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colo icaI T"hX&S t4c. G g Page 7 Additional Site Characterization &4'Quarter Groundwater Monitoring Project No. 1030.2 February 20,2004 volumes until the groundwater parameters (temperature, conductivity and pH) had stabilized (Appendix C) indicating that water representative of actual aquifer conditions was entering the well. Groundwater parameter stabilization was characterized by three successive readings within 10%. Before a sample was collected, the well's water level was allowed to recharge to at least ' 80% of its initial level. MW-4 and MW-101 recharged to approximately 67% of their initial level prior to sample collection due to slow recharge in these wells. All water removed from the monitoring well and not used as a sample was placed in a 55 gallon DOT approved container that is properly labeled and temporarily stored on-site. A Waterra pump and dedicated tubing were used to collect each sample. Extreme care was exercised while collecting samples to prevent agitation of the water contained in the Waterra pump. With minimal sample aeration, water samples were transferred from the pump into 40-m1 VOA vials preserved with hydrochloric acid or trisodium phosphate. All samples were checked for headspace bubbles, labeled, inserted into foam holders and placed into a cooled ice chest for transport to the laboratory. The sampling technician wore disposable gloves while collecting all samples. A chain of custody document, listing all samples collected and their intended analyses, accompanied the samples from field to the laboratory, thereby providing a means to track the movement of and ensure the integrity of the samples. The depth-to-water data was submitted electronically to GeoTracker as required under AB2886 on January 7, 2004. The confinnation number is 8070846378. 2.4.2 Groundwater Laboratory Analyses Groundwater samples collected on October 16, 2003, were delivered to Sherwood Labs of Hilmar, California (certification#1400) for analyses of: ❑ Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX)by EPA method 8020 ❑ Gasoline Range Organics (TPH-G) by EPA method 802018015(M) ❑ MTBE by EPA method 8020 • Positive results were confirmed by EPA method 8260 The results of the laboratory analyses are listed in Table 5 of Appendix A. Detection limits and analytical results are presented in Appendix B. As required under AB2886, the depth to groundwater data was submitted electronically to GeoTracker on November 6, 2003, and the confirmation number is 5185221314. ' 2.4.3 Groundwater Parameters Dissolved oxygen measurements ranged between 0.37 and 0.45 ppm during the October 2003 monitoring event. The low dissolved oxygen conditions at the site suggest that the site is not conducive to natural biodegradation. Historically, the site shows DO readings below --- 1 ppm. The decrease in dissolved oxygen in MW-4 over time suggests that contaminated ' groundwater has reached this downgradient well.