Holcim USA Inc. operates a cement manufacturing plant and associated quarry near the town of Holly Hill, SC.  Recently, as quarrying has continued, the moisture content of the quarried limestone has been increasing to a level that exceeds optimum.  Consequently, Holcim USA Inc. is interested in evaluating proactive ways by which the moisture content of the quarry limestone can be reduced by dewatering the limestone prior to it being quarried.  

The Earth Science and Resources Institute at the University of South Carolina (ESRI-SC) was contracted by Holcim USA Inc. to perform geological and hydrogeological studies to best characterize the hydrogeological properties of the shallow groundwater system.  To better understand how the groundwater system behaves ESRI-SC performed the following tasks in 2008. 

We continued monitoring shallow groundwater levels via quasi continuous data loggers and hand measurements 15 observation wells throughout the study area.  Hydrographs of each well were created for analysis resulting in physical evidence of trench dewatering effectiveness.  Three observation wells were consumed by the quarry during 2008. 

On March 11th we installed a continuous recording rain gauge for onsite accurate precipitation data for use in the on-going study including the consideration of groundwater recharge studies.  Monthly bar charts were created showing daily rain events for comparison to observation well hydrographs. 

An analysis and comparison of hydrographs inside the trench boundary versus outside the trench boundary was conducted to study the effectiveness of the trench in the dewatering strategy.  Physical evidence of this was spatially represented via observation well hydrographs imposed on an aerial photograph.   

We also conducted a thorough investigation showing physical evidence of dewatering predominately due to trenching versus drought.   This was evidenced by analysis of precipitation and a comparison of observation wells H-2S and H-9. 

Throughout the year, we conducted several experiments and data gathering exercises pertaining to understanding the spatial distribution of pH and electrical conductivity (EC) of Unit 1 groundwater at the Holcim USA, Inc. Holly Hill, SC quarry. The results of these analyses help demonstrate the effect of the trenching on Unit 1 groundwater and, as a result, the diminished influence Home Branch Diversion has on Unit 1 groundwater.  

Over the summer of 2008, a wellbore fluid displacement study was conducted using a brine solution injected into one of the observation wells.  Raw test data were fitted to a simulated displacement curve resulting in an estimate of the hydraulic conductivity equal to 1.2 ft/day (isotropic) and the specific yield equal to 0.2.  Surface electrical resistivity and well to well breakthrough studies were simultaneously performed with the displacement test to better characterize the shallow groundwater flow properties.   

In the fall of 2008, ESRI-SC participated in the extraction of five limestone cores to provide better in-situ estimates of moisture content of Unit 1 limestone (Plate 3).  Results of the moisture content are crucial to improving the predictive ability of the groundwater flow model.  Improving the prediction of the groundwater response to the existing trench system and any future trenching scenarios is dependent on understating the in place moisture content and how it varies spatially.