Onsite wastewater treatment system (OWTS) is a broad term referring to any system for the collection, storage, treatment, neutralization, or stabilization of sewage that occurs on the property.
A septic system is a type of OWTS, consisting of a septic tank that collects all the sewage. The sewage separates into a solid (sludge) that settles to the bottom, and a liquid effluent that then flows into a leach field for final treatment by the soil.
OWTS are used to treat and dispose of relatively small volumes of wastewater, usually from houses and businesses that are not a part of or connected to a sewage treatment works.
Regulatory definition: OWTS – an absorption system of any size or flow or a system or facility for collecting, storing, treating, neutralizing, stabilizing, or disposing of sewage which is not a part of or connected to a sewage treatment works.
How an OWTS Works
There are two main parts to the basic OWTS: the tank and the drainfield.
- The household wastewater flows into the tank where the average detention time is 30 hours. The tank should have at least 1,000 gallon capacity.
- Three layers are formed in the septic tank. There are baffles in the tank which keep the wastewater flowing though the tank at a level near the middle of the tank.
- Solids settle to the bottom, forming a layer of sludge. The grease and foam float to the top, forming a scum layer. Both the sludge and scum layers remain in the tank where bacteria work to break them down. In time, the layers build in size. When the layers become too large and take up too much space in the tank, the tank needs to be pumped. Every 3 years, the tank should be pumped out by a licensed OWTS cleaner. If the system is not pumped out when it is full of solids, the wastewater is not fully treated, and solid material can be carried into the drainfield.
- Solids in the drainfield can clog pipes and seal pores in the soil. When the pores become sealed with solids, the water no longer percolates as it should. The drainfield provides additional treatment of the wastewater. In the drainfield, wastewater trickles though a series of perforated pipes, though a layer of gravel, and down though the soil. The soil and soil bacteria act as a natural filters that help treat the wastewater.
Identifying a Problem with Your OWTS
Home owners should be alert to the following warning signs of a failing OWTS:
- Test results of well water show the presence of bacteria.
- The ground in the area is wet or soggy.
- Grass grows greener or faster in the area.
- Sewage odors in the house or yard.
- Plumbing backups into the house.
- Slowly draining sinks and toilets.
- Gurgling sounds in the plumbing.If one or more of these warning signs exist, the home owner should contact a licensed OWTS cleaner to have the system inspected and pumped.
Locating your OWTS
Boulder County Public Health issues permits and inspects systems as they are installed. If your system was installed during the last 20 – 30 years, we may have a sketch of the layout of your system.
OWTS cleaners can usually find the tank by using a soil probe in areas where they would expect to find a tank. Tanks are usually behind the house, near the bathroom, and about 10 feet away from the foundation.
Keeping your OWTS Working Properly
Many products claim to help the OWTS work better or cleaner; however, there is no magical potion to cure an ailing system. Most engineers and sanitation professionals believe that most of these products are unnecessary and are potentially harmful to the system.
Some chemical products can cause soil pores to clog in the field or add pollutants to the ground-water. Bacteria, enzymes, and yeast products are usually harmless, but are unnecessary because the wastewater will already contain enough bacteria to break down the organic matter.
The Cost of Installing an OWTS
For exact costs associated with design, installation, or cleaning an OWTS, it is best to contact the professionals involved directly.
A rough range of potential costs would be from $6,000 – $30,000. Costs are very dependent on specific site constraints and sizing of the system.
Checking the Status of Your OWTS Permit
You may contact Boulder County Public Health’s Water Quality Program at 303-441-1564 to inquire about a system or search for your inspection record online.
The Cause of OWTS Failure
Most OWTS failures are related to inappropriate design and poor maintenance. Some soil-based systems (with a leach or drain field) have been installed at sites with inadequate or inappropriate soils, excessive slopes, or high groundwater tables.
These conditions can cause hydraulic failures and water resource contamination. Failure to perform routine maintenance, such as pumping the septic tank at least every 3 to 5 years, can cause solids in the tank to migrate into the drain field and clog the system.
What Not to Put Down an OWTS
Do not put the following items into sink drains or toilets:
- Hair combings
- Coffee grounds
- Dental floss
- Disposable diapers
- Kitty litter
- Feminine hygiene products
- Cigarette butts
- Gauze bandages
- Fat, grease, or oil
- Paper towels
- Paints, varnishes, or thinners
- Waste oils
- Photographic solutions
Responding to a System Backup
If sewage from your plumbing fixtures or onsite system backs up into your basement, avoid contact with the sewage and the possibly harmful pathogens it might contain.
