ARCHIVED REPORTS_PRELIMINLARY SUBSURFACE INVESTIGATION

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Preliminary Subsurface Investigation City of Stockton, former Westem Pacific Railroad Property,Stockton, CA May 27, 1992 W0601.1D soil borings were backfilled with native soil at the site. To avoid cross-contamination, drilling augers were steam-cleaned before drilling each borehole. Drilling was conducted by Spectrum Exploration (Stockton, CA), using a hollow-stem auger drill ' rig. A field geologist was present to observe the shallow borings and log all drill cuttings and soil samples utilizing the Unified Soil Classification System from the three monitoring wells. Descriptions of soil types encountered, sample collection intervals, and well construction details were recorded on the well logs for the three wells and are included in Appendix C. Cored soil ' samples in borings MW-1 through MW-3 were collected above and below the water table at 5- foot intervals, to total depth of the boring, and in accordance with the site Soil Sampling Protocol (Appendix A). The soil sample collected at five feet below grade in each boring was submitted for laboratory analysis. The earth materials encountered at the site during this investigation consisted of silts and clays with sand lenses (Appendix C, Boring/Well Logs). Groundwater was first encountered in the borings at a depth of approximately 26.5 feet below ground surface. 1 4.2 Groundwater Monitoring Well Installation The monitoring wells (MW-1, MW-2, and MW-3) were constructed of 4-inch diameter F480 PVC well screen/casing and completed as shown on Figure 6. A well screen slot size of 0.010- inch and a Lone Star 2/12 sand was used as the filter pack. Neat cement was used to seal the ' well, in accordance with San Joaquin County and California Department of Water Resources guidelines. To protect the integrity of the well, a locking, water-tight well plug was installed ' on the well and a locking steel well monument was concreted over the well. R041392.SAY 8