250 R.I. Code R. 250-RICR-150-10-6.27

Current through December 26, 2024

Section 250-RICR-150-10-6.27 - Septic Tanks

A. See § 6.63 of this Part, Figure 5.

B. Septic Tank Capacity

1. Residential Dwellings - The required minimum liquid capacity of a septic tank, below the flow line, shall be based on the number of bedrooms in the dwelling. For three (3) bedrooms or less the minimum capacity shall be one thousand (1,000) gallons. For each additional bedroom, add two hundred fifty (250) gallons. A garbage grinder or a one hundred (100) gallon or greater tub will each require the septic tank capacity be increased by two hundred fifty (250) gallons.

2. Non-Residential Buildings - The required minimum liquid capacity of the septic tank shall be one thousand (1,000) gallons or two (2) times the design flow as determined from § 6.22(B) of this Part, whichever is greater.

C. Construction and Materials - Septic tanks shall be watertight. They shall be constructed of sound and durable materials not subject to excessive corrosion, decay or frost damage or to cracking or buckling due to settlement or soil pressures. Septic tanks shall be constructed of precast reinforced concrete, fiberglass, polyethylene or other material approved by the Director. In addition to the construction and material standards in §§ 6.27(C)(1) through (3) of this Part, all septic tanks shall meet the physical design standards in the remainder of § 6.27 of this Part.

1. Precast reinforced concrete septic tanks shall conform to the American Society for Testing and Materials "Standard Specification for Precast Concrete Septic Tanks C- 1227-10a " and any updates thereto, incorporated above at § 6.7(A) of this Part. Any weep holes in the precast reinforced concrete septic tank shall be placed on the side of the tank bottom to allow for safe inspection and assurance that the weep hole has been plugged.

2. Fiberglass septic tanks and polyethylene septic tanks shall conform to the International Association of Plumbing and Mechanical Officials "American National Standard for Prefabricated Septic Tanks IAPMO/ANSI Z 1000-2007 " and any updates thereto, incorporated above at § 6.7(B) of this Part.

3. Each septic tank shall be clearly and permanently marked at the inlet end of the tank with:

a. Date of manufacture;

b. Name or trademark of the manufacturer;

c. Septic tank capacity; and

d. Indication of external loads for which the septic tank is designed to resist.

D. Shape - There shall be no less than twenty-five (25) square feet of surface liquid area. The distance between the inlet wall of the tank and the outlet wall shall be no less than six feet (6'). The depth of the tank below the flow line shall be not less than thirty-nine inches (39") or more than eight feet (8'). There shall be at least nine inches (9") of air space between the surface of the liquid and the interior roof of the septic tank.

E. Compartments - All septic tanks shall have two (2) compartments with adequate connection at mid-depth, and all tanks shall meet the following requirements:

1. The first compartment shall have a liquid volume of approximately two thirds (2/3) of the required liquid volume for the entire tank.

2. The interior compartment wall shall not extend to the interior roof without providing for venting equivalent to the cross sectional area of at least a four inch (4") diameter pipe.

F. Inlet and Outlet

1. One (1) inlet and one (1) outlet shall be provided through the appropriate end or side wall of each tank. Where more than one (1) inlet is required for multiple building sewers, the tank shall be manufactured with the appropriate number of inlets.

2. Inlet and Outlet Elevations - The invert elevation of the outlet shall be at least three inches (3") below the invert elevation of the inlet, and above the seasonal high groundwater table, unless special construction approved by the Director is provided.

3. The inlet and outlet pipes shall be connected to the tank with a watertight sealed flexible joint. The pipe gasket shall be an integral part of all tanks and the pipe gasket shall be fastened to the pipe with a stainless steel retractable clamp.

G. Inlet and Outlet Tees - Septic tanks shall be provided with an inlet sanitary tee and outlet tees or other non-corroding equivalent device approved by the Director. The inlet and outlet tees shall be minimum SDR 35 PVC solvent welded. The tops of the tees shall extend a minimum of six inches (6") above the flow line, and shall be left open to provide ventilation. There shall be an air space of at least three inches (3") between the tops of the tees and the top interior of the tank.

