New Mexico Administrative Code
Title 20 - ENVIRONMENTAL PROTECTION
Chapter 7 - WASTEWATER AND WATER SUPPLY FACILITIES
Part 3 - LIQUID WASTE DISPOSAL AND TREATMENT
Section 20.7.3.805 - EVAPOTRANSPIRATION SYSTEMS

A. Evapotranspiration systems shall consist of a treatment unit and an evapotranspiration bed (ET bed) for disposal. Evapotranspiration systems shall meet the requirements of 20.7.3.302 NMAC. Unlined ET beds are a discharging system and shall meet the clearance, set back and lot size requirements for conventional absorption systems. Lined ET beds are non-discharging systems and shall be underlain by a liner as specified in Paragraph (3) of Subsection L of 20.7.3.7 NMAC.

B. The minimum bottom area of ET beds shall be determined from the following formula:

A = 391 x Q , EL, where: A = the bottom area of the bed in square feet; Q = the design flow in gallons per day; and EL = the average annual lake evaporation for the site in inches per year.

C. The average annual lake evaporation shall be determined from the map "Gross Annual Lake Evaporation, New Mexico", USDA, April 1972, or successor version or a mutually acceptable evaporation rate.

D. The minimum bed depth shall be 24 inches as measured from the bottom of the ET bed to the overflow level. The surface crowning, which increases runoff from the ET bed, is above the overflow level of the ET bed. Maximum ET bed depth shall be 30 inches. The bottom of the ET bed shall be level.

E. The ET bed location shall be in an area where exposure to the sun and wind will be maximized.

F. The distribution piping within the ET bed shall be embedded in gravel and covered meeting the specifications in 20.7.3.701 NMAC. Use of approved proprietary drainfield products may be used in lieu of pipe and gravel.

G. The capillary sand fill shall contain 85% or more sand; the percentage of silt plus one and one-half times the percentage of clay shall not exceed 15%. Fine to medium sand is preferred.

H. Loamy sand shall be used for the surface crown. Where loamy sand is not available, capillary sand may be used.

I. The crown surface shall be planted with vegetation suited to the climate and soil of the site and to the wastewater quality and quantity.

J. For a gravity feed system, the overflow height of the ET bed shall be lower than the invert of the septic tank outlet.

K. All ET beds shall be equipped with an inspection port that is suitable to use to pump the system, if needed.