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al � Canepa s Car Wash 6230 Pacific Avenue,Stockton,CA First Quarter Groundwater Monitoring Report,January 2005 Page 3 of 8 GROUNDWATER ELEVATIONS AND GRADIENT Groundwater elevation contours estimated for the shallow monitoring wells (MW-1, MW-2, MW-4, MW-5, MW-6, MW-7, MW-9, and MW-10) on January 21, 2005 indicate a groundwater gradient generally toward the northwest (consistent with historic gradients) but with a localized gradient toward MW-1 (cone of depression) MW-1 is currently used as the primary groundwater extraction well for the treatment system (Figure 2, Attachment A) The cone of depression around MW-1 on January 21, 2005, indicated a relatively small radius of influence (apparently measurable to a radius of less than 20 feet) because it was measured approximately 20 hours after the pumping was re-initiated following a down period of approximately 10 days The treatment system had been off for the 10 days prior to the monitoring event to repair a failed ring compressor The small cone of depression, therefore, is partly the result of insufficient time for the cone of depression to expand In addition, the pumping rate, once the pumping was re-initiated, was at a reduced rate of approximately 3 5 gallons per minute (down from a maximum rate of approximately 6 gallons per minute) The pumping rate, following the repair, was reduced because of scaling Subsequent efforts have been made to reduce the scaling and return the system to optimal performance An estimated groundwater gradient of 0 0051 ft/ft towards the northeast was measured using water level data from monitoring wells MW-6 and MW-9 MW-6 and MW-9 are upgradient and down-gradient, respective to MW-1, and were outside the radius of influence of the cone of depression formed by groundwater extraction activities in MW-1 during the monitoring event The average depth to groundwater measured in the shallow monitoring wells for this event, excluding MW-1, decreased (increase in groundwater elevation) by approximately 1 64 feet since October 14, 2004 A hydrograph of historic groundwater elevations is attached as Figure 3 It should be noted that the top of the well screens for shallow monitoring wells MW-1 through MW-7 were below the water table, consistent with much of the monitoring history at the site Table 2 Groundwater Elevation Data (January 21, 2005) WELL Well Casing Screen Well Collar Depth to Water Groundwater Interval (feet-bgs) Elevation' (feet) (feet) El nation fe MW-1 50-70 1548 4527 -2979 MW-2 50-70 1529 3907 -2378 MW-3 50-70 1553 3984 -2431 MW-4 50-70 15 83 4011 -2428 MW-5 50-70 1471 39 17 -2446 MW-6 45-65 1489 38 13 -2324 MW-7 45-65 15 80 3920 -2340 MW-9 25-45 1484 3925 -2441 MW-10 25-45 1472 38 19 -2347 MW_1125-45 15 12 3870 -2358 MW-12D 100-110 1499 3833 -2334 ` Well Collar Elevations are measured from a mark on the top of the well casing and are referenced to NCS benchmark HS0391 using NAVD 88 datum bgs=below ground surface �� CONDOR