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<br />1416
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<br />Agriculture Standards Laboratory for nitrate for
<br />quality control evaluation,
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<br />In addition to the inorganic parameters, all of
<br />the groundwater samples collected were analyzed
<br />for selected pesticides, The pesticide analysis was
<br />performed by the Colorado Department of
<br />Agriculture Standards Laboratory, A listing of
<br />pesticides was compiled for analysis based on those
<br />substances that have recently been, or are currently
<br />being utilized in the Arkansas Valley according to
<br />agricultural officials there, Budget restrictions
<br />would not allow testing for all pesticides used in the
<br />study area, To reduce the analysis cost, each
<br />pesticide was weighted according to its chemical
<br />properties of persistence and mobility in the
<br />environment, amount of active ingredient used per
<br />acre, and the amount of acreage within the study
<br />area that pesticide was used on, Pesticides were
<br />then selected according to their final score and the
<br />ability of the laboratory to detect their presence,
<br />
<br />The results from this sampling program have
<br />been entered into the CDPHE Groundwater Quality
<br />Data System, a database located at CDPHE, A
<br />detailed report describing the area sampled, the
<br />protocol for sampling and analysis, and the results
<br />of the analysis was provided to the Commissioner
<br />of Agriculture in early 1997,
<br />
<br />
<br />Analysis of laboratory results for the Arkansas
<br />Valley indicates that ground water in parts of the
<br />study area has been impacted by various
<br />agricultural chemicals, The major inorganic
<br />contaminant of concern is nitrate, Nineteen of the
<br />one hundred thirty nine wells sampled (14%)
<br />showed nitrate levels in excess of the EP A standard
<br />for drinking water (10 mg/L) , The drinking water
<br />standard is used as a benchmark for nitrate levels in
<br />all wells regardless of use because the alluvial
<br />aquifer is a significant source of drinking water in
<br />the valley, Twelve of the one hundred thirty nine
<br />samples ( 9%) showed positive for the herbicide
<br />Atrazine, One sample detected the herbicide
<br />Metolachlor and one sample detected the herbicide
<br />2,4-D, All pesticide detections where well below
<br />the drinking water standard,
<br />
<br />A confirmation sampling was performed on
<br />those wells that had a nitrate level above 10 mg/L,
<br />or a pesticide detection in 1994, The confirmation
<br />sampling tested 32 wells and found little change
<br />from 1994, indicating a high level of confidence 'in
<br />the initial wprk, Nitrate levels were statistically
<br />unchanged and the only pesticide detected was
<br />Atrazine. One well did contain Atrazine at a level
<br />above the standard of 3,0 ug/L,
<br />
<br />-';'-,-,,'"
<br />
<br />F(~sultsofPeSti6ide'4f1~lysis,ArkansasValley Aquifer, 1994.
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<br />,,'\--,,
<br />,/-''-
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<br />Pestibide Use No. Detections; DL MCL
<br />Atrazine Herbicide 12 0,05 3,0
<br />Metolachlor Hetbicide 1 0,05 100
<br />24:.D Herbicide 1 0,02 70
<br />,
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<br />Amounts~re given in micrograms per liter or parts perbillioh
<br />DL: ,Minimum concentration that can be detected by the laboratory
<br />MCL- The maximum amount allowed.in drinking water
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