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exceedances above the Method Detection Limit (MDL) / the number of <br />exceedances between the MDL and the Practical Quantitation Level (PQL) / <br />censored, that is, the number of sample values below the MDL but the MDL <br />was higher than the standard / the total number of samples. Below is a <br />summary of standards that were exceeded. <br />For downstream Site HGSD3, the total recoverable iron standard (1.0 <br />mg/1) was exceeded on June 23 with a value of 1.02 mg/l. NPDES2H was not <br />discharging at the time. NPDESIH is not likely to be the source of the <br />exceedance; its iron values were 0.57 mg/l on June 18 and 0.53 mg/l on <br />July 1. <br />The sulfide standard (0.002 mg/1, un-ionized) was exceeded at Site HGSD3 <br />on June 23, with a value of 0.0027 mg/l. The analytical method used <br />detects both dissolved sulfides and acid-soluble metallic sulfides <br />present in suspended matter. It is suspected that a large portion of the <br />sulfides detected is of the latter type, which would bias the un-ionized <br />results high. Any dissolved sulfides present in surface water should <br />eventually oxidize to sulfates. <br />The sulfide values provided in Table 3 differ from the values reported <br />in Appendix B. The sulfide data presented in Appendix B are the total of <br />both the ionized (S-) and un-ionized (H2S) forms of hydrogen sulfide. <br />The un-ionized form is the potentially toxic form, and is what the CDPHE <br />water quality standard is based upon. A procedure for calculating the <br />un-ionized form may be found on the website: <br />http://www.mullalyengineering.com.au/images/product/file/Problem of Hydr <br />ogen Sulphide in Sewers.pdf page 5, Table 1. The results of those <br />calculations are presented in Table 3 of this AHR. <br />The chronic selenium standard (4.6 ug/1) was exceeded in June at <br />upstream Site HGDS1, with a value of 5.2 ug/1. The acute standard (18.4 <br />ug/1) was not exceeded. Downstream Site HGSD3 did not exceed either <br />selenium standard. <br />HGT runs mercury tests with a Method Detection Limit (MDL) of 0.2 (or <br />sometimes 0.4) ug/1. All test values this year were less than the MDL. <br />3