This investigation project utilized multiple field screening analytical methods, including a wireline cone penetrometer (CPT) for discrete soil sampling, coupled with a direct sampling ion trap mass spectrometer (DSITMS) for analysis of soil and groundwater samples for trichloroethene (TCE) and other chlorinated volatile compounds. These real-time data allowed for real-time site sampling decisions where members of the team were responsible for making recommendations on field investigative activities (e.g., sampling locations and frequency) based on the preliminary conceptual site model (CSM) of the site and the most current data gathered during field operations. Lower costs allowed for increased sampling quantity and site coverage. The TCE plume source area was delineated rapidly, with more than 600 analytical samples analyzed in 9.5 days of fieldwork alongside 230 quality control (QC) samples. All samples were analyzed using EPA Method 8265. No fixed-base laboratory split samples were analyzed. Sampling depths ranged from 20 to 70 feet below ground surface (bgs), and analytical samples were frequently collected on 1 foot intervals.
|Site Name||Hill Air Force Base, Operable Unit 12|
|Site Regulatory ID||EPA ID#: UT0571724350/ Site ID#: SS107|
|Project Lead Type||U.S. Air Force Lead|
|Regulatory Lead Program||Superfund Remedial|
|Reuse Objective Identified||Yes|
|Proposed Reuse:||Industrial and Residential|
Operable Unit (OU) 12 is located in the northwest region of Hill Air Force Base (AFB) and is comprised of contaminated groundwater flowing off base from a source area near the western base boundary see Figure 2-1 of the Source Zone Delineation Demonstration Report [URS 2003]). The source area is located near a former Wastewater Treatment Plant (WWTP) and the Missile Assembly Maintenance and Storage-2 area of Hill AFB. Since 2000, the Air Force has tested 317 homes in the OU 12 area for chemical vapors, and is continuing to monitor and mitigate vapor intrusion into homes above the OU 12 plume.
The former WWTP was thought to be the source of the plume when the plume was initially discovered; however, a soil-gas survey and CPT/DSITMS direct push soil and groundwater sampling investigation in 2002 indicated that the source is located north of the former WWTP. This northern area is characterized by debris, half-buried drums, abandoned foundations, and several trench-like features.
Additionally, ash beds with vitrified material (suggesting possible rocket testing or propellant burning) were identified north and west of the former WWTP. Finally, increasing and or highly variable TCE concentrations in the OU 12 source area indicated a continuing source.
On the basis of the CPT/DSITMS investigation, the Air Force installed a groundwater removal system near the base boundary in 2003 called a “Groundwater Containment System to prevent additional contamination from moving off the base into local communities.” This system was expanded in 2008 and now consists of seven extraction wells that capture contaminated groundwater before it can leave the base. To date, the groundwater containment system has removed more than 17 pounds of TCE since startup in 2003.
A permeable reactive barrier (PRB) wall was installed in 2004. The underground barrier is 660 feet long, two feet wide, 30 feet deep and consists of a mixture of sand and iron filings that allow groundwater to flow through. As the contaminated groundwater moves through the wall, the TCE in the groundwater reacts with the iron and degrades into harmless components.
In 2008, three known areas of contaminated soil located on base, which were suspected to be sourcing chemicals to the groundwater, were excavated and disposed of at an of-site facility. The total amount of contaminated soil removed was approximately 3,100 tons. The Air Force will continue to monitor contamination levels at OU 12.
The cleanup decisions and remedies for OU 12 were formalized in a 2008 Record of Decision (ROD) that was signed by the Air Force, the Utah Department of Environmental Quality (UDEQ), and the Environmental Protection Agency (EPA). The Air Force will complete a Five-Year Review in 2013 as required by environmental clean-up laws.
The project team identified cost and time savings associated with a real-time dynamic work strategy (DWS) using CPT/DSITMS for soil and groundwater analysis. The use of CPT/DSITMS instead of conventional drilling technologies with off-site laboratory analysis was estimated to represent a 30% realized cost savings.
No systematic project planning was conducted for this project. In general, systematic project planning has been performed under a 5-Year Review format and the data quality objective (DQO) process has been used by the project team to organize and accomplish project objectives.
