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rr=s Hydraulic conductivity of the shallow water-bearing zone, as calculated from groundwater recovery testing,ranges from 2.49 x 10�to 2.35 x 10' ft/sec. These observed values are consistent with typically reported values for the soil types encountered at the site. 7.0 DISCUSSION OF RESULTS The results of field activities and laboratory analysis of soil and groundwater samples collected during this additional site investigation are discussed below: • Depth to groundwater measured in the monitoring wells ranged from 7.90 to 4.24 feet, with groundwater elevations ranging from 0.36 to 0.55 foot above mean sea level. • The groundwater gradient calculated from the September 3, 1998 monitoring data was approximately 0.001 across the site in a southwesterly direction. • Analysis of soil samples collected at depths of between 4 and 6 feet detected petroleum hydrocarbons in samples from Monitoring Wells MW-8 and MW-12 at concentrations of up to 1.5 mg/kg TPH-G, 0.0034 mg/kg benzene, 0.0055 mg/kg toluene, 0.008 mg/kg ethylbenzene, and 0.074 mg/kg total xylenes. • DIPE, ETBE, TBA, and TAME using EPA Method 8260 and MTBE.using EPA Methods 8260 and 8020 were not detected in any of the soil samples collected from MW-8 to MW-12. • TPH-G was detected in the groundwater samples collected from 6 of the 11 monitoring wells at concentrations ranging from 210 to 81,000 ug/1. • BTEX constituents were detected in groundwater samples collected in 6 of the 11 wells at concentrations of up to 1.2 ug/l benzene,360 ug/1 ethylbenzene, and 100 ug/1 total xylenes. Toluene was not detected in any of the samples. • Analysis of groundwater samples using EPA Method 8020 detected MTBE in 8 of the samples collected from the 11 wells at concentrations ranging from 19 ug/l in MW-8 to 78,000 ug/1 in MW-3. Confirmation analysis of the samples using EPA Method 8260 detected MTBE at concentrations ranging from 23 ug/l in MW-8 to 82,000 ug/1 in MW-3. • The concentrations of MTBE in groundwater samples have increased from a high of 1400 ug/1 in February 1996 in Well MW-2 to 78,000 ug/l in Well MW-3 in September 1998. • Analysis of groundwater samples for other fuel oxygenates (DIPE, ETBE, TBA, and TAME) using EPA Method 8260 detected only TAME in the samples collected from Wells MW-1, MW-2, and MW-5 at concentrations of up to 710 ug/1. • Dissolved oxygen measured in the groundwater samples collected from each well ranged from 5.8 to 6.6 parts per million. 10