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or ug/1) for each parameter. The units used for each parameter are the <br />same as those listed on the Surface Water Parameter List (Table 1) and <br />are the same as those used in the water quality reports. The frequency <br />column on Table 4 provides four values in the format 0/0/2/2. The first <br />numeral represents the number of exceedances above the Method Detection <br />Limit (MDL). The second numeral represents the number of exceedances <br />between the MDL and the Practical Quantitation Level (PQL) The third <br />numeral represents the number of sample values below the MDL but the MDL <br />was higher than the standard. Moreover, the fourth numeral represents <br />the total number of samples. A summary of the standards that were <br />exceeded is presented below. <br />HGT analyzed selenium in three forms this year, dissolved, potentially <br />dissolved and total recoverable, often on the same samples, to <br />investigate the difference in the three methods of analysis. From a <br />regulatory perspective, the potentially dissolved form is applicable to <br />NPDES sites, while the dissolved form is applicable to stream sites. The <br />total recoverable form was run only as a quality control check. The <br />following discussion will focus only on potential dissolved selenium <br />excursions at NPDES sites and dissolved selenium excursions at steam <br />sites. There were no excursions at NPDES Sites this year. <br />The chronic selenium standard (4.6 ug/1) was exceeded twice at upstream <br />Site HGSD1; 48.5 ug/l in April and 5.4 ug/l in September. Downstream <br />Site HGSD3 exceeded the chronic standard once; 5.5 ug/l in June. The <br />acute standard (18.4 ug/1) was exceeded at Site HGSD1 in April. <br />Irrigation return water from nearby hay fields is in part the cause of <br />the excursions at these sites. This entire area is composed of topsoils <br />derived from the Lewis Shale, which has naturally elevated <br />concentrations of selenium and salts, which contribute to dissolved <br />solids in local runoff. NPDES Sites did not flow this year, so they are <br />not responsible for the stream selenium exceedances. <br />The mercury Method Detection Limit (MDL) is 0.2 (or sometimes 0.4 ug/1). <br />All test values this year were less than the MDL. The mercury standard <br />is 0.01 ug/l. <br />61 <br />