Contact Boulder County Public Health at 303-441-1564. Cleanup personnel should wear protective clothing (e.g., long rubber gloves, face splash shields).
After cleanup is complete, all equipment, tools, and clothing used in the cleanup and the flooded basement area should be washed thoroughly and disinfected with a mixture of 90 percent water and 10 percent household bleach. The area should be dried out with fans, heat lamps, or other devices, and should not be used until it has been completely dry for at least 24 hours.
Questions or Concerns
The Boulder County Public Health Water Quality Program can assist you and can be reached at 303-441-1564.
If your system needs to be serviced, contact a licensed OWTS professional.
Risk of OWTS-caused Health or Water Quality Problems
OWTS that are properly planned, designed, sited, installed, operated, and maintained can provide excellent wastewater treatment. However, systems that are sited in densities that exceed the treatment capacity of regional soils and systems that are poorly designed, installed, operated, or maintained can cause problems.
The most serious documented problems involve contamination of surface waters and groundwater with disease-causing pathogens and nitrates. Other problems include excessive nitrogen discharges to sensitive coastal waters and phosphorus pollution of inland surface waters, which increases algal growth and lowers dissolved oxygen levels.
EPA has developed guidelines to assist communities in establishing comprehensive management programs for onsite wastewater systems in order to improve water quality and protect public health.
In most states, local health departments issue construction and operating permits to install OWTS under state laws that govern public health protection and abatement of public nuisances. Some states are beginning to add water resource protection provisions to their OWTS regulations because of the possible impacts from nitrogen and phosphorus.
Under most regulatory programs, the local permitting agency conducts a site assessment to determine whether the soils present can provide adequate treatment, to ensure that groundwater resources will not be threatened, and to stipulate appropriate setback distances from buildings, driveways, property lines, and surface waters.
Some states permit alternative systems if conventional soil-based systems are not allowable. Very few permitting agencies conduct regular inspections of OWTS after they are installed. Find out more about local regulations.
Improving OWTS Management
The Environmental Protection Agency (EPA) is partnering with federal agencies, states, tribes, local governments, and nongovernmental organizations to improve the management of OWTS. EPA’s guidelines for managing decentralized wastewater treatment systems can be tailored to meet the needs of states, counties, tribes, cities, towns, subdivisions, and other areas where OWTS might threaten public health or water resources.
The guidelines focus on the following areas where better management can achieve significant improvements in overall system performance:
- Planning to ensure that system densities do not exceed the ability of regional soils and water resources to treat and assimilate pollutants.
- Site evaluations that characterize and help to protect soil, groundwater, and surface water resources.
- System designs that provide predictable performance levels of treatment that are appropriate for protecting public health and the environment.
- Operation and maintenance procedures that ensure that systems are operated properly and that maintenance tasks (e.g., septic tank pumping, inspection of treatment units) are performed regularly.
- Monitoring and reporting to provide usable and easily accessible records on system inventories, capacity, and performance.
- Follow-up and corrective actions to ensure that failing systems are repaired, upgraded, or replaced before public health or water resources are adversely affected.
Help with a Community Solution
- The Boulder County Public Health Water Quality Program can assist you and can be reached at 303-441-1564.
- The National Small Flows Clearinghouse has a technical assistance hotline that can be accessed toll-free at (800) 624-8301, or at 304-293-4191.
- The Rural Community Assistance Program provides assistance to communities having problems with their OWS and can be reached at (888) 321-7227 or (202) 408-1273.
Identifying a Flood Plain
The City of Boulder is currently creating a map of the flood plain near Boulder Creek.
Verifying That Your OWTS is Adequate
Systems that were installed without the benefit of an engineer’s design or a licensed installer are extremely unlikely to conform to current standards that ensure adequate treatment of sewage. However, you may attempt to verify that the existing OWS is adequate by following our verification procedure.
This information is intended to provide a better understanding of the functions of onsite wastewater treatment and the need for proper design, installation, and maintenance. Always consult a licensed professional or public health official with questions regarding engineering, installation, and servicing of onsite wastewater systems.