ARCHIVED REPORTS_XR0006239 - Laserfiche WebLink

Home Browse Search

where ' T = transmissivity (ml/sec) (approximately 200 ft2/day from Table 3) t = time of pumping (sec) (11 hours) S = specific yield (average of 0.08 from Table 3) ' Judging from the results of this pumping test, the individual radius of influence for each well, pumped at a rate of 3 gpm, will be between 60 and 100 feet when observed after 11 hours of ' testing For transmissivity of 200 W/day, R would be 15 5 m (51 feet) as observed at RW3. Be- cause the groundwater elevation not only did not stabilize in the pumped well RW 1, but actually ' fell at a rate of about 0 05 feet every 10 minutes, the actual radius of influence is expected to grow with time as it is expected for unconfined aquifers ' Determination of a Capture Zone The capture zone for a pumped well can be defined by calculating the distance to the downgradi- ent point of groundwater flow stagnation induced by pumping The distance r to the downgradient point of stagnation is ' r = Q Y and Tsun/27ETI (Keel 1983, Javandel and Tsang 1986) g where Q = pumping rate, 16 m3/day ' T = transmissivity, 19 m2/day I = hydraulic gradient, 0.008 ' r = 16 7 m (55 feet) For three wells pumping 16 m3/day, the stagnation point would be at an approximate distance of 50 m (165 ft) in a downgradient direction Crossgradient extent of the capture zone for three wells will be D = Q/nTI (Todd 1980) D = 100 m (330 feet) Upgradient extent of the capture zone is Q/TI, i e , 315 m (1,040 feet) ' To simplify further calculations it is assumed that three recovery wells, RW 1, RW2, and RW3, are spaced along the straight line perpendicular to groundwater flow direction To check if the aquifer can support such a pumping rate, the Cooper-Jacob equation is used to calculate the drawdown in the middle well, RW3, as follows s = 2.3Q/47rT[log(2 25Tt/r2S) + 2log(2 25Tt/d2S)] vWws6n39a,zrd9i/m 7