Trace Contaminants in Surface Water in Sand Pits and Impact on Ground-Water Quality of a Midwest U.S. City

In response to a legislative bill, state and local agencies studied water-quality impacts of stormwater runoff into sand pits on ground water in Wichita, Kansas. The pits are usually used for residential development after sand and gravel mining. The agencies selected six pits for study and arranged for installation of three monitoring wells at each site, one upgradient and two downgradient relative to ground-water flow. The agencies contracted with the U.S. Geological Survey for sampling and analysis of the waters for a range of inorganic constituents, bacteria, and 252 organic compounds, and of pit bottom sediments for inorganic components and 32 organic chemicals.

Nineteen pesticide and degradate compounds were found in at least one pit surface-water sample. Nine of these compounds and two other pesticides were detected in water from at least one monitoring well. Six organic contaminants other than pesticides were detected in at least one pit water and two of these were found in well waters. None of these chemicals exceeded the maximum contaminant levels (MCL) for drinking waters. An additional 17 organic contaminant compounds were detected in at least one well water; eleven of these occurred at only one site and probably derived from contamination directly impacting ground water by migration through the unsaturated zone. Only one well water had an inorganic constituent (arsenic) that exceeded the MCL. Persistent pesticides and PCBs were found in the bottom sediment of two pits. The concentration distributions of pesticides and other organics at most of the study sites, as well as the general pattern in iron, manganese, and ammonium ion concentrations in downgradient well waters relative to upgradient well and pit waters, indicate that ground-water quality at the sites is impacted by contaminants in the pit surface waters.