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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 • Sulfate (mg/L Calcium (mg/L Arsenic Iron TDS m <br /> Water Quality Objective 10 250 10 50 50- 300 50 450 <br /> Background/Compliance Wells <br /> MW-302Hist.Sum.GW Quality -- -- <br /> - 10 -- -- -- -- <br /> 9/28/1988 Hist.Sum.GW Quality 4 <br /> 12/13/1988 Hist.Sum.GW Quality 10 <br /> 10/26/1989 Hist.Sum.GW Quality 43 <br /> 1/15/1990 Hist.Sum.GW Quality 157 <br /> 4/24/1990 Hist.Sum.GW Quality 41 <br /> 7/18/1990 Hist.Sum.GW Quality 56 <br /> 1/17/1996 Hist.Sum.GW Quality 480 <br /> 1/29/1997 Hist.Sum.GW Quality 110 <br /> 4/1/1998 Hist.Sum.GW Quality 20 <br /> 1/1/2001 Hist.Sum.GW Quality 5 <br /> 4/1/2006 Dudek 2007 Annual Rpt 7.6 <br /> 4/1/2007 Dudek 2007 Annual Rpt -- -- -- -- 3 -- -- -- -- <br /> 1/9/2008 Background 3.5 16.2 NA <5 <10 <10 167J <10 377 <br /> Historic Concentration Range 377 <br /> WDR/MRP Suggested Upper Limit Background Concentration 450 <br /> Proposed Upper Limit Background Concentration <br /> 4/1/2008 2nd Qtr./Compliance 3.4 23.2 NA <5 10 <10 140 <10 423 <br /> 7/10/2008 3rd Qtr./Compliance 4.2 24.5 NA <5 <10 <10 492 <10 471 <br /> 10/21/2008 4th Qtr./Compliance 4.5 18.7 NA <5 13 <10 <100 <10 436 <br /> 1/9/2009 1st Qtr./Compliance 4.5 20.3 NA <5 37 <10 <100 <10 464 <br /> 4/7/2009 2nd Qtr./Compliance 3.9 57.1 NA <5 <10 <10 340 <10 537 <br /> 7/14/2009 3rd Qtr./Compliance NA 23.1 <5 <10 <10 386 <10 474 <br /> 10/12/2009 4th Qtr. NA 24.8 4.0 9 <10 326 <10 455 <br /> 2/1/2010 1st Qtr. NA 17.2 4.0 14 <10 290 <10 388 <br /> 4/14/2010 2nd Qtr. NA 18.9 4.0 14 <10 134 <10 404 <br /> 7/7/2010 3rd Qtr. NA 16.6 4.0 9 <10 371 <10 386 <br /> 10/13/2010 4th Qtr. NA 16.7 4.OJ 10 <10 287 <10 388 <br /> 1/21/2011 1st Qtr. NA 15.4 NA 5.0 6J 2.04 155 <10 426 <br /> 4/14/2011 2nd Qtr. NA 14.6 NA 5.0 8J 1.59 129 <10 334 <br /> 7/20/2011 3rd Qtr. NA 14.3 NA 4J 3J <10 232 30 322 <br /> 10/12/2011 4th Qtr. NA 48.2 NA 3J 4J 2.11 227 <10 499 <br /> 1/25/2012 1st Qtr. NA 29.0 NA 3J <10 1.47 169 5J 402 <br /> 4/24/2012 2nd Qtr. NA 16.0 NA 5.0 <10 1.35 123 <10 333 <br /> 7/23/2012 3rd Qtr NA 23.0 NA 4J 4J 1.02 126 <10 374 <br /> 10/23/2012 4th Qtr NA NA NA NA 4J NA NA NA NA <br /> 1/25/2013 1st Qtr. NA NA NA NA <10 NA NA NA NA <br /> Page 6 of 10 <br />