ARCHIVED REPORTS_SEPARATE PHASE HYDROCARBON INVESTIGATION UNOCAL EXTRACTION WELL PILOT STUDY 2011

Home Browse Search

Stantec Report of Findings for the Waterfront Towers Separate Phase Hydrocarbon Investigation . and Unocal Extraction Well Pilot Study Waterfront Towers Parking Lot March 4, 2011 As with GWE-1, GWE-2 was advanced using an HSA rig to a depth of approximately 19.5 feet bgs using 12-inch augers. Soil samples were recovered for lithologic logging at approximately five-foot intervals. GWE-2 was completed to approximately 17.5 feet bgs with four-inch diameter Schedule 40 PVC. Pre-manufactured 0.010-inch slotted casing was installed from 17.5 to 10 feet bgs. The well annulus was backfilled from 19.5 to 15.5 feet bgs with Monterey #3 Sand, from 15.5 to 9.5 feet bgs with 3/-inch pea gravel, and from 9.5 to 7.5 feet bgs with hydrated bentonite chips. Neat cement grout seal was installed from 7.5 feet bgs to ground surface, with a traffic rated vault installed at the surface. Logging of soils during advancement of GWE-1 and GWE-2 was performed to analyze and record the encountered lithology in each boring under the direction of a California Professional Geologist and using the USCS and standard geologic techniques. Because these borings were advanced into an area of the UOU that was previously excavated and backfilled, soils were logged based on cuttings. Encountered soils consisted of non-native backfill, observed from ground surface to approximately ten feet bgs. From 4.5 to 9.5 feet bgs fill soils were further defined as lean clay; and from 9.5 to 17.5 feet bgs 2" minus drain rock was encountered. Groundwater was encountered at 12 feet bgs. Well construction logs are included in Appendix D. • 4.2.3 Well Development On August 9, 2010, the GWE wells were developed. Development was accomplished by surging each well with a vented surge block and bailer. Final purging was performed with a submersible pump to remove approximately ten casing volumes. Temperature, pH, and conductivity were measured at regular intervals during purging. Development was considered completed after physical-chemical parameter trends stabilized over at least three consecutive measurements (<0.05 variability in pH, 3% variability in conductivity, and 10% variability in temperature). Well development field data sheets are included in Appendix D. 4.2.4 Well Surveying On January 27, 2011, Stantec used a licensed professional engineer to survey the newly installed GWE wells, GWE-1, and GWE-2, for geologic purposes and to tie the elevations of the new wells in with existing wells at the Site. The measurements were obtained from conventional survey and GPS techniques using NAVD 88 Datum and NAD 83 Datum. A copy of the Stantec survey data is included in Appendix J. 4.2.5 Investigation Derived Waste Decontamination rinsate, purge water, and soil cuttings generated during the GWE well installation activities were temporarily stored in DOT approved 55-gallon capacity steel drums. The drums were transported by BESI to a licensed disposal facility. The waste data forms for the drums are included in Appendix F. 4.6