AWWA ACE58084 ✓ Most Recent

Recovering turbid water from Aquifer Storage and Recovery (ASR) wells presents problems that can vary in severity according to the origin of the turbid water. In the Atlantic Coastal Plain, recovered water may exhibit elevated turbidity if the storage aquifer naturally produces turbid water, or if the chemistry of the recharge water is incompatible with the water or minerals in the storage aquifer. Analysis of filtrate residue from several ASR sites indicates that clay minerals comprise over 99 percent of the entrained particles causing turbidity. At all sites considered, kaolinite is the most abundant clay mineral in the filtrate by a factor of 2 to 3 times, even though the clay mineral suite in the storage aquifers is dominated by other minerals including illite, smectite, and chlorite. Kaolinite is the dominant clay mineral in filtrate samples irregardless of whether turbidity is naturally produced or induced by ASR operations. Mitigation in naturally turbid storage aquifers requires in situ treatment of the entire operational aquifer storage volume with a calcium, potassium, or aluminum salt solution, or coagulating (alum, organic polymers) agents. In situ treatments result in significant, yet unpredictable degradation in specific capacity of the ASR well. Often treatment of the recovered water at the ground surface by filtration technology is a safer alternative than in situ treatment, that risks bulk destruction of the intrinsic permeability of the storage aquifer. Mitigation of turbidity induced by ASR operations is more easily accomplished than naturally occurring turbidity through simple operational steps. Turbidity can be reduced by correctly adjusting the pH or cation chemistry of the recharge water and controlling pumping rates (flow velocities) upon the initiation of recovery. Extending storage times to several months can also effectively mitigate the turbidity of the recovered water. Includes 2 references, figures. See more