Turbidity in Aquifer Storage and Recovery Wells

摘要

Recovering turbid water from Aquifer Storage and Recovery (ASR) wells can present problemsrnthat vary in severity according to their origin. In the Atlantic Coastal Plain, recovered water mayrnexhibit elevated turbidity if the storage aquifer naturally produces turbid water, or if the chemistryrnof the recharge water is incompatible with the water or minerals in the storage aquifer.rnAnalysis of filtrate residue from several sites indicates that clay minerals comprise over 99rnpercent of the entrained particles causing turbidity. Kaolinite is the most abundant clay mineral inrnthe filtrate by a factor of 2 to 3 times, even though the clay mineral suite in the storage aquifers isrndominated by other minerals including illite, smectite, and chlorite. Kaolinite is the dominant clayrnmineral in filtrate samples irregardless if turbidity is naturally produced, or induced by ASRrnoperations.rnMitigation in naturally turbid storage aquifers requires in situ treatment of the entire operational,rnaquifer storage volume with a calcium, potassium, or aluminum salt solution, or coagulatingrn(alum, organic polymers) agents. In situ treatments result in significant, yet unpredictablerndegradation in specific capacity of the ASR well. Often treatment of the recovered water at thernground surface by filtration technology is a safer alternative than in situ treatment, that risks bulkrndestruction of the intrinsic permeability of the storage aquifer. Mitigation of turbidity induced byrnASR operations is more easily accomplished than naturally occurring turbidity. Turbidity can bernreduced by correctly adjusting the pH or cation chemistry of the recharge water and controllingrnpumping rates (flow velocities) upon the initiation of recovery.