The Triad investigation for Site 14 at Naval Air Station (NAS) Lemoore in Lemoore, California, occurred over a 1-year period, with data collected from April 2005 through March 2006. Systematic project planning (SPP), dynamic work strategies (DWS) and real-time measurement technologies were instrumental in developing and evaluating two conceptual site models (CSM). The CSMs, referred to as conceptual model alternatives (CMA) for this project, were designed to evaluate whether the source of contamination was from a surface release or a subsurface release. An innovative conduit focused evaluation of solvent sources (CFESS) was used to select sampling targets based on suspected release locations in the storm sewer system. CFESS entailed smoke testing, dye testing, a video survey and pressure testing/air sampling at individual sewer joints using a sewer grouting plug, narrowing investigation to four confirmed defects in over 1,000 linear feet of storm sewer. Membrane interface probe (MIP) responses indicated the potential presence of dense non-aqueous phase liquid (DNAPL) 100 feet below the concrete surface at one of the four defect locations. MIP and cone penetrometer testing (CPT) technologies were used simultaneously to evaluate contaminant migration in groundwater, and define the physical properties that influence contaminant migration.
|Site Name||Naval Air Station (NAS) Lemoore|
|Site Type||Aircraft Rework Facility|
|Project Lead Type||U.S. Navy Lead|
|Reuse Objective Identified||Yes|
NAS Lemoore is located in the central portion of the San Joaquin Valley. It was commissioned in July 1962 and is an active aviation maintenance and operation facility that provides services and material to support aviation. Site 14 is located in the aircraft operations area of NAS Lemoore and consists of maintenance buildings, hangars and aircraft parking areas. Base personnel have stated that best management practices adopted in the 1980s, such as minimization of solvent use and containment and recycling of solvents and chemicals, sharply reduced the possibility of contamination from the 1980s to the present. Soil, soil gas and groundwater contaminants beneath Site 14 include volatile organic compounds (VOC) and fuel constituents. Chlorinated solvents, principally trichloroethene (TCE) and 1,1-dichloroethene (1,1-DCE), make up the bulk of the contamination in all three media, although localized concentrations of fuel constituents are related to activities near Building 188 and the former jet engine test cells. There are two discernible VOC plumes: one in the Building 180 area and one located south of Building 170 [Figure 5-1].
Based on the preliminary CSM, several suspected source areas were identified, including stormwater and wastewater lines, a wash rack, aircraft parking and maintenance areas, and six former underground storage tanks (UST). The USTs were removed and the wastewater lines repaired, but the source area was not remediated and isolated “floating product” remained. State and local regulatory agencies requested that the Navy expedite source characterization and plume delineation in order to fill CSM data gaps and move toward a remedy.
The initial CFESS investigation located potential leaks in the sewer system. These potential leak locations were targeted during a second mobilization where a MIP was used to profile the contamination associated with the leaks. After reviewing results from the first two mobilizations, monitoring wells were installed using sonic drilling equipment during the third mobilization. The decision logic was designed to ensure optimum placement of monitoring wells, such as adjacent to the suspected non-aqueous phase liquid (NAPL), or just beyond the edges of the plume, to serve as point of compliance monitoring wells. This strategy enabled the construction of only 15 monitoring wells, rather than the 35 wells initially proposed by the regulatory agency, providing a cost savings to the Navy. The sampling results and revised CSM contributed to remedial plans to reduce contaminant mass in the most concentrated portions of the plume and promote natural attenuation of any residual contamination.
The improved CSM resulted in a reduction of monitoring wells from 35 to15, providing a cost savings to the Navy. Project goals were achieved in a shorter time frame through the use of real-time technologies and a DWS that was supported by the regulatory agencies.
The preliminary CSM used historical site data from the 1990s and 2001 remedial investigations and evolved with ongoing input from the base environmental team and site stakeholders including the regulatory agencies (California Department of Toxic Substances Control [DTSC] and California Regional Water Quality Control Board [RWQCB]). The preliminary CSM was completed during SPP and included two CMAs to provide multiple working hypotheses for the plumes’ sources and evolution. Data gaps indicated that multiple sources could be contributing to the plume. An innovative investigation approach using real-time measurement technologies within a DWS framework was implemented to resolve these site uncertainties.
