Factor (F) |
A | 0.60 |
B | 0.35 |
C | 0.25 |
D | 0.10 |
F. The recharge volume is considered as part of the total water quality volume that must be provided at a site and must be achieved by disconnection of impervious areas (see § 8.18 of this Part), a structural practice that infiltrates stormwater into the underlying soils or substratum, or a combination of the two.G. Roof runoff may be infiltrated without pretreatment unless the roof is deemed to have a higher potential pollution load pursuant to § 8.14(C) of this Part. Recharged roof runoff can be subtracted from WQv but not from larger storm calculations, unless applicant verifies that the drywells are sized for the 100-year, 24-hour Type III storm event.250 R.I. Code R. 250-RICR-150-10-8.8
Amended effective 11/13/2018