Treatment of a PHC Source Zone using Land Application of Sulfate
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This pilot-scale experiment was performed in the sand pit area at the University of Waterloo Groundwater Research Facility at CFB Borden located near Alliston, ON. A multicomponent PHC source zone (3 m x 3 m) was emplaced in 2012 between 1 and 3 m below ground surface inside a sheet pile walled experimental gate. Simulation tools were used to design an optimal sulfate dosage system that would satisfy the reagent delivery and remediation requirements. Three episodes of sulfate release (5 m3 of 5-20 g/L Na2SO4, and 0.3 g/L (NH4)2SO4) at the ground surface were conducted over an 8-month period. A host of multilevel monitoring wells in conjunction with a real-time resistivity data collection system was employed to continuously track sulfate patterns and migration. Treatment performance was evaluated based on changes in sulfate concentration in the plume and PHC mass discharge across a downgradient monitoring fence line. Results from compound specific isotope analysis (CSIA) and biomarker tools were combined with the conventional monitoring data to assess enhanced sulfate reduction of the PHCs. General sulfate migration pathway was captured during EC monitoring. These results demonstrated 5 g/L Na2SO4 did not provide sufficient infiltration, while 15-20 g/L Na2SO4 created strong density-dependent flow. EC results of sulfate monitoring showed the real-time resistivity system allowed the collection of high resolution data. PHC mass discharge results showed significant attenuation of benzene, toluene and xylene after the sulfate application. CSIA data showed the occurrence of PHCs biodegradation associated with sulfate reduction. The sulfate isotope data support the occurrence of sulfate reduction. The concentration and isotope patterns observed for DIC are also linked to PHCs biodegradation. The microbiological data showed the occurrence of biodegradation under both aerobic and anaerobic conditions in the PHC plume.