Managed Aquifer Recharge (MAR) is used worldwide in different applications to replenish overexploited aquifers and to improve water quality, although details of the functioning and role of relevant hydrological and biogeochemical processes and pathways still need to be better understood. In a broad sense, MAR is a low-energy and low-cost water recycling technology and in practice the only technology available to restore depleted aquifers. The water is purified during passage through the soil and aquifer sediment, and ultimately increases the groundwater recharge.
The major concerns with MAR still arise from the potential contamination of the aquifer with trace concentrations of organic chemicals, nutrients and pathogens not removed during infiltration. To minimize the pollution risks, specific reactive barriers placed in the infiltration basins have been suggested. Further, combinations of engineered and natural treatments may be used to achieve safe use.
Another issue hampering the MAR technology in general is the potential clogging of the subsurface. Despite these challenges, many large scale MAR projects have succeeded in both restoring aquifers and improving water quality because careful research took place to fully address real and perceived risks. A key challenge associated with infiltration of river and reclaimed waste water, is the presence of numerous trace organic contaminants and micro-pollutants that can be harmful to ecosystem and human health. For successful MAR application the concentrations of organic pollutants such as pharmaceuticals, hormones, and personal care products must be reduced to certain levels depending on the purpose of the water use.
Although MAR is a well-known technology, tools for proper management of degradation processes securing safe water for multiple purposes are still lacking. In this project we will develop a dual-stage MAR (DUST-MAR) concept with two treatment steps. Initially, river water (or reclaimed waste water) is infiltrated to shallow aquifers for removal of pathogens and easily degradable organic compounds; secondly this purified water will be infiltrated or injected to deeper aquifers for storage and further degradation of more recalcitrant pollutants. Water from the shallow aquifer may be used immediately for purposes where water quality demands are lower e.g. irrigation, while the stored water may be used for drinking either directly or following further treatment at the waterworks.
While it is recognized that MAR is important for replenishment of overexploited and depleted aquifers, and may improve water quality following proper management, it is unknown to which extent MAR will be able to significantly alleviate the water scarcity in the North China Plain (NCP). The potential impact of large scale MAR schemes can only be studied by scenario analysis, which requires an integrated surface water groundwater model to provide reliable distributed estimates and accounting for all major water fluxes.
An appropriate regional scale model should be able to quantify the major boundary fluxes and internal water flows for the NCP. These include the surface and groundwater inflow from the upstream mountains in the Haihe basin, the extensive irrigation throughout the NCP and groundwater pumping for human and industrial consumption. In addition, the anthropogenic water transfers related to the SNWT and the discharges of treated wastewater should be quantified. There is a need to gather existing hydrological data, new satellite based information and previous modelling efforts on the NCP in an updated regional scale integrated surface water groundwater model tailored to address the questions related to the potential for large-scale MAR implementation.