The Governing Framework

New Mexico regulates onsite wastewater under:

• 20.7.3 NMAC — Liquid Waste Regulations. The substantive rule covering onsite wastewater statewide.
• § 20.7.3.201 — Procedures; General Requirements (including capacity calculations and Table 201.2).
• § 20.7.3.808 — Holding Tank Requirements.
• Table 301.1 — Setback distances.
• New Mexico Environment Department (NMED) — state-level regulator. The Liquid Waste Program within NMED administers 20.7.3 NMAC.

Septic Tank Capacity — The "Whichever Greater" Rule

New Mexico's capacity rule combines a bedroom-based table with a flow-based floor:

Setback Distance — The Horizontal-Distance Rule

20.7.3 NMAC defines setback distance as the distance measured by a straight horizontal line between the on-site liquid waste system, or portion thereof, and the object being considered. Setbacks are specified in Table 301.1 for distances to water wells, surface water, property lines, structures, and water supply lines.

The horizontal-distance specification matters on steep terrain and in arroyo-country parcels where vertical-drop apparent distance doesn't count toward code setback. Surveyor-precision measurement is common for marginal lots.

Holding Tank Requirements — § 20.7.3.808

For installations without absorption fields (remote cabins, commercial temporary installations, lots where soil fails site evaluation), holding tanks are regulated under 20.7.3.808. Key requirements:

• Tank capacity based on expected use volume and pump-out frequency
• High-liquid alarm required
• Structural integrity to prevent collapse under full-load conditions
• Access for inspection and pumping
• NMED-approved installer for commercial holding tanks

Permit Process

1. Contact NMED or your local liquid-waste authority. Some counties and tribal areas have delegated authority; others refer to NMED directly.
2. Site evaluation. Certified soil evaluator per 20.7.3 NMAC protocols.
3. Design submission. Plot plan, soil evaluation, system sizing per Table 201.2 and the 2.5× rule.
4. Permit application. Through NMED Liquid Waste Program. Fees vary.
5. Licensed installer construction.
6. Inspection before cover. NMED or delegated authority.

Regional Considerations

• Albuquerque Metro (Bernalillo County): Largely on municipal sewer. Remaining septic on the East Mountain and West Mesa fringes.
• Santa Fe / Los Alamos: High-elevation with caliche layers and some karst. Alternative systems common. LANL area has specific environmental considerations for proximity to Los Alamos National Laboratory.
• Las Cruces / Mesilla Valley: Deep alluvial soils, low rainfall, irrigation water-table concerns. Standard systems work well.
• Chama / Jemez / Taos: Mountain communities with deep snow and shallow soil over volcanic tuff. Deep-bury requirements for frost protection.
• Eastern plains (Roosevelt, Curry, Lea): Flat, deep soils, moderate percolation. Standard systems typical.
• Tribal jurisdictions: Navajo Nation, Pueblo communities, Apache reservations have separate tribal environmental authorities. Projects on tribal land are NOT under NMED 20.7.3 NMAC jurisdiction. Contact tribal EPA offices.

Material Approvals

NMED maintains an approved-products list for septic tanks. Polyethylene tanks meeting state construction standards are listed:

• IAPMO PS 1 or NSF 46 listing
• Ribbed polyethylene rated for burial
• Two-compartment preferred
• Check the NMED Approved Products list for current model acceptance

Frequently Asked Questions

Is my parcel on tribal land?

In New Mexico, many parcels that appear "rural" on standard maps are actually within Navajo Nation, Pueblo, or other tribal reservations. Tribal environmental authority (not NMED) governs septic installations on tribal land. If you're unsure, contact both NMED and the nearest tribal environmental office.

What's a "fixture unit" for commercial capacity?

Plumbing fixture unit (PFU) is a standardized measure of plumbing load from the Uniform Plumbing Code. Each type of plumbing fixture (toilet, sink, shower, floor drain) contributes a specific number of PFUs. Total PFUs determine commercial tank size under Table 201.2. Your designer calculates PFUs from the building plumbing plan.

What's the 2.5× design flow method for?

Used when Table 201.2 doesn't clearly apply, or when the calculated flow is higher than what Table 201.2 produces. A 2,000 gpd design flow needs 2.5 × 2,000 = 5,000 gallon minimum tank. This is commonly the controlling calculation for larger commercial or unusual-use installations.

Can I use a holding tank instead of an absorption field?

