N.M. Admin. Code § 20.7.3.502

Current through Register Vol. 35, No. 23, December 10, 2024

Section 20.7.3.502 - DESIGN; CONVENTIONAL TREATMENT UNITS; CONSTRUCTION STANDARDS

A. All conventional treatment units, regardless of material or method of construction and unless otherwise specified in this part, shall be designed to produce a clarified effluent and shall provide adequate space for sludge and scum accumulations based on a minimum hydraulic retention time of 24 hours at maximum sludge depth and scum accumulation.

B. Septic tanks shall have a minimum of two compartments. The inlet compartment of a septic tank shall be 2/3 of the total liquid capacity of the tank, but not less than 500 gallons liquid capacity, and shall be at least three feet in width and five feet in length. Liquid depth shall be not less than two feet and six inches nor more than six feet. The second compartment of a septic tank shall have a liquid capacity of 1/3 of the total capacity of such tank. In septic tanks having over ,1500 gallons capacity, the second compartment may not be less than three feet in length.

C. Multiple tanks installed in series may be allowed with department approval provided the total tank volume is at least 2.5 times the system design flow. Minimum tank sizes are as follows:

(1) for flows up to 1,000 gpd, the capacity of each tank must be at a minimum 900 gallons; and

(2) for flows between 1,000 and 5,000 gpd, the capacity of each tank must be a minimum of 1,200 gallons.

D. Access to each septic tank shall be provided by at least two access openings, each of which shall be at least 20 inches in minimum dimension. One access opening shall be placed over the inlet and one access opening shall be placed over the outlet. Whenever a first compartment exceeds 12 feet in length, an additional access opening shall be provided over the baffle wall. Each access opening shall be extended to the surface of the ground with a secure lid. These access risers shall be 24 inches in diameter for depths of zero to three feet and for depths greater than three feet shall be at least 30 inches in diameter. If the access risers are made of concrete, they shall be coated with a coating approved by the department. "Wet-or-dry" coatings and mastics, or other water-based materials are not acceptable. Access risers shall be constructed of precast concrete, premanufactured plastic made for risers, culvert or double wall high density polyethylene or equivalent plastic with proper covers or lids. Rain barrels, trash cans or 55-gallon drums or other inappropriate materials are not acceptable access riser material.

E. The inlet and outlet pipe openings shall be not less in size than the connecting sewer pipe and shall have a watertight seal approved by the department. The vertical leg of round inlet and outlet fittings shall not be less in size than the connecting sewer pipe nor less than four inches. A baffle type fitting shall have the equivalent cross-sectional area of the connecting sewer pipe and not less than a four inch horizontal dimension when measured at the inlet and outlet pipe inverts, unless it is a pumped system.

F. The inlet and outlet pipe or baffle shall extend at least four inches above and at least 12 inches below the water surface. The invert of the inlet pipe shall be at a level not less than two inches above the invert of the outlet pipe. Inlet and outlet pipe or baffles shall be, at a minimum, schedule 40 PVC, ABS or cast-in-place concrete.

G. Inlet and outlet pipe fittings or baffles and compartment partitions shall have a free vent area equal to the required cross-sectional area of the building sewer or private sewer discharging into the septic tank to provide free ventilation above the water surface from the disposal field or seepage pit through the septic tank, building sewer and stack to the outer air.

H. All septic tanks shall include an effluent filter approved by the department, installed on the outlet of the tank before final discharge, with an access riser installed to grade, and with a handle extending to within six inches of the top of the riser.

I. The sidewalls, except on cylindrical tanks, shall extend at least nine inches above the liquid depth. The cover of the septic tank shall be at least two inches above the back vent openings.

J. Partitions or baffles between compartments shall be of solid, non-corrosive, durable material and shall extend at least four inches above the water level. Metal or wooden baffles are prohibited.

(1) An inverted fitting equivalent in size to the tank inlet, but in no case less than four inches in size, shall be installed in the inlet compartment side of the baffle with the bottom of the fitting placed midway in the depth of the liquid.

(2) If a horizontal slot is used, the slot shall extend the width of the tank, be no more than six inches in height and located midway in the depth of the liquid.

K. Fiberglass or reinforced plastic tanks shall be certified to current IAPMO standards.

(1) Each access and inspection hole cover shall have approved fasteners not subject to deterioration by liquid or gases normally present in septic tank systems to assure that the covers will remain in place. All covers shall overlap the hole by a minimum of two inches in all directions.

(2) Each tank shall be free from visual defects such as foreign inclusions, dry spots, air bubbles, pimples and delamination. The inner and outer surfaces shall have a smooth, continuous finish with no exposed fibers. Both the inner and outer surfaces shall have a continuous resin rich surface and no fibers shall be exposed either directly from cracks, porosity or holes, or indirectly through bubbles that may break and expose fibers.

N.M. Admin. Code § 20.7.3.502

20.7.3.502 NMAC - Rp, 20.7.3.502 NMAC, 9/1/13

Amended, New Mexico Register, Volume XXV, Issue 15, August 15, 2014, eff. 9/15/2014