Published on November 8, 2007
Slide1: Household Wastewater Systems Mike Kizer OSU Extension Biosystems & Agricultural Engineering Slide2: Typical Waste Water System Well Renovated Wastewater Wastewater System Regulation: Wastewater System Regulation Regulatory agency in Oklahoma is: Department of Environmental Quality (DEQ) 707 N. Robinson, OKC (Tel: 405-702-6100) DEQ field offices in many counties Check local listing under: Oklahoma – State of – Regulations are outlined in Title 252 of Oklahoma Administrative Code, Ch. 641 DEQ wastewater system website: http://www.deq.state.ok.us/ECLSnew/septic.htm Minimum Lot Size for Wastewater Disposal Systems: Minimum Lot Size for Wastewater Disposal Systems Wastewater System Separation Distances(distance in feet): Wastewater System Separation Distances (distance in feet) Wastewater System Components: Wastewater System Components Water-tight sewer lines Septic tank Disposal system Subsurface drain field Absorption trenches Infiltration chambers ET/Absorption trenches Aerobic system with sprinkler Total retention lagoons Pre-approved alternative disposal systems Slide7: Household Plumbing Sewer and Vent System Sewer lines in the house collect waste water for conveyance to the septic tank Roof vents and the traps under sinks, tubs, showers, toilets and wall/floor drains prevent sewer gas from entering the house. Screen vent pipe opening to prevent blockage by birds, squirrels, etc. Main Sewer Pipe Septic Tank: Septic Tank All household wastewater systems will have a septic tank Microbial action digests solid wastes Liquids flow through tank to disposal area Tank size 1000 gallon liquid capacity (4-BR house or less) Add 250 gallons per additional bedroom Slide9: House Foundation Typical Septic Tank Installation Two-Chamber Tank Baffles Wastewater Piping Materials: Wastewater Piping Materials Water-tight Sewer Conveyance Lines Cast iron PVC (Sch. 40 is preferred weight) Transite (asbestos-cement) Orangeburg (paper-tar product: old houses) Drain Field Lines Perforated PVC Polyethylene infiltration chambers Clay tile (old houses) Effluent Disposal Area Options: Effluent Disposal Area Options Absorption field Absorption trenches Infiltration chambers ET/Absorption trenches Lagoons Aerobic systems Authorized alternative systems Subsurface Absorption Field Approval: Subsurface Absorption Field Approval Percolation Test 3 test holes in drainage area perc at a rate of 60 min/inch of water or faster Soil Profile Description 3 test holes without any of the following: (1) impervious material (bedrock, clay pan) (2) water saturated soil (discoloration) (3) loamy coarse sand or coarser soil, or (4) sandy clay or finer soil Slide13: The size and type of waste water disposal system is very dependent on the soil at the building site. Even before a percolation test or soil profile evaluation you can get an idea of site suitability from the county soil survey. Slide14: Cross-Section of Subsurface Absorption Trench Perforated Pipe 8-ft minimum distance to center of next trench Slide15: 150’ MAX. Slide16: Lateral lines following the slope contour 150’ max. length Slide17: Infiltration Chambers Polyethylene infiltration chamber has 100% open volume vs. 50% for gravel-filled absorption trench Corrugated design gives strength to support ground traffic over its 2-ft width Chamber cost per unit length is approximately equal to unit cost of perforated PVC pipe, plus gravel and installation ET/Absorption Trench System: ET/Absorption Trench System Used when soil percolation rate is too slow for ordinary subsurface absorption trenches Uses evapotranspiration (ET) of grasses plus soil absorption to dispose wastewater Plant a mix of cool and warm season grasses for year-round ET Slide19: Cross-Section of ET/Absorption Trench Cool-Warm Season Grass Mixture Perforated Pipe Lagoons: Lagoons Used when soil percolation rate is too slow for soil absorption systems Require 2 ½ acre minimum lot size Fencing required around the lagoon Size based on house size, and rainfall and evaporation of geographic zone Must retain all wastewater (no overflow) Slide21: 3 1 Typical Lagoon Installation 5 ft max. 7 ft 4 ft Concrete Pad 1 ft min. 2.5 acre minimum lot size required 4-ft high fence required lagoon size based on house size and local rainfall Slide22: Location & Lagoon Size The required size of total retention waste water lagoons (because of their annual hydraulic balance) makes them less desirable the farther east you build in Oklahoma. Aerobic Systems: Aerobic Systems Used to treat septic tank effluent where subsurface disposal is not possible Bubbling air through effluent supports aerobic bacteria for further digestion Exposure to oxygen kills most pathogens Chlorination allows surface land application of wastewater through sprinklers Slide24: (Septic Tank) Onsite Aerobic Treatment System Onsite aerobic treatment systems treat septic tank effluent further by aerobic digestion, chlorination to kill pathogens, and surface application through a spray head sprinkler system. Slide25: Typical Aeration Chamber of Aerobic Treatment System DIFFUSER EFFLUENT FROM SEPTIC TANK WASTEWATER TO CHLORINATOR & SPRINKLERS Slide26: Stack-Feed Contact Tablet Chlorinator Chlorine Tablet Feed Tubes Ca(OCl)2 Tablets Effluent Inlet Effluent Outlet Slide27: Pump Chamber and Surface Application System Pump Pump Control & Alarm Floats Access