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L.M. Roberts

Publications and source records attributed to L.M. Roberts.

5 recordsLinked to original sources
USGS2007

The relative merits of monitoring and domestic wells for ground water quality investigations

The results of two studies of the effect of agricultural land use on shallow ground water quality indicate that monitoring wells may be a better choice than domestic wells for studies of pesticide occurrence or transport, or for use as early-warning indicators of potential drinking water contamination. Because domestic wells represent the used resource, and because domestic well water may be affected by historical rather than current pesticide and land- use practices, domestic wells would be the best choice for an investigation of drinking water quality. The key difference between the domestic and monitoring wells appears to be that the monitoring wells in this study were installed exclusively to sample the shallowest possible ground water. For these studies, 48 shallow domestic wells and 41 monitoring wells were located randomly within two land-use settings (row crops and orchards) in an irrigated agricultural region of eastern Washington and sampled for 145 pesticides (including nine pesticide degradates) and common water quality indicators. Constructing and sampling monitoring wells required approximately four times the resources (including manpower and materials) as locating and sampling domestic wells. Sample collection and quality assurance procedures and analytical techniques were identical except that a portable submersible pump was required for monitoring wells. In both land-use settings, no significant difference in nitrate concentration was found between well types; however, the average number of pesticides detected per well was significantly higher (p<0.05) in the monitoring wells. A greater variety of pesticides was detected in monitoring wells; many were detected only in monitoring wells. More than 60% of detections of pesticides that were found only in domestic wells were of compounds that are no longer in use. These differences in ground water quality found in this study relate to the depth of the well and are apparently related to the age of ground water in the two types of wells and the greater effects of sorption, degradation, dilution, and dispersion that accompany longer groundwater residence times. The decision to invest resources in monitoring wells should be made in light of the study objective and should consider these differences in results from the two types of wells as well as the relative costs.

Ground Water Monitoring and Remediation↗
USGS1995

Agricultural pesticide applications and observed concentrations in surface waters from four drainage basins in the Central Columbia Plateau, Washington and Idaho, 1993-94

As part of the U.S. Geological Survey's National Water-Quality Assessment Program, the use and occurrence of agricultural pesticides were investigated in four drainage basins--two dominated by irrigated agriculture and two by dryland agriculture--in the Central Columbia Plateau of eastern Washington. For this study, 85 pesticides or pesticide metabolites were selected for analysis from a list of nearly 400 compounds commonly used in the United States. Pesticide-use data included estimates of the total quantity of herbicides, insecticides, and fungicides applied to croplands in each of the four drainage basins and reported times of application for selected pesticides. Pesticide-occurrence data included concentrations of pesticides in samples collected at one surface-water site at or near the outflow of each of the four drainage basins, where surface waters were sampled one to five times a month from March 1993 through May 1994. Of the 85 pesticides or pesticide metabolites targeted for analysis, a total of 45 different compounds were detected in samples from the four sites, ranging in concentration from at or near the limit of detection (as low as 0.001 microgram per liter) to a maximum of 8.1 micrograms per liter. None of the concentrations of pesticides exceeded the U.S. Environmental Protection Agency (USEPA) drinking water standards, but concentrations of five pesticides exceeded the USEPA freshwater-chronic criteria for the protection of aquatic life. Forty-one different pesticides or pesticide metabolites were detected in surface waters sampled at the two sites representing irrigated agriculture drainage basins. The herbicides atrazine, DCPA, and EPTC were detected most frequently at the two sampling sites. Not all pesticides that were applied were detected, however. For example, disulfoton, phorate, and methyl parathion accounted for 15 percent of the insecticides applied in the two irrigated drainage basins, yet none of these pesticides were detected in samples from the two irrigated-agricultural sites. Concentrations of pesticides found in surface waters at the two sites representing irrigated agriculture did not exceed drinking water standards, but some concentrations of the insecticides carbaryl, chlorpyrifos, diazinon, and azinphos-methyl exceeded the freshwater-chronic criteria for the protection of aquatic life. Twenty-three different pesticides or pesticide metabolites were detected in samples from the two sites representing dryland agricultural drainage basins. Herbicides were the type of pesticides most heavily applied in these drainage basins, and the herbicides atrazine, triallate, and simazine were detected most frequently in samples. Some herbicides, for example triallate in the Palouse River drainage basin, were both heavily applied and frequently detected. Others, like atrazine and simazine, were not typically applied to cropland, but were frequently detected in surface-water samples. Several insecticides (Lindane, ethoprop, carbaryl, and azinphos-methyl) were detected in samples from the two sites, although they were not reported as commonly applied to croplands in the dryland agricultural drainage basins. Concentrations of pesticides found in surface waters at the two sites did not exceed drinking water guidelines, but concentrations of the insecticides diazinon and azinphos-methyl and the herbicide triallate exceeded freshwater-chronic criteria for the protection of aquatic life.

Water-Resources Investigations Report↗