Attenuation of Chlorinated Contamination in Three Different Depths of Aquifers at Remediation Site

The cleanup of carbon tetrachloride(CCl4)in groundwater is challenging due to its high volatility and tendency to form a dense nonaqueous liquid phase.From the engineering applications perspective,the pump-and-treat(PAT)technology has substantial advantages owing to its large-scale implementation ability to solve groundwater contamination.However,few studies focused on the variation in chloride contaminants in remediation sites after the contaminated groundwater was pumped and treated.Herein,we monitored the changes in chlorinated contamination in groundwater from 12 aquifers at the field level for 6 months.Considering that the natural attenuation of chlorinated contamination is inseparable from the action of microorganisms,the major environmental factors influencing biodegradation were also evaluated.A redundancy analysis(RDA)showed that inorganic salts(DS,DN,and DF)were the most important factor(>60%)affecting the concentration of chloride contaminants,including the negative correlation between DN and the degradation of contaminants in shallow aquifers.In deep aquifers,DS,DF,and pH explained most of the degradation of chloride contaminants.For bedrock layers,DCl was positively relevant to the chloride contaminants in wells PTJ2 and PTJ10.In addition,EC and DS accounted for 73.2%and 92.4%of the contaminant’s variance in wells PTJ4 and PTJ8,respectively.Moreover,the concentrations of the corresponding contaminations and physicochemical variation in three different depths of aquifers were compared;the shallower aquifers showed a higher biodegradation.The in situ monitoring and analysis of contaminated groundwater in remediation sites under PAT will promote practical wastewater treatment technologies in engineering applications.