Between 2004 and 2033, an estimated $200 billion will be spent on environmental restoration, of which 10-16% is estimated to be spent on site characterization. New methods and instruments that reduce costs, improve data quality, or provide complementary data at a reasonable cost, can have a significant impact on the direction of environmental restoration projects. The objective of this project was to demonstrate a new tool for monitoring contamination in ground and surface waters, the In Situ Sampler (IS2). The project provided an account of the theory, the engineering design process, and the first field data generated with this tool and method. This report provides users and stakeholders preliminary guidance for decision-making with respect to feasibility for future studies and field implementation.
The IS2 is a method and instrument for solid-phase extraction in situ. The IS2 sampler is inserted to a desired depth in a monitoring well, where it meters 10s to 1000s of milliliters (mL) of fluid, such as groundwater, to an array of sorbent cartridges over a time-scale from hours to weeks. Unlike many passive technologies, the IS2 does not require compound-specific calibration—concentration data is derived directly from the mass of analyte recovered from the sorbent cartridge and the known volume of water processed. This preconcentration step provides significant magnification of analyte concentration, improving reporting limits (RL). The samples returned by the IS2, while weighing only a few grams, can represent chemical constituents concentrated from several kilograms of water. This makes the handling and shipment of large numbers of samples significantly more cost effective as well as “green,” with respect to energy requirements and the carbon footprint of monitoring. The automation made possible by the IS2 reduces sample handling by technicians, with the potential to improve reproducibility, by limiting opportunities for contamination during processing in the analytical laboratory.
The IS2 was demonstrated at two sites: the Former Williams Air Force Base (AFB) in Mesa, Arizona, and Naval Air Station North Island (NASNI) in Coronado, California. At the Former Williams AFB, the device was inserted to a depth of 200 feet (ft) and generated 24-hour composite samples from micrograms per liter (μg/L) quantities of fuel components including naphthalene. At NASNI, the sampler was deployed to generate 28-day composite samples in a shallow well with hexavalent chromium contamination that was demonstrated to be driven by tidal influence. In both cases, the sorbents used were commercially available and the analysis methods typical for the analytes. The IS2 system provided data comparable to liquid samples, while also providing short-term or long-term integrated data from the preconcentration of analytes in situ.
The IS2 groundwater monitoring strategy performed most reliably when collecting solid analyte samples only, as is the case in most typical monitoring applications. For technology validation purposes, the device was modified to also capture the liquid that was extracted in situ. In this configuration, the challenge arises of preventing the hydrostatic pressure of water at depth to drive flow through the metering pumps. Passive check valves were used to counter the hydrostatic pressure, but sourcing and properly sizing these valves turned out to be time-intensive. The most common and most desirable configuration of the device is one where only solid-phase samples are collected and processed water is returned to the well bore. This greatly reduces the engineering requirements for the instrument, as the equal inlet and outlet pressures enable a relatively simple valve system to control the flow precisely.