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TABLE 6 HISTORIC GROUNDWATER ANALYTICAL RESULTS AND PROPOSED COMPLIANCE WELL BACKGROUND CONCENTRATION LIMITS FULL SCALE IN SITU HEXAVALENT CHROMIUM REDUCTION TREATMENT FORMER MARLEY COOLING TOWER SITE STOCKTON, CALIFORNIA Laboratory Analyses Hexavalent Nitrate as N Chromium Chromium Manganese 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 Water Quality Objective 10 250 -- 10 50 50** 300 50 450 Background/Compliance Wells MW-304(Continued) 4/13/2011 2nd Qtr. NA 39.9 NA 3J 15 8.04 424 <10 856 7/20/2011 3rd Qtr. NA 41.1 NA 3J 17 <10 569 <10 856 10/12/2011 4th Qtr. NA 42.4 NA 2J 6J 3.13 418 <10 859 MW-310(Supplemental) 11/11/1986 1985-1987 Common Ion 36.9 36 -- 13 -- -- -- 660 1/28/1987 1985-1987 Common Ion 69.6 42 -- -- -- -- -- 810 7/13/1988 Hist. Sum.GW Quality -- -- -- 10 -- -- -- -- 1/1/2001 Hist. Sum.GW Quality -- -- -- 10 8 -- -- -- 4/1/2001 Hist. Sum.GW Quality -- -- -- -- 5 -- -- -- 7/1/2001 Hist. Sum.GW Quality -- -- -- -- 6.5 -- -- -- 1/1/2002 Hist. Sum.GW Quality -- -- -- 9 -- -- -- -- 1/1/2003 Hist. Sum.GW Quality -- -- -- 6 -- -- -- -- 4/1/2006 Dudek 2007 Annual Rpt -- -- -- -- 8 -- -- -- -- 4/1/2007 Dudek 2007 Annual Rpt -- -- -- -- 10 -- -- -- -- 1/21/2008 - 1/21/2008 Background 6.4 16.5 NA 6.0 <10 <10 243 <10 377 Historic Concentration Range 6.4-69.6 16.5-42 6 6- 13 5-<10 243 <10 377-810 WDR/MRP Suggested Upper Limit Background Concentration 8.3 21.5 21.5 7.8 13 300 50 450 Proposed Upper Limit Background Concentration 21.5 10 50 4/1/2008 Dudek 2008 Semiannual Rpt -- -- -- -- 17 -- -- -- -- 4/1/2008 2nd Qtr./Compliance 9.9 21.0 NA 7.0 11 <10 187 <10 463 7/10/2008 3rd Qtr./Compliance 9.6 20.9 NA 8.0 <10 <10 519 <10 476 10/21/2008 4th Qtr./Compliance 12.9 40.6 NA <5 46 <10 <100 <10 748 1/9/2009 1st Qtr./Compliance 12.2 23.6 NA 8.0 25 <10 <100 <10 608 4/7/2009 2nd Qtr./Compliance 12.4 27.9 NA 7.0 <10 <10 456 <10 545 7/14/2009 3rd Qtr./Compliance NA 38.4 <5 10 <10 626 <10 743 10/12/2009 4th Qtr. NA 52.2 4.0 8 <10 569 10 777 2/1/2010 1st Qtr. NA 39.6 4.0 41 <10 605J <10 780 4/13/2010 2nd Qtr. NA 37.8 4.0 12J <10 402UJ <10 821 7/7/2010 3rd Qtr. NA 40.0 3.0 30 <10 628 <10 754 10/13/2010 4th Qtr. NA 44.4 4.OJ 26 <10 789 <10 767 1/21/2011 1st Qtr. NA 45.0 NA 5.0 19 7.44 542 <10 899 4/13/2011 2nd Qtr. NA 40.6 NA 3J 14 7.04 458 <10 755 7/20/2011 3rd Qtr. NA 47.0 NA 3J 17 <10 515 <10 787 10/12/2011 4th Qtr. NA 44.2 NA 1J <10 <0.5 413 20 837 (Page 7 of 9)