Sometimes. Holding tanks per 20.7.3.808 are allowed where absorption isn't feasible, but require periodic pumping (cost liability) and high-liquid alarms. Temporary installations (construction sites, remote cabins, seasonal-use properties) use holding tanks more often than permanent residences.

Source Citations

• NMED Liquid Waste Regulations
• 20.7.3 NMAC full text on SRCA
• § 20.7.3.201 Procedures and General Requirements
• § 20.7.3.808 Holding Tank Requirements on Cornell LII
• NMED Liquid Waste Permitting Process
• NMED Approved Products List
• NMED Homeowners Guide to Septic Tank + Drainfield (PDF)

Agricultural Tank Regulations — New Mexico Department of Agriculture (NMDA)

The New Mexico Department of Agriculture (NMDA), housed at New Mexico State University, regulates pesticide, fertilizer, and feed storage under NMAC Title 21, Chapter 17, with statutory authority at NMSA Chapter 76:

• NMAC 21.17.5 — Pesticide rules including registration, labeling, and applicator licensing.
• NMAC 21.17.50 — Bulk pesticide storage and containment rules.
• NMAC 21.17 (broader chapter) — Fertilizer and soil conditioner rules including bulk storage at agricultural supply dealers.
• NMSA 76-4 — Pesticide statutory authority.
• NMSA 76-12 — Commercial Fertilizer and Soil Conditioner Law.

New Mexico agriculture is bimodal: small irrigated operations along the Rio Grande, Pecos, and San Juan valleys (chile, pecans, alfalfa, onions, vineyards) and large cow-calf rangeland in the Chihuahuan and Sonoran basins. Commercial ag-retail facilities with bulk liquid fertilizer (UAN-32, 10-34-0, ammonium thiosulfate) and bulk pesticide storage must follow NMDA containment rules — specifically NMAC 21.17.50 for pesticide bulk storage — with 110% largest-tank containment, impermeable liner, and documented inspection. NMDA coordinates with New Mexico Environment Department (NMED) on incident response. Anhydrous ammonia storage references ANSI K61.1; the compressed spring pre-plant window in the Mesilla Valley and the Pecos corridor concentrates nurse-tank activity.

Oil & Gas Produced Water — New Mexico Oil Conservation Division (OCD)

The New Mexico Oil Conservation Division (OCD) within the Energy, Minerals, and Natural Resources Department (EMNRD) regulates upstream oil and gas under NMAC Title 19, Chapter 15:

• NMAC 19.15.17 — Pits, closed-loop systems, below-grade tanks, and sumps: construction, lining, freeboard, closure.
• NMAC 19.15.29 — Produced water disposal, injection wells, and beneficial reuse.
• NMAC 19.15.36 — Surface waste management facilities.
• NMSA 70-2 — Oil and gas conservation statutory authority.

The New Mexico Permian Basin (Lea and Eddy counties) is one of the most prolific oil and gas plays in North America; the San Juan Basin (San Juan and Rio Arriba counties) handles significant gas and coalbed-methane produced water. OCD permits pits and tank batteries under NMAC 19.15.17 with strict construction and lining standards — the 2008 pit rule tightened liner thickness, freeboard, and closure specifications substantially in response to groundwater concerns. Polyethylene tanks are common at chemical-injection skids (scale inhibitor, biocide, methanol, corrosion inhibitor); fiberglass and steel dominate high-volume produced-water service. Produced-water beneficial reuse under NMAC 19.15.29 and New Mexico's 2019 Produced Water Act (HB 546) has been an active regulatory frontier.

Petroleum USTs — NMED Petroleum Storage Tank Bureau (PSTB)

The New Mexico Environment Department regulates petroleum storage tanks through the Petroleum Storage Tank Bureau under NMAC Title 20, Chapter 5:

• NMAC 20.5.101 et seq. — UST technical standards (design, installation, release detection, corrective action, closure).
• NMAC 20.5.17 — AST rules for aboveground petroleum storage.
• NMSA 74-4 — Hazardous Waste Act statutory authority for related spill and response programs.
• Corrective Action Fund — state reimbursement for eligible cleanup costs.

New Mexico UST owners register with NMED PSTB, pay annual fees supporting the Corrective Action Fund, maintain 2018 federal rule upgrades (release detection, spill/overfill, secondary containment for new tanks, operator training), and report suspected releases within 24 hours. AST rules under NMAC 20.5.17 apply on top of federal SPCC for facilities above threshold volumes.

