New Septic System in Arivaca

Pima County contacted GLHN to help with an interesting project in the small town of Arivaca, Arizona. The local community center is situated on 9 acres and has a meeting building, a playground, tennis courts, and a volunteer fire station.  The community center uses an onsite sewer septic system that is over 30 years old and failing. Pima County, who originally built the Center and helps to fund its operation, asked GLHN to work with the community to design the new system.

Arivaca residents wanted to use the wastewater to create a wetlands. They envisioned an attraction for wildlife and a garden setting to teach area students about water conservation. GLHN Civil Engineers looked for ways to achieve this, however, it quickly became clear that the heavy maintenance required for wetlands sewer treatment would be too much even for the committed community of Arivaca.

The second option was a conventional septic system, where most of the treatment happens in a septic tank. The solids settle out and get digested, and the clear liquid drains to an underground field, where it percolates into the soil. Unfortunately, it was discovered that the soils on the site wouldn’t drain, meaning the septic system wouldn’t work.

In the end, the least expensive option was to build a newer, better version of what was previously used, an evapotranspiration bed. An ET bed for short, it starts with the same septic tank but the liquid drains to an open bed of sand, where it evaporates up instead of percolating down. When the GLHN engineers began to design the ET bed to

state administrative code, they found that the testing method for the sand no longer existed. After discussions with Pima County Department of Environmental Quality, it was agreed that if GLHN proposed a material and tested it, Pima County would accept the test results.

GLHN’s Civil Engineering Department was quickly transformed into a Sand Lab. The project required sand that could make water rise over two feet by capillary action. With the help of a local contractor, staff found a local sand pit and collected samples. The sand lab was built with 5 feet of tubing taped it to a vertical surface. The tube was filled with sand and placed in a bucket with six inches of water. Within two days, 30 inches of the sand was wetted. DEQ approved the sand selection and the project went into construction. The ET bed sandbox is over 7,000 square feet and averages 2.5 feet deep and required 50 truckloads of sand. The community of Arivaca now has a worry-free system that was completed under budget.

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