Evaluation of methods for diagnosing contamination in rural wells

Three diagnostic procedures were tested to determine their potential useful ness in identifying faulty rural wells: (1) monitoring wells were construct ed at three depths near each of three rural wells having a history of nitra te-nitrogen and/or herbicide contamination, and all wells were samples dail y for four weeks and tested for nitrate-nitrogen, atrazine, alachlor, metol achlor, 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 8-h pumping period to obs erve contaminant variability during periods of continuous drawdown. Daily s ampling revealed little temporal variability in the quality of water from t he monitoring wells or the contaminated water supply wells. The monitoring wells, though limited in number, identified significant contaminant stratif ication within the shallow glacial drift aquifers supplying the water suppl y 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 vi a preferential flow from that occurring through matrix flow in two of the c ase study wells, but proved ineffective on a third well where monitoring we ll data strongly suggested casing leakage. Nitrate-nitrogen and herbicide d ata showed little variability during the 8-h period of continuous well draw down.