VOLATILE ORGANIC COMPOUNDS IN OHIO'S GROUND WATER

Volatile Organic Compounds (VOCs) have been regularly monitored in treated water from Ohio's Public Water Systems (PWS) since 1991. Review of this data set includes analysis of some 50,000 VOC samples from approximately 1,900 PWSs. Untreated ground water in Ohio has been monitored since the mid 1980s through the Ambient Ground Water Monitoring Program (Ambient) and currently comprises approximately 1,300 VOC analyses from 228 sites. A reporting level of 0.5 ug/L has been in consistent use since the early 1990s across both programs. The VOC data sets have been screened to ensure that only confirmed detections are used in this analysis. Less than 8% of the PWSs and approximately 12% of the Ambient stations have confirmed VOC detections in ground water.

The majority of all PWS and Ambient wells are located within sensitive aquifers, such as sand and gravel or bedrock with thin overlying glacial drift. These wells are 2.5 to 5 times more likely to be impacted by VOCs than those located in more protected aquifers. VOCs are 1.5 to 2 times more likely to impact wells located within areas that contain higher percentages of urban land use (such as commercial, industrial, transportation, and residential areas) within drinking water source protection areas. Solvent and petroleum compounds were the most frequently detected VOCs in the PWS data set. Chloroform was the most frequently detected compound in the Ambient data set (~20% of the wells), followed by solvents and petroleum compounds. The source for chloroform in untreated water is most probably from recharge of treated water or well disinfection, but chloroform can be generated, at low concentrations, naturally in soils. Almost 90% of the sites with chloroform are also located within a sensitive aquifer setting.

Nitrate concentration is not a good predictor of VOC impacts. Only 15% of the PWSs with VOC detections also exhibit elevated nitrate. This poor correlation is most likely related to the geochemically reduced nature of the ground water associated with VOC contamination.