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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-210 6/26/1985 1985-1987 Common Ion 44 21 -- -- -- -- 560 <br /> 7/24/1985 1985-1987 Common Ion 19 22 -- 10 -- -- 510 <br /> 7/29/1985 1985-1987 Common Ion 24 22 -- -- -- -- 430 <br /> 1/28/1987 1985-1987 Common Ion 14.2 30 -- -- -- -- 475 <br /> 7/12/1988 Hist. Sum.GW Quality -- -- -- 30 -- -- -- <br /> 9/30/1988 Hist. Sum.GW Quality -- -- -- 3 -- -- -- <br /> 12/13/1988 Hist. Sum.GW Quality -- -- -- 3 -- -- -- <br /> 4/19/1989 Hist. Sum.GW Quality -- -- -- 1 -- -- -- <br /> 8/1/1989 Hist. Sum.GW Quality -- -- -- 52 -- -- -- <br /> 10/26/1989 Hist. Sum.GW Quality -- -- -- 4 -- -- -- <br /> 4/24/1990 Hist. Sum.GW Quality -- -- -- 3 -- -- -- <br /> 4/1/2006 Dudek 2007 Annual Rpt -- -- -- -- <5 -- -- -- <br /> 4/1/2007 Dudek 2007 Annual Rpt -- -- -- -- 4 -- -- -- <br /> 1/9/2008 Background 7.1 22.3 NA <5 <10 <10 161 <10 445 <br /> Historic Concentration Range 21 -30 1 - 2 <10 161 <10 430-560 <br /> WDR/MRP Suggested Upper Limit Background Concentration 29 209 490 <br /> Proposed Upper Limit Background Concentration 29 490 <br /> 4/1/2008 2nd Qtr./Compliance 6.5 19.4 NA <5 11 <10 160 <10 415 <br /> 7/10/2008 3rd Qtr./Compliance 5.8 16.5 NA <5 <10 <10 400 <10 424 <br /> 10/21/2008 4th Qtr./Compliance 5.0 15.7 NA <5 <10 <10 <100 <10 470 <br /> 1/8/2009 1st Qtr./Compliance 4.4 20.2 NA <5 10 <10 <100 <10 479 <br /> 4/7/2009 2nd Qtr./Compliance <1.0 10.5 NA <5 <10 <10 270 <10 412 <br /> 7/14/2009 3rd Qtr./Compliance NA 24.0 <5 <10 <10 271 20 405 <br /> 10/12/2009 4th Qtr. NA 24.6 2.0 6 <10 278 30 416 <br /> 2/1/2010 1st Qtr. NA 29.7 2.0 14 <10 284 20 413 <br /> 4/13/2010 2nd Qtr. NA 25.5 4.0 12 <1 OUJ 159 <10 416 <br /> 7/7/2010 3rd Qtr. NA 20.4 3.0 10 <10 285 <10 386 <br /> 10/12/2010 4th Qtr NA 23.3 3.OJ 17 <10 296 <10 488 <br /> 1/20/2011 1st Qtr. NA 21.6 NA 3J 6J 1.26 224 <10 503 <br /> 4/13/2011 2nd Qtr. NA 21.3 NA 3J 81 1.31 229 <10 429 <br /> 7/19/2011 3rd Qtr. NA 17.8 NA 2J 4J <10 135 <10 377 <br /> 10/12/2011 4th Qtr. NA 20.6 NA 2J <10 <0.5 253 6J 501 <br /> (Page 4 of 9) <br />