Septic System Basics Kitt Farrell-Poe Extension Water Quality Specialist Ag & Biosystems Engineering Dept. Today s Presentation: What is an onsite wastewater treatment system? Components of a septic system Treatment & dispersal Management
Common Domestic Pollutants Microorganisms Bacteria, viruses, protozoa, etc. Nutrients Ammonia, nitrate, phosphorus Suspended Solids Toxics Heavy metals, pharmaceuticals Organics pesticides What is an Onsite Wastewater Treatment System? Source Pretreatment Final treatment & dispersal
What should an onsite wastewater treatment system do? Treat sewage Public health concerns Environmental quality concerns Disperse sewage Provide acceptable level of risk put the odds on our side Goals of Treatment Separate solids * Reduce organic materials (BOD)* Reduce nutrients Reduce pathogens Reduce toxic discharges * Septic tank Soil treatment area
Goals of Dispersal Disperse effluent evenly across soil treatment area to keep soil unsaturated and aerobic. Provide enough time in the soil for treatment to take place. Percolate to groundwater so original water can be recycled back into the water cycle. Components
OWTS Components Source Application- Distribution Pretreatment Final Treatment & Dispersal Source: All Sewage! EXCEPT: Place all water softener backwash into a separate component if possible.
Conserving water helps - Maintain retention time in septic tank Promote oxygen levels in drainfield Properly dispose of cooking oils
Chemicals & Other Materials * NOTE: Septic tanks should only receive pre-digested foods Garbage Disposals Higher risk of solids carryover to drainfield Recommend composting kitchen scraps If used, then increase septic tank size (2X) Expect to pump solids more often (2X) Use an effluent screen
OWTS Components Source Application- Distribution Pretreatment Final Treatment & Dispersal Pretreatment Purpose: Pretreat wastewater so downstream component(s) can function more reliably for longer terms. Pretreatment: Septic Tank Functions Separate solids, oils, and greases from liquid Anaerobic decomposition (some, not a lot) Keep sewage in tank at least 24-36 hours Store solids Dissipate energy of wastewater As scum and sludge layers build and come closer together, the 2-day detention time becomes less and solids removal efficiency drops. Screen
Pretreatment: Septic Tank Components Sanitary tees Compartments Effluent screen Inspection port Manhole Screen screen
Septic Tank - Materials Tanks should be tested for water tightness
Septic Tank Outlet Screens Functions Helps keep solids out of drainfield Helps lessen energy of surge flows Goes in outlet of tank or replaces it Variety of types of models Will plug periodically Needs careful periodic cleaning Septic Tank Management Pump -- sludge & scum accumulations 25-33% = need to pump Inspect Structural soundness All baffles/inlets/outlets, etc. are intact
Septic Tank Additives No published scientific evidence showing additives increase system lifespan. Never pump again works against the whole purpose of the septic tank, which is to trap solids and prevent them from getting to the drainfield. OWTS Components Source Application- Distribution Pretreatment Final Treatment & Dispersal
Soil Treatment Area Receives effluent & transmits to soil Soil underneath provides treatment physical filtration biological activity chemical reactions Soil should remove disease-causing organisms and some chemicals of concern Pathogen capture Courtesy of National Assn of Wastewater Transporters
Pathogen removal Courtesy of National Assn of Wastewater Transporters How effluent moves
Conventional Soil Treatment Systems Drainfield [Soil treatment area] Network of trenches, beds, chambers, seepage pits Gravity distribution Trench
Bed Seepage Pit
Chamber Technology Alternative Soil Treatment Systems Usually pressure distribution Examples include mound and drip systems
Alternative Soil Treatment Systems Greater space needed Limits on slopes Requires pump O&M Allows use of septic systems in areas with poor soils, shallow bedrock, or high water table Operates in all climates Higher installation cost than conventional drainfields Distribution Media
How are the pieces connected? Parallel Serial Drop box Distribution box Construction Concerns Compaction Material selection Clean? Soil conditions Divert run-on away
Drainfield Management Traffic control Surface water Inspection pipes 1-½ to 4 At the end of the system Connected into the system REMEMBER: Conventional Septic System Effective where lots are appropriate Must have well-drained soils with limited slopes Requires regular inspection and periodic pumping Alternatives broaden applications and can improve effectiveness Avoid garbage grinders Groundwater problems are possible Systems fail if forgotten 6.22
IN SUMMARY: What conditions are important to maximize system function? An environment that allows bacteria to thrive proper temperature and ph, no deterrent to growth anaerobic conditions in septic tank Watertight and structurally sound septic tank Sufficient time in tanks and soil 2-5 feet of slow, downward flow through dry, aerobic soil but not too coarse Certain horizontal distances from wells, surface water, etc. to soil treatment area QUESTIONS?? http://ag.arizona.edu/waterquality/onsite Or http://extension.arizona.edu/water-portal/onsitewastewater-education-program