Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02c. In Situ Activated Carbon-Based Amendments: Assessing Effectiveness and Performance

Formatted Title:

Innovative Activated Carbon Soil Remediation for Site Redevelopment at a Former MGP Facility

Background/Objectives:

A former manufactured gas plant (MGP) site within an urban area of the northeast US is being redeveloped into a mixed-used commercial high-rise building. The surrounding areas of the former MGP site have already been developed into office, research, and residential buildings. Soil pre-characterization data revealed portions of the Site soils classified as RCRA hazardous waste due to elevated benzene concentrations. During the soil excavation for Site redevelopment, control of the odor and VOC concentrations has been a top priority, particularly given the close proximity to abutters in an urban setting. Initially, a multi-phase tented excavation utilizing multiple air exchange units (sprung tents) equipped with vapor treatment systems was initially planned to manage odor and VOCs generated during Site excavation. However, external logistical challenges required the project team to adjust the excavation approach due to the time and effort required for tent assembly and maintenance. To meet the evolving needs of the project, powdered activated carbon (PAC) blending was proposed in lieu of the tented excavation. An on-Site treatability study and a field-scale pilot study were conducted to develop design and implementation recommendations for the application of PAC to manage odors and VOC concentrations during excavation. To date, using PAC has been proven to be successful for this Site redevelopment.

Approach/Activities:

During the treatability study in August 2022, several commercially available odor control products including odor suppression sprays, odor control foams, and oxidants were tested along with activated carbon (granular activated carbon [GAC] and PAC) for their odor and VOC control capabilities. The effectiveness of these products applied to Site soil was quantified using PID, field GC unit (to analyze chlorinated solvents, BTEX, and naphthalene), and hydrogen sulfide vapor meter. All commercial products showed limited effectiveness for the MGP soil, especially when agitation (to simulate excavation) occurred. Activated carbon showed high effectiveness under a range of circumstances including high agitation conditions. PAC was selected over GAC because PAC showed a much faster reaction rate and also demonstrated effectiveness at lower dosages. Based on the treatability test, the recommended dosage of PAC was 3% by weight. In December 2022, a field-scale pilot study was conducted to confirm the recommended dosage effectiveness during the excavation of MGP soil and also evaluate the application and dust control methods. Confirmatory VOC samples collected were using summa canisters and PIDs at various locations around the excavation.

Results/Lessons Learned:

Using PAC for odor and VOC management is an innovative approach that successfully facilitated the excavation of more than 30,000 cubic yards of contaminated soil in a close urban setting. Compared with the ventilation and VOC air treatment equipment required for the tented excavation, the application using regenerated PAC significantly reduced greenhouse gas (GHG) emissions and energy usage. Further, lessons learned during the field implementation include:

The PAC mixing is most manageable when conducted in 2- to 3-foot lifts. PAC can be effectively blended with Site soils for odor and VOC control using standard excavation equipment. Clay soils require additional effort for blending but can be treated successfully.
Dust control is an important consideration for both worker safety due to particle size and public perception. The PAC is a fine-grained black powder that readily migrates with winds if proper dust control is not in place.

Sara Roy

Affiliation

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(Group 1, Poster Board #59) Innovative Activated Carbon Soil Remediation for Site Redevelopment at a Former MGP Facility