You are here:
Primary and Secondary Contamination Mechanisms for Consideration in ASR Modeling and Practical Management
Citation:
Yang, J., Y. Jun, D. Schuppe, AND D. Burnell. Primary and Secondary Contamination Mechanisms for Consideration in ASR Modeling and Practical Management. Presented at EWRI Conference, #1046, Cincinnati, OH, May 20 - 23, 2013.
Impact/Purpose:
Communication of EPA ASR research progress to scientific community
Description:
Aquifer storage and recovery (ASR) is a useful water resource management option for water storage and reuse. Its increased use is recognized in adaptation to the ever increasing problem of water availability, both in timing and flow. Challenges in the ASR process may arise from both primary contaminants in injected water and secondary contamination due to contaminant remobilization from the aquifer materials. Based on our experimental results, the modification of injected water composition according to site soil and groundwater geochemistry has the potential to reduce the groundwater contamination risk at an ASR site. This paper describes the contamination mechanisms for an ASR site composed of an unsaturated vadous zone overlying an unconfined aquifer. Injected secondary wastewater effluent is oxygen-rich and contains low levels of macronutrients (N, P) and the carbomate pesticide aldicarb; the latter is a model recalcitrant endocrine disrupting compound (EDC). Pilot-scale and bench-scale experimental tests and microscopic analyses lead to following conclusions: 1) nearly all aldicarb and other organic injectants are retained in the upper 1-2 meters of the unsaturated soil column with increased retardation occurring by addition of carbonate rock chips on soil top; 2) downward mitigation of parent and daughter aldicarb compounds occurred at a extremely small rate in the 30- and 45-day testing periods; and 3) infiltration of oxygenated treatment effluent created a geochemical stratification at the shallow groundwater layer below the vadous zone, leading to changes in groundwater conditions that favor the dissolution of indigenous arsenopyrite, an arsenic-bearing iron oxide commonly found in soil and sediments. The occurrence and rate of the arsenic remobilization depended on the pH, redox potential (Eh), groundwater temperature, and co-existing soil constituents. The observations and quantitative analysis provide a basis to develop an operational model that can quantitatively simulate on injectant transport as well as geochemical reactions at an ASR site. This mechanistic simulation can thus serve as a tool to select effective above-group treatment options in preconditioning of injected water, and thus both to retain primary organic EDCs in upper soil by adsorption and reduce arsenic remobilization in the saturated strata.
