Laserfiche WebLink
Peabody Sage Creek Mine <br />SL -3 Phase III Bond Release Request <br />July 2014 <br />this standard occurred at PSCM NPDES2 therefore, these excursions on Grassy Creek are not <br />caused by the mining operation. <br />Seven out of thirty seven samples from NPDES2 exceeded the chronic selenium standard of 4.6 <br />ug /1 and ranged between 4.7 and 11 ug /1. One of the seven PD excursions had a TR value that <br />was less than the PD value, which indicates possible matrix interference with the PD method. <br />The TR value in that case was less than 4.6 ug /1. The acute standard, 18.4 ug /1, was not <br />exceeded in the PD form. <br />One sample at lower Grassy Creek Site YSG5 exceeded the dissolved chronic selenium standard <br />of 4.6 ug /1, with a value of 4.9 ug /1 on 4/29/2013. A sample collected the same day upstream at <br />NPDES2 displayed a PD selenium value of 4.5 ug /1. A sample collected the same day upstream <br />at steam Site G- SG -1A, a temporary surface water monitoring site established on lower <br />Scotchman's Gulch during 2013 as part of a special selenium study, displayed a PD selenium <br />value of 15.6 ug /1. The Scotchmans Gulch confluence with Grassy Creek approximately one - <br />quarter mile upstream of Site YSG5, and runoff from Scotchmans Gulch and its associated <br />tributaries flow over soils derived from the Lewis Shale, which is naturally high in selenium. <br />Steam Site SSG2 (located downstream of NPDES2 and upstream of stream Sites YSG5 and G- <br />SG-1A) is in compliance with the selenium stream standard using CDPHE 303d listing criteria <br />(85`h percentile of PD selenium values over the past five years (2009- 2013)) with a dissolved value <br />of 2.9 ug /1 (2.47 ug /1 PD values). Site YSG5 is out of compliance (using the same criteria) with a <br />PD value of 6.25 ug /1 (dissolved values were only recently being collected at this site). The high <br />selenium concentrations measured at temporary surface water monitoring sites established on <br />Scotchman's Gulch and tributaries during 2013 indicate these drainages are causing the high <br />selenium concentrations measured at Site YSG5. <br />The sulfide values provided in Tables 7 and 10 differ from the values reported in Tables 6 and 9. <br />The sulfide data presented on Tables 6 and 19 are the total of both the ionized (S) and un- <br />ionized (HZS) forms of hydrogen sulfide. The un- ionized form is the potentially toxic form, and is <br />what the CDPHE water quality standard is based upon. A procedure for calculating the un- <br />ionized form may be found on the website: <br />28 <br />