Septic System Sizing Deep Dive

New Mexico regulates onsite wastewater (Liquid Waste Systems) through the NMED Liquid Waste Program under NMAC 20.7.3. Minimum residential capacity:

New Mexico soils range from deep aeolian loess on the Eastern Plains to shallow caliche-rich profiles across the Chihuahuan Desert, decomposed volcanic tuff on the Pajarito Plateau, and thin rocky profiles on the Sangre de Cristo foothills. NMAC 20.7.3 mandates soil and site evaluation, licensed installer, and NMED or delegated-authority permit. Alternative systems for failed perc include aerobic treatment units, mounds, drip dispersal, and evapotranspiration beds — especially popular in high-desert counties where perc is slow and water is scarce. Santa Fe, Los Alamos, and Taos county OWTS often default to ATU plus drip dispersal to manage shallow bedrock and protect groundwater.

Chemical Storage Secondary Containment & Spill Reporting

Federal SPCC (40 CFR 112) applies at 1,320 gallons aggregate aboveground oil. New Mexico layers on:

• NMSA 74-6-7 — Water Quality Act release-reporting authority under NMED Surface Water Quality Bureau and Ground Water Quality Bureau.
• NMAC 20.6.2 — Ground water protection regulations.
• NMAC 19.15.29 — OCD spill reporting for upstream oil and gas releases.
• New Mexico Department of Homeland Security and Emergency Management (DHSEM) — EPCRA Tier II and State Emergency Response Commission.

Report non-oil-and-gas releases to NMED (Surface Water Quality Bureau or Ground Water Quality Bureau) and federal RQ releases to the National Response Center at 1-800-424-8802. Upstream oil and gas releases go to OCD. Secondary containment at 110% is the SPCC and industry default. For state-specific RQ thresholds that diverge from 40 CFR 302.4, consult NMED directly.

Permit Pathways at a Glance

• Residential liquid waste (septic): NMED Environmental Health Bureau (or delegated local authority) under NMAC 20.7.3.
• Fertilizer & pesticide registration: NMDA under NMAC 21.17 and NMSA 76.
• Pesticide applicator license: NMDA under NMSA 76-4.
• Oil & gas produced water storage: NM OCD under NMAC 19.15.17 / 19.15.29.
• Petroleum UST: NMED PSTB under NMAC 20.5.
• SPCC > 1,320 gal oil aggregate: Federal SPCC plan; state spill reporting to NMED or OCD.
• NPDES industrial stormwater: EPA Region 6 (New Mexico is not a delegated NPDES state for most programs).

Current fees change; verify with NMDA, NMED, or OCD before budgeting.

More New Mexico FAQs

How does the 2019 Produced Water Act change things in the Permian?

HB 546 (2019) established a statutory framework for produced-water handling, reuse, and research in New Mexico. OCD retains jurisdiction over upstream produced water; NMED handles produced water reused outside the oilfield. The state is actively pursuing science-based rulemaking on pilot-scale beneficial reuse (e.g., non-potable industrial uses) while protecting fresh water.

Do pit liner standards differ in the Permian versus San Juan Basin?

NMAC 19.15.17 applies statewide with prescriptive liner thickness, leak detection, and closure requirements tightened in 2008 in response to documented groundwater contamination. Permian Basin groundwater protection and San Juan Basin specific hydrogeology drive consistent statewide standards with site-specific engineering.

Who regulates a 2,000-gallon pesticide bulk tank at my ag co-op?

NMDA under NMAC 21.17.50. The bulk pesticide rule requires registration, construction standards, secondary containment, and loading-pad rinsate recovery at commercial facilities. Combine with EPA Pesticide Container Containment Rule (40 CFR 165 Subpart E) compliance.

How does high-altitude septic design differ in northern New Mexico?

Taos, Rio Arriba, and Los Alamos county OWTS face shallow bedrock, cold soils, and protected watersheds. NMED and local health departments push ATU plus drip dispersal, mounds, and evapotranspiration beds to manage site constraints and protect shallow aquifers.

Does New Mexico run its own NPDES program?

No — New Mexico is not a delegated NPDES state for most industrial and municipal discharges; EPA Region 6 administers federal NPDES permits. NMED handles state-level ground water, surface water quality standards, and non-NPDES regulatory functions.