Geology topics

Michael R. Burkart

Publications and source records attributed to Michael R. Burkart.

3 recordsLinked to original sources

USGS1999

Tributary stream infiltration as a source of herbicides in an alluvial aquifer

Where Walnut Creek flows across the South Skunk River alluvial aquifer, it provides a potential source of herbicides and herbicide metabolites. This straightened reach of the creek loses water and dissolved contaminants to the alluvial aquifer through a layer of fine-grained flood plain deposits. Estimates of potential flux of chemicals were based on measurements taken during baseflow in April 1994 before herbicides were applied to the watershed and in June 1994 after chemical application and when stream discharge included runoff and tile-drainage water. Hydraulic head measurements between the creek and flood plain deposits and between the creek and aquifer confirmed the potential for downward groundwater flow during both sampling periods. Hydraulic conductivity estimates from slug tests were used to calculate an average linear groundwater velocity of 0.5 m d −1 in the fine-grained flood plain deposits. At this velocity, contaminants could be advectively transported to the aquifer within 6 d. The potential for atrazine (2-chloro-4-ethylamino-6-isopropylamino- s -triazine) flux to the aquifer from the creek was estimated to be between 60 and 3000 µg d −1 m −2 . This rate is one to three orders of magnitude greater than the estimated flux via leaching beneath a typical field. If the process of vertical stream leakage occurs in many hydrologic settings, it may constitute a substantial source of herbicides to shallow alluvial aquifers in many areas of the Midwest.

Iowa↗

USGS1994

Herbicides and nitrate in near-surface aquifers in the midcontinental United States, 1991

The occurrence and distribution of selected herbicides, atrazine metabolites, and nitrate were determined for near-surface aquifers (within 50 feet of land surface) in the corn- and soybean-producing region of the midcontinental United States. The study region included all or parts of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin. Water samples were collected during the spring and summer of 1991 from 303 wells completed in near-surface unconsolidated and near-surface bedrock aquifers. At least one herbicide or atrazine metabolite was detected in 24 percent of 579 water samples analyzed for herbicides, based on a reporting limit of 0.05 microgram per liter. However, no herbicide concentration exceeded the U.S. Environmental Protection Agency's maximum contaminant levels or health advisory levels for drinking water. The most frequently detected herbicide compound was desethylatrazine, an atrazine metabolite (18.1 percent), followed by atrazine (17.4 percent); deisopropylatrazine, an atrazine metabolite (5.7 percent); prometon (5.0 percent); metolachlor (2.7 percent); alachlor (1.7 percent); simazine (1.0 percent); metribuzin (1.0 percent); and cyanazine (0.7 percent). The herbicides ametryn, prometryn, propazine, and terbutryn were not detected during this study. Nitrate concentrations equal to or greater than 3.0 milligrams per liter (excess nitrate) were detected in 29 percent of the 599 nitrate analyses, and ammonium concentrations equal to or greater than 0.01 milligram per liter were detected in 78 percent of the 584 ammonium analyses. Nitrate concentrations equal to or greater than the U.S. Environmental Protection Agency's maximum contaminant level for drinking water of 10 milligrams per liter were found in 6 percent of the samples. The frequency of herbicide detection was, in part, affected by the analytical method's reporting limit. Results from this study show that the frequency of atrazine detection increases as the reporting limit decreases. Herbicide metabolite concentrations are critical to understanding the detection of herbicide residues. The frequency of detection of atrazine residue (atrazine + desethylatrazine + deisopropylatrazine) was 22.1 percent, which was more than the frequency of detection of atrazine alone (17.4 percent). Prometon was detected more frequently than every other herbicide except atrazine. The prometon appears to be derived from areas of nonagricultural land use, such as golf courses and residential areas. Herbicides and excess nitrate were both rarely detected in the eastern part of the study region, even though this is an area of intense herbicide and nitrogen-fertilizer use. Hydrogeologic factors, land use, agricultural practices, local features, and water chemistry were analyzed for possible relation to herbicide and excess-nitrate detections. Herbicides and excess nitrate were detected more frequently in near-surface unconsolidated aquifers than in nearsurface bedrock aquifers. The depth to the top of the aquifer was inversely related to the frequency of detection of herbicides and excess nitrate. The proximity of streams to sampled wells also affected the frequency of herbicide detection. Significant seasonal differences were determined for the frequency of herbicide detection, but not for the frequency of excess nitrate.

Illinois, Indiana, Iowa, Kansas, Michigan, Minneso↗

USGS1993

Hydrologic and land-use factors associated with herbicides and nitrate in near-surface aquifers

Selected herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) metabolites, and NO − 3 were examined in near-surface unconsolidated and bedrock aquifers in the midcontinental USA to study the hydrogeologic, spatial, and seasonal distribution of these contaminants. Groundwater samples were collected from 303 wells during the spring and late summer of 1991. At least one herbicide or atrazine metabolite was detected in 24% of the samples collected for herbicide analysis (reporting limit 0.05 µ g/L). No herbicide concentration exceeded the USEPA's maximum contaminant level (MCL) or health advisory level. The most frequently detected compound was the at razine metabolite deethylatrazine [2-amino-4-chloro-6-(isopropylamino)-s-triazine] followed by atrazine, deisopropylatrazine [2-amino-4-chloro-6-(ethylamino)-s-triazine], prometon (2,4-bis(isopropylamino)-6-methyoxy-s-triazine), metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1methylethyl)acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], metribuzin [4-amino-6-( tert -butyl)-3-methylthio- as -triazine-5(4H)-one], simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropionitrile]. Nitrite plus nitrate, as nitrogen (N), exceeding 3.0 mg/L (excess NO − 3 ), was found in 29% of the samples, and 6% had − 3 exceeding the MCL of 10 mg/L. Ammonium as N was detected in excess of 0.01 mg/L in 78% of the samples. A nonlinear increase in the frequency of atrazine detection occurred with decreases in reporting limit. The frequency of atrazine residue detection (atrazine + deethylatrazine + deisopropylatrazine) was 25% greater than for atrazine alone. Herbicide detections and excess NO − 3 were notably lacking in the eastern part of the study region where it was estimated that herbicide and fertilizer use were among the largest in the region. Prometon, the second most frequently detected herbicide, was associated with non-agricultural land use. Herbicide and excess NO − 3 were more frequent in unconsolidated aquifers than in bedrock aquifers. Aquifer depth, as direct measurement of proximity to recharge sources, was inversely related to frequency of herbicide detection and excess NO − 3 .

Journal of Environmental Quality↗