Presented by Brian Harper

Soil 350- Soils and Land Use

The following page was written to help students and any other interested parties understand the procedures and regulations involved in New Mexico for the construction and use of septic tank systems. Information is also available about  septic tanks maintenance and replacement

New Mexico Environmental Improvement Board

Title 20: Environmental Protection

Chapter 7: Wastewater and Water Supply Facilities

Part 3: Liquid Waste Disposal

Subpart 1-Definitions

Aerobic treatment system- any treatment system which stabilizes liquid waste through the addition of supplemental air or dissolved oxygen by means of mechanical or diffused aeration. Diffused oxygen content must be maintained at a minimum of 2.0 mg/L for a system to be considered an aerobic system.

Alternative system- any on-site liquid waste system utilizing a method of liquid waste treatment and disposal that is not recognized and allowed by the New Mexico Design Standards.

Anaerobic treatment- a biological process through which organic material is decomposed in an environment containing no dissolved oxygen.

Biochemical oxygen demand(BOD)- the rate at which organisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions.

Black water- waste from a liquid flushing toilet, urinal, or garbage disposal.

Cesspool- an excavation or non-water tight unit which receives untreated water-carried liquid waste allowing direct discharge to the soil.

Clearance- the vertical thickness of suitable soil between the lowest point of a liquid waste disposal system and the seasonal high ground water table, bedrock, or other limiting layer.

Design flow- the flow rate for which an on-site liquid waste system must be designed in order to assure acceptable system performance, assuming the use of conventional plumbing fixtures.

Disposal system- a generally recognized system for disposing of the discharge from a liquid waste treatment unit and includes, but is not limited to, seepage pits, drainfields, evapotreanspiration systems, sand mounds, sand filters, and approved surface applications.

Effluent- treated liquid waste

Enclosed system- a watertight on-site liquid waste system which does not discharge to the soil, including, but not limited to, holding tanks and lined evapotranspiration systems.

Established on-site liquid waste system- an on-site liquid waste system which has been in active and trouble free use at any time during the 10 years prior to submission of a permit application.

Greywater- water carried waste from kitchen (excluding garbage disposal) and bathroom sinks, wet bar sinks, showers, bathtubs, and washing machines. Greywater does not include water carried wastes from kitchen sinks equipped with a garbage disposal, utility sinks, any hazardous materials, or laundry water from the washing of material soiled with human excreta.

Ground water- interstitial water which occurs in saturated earth material and which is capable of entering a well in sufficient amounts to be utilized as a water supply. To see groundwater in the hydrologic cycle- click here

Holding tank- a watertight tank designed to receive and retain liquid waste for periodic pumping and disposal off-site.

Impervious formation- any soil or rock formation with a percolation rate slower than 120 minutes/inch.

Interstitial water- water in spaces between solid earth particles.

Limiting layer- an impervious formation or soils with a percolation rate faster than 5 minutes/inch.

Liner- a manufactured or naturally occurring substance which restricts seepage to no more than 0.5 acre-foot per year per acre over the design service life of the lined unit.

On-site liquid waste system- a liquid waste system, or part thereof, serving a dwelling, establishment or group, and using a liquid waste treatment unit designed to receive liquid waste followed by either a soil treatment or other type of disposal system. On-site liquid waste systems include enclosed systems and privies but do not include systems or facilities designed to receive or treat mine or mill tailings or wastes.

Percolation rate- the rate of entry of water into soil as determined by a standard soil test at the depth and location of the proposed soil disposal system.

Primary treatment- a liquid waste treatment process that takes place in a treatment unit and allows those substances in wastewater that readily settle or float to be separated from the water being treated.

Seasonal high ground water table- the highest level to which the upper surface of ground water may be expected to rise within twenty-four consecutive months.

Seasonal high water flow- the highest level which perennial or intermittent surface waters may be expected to rise within twenty-four consecutive months.

Secondary treatment- a wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. The process is commonly a biological treatment process followed by settling and clarification.

Septage- the residual wastes and water periodically pumped from a liquid waste treatment unit or from a holding tank.

Septic tank- liquid waste treatment units designed to provide primary treatment prior to disposal.
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Setback distance- the distance measured by a straight horizontal line between the on-site liquid waste system, its designated replacement area, or portion thereof and the object being considered.

