BUREAU OF. GEOLOGY
TABLE 1
Estimated values of hydraulic conductivity and specific storage for porosities ranging from 10 to 50 percent.
percent porosity
S s specific storage, ft"1
K hydraulic conductivity, ft day"1
0 K Ss
10 4.3 x 104 2.0 x 10-7
20 8.6 x 104 4.1 x 10-7
30 1.3 x 105 6.1 x 10-7
40 1.7 x 105 8.2 x 10-7
50 2.1 x 105 1.0 x 106
60 2.6 x 105 1.2 x 10-6
70 3.0 x 105 1.4 x 10.6
80 3.4 x 105 1.6 x 10-6
90 3.9 x 105 1.8 x 106
A method suggested by Bredehoeft (1967, p. 3083), was also used to estimate specific storage and porosity. The method assumes that Poisson's ratio for the aquifer is known. The specific storage was calculated to be 1.4 x 10"7 ft-, based on the assumption that the earth tide component (0.13 ft) at the well is equal to the change in head produced by the tidal dilitation at the earth's surface (At) and on other assumptions used by Bredehoeft (1967, eq. 25). The porosity of the aquifer was calculated to be 7 percent using equation 9; and the hydraulic conductivity was calculated to be 3.0 x 104 ft/day"1 using equation 10.
A comparison of values of K and Ss for 50 percent porosity (table 1) with the values derived by the Bredehoeft method suggests that a 15-foOt thick aquifer with 50 percent porosity is hydraulically equivalent to a 105-foot thick aquifer with 7 percent porosity. Therefore it is conceivable that the true values of hydraulic conductivity and specific storage for-the aquifer could range between those for 7 percent porosity and 50 -percent porosity, depending upon the thckness of the permeable zone. In-the author's opinion, the-physicalsituation supports the values for a 15-foot thick aquifer. -