ARCHIVED REPORTS XR0001411 - Laserfiche WebLink

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�AMAWuAM Working to Restore Nature 4.2 Assessment of Groundwater 4.2.1 Groundwater Monitoring Well Construction To delineate the extent of dissolved hydrocarbons in groundwater and evaluate the groundwater gradient at and near the site, five groundwater monitoring wells (MW-1 through MW-5) were installed onsite in borings B-5, B-6, B-8, B-14, and B-16, respectively (RESNA, August 11, 1992 and RESNA, June 9, 1993) Two groundwater monitoring wells (MW-6 and MW-7) were installed offsite in borings B-20 and B-21 (RESNA, February 15, I 1994) Details on the construction of the wells are summarized in Table 3 and shown on the Logs of Borings (Appendix B) Well locations are shown on Plate 2 4.2.2 Quarterly Groundwater Monitoring RESNA began periodic groundwater monitoring at the site in May 1992 The purpose of groundwater sampling is to verify the extent of hydrocarbons in groundwater, monitor fluctuations in concentrations of dissolved hydrocarbons in groundwater, and monitor depth to water and the hydraulic gradient During the sampling events, a technician measured the depth to water, purged the wells, and then collected samples for subjective and laboratory analyses. A cumulative record of depth to groundwater measurements is presented in Table 4 Additional information on groundwater monitoring is discussed in our Reports 31009-4 (August 11, 1992), 31009-6 (January 7, 1993), 31009-6 (March 12, 1993), 31009-9 (June 9, 1993, September 14, 1993, November 1, 1993, and January 11, 1994) Copies of the Chain of Custody Records and laboratory reports for the water samples are in Appendix C. Our field methods for groundwater sampling are described in Appendix A. The monitoring wells were surveyed by a licensed land surveyor to provide the elevation of each wellhead relative to mean sea level A copy of the surveyor's map is included in 40 31009-10