Sampling of groups of small-diameter shallow observation wells and nearby public-supply wells screened in the upper glacial aquifer at three well fields showed that detergents (MBAS) were distributed through almost the entire saturated thickness of the aquifer. Concentrations of MBAS in water from all the wells sampled ranged from less than 0.02 to nearly 5 mg/l (milligrams per liter), whereas MBAS concentrations in water pumped from shallow public supply wells ranged from about 0.1 mg/l to about 1.3 mg/l. Upward trends in MBAS concentrations, which were observed at most of the shallow observation wells from 1961 to 1966, nearly stabilized or declined to some extent by 1968. A slight to distinct upward trend in the MBAS content of water pumped from shallow public-supply wells was observed during the same period at two of the three well fields investigated.
Chloride concentrations in the upper glacial aquifer, which ranged from about 5 to 80 mg/l, had a distinct upward trend at some wells apparently due to infiltration of both sewage effluent and deicing salts which were applied to roads in the winter. Nitrate concentrations also increased slightly but remained below the recommended limit for drinking water.
No MBAS was detected in water from public-supply wells tapping deeper zones in the underlying Magothy aquifer, and significant amounts of MBAS and associated contaminants are unlikely to reach those zones for many years, if present flow patterns and head relationships are not markedly changed.
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USGS Numbered Series
Detergents and associated contaminants in ground water at three public-supply well fields in southwestern Suffolk County, Long Island, New York