Innovative Technologies And Vadose Zone Treatment Of Chlorinated Volatile Organic Compounds - Case Study Page: 11 of 35
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clogging of the sample port screen when advancing through clayey zones. Seventy-two soil vapor
samples were collected and analyzed for TCE and CC14 using the B&K monitor and 18 duplicates
were collected in TedlarTM bags for analysis using gas chromatography.
Sediment and soil gas data were compiled into contour maps and cross-sections for further
analysis to select screen intervals for SVE wells. Figure 8 illustrates TCE concentrations at sample
depths and selected screen zones in cross-sectional view. The stratigraphy was divided into four
zones, Zone A (shallowest) through Zone D (deepest), Figure 8. Zones B and D were permeable
enough to collect soil gas samples, while Zones A and C were too clayey to yield soil gas samples.
The upper permeable zone, Zone B, varied in thickness from 3 to 5.5 meters (10 to 18 ft.) and
consisted of sand with minor interbeds of silty and clayey sands. The lower permeable zone, Zone
D, varied in thickness from 1.2 to 2.1 meters (4 to 7 ft.) and consisted of primarily fine grained sand
and silty sand. This zone extended into the capillary fringe at several of the locations. TCE
concentrations in Zones B and D are illustrated in Figure 9.
SVE wells were installed at locations with detectable CVOC concentrations and screens were
placed into the permeable zones. Wells were designated as U (upper) for Zone B and L (lower) for
Zone D. Well spacing was based on drawdown test results from previous SVE pumping tests and
the anticipated surface seal effect of the foundation of building 672-T. More wells were screened in
zone D since CVOCs were found in higher concentrations and over a wider area (Figures 9 and 10).
Well Installation
Direct Push Technology (DPT) was selected to install the SVE wells because it has been
found to produce high quality and cost efficient SVE wells in unconsolidated vadose zone sediments
(WRSC, 2001b). The well installation process involves pre-pushing a pilot hole using a standard
DPT rod and tip to total well depth. The pilot hole is enlarged to receive the well materials by10
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NOONKESTER, JAY V.; NICHOLS, RALPH L. & DIXON, KENETH L. Innovative Technologies And Vadose Zone Treatment Of Chlorinated Volatile Organic Compounds - Case Study, article, August 2, 2005; Aiken, South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc875585/m1/11/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.