On-site Wastewater Disposal System Design Trinity River Elder’s Village

The Yurok Indian Housing Authority (YIHA) proposed the construction of 12 new ADA accessible two-bedroom residences and a 1,200-square (±) foot community center at the site of a former trailer park, south of the town of Hoopa in the Trinity River valley. Prior to the new developments, the site was formerly a dilapidated 24-space trailer park with a laundry facility and two well pump-houses. A single gravity-fed disposal system of unknown size and working condition served the former trailers. The disposal field, septic tanks, and all associated plumbing were removed or abandoned in-place to make way for a new system of holding tanks, a pump vault, and a pressurized subsurface disposal field.

LACO designed the new on-site wastewater treatment system (OWTS) that will serve the future Trinity River Elder’s Village to treat low strength residential wastewater with a total estimated flow of 4,000 gallons per day (gpd). The OWTS design consisted of a single-compartment bio-solids storage tank and a dual-compartment effluent storage tank, with a total capacity of 12,000 gallons. Our project team also designed the effluent storage tank to serve as a pump vault. Disposal of effluent will occur through dosing of a shallow in-ground low-pressure pipe distribution network constructed within two separate gravel absorption beds in order to provide maximum longevity of the system and the disposal field site.

The site was physically constrained due to its minimal parcel size and the large number of residential units proposed by YIHA. In order to accommodate the anticipated daily effluent loads, LACO designed a holding tank and disposal field system that maximized the available usable area without compromising the desired number of residences. Our project team integrated the disposal field into an open “green” space area surrounded by landscaping for general use by the occupants of the Elder’s Village.

Because of our long-standing working relationship with the local Tribal entities, we were able to rapidly mobilize a field investigation team and utilize Tribal equipment and an operator to complete the work in a timely fashion.

Despite an aggressive schedule, LACO completed the project on time and on budget, gaining approval from Tribal EPA for the design of an effective treatment and disposal system that allowed the project to move forward.

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