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REMEDIATION

Micron-scale colloidal remedial fluid effectively reduces contaminant levels By Todd Herrington

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t a petroleum bulk storage facility that was in operation from 1917 to 2002, dissolved phase contamination was found to have leaked from aboveground and underground storage tanks, and contaminant had migrated off-site. Consequently, the site had been sitting idle for years. In 2016, the property owner received a request for compliance from the regulatory authorities. They subsequently retained Patriot Engineering to design and implement a remedial plan to address the environmental impacts at the property. Seeing gaps in the available site data, Patriot installed additional wells, replaced old wells that had been destroyed, and delineated the entire extent of the non-aqueous phase liquid (NAPL) contaminant plume. The challenges on this particular site were that the impacted area was quite large and had fairly high levels of dissolved phase petroleum. Previous remediation at a nearby site using a pump and treat system had actually expanded the plume even further. Considering in-situ chemical oxidation (ISCO) combined with enhanced aerobic degradation as a potential remedial option, Stephen Sittler, a senior project geologist with Patriot Engineering, contacted REGENESIS, a provider of environmental remediation solutions, for assistance in developing a plan. The idea discussed was to perform an on-site beta test of REGENESIS’s PetroFix carbon-based remediation fluid, in lieu of more conventional approaches. The purpose of the test would be to evaluate PetroFix for possible full-scale use. On why PetroFix was chosen for this site, Paul Erickson, a senior research scientist with REGENESIS explained: “Contaminant levels were pretty high and we knew this would be a good test of the product balance. We wanted to see how far we could push PetroFix. Also, 50  |  June 2019

After the beta test design was finalized and approved, the injections were performed using a REGENESIS injection trailer hooked up to Patriot drill rigs.

the transport was a little bit different from other beta sites we had done, just to give us a little variety in how we were testing the product before release.” PetroFix is a highly concentrated water-based suspension consisting of micron-scale activated carbon and biostimulating electron acceptors designed to remediate petroleum hydrocarbons (TPH-d, TPH-g, MTBE, BTEX) and provide immediate results for gas station and underground storage tank sites. The environmentally-compatible formulation of micron-scale activated carbon is combined with both slow and quick-release inorganic electron acceptors (a preferred sulfate and nitrate combination blend, or the option of a sulfate only blend) and injected together. It works by first removing hydrocarbons from the dissolved phase by adsorbing them onto activated carbon particles and then stimulating hydrocarbon biodegradation through the addition of electron acceptors. For years, activated carbon has been

widely used in the remediation of soil and groundwater. Structurally, activated carbon is a highly porous material, made up almost entirely of elemental carbon. Due to its high surface area and unique pore structure, small organic molecules (such as environmental contaminants) are readily adsorbed from target solutions (i.e., groundwater). While activated carbon can be found in a wide range of physical forms, corresponding to various uses, contaminants, and mediums, there is typically an optimum form and particle size for each application. For in-situ groundwater remediation applications, small-particle activated carbon is preferred due to its ability to move effectively within an aquifer. Because of this preference, particles in PetroFix are 1 – 2 µm in size, allowing for the free flow of an aqueous suspension of activated carbon through an aquifer during an injection. As PetroFix moves through the pore space, it coats the surface of the soil particles versus occluding the pore space, allowing groundwater to

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Environmental Science & Engineering Magazine | June 2019