Review of monitoring wells exhibiting elevated pH in F and H Area

Several of the monitoring wells installed at the Savannah River Plant in the past few years exhibit pH values of 8 or higher. These pHs are significantly higher than average values for the aquifers involved and are also higher than expected for natural waters. They are also inconsistent with observations in nearby wells. It is therefore suspected that the high pHs are not representative of true aquifer conditions. Two previous studies conducted at SRP (Price, 1984; Schreeder, 1986) conclude that high pH readings in M-Area monitoring wells and Z-Area piezometers are the result of contact between groundwater and grout. Price bases his conclusion on water chemistry. Schreeder`s evidence is the relationship between pH and amount of water withdrawn from the piezometers--an initially high pH drops as more water is removed. This conclusion is supported by laboratory measurements on water samples collected from cement-bentonite grout which show pH values of 13. This investigation was undertaken to evaluate contamination by grout and drilling fluid as a possible cause of elevated pH in monitoring wells at SRP and to develop techniques to rehabilitate the affected wells. FSB and HSB wells were used in this study