USGS Washington Water Science Center
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WA417 - Study of Fumigant-Derived Compounds in Shallow Ground Water, Whatcom Co., WA - Completed FY1999
Background - The glacial outwash aquifers in the northern portions of Whatcom County and Canada typically have shallow depths to the water table and are very permeable. These factors coupled with the intensive agricultural activity in this region have made the aquifers vulnerable to contamination. The Puget Sound Basin NAWQA project is conducting a land-use study to assess the effects of raspberry production on ground water in some of these aquifers, and a flow-path study to estimate denitrification rates in one aquifer.
Previous studies of these aquifers show that nitrate concentrations in ground water often exceeded the maximum contaminant level (MCL) for drinking water. Ethylene dibromide (EDB) and 1,2-dichloropropane (1,2-D) were frequently detected in samples, and concentrations of both compounds exceeded MCLs in certain areas (Erickson and Norton, 1990; unpublished data collected by the Washington State Department of Health and the USGS). The presence of 1,2-D and EDB in ground water is related to the past usage of soil fumigants on crops. In two separate actions (1983 and 1984) EPA canceled all major agricultural uses of EDB. Soil fumigants currently used in northern Whatcom County include metam sodium (sodium N-methyldithiocarbamate), Telone II (1,3-dichloropropene with trace amounts of 1,2-D), and methyl bromide.
The Puget Sound Basin NAWQA land-use and flow-path wells were sampled during 1997. 1,2-D was found in water from 22 of 35 wells sampled, and although concentrations were generally low, concentrations in two samples were above the MCL. Concentrations of nitrate in water from about 34 percent of sampled wells exceeded the MCL. EDB and methyl bromide were not detected. The continued presence of 1,2-D in ground water prompted the Whatcom County Executive to send a letter to Cynthia Barton, USGS Washington Water Science Center Chief, requesting a study to help delineate the extent of ground-water quality problems in the area. In contrast to the NAWQA land-use study, this study would evaluate the effects of fumigant applications to all crops, not just raspberries. The sampling will be coordinated with sampling planned by state and local agencies. This proposal represents work that will help address the needs of Whatcom County, and at the same time, augment the ongoing NAWQA land-use and flow-path studies.
Objectives - The objectives of this study are to 1) provide additional information on the presence and concentrations of nitrate and soil-fumigant-related compounds in ground water in the Fishtrap and Bertrand Creek watersheds, and 2) attempt to correlate past usage of soil fumigants with the presence of the fumigants or their breakdown products in ground water. It is hoped that the study will lead to recommendations regarding the use of soil fumigants over sensitive aquifers such as those in northern Whatcom County.
Relevance and Benefits - The project was coordinated with the Puget Sound Basin NAWQA study of fumigants in ground water in an agricultural area in Whatcom County and British Columbia, Canada. Two elements of the project, collecting additional ground-water samples for analysis of fumigants and collecting fumigant application data, made a more comprehensive assessment of the effects of fumigants on ground-water quality possible.
Approach - Objective 1: A total of 18 ground-water samples collected from existing wells in the Fishtrap and Bertrand Creek watersheds will be analyzed for nitrate, fumigants, and fumigant breakdown products. Included are EDB, 1,2-D, methyl bromide, breakdown products of 1,2-D (chloropropene, 1,2,2-trichloropropane, 2-chloropropane, and 1-chloropropane), and breakdown products of metam sodium (methyl isothiocyanate and methyl sulfide). Field measurements will be made to determine water temperature, specific conductance, pH, and the concentration of dissolved oxygen. Two field blanks will be submitted for analysis.
Objective 2: The presence or absence of fumigants and their breakdown products in ground water sampled from the 18 wells and from about 30 NAWQA land-use and flow-path wells will be related to fumigant applications overlying and upgradient of sampled wells. Application data for the years 1991-1997 will be obtained from the Washington State Department of Agriculture.PN346 - Ground-Water Resources of Portions of the Lower Nooksack and Upper Sumas River Basins, Whatcom County, Washington - Completed FY1992
Problem - The Nooksack lowland and the upper Sumas valley region is a farming area developed on glacial sediments of the northern Puget Sound. Shallow ground water currently supplies much of the water needs of the area. Although the supply of shallow ground water is ample and its quality was generally considered to be good, an increasing number of water quality problems have been identified in the area. Some ground waters within the area have been found to be contaminated with pesticides associated with agricultural practices. Large concentrations of nitrate and iron are commonly found in ground water throughout the region, as well as areas of salt and corrosive waters. Wells with available historic data show a trend of increasing nitrate concentrations with time. Previous hydrologic investigations within this area have been limited in scope and/or areal extent.
Objectives - The objective of this study is to conduct an appraisal of the ground-water hydrology and water quality of the area which will provide local water managers sufficient information on which to make informed decisions. The focus of this study will be to describe the hydrologic framework and flow system, document the extent of current water-quality problems, and evaluate potential significant sources of these problems.
Approach - The hydrologic framework will be described utilizing available data from well files, geologic maps, reports, and approximately 600 drillers' logs. The ground-water flow system will be defined from water-level data from the wells and water-level contour maps, and from specific-capacity data from drillers' logs. Description of the general ground-water chemistry as well as the distributions of known inorganic contaminants will be based on historical data and water-quality sampling during this project. Evaluation of the probable sources of inorganic contaminants in the ground-water system will be based on the distribution of contaminants in the ground-water system within the study area and information regarding sources of occurrence.