Suitable soil- a soil, whether naturally occurring or introduced, which will treat the effluent effectively and act as an effective filter and remove organisms and suspended solids prior to the effluent reaching ground water, bedrock or a limiting layer, and which will provide adequate transmission to prevent a failed system. Suitable soils are minimally characterized by percolation rates between five (5) and one hundred twenty (120) minutes per inch.

Surface application- the application of disinfected effluent to the ground surface.

Subpart 2- Procedures

201. Liquid Waste System Permits

A. No person shall install or have installed a new on-site liquid waste system or modify or have modified an existing on-site liquid waste system, unless that person obtains a permit issued by the Department prior to construction of such installation or modification.

B. Obtaining a permit from the Department for installation or modification of an on-site liquid waste system does not relieve any person from the responsibility of obtaining any other approval, license or permit required by the state, city, or county regulations or ordinances or other requirements of state or federal laws.

C. Any person seeking a permit shall do so by submitting an application to the field office of the Department having jurisdiction for the area where the system is to be installed or modified.

D. The Department may require any or all of the following information before a permit is issued for an on-site liquid waste system, or at any time during its construction.

E. Except as otherwise provided in Section 201.E.2, the Department shall, within ten (10) working days after receipt of the completed application, grant the permit, grant the permit subject to conditions, or deny the permit and shall notify the applicant of the action taken.

F. If the Department finds that specific requirements in addition to or more stringent than those provided in Subparts III and IV of this Part are necessary to prevent a hazard to public health or the degradation of a body of water, the Department may issue permit conditions with more stringent requirements or additional specific requirements. Such additional or more stringent requirements may apply to system design, sitting, construction, inspection, operation and monitoring.

G. The Department shall deny the permit if the proposed system will not meet the requirements of this Part or the New Mexico Design Standards.

H. The Department shall maintain a file of all permits issued and denied. The file shall be open to the public.

I. The installation or modification of an on-site liquid waste system shall be in accordance with the permit. Any change from the permitted installation or modification, including a change of contractor, must receive written Department approval prior to implementation.

J. No person shall operate or use an on-site liquid waste system until the Department has granted final approval of the system after installation or modification of the system is done. No person shall occupy a newly constructed or transported dwelling for which an on-site liquid waste system is required until the Department has granted such final approval, and, if applicable, until the governmental body with authority to regulate construction has granted an occupancy permit. The Department shall not grant final approval if the system as installed or modified does not meet the requirements of this Part and the New Mexico Design Standards.

K. The Department may cancel a permit if the installation or modification of the on-site liquid waste system has not been completed within one (1) year after issuance, or if the Department determines that information in the application is false, incomplete, or inaccurate and that the correct information would have resulted in the Department denying the original application.

202. Variances

A. Any person seeking a variance from the requirements contained in this Part shall do so by filing a petition with the field office of the Department having jurisdiction for the area where the system is to be installed.

B. The Department shall, after a minimum of ten (10) but not more than twenty (20) working days following reception of the completed petition, grant the variance, grant the variance subject to conditions, or deny the variance and shall so notify the applicant and any other person making a written submission concerning the petition.

C. The Department shall deny the variance petition unless the petitioner establishes by clear and convincing evidence that:

D. The factors listed below as applicable, shall be considered in evaluating petitions for variances from the principal requirements of Subpart III. This list is illustrative, not exhaustive. Some of the factors listed within a category may not be important in specific cases.

203. Appeals

A. Any affected person who is dissatisfied with action taken by the Department on a permit application or variance petition may appeal to the Secretary. The request must be made in writing to the Secretary within fifteen (15) working days after notice of the Department's action has been issued.

B. If an appeal is received within the fifteen (15) working days time limit, the Secretary shall hold a hearing within fifteen (15) working days after receipt of the request.

C. In the appeal hearing, the burden of proof is on the person who requested the hearing. Where the Department requires standards more stringent than those provided in this Part, the burden of proof of the necessity for the more stringent standards shall be upon the Department.

Subpart 3- Standards

301. General Requirements

A. No person shall discharge untreated liquid waste except into a permitted enclosed system, a permitted liquid waste treatment unit, or a public sewer system. No person shall discharge liquid waste or effluent into a cesspool or effluent disposal well. A privy must be used for the disposal of human excreta and toilet paper, but not for the disposal of other liquid wastes.

B. No person shall install, have installed, modify or have modified, own, operate, or use an on-site liquid waste system which, by itself or in combination with other on-site liquid waste systems, may cause a hazard to public health or degrade any body of water.

