The site includes fractured limestone bedrock lithology.
Targeted Environmental Media:
 Fractured Bedrock - Light Non-aqueous Phase Liquids (LNAPLs)
A non-aqueous phase liquid (NAPL) layer ranging from 0.01 to 0.22 feet in thickness was identified in the groundwater and smear zone at 18 to 22 feet below ground surface (bgs).
Major Contaminants and Maximum Concentrations:
- Gasoline (var)
No technologies selected.
- Flushing (In Situ)
- Bioremediation (In Situ)
Comments:
For several years, passive and temporary/intermittent recovery methods (bailers, sorbent socks, 8-hour vacuum events) were applied, but persistent NAPL thickness remained in monitoring well 1 (MW-1). In 2009, a surfactant injection/extraction event was proposed, approved, and implemented. The event consisted of PetroSolvý surfactant injection into MW-1, MW-11, and MW-10, with simultaneous extraction of fluid from MW-1 to maintain hydraulic control. Following surfactant injection and extraction, biological amendments were injected to stimulate biological degradation of residual dissolved-phase compounds in groundwater. 60 gallons of PetroSolvý and 150 pounds of Custom-Blend Nutrients [CBNý] were used for the entire project.
With fractured bedrock lithology, hydraulic capture of NAPL and surfactant solution is critical, requiring a focused injection/extraction procedure. For this site, the following procedure was used: (1) a small volume of 7% PetroSolvý solution was injected at low pressure into MW-1. After injection, MW-1 was surged using a surge block to promote better contact with surrounding NAPL-impacted fractures and voids, and allow better peripheral distribution of the surfactant solution around MW-1; (2) after surging MW-1, groundwater extraction from MW-1 was implemented to remove the injected PetroSolvý solution and produce a cone of depression around MW-1; (3) water levels in monitoring wells MW-10 and MW-11 were gauged during groundwater extraction from MW-1 to ensure an adequate cone of depression before injecting into W-10 and MW-11. After 90 minutes of groundwater extraction, drawdown of 0.21 feet and 0.46 feet were observed in MW-10 and MW-11, respectively, indicating that an adequate cone of depression was established to induce flow toward MW-1; (4) after the cone of depression was established, a 13% PetroSolvý solution was injected into MW-10 and MW-11, while groundwater extraction was maintained at MW-1. The PetroSolvý solution injected into MW-10 and MW-11 included a red dye to verify that the injected solution was captured at MW-1. The groundwater extraction hose was equipped with a clear sight tube to allow visual observation of the extracted liquid. Red dye was observed at MW-1 about 30 minutes after initiating injection at MW-10 and MW-11; (5) groundwater extraction at MW-1 continued for 1 hour after the surfactant injection in MW-10 and MW-11. Water level measurements collected from MW-10 and MW-11 indicated that a cone of depression was maintained around MW-1 during and after surfactant injection. The red dye observed in the sight tube was significantly reduced during the continued extraction at MW-1, indicating that the majority of the injected surfactant was recovered; (6) following extraction at MW-1, the wells were allowed to recharge. During groundwater recharge at MW1, a small volume of 10% PetroSolvý solution was injected at low pressure into MW-1. This allowed the surfactant solution to flow into exposed fractures and voids, helping optimize contact with any trapped NAPL. MW-1 was again surged to promote better contact with the surrounding fractures and voids; (7) After surging MW-1, groundwater extraction from MW-1 was re-activated for approximately 1 hour to re-create an adequate cone of depression before re-injecting into MW-10 and MW-11. Drawdown of approximately 0.43 feet and 0.67 feet below static levels were observed in MW-10 and MW-11, respectively, prior to reinjection at MW-10 and MW-11; (8) once the cone of depression was re-established, a small batch of 10% PetroSolvý solution (with red dye) was simultaneously injected into MW-10 and MW-11 using the previous methodology (see item #4). Red dye was observed in the sight tube at MW-1 approximately 20 minutes after initiating the re-injection at MW-10 and MW-11; (9) groundwater extraction at MW-1 continued for approximately 2 hours following the re-injection in MW-10 and MW11 to ensure recovery of the injected surfactant solution. The red dye observed in the sight tube was significantly reduced during continued extraction at MW-1, indicating that the majority of the injected surfactant was recovered; (10) over the course of the pilot test, 600 gallons of PetroSolvý solution was injected into MW-1, MW-10 and MW-11, while 3,000 gallons of fluid was removed from MW-1. This extraction volume was five times the volume of surfactant solution that was injected, thus promoting effective hydraulic control. Furthermore, red dye was not detected in any surrounding monitoring wells during or after the injection event; (11) after surfactant injection/extraction was completed, 150 pounds of CBNý nutrients were mixed with approximately 200 gallons of water and injected evenly into each of the injection wells (MW-1, MW-10, and MW-11). The nutrient addition was intended to stimulate biological degradation of remaining dissolved-phase constituents.
Not documented.
Treatment has been completed and no additional NAPL has been detected in MW-1 for 5 consecutive months of post-injection monitoring. In addition, no increases in dissolved-phase constituents have been identified in surrounding monitoring wells, indicating successful capture of residual NAPL and surfactant solution. A total of 60 gallons of PetroSolvý and 150 pounds of CBNý nutrients were used for the entire project, at a total cost of $4,000, including shipping. Consultant labor and equipment costs were not available for the project.
With fractured bedrock lithology, hydraulic capture of NAPL and surfactant solution is critical and the specialized procedure included in this description was followed. PetroSolvTM surfactant injection with simultaneous groundwater and free phase product extraction followed by CBNTM nutrient injection was successful in eliminating the NAPL layerýs thickness by 99 percent.
References:
Timmins, Brian. "Surfactant-Enhanced LNAPL Recovery." Case Study. ETEC LLC. Accessed at: http:www.etecllc.comdocsSurfactant_Flushing_Fractured_Bedrock_PA.pdf
EPA. 2012. Technology Innovation News Survey. Surfactant-Enhanced Remediation Via Short-Term Recirculation Process. Summary of Presentation by Timmons, B, at the 17th Annual Florida Remediation Conference, Orlando, 13-14 October 2011. December 16-31 Issue of TINS.
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