Possible Sources of Arsenic in Ground Water from South Louisiana

Ground water with arsenic levels exceeding the government mandated limit was found in Louisiana domestic water wells sampled in 2004. Because As is a known carcinogen, there was public concern and demand for action. State and private investigations suggested possible sources for the As, but none was conclusively proven. This paper identifies some potential sources of As and suggests others as less likely.

The area of concern is around the towns of Cow Island and Forked Island in Vermilion Parish, Louisiana, where ground water is commonly used. As part of the Gulf Coastal Plain, it has minimal elevation and relief. Abundant precipitation and relatively young, unconsolidated rocks produce plentiful ground water and a water table that is near the surface. Determining the potential source and possible movement of As is important for assuring an adequate supply of good quality water.

Possible sources of contamination include natural and anthropogenic releases of As. Ideal geologic and geochemical conditions could produce a natural source of As. Two potential anthropogenic sources, cattle baths and old cemeteries, are both found near the contaminated wells. These and other sources are evaluated in light of the regional and local hydrogeologic setting. Examination of surface and subsurface data coupled with public data can help provide clues related to the potential source, movement, and possible remediation of the affected ground water.