Electric logs provide a means of estimating ground-water quality in ar
eas where water analyses are not available. Most of the methods for in
terpreting these logs have been developed for the petroleum industry a
nd are most reliable in saline aquifers (concentration of dissolved so
lids as sodium chloride greater than about 50,000 mg/l). The resistivi
ty-porosity and spontaneous-potential methods were evaluated to determ
ine if they could be applied to identify zones of fresh water (concent
ration of dissolved solids as sodium chloride less than 1,000 mg/l) in
three potential aquifers in central Wyoming. The potential aquifers h
ave different lithologies-sandstone, clayey sandstone, and carbonate.
The two methods generally were reliable predictors of water quality in
the sandstone and carbonate potential aquifers. In the clayey sandsto
ne potential aquifer, predictions of the dissolved-solids concentratio
n using the two methods differed by more than an order of magnitude in
several cases. When the resistivity values are corrected for the pres
ence of clay and shale as identified on a natural gamma log, the agree
ment between the results of the two methods improved by an average of
58 percent.