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Onsite Sewage Systems

Onsite Sewage Systems

Homes not served by public sewers and water systems use an onsite sewage system, usually a septic tank and drain field, to treat and dispose of their wastewater. When the system is designed, installed, and maintained properly, they provide years of low-cost service that is just as good as the public sewer systems. However, when they fail or are not maintained, the results can be catastrophic. Property damage, groundwater contamination, surface water pollution, and disease outbreak are just a few effects of a failed OSS.

As the results of a failed system place the entire community at-risk, all new OSS builds require an application and permit. This ensures the conditions for traditional systems are met, the design and installation are done professionally, and sets the system, homeowner, and community up for many years of safe waste management. No matter the system, the septic tank requires inspection every three to five years and pumping as needed.

Type of OSS

While there are several types of OSS options, depending on the environmental factors, most of the Lincoln County OSS builds are the traditional gravity OSS. This requires a minimum of three feet of good soil between the bottom of the drain field trench and a restrictive layer (solid rock or ground water) to provide adequate wastewater treatment. The traditional gravity system capitalizes on the natural environment to treat the water before it reaches the water table or water source.

What is good soil?

Good soil

Good soil is defined as gently sloping, thick, oxygenated, permeable soil which allows the water to pass through and be purified

Septic tanks are made of concrete, fiberglass, or polyethylene which captures all wastewater, whether from your toilet, sink, bath, laundry, etc. Tank size is determined by the number of bedrooms in the home. The tank is divided into two compartments to help separate solids from liquids. Heavy solids settle to the bottom of the tank where bacteria decompose them into a sludge and produce gas. Lighter solids, such as fats or soap, rise to the top and create a scum layer. The tanks use a barrier, called a tee or baffle, to help the layers remain steady as new water comes into the tank. The baffles also help keep solids in the tank rather than moving to the drain field. The scum and sludge layers build up over time, which is why tanks need to be regularly drained.

The water layer, now called effluent, continues through the tank into the drain field. The effluent has been partially treated by separation and bacteria decomposition, but it is still contaminated with pollutants and pathogens, so further treatment is required before it is released.

Remember—your tank will continue to build up scum and sludge. Regular pumping is required to maintain a working system. All tanks should be inspected every three to five years. If you need your tank pumped, a list of licensed pumping companies is available.



While there are products on the market that claim to reduce the scum and sludge in your tank, there is no evidence these claims are true.

The drain field is where the effluent goes after it leaves the septic tank. The field is a network of perforated pipes in three feet wide gravel trenches. Effluent slowly trickles out the pipes, through the gravel, and into the surrounding soil. The size of the drain field will depend on the estimated daily wastewater flow, the soil type, and the soil conditions. This ensures the effluent will not overwhelm the filtration process.

Every OSS location is required to have a designated and reserved replacement drain field area on the property in case the primary drain field becomes unusable or fails.

The soil is the final step in the treatment process, which is why the condition of the soil is so critical. The effluent soaks into the soil below the drain field, where it will slowly filter before it returns to the groundwater supply. The natural properties of the soil treat the effluent through chemical and biological reactions, allowing clean water to return. Plants and evaporation also help clean the water before it returns to the source.

OSS Permitting

All new OSS installations must have a permit to ensure the safety of the community. The process can be a long one, due to the nature of the required inspections, but understanding the steps, using an approved installer, and following through with seasonal considerations can help speed up the process.

Property owners wishing to install an OSS will need to submit a completed OSS application, including the preliminary designs of the project, and the application fee to the LCHD. In addition to the application, a minimum of two test holes must be dug and meet the minimum requirements where the proposed installation will occur to allow for inspection. LCHD allows for owner-designed systems when a traditional gravity system is being used. If an alternate system is required, the system must be designed by a professional engineer or licensed designer.

Once the application is received and the fees are paid, an environmental health team member will schedule a site evaluation. The evaluation is ensuring the environmental requirements are met to protect the watershed. After the evaluation, the inspector will mail or email a letter to the owner listing any requirements or additional submissions which must be completed prior to the permit being issued.

Seasonal Consideration

If the project will occur in winter, test hole digging should be scheduled with LCHD to allow for same-day inspection. This protects the property owner from any delays resulting from snow, ice, or other environmental influences.

When the design is approved and the permitting paperwork is completed, an OSS permit will be issued. The permit is valid for two years from the date of issuance.  Once the permit is issued, the OSS system can be installed. Just like design, the installation can be completed by the homeowner or by a LCHD approved, licensed installer.

When the installation is complete, the property owner must contact LCHD for a final as-built inspection. The final inspection is generally scheduled within a week of request.  An as-built drawing is created as part of the inspection, which shows the exact location of all components of the system and will become the permanent record of the system.

The owner will be mailed a copy of the as-built drawing, which will include the required approval signatures from LCHD. Additional copies can be requested by contacting us. Copy requests must include the installation permit number and the name on the installation permit or the land parcel number and section, township, and range numbers.