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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 <br />MDL was higher than the standard. Moreover, the fourth numeral <br />represents the total number of samples. A summary of the standards that <br />were 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. <br />There were no excursions at NPDES Sites this year. The chronic selenium <br />standard (4.6 ug/1) was exceeded twice at upstream Site HGSD1; 27.3 ug/1 <br />in April and 5.5 ug/1 in September. Downstream Site HGSD3 exceeded the <br />chronic standard once; 5.5 ug/1 in June. The acute standard (18.4 ug/1) <br />was exceeded at Site HGSD1 in April. Irrigation return water from nearby <br />hay fields is in part the cause of the excursions at these sites. This <br />entire area is composed of topsoils derived from the Lewis Shale, which <br />has naturally elevated concentrations of selenium and salts, which <br />contribute to dissolved solids in local runoff. NPDES Sites did not flow <br />this year, so they are not responsible for the stream selenium <br />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. No mercury excursions occurred this year. <br />7 <br />