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- . GeolagualTecltnicsCnc. Page 8 Dual Phase Extraction Pilot Test Report Project No.723.2 November 5,2004 4.2 Groundwater Extraction e NOTE: GTI intended to prepare time draw down graphs to document response to groundwater extraction. But a problem was encountered in using the Solinst Leveloggers® (Leveloggers) to record depth to groundwater in the wells. A week before the test, Solinst 1 Canada called GTI to inform us that their 30' range Leveloggers would not be available for the test and would 15' range models work? Not expecting a 15' drawdown in surrounding wells, GTI said yes that the 15' models would suffice. The 15' models were delivered and placed in the wells for the test. Unfortunately, the probes were set at the base of the shallow 7 wells that left them approximately 18—35 feet below the water table. After the fact we found out that the 15' model Leveloggers need to be within 15 feet of the water table otherwise the x water pressure exceeds the measurement capacity of the probe. Because the water column h height exceeded the range of the instrument, the probes registered a straight line trace with no groundwater drawdown measured(see Appendix D for Levelogger graphs). This problem was caused by a misinterpretation of the measurement range limitation of the instruments versus the water column height limitation of the instruments. Had Solinst Canada provided the original equipment to specifications (30' range) the problem still would have been encountered in well MW-1 since its base (70 feet bgs) was over'30 feet below the water table (37 feet bgs). In retrospect, the probes should have been suspended in the wells several feet below the initial water table depth since a significant draw down (>15 feet) was not expected. `Manual measurements of water depth were taken from well VEW-1 during groundwater pumping initialization in EW-1 and these data will be discussed in greater ' detail below. The dual phase extraction equipment removed soil vapor and groundwater together through t the same stinger hose. In this fashion the water could not be metered to measure the extraction rate. The extracted water was contained in a tank on the treatment trailer until the + tank's upper limit switch was activated by the rising water level. Upon activation, a pump would transfer-the water through a meter and into the 5200 gallon tank trailer supplied by American Valley. GTI staff monitored the transfer meter and used the data to determine pumping rates by dividing the gallons pumped by the elapsed time. Table 4 in Appendix A contains the groundwater pumping rate data. In addition, GTI performed field estimates of pumping rates utilizing a calibrated tube on the trailer's holding tank. The volume between two calibration marks was divided by the time required to fill the tube between the marks to produce the pumping rate. These data are included in Table 4 in the"field est. rate"column. The calculated groundwater extraction rates from-EW-1 varied 3.0— 6.2 gpm on the first day of the pumping test-Tuesday, July 27th. By 8:90 A.M. on the next day, the rates had fallen to less than 1 gpm and then the well essentially went dry by 9:09 A.M. At this point the stinger was lifted from 50 feet bgs to 39 feet bgs to allow the well to stabilize. Water started flowing again and GTI staff determined by trail and error that a stinger level of 47 feet bgs was' e optimal. It is presumed that the stinger depth controls vapor movement in the well and pneumatic effects can clog the well screen and inhibit water flow. Mako staff confirmed that 4.d .v