Hatch Spray Heads Finding Waste Water System Components: Finding Waste Water System Components Waste water components are normally downhill from the house (gravity flow) Septic tank can be no less than 5 feet, and is normally no more than 50 feet from house Two-way sanitary sewer clean-outs located: Within 5 feet of the house Within 5 feet of every bend greater than 45º Every 100 feet of straight sewer line Grass over septic tank may be brown in summer Grass over drain field will be greener in summer Slide29: Clean-outs on main sewer line Locating Waste Water System Components Slide30: Sewer system roof vents 4-inch roof vent on main sewer line 2 1/2-inch roof vent on branch line Locating Waste Water System Components Slide31: Largest roof vent on main sewer line Clean-outs on main sewer line exiting house Locating Waste Water System Components Regular green stripes in a dry lawn are the lateral lines: Regular green stripes in a dry lawn are the lateral lines Household Water Use: Household Water Use Typical Usage: 50-100 gallons/person-day Clothes washer: 30-50 gallons/load Dishwasher: 7-15 gallons/load Garbage Disposal: 4 - 6 gallons/day Shower/Bathtub: 25-60 gallons/use Ordinary toilet: 1.6 - 5 gallons/flush Water softener: 50-100 gallons/regeneration Septic System Additives: Septic System Additives Biological Bacteria Yeast Enzymes Combination Chemical Acids Bases Organic Solvents Flocculants Biological Additives: Biological Additives Will not eliminate need for tank pumping 20% of sludge is inorganic (indigestible) Billions of bacteria live in septic tanks-- a few million more have little effect If natural bacteria have been killed, added bacteria will die also Normal population is restored in 30-60 hours even if 99.99% has been killed Maximum Safe Levels of Cleaners(Single dose in 1000-gallon septic tank): Maximum Safe Levels of Cleaners (Single dose in 1000-gallon septic tank) Bleach (5.25% Cl): 1.3 gallons Cleansers/Disinfectants: 2.5 gallons Drain Cleaners: 0.65 ounces Chemical Additives: Chemical Additives Strong Acids and Bases Disrupt normal tank biological activity Harm soil structure in drain field Organic Solvents Clean thin layers of sewer line build-up Contaminate ground water Annual Cost of AdditivesAmherst, MA Retailers Study - 1989(using manufacturer’s recommended rates): Annual Cost of Additives Amherst, MA Retailers Study - 1989 (using manufacturer’s recommended rates) Biological (11): $19.75/yr Solvents (3): $78.00/yr Acid/Base (8): $13.48/yr Annualized Pumping Cost(USPHS Pumping Frequency Estimate) $150 Pumping Cost for 1000-gal tank: Annualized Pumping Cost (USPHS Pumping Frequency Estimate) $150 Pumping Cost for 1000-gal tank Septic System AdditivesConclusions: Septic System Additives Conclusions Biological additives are harmless but of little use Chemical additives can damage septic system and contaminate ground water Don’t use if active ingredients are unspecified Annualized cost of additives is about the same as for tank pumping on recommended schedule “These products make a lot of money for the people that sell them.” Waste Water System FailuresCommon Causes: Waste Water System Failures Common Causes Hydraulic overloading (too much water) Solids migration to drain field Failure to pump tank on schedule Baffle failure Root intrusion into sewer lines Traffic damage to drain field Garbage disposal overuse Reducing Hydraulic Loading: Reducing Hydraulic Loading Equipment Adjustments Low flow toilets (1.6 gpf and 0.6 gpf) Water-saving showerheads Front-loading washing machines Lifestyle Adjustments Shower vs. bath Distribute laundry loads throughout week Distribute bathing morning & evening Full loads only for washer & dishwasher Root Damage: Root Damage Plant no trees or shrubs near sewer lines Copper sulfate to kill tree/shrub roots Treatment is not toxic to plants Once intruding roots are killed, absorption ends Add ½ cup of crystals to distribution box or to cleanout downstream from septic tank If added through toilet, 2 pounds of crystals are needed (not harmful to tank bacteria) See OSU CR-6428 for more information Traffic Damage: Traffic Damage No vehicle parking over drain field No vehicle traffic except lawn mowers No traffic at all if ground is saturated Solids & Drain Fields: Solids & Drain Fields Solids must be retained in septic tank Baffles should be inspected when tank is inspected or pumped Use of additives that “liquefy” sludge and scum can lead drain field failure Septic tanks: like fuses in electrical wiring (failure in controlled location; cheap to fix) Garbage Disposals: Garbage Disposals Add to hydraulic load (running water) Add to solids (more frequent pumping) Poorer digestion environment (Carbon:Nitrogen ratio is more unfavorable) Water Softeners & Septic Systems: Water Softeners & Septic Systems Salt does not affect septic tank functioning Added hydraulic load (regeneration water) Use water meter or sensor controlled regeneration rather than time clock alone Added sodium can affect marginal drain fields (dispersal of clays slows perc rate) Use potassium chloride (KCl) salt if a problem Slide48: On-Site Wastewater System Resources MWPS-24 Home*A*Syst OK DEQ Ch. 641 Onsite Domestic Sewage Worksheet #3 www.deq.state.ok.us Disposal Handbook Slide49: If you don’t maintain your on-site wastewater system, it will demand your attention when it is most inconvenient.