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flow unimpeded. The small diameter of PetroFix also increases the immediately available surface area of the carbon in it, which then results in faster than normal sorption of contaminants. With this fast sorption capability, coupled to the ability to distribute and fully coat highly conductive transport zones, the material is an excellent way to lock contaminants in place and immobilize a plume for treatment. PetroFix also acts as a sorption barrier for those situations where persistent diffusion of contamination from tight soils into more conductive transport zones is a chronic concern. Once contaminants are immobilized, the second step in the PetroFix process is biological destruction. The activated carbon is responsible for the initial removal of contaminants from groundwater, which can lead to rapid results. However, the contaminants, although immobilized, remain intact until they are degraded by naturally occurring bacteria in the aquifer. This is a principle that has already been successfully employed in the wastewater treatment field, with processes such as bio-GAC. When its applied as recommended, PetroFix contains a blend of nitrate and sulfate salts that act as electron acceptors to enhance the degradation of sorbed petroleum hydrocarbons. These salts are water soluble and thus will flow with the product. Nitrate is used more rapidly, typically weeks, while the sulfate is utilized over months. While many bioremediation approaches degrade petroleum hydrocarbons via aerobic pathways, research has shown that they can also be efficiently degraded anaerobically via syntropic processes, or a community of bacteria fulfilling different roles. These degradation processes, while enhanced by additional electron acceptors, will continue even after those electron acceptors have been depleted. For in-situ remedial applications, it is important to achieve sufficient coverage of the impacted subsurface, as the primary factor determining the success of a project is contact between the contaminant and the remediation chemical. For PetroFix, the goal is to not just have sufficient dosage to remediate the hydrocarbon mass, but for the total solution volume applied to theoretically @ESEMAG

Dissolved phase contamination was found to have leaked from aboveground and underground storage tanks, and contaminant had migrated off-site.

gasoline-range organics were essentially eliminated from the groundwater at one month post-injection and remained so at six months.” Nitrate and sulfate levels spiked at one month post injection due to their initial addition as electron acceptors. These levels saw a sharp reduction during the threemonth sampling event, indicating utilization by microbes and biodegradation. “This conclusion was strongly supported by microbial analyses,” said Sittler. “The microbial analyses indicated a shift towards anaerobic petroleum degraders caused by the more favorable environment induced by the nitrate and sulfate injected with PetroFix.” Based on the success of the beta test, Patriot decided to move forward with the design and implementation of full-scale remediation using PetroFix, which had proven itself to be a viable remedial option. “Concentrations were in the 30,000 – 40,000 ppb range,” said Sittler. “Now they’re gone. That was the big question.” Sittler incorporated lessons from the beta test into the full-scale design. “In the beta test, we easily got distribution between the points, which were 1.52 m apart. We took samples between the points and saw PetroFix. For the fullscale we increased spacing to 2.1 m., and we may add more water to spread it out more without increasing costs. We should be able to scale up to 2.1 m and save a lot of money and still get the same amount of product into that area.” The full-scale design has focused on treating several hotspots on the site. Because the area was very large, mechanical remediation was not practical and it would have been prohibitively expensive to perform a grid injection across the entire site. “A product like PetroFix acts like a filter,” Sittler explained. “We can put it in some smaller areas and allow the contaminants to flow through them and treat the entire site. A series of grids in the hottest areas act as a big barrier. We can clean up the site and prevent off-site migration.” The full-scale design has since been approved and implemented on the site. Monitoring is ongoing.

fill more than half of the effective porosity present. Both those conditions must be met in order to achieve success. PetroFix comes paired with a virtual design assistant that helps site managers determine how much product is necessary for treatment and create a design for the application. After inputting site data, the design assistant will determine the number of injection points and total volume of PetroFix required. Shipped as a viscous liquid of approximately 1,500 – 3,500 centipoise, PetroFix has a viscosity similar to corn syrup. It is then typically diluted greater than 10:1 with water in the field so that injection into the subsurface can be performed at low pressures (typically < 30 psi). This allows PetroFix to flow outwards from the injection point through naturally occurring permeable strata, following the same transport pathway as the target hydrocarbons. As with any remediation project, it was necessary to acquire approval from the overseeing regulatory body. Fortunately, according to Sittler, the approval process for this project was smooth. He said that “they really wanted something done on this site. The fact that anything being proposed was a plus. But it helped that REGENESIS has a good reputation. There really wasn’t any pushback at all.” After the beta test design was finalized and approved, the injections were performed using a REGENESIS injection trailer hooked up to Patriot drill rigs. “Early post-injection groundwater monitoring results from the PetroFix pilot test look very promising,” said Sittler. “Petro- Todd Herrington is with REGENESIS. leum volatile organic compounds and Email:

June 2019  |  51

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Environmental Science & Engineering Magazine | June 2019