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c?"(0glcal recknles In' Page 2 3"Qum ter 2003 cliouiulwiiici Monitoring Report Piolmt No 507 2 Noveiiibei 13, 2003 ' issued apps ova I o I'the woi k plan in then September 10, 2003 letter The implementation of the work plain wiII be Scheduled pending cost pre-approval from the USTCFP ' 1 0 GROUNDWATER MONITORING 1.1 l lydi ogeology of Site ' The geology o[' the site is piedommately clays and sandy clays with lesser amounts of silts and sands The avei fate gioundwater elevation was--11 99 feet below msl on September 11, ' 2003, which coi i e5iponds to approximately 17 feet below grade surface (bgs) This elevation t epi esents tin dcci case of 1 12 feet since the June 24, 2003 monitoring event A gioundwatet gtadrent was calculated for the event and found to be flowing N49°E at 0 003 ' ft/tt This site consistently exhibits a flat groundwater gradient The gradient direction lot the September monitoring event is shown in Figure 2, and the ' hlstotleal gioundwatei diiections and gradients are shown in Figure 3, Groundwater Giadient Rotie Dingi ani The gioundwater elevation data are summarized in Table 1, Appendix A 'fable 5 pi ovides a summary of monitoring well construction The gioundwatei giachent is relatively flat and the direction of groundwater flow has varied during the Louise of the investigation As evident in Figure 3, groundwater exhibited a ' strong bifurcated flow regime to 2000, trending predominantly to the southwest or north- northeast at appioxuiititely 180-degice direction reversal Since the installation of wells ' MW-7 and MW-10 in May 2001, the direction bad been predominantly to the northeast The site is quite close to the San Joaquin River and tidal fluctuations may contribute to some of the obsei ved changes in groundwater direction ' Vertical Groundwatei 0taiients Under vertical gioiindwtatci flow conditions, the water level in a monitoring well is a 1 function of the length o I the well sci een and its depth or vertical position in the aquifer As with horizontal flow conditions, the diameter of the well or piezometer is immaterial ' The following procedure is used to calculate vertical groundwater gradient • Detcimine the vei tical distance between the two measuring devices by the distance from the mid-point between the top and bottom seal of the deep well (MW-109) and the mid- point between the gioundwater- elevation and the bottom seal in the shallow well (MW- 9) ' • Measure the head in both wells used in the calculations if the lateral distance between the well pair is greater than a few feet, then calculations must be made to collect the down-giadient piezometric head to account for the sloping