Groundwater sampling occurred over a three-year period after PRB installation. Sampling occurred weekly for the first 2 months of operation (6 monitoring events), biweekly during the next 4 months (8 events), monthly for the following 6 months (6 events), and a shortened sampling event (Fe(II) was the only parameter measured) in the 16th month of PRB operation. A sampling gap occurred over the next 7 months, followed by quarterly sampling during the final 13 months of operation (5 monitoring events).