3 August 1998
B-2. SITE SELECTION. Figure B-1 has been prepared from a U.S.G.S. topographic map.
Contours, drainage and land use have been shown but vegetation has been omitted for clarity.
The well must be located within the site boundary for security and to minimize the length of
pipelines. Since the existing towns use the river plains area as a source of ground water, the
flatland in the northeast has been chosen as a site for test drilling. It has good potential for
recharge from the surface drainage and from the river. Available records indicate the 100 year
flood level to be approximately at elevation 675 feet; therefore, the site is not subject to
flooding. Three test wells were driven in the locations shown on figure B-1 and indicated by
PW (pumping well), W1 and W2 (observation wells). A cross section of these three wells is
represented by figure 5-3. The depth to the bottom of the aquifer is found to be 150 feet.
Depth to static water level is 100 ft. A pumping test gives the following data.
= 200 gpm
= 50.0 ft
= 47.5 ft
= 300.0 ft
= 49.0 ft
Calculate aquifer permeability using equation 5-3
1055 Q log (r2/r1)
(h22 - h12 )
(1055) (200) log (300/50)
(49.02 - 47.52)
B-3. SIZE THE WELL.. A yield of 350 gpm is required. Table 5-3 indicates that a pump of 6-
inch diameter will be required and the smallest well casing (and screen size) should be 8
inches. (Current pump manufacturers and screen manufacturers literature should be reviewed
to confirm this.) Assuming R = 1000 ft. and a maximum drawdown of 15 ft. as depicted in
figure 5-4, calculate the available yield:
P (H2 - h2)
1055 log (R/r)
(1134) (502 - 352)
(1055) log (1000/.33)