SITE INFORMATION AND CORRESPONDENCE FILE 2

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Nomelllini Property 1045 W. Charter Way, Stockton CPT report comment Page 2 of 3 • Ground water monitoring: - Without the current status of impacted groundwater (4'aQuarter — 2004 , 1 " Quarter — 2005) known , the concentration trends cannot be determined . SJCEHD requires that quarterly ground water monitoring , sampling , and reporting be reinitiated immediately. All of the constituents listed on Table 5 of Quarterly Report — Third and Fourth Quarter 2004 (dated March 9, 2005 ) are to be analyzed for in the quarterly monitoring (QM) event samples , starting with QMR 3rd — 2005. • CPT Report: The vertical and lateral extent of contaminants is not adequately delineated . This is especially true for 1 ,2-DCA. Additional assessment is needed . There was no technical justification presented for excluding impacted sampling points (CPT- 190' bgs , CPT-274' bgs and ~94' bgs) from inclusion in the main plume of impacted soil , or CPT- 1 - 100' bgs from the main plume of impacted groundwater. • The silty fine sand interval between approximately 54' bgs and 62 ' bgs , near the top of HU-5 , does not have a distinctive signature on the CPT logs ; the interval may consist of thin sand/silt-clay interbeds and have a slightly higher hydraulic conductivity than the immediately overlying and underlying fine-grained units . SJCEHD will require one short-screened well in this interval , immediately down-gradient of the source area , to check this interval for contaminants of potential concern , and evaluate the interval as a potential contaminant migration pathway. • Additional cross sections should be prepared ; the sand intervals should be mapped if possible . EHD has analyzed the analytical data from the December 2003 monitoring event by well and screen interval to determine where the dissolved plume has been delineated , and by inference , where it has not. SJCEHD findings : • HU-1 : Impacted groundwater occurs in an elongated , NE-SW trending plume delineated toward the NW by VW-5 and toward the SE by VW-3 and VW-7. • HU-2 : Impacted ground water is delineated toward the NNE by MW-8 and toward the SW and SSW by MW-6 and MW-9, respectively. The problem with MW-8 is that it is approximately 250 feet from the former UST pit. • HU-3 : No dedicated wells , but as a fine-grained unit, it is unlikely to serve as a significant contaminant lateral migration pathway. • HU-4 : Delineated toward the ENE by MW-5 . The plume in each HU should be assessed and monitored by dedicated wells in the undelineated directions .