Water quality in the White River Basin is impacted by urban and agricultural activities, according to the results of a five-year investigation by the U.S. Geological Survey (USGS), Department of the Interior.
A variety of pesticides used for agricultural or urban uses were commonly found in streams throughout the White River Basin. In contrast, only a few pesticides were found in ground water, and these were at much lower concentrations. Pesticide concentrations in streams in the White River Basin were among the highest found at USGS monitoring stations nationwide.
Twenty-five different pesticides or pesticide degradation products were found in at least 5 percent of samples near the mouth of the White River. The widely used agricultural herbicides atrazine and metolachlor were always found. "In a few samples, concentrations of the herbicides atrazine, alachlor, or cyanazine exceeded Federal drinking-water standards or advisories; however, annual average concentrations of each of these compounds in the White River were below their respective standard or guideline," said USGS hydrologist Charles G. Crawford, project leader of the White River Basin study.
Fourteen different pesticides were found in a network of 94 shallow monitoring wells; six were found more than once. However, Crawford said, "No pesticide concentration found in ground water came close to exceeding a Federal drinking-water standard or advisory." In cropland areas with a surficial sand and gravel aquifer that is particularly vulnerable to contamination but is also an important source of drinking water for residents of the basin, atrazine compounds were found in two-thirds of monitoring wells but only at trace levels. Shallow wells are most susceptible to contamination and provide insight into the effects of pesticides and fertilizers on ground-water quality. Pesticide concentrations typically decrease with depth in an aquifer. The presence of only low pesticide concentrations in shallow wells indicates they are probably not present in the deeper ground water used most commonly for domestic or public supply.
Most, but not all, of the pesticides found were associated with agricultural use. Pesticide concentrations in streams differ according to land use. Crawford said that lawn insecticides (such as diazinon) are commonly found in streams in urban areas, whereas corn herbicides (such as atrazine) are more commonly found in streams in agricultural areas. Pesticide concentrations in streams are highest in areas with permeable, well-drained soils, all other factors being equal. Agricultural tile drains play a major role in transporting pesticides to streams in areas with poorly drained soils. Nitrate concentrations in ground water are low (commonly not found) in some aquifer settings and high (sometimes exceeding the Federal drinking-water standard) in others. Nitrate concentrations in stream water typically are between these extremes. Median concentrations of nitrate at monitoring sites in streams generally ranged from 2 to 6 milligrams per liter-higher than those at most other USGS monitoring sites in the United States.
Soil drainage is a major factor controlling nitrate concentrations in streams. "Concentrations tend to increase as the proportion of naturally or artificially drained soils in the basin increases," said Crawford. "Manure from farm animals also increases nitrate concentrations in some streams." Nitrate concentrations in stream water rarely exceeded the Federal drinking-water standard of 10 milligrams per liter.
Surficial sand and gravel aquifers underlying cropland had high nitrate concentrations. Samples from 17 percent of shallow monitoring wells in this setting exceeded the Federal drinking-water standard. However, deeper wells (25 to 50 feet below the water table) in these unconfined aquifers typically had little or no detectable nitrate. In many parts of the basin, nitrate concentrations in ground water were low. For example, sand and gravel aquifers protected by overlying clay typically had low concentrations of nitrate. Such aquifers are present in more than half the basin and are a common source of water for rural domestic users.
Runoff from urban areas degrades the quality of streams and ground water. "Concentrations of trace metals and organic compounds in streambed sediments tended to be above background concentrations in urban areas, particularly Indianapolis," said Crawford. "Concentrations are generally not a human-health concern; however, fish-consumption advisories for PCB's and mercury are in effect for some locations in the basin." Several chemicals whose use has long been banned (chlordane, dieldrin, and PCB's) persist in streambed sediments and are concentrated in organisms such as freshwater clams.
Fish communities have significantly improved since the early 1970's, although degraded communities of fish still are found in streams with poor water quality. Some streams with good fish habitat presently have degraded communities of fish, a disparity indicating nonhabitat stresses (such as poor water quality). In areas where the fish communities are poorer than expected on the basis of fish habitat present, nutrient and pesticide concentrations are high.
The White River Basin study is one of more than 50 studies across the nation being done by the U.S. Geological Survey as part of its National Water-Quality Assessment (NAWQA) Program. Through the NAWQA Program, the USGS provides policymakers and citizens with information about current conditions and trends in water quality and an assessment of the factors that affect water quality across the United States.
The report, "Water Quality in the White River Basin, Indiana, 1992-1996," by Joseph M. Fenelon is published as U.S. Geological Survey Circular 1150. Copies of the report are available free of charge from the USGS Indiana District Office, 5957 Lakeside Boulevard, Indianapolis, IN 46278, (317) 290-3333 or the USGS Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, (303) 202-4700 [fax requests to (303) 202-4693; an order form is available at URL: http://www-nmd.usgs.gov/esic/to_order.html].