Engineered Injection and Extraction for In Situ Remediation of Sorbing Solutes in Groundwater

Abstract

Engineered injection and extraction (EIE) is a method of in situ remediation of contaminated groundwater in which a treatment chemical that reacts with the contaminant is injected into the contaminated aquifer, and a series of injections and extractions of clean water are performed in nearby wells to promote the spreading of the treatment chemical throughout the contaminated aquifer. Numerical simulations are used to investigate the use of EIE for sorbing groundwater contaminants. The aquifer is homogeneous and confined with negligible ambient groundwater flow. A range of sorption parameters are considered for both linear equilibrium sorption and linear kinetic sorption, and both instantaneous and rate-limited bimolecular reactions are discussed. An effective EIE sequence is developed for a sorbing contaminant and is compared with a sequence developed for aqueous, nonsorbing contaminants. The results show that for contaminants that exhibit fast sorption and fast reaction, the EIE sequence developed for sorbing contaminants can achieve nearly complete contaminant degradation. For contaminants with linear equilibrium sorption and rate-limited reaction, the sequence can achieve nearly complete degradation if the duration of the remediation process is scaled with the inverse of the reaction rate constant. For contaminants that exhibit slow sorption, the EIE sequence designed for aqueous, nonsorbing contaminants achieves higher overall contaminant degradation, but requires more energy and higher injection and extraction rates.