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' GeologEcaf7echnus inc Page 2 Groundwater Monitoring Report ' Project No 723 2 December 6, 1999 ' 1.0 GROUNDWATER MONITORING ' 1.1 Hydrogeology of Site On September 21, 1999, the tops of casing elevations were surveyed into the City of Stockton ' Benchmark, BM#20 by Spencer Land Surveying Table 1 shows the new top of casing elevations and the groundwater elevations for previous monitoring events were normalized to the new elevations to allow for comparisons A properly scaled site map was also prepared ' A site-specific groundwater gradient and bearing was calculated from the depth to water measurements taken during the groundwater monitoring The gradient was 0 0202 ft/ft ' flowing N850E This is the second event where a site specific groundwater gradient was calculated A three-point problem was used on MW-4, MW-5 and MW-6 because these three ' wells are constructed relatively similar in regards to depth of screen interval The average elevation of groundwater under the site was —17 74 feet below mean sea level Depths to water ranged from 27 7 to 28 6 feet bgs ' Figure 2 is a groundwater gradient map for the September 13, 1999 event ' This is the first event where the deep discretely screened well, MW-101, was monitored A shallow well was not installed next to MW-101 so a vertical gradient cannot be calculated, however the groundwater head is lower in MW-101 then the shallower wells so it appears that there is a downward vertical gradient at the site Table I in Appendix A contains the groundwater elevations and gradients for the site 1.2 Groundwater Sampling Procedure On September 13, 1999, Del-Tech Geotechnical Support personnel arrived on-site, opened the wells, and measured the depth to water with an electrically actuated sounding tape The water level reading was recorded to an accuracy of 0 01 foot In wells where free floating product was suspected, a clear disposable bailer is used to gauge the interface During this monitoring no free product was noted, however sheen was observed in MW-3 Stagnant water in the well casing was purged using a Waterra pump as recorded in the field logs' (Appendix C) The rate of well purging was monitored The wells were purged of approximately three casing volumes and until the groundwater parameters (temperature, conductivity, and pH) had stabilized (Appendix C) indicating that water, representative of actual aquifer conditions, was entering the well Groundwater parameter stabilization was Icharacterized by three successive readings within 10%