Tribal Onsite Sewage System Evaluation Project
Evaluating Large Capacity On-site Systems in Indian Country
The Environmental Protection Agency (EPA) and Indian Health Service (IHS) are working together to evaluate large capacity on-site systems (designed to serve 20 or more people) serving Tribal Casino’s, offices or schools within Region 10. The purpose of this evaluation is to assess the performance and identify any impacts to ground water.
PROJECT OVEVIEW
The evaluation will include an engineering review of the wastewater collection, treatment and disposal systems design, construction plans, and current and past operation practice. The evaluation will also evaluate treatment efficiencies in the receiving to determine if there is any impact to underlying ground water. The evaluation plan calls for the installation of small diameter monitoring wells in and around the injection well (drainfield).
Analyte testing will look at ammonia, nitrite and nitrate as nitrogen, and Total Kjeldahl Nitrogen (TKN), to determine at what stage nitrification and/or de-nitrification is occurring as wastewater percolates through the soil. In addition, some fecal coliform testing will be done to test the standard assumption that this is filtered out in the soil matrix. Oil and Grease will also be tested for to assess soil clogging action within the drainfield bed. Collected field samples will include measurements for conductivity, pH, dissolved oxygen and temperature to assist with quantifying collected sample conditions.
OUTCOMES
Possible outcomes from this project include recommendations for individual system operators and supporting data for EPA to use in setting environmental policy related to large capacity on-site systems.
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SUPPORTING DOCUMENTS
Quality Assurance Project Plan
CONTACTS
U.S. Environmental Protection Agency
1200 Sixth Avenue (OW-137)
Seattle, WA 98101
(206) 553-1673
Engineering Consultant
Indian Health Service
2201 6th Avenue, Room 300
Seattle, WA 98121
(206) 553-1673