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I PR06LEM ASSESSMENT REPORT 14800 West Frontage Road Manteca California The well was developed using a PVC bailer Well development water and rinse water was stored temporarily on site in DOT-approved 55-gallon drums, pending laboratory analysis of the groundwater samples Following receipt of the laboratory results, the water was transported, by a licensed hauler, from the site to an appropriate disposal facility 3.4 Drill Cuttings and Monitoring Well Purge Water All drill cuttings were stored temporarily on site, on and under plastic sheeting, pending laboratory analysis of samples required in order to determine proper disposal Following receipt of the laboratory results, the drill cuttings were transported, by a licensed hauler, from the project site to an appropriate disposal facility IPurge water generated during sampling of the well was stored temporarily on site in DOT-approved 55-gallon drums, pending laboratory analysis of the groundwater samples Following receipt of the laboratory results, the water was transported from the project site to an appropriate disposal facility I4.0 PROBLEM ASSESSMENT 4 1 Site Subsurface Conditions Monitoring wells MW-1 through MW-9 were installed to a maximum depth of 49 feet below ground surface During drilling of MW-9, the subsurface soils and alluvial materials of the unsaturated (vadose) zone were sampled at 5-foot intervals A log of the well was generated based on field descriptions, and is included in Appendix B Figure 2 shows locations of cross-sections A-A', B-B', and C-C' (Figures 4A, 4B, and 4C, respectively) As shown on the cross-sections, the first 10 to 15 feet of the subsurface I is silty sand Below the silty sand, to a depth of approximately 30 feet, are alternating layers of clay, silt, sand, silty sand, sandy clay, and clayey sands in varying thickness and horizontal extent A layer of sand occurs at approximately 30 to 40 feet below surface I (Figure 4A) This same layer of sand is present on the southern borders of the site, but is not present in MW-6 or MW-9 (Figures 4B and 4C) Beneath the sand to approximately 49 feet below surface is predominately silty clay and silty sand ISaturated soil horizons across the site were first encountered at approximately 30 to 35 feet below the surface I4 2 Distribution of Petroleum Hydrocarbons in Soil ' Figure 5 indicates the distribution of concentrations of TPH, as gasoline, in soil from 5 to 30 feet below surface As shown on the figure, the highest concentration of petroleum hydrocarbons in soil detected to date is located at the south end of the west dispenser ' island I90-097A PAR 7