Statutes, codes, and regulations
Rhode Island Administrative Code
Title 250 - Department of Environmental ManagementChapter 150 - Water ResourcesSubchapter 10 - Wastewater And Storm Water
Part 6 - Rules Establishing Minimum Standards Relating to Location, Design, Construction and Maintenance of Onsite Wastewater Treatment Systems
Section 250-RICR-150-10-6.35 - Concrete Chambers

250 R.I. Code R. 250-RICR-150-10-6.35

Download
PDF
Current through December 26, 2024
Section 250-RICR-150-10-6.35 - Concrete Chambers
A. See § 6.68 of this Part, Figure 10.
B. An OWTS using precast concrete chambers may be constructed in lieu of a dispersal trench OWTS. Concrete chambers must be preceded by a septic tank and must be installed in a trench configuration. Deep concrete chambers meeting the requirements of § 6.35(F) of this Part will not be permitted except for OWTS Applications for Repair when no other type of leachfield can be utilized.
C. Shallow Concrete Chambers
1. Dimensions - Shallow concrete chambers are four feet (4') by eight feet (8') by eighteen inches (18") deep with an open bottom and perforated side walls.
2. Site limitations - Shallow concrete chambers shall not be permitted where any of the following occur:
a. The chamber invert would be more than one foot (1') above the original grade;
b. The chamber inverts would be set at different elevations; or
c. The seasonal high groundwater table is less than four feet (4') from the original ground surface.
D. Shallow Concrete Chamber Effective Leaching Area - Effective leaching area for shallow concrete chambers shall be calculated based on § 6.35(E) of this Part. Required minimum leaching area shall be calculated in accordance with § 6.33(B) of this Part.
E. Shallow Concrete Chamber Effective Leaching Area

Shallow Concrete Chambers

12" stone below

24" stone below (Note 1)

Each end unit (sq. ft.)

78

102

Each Interior Unit (sq. ft.)

64

80

Note 1: Shallow concrete chambers installed with twenty-four inches (24") of stone below the chamber may be used for OWTS Applications for Repair only.

F. Deep Concrete Chambers
1. Dimensions - Deep concrete chambers are approximately equal in width and depth with an open bottom and perforated side walls.
2. Limitations - Deep concrete chambers are prohibited for OWTS Applications for New Building Construction and OWTS Applications for Alterations to a Structure. Deep concrete chambers will not be permitted for OWTS Applications for Repair where another type of leachfield designed in accordance with §§ 6.33, 6.34, and 6.35 of this Part can be sited and is deemed acceptable by the Department. The Licensed Designer must demonstrate that the repair alternatives to a deep concrete chamber, other than a bottomless sand filter or pressurized shallow narrow drainfield, are not feasible.
G. Deep Concrete Chamber Effective Leaching Area - Effective leaching area for deep concrete chambers shall be calculated based on § 6.35(H) of this Part. Required minimum leaching area shall be calculated in accordance with § 6.33(B) of this Part.
H. Deep Concrete Chamber Effective Leaching Area

Deep Concrete Chambers

12" stone on sides, 12" stone below

Each end unit (sq. ft.)

98

Each Interior Unit (sq. ft.)

58

I. Concrete Chamber Construction
1. Concrete chambers shall be constructed of precast concrete. The bottom of the chambers shall be open and the sides and end (end units) shall be perforated.
2. Access - The top of the chamber trench shall have an access opening into a chamber at intervals not greater than fifty feet (50') that consists of a removable cover of concrete, iron or other durable material. For OWTSs designed to dispose of up to two thousand (2,000) gallons per day and OWTSs that are not located under a paved area, the top of the access opening shall accommodate a riser and shall be brought to within one foot (1') of the finished grade and properly marked. For OWTSs designed to dispose of greater than two thousand (2,000) gallons per day, commercial OWTSs, and all OWTSs located under paved areas, the access openings shall meet the following requirements:
a. Access openings shall have a riser and shall be brought to finished grade;
b. Lids on the top of the concrete chambers should remain in place where practical. Lids for the openings at finished grade shall prevent unauthorized entry by meeting either of the following:
(1) Lids shall weigh a minimum of fifty-nine (59) pounds and fit tightly into the riser as shown in § 6.64 of this Part, Figure 6; or
(2) Lids shall be tamper resistant and mechanically fastened.
c. Surface water shall be diverted away from the access openings; and
d. Concrete chambers in place as of January 1, 2008 that have access openings to finished grade shall be in compliance with the provisions of § 6.35(H)(2)(b) of this Part no later than January 1, 2013.
J. Excavation and Construction of a Concrete Chamber Leachfield
1. The overall width of the trench must not exceed six feet (6').
2. Spacing - The minimum distance between walls of adjacent trenches in a concrete chamber leachfield shall be at least six feet (6').
3. The soil between the dispersal trenches shall remain undisturbed. The Director may approve designs where the soil within the entire area of the leachfield is removed if the applicant shows that trench excavation is impractical, for example due to the presence of excessive boulders or stumps. When the soil within the entire area of the leachfield is removed, the soil shall be replaced with properly compacted gravel meeting the requirements of § 6.33(M) of this Part to a depth that will be to the top of the chamber. The trench shall be excavated out of the compacted gravel.
4. A six inch (6") layer of gravel meeting the requirements of § 6.33(M) of this Part shall be placed below the stone in the trench. Where the bottom of the stone lies on or within a soil horizon that meets the description of Soil Category 1 from § 6.16(L) of this Part and such horizon is at least six inches (6") thick below the stone, the six inch (6") gravel base layer is not necessary. However, if this Soil Category 1 horizon is described as extremely cobbly, the six inch (6") gravel base layer shall be required.
5. Stone - Stone meeting the requirements of § 6.33(K) of this Part shall be placed beneath the chamber in accordance with §§ 6.35(E) or (H) of this Part. The space between the excavation and the chamber wall shall be twelve inches (12") and shall be backfilled with stone to the top of the chamber. The stone and the top of the chambers shall be covered with filter fabric that meets the requirements of § 6.33(K) of this Part.
K. Effluent Distribution
1. The invert of the inlet of the chamber shall be two inches (2") lower than the invert of the outlet of the distribution box.
2. The maximum length of a chamber trench shall be as follows:
a. Without dosing - fifty feet (50');
b. With a tipping distribution box - seventy-five feet (75)'; or
c. With a pump - one hundred feet (100').
3. Effluent shall be applied to the chamber trenches at least every twenty-five feet (25').
4. For multiple trench concrete chamber leachfields, the ends of the chamber trenches shall be interconnected with imperforated SDR 35 PVC pipe laid with watertight joints. If the pipe will be subject to vehicular traffic, it shall be Schedule 40 PVC.
L. Location Under Traffic Areas - The area subject to vehicular traffic, including parking areas, shall be limited to twenty-five percent (25%) of the leachfield area. Where any portion of the leachfield is installed under an area subject to vehicular traffic, the structure must be capable of withstanding HS-20 wheel loads. All access manholes in areas subject to vehicular traffic shall be brought to grade with covers and frames capable of withstanding HS-20 wheel loads and meeting the requirements of §§ 6.35(I)(2)(a) through (d) of this Part. Such OWTSs must be vented with screened vents located in a protected area.

250 R.I. Code R. 250-RICR-150-10-6.35

Amended effective 11/25/2018
Amended effective 12/28/2021
Amended effective 7/1/2022