Optimal Remediation Scheme for a Wastewater Recharge Site: Contaminants Fate and Transport Model.

A 3-dimensional hydrologic groundwater flow and contaminant transport model was developed to address the feasibility and relevant time-scales for remediation of a large soil aquifer treatment (SAT) site for domestic wastewater. The model accounted for a range of organic pollutant retardation factors and biodegradation kinetics. In order to detect the effect of the most retained and the most refracted/recalcitrant pollutants, it was crucial to model fractions of different properties rather than with average set properties. Four aquifer remediation scenarios, including two active washing procedures and two involving natural attenuation, were evaluated. The remediation efficiencies, in terms of residual plume size and mass of pollutant washout, were compared to each other and to the current operation scheme. According to the results, remediation mainly via natural attenuation rather than some form of intense pump and treat technology, is feasible, unlike the situation with hazardous waste sites. Enforced washout becomes less efficient with time due to increasing retardation of the residual pollutants. Therefore, pollution containment with natural biodegradation, which removed 95% of the emerging contaminants within 30 to 40 years was found to be the most valuable remediation scheme.

Quantitative evaluation of tracers for quantification of wastewater contamination of potable water sources.

Quantitative criteria for selection of tracers for assessment of mixing of wastewater and pristine water are proposed and evaluated for leakage from a wastewater effluent recharge system to nearby pristine water wells and the dilution of the effluents in a reclamation well by pristine water from the surrounding aquifer. Two molecular tracers were compared: carbamazepine, an organic drug whose refractory behavior was evaluated on-site, and chloride, a widely used conservative tracer. The mixing ratios and the corresponding uncertainty levels in their calculation were evaluated using actual field data. Uncertainty level analysis illuminates the effects of the analytical errors in the determination of trace micropollutants on one hand and the high level of chloride in the background on the other. Uncertainty level calculations revealed that chloride is a somewhat better tracer for the estimation of the dilution of wastewater by flow from a pristine aquifer, whereas carbamazepine is a much better tracer for the calculation of wastewater contamination of nearby drinking water wells. Surprisingly, we show that even when carbamazepine degrades to a large and unknown extent, it can still be used to estimate accurately the probability that a site is contaminated by a wastewater stream.