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from NPDES and stream sites in the Grassy Creek basin. Standards that <br />were exceeded (excluding ammonia and sulfide) are: <br />Parameter # of Sites / # of Excursions <br />Iron 2/2 <br />Mercury 1/1 <br />J <br /> <br />Both iron excursions occurred in April, and were the result of high <br />suspended solids caused by snowmelt runoff. One site is upstream of <br />mining (SSG1) and one site (SSG3) drains a pre-SMCRA mining area. <br />There were five chromium values (from NPDES2 and 3 and SSG2) that had <br />elevated detection limits higher than the acute and chronic standards. <br />The cause of thesc=_ elevated detection limits was a decision by the <br />laboratory to dilute the samples prior to analyses in order to reduce <br />the effects of interferences (primarily, high salinity). <br />One site, NPDES2, experienced a mercury value of 0.3 ug/1. Lab error is <br />suspected, since the last time this site experienced a mercury value <br />above the detection limit was 1996, with a value of 0.2 ug/1 (which is <br />equal to the detection limit). All other mercury values reported were <br />less than the most sensitive available detection limit, 0.2 ug/l. The <br />standard for mercury is 0.01 ug/1. <br />Ammonia values require extra calculations to determine exceedences. The <br />standard is 0.06 mg/1 un-ionized NH3, while the method detects both un- <br />ionized NH3 and ionized NH4. The following table calculates the actual <br />un-ionized NH3 concentration of the exceedences reported on Table 14. <br />Site Date NH3+NH4,mg/1 yH Temp,C $NH3 NH3 conc., mg/1 <br />No samples exceeded the ammonia standard this year. There were one <br />sample (from SSLGS) that had an elevated detection limit higher than the <br />standard. <br />23 <br />