Innovations in Site Characterization. Case Study: Hanscom Air Force Base, Operable Unit 1 (Sites 1, 2, and 3)


Courtesy of US EPA - Environmental Protection Agency

 Executive Summary

Field analytical instrumentation and methods were used to support a site characterization study at the Airfield at Hanscom Air Force Base (HAFB) Operable Unit 1. HAFB is located in Middlesex County, Massachusetts, and occupies land in the towns of Bedford, Concord, Lexington, and Lincoln. U.S. Air Force military operations began in 1941 and continued through 1973. With the cessation of military flying activities in 1973, the airfield and the surrounding land was given to the Massachusetts Port Authority (MASSPORT), which currently operates a civilian airport as L.G. Hanscom Field. The U.S. Air Force continues to occupy 396 acres and operates the Electronic Systems Division of the Air Force Systems Command at HAFB.

As part of EPA’s Environmental Technology Initiative (ETI), a demonstration of a dynamic site investigation using an Adaptive Sampling and Analysis Program was utilized at HAFB for Operable Unit 1. The goal of the HAFB investigation was to demonstrate the ability of field analytical methods to produce data of sufficient quality to support remedial decisions. The specific project objectives used the EPA Soil Screening Level action limits to determine if residual soil contamination posed a risk via the soil to ground water pathway [5]. The HAFB investigation relied on data produced in the field to make decisions as to the location of samples collected and the types of analysis performed. When compared with the traditional site characterization process, the dynamic workplan/adaptive sampling and analysis program for HAFB resulted in a faster and cheaper site investigation. The adaptive sampling and analysis program provided information on a “real-time” basis to support on-site decision making. The field methods were “performance based” and provided data of sufficient quality to achieve site-specific data quality objectives (DQOs), with sample analysis rates that supported the dynamic site investigation process.

Innovative sampling and analytical technologies used at HAFB include Geoprobe; Bruker Thermal Desorption Gas Chromatography/Mass Spectrometry (TDGC/MS); Tekmar Purge and Trap with a Hewlett-Packard (HP) GC/MS; a Tufts designed thermal desorber inlet and HP GC/MS (TDGC/MS); and Ion Fingerprint Detection (IFD) software, as well as an on-site laboratory field rugged ICP/OES. During the HAFB investigation, an average of 75 soil samples per day were screened for volatile organic compounds (VOCs) by the Bruker TDGC/MS. In a two-week period, a total of 601 samples were analyzed. Quantitative VOC analysis of 158 soil samples by the Tekmar purge and trap GC/MS was made to confirm the screening results and to delineate the extent of contamination. Quantitative analyses of 69 soil samples for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were performed by the Tufts TDGC/MS and 121 soil samples for metals were performed by the ICP/OES.

Some important observations and lessons learned during the project were the following:

Field analytical methods employing performance-based methods can produce data of equal quality to commercial laboratories employing standardized EPA methods, can support a dynamic workplan/adaptive sampling and analysis program, and can support cleanup verification programs.

Cost effectiveness is maximized when site DQOs, analytical throughput rates, data turnaround times, sample collection rates, and sample analysis costs are evaluated and optimized to meet the site-specific scientific and engineering questions under investigation prior to the beginning of the field work. TDGC/MS and the mass spectrometry data analysis algorithms allow PCB/PAH analyses to be performed at the same time without the need for sample cleanup and fractionation time. Analytical run times can be reduced from 40 minutes to 10 minutes.

DQOs were met for all target compounds except vinyl chloride. Trade-offs may need to be considered between achieving low limits of detection for VOC gaseous compounds and meeting DQOs for all other (less volatile) VOC target compounds.

Download the full case study in pdf format (1.64 Mb)

A full copy of the report on which this case study is based, “A Dynamic Site Investigation: Adaptive Sampling and Analysis Program for Operable Unit 1 at Hanscom Air Force Base, Bedford, Massachusetts” can be downloaded in pdf format (1 Mb).

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