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r <br /> �. Stalnte[ <br /> SECOND QUARTER 2009 OPERATIONS MAINTENANCE AND MONITORING REPORT <br /> SHOP 10 MAINTENANCE STATION <br /> Field Activities <br /> July 31, 2009 <br /> monitoring continued through this quarter and the system was shut down on June 25, 2009, due to low <br /> levels at system influent and a request for Site closure is pending. Recent air laboratory analytical results <br /> are attached in Appendix A. <br /> 2.2 GROUNDWATER DEPTH SOUNDING, PURGING, AND SAMPLING <br /> Twelve monitoring wells were sounded by Stantec personnel on May 26, 2009, using a water-level <br /> indicator. Depth-to-water in each of the monitoring wells was measured to the nearest 0.01 foot below <br /> top of casing (TOC). The water-level indicator was decontaminated with de-ionized water prior to each <br /> measurement. The AS and SVE systems were shut down temporarily prior to groundwater level <br /> measurement to reduce any potential influence introduced by these systems. Well construction <br /> �.. specifications, sample collection data, and groundwater elevations are summarized in Tables 1 and 2, <br /> and Figure 4. <br /> �-• Groundwater elevations were used to create a groundwater elevation contour map and to calculate <br /> groundwater flow direction and hydraulic gradient(Figure 4). Groundwater flowed to the east-southeast <br /> at a hydraulic gradient of 0.0011 foot per foot, which is consistent with historical gradient and direction. <br /> Groundwater elevations have risen an average 7.88 feet across the Site over the last 16 quarters. SVE <br /> well screens remain on average 2 to 4 feet above the water level surface and do not represent a risk of <br /> water intrusion at this time. <br /> Monitoring wells were purged prior to sampling using a submersible pump and dedicated tubing. Each <br /> well was purged of least three well volumes and until measurements of pH, temperature, and conductivity <br /> stabilized. To minimize the potential for cross-contamination, the order of wells purged and sampled was <br /> as follows: MW-20, MW-11, MW-9, MW-16, MW-25, MW-19, MW-24, MW-13, MW-12, VM-1, VM-2, and <br /> MW-14A. Measurements of dissolved oxygen (DO)were collected and recorded before purging. <br /> Measurements of ferrous iron (Fe 2+) and oxygen-reduction potential (ORP) were stopped in November <br /> 2008 due to low concentrations remaining in groundwater, and sufficient monitoring history indicating that <br /> r�. conditions favoring bio-attenuation exist during air sparging on-site. Field measurements are included in <br /> Table 3 and field data sheets are included as Appendix B. <br /> Groundwater samples were collected on May 27 through 29, 2009, with disposable bailers. After <br /> collection, all samples were immediately placed on ice for shipment to the laboratory. Samples were <br /> transported under chain-of-custody (COC) procedures to a state of Caiifornia-certified laboratory for <br /> �.. analysis. Groundwater laboratory analytical reports and COC documentation are included in Appendix A. <br /> 2.3 QUALITY ASSURANCE/QUALITY CONTROL MEASURES <br /> Laboratory quality assurance/quality control (QA/QC)for groundwater samples included analysis of one <br /> method blank, one matrix spike/duplicate, and a laboratory control sample/duplicate for each batch of <br /> samples sent to the laboratory. One trip blank and one equipment blank were also collected during the <br /> May 2009 groundwater sampling event. <br /> V <br /> js%Ws1329-fDl4secoriprojecl-054oaltranskstockton-shop 105om&m and gw reporting12009t2nd qtr 20D91g2_09 omm_fnl.doc 2-2 <br /> rr <br />