Water Quality in the White River Basin, Indiana, 1992-96

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Summary of Findings

A variety of pesticides were commonly found in streams throughout the White River Basin. In contrast, only a few pesticides were detected in ground water, and these were at much lower concentrations (p. 6).

In streams:

• Pesticide concentrations at urban and agricultural sites were among the highest in the Nation (p. 20).
• Twenty-five different pesticides or pesticide degradation products were detected in at least 5 percent of samples near the mouth of the White River. Atrazine and metolachlor were always detected, whereas cyanazine and alachlor were frequently detected (p. 6). In a few samples, concentrations of atrazine, alachlor, or cyanazine exceeded Federal drinking-water standards or advisories (p. 26); however, annual average concentrations of each of these compounds in the White River were below their respective standard or guideline.

In shallow ground water:

• Fourteen different pesticides were detected in a network of 94 monitoring wells; six were detected more than once (p. 6). No pesticide concentration came close to exceeding a Federal drinking-water standard or advisory.
• In cropland areas with a surficial sand and gravel aquifer that is vulnerable to contamination but is also an important source of drinking water for residents of the basin, atrazine compounds were commonly detected (found in two-thirds of monitoring wells) but only at trace levels.

The occurrence of pesticides in streams is controlled by a variety of factors (p. 8-11).

Regional patterns in pesticide use (p. 8):

• Concentrations of individual pesticides in streams are greatest where pesticide use is greatest.

Temporal patterns in pesticide use (p. 9):

• New pesticides introduced to the market can quickly show up in streams. Within 2 years of its registration in 1994, maximum concentrations of the corn herbicide acetochlor in the White River were about 2 µg/L, similar to those of other commonly used herbicides. In contrast, concentrations of alachlor in the White River are declining as alachlor use in the basin declines.

Land use (p. 10):

• Pesticide concentrations in streams differ according to land use. Lawn insecticides (such as diazinon) are more commonly detected in urban watersheds, whereas corn herbicides (such as atrazine) are more commonly detected in agricultural watersheds.

Soil drainage (p. 10-11):

Nitrate concentrations in ground water are low (commonly not detected) 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 (p. 12-15).

In streams:

• Median concentrations of nitrate at monitoring sites generally ranged from 2 to 6 mg/L-higher than those at most other NAWQA monitoring sites in the United States (p. 20). Sample concentrations rarely exceeded the Federal drinking-water standard.

In ground water:

• 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 of 10 mg/L. 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.

Urban areas degrade the quality of streams and ground water (p. 16-17).

In streams:

• Concentrations of trace metals and organic compounds in streambed sediments tended to be above background concentrations in urban areas, particularly Indianapolis. Measured concentrations are generally not a human-health concern; however, fish-consumption advisories for PCBs and mercury are in effect for some areas of the basin. Several chemicals whose use has long been banned (chlordane, dieldrin, and PCBs) persist in streambed sediments and are concentrated in organisms such as freshwater clams.
• Stormwater runoff and sewer overflows are a continuing problem and have contributed to fish kills in the basin by depleting oxygen in the stream water. One such incident in the White River at Indianapolis in 1994 killed 510,000 fish.

In ground water:

• Volatile organic compounds were detected in more than half the shallow monitoring wells in urban areas, as compared to 6 percent of shallow wells in cropland areas. Chloroform was the most common volatile organic compound found in urban ground water. No volatile organic compound was measured at a concentration in ground water that exceeded a Federal drinking-water standard or guideline.

Fish communities have significantly improved since the early 1970's. However, poor communities of fish are still found in streams with poor water quality (p. 18-19).

U.S. Geological Survey Circular 1150

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Last modified: April 6, 1998 2:23 pm