Water quality changes related to the development of anaerobic conditions during artificial recharge

Artificial recharge basins or spreading sites commonly exhibit reductions in infiltration rates after prolonged periods of submergence. This loss in infiltration rate has often been shown to be associated with a large population of anaerobic or facultative anaerobic bacteria in the material underlying the basin floor. An artificial recharge experiment in a spreading basin at Lubbock, Texas, showed a significant change in the chemical quality of recharged water that was associated with the growth of anaerobic bacteria. Sulfate‐reducing bacteria reduced the sulfate concentration of the recharge water at this location by 80 mg/l. The bicarbonate concentration was increased by more than 150 mg/l, and the pH decreased 1 unit during the same time period. The change in chemical quality occurred suddenly and corresponded to a dramatic decrease in the infiltration rate in the basin. These observations on the chemical changes in recharged water make it possible to differentiate between anaerobic bacteria and other causes of reduced hydraulic conductivity in this recharge basin. The anaerobic conditions appear to start at depth and work toward the surface, thereby suggesting a process that involves adsorption of organic material and consumption of dissolved oxygen with depth.