U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Herbicides and herbicide degradates in shallow ground water and the Cedar River near a municipal well field, Cedar Rapids, Iowa

By Robert A. Boyd

This report is available in pdf format: Boyd.pdf

Abstract

Water samples were collected near a Cedar Rapids, Iowa municipal well field from June 1998 to August 1998 and analyzed for selected triazine and acetanilide herbicides and degradates. The purpose of the study was to evaluate the occurrence of herbicides and herbicide degradates following springtime application of herbicides to upstream cropland. The well field is in an alluvial aquifer adjacent to the Cedar River. Parent herbicide concentrations generally were greatest in June and decreased in July and August. Atrazine was most frequently detected and occurred at the greatest concentrations; acetochlor, cyanazine, and metolachlor also were detected, but at lesser concentrations than atrazine. Triazine degradate concentrations were relatively small (<0.50 micrograms per liter) and generally decreased from June to August. Although the rate of ground-water movement is relatively fast (about 1 meter per day) in the alluvial aquifer near the Cedar River, deethylatrazine (DEA) to atrazine ratios in ground-water samples collected near the Cedar River indicate that atrazine and DEA probably are gradually transported into the alluvial aquifer from the Cedar River. Deisopropylatrazine (DIA) to DEA ratios in water samples indicate most DIA in the Cedar River and alluvial aquifer is produced by atrazine degradation, although some could be from cyanazine degradation. Acetanilide degradates were detected more frequently and at greater concentrations than their corresponding parent herbicides. Ethanesulfonic-acid (ESA) degradates comprised at least 80 percent of the total acetanilide-degradate concentrations in samples collected from the Cedar River and alluvial aquifer in June, July, and August; oxanilic-acid degradates comprised less than 20 percent of the total concentrations. ESA-degradate concentrations generally were smallest in June and greater in July and August. Acetanilide-degradate concentrations in ground water adjacent to the Cedar River indicate acetanilide degradates are transported into the alluvial aquifer in a manner similar to that indicated for atrazine and DEA.