GROUNDWATER QUALITY IN WASHINGTON COUNTY, MARYLAND: A COMPARISON OF TWO STUDIES CONDUCTED TEN YEARS APART

Abstract

This research was conducted from 1989 to 1991 to evaluate ground water quality in Washington County, Maryland. Results of a study conducted in 1981 of water quality in 296 wells were used as a baseline to determine if ground water quality improved during the elapsed ten years. Analysis of water from 134 sites of the original study indicated that not only did ground water quality not improve, but that it actually declined slightly in the study area. Samples collected in 1991 showed an overall total coliform contamination rate of 31% and a fecal coliform contamination rate of 9% while the 1981 sampling indicated a total coliform contamination rate of 22% and a fecal coliform contamination rate of 7%. Mean nitrate concentrations increased 17% in all aquifer units sampled. Although the construction of the wells sampled in the 1981 study remained unchanged during the 10-year period, all new and repaired septic systems were built in accordance with strict regulations promulgated in 1983. Thus, there has been in Washington County an attempt to remediate contamination of the aquifers from which the sample sites derive their supply. The effectiveness of this attempt at remediation should be reflected by an overall increase in ground water quality. Concurrent with the resampling of the 1981 sites, a study was conducted of wells drilled since 1981. All of these sites had been constructed in accordance with Maryland Department of the Environment guidelines and had no contamination at the time of construction. These wells, located throughout the County, showed contamination rates in 1991 comparable with the original 1981 study, indicating that neither septic system siting and construction nor well siting and construction has had an appreciable effect on improving ground water quality. The results indicated wide variation in water quality obtained from a single source, eg, a well, when successive samplings were conducted over a period of time. Also, when samples were tested for coliform bacteria by a presenceabsence versus a most probable number technique, there was a dramatic increase in sensitivity to the presence of these organisms in the presence-absence tests. The results also indicated that rigid well and septic system construction practices, put into place in 1983, did not alter ground water quality during the period 1981 to 1991. The approval of water supplies based on satisfactory samples at time of initial service is not a reliable way to ensure potable water.