NITRATE-NITROGEN AND PESTICIDES IN GROUNDWATER IN THE JACKSON PURCHASE AREA, KENTUCKY

Nitrate-Nitrogen (nitrate-N) and pesticides appear to be major contaminants of groundwater in the Jackson Purchase Area, Kentucky. Data from the Kentucky Groundwater Education and Testing Program conducted between 1989 and 1991 showed that an average of 5.5 percent of wells in the Purchase contained groundwater that exceeded the MCL of 10 mg/L nitrate?N, and 13.7 percent exceeded half of the MCL. Ninety-seven percent of 424 wells sampled and 93 percent of 201 wells sampled contained triazines and alachlor, respectively. Between 1998 and 2003, 180 domestic water wells were sampled by the Kentucky Geological Survey. Eight percent of the sampled wells exceeded the nitrate?N MCL, and 24 percent exceeded half of the MCL. Of the 180 wells sampled for pesticides, 33 percent contained triazines, 28 percent contained metalochlor, 8 percent contained alachlor, 7 percent contained carbofuran, 6 percent contained paraquat, and no wells contained 2,4-D. Nitrate?N contamination in the Purchase is generally attributed to four likely sources: (1) chemical fertilizers, (2) sewage effluent, (3) active animal feedlots, and (4) abandoned animal feedlots. The application of herbicides and insecticides to crop fields and localized chemical spills are the two major sources of pesticides to the groundwater system. Nitrate-N and pesticide contamination may be influenced by poorly constructed water wells. To better determine the source of these contaminants, land-use and well construction data were collected for each well sampled and caffeine and nitrogen isotope samples were collected from several wells. Bromide traces were also conducted on 35 water wells in the Purchase. Eight of the wells were 24-inch diameter wells (bored wells) and 27 of the wells were 4-inch diameter wells (drilled wells). After a 7-day sampling period, bromide was detected in 7 of the 35 wells (1 drilled well and 6 bored wells). Presence of bromide indicates poor water-well construction, which may allow contaminated surface water and/or shallow groundwater to enter the well. Results to date indicate that land-use practice, water well construction type and hydrostratigraphy all play a major role in groundwater quality in the Purchase.