NITRATE POLLUTION OF GROUND WATER IN GILBERTVILLE, IOWA

The transmission of nutrients and contaminants into the aquifer surrounding Gilbertville, Iowa, were monitored over a six-month period. The Gilbertville water supply is obtained from the Silurian-Devonian aquifer, which has been determined to be highly susceptible to contamination because of the characteristics of the aquifer and overlying materials that allow contaminants to move through the aquifer fairly quickly. Monthly water samples were collected from April through September of 2004 from 26 private wells and 5–10 surface water sites within the source water protection area of the town's three wells. A source water protection area consisting of a fixed radius of one-mile was delineated around each well as recommended by the United States Environmental Protection Agency when the aquifer consists of karst conditions and/or highly fractured bedrock. Each sample was tested for dissolved oxygen, temperature, conductivity, total dissolved solids, pH, nitrate, sulfate, chloride, sodium, potassium, calcium, and magnesium.

Sixty-four percent of the wells sampled had their lowest nitrate levels in April, 16% of which were below detection. Only 12% of the wells exceeded 45 ppm in April. Nitrate levels increased in May and June with 23% of the wells exceeding 45 ppm. The highest concentration of nitrates in a private well, 85.944 ppm, also occurred during June. A slight decrease of nitrate levels occurred in July. The highest percentage of nitrate levels occurred in August with 28% of the wells exceeding 45 ppm. Throughout the six-month period, 16% to 20% of the wells sampled had no nitrates detected. Nitrates exceeded 45 ppm in the Cedar River during the months of June and July at an average of 56.41 and 45.45 ppm, respectively. The lowest nitrate level in the Cedar River, an average of 17.13 ppm, occurred during September of 2004.

Total dissolved solids in the wells ranged from 289 ppm to 663 ppm while pH ranged between 6.30 and 8.00 during the study. All other parameters fell within the normal range for natural waters. This study indicates that the ground water in the Gilbertville area is significantly impacted by agricultural practices.