UCLA

Titration experiments and geochemical modeling can be performed to study the effects of pH on groundwater chemistry. This study focused on the effect of acidification on mineral dissolution to identify the type of mineral that is responsible for the buffering of pH in groundwater. The study site consists of arsenic- contaminated and uncontaminated regions of the saturated zone of an aquifer. Alkalinity titrations were carried out on contaminated and uncontaminated samples followed by geochemical modeling using PhreeqC Interactive 3.1.7-9213. Artificial groundwater was made for each site in the study region based on constituent data collected by the monitoring wells and then mixed with the associated sediment for 24 hours. During titration, samples were collected at each increment to be analyzed for metals and phosphate. Results show that calcite is likely to be the buffering mineral and the model determined that it is present at 10-6 to 10-4 moles per 2 liters of solution. This work will be incorporated into a larger model used to predict the transport of arsenic in groundwater under remediation schemes.