Question

The drawdown doserved at a confined aquifer well after pumping it during 1400 minutes at a flow rate of 500 gal/min is 20.39 ft. The drawdowns observed at the same time at two observation wells located at 10 ft and 100 ft from the pumped well are 20 and 19.7 ft, respectively. Find the transmissivity of the aquifer and the well radius. Answ: T-8.8x105 gpd/ft, r-0.5 ft. 3.

Answer 1

Given rightarrow confined aquifer s_w = 20.39 ft = > r_w = ? Q = 500 gal/min = 500/(1/60 times 24) gal/day = 500 times 60 times 24 gal/day Q = 720000 gal/day s_1 = 2 0ft = > r_1 = 10 ft s_2 = 19.7 ft = > r_2 = 100 ft for confined aquifer = > Q = 2 pi T (s_1 - s_2)/ln (r_2/r_1) where T = transmissivity s_1, s_2 = Draw downs at observation wells r_1, r_2 = radial distances of observation wells 720000 = 2 pi times T (20 - 19.7)/ln (100/10) 1657861.267 = 2 times pi times T (0.3) T = 879522.7 gpd/ft T = 8.79 times 10^5 gpd/ft T = 8.8 times 10^5 gpd/ft = > Q = 2 pi T(s_w - s_1)/ln (r_1/r_w) = > 7.2 times 10^5 = 2 times pi times 8.8 times 10^5 (20.39 - 20)/ln (10/r_w) = > ln(10/r_w) = 2.99 = > 10/r_w = e^2.99 = > r_w = 10/19.88 = > r_w = 0.5 ft