The Old Jet Engine Test Cell (Area of Concern [AOC] 33) is a two acre area located at Seymour Johnson AFB. The Site was used for the live testing of jet engines from 1955 through 1984. Jet Propellant 4 (JP-4) fuel was released to site soil and groundwater some time during this period. The fuel was stored in several ASTs. Petroleum hydrocarbon impacts to soil and groundwater were confirmed by investigations conducted following installation of a new fire training facility at the Site in 2001-02. The selected remedial action (RA) was source excavation followed by in situ treatment of contaminated groundwater with an injected oxygen-releasing compound (PermeOx®). Systematic planning was conducted with regulators, Base Managers, the USACE project manager and chemist, and the supporting subcontractor technical team (TN and Associates). The project team reached consensus on cleanup goals and field decision logic. Real-time field measurement data (from a hand-held photoionization detector, or PID) was used to direct source removal (contaminated soil excavation) following the established decision tree. Additional PID readings, other field observations, and excavation confirmation sample results were used to adjust the in situ treatment (injection point) grid spacing and dosage of oxygen-releasing compound. The project was completed in two brief mobilizations on an expedited schedule (within 3 weeks).
|Site Name||Seymour Johnson Air Force Base|
|Project Lead Organization||Seymour Johnson Air Force Base (SJAFB)|
|Project Lead Type||U.S. Air Force Lead|
|Regulatory Lead Program||Voluntary Cleanup Program|
|Triad Project Status||Field Program Completed|
|Reuse Objective Identified||Yes|
|Proposed Reuse:||Military - Continued use of Site as fire training area by Air Force (equivalent to commercial/industrial)|
AOC 33 consists of two former jet engine test cells and associated fuel storage tanks. Both cells were used for live testing of jet engines from 1955 through 1984. All test cell buildings and exhaust deflection mounds were removed between 1989 and 1994. In 2000 and 2001, a petroleum sheen and odor were detected during installation of a fire hydrant thrust block for the new fire training tower in the area of the former jet engine test cells. Investigations conducted in 2001 and 2002 confirmed the presence of soil and groundwater impacts from petroleum hydrocarbons that were greater than North Carolina Soil-to-Groundwater risk based limits and groundwater standards.
The selected removal action incorporated both source removal and in situ treatment of the saturated zone with an oxygen-releasing chemical for the purpose of enhancing biodegradation of dissolved contaminants. Excavation of contaminated soils was planned based on available limited sampling data and was estimated to produce 362 tons of soil. By following established field decision logic supported with real time data (PID screening of soils), the excavation was expanded by approximately 50% to 550 tons to meet the RA objective of source reduction. Some contaminated soil was left in place beneath the new fire training building to preserve its structural integrity. A PermeOx® slurry was applied to the completed excavation floor to enhance oxygenation of the saturated zone beneath it.
The field and laboratory data generated during the soil removal action was used to revise the CSM. Based on the revised CSM, the injection plan was altered to maximize the effectiveness of the in situ treatment approach. In situ treatment of the saturated zone using PermeOx® was originally planned on a 20 ft x 20 ft grid with equal amounts of PermeOx® injected at equal depths at each injection point on the grid. This plan was adjusted in the field to 1) apply higher doses of PermeOx® to residual source areas at the new building (adjusting application to supply greater oxygen delivery to areas with greater contaminant concentration), and 2) adjust injection point grid spacing to achieve a greater density of injection points in residual source areas and lesser density of injection points at locations downgradient of the source areas. Field observations during the direct push technology (DPT) injection of the PermeOx® were used to make final adjustments of the grid and mass-balance dosages during plan implementation.
Remove a fuel-contaminated soil source area by excavation, and then treat associated groundwater contamination in situ using an oxygen-releasing compound (PermeOx®).
Following the Triad approach allowed the project team to avoid work stoppage or slow-down when field conditions were different than expected. The field team was empowered to adjust excavation boundaries and volumes following established decision trees. Hence the excavation was expanded and more source materials were removed without the need to stop for permission from the State and other stakeholders to proceed. Excavation confirmation sampling for off-site laboratory analysis was minimized. The in situ treatment was subsequently targeted to the highest concentration up-gradient areas. The more focused PermeOx® injection grid plan resulting from the completed Conceptual Site Model (CSM), refined in real-time in the field, is anticipated to ultimately save substantial costs as compared to a more traditional RA approach. Stakeholders were very satisfied with the RA implementation.