302. Lot Size Requirements

A. An on-site liquid waste system, including its replacement area, shall be located wholly on the same lot which is the site of the dwelling or commercial unit served by the on-site liquid waste system. A copy of the recorded deed or easement for the lot shall be submitted with the application for the on-site liquid waste system installation or modification petition.

B. On-site liquid waste systems on lots with record dates after February 1, 1990, shall not exceed the total design flow limitation given by the following formula:

Total Design Flow (gallons per day) = Lot Size (acres) x 500 qpd

C. The minimum lot size required for an on-site liquid waste system on a llot with record date after February 1, 1990 is 0.75 acres.

D. The total design flow of on-site liquid waste systems initially installed after February 1, 1990, on lots with record dates prior to February 1, 1990, without established on-sire liquid waste systems shall not exceed:

303. Setback Requirements

A. On-site liquid waste systems shall be located to meet setback distances, in feet, specified in table 303.1. Setback distances apply to any part of the on-site liquid waste system and its designated replacement area.

B. Setback distances to watercourses, canals, and arroyos shall be measures from the edge of the seasonal high water flow to the on-site liquid waste system component. Setback distances to artificially controlled lakes or reservoirs shall be measured from the closest projected shoreline at the maximum controlled water level.

304. Clearance Requirements

A. No on-site liquid waste system shall discharge liquid waste into the soil where the vertical clearance to seasonal high ground water table, impervious or other limiting layer is less than four (4) feet.

B. Unlined privy pits shall provide a clearance of no less than four (4) feet to the seasonal high ground water table, the seasonal high water flow, impervious formation or other limiting layer.

305. Holding Tank Requirements

A. Non-discharging holding tanks shall not be installed after February 1, 1990, to serve any design flow greater than three hundred-seventy-five (375) gallons per day, except to replace an existing holding tank.

B. Holding tanks shall be constructed of the same materials and by the same procedure to the same standards as described in Section 402 except that they shall have no discharge outlet.

C. All holding tank installations shall be tested on site for water tightness. Holding tanks shall be filled with water to the point of overflow at least twenty-four (24) hours prior to inspection. There shall be no signs of external leakage or tank deformation at the time of inspection.

D. The minimum size of a holding tank shall be 1000 gallons or four (4) times the design flow, whichever is greater. For commercial units the minimum tank size shall be five (5) times the design flow.

E. Holding tanks shall be located in an area readily accessible to a pump vehicle under all weather conditions and where accidental spillage during pumpage will not create a nuisance or a hazard to public health. Any spillage that may occur during tank pumpout shall be cleaned up immediately and the spill area disinfected with a sodium or calcium hypochlorite solution.

F. Holding tanks shall be protected against flotation under high ground water conditions by weight of tank (blasting), earth anchors, or by surface or shallow installation.

G. Holding tanks shall be equipped with a visible and audible high water alarm system. The alarm shall be set to activate at 80% of the tank capacity.

H. The owner of a holding tank periodically shall have the tank pumped and the liquid waste (septage) properly disposed of in compliance with all applicable laws and regulations as needed to prevent discharge from the tank.

I. No person shall install, operate, modify, or maintain a holding tank which allows discharge to the soil.

J. The Department may perform site inspections periodically to ensure that a holding tank does not discharge.

K. All dwellings or commercial units served by a holding tank shall be connected to a public or private wastewater treatment plant and the holding tank properly abandoned within 180 days after the installation within two-hundred (200) feet of the lot of a collection line for the wastewater treatment plant.

308. Operation Requirements

A. No person shall introduce motor oil, gasoline, paint, varnish, solvents, pesticides, fertilizer, or other materials of a composition or concentration not generally considered liquid waste to an on-site liquid waste system.

B. No person shall introduce any chemicals defined by the New Mexico Water Quality Control Commission as a toxic pollutant into an on-site liquid waste system.

309. Maintenance of On-Site Liquid Waste System

A. The owner of an on-site liquid waste system shall operate and maintain the system according to the recommendations of the manufacturer or installer of the system.

B. Liquid waste treatment additives shall not be used as a means to reduce the frequency of proper maintenance and removal of septage from a treatment unit.

Subpart 4- Design

401. General

A. The type of on-site liquid waste system shall be determined on the basis of location, lot size, soil and site characteristics, seasonal high water table or other impervious formations or limiting layers and shall be designed to receive all design flows from the property. The system, except as otherwise approved, shall consist of a liquid waste treatment unit and associated disposal system.

