Site characterization currently represents at least one-third of the cost of remediation efforts by the Department of Defense (DoD). Problems associated with the traditional trial-and-error site characterization methods such as cost, sample transport, timeliness, and uncertainty have frequently hampered DoD's remediation efforts. This ESTCP project demonstrated the field application of a laser-induced fluorescence (LIF) petroleum sensor mounted in a penetrometer.
The LIF petroleum sensor uses an instrumented probe that can be pushed into the ground with a truck-mounted hydraulic system called a cone penetrometer. The cone penetrometer makes real-time chemical measurements of petroleum hydrocarbons in subsurface soil up to a potential maximum depth of 50 meters. The chemical sensor uses a laser to generate a characteristic "glow" from the petroleum contaminants. The "glow" can then be measured to determine the level of these contaminants. The optical screening method provides a nearly continuous profile of the petroleum contaminant distribution as the probe is pushed into the ground. This unique ability is a marked improvement over traditional core sampling procedures that may be compromised by core sample contamination or loss of well integrity. Real-time analysis of site contamination also eliminates complicated drilling procedures and the long process of packing and shipping samples to a laboratory.
This demonstration has successfully shown that the LIF system can rapidly determine the location and relative extent of petroleum hydrocarbon contamination in soil and groundwater. Detection thresholds for the LIF technology vary somewhat from site to site, but are typically 100 to 300 mg per kg. In general, LIF data shows a better than 85% agreement with the U.S. Environmental Protection Agency laboratory analytical data for total petroleum hydrocarbons and total recoverable petroleum hydrocarbons samples. The Site Characterization and Analysis Penetrometer System LIF technology has met California Environmental Protection Agency standards and was certified as a Site Characterization Technology in California by the State's Department of Toxic Substances Control.
Since the LIF technology has only been validated as a semi-quantitative methodology (detect/non-detect), it does not completely eliminate the need for traditional sampling. However, the technology does improve the placement of monitoring wells thereby reducing the number of wells needed for site characterization. Assuming that a site using the LIF sensor can avoid drilling half of the traditional wells, a 30 to 50 percent reduction in cost can be achieved. This reduction would translate into a greater than $15 to $25 million per year savings for DoD. On a per sample basis, LIF sampling is 100 times less expensive than conventional sampling.
The results of this demonstration show the LIF technology is a promising technology ready for technology transfer. (Project Completed - 1997)