UTILIZATION OF THE CRETACEOUS AQUIFER SYSTEM FOR STORAGE AND RECOVERY OF TREATED SURFACE WATER IN GREENVILLE, NC

Greenville Utilities Commission (GUC) has had steady increases for water services due to population growth. Peak water demands will exceed treatment capacity in the near future. The GUC water treatment plant (WTP) is being expanded to treat 22.5 mgd by 2001. This expansion will provide water supply capacity to meet projected demands until 2010, when peak daily demands for water will exceed Tar River allocations. Aquifer storage and recovery (ASR) can provide water storage and meet peak demands prior to and beyond 2010. By storing treated drinking water in the aquifers during periods of low demand (winter months), GUC can meet peak demands in summer months and defer further expansion of their WTP. Selection of an initial ASR site was based on property costs, hydrogeology, proximity to the distribution system and existing production wells. Cores were recovered from 200 to 502 feet below the land surface. The section (0-516 feet) can be divided into six distinct stratigraphic units containing 3 sandy aquifers. Two candidate aquifer zones were selected for hydrological evaluation. Pyrite found in both the candidate aquifer zones could react with recharge water and yield dissolved iron to the stored water, possibly elevating levels above primary potable water standards. An ASR test well has been constructed and tested to determine initial water chemistry and storage capabilities of Sands 2 and 3. The next phase, cycle testing, involves the analysis of changes in aquifer conditions and changes in recharge water quality during successive periods of storage within the aquifers. Two aquifer-specific monitoring wells will be installed within 500 feet of the ASR test well. Eight ASR wells may be needed to meet peak demands, and groundwater flow models are being utilized to optimize groundwater recovery. Test results and groundwater modeling will be used to determine the best ratio of recovery-only ASR wells to recharge/recovery ASR wells, and to evaluate well spacing.