Rhode Island Code of Regulations › Title 250 - Department of Environmental Management › Chapter 150 - Water Resources › Subchapter 10 - Wastewater And Storm Water › Part 8 - Stormwater Management, Design and Installation Rules › Section 250-RICR-150-10-8.21 - Stormwater Infiltration Practices

Current through June 14, 2024
A. Stormwater
				  infiltration practices in this section capture and temporarily store the WQv
				  before allowing it to infiltrate into the soil over a maximum period of 48
				  hours. The requirements for stormwater infiltration practices in this section
				  apply to infiltration basins, infiltration trenches, subsurface chambers and
				  dry wells. This section does not apply to those practices that infiltrate
				  stormwater into the soil addressed in §
										8.22 of this Part
				  (Permeable Pavement), §
										8.23 of this Part
				  (Filtering Systems), and §
										8.25 of this Part (Open
				  Channel Systems).
B. Feasibility
1. Roof runoff from non-LUHPPL sites can be
				  infiltrated directly, without pretreatment, and counted toward both Rev and WQv
				  requirements.
2. In order to meet
				  the water quality standard, the bottom of infiltration practices must be
				  located in the soil profile. Where a TMDL or CRMC goal requires maximum
				  treatment of runoff, the bottom of infiltration practices shall be within the
				  uppermost soil horizons (A or B) or another BMP is required.
3. To be suitable for infiltration,
				  underlying soils shall have an in-situ infiltration rate of at least 0.5 inches
				  per hour, as initially determined from US Natural Resources Conservation
				  Service soil textural classification, and subsequently confirmed by field
				  geotechnical tests in accordance with §
											8.21(E)(4)(b)
				  of this Part. The minimum geotechnical testing at the site of a proposed
				  infiltration practice is 1 test hole per 5,000 square feet, with a minimum of 1
				  boring or test pit (taken within the proposed limits of the facility). However,
				  for residential rooftop runoff, testing requirements are reduced to 1
				  infiltration test and 1 test pit per 5 lots assuming consistent terrain and
				  within the same US Natural Resources Conservation Service soil series. If
				  terrain and soil series are not consistent, then requirements increase to 1
				  infiltration test and 1 test hole per 1 lot.
4. Soils shall also have a clay content of
				  less than 20% and a silt content of less than 60%.
5. The bottom of infiltration practices
				  cannot be located in fill with the exception for strictly residential land
				  uses, for which the bottom of practices may be located in up to 2 feet of fill
				  consisting of material suitable for long-term infiltration after placement.
				  Practices for non-residential sites that cannot be placed in natural soil may
				  be designed as filtering systems. Such cases shall meet the media requirements
				  of sand filters as described in §
											8.23 of this
				  Part.
6. To protect groundwater
				  from possible contamination, runoff from designated LUHPPLs or activities shall
				  not be directed to an infiltration facility.
7. The bottom of the infiltration facility
				  shall be separated by at least 3 feet vertically from the SHGT and the bedrock
				  layer (when treating WQv), as documented by on-site soil testing. The SHGT
				  elevation in the area of each infiltration facility must be verified by a
				  DEM-licensed Class IV Soil Evaluator or RI-registered Professional Engineer.
				  The distance may be reduced to 2 feet for strictly residential land uses,
				  excluding roadways.
8. Infiltration
				  practices that are designed for the 10-year storm event or greater and have a
				  separation from the bottom of the system to the seasonal high groundwater of
				  less than four feet shall provide a groundwater mounding analysis.
a. The groundwater mounding analysis must
				  show that the groundwater mound that forms under the infiltration system will
				  not break out above the land or jurisdictional water.
b. Infiltration practices designed for
				  residential rooftops < 1,000 ft2 are exempt from
				  this requirement.
9.
				  Infiltration practices cannot be placed in locations that cause water problems
				  (such as seepage which may cause slope failure) to downgrade
				  properties.
10. Infiltration
				  facilities must meet the minimum horizontal setbacks in the table below:
Minimum Horizontal Setbacks
From small-scale facilities serving residential
								  properties (feet)
From all other infiltration facilities
								  (feet)
Public Drinking Water Supply Well - Drilled
								  (rock), Driven, or Dug
200
200
Public Drinking Water Supply Well - Gravel
								  Packed, Gravel Developed
400
400
Private Drinking Water Wells
50
100
Surface Water Drinking Water Supply Impoundment
								  with Supply Intake1
100
200
Tributaries that Discharge to the Surface
								  Drinking Water Supply Impoundment1
50
100
Coastal Features
50
50
All Other Surface Waters
50
50
Up-gradient from Natural slopes > %15
25
50
Down-gradient from Building Structures2
10
25
Up-gradient from Building Structures2
10
50
Onsite Wastewater Treatment Systems
15
25
1 Refer to DEM Rules Establishing Minimum Standards
					 Relating to Location, Design, Construction and Maintenance of Onsite Wastewater
					 Treatment Systems, Figures 14-16 for maps of the surface water drinking water
					 impoundments.
2 Setbacks from building structures applies only where
					 basement or slab is below the ponding elevation of the infiltration
					 facility.