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<br />Nuela East Water Quality Data. Two monitoring wells, Loth compl ated in the lower <br />Dakota coal, yi etd hater semplea wl th pH~a lower than 5.0. GW-N14 has produced sampl ea <br />pith pH's of 5.05, 6.47. 5.80, 4.90 and. 4.91. ' <br />Tha sample with a pH of 4,90 had a cadent ws concentration of 1D ug/1 (the Drl nking Water <br />5tanda rtl). No other Primary 5tandsrda were hat or exceeded. The cadmium concentration <br />may not be a function of pH, however. Well OTI-N15, which samples the overburden et this <br />site, has a neutral pH and higher cadmium coneentrati ohs. Tha arsenic coneentratt on in <br />the same sample was 8 ug/1, and the arsenic concantrati on in the 4.91 pH sample was 7 ug/1 <br />(The detection limit). The Primary Drf nking Water 5tandsrd is 50 uq/1. No other samples <br />had detectable araenle. <br />The oihar Hall with Ion pH Hater is t:W-N20, also completed in the coal. Through time, the <br />pH of its Hater has been 4.68, 4.95, 5.52, 5.82, and 5.65. Only the first sample hatl <br />detectable arsenic (4.0 ug/1) and lead (7o ug/1). 7hs lead data are very au sped (Wells <br />CW-N13, GW-N14, GW-N1B, 47f-N2D, GW-N27, and f:W-N22 had reported lead eoncentrati ohs <br />ranging fr«e 40 [0 60 uq/7 for semplea tollectad in July 1966). No other aaapl as from any <br />of the ea wells have had detectable lead. Semple contamination or laboratory problems may <br />• have occurred. Of interest in the t:W-N20 aanpl es is the increase in sample pN through <br />time. This welt has a higher yield than CN-N74 does. The Increase in pH (and <br />coincidental decrease in sulfate and many other parameters) suggest that the sow pH water <br />in the coal has been removed during sampling and has been rapl aced by other nearby water. <br />The rate of sold productton is not rabid enough to maintain pH's leas than 5.0. <br />Table 17-9 auvnartzas the available daW on pH of water samples from the Nucla East area, <br />as a funeti on of stretigraphy. Twenty parcenC of Ne neasurementa were less than pH 6. <br />All of the sew pH reads nga are for sempl es collected tram the Dakota coals presumably any <br />probl qos assort atad wtth the coal MI1 decrease when 1t is ni ned. Monl tors ng wells Mitch <br />sample the interhurden al ao aaapie the overburden so that it 7a hoe possible to determine <br />the Qusllty et the interbarden watery especially Tram the upper and lower interbeds. <br />However, no sampl ea with pH leca than 6.0 have heen Boll eeted from these wells. Presuming <br />that acidic water Is present, mi sing easily neutrahizea the aoid. <br />NT xiig of acidic xater Stan G11-N20 (eoel) and neutral water from GW-N21 (overburden) was <br />investigated uai nq PHREEOE. The results can ba easily summarized. If no mt nerals (such <br />as calcite) ors (thsoratica7ly) alloned to dt asol ve or Areal pi rate, a ni xture of BO <br />17-42 Revt ned 04/77/88 <br />• <br />REVISED MARCH 2006 Attachment 2.05.6(32-50 <br />