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Current Phase of Project: Monitoring/Interim Remediation Frequency of Groundwater Sampling: All Monitoring Wells=Quarterly Frequency of Groundwater Monitoring: Quarterly Sampling Date: December 11, 2002 Is Free Product(FP) Present on Site: No FP Recovered Thisua r Q rte . NIA Cumulative FP Recovered to Date: NIA Approximate Depth to Groundwater: 42.63 to 43.33 feet bgs Groundwater Flow Direction: Northeast Groundwater Gradient: 0.001 ft/ft DISCUSSION. Groundwater elevations have decreased approximately 0.75 to 0.93 feet since the previous sampling event (September 19, 2002). The groundwater flow direction on December 11, 2002, was calculated to be towards the northeast at a gradient of approximately 0.001 ft/ft. Groundwater flow directions have predominantly been toward the northeast and east during previous monitoring events. Depth-to-water measurements were corrected to mean sea level (MSL) and used to construct a groundwater elevation contour map (Figure 2). MTBE was detected in groundwater samples collected from wells MW-1 and MW-3 through MW-10. Concentrations ranged from 0.68 pg/L up to 85,000 pg/L, with the highest concentration being detected in well MW-6. TPHG and benzene were detected in wells MW-7 (73 pg/L, and 1.2 pg/L) and MW-8 (29,000 pg/L, and 9,600 pg/L). TPHG was also detected in wells MW-5 (2,000 pg/L) and MW-6 (39,000 pg/L). Benzene was detected in wells MW-4 (3,700 pg/L) and MW-10 (0.58 pg/L). Toluene, ethylbenzene, ETBE, TBA, TAME, or EDB were not detected in any of the wells. Analytical results of the TPHG, benzene, and MTBE for groundwater samples collected on December 11, 2002 are presented in Figure 3. TPHG concentrations appear to be increasing in wells MW-4, MW-5, and MW-6. After an anomalous spike in TPHG concentrations during the third quarter 2002 in well MW-7, concentrations have dropped back down to near non-detect concentrations. MTBE concentrations appear to be decreasing in well MW-5, and increasing in wells MW-6 and MW-7. All other concentrations appear to be fluctuating within the historical range. A summary of the laboratory quality assurance notations is included in Table 3. The ozone injection remediation system was installed on December 3, 2002 to provide interim remediation to petroleum hydrocarbon impacted soil and groundwater. Additional groundwater samples were collected on December 11 and 23, 2002 from select monitoring wells (MW-1, MW-2, MW-4, MW-5, MW-7, and MW-9) to establish baseline groundwater conditions before initiating operation of the ozone injection system. The ozone injection system was started on December 26, 2002 and is programmed to inject ozone for 14 minutes in each injection well (IW-1 through IW-5) cyclically. A 30-day remediation status report will be submitted by January 31, 2003. This report will discuss installation of the ozone injection equipment, results of the baseline samples collected on December 11 and 23, 2002, and verification samples collected after initiating system operation. P:\Bp-Ano for URS\54691Quarterly120021Arco_5469_4Q02.doc 5TRA rUS