Final Report: Integrated Downhole Gas Chromatograph and Automated Sampler for Direct Push

EPA Contract Number: 68D00271
Title: Integrated Downhole Gas Chromatograph and Automated Sampler for Direct Push
Investigators: Jarski, Paul
Small Business: Dakota Technologies Inc.
EPA Contact: Richards, April
Phase: II
Project Period: September 1, 2000 through September 1, 2002
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2000) Recipients Lists
Research Category: Small Business Innovation Research (SBIR)

Description:

The primary purpose of this project was to construct and operate a custom, high-performance gas chromatograph within the interior of a cone penetrometer probe equipped with a membrane interface probe (MIP). This unique instrument enables semi-quantitative measurement of subsurface chemical contaminants in either the vadose or saturated soil zones without the need to transfer vapor or water to the ground surface.

The research builds on prior Dakota Technologies, Inc. (DTI) efforts in which gas chromatography (GC) detectors were adapted for direct-sensing operations in subterranean environments (i.e., "downhole"). The modified GC detectors were positioned in the push pipe behind the heated MIP, which transfers volatile organic compounds (VOCs) from the soil formation into a carrier gas stream. Transitioning to a fully functioning downhole GC (dhGC) required: (1) developing an analyte trap to preconcentrate VOCs passing through the MIP, (2) heating the trap and launching the analytes onto the column in as narrow of a temporal band as possible, and (3) arranging the column in a compact configuration. It also was necessary to integrate the components within the pipe and develop an umbilical cable to remotely support GC power, control, and communication demands.The primary purpose of this project was to construct and operate a custom, high-performance gas chromatograph within the interior of a cone penetrometer probe equipped with a membrane interface probe (MIP). This unique instrument enables semi-quantitative measurement of subsurface chemical contaminants in either the vadose or saturated soil zones without the need to transfer vapor or water to the ground surface.

Summary/Accomplishments (Outputs/Outcomes):

The research focus during this project was to further refine and miniaturize several key components of the dhGC initially developed during Phase I. Several modifications were made to the original dhGC system to improve its performance, including: additional valving to allow for both screening and GC modes to be performed with the same instrument, integration of a custom column assembly for analyte separation, development of a sustained heating system for the trap to minimize analyte carryover, and miniaturization of a photoionization detector. Several aspects of the dhGC layout also were refined, including: implementing a unibody frame design for support of the GC components, a shock mounting system for protection of the dhGC, and a water block and coated umbilical cable to eliminate water intrusion into the system. After completion of the dhGC engineering tasks, a calibration procedure was developed for use during field deployment. This calibration procedure allowed the operator to quickly determine the retention times for several VOCs in a single calibration run.

The advances made in the development of the dhGC culminated in a field test at a local site in September 2002. Three pushes were conducted to an average depth of 20 feet over a 2-day period. Prior to each push, a calibration run was performed to determine the retention times of several important VOCs. Fourteen chromatograms were collected at this site over a wide range of depths using two different operational modes. The first of these modes, referred to as the discrete sampling mode, collected the sample onto the trap from single depths. The second mode, referred to as the integrated sampling mode, collected the sample onto the trap over specified depth ranges. The chromatograms using both methods clearly indicated that numerous contaminant species were present at the site, and that their relative concentrations changed considerably over the area investigated.

Conclusions:

DTI is developing technology that rapidly characterizes and analyzes biological samples; chemical mixtures; environmental media (soil, water, and air); and industrial processes by using highly sensitive, innovative, and reliable technology. DTI employs the latest advances in lasers, optics, electronics, direct chemical-sensing technology, automation hardware, and control/analysis software.

DTI's environmental solutions fill a market need, providing both in situ and chemically specific analytical-quality data for important VOCs. This environmental equipment can be used for comprehensive site characterization, long-term monitoring, air quality, and forensic services at former manufactured gas plant sites, wood-treating facilities, and current and former dry cleaning facilities, fuel refineries, storage depots, along distribution pipelines, at landfills, in wetlands and harbors, and at military installations and industrial sites under consideration for redevelopment (Brownfields).

The dhGC, along with DTI's suite of environmental solutions, contains proprietary tools, software, and procedures that allow DTI to pinpoint the location and nature of contaminant sources and accurately map their spatial distribution much faster, more reliably, and with much better spatial resolution than anyone else in the industry. This suite of environmental solutions will allow DTI to handle all major contaminant classes (fuels and petroleum, chlorinated solvents, methyl tertiary butyl ether, heavy metals, pesticides, microbiological species) and all media (soil, groundwater, and air).

The Phase II results have shown that the dhGC can be used for several applications including: tracking dissolved-phase plumes in near real-time to levels below the maximum contaminant level, installing monitoring wells after the location and thickness of the contamination zones are known, rationally choosing where to collect chromatograms in the vertical profile, and following the course of remediation procedures. Individually and collectively, these attributes represent an enormous advance over the current state-of-the-art for site characterization and monitoring.

Supplemental Keywords:

gas chromatograph, sorbent traps, direct push probe, membrane interface probe, in situ, volatile organic compounds, contaminant source, VOCs, site characterization, BTEX, PCE, TCE, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Environmental Monitoring, Engineering, Environmental Engineering, Ecological Indicators, gas chromatography, dhGC, sampling, downhole gas chromatograph


SBIR Phase I:

Miniature Membrane Inlet Gas Chromatograph for Cone Penetrometers  | Final Report