Ambient Air Monitoring During Remediation of a Former MGP Plant

摘要

From the early 1800s through the mid-1900s, manufactured gas plant (MGP) sites were operated nationwide to produce gas from coal or oil for lighting, heating, and cooking. The gas manufacturing and purification processes conducted at the plants yielded gas plant residues that included tars, sludges, lampblack, light oils, spent oxide wastes, and other hydrocarbon products. Although many of the byproducts were recycled, excess residues remained at MGP sites. The residues contain polycyclic aromatic hydrocarbons (PAH), petroleum hydrocarbons, benzene, cyanide, metals, and phenols. The base contaminant, coal tar, is composed of a complex mixture of PAHs (primarily Napthalene) that generally exhibit low volatility, low solubility, and low biodegradability and some other volatiles (Benzene, Toluene etc). There are an estimated 3,000 to 5,000 former MGP sites across the country; some of those sites still are owned by the successors to the utilities that founded them and eventually will require remediation. MACTEC developed an air monitoring plan for a typical site in a Southeastern State that was to be remediated by removing some material and stabilizing the rest in-situ by chemical addition. The site was located within an urban environment so appropriate monitoring to ensure safe levels of exposure were maintained was critical. The plan that was generated called for both real-time monitoring using "gas chromatograph electronic noses" (later switched to PID devices) and "compliance" monitoring using high volume samplers that were placed along the perimeter of the site. Safe level of exposure was determined through a risk analysis and determining expected dilution based on air model runs (ISCST). This procedure followed state guidelines for assessment of toxics from industrial sources. This paper provides an overview of the monitoring plan, provides an analysis of what methods were used for monitoring and what techniques were successful as compared with those that were not.