The impacts of on-site septic systems on the water quality of the Buffalo River near Gilbert, Arkansas

Mott, David; Mays, N; Ursey, F; Maner, M; Aley, T; Cassat, D

The town of Gilbert's waste-water production is routed to individual on-site septic systems which are situated over karstic limestone bedrock within shallow soils. Karst systems are highly susceptible to groundwater pollution because of their internal drainage, numerous sinkholes, caves, and springs. Water quality monitoring over the past fifteen years at Gilbert Spring showed this spring to be the most contaminated spring within Buffalo National River. Fecal coliform bacteria counts have been measured far above the state standard of 200 col/ 100 mL, and average nitrate values are thirteen times higher than average nitrate values in the Buffalo River. Gilbert's ground water hydrology and septic systems were studied to quantify the impacts of Gilbert's septic fields on the water quality of Gilbert Spring and the Buffalo River. Should chronic failure of septic systems be documented, the need and feasibility of converting from on-site septic systems to a sewage treatment plant would also be investigated. The water quality studies and related assessments were conducted through a cooperative effort between Buffalo National River and the Arkansas Department of Environmental Quality (ADEQ). A series of three town meeting were held at Gilbert to discuss this project with the mayor, city council members, and residents. The residents were initially concerned as to what they would be required to do if the investigators found problems. Buffalo National River's superintendent and representatives from ADEQ assured them that this was not an effort to force people into some type of compliance and that fair measures to correct problems would be sought. A number of residents volunteered to have their septic systems tested at this meeting. Over 30 individual dye traces were conducted from 29 septic systems in the town of Gilbert (85 percent of the targeted systems). There were two major objectives defined for the septic system traces: 1.) determine if septic systems constructed in accordance with Arkansas State Regulations for septic systems are capable of functioning in the karst setting of Gilbert, and 2.) find any systems which are contributing leachate directly to Gilbert Spring. To address objective 1, we traced seven of the best septic systems identified in Gilbert simultaneously using two types of dye. Very small amounts of fluorescein were recovered from these traces, and we conclude that these systems are over 98 percent efficient in removing the tracer dye from the leachate. Our conclusion is that septic systems can and do work well in Gilbert's karst setting where they are properly constructed and maintained.