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SCC ran selenium in three forms this year, often on the same samples, so <br />as to investigate the difference in the three methods. However, in a <br />regulatory sense, the potentially dissolved form is applicable to NPDES <br />sites, and the dissolved form is applicable to stream sites. The total <br />recoverable form was run only as a quality control check. The following <br />discussion will focus only on potential dissolved excursions at NPDES <br />sites and dissolved excursions at steam sites. <br />One stream site exceeded the dissolved chronic selenium standard, 4.6 <br />ug /l. Lower Grassy Creek site YSG5 displayed a value of 4.9 ug /1 on <br />April 29'' '. Selenium values at all outfalls (010 and 011 at Yoast, and <br />002 at the Peabody Sage Creek Mine) from samples collected on the same <br />day were all below 4.6 ug /1. However, the dissolved selenium value at <br />Lower Scotchman Gulch Site G -SG -1A (part of a special selenium study) on <br />a sample collected the same day was 15.6 ug /l. Scotchman Gulch flows <br />over soils derived from the Lewis Shale, which are naturally high in <br />selenium. This gulch joins Grassy Creek just upstream of Site YSG5. <br />One NPDES site, NPDESI3, exceeded the potentiall dissolved chronic <br />standard, 4.6 ug /1 twice this year. The value on April 19th was 8.5 ug /1 <br />and the value on May 2nd was 17.2 ug /1. The selenium value at stream <br />site YSS2 (located on Sage Creek immediately downstream of Outfalls 012, <br />013 and 014) on May 2nd was only 1.5 ug /1 (dissolved)_ This indicates <br />that while NPDESI3 was out of compliance in May, Sage Creek was in <br />compliance. Site YSS2 was not sampled in April, however, a similar <br />situation (Outfall out of compliance, but stream in compliance) is <br />expected. See the following ` NPDES Effluent Criteria' section for a <br />further discussion. <br />The sulfide data presented in Appendix D are the total of both the <br />ionized (S -) and un- ionized (HzS) forms of hydrogen sulfide. The un- <br />ionized form is the potentially toxic form, and is what the CDPHE water <br />quality standard is based upon. A procedure for calculating the un- <br />ionized form may be found on the website: <br />http://www.mullalyengineerin .com.au /ima es/ roductjfile /Problem of Hydr <br />13 <br />