MODELING ASSESSMENT OF ASR SYSTEM PERFORMANCE

Aquifer storage and recovery (ASR) has become a cost-effective method for storing surplus water in an aquifer during periods of high supply or low demand for use in periods of low supply or high demand. This technology is being used increasingly in the U. S. to assist water managers, particularly in the arid southwest and in coastal areas. ASR system performance, typically quantified by recovery efficiency, is influenced largely by the transmissivity of the storage zone and the vertical anisotropic ratios of the aquifer, the regional groundwater gradient and the salinity contrast between injected water and native water in the aquifer. Understanding the hydraulic factors favorable for high recovery efficiencies is important for assessing the likely performance of future ASR systems.

The effects of aquifer anisotropy and heterogeneity on ASR recovery efficiency were investigated using SEAWAT, a three-dimensional variable-density groundwater flow program. A simple 3-dimensional test model was developed for this study. The injection and recovery rates used in the study were 2 MGD.

The modeling results indicate that both aquifer anisotropy and heterogeneity can have significant impacts on ASR system performance. Strong regional groundwater gradient will reduce the recovery efficiency of an ASR system. ASR system performance in brackish water aquifers may be adversely impacted by the buoyancy-driven migration flow of injected fluids. In general, high ASR system recovery rates are not dependent upon any one variable, but instead require combinations of hydraulic parameters that minimize the vertical migration of injected water from the storage zone.