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' Gecfogwa(Te_cfriucs inc Page 2 Groundwater Monitoring Report ' Project No 724 2 December 21, 1999 ' 1.0 GROUNDWATER MONITORING ' 1.1 Hydrogeology of Site September 22, 1999 the top casing for each monitoring well was surveyed in City of ' Stockton Benchmark (BM #H) by Spencer Land Surveying The groundwater elevations on Table 1 were recalculated for the new top of casing elevations to allow for comparison among earlier events ' A site-specific groundwater gradient and bearing was calculated from the depth to water measurements taken during the groundwater monitoring The gradient was 0 0019 ft/ft ' flowing S85°E The average elevation of groundwater under the site was —17 73 feet below mean sea level The water level has risen over 22 feet at the site since October of 1992 ' Depths to water were approximately 33 feet bgs Figure 2 is a groundwater gradient map for the November 16, 1999 event ' Table I in Appendix A contains the groundwater elevations and gradients for all events back to October 1992 It is noted that historically groundwater gradient has flowed predominately ' to the NE, while this monitoring event is towards the SE 1.2 Groundwater Sampling Procedure On November 16, 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 event, a hydrocarbon sheen of droplets was observed on the water purged from MW-2 Stagnant water in the well casing was purged using a purger pump as recorded in the field logs (Appendix C) The rate of well purging was monitored The wells were purged of at least three casing volumes until the groundwater parameters (temperature, conductivity, and pH) had stabilized (Appendix C) This indicated that water, representative of actual aquifer conditions, was entering the well Groundwater parameter stabilization was characterized by three successive readings within 10% IBefore a sample was collected, the wells water level was allowed to recharge to at least 80% of the initial level All water removed from the monitoring well and not used as a sample, ' was placed in a 55 gallon DOT (Department of Transportation 17-H) approved container that is properly labeled and temporally stored on-site I