The USGS, in cooperation with the NHDES and USEPA, has established a contaminant monitoring system for the Savage Well Superfund Site in Milford, N.H. The area is underlain by a large 0.5 mi2 plume of volatile organic compounds (VOCs). The monitoring system is designed to document the rate of clean-up of the VOC plume after installation and operation of a remediation system.

A sampling program began in 1997, using low-flow sampling procedures before the installation of the remediation system. Low-flow sampling involves purging a low volume of water from a well until water-quality parameters stabilize enough to collect a sample. Low-flow sampling can take up to several hours per well to purge and collect a sample. To increase the amount of sampling and reduce sampling costs, passive diffusion sampling was introduced in 1998 to coincide with the start of remedial operations.

A passive diffusion sampler consists of a polyethylene bag containing deionized, contaminant-free water (see photograph) suspended in well water inside a mesh sleeve. Contaminants in the well water diffuse through the polyethylene bag until the concentration inside the bag matches the concentration in well water.

 

 

Passive diffusion sampling proved to be an easy and inexpensive approach to collecting water-quality samples and was completed in one-fifth the time of the traditional low-flow sampling. At the site, concentrations of VOCs were similar in diffusion samples and in low-flow samples. By reducing the cost of sampling, the frequency of sample collection can be increased, which leads to an better understanding of how contaminants are transported through the site.

 

--Philip Harte (603) 226-7813 or ptharte@usgs.gov

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