Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6e. Surfactant-Enhanced Remediation

Formatted Title:

Optimizing NAPL Remediation in a Complex, Urban Setting: Surfactant Enhanced Extractions and In Situ Chemical Oxidations

Background/Objectives:

In situ remediation of NAPL in low permeability and heterogenous lithologies is a challenge for remediation practitioners. Common remediation methods like excavation, ex situ thermal desorption, and in situ soil mixing can prove difficult to implement, especially in deeper zones, areas with critical utility lines, or in urban settings. Complex, expensive equipment and emissions controls can be required for such applications. And in these complicated settings, other in situ remediation methods like dual-phase extraction and pump and treat are often operated for many years due to their limited capture rates from heterogeneous, low permeability soils. In such settings, a sequenced treatment train approach of combined remedies may be appropriate to maximize NAPL removal/destruction rates during shorter operational timeframes.

Approach/Activities:

This presentation will focus on a recent and yet-to-be publicized 2022-23 case study where remedial design and implementation were both optimized to enhance NAPL removal/destruction rates to meet long-term objectives in less than one year so the Site could be transferred for public use. The Site included a former MGP facility and gas holder. DNAPL impacts including polycyclic aromatic hydrocarbons (PAHs) were present from approximately 15 to 40 feet below ground surface (ft bgs) across the nearly 29,000 square foot treatment area. Extraction of free phase DNAPL was accomplished through 34 dual-purpose extraction/injection wells. Surfactant enhanced product recovery (SEPR) was conducted to increase mass extraction rates by injecting surfactant solutions at fixed wells and temporary DPT points. After diminishing mass extraction rates were achieved, in-situ chemical oxidation (ISCO) injections were performed at over 210 locations to destroy residual, non-extractable PAH impacts.

Results/Lessons Learned:

Four types of NAPL extraction pumps were fielded to maximize recovery rates from different zones across the Site (using nearly 30 pumps in total). Optimizations to the aboveground liquid treatment system were designed to “de-emulsify” extracted NAPL from surfactants and groundwater. SEPR operations removed ~165,000 gallons of DNAPL-surfactant-groundwater emulsion from the Site’s subsurface. During the second phase of remediation, ~70,000 pounds of ISCO amendments were injected. Portions of the extraction system were dynamically operated to enhance ISCO distribution during several portions of the ISCO injection phase. This presentation will highlight the interpretation and use of on-site data to optimize the performance of sequential SEPR and ISCO remedies.

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Brian Holderness