Introduction Contamination of surface and ground referred to as organonitrogen herbicides, provide water-utility managers, water- water from nonpoint sources is a national were the four most commonly applied resource planners and managers, and issue. Examples of nonpoint-source herbicides (1991) in the Central Nebraska State regulators an improved contaminants from agricultural activities Basins (CNB), the area shown on the understanding of the distributions of are pesticides, which include fungicides, map. These herbicides are used for corn, concentrations of pesticides in streams herbicides, and insecticides; sediment; sorghum, and soybean production. and their relation to respective drinking- nutrients (nitrogen and phosphorus); and Atrazine was the most extensively water regulations or criteria, and (2) to fecal bacteria. Of these contaminants, applied pesticide (1991) in central describe concentrations of pesticides in pesticides receive Nebraska. Insecticides streams draining a selected small the most attention Atrazine was the most are used to protect the agricultural basin and a large agricultural because of the extensively applied pesticide crop seeds in storage area. This Fact Sheet is based on pesticide potential toxicity to (1991) in central Nebraska. prior to planting and data collected from May 1992 through aquatic life and to also to protect the March 1994 at the Platte River at humans. Most farmers use pesticides to plants from destruction once the seeds Louisville and Maple Creek near increase crop yields and values. have germinated. Like herbicides, Nickerson sites (see map). Samples were Herbicides prevent or inhibit the growth insecticides are also used in urban areas collected monthly, with additional of weeds that compete for nutrients and to protect lawns, trees, and ornamentals. samples collected over a wide range of moisture needed by the crops. hydrologic conditions. Herbicides are applied before, during, or Many of the 46 pesticides shown in the following planting. In addition to table have either a Maximum Study Area agricultural use, herbicides are used in Contaminant Level (MCL) or Health urban areas, often in larger rates of Advisory Level (HAL) established by the The CNB lies entirely within Nebraska application, for weed control, such as U.S. Environmental Protection Agency and includes the Platte River drainage along rights-of-way. Alachlor, atrazine, (USEPA) for public water supplies. The between the confluence of the North and cyanazine, and metolachlor, which are purposes of this Fact Sheet are (1) to South Platte Rivers near North Platte in western Nebraska to its confluence with the Missouri River at the eastern boundary of Nebraska (see map). The two major tributaries to the Platte River are the Loup and Elkhorn Rivers. The Platte River at Louisville sampling site represents the outflow of the CNB, which encompasses approximately 30,000 square miles (mi2) and is one of 60 study areas being assessed as part of the U.S. i Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program. The sampling site at Louisville on the Platte River is downstream from CORN,' AS AN ESTIMATED PEFICP.NT&Q the confluence of the Platte and Elkhorn Rivers (see map), and the quality of water at this site is *§ than 45 percent ng data considered representative of the water that the cities of Lincoln and Omaha The Central Nebraska Basins study area is predominately agricultural; most corn is produced in the withdraw from the adjacent eastern part and in the Platte Valley. alluvial aquifer for public supplies. daily streamflow of Maple Creek near Mean daily streamflow of the Platte Nickerson is 72.1 ft3/s. River is about 2,500 cubic feet per second (ft3/s) at the western (upstream) Land use in the study area is boundary of the study area near North predominately agricultural. Platte and 6,735 Rangeland and ft3/s at the eastern Rangeland and pastureland pastureland account boundary at account for about 54 percent of for about 54 percent Louisville. Maple of the land use, and Creek drains 388 the land use, and cropland cropland accounts mi2 and is a accounts for about 37 percent. for about 37 percent. tributary to the Rangeland Elkhorn River. The sampling site at characterizes most of the northern and Nickerson on Maple Creek is considered western parts of the area, whereas representative of surface-water quality in cropland dominates the southern and the eastern part of the study area. Mean eastern parts. Major crops are corn, Forty-six pesticides in water were analyzed by solid-phase extraction followed by gas chromatography and mass spectrometry Name Minimum reporting Maximum Contaminant Level or level, in micrograms Health Advisory Level, in per liter micrograms per liter Alachlor 0.005 22.0 Atrazine .002 23.0 Azinphos, methyl- .005 Benfluralin .005 Butylate .02 350 Carbaryl .01 700 Carbofuran .005 240 