The project team estimates that this small project (the soil delineation and excavation program cost only $9,000) yielded approximately $15,000 in cost savings and a minimum of approximately 3 weeks in time savings relative to a traditional phased approach, primarily because the number and length of mobilizations were minimized, and the time between the mobilizations was also minimized.
The original CSM was developed based on two prior subsurface investigations conducted in 2001 and 2002. While the density of subsurface sampling was sufficient for the 2-acre Site overall, there were relatively few borings in the source area near the former test cell buildings. Therefore, there was uncertainty in the size and location of the area for source removal. To manage this uncertainty, the project team selected PID screening as the approach to determine whether suspect soils were contaminated by jet fuel. The PID head-space screening approach was designed to provide the real time data that would drive the field decision making on how far to extend the excavation and where to collect confirmation samples for laboratory analysis. Written decision trees were developed during the planning process to be used by the field team in deciding excavation limits.
The decision to follow the Triad Approach for the soil removal action and subsequent in situ treatment was made after a more traditional RA work plan had already been prepared. The Project Team, consisting of the State Remedial Project Manager (RPM), USACE project manager and project chemist, SJAFB representatives, and the technical team of the USACE's supporting contractor (TN and Associates [TN&A]) met together with the regulators and determined that the Triad Approach was appropriate and would facilitate timely execution of the project. The decision logic for the field event was also devised during a planning meeting that included the whole Project Team and the regulators.
Project goals and dynamic work strategies were developed during meetings and discussions with the Project Team and regulators (the stakeholder group). Field work was executed according to an approved work plan amended with written field decision trees and standard operating procedures (SOPs). Verbal approvals for final excavation amounts were obtained from the stakeholder group while the TN&A field team was working at the Site. Communication of progress to the stakeholder group was through informal verbal reports and daily quality control reports submitted to the USACE project manager. The decision trees as supported by the communication strategy provided the basis for the TN&A field team to make decisions in the field using real-time data to adjust the RA. Hence the excavation was expanded and more source materials were removed without the need to stop for permission to proceed from the State RPM and the other stakeholders (USACE and SJAFB). The USACE provided oversight during the injection process.
Decision trees were established for both the soil excavation and PermeOx® in situ treatment. Real-time data generated from PID screening of soil samples collected regularly during the soil excavation drove the field decisions. Essentially, the field team determined if soils were contaminated enough to continue the excavation, or if the removal action was complete at a particular location and a confirmation sample could be collected for laboratory analysis. For the in situ treatment, the decision tree involved visual observation of drill rods during DPT drilling. PermeOx® dosage was adjusted based on field indications of the relative levels of contamination present in the subsurface.
Excavation side walls were confirmed below decision tree action levels with PID headspace analysis. A site-specific SOP was developed for the PID head-space method to improve consistency and thereby reduce uncertainty related to the field method. The team determined the additional step of performing a methods applicability study to compare PID data with laboratory analysis for TPH was not necessary to meet the decision objectives and data needs for this project.
TQRS not prepared
Confirmation sampling (using Encore® samplers) was performed on each excavation side wall, and sent to the analytical lab for quick turn around sample analyses. Encore sample data were used to determine if cleanup criteria were met; this allowed the field team to verify excavation extent before demobilization.
During excavation, the laboratory sent Electronic Data Deliverables for confirmation samples to the TN&A chemist, who entered this information into TN&A's Environmental Data Management System database, from which spreadsheet tables were derived and emailed to field crew for review and action. PID readings were recorded on field data sheets and entered into spreadsheets manually.
Excavation from 7/13/04 to 7/20/04, followed by PermeOx® application and backfill from 7/23/04 to 7/24/04.
Additional PermeOx® injections from 8/03/04 to 8/11/04.
To update this profile, contact Cheryl T. Johnson at Johnson.Cheryl@epa.gov or (703) 603-9045.