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I ' Site Background Information Sierra Lumber Manufacturers (Case #2) Page 2 of 3 the estimated depth to ground water at the site is approximately 20 feet below surface grade (bsg) ' Review ofLrnes of Equal Elevation of Ground Water Spring 1999(FCD&WCD)shows the regional ground water flow direction toward the northeast However, based on data collected during recent ground water monitoring events conducted at the site,ground water flow appears to fluctuate toward ' the northeast and southwest, flow direction vary due to local recharge and discharge patterns Review of historical depth to ground water maps (FCD&WCD) dating back to 1971 suggests that ground water depth near the site has fluctuated between 15 feet and 50 feet bsg, though in recent ' ground water monitoring events, ground water is encountered at approximately 20 feet bsg ' PREVIOUS INVESTIGATIONS In June 2004, a series of soil borings were advanced at the site by Alta EM, Inc (AEI) as part of a tproperty transfer Three soil borings (Alta-B3, Alta-B7, and Alta-B8) were advanced near the southeast corner of the Plant#2 building, in the area of a former underground storage tank (UST, Tank Area B) Petroleum hydrocarbons were detected in soil and ground water samples collected from the boring advanced within the presumed former tank pit excavation Total petroleum hydrocarbons quantified as gasoline (TPH-g) and volatile aromatic compounds benzene, toluene, ethylbenzene, and total xylenes (BTEX) were detected in soil samples at concentrations as high as 4,920 milligrams per kilogram (mg/kg) TPH-g and BTEX were detected in a grab ground water sample collected from boring Alta-B3 at concentrations as high as 400,000 micrograms per liter (µg/1)and 25,300 µg11, respectively The approximate locations of the borings advanced and sampled ' by AEI are illustrated on Figure 2 Analytical results of borings Alta-B3, Alta-B7, and Alta-138 are summarized in Tables 1 and 2 of this appendix ' On 29 March 2005, three ground water monitoring wells (MW-9 through MW-1 l) were installed at the site Pilot borings MW-9 through MW-I I. were completed as ground water monitoring wells ' of the same designations using 2-inch diameter, Schedule 40 polyvinylchloride(PVC)casing with a 0 020-inch slotted screen installed from 20 feet to 40 feet bsg TPH-g was detected in soil samples MW9-25, MW9-30, MW9-35, and MW9-40 at concentrations ranging from 14 mg/kg to ' 2,400 mg/kg BTEX compounds were detected in samples MW9-25, MW9-30, MW9-35, and MW9-40 at maximum concentrations in sample MW9-35 of 17 mg/kg toluene, 59 mg/kg ethylbenzene, and 352 mg/kg total xylenes Analytical results of monitoring well installation soil samples are included in Table 3 of this appendix ' STRATIGRAPHY In general, silty clay, clayey silt, and sandy silt were encountered from surface grade to between ' 20 feet and 25 feet bsg From approximately 25 feet bsg to the total depth of borings MW-9 through MW-11 (40 feet bsg) sand, silty sand, sandy silt, and silt were encountered Saturated soil was not • observed in recovered soil samples until a depth of 25 feet bsg Advanced GeoEnvironcnental,Inc 1