S.C. Code Regs. § 61-56.503

Current through Register Vol. 48, No. 07, July 26, 2024

Section 61-56.503 - Minimum Design Standards for Tank Construction

503.1. Introduction.

The following standards describing tank designs intended to be utilized for septic tanks, grease traps, or pump chambers for onsite wastewater systems have been adopted in an effort to assure a quality product of sufficient strength and resistance, capable of fulfilling its intended purpose.

503.2. Design Approval.

(1) No person shall manufacture tanks intended to be utilized for septic tanks, grease traps, or pump chambers for onsite wastewater systems without receiving approval from the Department. All manufactured tanks must receive approval of design and reinforcement methods prior to manufacturing.

(2) Any person desiring to manufacture tanks shall submit a written application on forms provided by the Department. Such application shall include the name and address, the location of the facility, tank capacity, and design information.

(3) Prior to approval, the Department shall review the tank design, reinforcement, and manufacturing methods to determine compliance.

(4) The Department shall approve plans for manufactured tanks to ensure compliance with the South Carolina Minimum Design Standards for Tank Construction.

(5) The Department shall approve plans for fabricated tanks, other than those for precast reinforced concrete tanks, on an individual basis. Fabricated tanks shall meet the requirements of precast reinforced concrete tanks to provide equivalent effectiveness.

(6) The Department shall issue an approval to the tank manufacturer if the tank design, reinforcement and manufacturing method complies with the South Carolina Minimum Design Standards for Tank Construction. Tank manufacturing approvals are not transferable. When a change of ownership occurs, the new owner shall submit a written application on forms provided by the Department.

(7) The Department shall revoke approval to manufacture tanks for onsite wastewater systems if the tank manufacturer fails to comply with the South Carolina Minimum Design Standards for Tank Construction.

503.3. General.

(1) Septic tanks and grease traps shall be manufactured as single compartment or partitioned tanks.

(2) If septic tanks and grease traps are manufactured with a partition so that the tank contains two (2) compartments, the inlet compartment of the tank shall contain two-thirds (2/3) of the overall capacity, and the outlet compartment shall contain one-third (1/3) of the overall capacity. The top of the partition shall terminate two (2) inches below the bottom side of the tank top in order to leave space for air or gas passage between compartments. The top and bottom halves of the partition shall be constructed in such manner as to leave a four (4) inch water passage at the vertical mid-point of the partition wall for the full width of the tank.

(3) The minimum liquid capacity requirements shall be met by the use of a single septic tank or two (2) or more tanks installed in series. Septic tanks joined in series shall be interconnected by an upper effluent pipe(s) with a minimum diameter of four (4) inches and a lower sludge pipe(s) with a minimum diameter of twelve (12) inches. The upper connection(s) shall be installed level from tank to tank, and the lower sludge pipe connection(s) shall be installed level and shall be placed twelve (12) inches above the bottoms of the tanks. The lower sludge pipe connection(s) can be eliminated if the first tank in series contains at least two-thirds (2/3) of the total required liquid capacity. There shall be no more than two (2) inches of fall from the inlet invert of the first tank to the outlet invert of the last tank in series.

(4) It is required that all pump chambers function as a single compartment tank. If a two (2) compartment tank is used, at least two (2) six (6) inch diameter holes or equivalent, must be provided in the partition wall six (6) inches from the tank bottom.

(5) The septic tank and grease trap tank length shall be at least two (2) but not more than three (3) times the width.

(6) The liquid depth shall not be less than four (4) feet.

(7) A minimum of nine (9) inches of freeboard shall be provided in all tanks, unless otherwise approved by the Department.

(8) Useable liquid capacity for septic tanks or grease traps shall not be less than one thousand (1000) gallons.

(9) The pump tank shall have sufficient capacity to accommodate all level control and alarm switches; to keep the pump(s) totally submersed in liquid at all times and to provide the required dosing volume and minimum pump run time. It is strongly recommended that pump tank capacities be as large as possible in order to provide emergency storage in the event of pump or power failure.

(10) There shall be a minimum of two (2) openings in the tank wall located at the inlet and outlet ends or sides of the inlet and outlet ends of the tank. The knockouts for the inlet and outlet openings of pre-cast concrete tanks shall have a concrete thickness of not less than one (1) inch in the tank wall. The openings shall allow for a minimum of four (4) inch pipe or a maximum of six (6) inch pipe. No openings shall be permitted below the tank liquid level.

