New Mexico Administrative Code › Title 20 - ENVIRONMENTAL PROTECTION › Chapter 7 - WASTEWATER AND WATER SUPPLY FACILITIES › Part 3 - LIQUID WASTE DISPOSAL AND TREATMENT › Section 20.7.3.703 - DESIGN; AREA OF DISPOSAL FIELD AND SEEPAGE PITS

Current through Register Vol. 35, No. 13, July 16, 2024
A. The minimum required absorption area in a
				disposal field in square feet, and in seepage pits in square feet of side wall,
				shall be predicated on the liquid waste design flow rate and shall be
				determined by utilizing the following Table 703.1 based on the soil
				classification found in the proposed location of the disposal field.
B. Two test holes, located at opposite ends
				of the proposed disposal area, may be required for obtaining the soil profile
				and as provided in Subsection A of 20.7.3.203 NMAC.
C. A detailed soil profile, in accordance
				with USDA soil classification methodology, shall be submitted with the liquid
				waste application for each hole, indicating soil horizons, horizon thickness as
				a function of depth, and soil texture.
D. USDA soil surveys may be used where
				available to help assess typical soils in the area of the proposed
				installation.
E. The required
				absorption area shall be sized on the most restrictive soil horizon located
				below and within four feet of the bottom of the absorption area.
F. Conventional treatment systems shall not
				be constructed in type Ia soils where the depth to groundwater is less than 30
				feet. For these soils, refer to 20.7.3.605 NMAC.
G. Effluent distribution to type IV soils
				shall be accomplished with an appropriate disposal method as approved by the
				department such as timed low pressure dosed distribution or alternating
				drainfields.
H. The required
				absorption area shall be calculated by the following formula: ABSORPTION AREA =
				Q X AR, where: Q = the design flow rate in gallons per day; AR = application
				rate (from Table 703.1)
Table 703.1: Application Rates by Soil Types for
				  Conventional Treatment Systems
Soil Type
Soil Texture
Application Rate
(AR)
(sq. ft./gal/day)
Ia
Ib
Coarse Sand
or up to 30% gravel
Medium Sand, Loamy Sand
1.25
(See Subsection F of 20.7.3.703 NMAC)
2.00
II
Sandy Loam, Fine Sand , Loam
2.00
III
Silt, Silt Loam, Clay Loam, Silty Clay Loam,
Sandy Clay Loam
2.00
IV
Sandy Clay, Silty Clay, Clay
5.00
(See Subsection G of 20.7.3.703 NMAC)
I.
				The gravel content of in-place natural soil shall not exceed 30%. The
				department may identify and map areas of the state where groundwater is not at
				risk from microbial contamination from on-site liquid waste disposal systems
				that discharge into gravel, and where gravel contents greater than 30% may be
				allowed. The following hydrogeologic conditions may be considered when
				determining if groundwater is not at risk:
(1) groundwater does not exist;
(2) uppermost groundwater contains a total
				dissolved solids concentration greater than 10,000 milligrams per
				liter;
(3) uppermost groundwater
				occurs under confined conditions; and
(4) uppermost groundwater occurs at a depth
				of 30 feet or greater with at least four feet of suitable soil in the vadose
				zone.