Presence and distribution of nitrate and selected pesticides in surficial-sand aquifers and selected lakes, 1993-94, East Otter Tail County, Minnesota
This report presents selected data collected during the first year (December 1993 to September 1994) of a three year water-quality study of surficial-sand aquifers and selected lakes in east Otter Tail County, Minnesota. The objectives of the study are (1) to determine the presence and distribution of nitrate-nitrogen and selected pesticides in ground water from the surficial-sand aquifers; and (2) to characterize the water quality of selected lakes and the Otter Tail River. Ground water was sampled from 73 wells. The concentration of nitrate nitrogen in ground water was above 10 mg/L (milligrams per liter) in 30 of the sampled wells (38 percent). The concentration of triazine herbicide compounds, as determined by immunoassay, was above the detection limit 0.10 ug/l (micrograms per liter) in water from 17 of the sampled wells (24 percent). The nitrate- nitrogen concentration in water from 14 wells, compared to data collected during a previous study in 1979-81, increased in water from 4 wells and decreased in water from 4 wells. Lake water was sampled from 11 sites on Little Pine, Big Pine, Rush, and Otter Tail Lakes. Nitrate-nitrogen concentrations were all below the detection limit (0.05 mg/L). The concentration of triazine herbicide compounds, as determined by immunoassay, was at or below the detection limit (0.10 ug/L) at all 11 sites. Dissolved oxygen concentrations at the sites ranged from 7.3 to 10.1 mg/L at the water surface, and from 5.3 to 9.7 mg/L at depth. Secchi disk transparency readings ranged from 4.0 to 7.4 feet. Total phosphorus concentrations were generally near or below the detection limit (0.01 mg/L) except at one site where the water had a total phosphorus concentration of 0.06 mg/L.