DELAWARE--A STATEWIDE DRINKING WATER ASSESSMENT

DELAWARE--A STATEWIDE DRINKING WATER ASSESSMENT

In 2001-02, following the detection of BCEE in a groundwater water supply in the Llangollen area of New Castle County, Delaware, a state-wide water quality assessment was conducted in order to determine whether other public drinking water sources were similarly impacted by nearby hazardous sites (e.g., landfills, Superfund sites, USTs).

Agencies involved included the Dept. of Natural Resources and Environmental Control, which has regulatory authority for the water resource, and the Dept. of Health and Social Services, whose responsibilities include drinking water quality. A review of well databases, field surveys and discussions with local governments and water providers, identified numerous public water supplies located in proximity to known hazardous sites. Thirty-nine groundwater supply wells were selected for inclusion in the study, ones that were deemed the most susceptible and vulnerable and/or had a history of contamination. Four New Castle County surface water intakes were also included due to the inherent susceptibility of surface water bodies to contamination.

Both pre- and post-treatment water samples were collected from each site, and were submitted for laboratory analysis of 167 organic and inorganic compounds, making it the most comprehensive water quality study ever conducted in Delaware. Of the 167, only 72 chemicals are regulated under the Safe Drinking Water Act, and have maximum contaminant levels (MCLs). The remaining 95 analytes are not presently regulated, and thus are not included in routine water quality analyses.

Results from the untreated samples identified many detections of MTBE, plus chlorinated aliphatics, trihalomethanes, BTEX compounds, pesticides, and unregulated compounds with a few exceeding their respective MCLs. In contrast, post-treatment results revealed that all regulated chemicals were in compliance with their MCLs excepting one nitrate result. Additionally, none were present in concentrations exceeding any risk-based screening values except for a few disinfection by-products.

The study confirmed the importance of diligent water quality monitoring and the effectiveness of water treatment technology, and stressed the importance of zoning when citing water supply systems.