Evaluation of Methods for Diagnosing Contamination in Rural Wells

Three diagnostic procedures were tested to determine their potential usefulness in identifying faulty rural wells: (1) monitoring wells were constructed at three depths near each of three rural wells having a history of nitratenitrogen and/or herbicide contamination, and all wells were sampled daily for four weeks and tested for nitrate-nitrogen, atrazine, alachlor, metolachlor, and chloride; (2) a chloride tracer solution was ponded around each of the water supply wells, and the shallowest monitoring well at each test site, for a period of 8 h during which the wells were continuously pumped and sampled for the tracer; and (3) nitrate-nitrogen and herbicide samples were collected from the water supply wells during the 8-h pumping period to observe contaminant variability during periods of continuous drawdown. Daily sampling revealed little temporal variability in the quality of water from the monitoring wells or the contaminated water supply wells. The monitoring wells, though limited in number, identified significant contaminant stratification within the shallow glacial drift aquifers supplying the water supply wells, and identified one water supply well that was producing water with much poorer quality than the shallow aquifer was capable of producing. The chloride tracer test was successful in distinguishing contaminant entry via preferential flow from that occurring through matrix flow in two of the case study wells, but proved ineffective on a third well where monitoring well data strongly suggested casing leakage. Nitrate-nitrogen and herbicide data showed little variability during the 8-h period of continuous well drawdown.