USEPA - Technology Innovation and Field Services Division (TIFSD)

Triad use at Naval Base San Diego saves an estimated 6 years and US$3m for site investigation

The U.S. Naval Facilities Engineering Command Southwest (NAVFAC SW) used the Triad approach to collect an integrated hydrogeologic and chemical dataset for expediting and optimizing characterization of a volatile organic compound (VOC) plume at Naval Base San Diego (NBSD), CA. The 295-acre 'IR Site 22' was identified in 2003 when VOC concentrations reaching 100 mg/L were reported in an upgradient well as part of a remedial investigation at 'NBSD IR Site 4.' As a result, NAVFAC SW initiated investigative actions to identify potential sources of VOC contamination in ground water, determine whether the source(s) were caused by Navy activities, and delineate VOCs in ground water.

IR Site 22 is located approximately three miles southeast of downtown San Diego, on the east side of San Diego Bay. The site comprises reclaimed tidal lands covered by dredged material, and encompasses privately owned commercial and industrial properties in addition to the NBSD.

IR Site 22 investigations leveraged all three elements of Triad:

The stakeholder team initiated a systematic planning process early in the project; stakeholders included NAVFAC SW, the Space and Naval Warfare Systems Center (SPAWAR), the California Regional Water Quality Control Board, and the California Department of Toxic Substances Control. The team collaborated in developing data quality objectives (DQOs) and the conceptual site model (CSM), which was used to design a technical approach. Regulators visited the site several times during field work to participate in data interpretation and decisions to 'step out' sampling to additional locations.

Field staff collected real-time in situ measurements using a site characterization and penetrometer system (SCAPS) truck equipped with onboard cone penetrometer testing and a membrane interface probe (CPT/MIP) and a direct sampling ion trap mass spectrometer (DSITMS).

Stakeholders collaborated in developing a dynamic work strategy to allow the field team to step out dynamically to meet project-specific DQOs. Web-based, near-real time communication of project data allowed stakeholders to view daily reports and remain engaged in the project as the CSM evolved.

The field work was conducted in three phases. Between each phase, a systematic planning meeting was held to present current data and the updated CSM and to optimize the following work phase.

Phase I involved a two-week lithologic and dense non-aqueous phase liquid (DNAPL) investigation using CPT with MIP and DITMS to build a detailed lithologic site model and identify VOC source area(s). A total of 35 borings were advanced to depths reaching 58 feet below ground surface (bgs). Lithologic data from CPT were used to augment existing information and expand the CSM. Results indicated three potential VOC source areas.

Phase II comprised a four-week, site-wide investigation of ground water. Using Phase I CPT and MIP data to optimize locations and screened intervals, a total of 24 direct-push temporary ground-water wells were installed to depths of up to 40 feet bgs. Each temporary well was constructed using nominal ¾-inch PVC casing with a 10-foot screened interval. Ground-water samples were collected for 24-hour-turnaround VOC analysis by a fixed-base laboratory using U.S. EPA Method 8260B. Eleven of the wells were surveyed to determine hydraulic gradient across the site.

Following evaluation of Phase I and II results, Phase III was initiated to address data gaps regarding the extent of dissolved VOC plumes, include potential preferential pathways in the refined CSM, and assess continuity between identified VOC source areas and VOCs independently identified in IR Site 4 ground water. This eight-week phase involved collecting lithologic data from 16 CPT borings, installing 22 additional temporary wells, and collecting ground-water samples for laboratory analysis of VOCs.

The collaborative data revealed two VOC plumes including tetrachloroethene (PCE) originating from offsite sources on private properties (Figure 1). Results also suggested contaminant migration favoring a subsurface paleochannel preferential pathway. In total, the SCAPS project team collected 2,775 vertical feet of lithologic data and 790 linear feet of VOC concentration data representative of the 295-acre site. The collaborative dataset included analytical results from 49 ground-water samples.

Triad implementation provided an expedited high-density dataset and a refined CSM in near-real time, resulting in cost avoidance estimated at $3 million and schedule savings of approximately six years. The Navy continues to work with regulatory stakeholders in developing a remedial strategy for IR Site 22.

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