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TABLE 6 <br /> HISTORIC GROUNDWATER ANALYTICAL RESULTS AND PROPOSED COMPLIANCE WELL BACKGROUND CONCENTRATION LIMITS <br /> FULL SCALE IN SITU HEXAVALENT CHROMIUM REDUCTION TREATMENT <br /> FORMER MARLEY COOLING TOWER SITE <br /> STOCKTON, CALIFORNIA <br /> Laboratory Analyses <br /> Hexavalent <br /> Nitrate as N Chromium Chromium Manganese <br /> Well Sample Date Event/Purpose m L * Sulfate (mg/L Calcium (mg/L Arsenic(pg/L) (gg/L L Iron L /L TDS m L <br /> Water Quality Objective 10 250 -- 10 50 50** 300 50 450 <br /> Background/Compliance Wells <br /> MW-211 (Supplemental) 6/25/1985 1985-1987 Common Ion 11 10 -- -- -- -- -- 260 <br /> 7/24/1985 1985-1987 Common Ion 9 11 -- -- -- -- -- 280 <br /> 7/29/1985 1985-1987 Common Ion 12 9 -- -- -- -- -- 310 <br /> 1/28/1987 1985-1987 Common Ion 22.2 17 -- -- -- -- -- 335 <br /> 7/1/2000 Hist. Sum.GW Quality -- -- -- 4 -- -- -- -- <br /> 10/1/2000 Hist. Sum.GW Quality -- -- -- -- 1.1 -- -- -- <br /> 1/1/2001 Hist. Sum.GW Quality -- -- -- 6 3 -- -- -- <br /> 4/1/2001 Hist. Sum.GW Quality -- -- -- -- 6 -- -- -- <br /> 7/1/2001 Hist. Sum.GW Quality -- -- -- -- 2.8 -- -- -- <br /> 1/1/2002 Hist. Sum.GW Quality -- -- -- 4 -- -- -- -- <br /> 4/1/2007 Dudek 2007 Annual Rpt -- -- -- -- 3 -- -- -- -- <br /> 1/21/2008 MWH Background(Dup) 7.0 28.8 NA <5 <10 <10 214 <10 384 <br /> Historic Concentration Range 6.4-22.2 9-29.6 -<10 1.1 -<10 214 260-198 <br /> WDR/MRP Suggested Upper Limit Background Concentration 9.1 38.5 13 13 300 450 <br /> Proposed Upper Limit Background Concentration 38.5 313 <br /> 4/1/2008 Dudek 2008 Semiannual Rpt -- -- -- -- 7 -- -- -- -- <br /> 4/1/2008 2nd Qtr./Compliance 7.3 30.3 NA <5 <10 <10 138 <10 417 <br /> 7/10/2008 3rd Qtr./Compliance 6.3 31.6 NA <5 <10 <10 374 <10 438 <br /> 7 <br /> 10/21/2008 4th Qtr./Compliance 6.8 31.5 NA <5 <10 <10 <100 <10 414 <br /> 1/8/2009 1st Qtr./Compliance 7.7 38.0 NA 6.0 17 <10 <100 <10 422 <br /> 4/7/2009 2nd Qtr./Compliance 8.7 30.6 NA 5.0 <10 <10 277 <10 419 <br /> 7/14/2009 3rd Qtr./Compliance NA 31.7 <5 <10 <10 388 <10 441 <br /> 10/12/2009 4th Qtr. NA 28.4 4.0 8 <10 320 <10 461 <br /> 2/1/2010 1st Qtr. NA 29.4 4.0 16 <10 329 <10 462 <br /> 4/13/2010 2nd Qtr. NA 27.5 5.0 13 <IOUJ 185 <10 479 <br /> 7/7/2010 3rd Qtr. NA 29.6 4.0 11 <10 389 <10 446 <br /> 10/12/2010 4th Qtr. NA 32.5 4.OJ 10 <10 264 <10 431 <br /> 1/20/2011 1st Qtr. NA 29.9 NA 5.0 5J 1.78 210 <10 512 <br /> 4/13/2011 2nd Qtr. NA 29.7 NA 4J 5J 2.07 184 <10 419 <br /> 7/19/2011 3rd Qtr. NA 30.2 NA 4J 4J <10 155 <10 389 <br /> 10/12/2011 4th Qtr. NA 20.4 NA 4J <10 0.61 129 6J 311 <br /> (Page 5 of 9) <br />