New Mexico
Environment Department

Contact Information:
(505) 827-2855 MAIN // 1-800-219-6157 (toll free)
Environmental Emergencies:
505-827-9329 (24 hrs)

Liquid Waste Program

Operation and Maintenance

Septic Systems Need Maintenance!!!

Every septic system has a limited lifespan. 

  • Components wear out. 
  • Concrete breaks down. 
  • Drainfields (leachfields) get plugged up. 
  • Tree roots invade drainfields. 
  • Tanks fill up with solids (sludge) and “floaters” (scum) such as fats, oils and greases.
  • Drainfields get plugged up with solids, bio-mat, fats, oils and greases, roots, etc.


  • For these reasons it is important to have your septic tank(s) pumped out every 3-5 years
  • The pumping frequency can vary depending on what you put into the system. 
  • The use of a garbage disposal can add much more solids to the tanks.  A tank that is full with sludge and scum can reduce settling and allow more waste components to make their way through the tank, negatively impacting the drainfield. 
  • What you put down your drain can shorten the life of your septic system. 
  • Do not put hazardous materials down the drain.
  • Clean the effluent filter as needed.

The Department does not endorse the use of proprietary additives to septic systems.  The efficacy of such products must be evaluated by the consumer.  

Liquid Waste Treatment and Disposal Systems (Septic Systems)


  • Treatment is a term that describes the reduction in concentration of waste water constituents such as BOD, TSS, TN and FOG.
    • Waste strength is often measured with parameters such as Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), Total Nitrogen (TN) and Fats, Oils and Greases (FOG).
  • Mechanical, chemical and biological processes may be utilized to accomplish treatment. 
  • Primary Treatment occurs in the septic tank and includes settling of solids (sludge) and Fats, Oils and Greases (scum).
  • Conventional Systems utilize Primary Treatment.
  • Advanced Treatment Systems utilize either Secondary or Tertiary Treatment
  • Advanced Treatment utilizes both physical, chemical and biological processes, often focusing on aeration as a means to accomplish advanced treatment.
Conventional Treatment Advanced Treatment
Primary Treatment Secondary Treatment Tertiary Treatment
  • 2 Compartment Tank
  • Allows of settling of solids to form “Sludge” layer in bottom of tank
  • Flotation of Fats, Oils, and Greases (FOG) to form “Scum” layer
  • Aeration (aerobic)
  • In addition to Primary Treatment, also includes:
  • Reduction in TSS and BOD
  • Aeration (aerobic)
  • In addition to Secondary Treatment, also includes:
  • Reduction in TN (as calculated)
Treatment Standards
  • BOD 200 mg/L
  • TSS 100 mg/L
  • TN 60 mg/L
  • FOG 60 mg/L
  • TSS 30 mg/L
  • BOD 30 mg/L
TN (mg/L) = [lot size (in acres) / design flow (in gpd)] x 30,000


Disposal involves the discharge of treated effluent to some type of drainfield/leachfield.  The Soil Treatment Area (STA) is another term used for the drainfield/leachfield.  Additional biological treatment can occur in the STA as microbes further consume and breakdown nutrients and pathogenic (disease causing) microbes.

  • There are many types of disposal systems, some of which include:
    • Pipe and Gravel Trenches
    • Proprietary Drainfield Products (chambers, synthetic aggregate, etc.)
    • Mounds
    • Evapo-Transpiration Beds
    • Seepage Pits
    • Holding Tanks
    • Pressure Dosed Drainfields
    • Emitter Tubing

New Mexico Homeowner Guide Septic Smart – for useful information about maintaining your septic system.

How does a septic tank (treatment unit) work?  

Septic Tanks typically have two compartments and are designed to allow for solids to settle and get trapped in the tank behind the baffle wall that separates compartments 1 and 2.  Fats, Oils and Greases float to the water surface and also get trapped in compartment 1.  Relatively clear wastewater passes through the baffle at mid-water-column-height.  Further separation occurs in compartment 2.  The outlet sanitary Tee fitting also prevents “floaters” from flowing out of the tank and into the disposal component of the septic system.  The outlet Tee also utilizes an effluent filter that must be periodically removed and cleaned as part of routine maintenance.


Treatment Units in Motion:  Click the icon to download slideshow showing how tanks handle liquids, solids and gases.

Download and play this animated Power Point presentation that demonstrates how a septic tank allows solids (sludge), “floaters” (scum = Fats, Oils and Grease) to settle out of suspension.  You will also see how gases develop in the tank and need to vent out of the tank and  back through the vents on the structure.