(11) The inlet and outlet for septic tanks and grease traps shall be a cast-in-place concrete tee, a polyvinyl chloride (PVC) tee, an acrylonitrile butadiene styreneor (ABS), or a polyethylene (PE) tee made of not less than Schedule 40 pipe or equivalent fittings and material. The cast-in-place concrete tees shall have a minimum thickness of not less than two (2) inches. The invert of the outlet shall be at least two (2) inches lower in elevation than the invert of the inlet. The inlet and outlet tees shall extend above liquid level a minimum of six (6) inches and to no less than one (1) inch from the top of the tank to allow venting between tank compartments and multiple tank configurations.

(12) The inlet tee for septic tanks and grease traps shall extend sixteen (16) inches below the liquid level.

(13) The outlet tee for a septic tank shall extend eighteen (18) inches below the liquid level and the outlet tee for a grease trap shall extend between six (6) and twelve (12) inches above the tank bottom.

(14) The inlet, outlet, and wiring conduit openings of all tanks must utilize a resilient, watertight, non-corrosive connective sleeve. The use of grout is prohibited.

(15) Access to each tank or compartment shall be provided by an opening located above the inlet and outlet with an inside dimension of at least eighteen (18) inches square (18 x 18) or in diameter, with removable tank access lids.

(16) Concrete tank access lids shall be equipped with steel lift rings at least three-eighths (3/8) inch diameter or by an alternative method approved by the Department.

(17) Should risers or manholes be utilized to allow access into septic tanks, grease traps, or pump chambers, the risers or manhole covers, as applicable, shall be constructed to prevent the release of odors, entry of vectors, and water. Grade level riser/manhole covers shall be secured by bolts, locking mechanisms, fasteners that can only be removed by tools, or have sufficient weight to prevent unauthorized access. The ground shall slope away from any access extended to grade level.

(18) Risers/manholes shall be sealed to the tank by using bituminous mastic, butyl rubber, or other pliable sealant that is waterproof, corrosion-resistant, and approved for use in tank construction. The sealant shall have a minimum size of one (1) inch diameter or equivalent. The joint shall be smooth, intact, and free of all deleterious substances before sealing.

(19) After curing, all multi-piece tanks shall be joined and sealed at the joints by using a bituminous mastic, butyl rubber, or other pliable sealant that is waterproof, corrosion-resistant, and approved for use in tank construction. The sealant shall have a minimum size of one (1) inch diameter or equivalent. The joint shall be smooth, intact, and free of all deleterious substances before sealing. The use of grout is prohibited.

(20) All concrete tanks must pass the ASTM C-1227 Standard for watertight testing. The Department will choose tanks at random for testing. Tanks will be approved for use in South Carolina after the Department ascertains that the standard is met. After joining, tanks manufactured in multiple sections shall be plastered along the section joints with hydraulic cement or other waterproofing sealant. Other methods of waterproofing tanks may be used as specifically approved in the plans and specifications for the tank. Prior to backfilling, the Department shall make a finding that multiple section tanks are watertight if a soil wetness condition is present within five feet of the elevation of the top of the tank. Any tank found to be improperly sealed, having cracks or holes, which will allow for water infiltration or discharge of sewage from the tank bottom, walls, or top, will not be approved for use.

(21) Concrete tank manufacturers must have equipment and capabilities for portion control to maintain constant mixture formulation ratios and provide for systematic inspection of finished products to ensure compliance with the minimum tank construction and design standards.

(22) The concrete mix used for concrete tank components must be formulated to yield a minimum twenty-eight (28) day compressive strength of four thousand (4,000) pounds per square inch (psi).

(23) The aggregate size utilized in the concrete mix shall not exceed one-third (1/3) of the wall thickness. Suitable aggregates include sand particle sizes from a fine to one-fourth (1/4) inch gravel or crushed stone. Granite dust or fine screenings from a crusher operation may be used in lieu of sand.

(24) An identifying seal must be cast, molded, or permanently affixed by an approved method from the Department on the outlet tank wall within six (6) inches of the top. The identifying seal shall identify the manufacturer and the liquid capacity of the tank. The concrete tank's cast date shall be located on the identifying seal or imprinted on the top of the tank within six (6) inches from outlet tank wall near the identifying seal. The lettering on the identifying seal or date imprinted on the top of the tank shall be no more than six (6) inches in height.

