60 MGD Quarry Dewatering: Engineering Approaches to Reducing Karstic Discharge at a Cement Quarry In Eastern Pennsylvania

A high volume of groundwater has been upwelling through a distal part of a cement quarry floor in karstic eastern Pennsylvania since the mid 1990’s. Hydrogeologic investigations indicated that as much as 50% of the inflow was recharged by a creek bed located approximately one mile to the east. Requiring considerable O & M cost, the inflows are pumped back to the creek under a 60 mgd NPDES permit. Mitigation efforts for the creek-derived flow involve mine planning, regulatory, and engineering approaches. This paper focuses on engineering approaches to 1.) fill swallow-holes, 2.) line and restore two stream reaches identified as areas of significant stream loss and potential quarry inflow recharge, and 3.) construct an in-quarry grout curtain wall. Swallow-hole filling has historically followed two backfill approaches, impervious and inverted filters. Stream lining has consisted of multi-layer, flexible membrane liner systems utilizing both piped and channelized stream bypasses. Lining of the first reach reduced quarry inflows an estimated 10-15 mgd, and lining of the second reach reduced inflows by an estimated 5 mgd. The latest inflow mitigation measure, completed in 2008, consisted of an in-quarry 210-foot deep grout curtain wall just upgradient of the discharge area. The grouting program reduced inflows by an estimated 6-7 mgd. Flows will continue to re-adjust with time. Inflow mitigation has been encouraged by PADEP as means to reduce the high-volume quarry inflows and NPDES discharges, reduce stream loss, maintain creek flow and habitat, and reduce the incidence of sinkholes in the karstic creek valley vicinity. Estimated post-grouting quarry dewatering flow is approximately 51-52 mgd.