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' Mr. Marty Hartzell February 16, 2001 Page 6 of 8 ti depth of approximately 40 feet, where TPHg at 1.4 ppm was detected in boring SB3, located approximately 13 feet southeast of boring SB 1. SB 1 was presumed to be the approximate center of the source area and SB3 was presumed to be the lateral limit of contamination at that depth. Subsurface was divided into five zones and radii impact in these zones were estimated based upon soil type and concentration at the source (SBI) within each zone. Accordingly, the approximate zones of contamination and estimated radii of impact are as follows: . ' Zone 1: 13-23 feet bgs; silt underlain by sand, radius of approximately 6 feet. Zone 2: 23-38 feet bgs; clay/silt underlain by sand,radius of approximately 10 feet. Zone 3: 38-43 feet bgs; silt, radius of approximately 13 feet. Zone 4: 43-48 feet bgs; sand and silt, radius of approximately 10 feet. Zone 5: 48-60 feet bgs; clay and silt,radius of approximately 10 feet, low level xylenes only. ' The mass of residual contaminants in the soil was calculated using the following equation: mass of analyte in soil= (avg conc. in mg/kgx 10-)(bulk density in kg�ft3)(vol. affected soil in ftp) ' The average concentration used in the calculation for each zone of contamination is equal to '/i of the detected concentration at the source, or 1/2 the detection limit (in essence the average of highest ' and lowest(non-detect) concentration in each zone). Contaminant Total Mass in Vadose Zone k Avg. Conc. in Vadose Zone (rng/kgj MTPHd 25 54 TPHg 2068 4515 Benzene 5.4 12 ' Toluene 56 121 Eth lbenzene 52 113 X lenes 256 407 Details of mass calculations are presented in Attachment 3. 5.0 SUMMARY Soils found at the site can generally be characterized as interbedded layers of sand, silt, and clay. Fine grained soils consisting of predominantly clay with some silt extended to approximately 13 to ' 18 feet bgs; sand with some clay was encountered from approximately 13-18 feet bgs to approximately 38 feet bgs, and alternating beds of silts and clays were encountered from approximately 38 feet bgs to at least 60 feet bgs, the maximum depth explored. Groundwater was first found at a depth of 60 feet bgs. Strong petroleum hydrocarbon odors were noted in boring SBI at a depth of approximately 40 feet ' bgs, moderate odors were noted at depths of 15 feet and 25 feet bgs, and slight odors were noted at depths of 20, 30 and 45 feet bgs. Slight odors were detected in only one sample collected from boring SB3 (40 feet bgs), but no odors were detected in any samples collected from borings SB2 or detslgrounulgonzslee�swnrpt.doc