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Ms. Kristin Shelton <br /> Page 9 of 10 <br /> Long-term Trends in Groundwater Contaminant Concentrations <br /> Site-wide, the extent and magnitude of dissolved petroleum hydrocarbon contamination (TPHg, <br /> ' TPHd and BTEX) is stable. hi particular, recent results from wells MW2, MW4,MWS, MW 10, <br /> MW 11, MW 12 and MW 14 were non-detect for all hydrocarbons. High levels of dissolved <br /> hydrocarbons persist in wells MW6R and MW8, however, the concentration of TPHg in MW8 <br /> during the fourth quarter sampling event was the lowest to date. High levels of dissolved <br /> hydrocarbons have previously been present in wells MW9R and VEW 1-D, however, well <br /> MW9R was not sampled in 2015 due to the presence of free product and well VEW 1-D was not <br /> ' sampled due to the operation of the SVE system. Moderate concentrations of dissolved <br /> hydrocarbons remain in wells MW3, MW7 (although MW7 could not be sampled in 2015 <br /> ' because the well was dry) and MW13. Well MW9R and occasionally well MW6R continue to <br /> exhibit periodic free product. <br /> ' MTBE is currently the only oxygenate detected at the site and is found in wells MW3, MW6R, <br /> MW8 and MW13, and although MTBE has been regularly present in wells MW7, MW9R and <br /> VEW 1-D, well MW7 could not be sampled in 2015 because the well was dry, well MW9R was <br /> ' not sampled in 2015 due to the presence of free product and well VEW 1-D was not sampled due <br /> to the operation of the SVE system. The concentrations of MTBE detected in wells MW6R, <br /> MW8 and MW13 appear to be on a trend of increase; the concentrations of MTBE detected in <br /> MW6R during the first quarter and wells MW8 and MW13 during the fourth quarter were the <br /> highest to date in each respective well. Graphs of contaminant concentrations over time in select <br /> site wells are included in Attachment C. <br /> ' Water level monitoring and analytical data from deep monitoring well MWID, which was <br /> installed in January 2002, continue to indicate that a clean aquifer zone underlies the <br /> ' contaminated shallow groundwater at the site. <br /> Despite the operation of the SVE system, which has removed more than 15,500 pounds of <br /> ' hydrocarbons from the subsurface, free product has not yet been eliminated. It is our intention to <br /> continue with the remedial efforts until such time as free product is absent and dissolved <br /> concentrations of contaminants begin to decline. At that time the case will be evaluated for <br /> ' closure utilizing the criteria set forth in the State Water Resources Control Board's Low-Threat <br /> Underground Storage Tank Case Closure Policy, which should be relevant and appropriate for <br /> this above-ground storage tank case. <br /> 1 <br /> G:tData\GROUNDZBWOOLSEY.ROB\Repom\QMR\2015 QMRsWNNUAL REPORTTiml Teztjw.doc <br />