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WELL HYDRAULICS 215
<br />of the water table or potentiometric surface does cause distortion of the cone of
<br />depression, making it more elliptical than circular.
<br />Flow in all regions of an aquifer is considered to be laminar. Some investigators
<br />have theorized that turbulent flow near a well could result in relatively high head
<br />losses. Laboratory and field tests show, however, that some departure from laminar
<br />flow near a well causes only small additional head losses (Mogg, 1959).
<br />Determining Aquifer Hydraulic Conductivity
<br />Equations 9.1 and 9.2 can be modified to calculate hydraulic conductivity if Q, H,
<br />and R are determined from a pumping test, and b is known from the driller's log. For
<br />an unconfined aquifer, the equation for calculating K is:
<br />K = 1055 Q log r, /r,
<br />(h2' - h,z)
<br />where
<br />r, = distance to the nearest observation
<br />well, in ft
<br />r, = distance to the farthest observation
<br />well, in ft
<br />h, = saturated thickness, in ft, at the
<br />farthest observation well
<br />h, = saturated thickness, in ft, at the
<br />nearest observation well
<br />All other terms are as defined in Equa-
<br />tion 9.1
<br />K
<br />Q log r, /r, ( 9.3 )
<br />1.366 A2 - hi 2)
<br />where
<br />r, = distance to the nearest observation
<br />well, in m
<br />r, = distance to the farthest observation
<br />well, in m
<br />h, = saturated thickness, in m, at the
<br />farthest observation well
<br />h, = saturated thickness, in m, at the
<br />nearest observation well
<br />All other terms are as defined in Equa-
<br />tion 9.1
<br />All the parameters on the right -hand side of Equation 9.3 can be determined from
<br />a pumping test. Two observation wells, located at distances r, and rZ from the pumped
<br />well, are required to determine h, and h,
<br />Figure 9.10 shows a sectional view of a pumping test layout in an unconfined for-
<br />mation for determining the hydraulic conductivity of the formation. All pertinent fac-
<br />tors are easily measured in this kind of test, and the hydraulic conductivity of the aqui-
<br />fer can be determined accurately.
<br />For confined conditions, the equation for determining the hydraulic conductivity
<br />from a test installation similar to Figure 9.10 is:
<br />K = 528 Q log r,/r,
<br />b (h; — h,)
<br />where
<br />all terms except the following are
<br />the same as for Equation 9.3
<br />b = thickness of the aquifer, in ft
<br />h, = head, in ft, at the farthest obser-
<br />vation well, measured from the
<br />bottom of the aquifer
<br />h, = head, in ft, at the nearest obser-
<br />Q log r2/r, K = 2.73 b (h, — h,) (9.4)
<br />where
<br />all terms except the following are
<br />the same as for Equation 9.3
<br />b = thickness of the aquifer, in m
<br />h, = head, in m, at the farthest obser-
<br />vation well, measured from the
<br />bottom of the aquifer
<br />h, = head, in m, at the nearest obser-
<br />
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