Pesticides and Groundwater Quality Issues and Problems in Four States (1986) / Chapter Skim
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1 California
1 California
Pages 14-30
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From page 14... ...
The current understanding of the extent or seriousness of agricultural chemicals in groundwater is extremely limited and disjointed because of the incomplete data base currently available. Nearly everyone interviewed agreed that additional sampling and monitoring of water quality trends is needed to establish the extent of pesticide contamination of groundwater.
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From page 15... ...
Many of the sampling programs were conducted under time and budgetary constraints in response to a specific contamination incident and thus lacked adequate sampling protocol development. Past monitoring efforts have been severely limited in two ways.
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From page 16... ...
Multiresidue analytic techniques to better assess water quality in areas susceptible to contamination from agricultural chemicals need to be developed. But despite these significant gaps, more than 50 different pesticides have been found in the groundwater of 23 California counties.
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From page 17... ...
Despite increasing concern about contamination of groundwater resources, the research budgets for development of baseline and trend water quality data and for special investigative projects have not risen signif~cantly. In fact, the WRCB budget for development of baseline water quality data has been cut over the last 5 years from $400,000 to approximately S240, 000.
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From page 18... ...
The samples are tested for the presence of organic chemicals. This investigation was authorized by California Assembly Bill 1803, Passed in September 1983, as one response to concerns about toxic chemicals in drinking water sparked by the rice herbicide controversy in the Sacramento area (see subsection Best Management Practices for Pesticide Use)
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From page 19... ...
This table includes numerous detections associated with point sources, but the data do not distinguish sources in individual cases. CRITICAL PROBLEMS AND NEEDS Nemo tocides One class of agricultural chemicals , nematocides, poses a particularly high risk of groundwater contaminatzon.
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From page 20... ...
20 TABLE 1-1 Pesticides in California Groundwater Number of Positive Detects ( total number of wells Maximum EPA-Suggested sampled if information Concentration Analytic Pesticide availablea)
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From page 21... ...
Data Base and the Need for a Multiresidue Analytic Screen A lack of water quality data impedes efforts to determine the severity of groundwater contamination caused by agricultural chemicals. Often, samples from wells have not been analyzed for pesticides.
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From page 22... ...
One state water quality official interviewed believed that relatively inexpensive water available to growers in California prompted excessive irrigation and thus contributed to the groundwater problems in the San Joaquin Valley. Higher priced irrigation water most probably would result in more efficient use of the resource and could lead to the substitution of drip irrigation for flood irrigation methods.
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From page 23... ...
Ground and Aerial Applicators Work yards of ground applicators and airstrips used by aerial applicators of pesticides have on occasion been the sites of poor disposal practices of residual pesticide solutions and tank rinse waters. Approximately 500 aerial and ground applicator sites exist in the Central Valley Region alone.
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From page 24... ...
Also, the implementation of such a strategy would be difficult because the delineation of areas vulnerable to groundwater contamination would certainly not coincide with existing political boundaries, nor be readily accepted by all parties at risk. Public and Institutional Perceptions of California Groundwater Contami net ion Citing the number of public inquiries and requests for agency publications, officials in California water agencies pointed out that the average California citizen is becoming increasingly aware and concerned about the threat posed to groundwater resources by toxic organic chemicals from both agricultural and industrial sources.
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From page 25... ...
Others felt the problem could potentially be much broader and that an integrated research effort cutting across disciplines was critically needed to assess the dimensions of the problem and develop strategies to mitigate future problems. AGRICULTURAL MANAGEMENT STRATEGIES AVAILABLE TO MITIGATE PESTICIDE/GROUNDWATER QUALITY PROBLEMS Irrigation Efficiency The potential and limitations of irrigation efficiency to reduce pesticide leaching have already been mentioned.
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From page 26... ...
to mitigate c ontamr ination of groundwater from the use of pesticides include closely following label instructions, carefully calibrating spray equipment, efficiently scheduling arrogation, optimizing timing of pesticide applications, altering cropping patterns, and properly disposing of tank rinse water or residual pesticide solutions and containers. While everyone interviewed considered these BMPs important, some were skeptical of the effectiveness of promoting them, believing that some growers would likely ignore such recommendations for a variety of reasons, including lack of economic incentive and their determination to provide a stress-free growing environment for their crops.
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From page 27... ...
By slightly altering their practices, the rice growers lessened the environmental degradation associated with their operations and most likely avoided the cancellation of use permits for agricultural chemicals believed to be important for efficient production. Integrated Pest Management (IPM)
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From page 28... ...
Thus, Telone II remains available but the threat to groundwater is diminished. MODELS TO PREDICT THE TRANSPORT AND ENVIRONMENTAL FATE OF PESTICIDES Pioneering work on simulation models to describe the movement of trace organics in soil has been done in California.
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From page 29... ...
Also, factors such as permeability, organic matter content, texture, structure, hydraulic conductivity, and depth of soil horizons can vary widely in a single field And predictions of the transport and environmental fate of a chemical, based on observed environmental conditions, could be quite different within a relatively small area. In addition to soil heterogeneity, other features in the soil/water environment such as macropores could cause sizable errors when simulation models are used to predict pesticide movement in the field.
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From page 30... ...
The consensus was that the models were currently untested and unproved in field situations and, thus, could not be used with confidence outside the laboratory. It is generally believed, however, that simulation models could be of considerable value to regulators and manufacturers attempting to assess the environmental fate and impact of a specific chemical prior to registration and intensive manufacturing once they have been verified in the f ield.
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