Following identification of unconstrained chlorinated solvents in groundwater at OU 12, the DQO process selected a DWS using CPT/DSITMS to delineate contamination in both soil and groundwater at the site during investigation in 2002. Following data collection, a 3-dimensional model was constructed to provide insight on contamination nature and extent. The model was updated continually during the investigation and shared with project stakeholders (the Restoration Advisory Board [RAB] and City of Roy, Utah).
U.S. Air Force Environmental Management and Restoration (EMR) lead the effort with input requested from Utah Department of Environmental Quality (UDEQ) and US Environmental Protection Agency (USEPA).
A DWS was applied through the use of real-time field sample analysis to facilitate cost effective contaminant extent characterization, alternate source assessment, and uncertainty elimination. A flexible work plan and the rapid availability of analytical results provided by the DSITMS enabled an adaptive sampling program (in-the-field adjustments) that would not have been possible using an off-site laboratory as is customary with a conventional investigation approach. The real-time update of the CSM and the use of an adaptive sampling program also reduced the total amount of time required to characterize the area of investigation as compared with time delays normally associated with off-site sample analyses and subsequent data evaluation.
Investigation data was disseminated to the RAB team (including UDEQ and USEPA) before data was formalized and made available to the public.
This investigation project utilized multiple field screening analytical instruments, including a wireline CPT for discrete soil sampling, coupled with a DSITMS for soil and groundwater sample volatiles analysis. Real-time analysis allowed for real-time site sampling decisions.
The wireline CPT is an advancement over conventional CPT allowing nearly all characterization work to be accomplished in a single drill penetration. The wireline CPT system, unlike conventional CPT, is capable of retrieving and interchanging CPT “tools” without retracting the rod-string from the ground. CPT lithologic data is captured during drill bit penetration, where lithologic samples can be collected using the wireline retrieval system.
The DSITMS introduces sample materials directly into an ion trap mass spectrometer by means of a very simple interface, such as a capillary restrictor or a polymer membrane. There is typically very little, if any, sample preparation and no chromatographic separation of the sample constituents. This means that the response of the instrument to the analytes or contaminants in a sample is nearly instantaneous and analyses are typically completed in less than five minutes following sample retrieval.
Real-time DSITMS analysis allowed for real-time site sampling decisions where, members of the team were responsible for making recommendations on field investigative activities (e.g., sampling locations and frequency) based on the preliminary CSM of the site and the most current data gathered during field operations. Lower cost allowed for increased sampling quantity and site coverage. The TCE plume source area was constrained rapidly, based on more than 600 analytical samples analyzed in 9.5 days of fieldwork alongside 230 QC samples. All samples were analyzed using EPA Method 8265 (DSITMS). No fixed-base laboratory split samples were analyzed. Sampling depths ranged from 20 to 70 feet bgs, and analytical samples were frequently collected on 1 foot intervals.
TQRS not prepared
Data quality relied on high data density and field-based QC samples, with more than 600 analytical samples analyzed in 9.5 days of fieldwork alongside 230 QC samples, including daily calibrations, blanks, matrix spikes, and performance evaluation samples. All samples were analyzed using EPA Method 8265. No fixed-base laboratory split samples were analyzed.
Data management included near real-time generation of a 3-dimensional source zone map for contaminant delineation. Plan view tag-map figures were also prepared to communicate contaminant analysis data. Other figures included ground water flow direction maps, ground water sample results, site location maps, and down-gradient residential soil vapor sample location and results maps.
The near real-time CPT and DSITMS data were used to prepare 2- and 3-dimensional kriged model depictions of site lithologic and contaminant distribution to assist decision making and remedy implementation. Figure 5-9 of the Source Zone Delineation Demonstration Report (URS 2003) shows model output for contaminant extent as a 2-dimensional ‘cut-away’ slice of a pre-selected depth below ground surface. Figure 5-12 shows a 3-dimensional model output of contaminant extents, based on total DSITMS results, and Figure 5-20 shows a 2-dimensional cross-section correlation of both CPT lithologic results and DSITMS contaminant results.
|Hill AFB RAB OU12 Summary. Last Updated July 2010.|
|Operable Unit 12 Source Zone Delineation Demonstration Report. Hill Air Force Base, Utah. URS Corporation. March 2003. (7.11 MB)|
To update this profile, contact Cheryl T. Johnson at Johnson.Cheryl@epa.gov or (703) 603-9045.