Hvorslev (1951) developed the simplest slug test method in a piezometer, which relates the flow rate Q(t) at the piezometer at any time to the hydraulic conductivity and unrecovered head distance Ho — h in Figure 9.8.10 by

dt where F is a factor that depends on the shape and the dimensions of the piezometer intake. If Q = Qo at t = 0, then Q(t) decreases toward zero as time increases. Hvorslev defined the basic time lag To = ot2/FK and solved Equation 9.8(54) with initial conditions h = Ho at t = 0. Thus

When recovery H — h/H — Ho versus time is plotted on semilog paper, To is noted at t where recovery equals 37% of the initial change. For the piezometer intake length divided by radius, L/R greater than 8, Hvorslev has evaluated the shape factor F and obtained an equation for K as

Several other slug test methods have been developed for confined aquifers by Cooper et al. (1967) and Papadop-oulos et al. (1973). These methods are similar to Theis's in which a curve-matching procedure is used to obtain S and T for a given aquifer. Figure 9.8.11 shows the slug test curves developed by Papadopoulos for various values of variable a, defined as a = —— S r2

The obtained data are plotted and matched to the plotted type curves for a best match, from which a is selected for a particular curve. The vertical time axis t which overlays the vertical axis for Tt/rc = 1.0 is selected, and a value of T can then be found from T = 1.0^/^. Then, the value of S can be found from the definition of a. The method is representative of the formation only in the immediate vicinity of the test hole and should be used with caution (Bedient 1994).

The most commonly used method for determining hydraulic conductivity in groundwater investigation is the Bouwer and Rice (1976) slug test shown in Figure 9.8.12. Although it was originally designed for unconfined

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