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Page 3 of 14 <br /> r Please consider the environment before printing this email. <br /> From: Mike Infurna [EH] [mailto:MInfurna@sjcehd.com] <br /> Sent: Tuesday, January 18, 20113:18 PM <br /> To: Chevlen, Benjamin <br /> Subject: RE: 76 #5886 <br /> Ben.. <br /> thanks.. <br /> My PG and I and the CVRWQCB discussed the site. we pretty much all agree the <br /> site is very very close to NFA. <br /> The CVRWQCB had concerns with the extent of the MtBE plume past MW-9D and <br /> also not being able to review your model Flowpath II data. please provide the <br /> model info so that we/the CVRWQCB can review your input parameters and data <br /> for lateral extent. As outlined in the Model Setup section of Stantec's Results of <br /> Hydrogeologic Modeling, dated January 6, 2010, the following input parameters <br /> were utilized in the FLOWPATH II model: Rectangular area of 500' N-S by 800' E- <br /> W with a 10-foot grid spacing. Linear constant head boundaries based on <br /> extrapolated groundwater elevation data from 7/21/09 groundwater sampling event <br /> (included in Stantec's Quarterly Status Summary Report— Third Quarter 2009, <br /> dated December 26, 2010). Model assumed hydraulic conductivity and effective <br /> porosity (0.15) based on observed predominant lithology (silt/clay and silt/sand). <br /> An MTBE first-order decay rate of 0.0006 1/day was utilized, while the initial MTBE <br /> concentration was 160 ug/L — the highest concentration observed in any well over <br /> the previous 2 years (observed in MW-91 during 4Q07). The remaining model <br /> inputs were: hydraulic conductivity — 2 ft/day; retardation factor — 1.0; longitudinal <br /> dispersivity — 20 feet; transverse dispersivity — 2 feet; and diffusion coefficient — <br /> 0.00098 ft2/day. <br /> we'll also need time to WQO in MW-9D and MW-1 with regards to MtBE. As <br /> outlined in Figure 8 of Stantec's No Further-Action Request Report, dated October <br /> 6, 2010, based on a best-fit trend line set to the historical groundwater data, MTBE <br /> concentrations in well MW-1 are currently expected to meet the WOO. It should be <br /> noted that the R2 value of 0.77 indicates a significant correlation between time and <br /> concentration, but that some variation in observed concentrations is to be expected <br /> (MTBE concentrations over the past 3 sampling events had fluctuated up/down by <br /> approximately 1 order-of-magnitude). As for MTBE concentrations in well MW-9D, <br /> the best-fit line has an R2 value of 0.95, indicating a very high correlation between <br /> time and concentration and is expected to meet the WOO within 2 years. <br /> Soil mass: no estimated residual mass remains? that's why there are no actual <br /> soil mass calculations? there was some mention of residual soil but it needs some <br /> more of your details. As outlined in Section 3.2.1 of Stantec's No Further Action <br /> Request Report, dated October 6, 2010, Stantec calculated a residual mass of 32 <br /> pounds of MTBE in soil beneath the site (see Figure 6 for estimated lateral extent <br /> and Appendix E for the soil mass calculations). As outlined in Section 3.2.1, there <br /> are a limited number of unsaturated soil samples (only hand auger samples HA-1 <br /> 3/14/2011 <br />