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Site History Boyett Petroleum(419 S.Main St.,Manteca) Page 7 of k 1 groundwater flow direction to the southwest, consistent with that calculated for the July 22, 2003, groundwater monitoring event. In addition, the average groundwater elevation(13.55 feet) decreased with ' respect to the previous monitoring event by 0.77 feet. On September 30, 2003, a Condor representative was on site to measure water levels and collect 1 groundwater samples at monitoring wells MW-1 through MW-9. Monitoring wells MW-2, MW-4, and MW-5 were dry and monitoring wells MW-3, MW-6, MW-7, and MW-8 purged dry; as a result, groundwater samples were collected only from monitoring wells MW-1 and MW-9. Laboratory analytical ' results for the groundwater samples collected at the site on September 30, 2003, indicated that BTEX constituents, gasoline oxygenates/additives, other than MTBE, and TPH-G were not detected at or above the laboratory reported detection limits in the groundwater samples collected from MW-1 and MW-9; MTBE was detected in the groundwater samples collected from both monitoring wells. The laboratory ' analytical results for the September 2003 monitoring event indicated the lowest historical concentration of MTBE detected in the groundwater sample collected from MW-1. The decrease in the concentration of MTBE detected in the groundwater sample collected from MW-1 was attributed to the depth of the well's ' screened interval and low groundwater conditions present at the site. The average groundwater elevation decreased with respect to the last monthly monitoring event in August 2003 by 0.59 feet. An estimated groundwater gradient for the third quarter 2003 was not calculated due to the low groundwater elevations ' in monitoring wells MW-2, MW-6, and MW-8. On October 20 through 23, 2003, Condor conducted a groundwater investigation using direct push boring methods. The work was performed in general accordance with the Additional Groundwater Investigation Work Plan, dated June 25, 2003. Condor supervised the completion of four deep CPT boring pairs (CPT- 3 through CPT-6) and five shallow hydropunch borings (HP-1 through HP-5). CPT boring pairs were advanced in four locations to collect subsurface lithologic information and to evaluate the vertical and lateral extent of groundwater contamination in the vicinity of the USTs and in the predominant down- gradient direction of the contaminant plume. Borings CPT-3, CPT-4, and CPT-6 were advanced to depths of approximately 125 feet bgs; boring CPT-5 encountered refusal and was terminated at a depth of approximately 66 feet bgs. At each deep boring pair location, the first boring was advanced to provide a near-continuous log of the subsurface soil profile. The second boring at each pair location was advanced proximal to the first boring to collect a discrete groundwater sample from saturated horizons identified in ' geologic logs from the first borings. One soil sample was collected from each of borings CPT-3 through CPT-5 from immediately above a clay horizon defined in each boring's lithologic profile. Five hydropunch borings were advanced to collect groundwater grab samples to investigate the lateral extent of contamination in shallow groundwater cross- and down-gradient of the plume. A total of twenty-nine groundwater and three soil samples were collected from the borings and analyzed for TPH-G, BTEX and gasoline oxygenates/additives. ' Laboratory analytical results for the groundwater samples collected from CPT-3 through CPT-6 and HP-1 through HP-5 indicated that BTEX and TPH-G were not detected at or above the laboratory reported detection limits. MTBE was detected in groundwater samples collected from CPT-3 through CPT-6, HP- 1, and HP-3. TAME was detected in groundwater samples collected from CPT4 and HP-3. TBA was detected in a groundwater sample collected from CPT-4. 1,2-DCA was detected in groundwater samples collected from CPT-4, CPT-5, and CPT-6. Laboratory analytical results for the soil samples collected ' from CPT-3, CPT-4, and CPT-5 indicated that BTEX, gasoline oxygenates/additives other than MTBE, and TPH-G were not detected at or above the laboratory reported detection limits. MTBE was detected in the soil samples collected from CPT-3 and CPT4. The October 2003 groundwater investigation was ' described in Condor's Additional Groundwater Investigation, Monitor Well Destruction and Installation, and Interim Remediation Pump Test Report, dated January 30, 2004.