250 R.I. Code R. 250-RICR-150-10-8.22

Current through November 21, 2024

Section 250-RICR-150-10-8.22 - Permeable Paving

A. There are two major types of permeable paving:

1. Porous asphalt and pervious concrete. Although they appear to be the same as traditional asphalt or concrete pavement, they have 10%-25% void space and are constructed over a base course that doubles as a reservoir for the stormwater before it infiltrates into the subsoil or is directed to a downstream facility.

2. Pavers. Three alternative paver configurations will be acceptable to the approving agency as water quality BMPs. These are as follows:

a. Permeable solid blocks or reinforced turf: This type of permeable paving surface includes permeable solid blocks (where the blocks have a minimum void ratio of 15%) and contain open-cell grids filled with either ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate for (paving blocks) or sandy soil and planted with turf (for reinforced turf applications), set on a prepared base course consisting of a minimum of 1.5 inches of ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate, over a minimum of 4 inches of ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 57 washed stone. ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 2 washed stone is used as a reservoir course as necessary to manage variable storm sizes or provide other functions.

b. Solid blocks with open-cell joints > 15% of surface: This type of paver surface includes interlocking impermeable solid blocks or open grid cells that must contain permeable void areas (between the impermeable blocks) exceeding 15% of the surface area of the paving system. Permeable void areas are to be filled with ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate and compacted with a minimum 5,000 lbf plate compactor. Pavers are set on prepared base course materials consisting of a minimum of 1.5 inches of ASTM D 448 -12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate, over a minimum of 4 inches of ASTM D448 -12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 57 washed stone. ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 2 washed stone is used as a reservoir course as necessary to manage variable storm sizes or provide other functions.

c. Solid blocks with open-cell joints < 15% of surface: This type of paver surface includes interlocking impermeable solid blocks or open grid cells that must contain permeable void areas (between the impermeable blocks) less than 15% of the surface area of the paving system. Permeable void areas are to be filled with ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate and compacted with a minimum 5,000 lbf plate compactor. In order to meet the water quality treatment requirements of § 8.9 of this Part, these types of systems must be designed to provide one inch of surface storage above the permeable pavement system. Pavers are set on prepared base course materials consisting of a minimum of 1.5 inches of ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 8 washed aggregate, over a minimum of 4 inches of ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 57 washed stone. ASTM D448 - 12 Standard Classification for Sizes of Aggregates for Road and Bridge Construction, incorporated above at § 8.4(F) of this Part, No. 2 washed stone is used as a reservoir course as necessary to manage variable storm sizes or provide other functions.

B. Treatment Suitability: Permeable paving practices might not be able to provide overbank flood control (Qp) storage. Combine with other practices to handle runoff from large storm events, when required. Extraordinary care shall be taken to assure that clogging does not occur through the use of performance bonds, post-construction inspection and long-term maintenance.

C. There are two categories of permeable pavement:

1. Infiltration Facility: The base stores water and drains to underlying soil. There are no perforated drain pipes at bottom of base; however, they may have overflow pipes for saturated conditions and extreme storm events; and

2. Detention Facility: This design includes an impermeable liner at the bottom of the base aggregate, which then flows to a downstream facility for additional treatment and storage. This category is useful in sites with high groundwater, bedrock, LUHPPL, and areas with fill soils. If designed as a detention system, infiltration restrictions noted in § 8.22(D) of this Part do not apply.

D. Feasibility

1. In order to meet the water quality standard, the bottom of infiltrating permeable pavement practices must be located in the soil profile. Where a TMDL or CRMC goal requires maximum treatment of runoff, the bottom shall be within the uppermost soil horizons (A or B) or another BMP is required.

2. 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. The minimum geotechnical testing at the site of a proposed infiltrating practice is one test hole per 5,000 square feet, with a minimum of one boring or test pit per infiltration facility (taken within the proposed limits of the facility).

3. For infiltrating permeable paving practices, underlying soils shall also have a clay content of less than 20% and a silt content of less than 60%.

4. The bottom of an infiltrating permeable pavement practice cannot be located in fill with the exception for strictly residential land uses, for which the bottom may be located in up to 2 feet of fill consisting of material suitable for long-term infiltration. Practices for non-residential sites that must be placed in fill shall meet the media requirements of sand filters as described in § 8.23 of this Part.

