The Upper Snake River Reference Library
Search our reference library for Upper Snake River watershed information.
Teton County Westbank Groundwater Study
Mar 1, 1992
PROJECT DESCRIPTION This project is a reconnaissance level study of the groundwater contamination problems on the west side of the Snake River in Teton County. The study as proposed would determine the severity of the groundwater quality problem, determine the nature and extent of non-point source and/or point source pollution, identify control measures for correcting the groundwater quality problems and evaluate the feasibility of correcting the groundwater quality problems including an analysis of central sewerage systems. PROJECT GOALS AND OBJECTIVES Teton County developed the following preliminary goals and objectives for the study: 1. Determine the severity of the problem through- a. Water quality analysis of selected wells; b. Survey of local construction contractors, well driller, septic tank pumping contractors and property owners about drainfield and well failures; c. Monitoring groundwater movement in existing wells at different times of the year. 2. Define the nature extent and cause of water quality problems including the identification of the relative contributions of specific point and non-point source problems through - a. Determining the number and density of existing housing units, the average wastewater flow and the average organic loading. b. Projection of land use changes and subsequent wastewater hydraulic and organic loadings. c. Determination of aquifer characteristics in order to decide if the aquifer can assimilate the existing and projected pollutants. 3. Identify alternatives which can correct the groundwater quality problem. Alternatives may be a. specialize individual onsite systems b. Satellite treatment plants. c. Centralized sewage treatment facility. d. Centralized domestic water system(s). e. Zoning changes to reduce development density. 4. Conduct an economic analysis of each viable alternative including capital cost, operation and maintenance cost and total annual equivalent cost. 5. Provide a comparison of the non-economic factors affecting each alternative. 6. Provide recommendations for future actions to accommodate the best alternative including available funding sources. PROJECT NEED The west side of the Snake River in Teton County, Wyoming, currently has an estimated 1,670 residential family dwelling units. Approximately 1,400 of these homes draw their drinking water from the Snake River alluvial aquifer and discharge their treated sewage back into the Snake River alluvium. The existing number of dwelling units on the west side of the Snake River and the proliferation of new building permits, has prompted many residences to question the capacity of the Snake River alluvium to assimilate domestic wastes while continuing to yield safe drinking water. Specific concerns about septic tank/leachfields have developed because of the high groundwater table in this area. Current state and county regulations allow soil absorption (leachfield) systems only in areas where the seasonal high groundwater is two feet or more below the surface. These regulations may alleviate problems with new construction if the groundwater level is measured at the correct time of the year, if the soil adsorption systems are constructed properly and if the septic tanks are pumped on a regular basis, but they do not correct problems with existing septic systems. A cursory look into the drainfield failures indicates three major problems. The first problem has been inadequate design; the groundwater is sometimes higher than anticipated thus reducing the distance and time the septic tank effluent is exposed to the aerobic soil conditions necessary for adequate treatment. The second problem has been inadequate construction wherein the drainfield is not sufficiently elevated above the groundwater and/or the soils between the groundwater, and the drain pipes are too coarse to provide adequate filtration and detention time. The third problem is inadequate maintenance; the septic tanks are not pumped frequently, thus they fill up with solids and allow untreated sewage to discharge directly to the drainfield. There are currently two developments west of the Snake River with centralized sewer systems, Teton Village and the Aspens/Pines Subdivision. Teton Village has an advanced treatment plant with effluent discharge to aquifer recharge wells perforated 20 to 50 feet below the surface. The Aspens/Pines treatment plants recently converted from a package activated sludge plant with a large soil adsorption system to a new advanced treatment plant with final effluent discharge to injection wells. These two developments account for about 800 of the existing residential dwelling units, leaving 600 dwelling units on individual septic systems. The subdivided areas with individual septic systems that are of the biggest concern to Teton County are the Wilson area, Nethercott Subdivision area and Wenzel Lane area. The concern is primarily because of the density and the fact that these developments occurred prior to the promulgation of the current standards for septic tank/drainfield construction and domestic well construction.
Hard copy available at:
© Copyright 2007-2013, Teton Conservation District. All Rights Reserved.