The investigation decision logic was developed as part of SPP and was implemented during three sequential mobilizations over a 1-year period. The decision logic guided the selection of initial and adaptive sample locations, depths, types and numbers as the investigation progressed in real-time. Adaptive sampling locations were identified based on three-dimensional visualizations of the MIP response created with a free decision support tool, the EPA-supported Spatial Analysis and Decision Assistance (SADA) software. After the MIP/CPT data was entered into SADA, results were emailed to members of the RWQCB and DTSC. Input from team members was typically received within the same afternoon.
Real time measurement technologies were used during the first two mobilizations. The first mobilization consisted of a CFESS to investigate the CMA hypothesis that the plume resulted from contaminant releases to storm sewers. The CFESS consisted of smoke testing, dye testing, sewer video and the innovative use of a sewer-grouting packer string as a platform for pressure testing and air sampling individual joints in the storm sewer. These tools were used to investigate over 1,000 feet of sewer pipe and floor drain and utility connections in two large maintenance hangars; sampling was complicated because one of the hangers was undergoing major renovation.
The second mobilization took place over two-weeks and consisted of a DWS investigation based on vertical profiling of the plumes using real-time measurement technologies, including the MIP and CPT direct sensing tools. Initial profiling locations were selected based on storm sewer defects identified through the CFESS as well as historical knowledge. Additional adaptive sampling locations were identified based on three-dimensional visualizations from MIP responses and the EPA-supported SADA software, which was loaded on a field laptop computer. Mobile laboratory data were collected to calibrate the MIP instrument and to select additional locations for step-out samples to better characterize the VOC plumes.
The second CMA was also investigated during the second mobilization, which suggested that chemicals were released directly to the concrete flight apron and subsequently penetrated the concrete panels through grout in the joints. To investigate this CMA, the MIP was advanced at locations adjacent to points where the aircraft electric and water service lines were present at the concrete surface. In addition, soil samples were collected at several locations and analyzed for VOCs in an on-site mobile laboratory.
The collaborative data set obtained from the second mobilization included 24 MIP/CPT profiles, 31 soil borings (both chemical and physical soil samples), 6 direct-push technology (DPT) groundwater grab samples, 6 surface soil samples and 1 sludge sample; data were collected to depths greater than 100 feet below ground surface. The collaborative data set provided a “snapshot” of the plume in three dimensions and helped evolve the CSM by supporting the sewer release CMA. In fact, the strongest MIP response was recorded at a location close to the most substantial defect in the storm sewer system.
This MIP response was elevated into a range potentially indicative of NAPL being present immediately adjacent to the sewer defect. In contrast, the sample and MIP profile results immediately below the hypothesized surface release locations did not indicate significant contamination.
TQRS not prepared
The final sampling and analysis plan (Field Sampling Plan/Quality Assurance Project Plan) for Site 14 Triad investigation was followed as field data were compiled and used to determine the location of contaminant sources. A total of 95 soil and 6 groundwater samples were analyzed for VOCs using a mobile laboratory and 10% of those samples were submitted to an off-site laboratory for confirmation analysis. Mobile laboratory data were used to calibrate the MIP and assist in selecting step-out sampling locations. The soil data results from the mobile laboratory analyses were not validated or used to evaluate human health risks.
On-site mobile laboratory data were compared with off-site laboratory data. Soil samples were not collected as formal split samples. The sampling techniques and sampling intervals within the soil borings differed; this resulted in consistently lower TCE results in the mobile laboratory samples.
Adaptive sampling locations were identified based in part on three-dimensional visualizations of MIP response created with SADA software, which was loaded on a field laptop computer.
The Triad investigation for Site 14 occurred over a 1-year period, with data collected from April 2005 through March 2006. The final report was completed in March 2008.
|NAS Lemoore Figure 5-1 (380.16 KB)|
To update this profile, contact Cheryl T. Johnson at Johnson.Cheryl@epa.gov or (703) 603-9045.