B. All disposal systems that utilize subsurface discharge and soil absorption shall be designed so that additional seepage pits, drain fields, or other subsurface absorption areas equivalent to at least 100% of the required original disposal system, may be installed if the original system cannot absorb all the liquid waste.

402. Liquid Waste Tank Design and Construction

A. All treatment units and tanks, regardless of material or method of construction shall:

B. The design flow rates for the commercial unit usage set forth in the following Table 402.2 shall be used for determining liquid capacities for on-site liquid waste systems.

C. Plans for all septic tank design shall be submitted to the Department for approval, registration and certification. Such plans shall show all dimensions, reinforcement, structural calculations, and such other pertinent data as may be required by the Department.

D. Pump Stations and Equipment

403. Area of Disposal Field and Seepage Pits

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 either utilizing the following Table 403.1 based on the soil classification of the soil found in the proposed location of the disposal field, or by utilizing the formula specified in Section 404.E based on the results of a standard percolation test as described in Section 404.

404. Percolation Tests

A. The Department may require that percolation tests be performed and submitted with the permit application.

B. When a percolation test is utilized, the minimum required absorption area shall be computed using the formula:

405. Disposal Field Design and Construction

A. Distribution lines shall be constructed of perforated PVC pipe or other approved materials, provided that sufficient openings are available for distribution of the effluent into the trench area.
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B. Before placing aggregate material or drain lines in a prepared excavation, all smeared or compacted surfaces shall be removed from trenches by raking to a depth of one (1) inch and the loose material removed. Clean stone, gravel, slag, or similar aggregate material acceptable to the Department, varying in size from three fourths (3/4) inch to two and one half (2 1/2) inches shall be placed in the trench to the depth and grade required.

C. When seepage pits are used in combination with disposal fields, the aggregate material in the trenches shall terminate at least five (5) feet from the pit excavation and the line extending from such points to the seepage pit shall be constructed of approved pipe with watertight joints.

D. When more than five-hundred (500) lineal feet of leach line is required, a dosing tank shall be used. Dosing tanks shall be equipped with an automatic pump which discharges the tank a minimum of once every four (4) hours. The tank shall have a capacity equal to at least seventy-five (75) percent of the interior capacity of the pipe to be dosed at one time. Where the total length of leachline exceeds one thousand (1000) lineal feet, the dosing tank shall be provided with two (2) pumps dosing alternately and each serving one half (1/2) of the leach field.

406. Seepage Pit Design and Construction

A. The minimum capacity of seepage pits and absorption area shall conform to the requirements of Sections 403 and 404 of this Part.

B. Each seepage pit shall have an excavated horizontal dimension of not less than four (4) feet. 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.

C. All brick or block used in seepage pit construction shall have a minimum compressive strength of twenty-five hundred (2500) pounds per square inch.

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

E. An approved vented inlet fitting shall be provided in every seepage pit so arranged as to prevent the inflow from damaging the sidewall.

407. Special Liquid Waste Disposal

When liquid wastes are discharged containing excessive amounts of grease, garbage, flammable wastes, sand, or other ingredients which may affect the operation of an on-site liquid waste system, an interceptor for such wastes must be installed.

409. Aerobic Treatment Systems

Alternative on-site liquid waste systems employing aerobic treatment may be substituted for conventional septic tanks provided the permit applicant demonstrates that the proposed system will meet the requirements of Section 306, whether its aeration system is operating or not.

410. Abandoned Sewers and On-Site Liquid Waste Systems

A. Every abandoned building sewer, or part thereof, shall be plugged or capped utilizing a cap or plug prescribed by the Uniform Plumbing Code within five (5) feet of the property line.

B. Every cesspool, holding tank, septic tank, seepage pit or other liquid waste treatment unit which has been abandoned or has otherwise been discontinued from further use or to which no waste or building sewer from a plumbing fixture is connected, shall have the liquid waste pumped therefrom and properly disposed. The empty liquid waste treatment unit shall be completely filled with earth, sand, gravel, concrete, or other approved material.

C. The top cover or arch over the cesspool, holding tank, septic tank, seepage pit or other liquid waste treatment unit shall be removed before filling and the filling shall not extend above the top of the vertical portions of the sidewalls or above the level of any outlet pipe until inspection or authorization by the Department.

To download a program regarding septic tank function and design- click here