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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-310(Supplemental) 11/11/1986 1985-1987 Common Ion 36.9 36 -- 13 -- -- -- 660 <br /> 1/28/1987 1985-1987 Common Ion 69.6 42 -- 810 <br /> 7/13/1988 Hist.Sum.GW Quality -- -- 10 -- -- <br /> 1/1/2001 Hist.Sum.GW Quality 10 8 <br /> 4/1/2001 Hist.Sum.GW Quality 5 <br /> 7/1/2001 Hist.Sum.GW Quality -- 6.5 <br /> 1/1/2002 Hist.Sum.GW Quality 9 -- <br /> 1/1/2003 Hist.Sum.GW Quality 6 <br /> 4/1/2006 Dudek 2007 Annual Rpt 8 <br /> 4/1/2007 Dudek 2007 Annual Rpt -- -- -- 10 -- -- -- -- <br /> 1/21/2008 Background 6.4 16.5 NA 6.0 <10 <10 243 <10 377 <br /> Historic Concentration Range 6.4-69.6 243 377-810 <br /> WDR/MRP Suggested Upper Limit Background Concentration 8.3 21. 300 450 <br /> Proposed Upper Limit Background Concentration 21 <br /> 4/1/2008 Dudek 2008 Semiannual Rpt -- -- -- 17 -- -- -- -- <br /> 4/1/2008 2nd Qtr./Compliance 9.9 21.0 NA 7.0 11 <10 187 <10 463 <br /> 7/10/2008 3rd Qtr./Compliance 9.6 20.9 NA 8.0 <10 <10 519 <10 476 <br /> 10/21/2008 4th Qtr./Compliance 12.9 40.6 NA <5 46 <10 <100 <10 748 <br /> 1/9/2009 1st Qtr./Compliance 12.2 23.6 NA 8.0 25 <10 <100 <10 608 <br /> 4/7/2009 2nd Qtr./Compliance 12.4 27.9 NA 7.0 <10 <10 456 <10 545 <br /> 7/14/2009 3rd Qtr./Compliance NA 38.4 <5 10 <10 626 <10 743 <br /> 10/12/2009 4th Qtr. NA 52.2 4.0 8 <10 569 10 777 <br /> 2/1/2010 1st Qtr. NA 39.6 4.0 41 <10 605J <10 780 <br /> 4/13/2010 2nd Qtr. NA 37.8 4.0 12J <10 402UJ <10 821 <br /> 7/7/2010 3rd Qtr. NA 40.0 3.0 30 <10 628 <10 754 <br /> 10/13/2010 4th Qtr. NA 44.4 4.OJ 26 <10 789 <10 767 <br /> 1/21/2011 1st Qtr. NA 45.0 NA 5.0 19 7.44 542 <10 899 <br /> 4/13/2011 2nd Qtr. NA 40.6 NA 3J 14 7.04 458 <10 755 <br /> 7/20/2011 3rd Qtr. NA 47.0 NA 3J 17 <10 515 <10 787 <br /> 10/12/2011 4th Qtr. NA 44.2 NA 1J <10 <0.5 413 20 837 <br /> 1/24/2012 1st Qtr. NA 46.6 NA 2J 81 5.12 375 <10 779 <br /> 4/24/2012 2nd Qtr. NA 44.6 NA 4J 10 8.36 362 <10 789 <br /> 7/24/2012 3rd Qtr NA 45.7 NA 3J 15 7.82 349 <10 786 <br /> 10/24/2012 4th Qtr NA NA NA NA 91 NA NA NA NA <br /> 1/25/2013 1st Qtr. NA NA NA NA 91 NA NA NA NA <br /> 4/11/2013 2nd Qtr. NA NA NA NA 91 NA NA NA NA <br /> Page 8 of 10 <br />