N.M. Admin. Code § 20.9.4.13 - DESIGN CRITERIA FOR MUNICIPAL LANDFILLS, SPECIAL WASTE LANDFILLS AND MONOFILLS

A. Except as specified in 20.9.2.14 NMAC and Subsection C of this section, all new municipal and special waste landfills and lateral expansions to existing municipal and special waste landfills shall provide a containment layer beneath the solid waste which is constructed:

(1) with a composite liner consisting of two components;

(a) the upper component shall consist of a minimum 30-mil flexible or a 60-mil high density polyethylene (HDPE) geomembrane liner or equivalent material; the geomembrane component shall be installed in direct and uniform contact with the lower component; and

(b) the lower component shall consist of a geosynthetic clay liner (GCL) or a minimum 24-inch thick layer of compacted soil having a saturated hydraulic conductivity of no more than 1x10^-7 centimeters per second (cm/sec) throughout its thickness; the soil must be free of particles greater than one inch in any dimension; or

(2) with an alternative liner in accordance with a design, which provides protection equivalent to the composite liner defined in Paragraph (1) of this subsection.

B. When approving an alternative liner design under this section, the secretary shall consider at least the following factors:

(1) the climatic factors of the area; and

(2) the volume and physical and chemical characteristics of the leachate.

C. Asbestos waste monofills and scrap tire monofills may be exempted from the design criteria in this section if the owner or operator demonstrates to the secretary in the permit application that the waste will not generate leachate which poses a threat to ground water quality, but shall still comply with Subparagraph (h) of Paragraph (1) of Subsection A of 20.9.6.9 NMAC.

D. Scrap tire monofills shall be designed with trenches not to exceed a maximum depth of 15 feet, a maximum width of 50 feet, and a maximum length of 100 feet. A distance of 40 feet shall be maintained between trenches. Trenches shall be filled to original grade.

E. The design and construction of all liners shall conform to the following criteria:

(1) general requirements:

(a) all liners must be able to withstand the projected loading stresses and disturbances from overlying waste, waste cover materials, and equipment operation;

(b) all liners shall incorporate a leachate collection system that meets the requirements of 20.9.4.15 NMAC; and

(c) all liners must be constructed with a minimum two percent slope to promote positive drainage and facilitate leachate collection;

(2) requirements for geosynthetic components:

(a) geosynthetic components of a liner system must be compatible with the waste to be contained; they must be able to resist chemical attack from the waste or leachate; this shall be demonstrated by means of manufacturer's test reports, or laboratory analyses;

(b) any geosynthetic materials installed on slopes greater than 25 percent, or on any slope where waste is projected to be more than 100 feet deep, must be designed to withstand the calculated tensile forces acting upon the geosynthetic materials; the design must consider the maximum friction angle of the geosynthetic with regard to any soil-geosynthetic or geosynthetic-geosynthetic interface and must ensure that overall slope stability is maintained; and

(c) field seams in geosynthetic material shall be oriented parallel to the line of maximum slope (i.e., oriented along, not across the slope); the number of field seams in corners and irregular shaped areas shall be minimized; there shall be no horizontal seam within five feet of the toe of the slope;

(3) requirements for the soil component of all liners:

(a) the bottom geosynthetic layer, shall be placed on a prepared subgrade consisting of, at a minimum, of a 6-inch layer of in-situ soil or select fill compacted to 90 percent standard Proctor density;

(b) the surface of the soil upon which a geosynthetic liner will be installed must be free of stones greater than 1/2-inch in any dimension, organic matter, local irregularities, protrusions, loose soil, and any abrupt changes in grade that could damage the geosynthetic liner; and

(c) the soil component of the composite liner defined in Subparagraph (b) of Paragraph (1) of Subsection A of this section shall be compacted to a minimum of 90 percent standard Proctor density and shall have the following physical characteristics unless otherwise specifically approved by the department:

(i) plasticity index greater than 10 percent;

(ii) liquid limit between 25 percent and 50 percent;

(iii) portion of material passing the No. 200 sieve (0.074 mm and less fraction) greater than 40 percent (by weight); and

(iv) clay content greater than 18 percent (by weight);

(4) all liners shall have a top protective cover of at least two feet of granular soil or other material specifically approved by the department; the protective cover shall, in addition to providing physical protection for the liner, facilitate the collection of leachate in the leachate collection system; materials used to construct the protective cover must ensure the hydraulic leachate head on the liner does not exceeds one foot; the soil material shall be free of any organic matter and have the following physical characteristics unless otherwise specifically approved by the secretary:

(a) portion of material passing the No. 200 sieve (0.074 mm and less fraction) no greater than 5 percent by weight; and

(b) uniformity coefficient (Cu) less than 6 where Cu is defined as D60/D10.

Notes

N.M. Admin. Code § 20.9.4.13

20.9.4.13 NMAC - Rp, 20 NMAC 9.1.III.306, 08/02/07