Testing a Sorption/BioAmendment Combination in an Excavation Supported by Molecular Biological Tools
Many amendments have historically been applied in excavations at remediation sites. Ideally, the amendments would contact groundwater infiltrating the excavation leading to treatment of residual mass not accessed by soil removal. When first introduced, the liquid carbon sorptive product, PetroFix® (including a nitrate/sulfate electron acceptor blend), was developed for in situ injection grids and plume retarding barriers but use in an excavation was not initially contemplated.
At a former convenience store site, slow release oxygen pellets were proposed for residual treatment in the excavation. Demonstrating the efficacy of three electron acceptors in addition to the sorption effects of the carbon product was intriguing. Following excavation, new monitoring wells within and outside the footprint of the excavation were installed to monitor for reductions in BTEX concentrations and changes in geochemistry, field parameters, and microbial profile/gene functions using Molecular Biological Tools quarterly over a one year period. The microbial results were especially important in showing increased microbial growth and gene expression linked to degradation.
A total of 1800 cubic yards of soil was excavated, and a spray application of the amendment was made across the most impacted sides and base locations of the excavation. Later, a faster technique using a front-end loader and drums of amendment allowed a “painting” of the remaining walls and base. In total, 3600 pounds of sorptive media/electron acceptors and 1000 pounds of slow release oxygen pellets were applied to the excavation. After one year of monitoring, the site achieved regulatory closure with the aid of the amendment. A discussion of the site history/conditions, field activities, lessons learned with different amendment application techniques, and a summary of remediation results will be provided.