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TABLE 10 CHANGE IN GROUNDWATER CHROMIUM PLUME SIZE OVER TIME FORMER MARLEY COOLING TOWER SITE STOCKTON,CALIFORNIA Shallow Zone Intermediate Zone Area with Change Area with Change Area with Change Area with Change Area with Change Cr above Relative to Cr above Relative to Cr above Relative to Cr above Relative to Cr above Relative to 50 pg/L Previous 500 pg/L Previous 5,000 pg/L Previous 50 pg/L Previous 500 pg/L Previous Date (acres) Period (acres) Period (acres) Period (acres) Period (acres) Period April 1989 34 NA 23 NA 4 NA NA NA NA NA January 1992 NA NA NA NA NA NA 169 NA 20 NA January 1997 45.8 35% 25.9 11% 3 -19% 76 -55% 16 -20% April 1998 36.7 -20% 11.0 -58% 3 -26% 61 -20% 18 13% January 1999 38.9 6% 11.7 6% 2 -16% 38 -38% 38 111% January 2002 26.9 -31% 14.5 24% 4 95% 38 0% 26 -32% January 2004 39.8 48% 18.0 24% 3 -27% 34 -12% 8 -69% January 2005 47.3 19% 19.0 6% 3 0% 34 0% 9 13% April 2006 36.6 -23% 13.0 -32% 1 -67% 30 -10% 10 11% April 2007 33.6 -8% 12 -8% 0.1 -90% 36 20% 14 40% April 2008 32.0 -5% 8.0 -33% 0.0 -100% 31 -14% 17 21% April 2009 26.1 -18% 2.7 -66% 0.1 100% 34 10% 15 -12% April 2010 17.0 -35% 3 11% 0.2 100% 32 -6% 9 -43% April 2011 6.0 -65% 2 -33% 0.2 0% 16 -50% 7 -14% July-2011a 4.0 -33% 0.10 -95% NA NA 12 -25% 1 -86% October-2011a 4.0 0% 0.10 0% NA NA 12 0% 5 400% January-2012a 4.4 9% 0.01 -90% NA NA 6 -47% 1 -80% April-2012a 5.5 26% 0.06 500% NA NA 8 25% 7 553% July-2012a 3.0 -45% 0.06 0% NA NA 16 100% 5 -23% October-2012a 2.0 -33% 0.01 -83% NA NA 16 0% 5 0% From 1989/1992 -32 -94% -23 -100% -4 -95/o 0 -153 -91/a 0 15 -75/a 0 to October 2012 From April 2007 to October 20126 -32 -94% -12 -100% 0.1 100% -20 -56% -9 -64% Notes. Addition of monitoring points(new wells)over time provides greater accuracy for Cr concentration contouring;an apparent increase in plume size or concentration over time may represent an improved understanding of site conditions,not expansion of the plume. Plume surface area data provided by Dudek and Associates,Inc. a=Quantile Kriging used to estimate plume extents. Previous estimates used logarithmic interpolation. 6=Values reflect results from the full-scale in situ chromium reduction effort initiated in January 2009 gg/L=microgram per liter Cr=chromium(total dissolved) NA=not available