Anthropogenic Organic Compounds in Ground Water and Finished Water of Community Water Systems in the Greater Twin Cities Metropolitan Area, Minnesota and Wisconsin, 2004-05

摘要

As part of the U.S. Geological Surveys National Water-Quality Assessment (NAWQA) Program, two Source Water-Quality Assessments (SWQAs) were conducted during 200405 in unconfined parts of the glacial aquifer system and in unconfined parts of the Prairie du Chien-Jordan aquifer in the Greater Twin Cities metropolitan area of Minnesota and Wisconsin. SWQAs are two-phased sampling activities in the NAWQA Program. The first phase evaluated the occurrence of 265 (258 are included in this report) anthropogenic organic compounds (AOCs) through monitoring source water in 30 of the largest-producing community water system wells completed in the aquifers underlying the Greater Twin Cities metropolitan area. The AOCs included volatile organic compounds (VOCs), pesticides, and other AOCs. During the second phase of the study, 15 of the original community water system wells, those with the greatest number of AOC detections, were resampled along with associated finished water. Results from the first phase of sampling indicated that 40 AOCs were detected, and 83 percent of the samples had at least one detected AOC. Concentrations of AOCs detected in the source water generally were low (defined in this report as concentrations less than 1.0 microgram per liter). Human-health benchmarks for these compounds (Maximum Contaminant Levels for regulated compounds or Health-Based Screening Levels for unregulated compounds, when they existed) typically were not exceeded. Fifteen VOCs were detected in the source-water samples. However, concentrations were low. Seventeen pesticide compounds were detected generally at concentrations less than concentrations for VOCs. Most of the pesticide compounds detected were triazine- or alachlor-parent compounds or their breakdown products. Eight other AOCs were detected in the source-water samples but generally at low concentrations.