Comparing water quality during urban storm water MAR via ASTR and ASR

J. L. Vanderzalm, D. W. Page, K. E. Barry, P. J. Dillon

Technical stream: Geochemistry during infiltration and flow

Managed aquifer recharge (MAR) is increasingly being considered as a means of reusing urban storm water and waste water to supplement the available water resources. Subsurface storage is advantageous as it does not impact on the area available for urban development, while the aquifer also provides natural treatment. However, subsurface storage can also have deleterious effects on the recovered water quality through water-rock interactions which can also impact on the integrity of the aquifer matrix.  A recent investigation into the potential for storm water recycling via a carbonate aquifer was used to determine the important hydrogeochemical processes that impact on the recovered water quality. An extensive period of aquifer flushing allowed observation of water quality changes under two operating scenarios; (1) separate wells for injection and recovery wells, representing Aquifer Storage Transfer and Recovery; and (2) a single well for injection and recovery, representing Aquifer Storage and Recovery (ASR).

Calcite dissolution was found to cause changes to the quality of storm water following storage in the carbonate aquifer; independent of the mode of MAR operation (ASTR or ASR). Dissolution was induced primarily by the reactivity of the source water itself as indicated by the sub-saturation with respect to calcite. Additional dissolution occurred in response to redox processes, and the production of biogenic carbon dioxide. Aquifer storage provided some treatment through nutrient removal, mainly through removal of approximately 35% of the injected dissolved organic carbon (DOC). DOC removal was greatest during ASTR due to the enhanced removal by adsorption between the separate injection and recovery wells. However this adsorption, and cation exchange which was also evident during the ASTR mode only, may be limited to the initial pore flushes of the storage zone and thus did not affect the water quality in the ASR mode.