Topic Area: 7f. HRSC and Conceptual Site Models

Formatted Title:

Applying HRSC Tools to Identify and Target a Mass-Flux Based Remedy

Background/Objectives:

Historical release from a pipeline block valve station resulted in LNAPL and dissolved phase benzene plume with recent data indicating potential migration of dissolved phase impacts toward offsite receptors. The site complexities include inaccessible source area and lithology characterized by low-permeability storage zones and high-permeability transport zones. Therefore, high-resolution site characterization (HRSC) tools, the membrane interface probe (MIP) coupled with a hydraulic profiling tool (HPT) (collectively referred to as MiHpt), were used to conduct subsurface investigation across transects to develop a remedial strategy. MIP vertically profiles relative concentration of volatile organic compounds (VOCs) while HPT estimates the hydraulic conductivity of the soil. Combined these data provided a detailed high-resolution conceptual site model identifying contaminant flux zones to support remedial decision making.

Approach/Activities:

A MiHpt investigation was conducted to develop a mass flux model that was used to support the selection and implementation of a long-term and sustainable remedial action to mitigate off-site dissolved phase benzene. Real-time MiHpt data enabled dynamic field decisions ensuring comprehensive characterization to better delineate contaminant transport zones efficiently. The mass flux model identified mass transport zones, i.e., areas with high VOC concentrations and high conductivity, to be targeted with focused remedial actions. The investigation also leveraged slug tests to confirm hydraulic conductivity measurements, enhancing the reliability of the mass flux model.

The results were used to estimated mass flux to consider enhancing the existing biosparge system and evaluate supplemental remedial options to reduce flux migrating offsite. Additionally, an environmental footprint tool, e.g., SiteWise^TM, was used to compare the footprint of a traditional soil boring investigation versus the HRSC investigation.

Nicky Moody

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(Group 2, Poster Board #26) Applying HRSC Tools to Identify and Target a Mass-Flux Based Remedy