(25) The tank manufacturer shall guarantee all tanks in writing for two (2) years against failure due to poor workmanship and materials.

(26) Changes in approved tank design, construction, and alternative reinforcing methods will not be allowed without prior approval from the Department.

503.4. Pre-Cast Concrete Non-Fiber Reinforced Septic Tanks and Grease Traps.

(1) The tank walls and bottom shall be reinforced with six by six (6 x 6) inch ten (10) gauge wire mesh.

(2) Tank tops shall be reinforced with six by six (6 x 6) inch ten (10) gauge wire mesh, a minimum of five (5) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls beginning at the center spaced twelve (12) inches apart and four (4) sections of three-eighths (3/8) inch diameter steel reinforcing bars placed diagonally from the corners to the center of the tank. The length of the perpendicular reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall. The length of the four (4) diagonal steel reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall and six (6) inches beyond the closest perpendicular steel reinforcing bar.

(3) If a septic tank or grease trap is manufactured with a partition, the tank partition (both halves) shall be reinforced with six by six (6 x 6) inch ten (10) gauge wire mesh. The reinforcing wire shall be bent to form an angle of ninety (90) degrees on the ends in order to form a leg not less than four (4) inches long. When the wire is placed in the mold, the four-inch legs shall lay parallel with the sidewall wire and adjacent to it.

(4) The tank walls and bottom thickness shall be at least two and one-half (21/2) inches, and top thickness shall be at least three (3) inches.

(5) All reinforcing wire and rods must be covered by at least one-half (1/2) inch of concrete.

(6) An acceptable vibration method shall be employed in the construction of the tank to prevent voids in the tank walls, bottom, and top.

503.5. Pre-Cast Concrete Fiber Reinforced Septic Tanks and Grease Traps.

(1) Tank tops shall be reinforced with a minimum of five (5) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls beginning at the center spaced twelve (12) inches apart, and four (4) sections of three-eighths (3/8) inch diameter steel reinforcing bars placed diagonally from the corners to the center of the tank. The length of the perpendicular reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall. The length of the four (4) diagonal steel reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall and six (6) inches beyond the closest perpendicular steel reinforcing bar.

(2) Tank bottoms shall be reinforced with a minimum of seven (7) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls beginning at the center spaced twelve (12) inches apart. The length of the perpendicular reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall.

(4) The tank perimeter walls shall be reinforced with three-eighths (3/8) inch diameter steel reinforcing bars located one (1) inch from the tank's top and bottom section seams.

(5) The tank walls and bottom thickness shall be at least two and one-half (21/2) inches, and top thickness shall be at least three (3) inches.

(6) All reinforcing wire and rods must be covered by at least one-half (1/2) inch of concrete.

(7) Fiber products used with this reinforcement design must be added during the mixing process in order to achieve even distribution throughout the concrete mixture.

(8) Fiber length must range from at least one (1) to no more than two (2) inches.

(9) The fiber must be specifically manufactured for use as a concrete secondary reinforcement and be a polypropylene fibrillated (two-dimensional fiber mesh network) material.

(10) An acceptable vibration method shall be employed in the construction of the tank to prevent voids in the tank walls, bottom, and top.

503.6. Concrete Block Septic Tanks and Grease Traps.

(1) The tank walls and partition thickness shall be at least eight (8) inches and the top cover slabs thickness shall be at least four (4) inches.

(2) The tank bottom shall be a single pour concrete slab to a depth of at least four (4) inches within the first block course.

(3) If a septic tank or grease trap is manufactured with a partition, the tank walls and partition shall be constructed of solid sixteen by eight by eight (16 x 8 x 8) inch concrete blocks. The use of hollow blocks is prohibited.

(4) All joints between concrete blocks shall be mortared using masonry cement mortar or equivalent. The joints shall have a nominal thickness of three-eighths (3/8) inch.

(5) The upper partition wall may be supported by the use of two by four by eight (2 x 4 x 8) inch bricks (or equivalent support material) standing on edge located at the block seams of the upper partition wall.

(6) The top cover slabs shall be constructed such that the individual slabs will not exceed two (2) feet in width and the length will be sufficient to extend to the outside tank width with a minimum slab thickness of four (4) inches.

