Quantification of acid loads and delineation of hydrochemical facies at a phreatic mine spoil aquifer

Abstract

Acid mine drainage geochemistry and in situ alkaline injection were investigated at the DLM coal mine, Alton West Virginia. These included spatial and temporal investigations into hydrochemical controls that were initiated with reclamation efforts. Approaches included the delineation of hydrochemical facies and analysis of time series data to develop a methodology for estimating acid loads. Results of agglomerative hierarchical clustering were mapped to demonstrate spatial variations in response to reclamation efforts over time. Spatial patterns were determined and indicate that aquifer chemistry continued to evolve during the study period. Results confirmed that injection of alkalinity into the aquifer effected acid producing and neutralizing reactions in monitoring wells down gradient from the injection site. Low-frequency water chemistry was interpolated with natural cubic splines, resampled and multiplied by high-frequency flow to produce estimates of acid loads at high-frequency. Cross-correlation between high-frequency and low-frequency datasets showed an exponential decrease in correlation as the number of days between flow measurements increased. Result confirmed that natural cubic splines can be used for resampling hydrochemical time series data and the frequency at which flow is measured limits the accuracy of acid load estimates.