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Canepa s Car Wash 6230 Paufic Avenue,Stockton,CA Second Quarter Groundwater Monitoring Report,April 2005 Page 3 of 10 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 April 13, 2005 indicate a groundwater gradient generally toward the northwest (consistent with histone gradients) but with a localized gradient toward MW-1 (cone of depression) MVA'-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 April 13, 2005, indicated a relatively small radius of influence (apparently measurable to a radius of less than 25 feet) because it was measured approximately 6 days after the pumping was re-initiated following a down period of approximately 36 days The treatment system had been off for the 36 days prior to the monitoring event to repair a failed drain line The small cone of depression, therefore, is partly the result of insufficient time for the cone of depression to expand Th cone of depression measured on April 13, 2005 was larger than that measured during the previous quarter In addition, the pumping rate, once the pumping was re-initiated, was at a reduced rate of approximately 4 9 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 0052 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 MWA, decreased (increase in groundwater elevation) by approximately 0 62 feet since January 21, 2005 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-2 through MW-7 were below the water table, consistent with much of the monitoring history at the site Table 2 Groundwater Elevation Data (April 13,2005) Well Casing Screen Well Collar Depth to Water Groundwater WELL Interval (feet-bgs) Elevation' (feet) (feet) Elevation feet MW-1 50-70 1548 4696 -3148 MW-2 50-70 1529 3848 -23 19 MW-3 50-70 15 53 39 18 -2365 MW-4 50-70 15 83 3952 -2369 MW-5 50-70 1471 3854 -23 83 MW-6 45-65 1489 3747 -2258 MW-7 45-65 1580 3852 -2272 MW-9 25-45 1484 3862 -2378 MW-10 25-45 1472 3763 -2291 MW-11 25-45 15 12 3832 _2320 MW-12D 100-110 I4 99 3758 _2259 Well Col:ar Elevations are measured from a mark on the top of the well casing and are referenced to NGS benchmark HS0391 using NAVD 88 _datum—_ — • bgs=below ground surface �� CONDOR