Simulation of Reclaimed-Water Injection and Pumping Scenarios and Particle-Tracking Analysis near Mount Pleasant, South Carolina

Abstract

The effect of injecting reclaimed water into the Middendorf aquifer beneath Mount Pleasant, South Carolina, was simulated using a groundwater-flow model of the Coastal Plain Physiographic Province of South Carolina and parts of Georgia and North Carolina. Reclaimed water, also known as recycled water, is wastewater or stormwater that has been treated to an appropriate level so that the water can be reused. The scenarios were simulated to evaluate potential changes in groundwater flow and groundwater-level conditions caused by injecting reclaimed water into the Middendorf aquifer. Simulations included a Base Case and two injection scenarios. Maximum pumping rates were simulated as 6.65, 8.50, and 10.5 million gallons per day for the Base Case, Scenario 1, and Scenario 2, respectively. The Base Case simulation represents a non-injection estimate of the year 2050 groundwater levels for comparison purposes for the two injection scenarios. For Scenarios 1 and 2, the simulated injection of reclaimed water at 3 million gallons per day begins in 2012 and continues through 2050. The flow paths and time of travel for the injected reclaimed water were simulated using particletracking analysis. The simulations indicated a general decline of groundwater altitudes in the Middendorf aquifer in the Mount Pleasant, South Carolina, area between 2004 and 2050 for the Base Case and two injection scenarios. For the Base Case, groundwater altitudes generally declined about 90 feet from the 2004 groundwater levels. For Scenarios 1 and 2, although groundwater altitudes initially increased in the Mount Pleasant area because of the simulated injection, these higher groundwater levels declined as Mount Pleasant Waterworks pumping increased over time. When compared to the Base Case simulation, 2050 groundwater altitudes for Scenario 1 are between 15 feet lower to 23 feet higher for production wells, between 41 and 77 feet higher for the injection wells, and between 9 and 23 feet higher for observation wells in the Mount Pleasant area. When compared to the Base Case simulation, 2050 groundwater altitudes for Scenario 2 are between 2 and 106 feet lower for production wells and observation wells and between 11 and 27 feet higher for the injection wells in the Mount Pleasant area. Water budgets for the model area immediately surrounding the Mount Pleasant area were calculated for 2011 and for 2050. The largest flow component for the 2050 water budget in the Mount Pleasant area is discharge through wells at rates between 7.1 and 10.9 million gallons of water per day. This groundwater is replaced predominantly by between 6.0 and 7.8 million gallons per day of lateral groundwater flow within the Middendorf aquifer for the Base Case and two scenarios and through reclaimed-water injection of 3 million gallons per day for Scenarios 1 and 2. In addition, between 175,000 and 319,000 gallons of groundwater are removed from this area per day because of the regional hydraulic gradient. Additional sources of water to this area are groundwater storage relea...

Simulation of groundwater flow and pumping scenarios for 1900–2050 near Mount Pleasant, South Carolina

“…The Floridan aquifer system and Tertiary sand aquifer were considered one aquifer in this investigation, similar to previous modeling investigations (Aucott, 1988;Campbell and van Heeswijk, 1996;Petkewich and Campbell, 2007;Petkewich and Campbell, 2009).…”

“…7A). The simulated results indicate the recalibration is an improvement over previous calibrations (Petkewich and Campbell, 2009), which produced a simulated water level for well CHN-14 that was 27.5 ft lower than the 2008 average observed value. Since 2004, the observed groundwater level at well CHN-14 has been steady or rising ( fig.…”

“…The lateral model boundaries extend from the Oconee and Altamaha Rivers in Georgia to the Cape Fear River in North Carolina. As in the previous investigations (Petkewich and Campbell, 2007;Petkewich and Campbell, 2009), the focus of the current investigation is the six major aquifers within the Coastal Plain aquifer system in South Carolina and parts of Georgia and North Carolina ( fig. 4; Aucott and Speiran, 1985;Aucott, 1996) and, in particular, the Middendorf aquifer near Mount Pleasant, S.C. Land-surface altitudes range from 0 ft at the coast to more than 600 ft in the upper part of the Coastal Plain physiographic province (Aucott, 1996).…”

“…The aquifers were divided into units on the basis of relative permeability and not geologic formation; therefore, aquifers may cross formation boundaries in some instances (Aucott, 1996). Although previous and ongoing investigations in the study area may use different nomenclature to describe these aquifers, this report uses the nomenclature described in Aucott and Speiran (1985), Aucott (1988Aucott ( , 1996, Campbell and van Heeswijk (1996), Petkewich and Campbell (2007), and Petkewich and Campbell (2009).…”

“…The groundwater-flow system of the Coastal Plain physiographic province of South Carolina and parts of Georgia and North Carolina was simulated using an updated version of the calibrated model described in Petkewich and Campbell (2009), which uses the USGS finite-difference code MODFLOW-2000 (Harbaugh and others, 2000) and the conceptual model described in Petkewich and Campbell (2007). The original model (Petkewich and Campbell, 2007) consisted of a steady-state predevelopment (1900) In the original model, simulated recharge rates varied over time and were calibrated on the basis of average precipitation data from six weather stations located in the upper Coastal Plain section of the study area (Petkewich and Campbell, 2007).…”