New Mexico Administrative Code
Title 20 - ENVIRONMENTAL PROTECTION
Chapter 7 - WASTEWATER AND WATER SUPPLY FACILITIES
Part 3 - LIQUID WASTE DISPOSAL AND TREATMENT
Section 20.7.3.301 - STANDARDS; LOT SIZE REQUIREMENTS

Universal Citation: 20 NM Admin Code 20.7.3.301

Current through Register Vol. 35, No. 18, September 24, 2024

A. The requirements of this section apply to all conventional treatment systems that discharge to the soil. Compliance with the requirements of this section shall be based on the total design flow for the lot. Water conservation devices or demonstrated actual flows shall not be used to reduce the requirements of this section. For the purposes of 20.7.3 NMAC, lot sizes shall be calculated to the nearest hundredth (0.01) acre.

B. The date of record for a lot shall be considered to be either:

(1) the date of legal recording in the county clerk's office or validation by other means associated with the most recent change in lot size or boundaries; or

(2) for those lots in subdivisions having received final approval from governments having jurisdiction therein prior to February 1, 1990, such date of record shall be two and one-half years from the date of final government approval or July 1, 1992, whichever occurs first.

C. A conventional treatment system shall not be installed on a lot sized smaller than 0.75 acre, where there is not an established on-site liquid waste system, except as otherwise provided in Subsection F of 20.7.3.301 NMAC. The size of a lot shall be the total area of the lot plus or minus the area of any liquid waste disposal easements granted to or by another lot, respectively. The design flow for a conventional treatment system shall not exceed 500 gallons per day per acre. For total design flows that exceed the allowable flow or for lots that do not meet the minimum lot size, the total nitrogen discharged to the lot shall be reduced in accordance with Subsection B of 20.7.3.603 NMAC.

D. On-site liquid waste systems installed prior to the effective date of 20.7.3 NMAC shall meet the lot size requirements of the regulations in effect at the time of their initial installation or if there has been a permitted modification, the regulations in effect at the time of the most recent prior permitted modification.

E. Table 301.1 lists the minimum lot sizes required for typical flow rates for conventional treatment systems for lots with a date of record of February 1, 1990 or later.

Table 301.1

TOTAL DESIGN FLOW (gallons per day)

MINIMUM LOT SIZE (acres)

375 or less

0.75

440

0.88

500

1.00

750

1.50

1125

2.25

1500

3.00

1875

3.75

2000

4.00

F. The department may issue permits for lots not complying with Subsection C of 20.7.3.301 NMAC for areas the department has identified and mapped where groundwater is not at risk from nitrogen loading from on-site liquid waste systems. The following hydrogeologic conditions may be considered when determining if groundwater is not at risk:

(1) groundwater does not exist;

(2) the uppermost groundwater contains a total dissolved solids concentration greater than 10,000 milligrams per liter;

(3) the uppermost groundwater occurs under confined conditions;

(4) the uppermost groundwater occurs at a depth between 400 and 600 feet with one or more geologic strata in the vadose zone that may act as a capillary barrier; and

(5) the uppermost groundwater occurs at a depth greater than 600 feet.

In areas that have not been identified and mapped by the department, the applicant must demonstrate one of the above conditions exists prior to the issuance of a permit.

G. The following Table 301.2 summarizes the minimum lot size requirements, in acres, and permissible design flows in effect prior to February 1, 1990 and is for the purpose of determining the requirements existing at the time of initial installation or most recent permitted modification.

Table 301.2

RECORD DATE

01/01/60

to

11/01/73

11/01/73

to

09/07/79*

09/07/79

to

03/01/80

03/01/80

to

11/09/85

11/09/85

to

02/01/90

Minimum

Lot Size

Soil

Group

**

Min.

Lot

Size

Total

Design

Flow

(gpd)

Min.

Lot

Size

Total

Design

Flow

(gpd)

Min.

Lot

Size

Total

Design

Flow

(gpd)

Min.

Lot

Size

OFF-SITE

WATER**

0.25***

A

0.50

0-1000

0.50

0-375

0.33

0-375

0.33

B

0.75

1000-

1500

1.00

376-

1000

0.50

376-

750

0.50

C

1.00

1500-

2000

1.25

1000-

1500

1.00

750-

1125

1.00

D

****

1501-

2000

1.25

1126-

1500

1.25

1501-

2000

1.75

ON-SITE

WATER**

0.50***

A

0.75

0-1000

0.75

0-1000

0.75

0-375

0.75

B

1.00

1000-

1500

1.25

1000-

1500

1.25

376-

750

1.50

C

1.25

1500-

2000

1.70

1501-

2000

1.70

750-

1125

2.00

D

****

1126-

1500

2.75

1501-

2000

3.50
(1) * The maximum total design flow was 1,000 gpd for the lot sizes shown.

(2) ** See Subsection H of 20.7.3.301 NMAC.

(3) *** These requirements applied to lots in subdivisions that were required at the time of subdivision to obtain state health department review and approval.

(4) **** No on-site liquid waste disposal to soil allowed.

(5) NOTE: Roadways were excluded from figuring lot sizes from 11/09/85 to 9/1/13.

H. The following Table 301.3 lists the soil types for lot size determinations for the period November 1, 1973 to September 7, 1979: The minimum lot size required for the location of an individual liquid waste disposal system is determined by the most limiting soil group under which any soil characteristic falls.

Table 301.3

SOIL

CHARACTERISTICS

A

Slight

Limitations

B

Slight

Limitations

C

Moderate

Limitations

D

Severe

Limitations

1.

SOIL DEPTH

(depth to bedrock, in feet)

More than 6

and

More than 6

and

4 - 6

or

Less than 4

or

2.

PERCOLATION RATE

(rate of percolation of water into soil in minutes per inch)

0 - 15

and

16 - 30

and

31 - 60

or

More than 60

or

3.

SEASONAL WATER TABLE

(depth to shallowest water table during the year, in feet)

More than 12

and

More than 12

and

4 - 12

or

Less than 4

or

4.

SLOPE

(incline of the land surface, in percent)

0 - 8

and

0 - 8

and

8 - 25

or

More than 25

or

5.

FLOODING POTENTIAL

(overflow frequency,

in years)

None

None

No more than

1 in 25

More than

1 in 25

I. If the size or boundaries of a lot with an existing on-site liquid waste system are changed so that the total design flow for the lot exceeds the total design flow limitation provided for in Subsection C of 20.7.3.301 NMAC, the permit for the system shall be void.

J. If the size or boundaries of a lot with an existing on-site liquid waste system are changed so that the total design flow for the lot does not exceed the total design flow limitation provided for in Subsection C of 20.7.3.301 NMAC, an amendment to the existing permit shall be submitted.

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