1. The inlet sanitary tee shall extend downward at least one foot (1') below the flow line.

2. The outlet tee shall extend downward one third (1/3) of the depth below the flow line. All outlet tees or other approved outlet devices shall be equipped with an effluent screen approved by the Department pursuant to § 6.41 of this Part.

3. Specifications for inlet tees and outlet tees are for normal, low-flow conditions. High-flow conditions, created when liquid is pumped from another tank, may require other dimensions and considerations.

H. Access Openings - A minimum twenty inch (20") inside diameter access opening shall be located over both the inlet tee and outlet tee. All septic tank openings shall meet the following requirements:

1. The access opening over the outlet tee shall be brought to finished grade. Other access openings shall either be brought to finished grade or within twelve inches (12") of the finished grade. Where a riser is required, it shall be watertight;

2. Lids on the top of the septic tank (§ 6.64 of this Part, Figure 6) should remain in place where practical. Lids for the openings at finished grade shall prevent unauthorized entry by meeting either of the following:

a. Lid shall weigh a minimum of fifty-nine (59) pounds and fit tightly onto the riser as shown in § 6.64 of this Part, Figure 6; or

b. Lid shall be tamper resistant and mechanically fastened;

3. The septic tank manufacturers shall provide and the Licensed OWTS Installers shall attach a label of noncorrosive material in a prominent location at each access opening to warn that "Entrance Into the Tank Could Be Fatal"; and

4. Surface water shall be diverted away from the septic tank openings.

I. Accessibility - Septic tanks shall be so located on the lot as to be accessible for servicing and cleaning.

J. Installation - All septic tanks shall be installed in accordance with the manufacturer's minimum requirements. In addition, all septic tanks must meet the installation requirements specified in the remainder of these Rules.

1. Foundation - The septic tank shall be installed on a level, stable base that will not settle.

2. Backfill - Backfill shall be placed around the septic tank in such a manner as to avoid damage to it. All backfill placed around the septic tank shall be free of large stones, stumps, waste, construction material and rubbish.

3. Floatation - Where any portion of a septic tank is installed below the seasonal high groundwater table, the tank's susceptibility to floatation shall be determined, and provisions shall be made to prevent floatation where necessary as determined by the floatation calculations.

4. Septic Tanks in Coastal Velocity Zones - All fiberglass and polyethylene septic tanks larger than one thousand (1,000) gallons installed in a Federal Emergency Management Agency designated V-Zone shall be anchored to prevent floatation.

K. Septic Tanks in Series - Septic tanks placed in series are allowed provided they meet the following requirements:

1. Each tank shall be of single compartment design and the volume of the first tank shall be at least two thirds (2/3) the required tank size;

2. The outlet tee on the first tank shall extend down to the mid-depth of the liquid volume; and

3. An effluent screen that meets the requirements of § 6.27(G)(2) of this Part be provided on the outlet tee of the second (2^nd) tank.

L. Performance Testing - All septic tanks and their risers must be certified watertight by the manufacturer or by onsite testing. Onsite testing for septic tank leakage shall be conducted for tanks assembled at the installation site. The Director may require onsite testing on a case-by-case basis. The testing shall be conducted using either:

1. Vacuum Test - Seal the empty tank and risers and apply a vacuum to two inches (2") (50 mm) of mercury. The tank is approved if ninety percent (90%) of the vacuum is held for two (2) minutes; or

2. Water-Pressure Test - Seal the tank and risers, fill with water to the top of the risers, and let stand for twenty-four (24) hours. Refill the tank. The tank is approved if the water level is held for one (1) hour.

M. Pumping to Septic Tanks - Whenever more than twenty-five percent (25%) of the daily design flow is pumped into a septic tank, the tank capacity shall be increased by fifty percent (50%) beyond the minimum capacities specified in § 6.27(B) of this Part.

N. Depth of Cover - The minimum cover over the invert of the outlet shall be one and one half feet (11/2'). If the depth of cover exceeds three and one half feet (31/2'), the OWTS application shall include documentation of the tank's ability to structurally withstand the loading, and the tank's design shall allow for proper maintenance and access.

O. Existing Septic Tanks - Septic tanks in place as of January 1, 2008 shall be in compliance with the provisions of § 6.27(H)(2) of this Part no later than January 1, 2013.

250 R.I. Code R. 250-RICR-150-10-6.27

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