Formatted Title
Air Monitoring and No Complaints at a Former MGP Construction Site on Lake Superior
Background/Objectives
At an historical manufactured gas plant (MGP) remediation site on Lake Superior, potential air emissions of VOCs and particulates resulting from remedial construction were a concern. If air emissions could not be controlled, particularly for benzene, public health concerns and complaints could require construction of structures to contain excavation and soil management areas at significant expense.
Approach/Activities
An Air Monitoring Plan was prepared, approved by WDNR, and operated effectively for the construction project. Key air emission sources included soil excavation and management areas where benzene concentrations in soil were as high as 3,000 mg/kg and fugitive particulate emissions from construction activity and neighboring property industrial activity. Six real-time VOC and particulate monitoring instruments were installed at the perimeter of the 8-acre industrial site and used to detect total VOC emissions at the site perimeter. The real-time VOC monitoring system included a field gas-chromatograph at each of the six stations to obtain chemical-specific concentrations of BTEX and naphthalene if concentrations exceeded 0.5 ppmV measured using a photoionization detector. Since one element of the remediation plan for the site was in situ biosparging/soil vapor extraction (SVE), battery-powered, real-time VOC monitoring instruments were deployed at one sanitary sewer manhole and one storm sewer manhole. For confirmation, laboratory analyses of summa canisters were used to obtain 24-hr weighted average air emissions samples at perimeter stations, vapor monitoring points, and inside one building near the site for off-site laboratory testing. Additionally, 35 soil vapor monitoring points were installed throughout the biosparge/SVE area to document conditions during remediation.
Results/Lessons Learned
Effective management of potential VOC and particulate emissions resulted in no public complaints as a result of noticeable air emissions or odors. The air monitoring data demonstrated that the 24-hr weighted average sample data did not exceed the OSHA TWA level for benzene in air except for during two of 23 sampling events when the site excavation program was initiated and measures to reduce VOC emissions were being optimized. Optimization efforts included the adjustment of dosing rates of Rusmar Foam TechnologiesTM, reductions in excavation rate, and placement of soil cover. Particulate emissions never exceeded the WDNR 24-hr emission limit. Air monitoring at the two sewer manholes demonstrated that operation of the biosparge/SVE systems did not produce a statistically significant increase in VOC concentrations.