Section 250-RICR-150-10-6.24 - Subsurface DrainsA. Prior to seeking a permit for an OWTS that includes a subsurface drain, the applicant shall have all other relevant State or local approvals or permits for construction of the subdrain and discharge of the drainage effluent. Such approvals may include, but are not limited to, DEM Freshwater Wetlands Program, the Rhode Island Coastal Resources Management Council Preliminary Determination, the municipality or the Rhode Island Department of Transportation.B. Construction - A subsurface drain constructed to lower the groundwater table shall consist of not less than six inches (6") of washed stone three quarters of an inch (3/4") to two inches (2") in diameter, over which is laid a perforated pipe at least four inches (4") in diameter. The stone shall extend above the pipe to within two feet (2') of the ground surface. A layer of filter fabric meeting the requirements of § 6.33(L) of this Part shall be placed above, below and along the sides of the stone for the entire length of the drain. Changes in direction shall not exceed ninety degrees (90°). Where a change in direction is greater than forty-five degrees (45°), a manhole is required, unless the change in direction is achieved through the use of a thirty-six inch (36") radius sweep.C. Monitoring - The effectiveness of subsurface drains used to lower the groundwater table must be demonstrated through one (1) complete wet season, January 1 through April 15, before consideration can be given to an application for an OWTS permit. The Department may allow lesser periods of monitoring if site conditions and wet season conditions warrant.1. Groundwater table test holes shall be located within the area of the proposed leachfield with one (1) on the upgradient side and one (1) on the downgradient side. The test holes shall not be located within twenty-five feet (25') of the upgradient subsurface drain or within fifty feet (50') of the downgradient subsurface drain.2. Groundwater table initial readings shall be submitted on forms approved by the Director by January 30 in order to effectively allow the Department and the Licensed Designer to monitor the effects of the subsurface drain through the wet season.D. Hydraulic Gradient - If the subsurface drain causes the natural hydraulic gradient to be reversed, such drain shall be treated as a downgradient drain for the purpose of establishing appropriate minimum setbacks in accordance with § 6.23 of this Part. Where only an upgradient drain is installed, the applicant must demonstrate that the hydraulic gradient will not be reversed or treat the upgradient drain as a downgradient drain for the purpose of establishing appropriate minimum setbacks in accordance with § 6.23 of this Part.250 R.I. Code R. 250-RICR-150-10-6.24
Amended effective 11/25/2018
Amended effective 12/28/2021
Amended effective 7/1/2022