Risk-Based Decisions, Inc.  (916) 923-0570  916.923.0570
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Case Study 3.  To identify distinct source of DNAPL-like chlorinated solvent concentrations some 800 feet downgradient of site.
Objective.  To identify distinct source of DNAPL-like chlorinated solvent concentrations some 800 feet downgradient of site.

Site Information

  • Contaminated groundwater from site (with known DNAPL source) was migrating offsite

  • PCE at DNAPL-like concentrations was identified in groundwater some 800 feet downgradient of the site and attributed to our client's site.

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Sampling Strategy

  • Designed CPT/Hydropunch sampling strategy.

  • Data from the CPTs was used to develop 3D model of the subsurface lithology.

  • Depth-discrete preferential sand channels were identified in 3D.

  • Depth-discrete grab groundwater results were plotted in 3D.

Results

3D Modeling showed that;

  1. A new DNAPL source had been identified with 100,000 ppb PCE reported in CPT-5 at approximately 31 ft bgs.

  2. This elevated PCE was present in a thin sand lens outside the preferential pathway for flow of groundwater originating from our client's site.

  3. Concentrations of PCE upgradient were orders of magnitude lower than those at the newly-identified DNAPLlike source.

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Risk-Based Decisions, Inc.
2033 Howe Avenue (Suite 240)
Sacramento, CA 95825
P:  916.923.0570
F: 916.923-0611
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