(7) The individual top cover slabs shall be reinforced with a minimum of two (2) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls spaced twelve (12) inches apart from the center. The length of the perpendicular reinforcing bars shall be of sufficient length to extend the full length of the slab.

(8) The end cover slabs shall be constructed such that the individual slabs will not exceed three (3) feet in width and the length will be sufficient to extend to the outside tank width with a minimum slab thickness of four (4) inches.

(9) The end cover slabs shall be cast to allow access to each tank or compartment by providing an opening located above the inlet and outlet tee with an inside dimension of eighteen (18) inches square (18 x 18 inches) or in diameter with removable tank access lids.

(10) The individual end cover slabs shall be reinforced with two (2) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls spaced twelve (12) inches apart from the center and two (2) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls spaced sixteen (16) inches apart from the center. The length of the perpendicular reinforcing bars shall be of sufficient length to extend the full length of the slab.

(11) The top and end cover slab seams shall be sealed to the tank walls and at all joints by using a bituminous mastic, butyl rubber, or other pliable sealant that is waterproof, corrosion-resistant, and approved for use in septic tanks. The sealant shall have a minimum size of one (1) inch diameter or equivalent. The use of grout is prohibited.

(12) The tank top and end cover slabs shall be equipped with steel lift handles at least one half (1/2) inch diameter, or by an alternative method approved by the Department.

(13) All reinforcing rods must be covered by at least one-half (1/2) inch of concrete.

(14) The interior of the tank (walls and bottom) shall be plastered with a waterproofing cement compound.

(15) An acceptable vibration method shall be employed in the construction of the tank to prevent voids in the tank access lids, tank bottom, and top and end slabs.

503.7. Pre-Cast Concrete Non-Fiber Reinforced Pump Chambers.

(1) The tank walls and bottom shall be reinforced with six by six (6 x 6) inch ten (10) gauge wire mesh.

(2) Tank tops shall be reinforced with six by six (6 x 6) inch ten (10) gauge wire mesh, a minimum of five (5) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls beginning at the center spaced twelve (12) inches apart, and four (4) sections of three-eighths (3/8) inch diameter steel reinforcing bars placed diagonally from the corners to the center of the tank. The length of the perpendicular reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall. The length of the four (4) diagonal steel reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall and six (6) inches beyond the closest perpendicular steel reinforcing bar.

(3) The tank walls and bottom thickness shall be at least two and one-half (21/2) inches, and top thickness shall be at least three (3) inches.

(4) All reinforcing wire and rods must be covered by at least one-half (1/2) inch of concrete.

(5) An acceptable vibration method shall be employed in the construction of the tank to prevent voids in the tank walls, bottom, and top.

503.8. Pre-Cast Concrete Fiber Reinforced Pump Chambers.

(1) Tank tops shall be reinforced with a minimum of five (5) sections of three-eighths (3/8) inch diameter steel reinforcing bars oriented perpendicular to the tank sidewalls beginning at the center spaced twelve (12) inches apart and four (4) sections of three-eighths (3/8) inch diameter steel reinforcing bars placed diagonally from the corners to the center of the tank. The length of the perpendicular reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall. The length of the four (4) diagonal steel reinforcing bars shall be of sufficient length to extend two (2) inches into the sidewall and six (6) inches beyond the closest perpendicular steel reinforcing bar.

(3) The tank perimeter walls shall be reinforced with three-eighths (3/8) inch diameter steel reinforcing bars located one (1) inch from the tank's top and bottom section seams.

(4) The tank walls and bottom thickness shall be at least two and one-half (21/2) inches, and top thickness shall be at least three (3) inches.

(5) All reinforcing wire and rods must be covered by at least one-half (1/2) inch of concrete.

(6) Fiber products used with this reinforcement design must be added during the mixing process in order to achieve even distribution throughout the concrete mixture.

(7) Fiber length must range from at least one (1) to no more than two (2) inches.

(8) The fiber must be specifically manufactured for use as a concrete secondary reinforcement and be a polypropylene fibrillated (two-dimensional fiber mesh network) material.

(9) An acceptable vibration method shall be employed in the construction of the tank to prevent voids in the tank walls, bottom, and top.

S.C. Code Regs. 61-56.503

Added by State Register Volume 45, Issue No. 05, eff. 5/28/2021.