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U <br /> Response to SJCEHD's 8-19-08 Letter--Page 5 <br /> Joe's Travel Plaza,15600 S.Harlan Road <br /> not cost-effective; AS/SVE not technically viable due to limited vadose. Ozone injection not <br /> evaluated. Recommended remedial alternative: oxygen injection focused along MTBE plume <br /> axis at the property boundary. <br /> o January 2007 — SJCEfiD letter encouraged batch groundwater extraction be evaluated. ERG <br /> included this approach in their TRAP (submitted sometime in early May 2007 [Stratus does not <br /> have copy]). <br /> o May 2007 — SJCEHD reviewed IRAP but did not approve; stated that high costs difficult to <br /> justify for interim action, also USTCFpre-approval would be needed. SJCEHD suggested that <br /> costs to perform groundwater extraction for shorter period of time (Le one week per month) be <br /> evaluated. <br /> The plume is not defined to the north (water samples from MW 15A still have detections of MTBE) <br /> ).12 <br /> nor to the northwest(last sample from MW13AB was 110 Rg/t <br /> 12 See Comment No. 7 above. Well MW-15A has shown a 96.8% decrease in MTBE <br /> concentrations from its highest level of 71.8 ug/L (March 2007) to its current concentration of 2.3 ug/L <br /> (September 2008). The primary and secondary MCLS for MTBE are 13 and 5.0 Rg/L, respectively, thus, <br /> MW-15A, which was a significant cause of concern in EHD's August 19, 2008 letter has subsequently <br /> achieved regulatory compliance through.natural attenuation. We fully expect that given time, Well MW- <br /> 13A/B will do the same. As an example, please refer to.the Quarterly Groundwater Monitoring Report, <br /> Third Quarter 2008, Table 1. As shown in Table 1, MTBE concentrations at this site have historically <br /> fluctuated by as much as an order of magnitude before continuing a steady downward trend. The <br /> following excerpts from Table 1 show fluctuating (and ultimately downward trending) MTBE <br /> concentrations in a number of wells: <br /> Well Date MTBE <br /> (ug&) <br /> MW-1 2/12/00 240 <br /> 4/28/00 2,800 <br /> 9/20/00 160 <br /> 12/27/00 150 <br /> 7/30/01 40 <br /> 9/10/08 4 <br /> MW-2 8/29/02 44 <br /> 12/10/02 400 <br /> 3/28/03 1,300 <br /> 5/21/03 250 <br /> 9/15/03 13 <br /> -12/19/03 960 <br /> ... 9/10/08 45 <br /> MW-3 12/10/02 190 <br /> 3/28/03 550 <br /> 5/21/03 240 <br /> 5 <br />