• An innovative graded approach was used to identify CCl4 DNAPL zones and confirm those analyses with field sampling
• A wide variety of technologies have been used in our investigation
• The investigation utilized a graded approach with simple surface technologies over large areas and then used more focused investigative techniques in hot spots
• Updated the Site Conceptual Model and integrated it with the Feasibility Study for the Plutonium Waste Sites

Detailed Project Description

The objective of this work was to develop a conceptual model for the carbon tetrachloride (CCl4) contamination in the subsurface for Phase I and then conduct a field investigation using innovative, yet reliable, technologies for characterizing and quantifying the remaining carbon tetrachloride source terms in Phase II in order to validate and update the conceptual model.  A key to the success of this important project included Vista Engineering’s strong project execution.  Vista Engineering had to marshal a complex team of companies with the expertise necessary to answer questions regarding the nature and sources of contamination in the 200 West Area Subsurface.

The team lead by Vista Engineering used an adaptive, graded approach with innovative technology insertion points to conduct the field investigation.  This graded approach initially used broad, or coarse, characterization methods to economically gather data over a large study area.  These were characterization techniques typically deployed from the ground surface.  The potential sources identified in these coarse investigations were combined with numerical modeling studies, and investigated in more detail using invasive tools such as direct-push technologies, drilling with soil sampling, soil gas sampling, innovative ribbon-sampling devices and cross-well seismic techniques.

Most of these investigations were conducted at 216-Z-9 and 216-Z-1A, both Hanford waste sites receiving significant quantities or organics and radionuclides.  During the carbon tetrachloride project, the HHR was used extensively.  At 216-Z-9 waste site, 4,708ft of push rod was advanced at 9 unique locations down to target depth in a highly-consolidated/cemented calcic paleosol (approximately 120ft in depth).

Vista Engineering developed the ability to take multiple (continuous) soil samples in a single boring, up to ten samples per borehole.  Analytical data was validated and the extent and degree of CCl4, plutonium, and 241Am contamination was evaluated and incorporated in revised conceptual site models for these waste sites.  The new data are iteratively incorporated in the conceptual model, refining the next steps of the investigation.  Through this iterative and graded approach, the characterization proceeded in an efficient and economical manner.