N.M. Admin. Code § 20.7.3.702

Current through Register Vol. 35, No. 21, November 5, 2024

Section 20.7.3.702 - DESIGN; SEEPAGE PIT; DESIGN AND CONSTRUCTION

Seepage pits should only be installed on sites where conventional disposal systems cannot be installed due to site restrictions.

A. The minimum capacity of seepage pits shall conform to the requirements of 20.7.3.703 NMAC.

B. Multiple seepage pit installations shall be served through an approved distribution box or be connected in series by means of a watertight connection laid on undisturbed or compacted soil. The outlet from each seepage pit shall have an approved vented leg fitting extending at least 12 inches below the inlet fitting.

C. Each seepage pit shall have an excavated horizontal dimension of not less than four feet and the maximum horizontal dimension shall not exceed the vertical dimension. Each such pit shall be lined with approved type whole, new, hard-burned clay brick, concrete brick, concrete circular type cesspool blocks or other approved materials.

D. The lining in each seepage pit shall be circular and laid on a firm foundation. Lining materials shall be placed tight together and laid with joints staggered. Except in the case of approved type pre-cast concrete circular sections, no brick or block shall be greater in height than its width and shall be laid flat to form at least a four inch wall. Brick or block greater than 12 inches in length shall have chamfered matching ends and be scored to provide for seepage. Excavation voids behind the brick, block or concrete liner shall have a minimum of six inches of clean 3/4 inch gravel or rock.

E. All brick or block used in seepage pit construction shall have a minimum compressive strength of 2500 pounds per square inch.

F. Each seepage pit shall have a minimum sidewall (not including the arch) of 10 feet below the inlet pipe.

G. The arch, cover or dome of any seepage pit shall be constructed in one of the following three ways.

(1) Approved type hard-burned clay brick, solid concrete brick or block laid in cement mortar.

(2) Approved brick or block laid dry. In both of the above methods, an approved cement mortar covering of at least two inches in thickness shall be applied, said covering to extend at least six inches beyond the sidewalls of the pit.

(3) Approved type one or two piece reinforced concrete slab of 3000 pounds per square inch minimum compressive strength, not less than five inches thick and designed to support an earth load of not less than 400 pounds per square foot.

H. Each such arch, dome or cover shall be provided with a nine inch minimum inspection hole with plug or cover and shall be coated on the underside with an approved bituminous or other nonpermeable protective compound.

I. The top of the arch, dome or cover must be a minimum of 12 inches but not more than four feet below the surface of the ground. Risers must be provided to extend the arch, dome or cover to within 12 inches of the surface.

J. An approved vented inlet fitting shall be provided in every seepage pit so arranged as to prevent the inflow from damaging the sidewall. When using a one or two piece concrete slab cover, the inlet fitting must be an approved 1/4 bend fitting discharging through an opening in the top of the slab cover. On multiple seepage pit installations, the outlet fittings shall meet the requirements of Subsection B of 20.7.3.702 NMAC.

K. A six inch layer of bentonite clay shall be installed at the bottom of the seepage pit to restrict effluent flow through the bottom area. Alternative material to the bentonite clay may be approved by the department after review.

N.M. Admin. Code § 20.7.3.702

20.7.3.702 NMAC - Rp, 20.7.3.702 NMAC, 9/1/13