Turbidity in Aquifer Storage and Recovery Wells

摘要

Recovering turbid water from Aquifer Storage and Recovery (ASR) wells presents problemsthat can vary in severity according to the origin of the turbid water. In the Atlantic CoastalPlain, recovered water may exhibit elevated turbidity if the storage aquifer naturallyproduces turbid water, or if the chemistry of the recharge water is incompatible with thewater or minerals in the storage aquifer.Analysis of filtrate residue from several ASR sites indicates that clay minerals comprise over99 percent of the entrained particles causing turbidity. At all sites considered, kaolinite isthe most abundant clay mineral in the filtrate by a factor of 2 to 3 times, even though theclay 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 ifturbidity is naturally produced, or induced by ASR operations.Mitigation in naturally turbid storage aquifers requires in situ treatment of the entireoperational aquifer storage volume with a calcium, potassium, or aluminum salt solution, orcoagulating (alum, organic polymers) agents. In situ treatments result in significant, yetunpredictable degradation in specific capacity of the ASR well. Often treatment of therecovered water at the ground surface by filtration technology is a safer alternative than insitu 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 naturallyoccurring turbidity through simple operational steps. Turbidity can be reduced by correctlyadjusting 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 monthscan also effectively mitigate the turbidity of the recovered water.