5. To protect groundwater from possible contamination, runoff from designated LUHPPL land uses or activities must not be directed to permeable pavement unless designed as a detention facility (with an impermeable liner).

6. To avoid excessive nitrogen loading to coastal embayments, permeable pavements are not permitted to receive runoff from other areas. They shall only be used to manage precipitation that falls directly on the permeable pavement area.

7. The bottom of an infiltrating permeable pavement practice shall be separated by at least 3 feet vertically from the SHGT or bedrock layer (when treating WQv), as documented by on-site soil testing. The SHGT elevation in the area of an infiltrating permeable pavement 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 in strictly residential areas.

8. This practice is not appropriate for high traffic/high speed areas (> 1,000 vehicle trips/day) due to clogging potential.

9. To avoid frost heave, design base to drain quickly (depth > 24 inches).

10. Use permeable paving only on gentle slopes (less than 5%).

11. Infiltrating permeable pavement practices must meet the minimum horizontal setbacks in the table below:

	Minimum Horizontal Setbacks
	From small-scale facilities serving residential properties OR non-vehicle surface applications (feet)	For all other applications (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	25	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 drinking water impoundments.

2 Setbacks from building structures does not apply where basement or slab is at or above the surface elevation of the permeable pavement.

E. Conveyance

1. The overland flow path of surface runoff exceeding the capacity of the permeable paving system shall be evaluated to preclude erosive concentrated flow during the overbank events. If computed flow velocities exiting the system over-bank exceed erosive velocities (3.5 to 5.0 feet/second), an overflow channel shall be provided to a stabilized watercourse.

2. All permeable pavement systems shall be designed to fully de-water the entire WQv within 24 hours after the storm event.

F. Treatment

1. Permeable pavements used as infiltration practices shall be designed to exfiltrate the entire WQv through the floor of each practice (sides are not considered in sizing).

2. Base course is a reservoir layer which shall be a minimum 6 inches, but is generally 12 to 24 inches or greater (function of storage needed and frost heave resistance). Base material must be poorly graded (uniform size material), must maintain adequate evaluate bearing capacity, depending on the use, and compaction effort must be adjusted to meet design storage requirements. Base course also includes a filter course above reservoir layer (2 to 6 inches of smaller material).

3. The construction sequence and specifications for permeable pavement areas shall be precisely followed, particularly for infiltrating permeable paving practices. Experience has shown that the longevity of any infiltration practice is strongly influenced by the care taken during construction.

4. For infiltrating permeable pavements, design infiltration rates should be determined by using the Table in § 8.21(E)(4)(a) of this Part based on the soil texture of the underlying soil. These are conservative values that take into account future clogging as the practice is used over the years.

5. For permeable paving practices used for detention only, no runoff reduction is allowed, i.e., impermeable CNs shall be used in hydraulic and hydrologic models when calculating CPv and Qp.

G. Vegetation

1. Other adjacent construction shall be completed and site stabilized before installation of reservoir materials. A dense and vigorous vegetative cover shall be established over any contributing pervious drainage areas before runoff can be accepted into the facility.

2. Pavers that are planted with grass require species with deep root systems. Follow manufacturer's guidelines on appropriate species.

H. Maintenance

1. A legally binding and enforceable maintenance agreement shall be executed between the facility owner and the responsible authority.

2. Areas where infiltrating permeable pavement practices are proposed shall not serve as a temporary sediment control device during site construction phase.

3. Permeable paving surfaces require regular vacuum sweeping or hosing (minimum every three months or as recommended by manufacturer) to keep the surface from clogging. Maintenance frequency needs may be more or less depending on the traffic volume at the site.

4. Minimize use of sand and salt in winter months.

5. Do not repave or reseal with impermeable materials.

6. The SESC Plan shall specify at a minimum:

a. How sediment will be prevented from entering the pavement area;

b. A construction sequence;

c. Drainage management; and

d. Vegetative stabilization.

250 R.I. Code R. 250-RICR-150-10-8.22

Amended effective 11/13/2018