soybeans, sorghum, and wheat. Most of Chlorpyrifos .002 20 the corn is produced in the eastern part Cyanazine .01 1.0 of the study area and along the Platte DCPA .002 4000 Valley (see map) and is commonly DDE, p,p- .005 irrigated. Urban areas occupy a small Diazinon 1 .002 0.6 percentage of the land area (about 1 Dieldrin .005 Diethylanaline .01 percent), with Lincoln being the largest Dimethoate .005 city. Land use within the Maple Creek Disulfoton .002 0.3 drainage basin is composed of about 45 EPTC .002 percent corn, 20 percent soybeans, 2 Ethalfluralin .005 percent pastureland, and less than 1 Ethoprop .005 percent sorghum (Douglas Garrison, U.S. Fonofos .002 10 2 1.0 Soil Conservation Service, oral commun., HCH, alpha- .007 HCH, gamma- .011 20.2 1994). Linuron .039 Malathion .014 200 Lincoln, Omaha (outside the study Metolachlor .005 100 area), and smaller cities along the Platte Metribuzin .005 200 River withdraw water for public supplies Molinate .007 from the alluvium. The alluvium Napropamide .010 Parathion, ethyl- .022 adjacent to the Platte River has a direct Parathion, methyl .035 hydraulic connection to the river and Pebulate .009 thus is affected appreciably by the Pendimethalin .018 quantity and quality of water in the river. Permethrin, cis- .016 Phorate .011 Results Pronamide .009 50 Prometon .005 100 Propachlor .002 90 Distributions of concentrations are Propanil .016 shown (see graphs) for pesticides that Propargite .006 had 10 or more detections at the Maple Simazine .005 ^4.0 Tebuthiuron .015 500 Terbacil .030 90 Differences in the distributions of Terbufos .012 0.9 Thiobencarb .008 concentrations of pesticides at the Trial late .008 Maple Creek and Platte River sites Trifluralin .006 5.0 partly reflect differences in land use and land-management practices. 1 The use of trade names in this paper is for identification purposes only. 2 Value is Maximum Contaminant Level; other values are Health Advisory Levels. MAPLE CREEK near NICKERSON, NEBR. 11OOO Implications The distributions of concentrations of pesticides shown in the graph for the cK 100 Of 46 pesticides analyzed, it platte River at appears that., . alachlor,i , i Louisvillewhkh pestiddes site indicate could atrazine, and cyanazine pose affect the manage- 10 potential problems to public ment of Public . *. (Lincoln and Omaha) water supplies.r r waterv . supplies,. o withdrawn from the alluvium adjacent to the river because of possible exceedances EXPLANATION of a regulation or criterion. During ^ periods of considerable runoff, especially 0.1 ,c in May after the herbicides have been N '-jjj applied, herbicide concentrations in the to JJ5 Platte River can be quite large. For ^JG example, during a period of storm runoff 0.01 z 5 from May 16-30,1992, the maximum < c measured concentrations of alachlor, 95th percentile atrazine, cyanazine, and metolachlor | < CD O.O01 75th percentile were 10,30, 30, and 8.0 micrograms per \ liter (ug/L), respectively, in water from 50th percentile PLATTE RIVER at LOUISVILLE, NEBR. the Platte River at Louisville. 25th percentile 100O When the river stage is high, water 5s o" c 0? T 5th percentile can move from the river into the adjacent N CD N. Minimum alluvium, as shown in the schematic. tO TV CT> j-« o^ reporting level Water soluble compounds, such as S o^-^ o o - 100 Lu LU /=;cc ^° Maximum alachlor, atrazine, cyanazine, and Z Z 3 - Contaminant Level N N metolachlor, move with the water. When Health . ir |Z O CD n Advisory Level supply wells are pumped, the water and t I CC o - 10 compounds in solution move from the [Jj 1) -"METOLA 2 ^ river's alluvium to the treatment plant; 5 *? ! s CD Distributions of the water in the alluvium is replenished 1 ' i ^ K ^^ ^ O oo concentrations of partly from the river by induced - O ^ ^ in o "^ m, - pesticides with 10 or infiltration. In simplest terms, much of UJ ^ ^ ? 5T cc ~. :. ___ Z ?^ "*"*" CD n CD . more detections, and the ground water that is pumped by the <y m" &-, yo - ° s associated Maximum municipalities is filtered river water. The 5 5 ^ ^ - I s 5< ^-~i Contaminant Levels concentrations of herbicides in the 5) o y £ n 9k ^ 0.1 i? m ct 5 o o or Heath Advisory ground water in the adjacent alluvium ^ CC LL ' Levels, are plotted for may differ from the concentrations R i f 8 N CL O - rh z the Maple Creek near measured in the Platte River, depending D O _ \ LL ~ 0.01 Nickerson and the on streamflow rates, distance traveled in ?9a!rh r-,s r Platte River at the alluvium, amount of organic and clay LJ B :S; Louisville sites. materials in the alluvium, and hydraulic characteristics of the alluvium. 0.001 Of 46 pesticides analyzed, it appears that alachlor, atrazine, and cyanazine Creek and Platte River sites. Louisville site. Cyanazine usage is pose potential problems to public water Differences in the distributions of apparently greater, relative to atrazine supplies.