ASTM D6187-97(2010)

Direct push LIF is used for site investigations where the delineation of petroleum hydrocarbons and other fluorophores is necessary. Generic terms for these investigations are site assessments and hazardous waste site investigations. Continuous LIF is used to provide information on the relative amounts of contamination and to provide a lithological detail of the subsurface strata. These investigations are frequently required in the characterization of hazardous waste sites.

This technology provides preliminary results within minutes following the completion of each test. This allows the number, locations, and depths of subsequent tests to be adjusted in the field. Field adjustment may increase the efficiency of the investigation program.

The rapid fluorescence data gathering provided by direct push LIF provides information necessary to assess the presence of contamination in soils and associated pore fluids in the field. This method allows for immediate determination of relative amounts of contamination. This allows the number, locations, and depths of subsequent activities to be adjusted in the field. Field adjustment may increase the efficiency of the investigation program.

With appropriate sensors, the direct-push investigation program can provide information on soil stratigraphy and the distribution of petroleum and other fluorophores in the subsurface. This method results in minimum site disturbance and generates no cuttings that might require disposal (1).

This practice is confirmed using soil samples collected at given depths to confirm the fluorescence readings using a field deployed EPA Method 418.1 (2), EPA method 8015-modified, and a modified EPA 8270 Method (3), or equivalent methodologies, as compared to the fluorescence reading from the same depth from the sensor to verify that the fluorescence correlates with the contamination. The collected samples are also tested on the probe window in the truck to ensure the sample collected is representative of the region tested in situ.

This practice may not be the correct method for preliminary or supplemental investigations in all cases. Chemical and physical properties of site specific soil matrices may have an effect on site specific detection limits. Subsurface conditions affect the performance of the equipment and methods associated with the direct push method. Direct push methods are not effective in pushing in solid bedrock and are marginally effective in pushing in weathered formations. Dense gravelly tills where boulders and cobbles are present, stiff and hard clays, and cemented soil zones may cause refusal and potential probe breakage. Certain cohesive soils, depending on their moisture content, can create friction on the cone penetrometer probes which can eventually equal or exceed the static reaction force and/or the impact energy being applied. As with all direct push methods, precautions must be taken to prevent cross contamination of aquifers through migration of contaminants up or down the cone penetrometer hole.

The practicing of direct push techniques may be controlled by various government regulations governing subsurface explorations. Certification or licensing regulations, or both, may in some cases be considered in establishing performance criteria. For additional information see (4-15)

1.1 This practice covers the method for delineating the subsurface presence of petroleum hydrocarbons and other hydrocarbons using a fiber optic based nitrogen laser-induced fluorescence sensor system.

1.2 The petroleum hydrocarbon sensing scheme utilizes a fluorescence technique in which a nitrogen laser emits pulsed ultraviolet light. The laser, mounted on the cone penetrometer platform, is linked via fiber optic cables to a window mounted on the side of a penetrometer probe. Laser energy emitted through the window causes fluorescence in adjacent contaminated media. The fluorescent radiation is transmitted to the surface via optical cables for real-time spectral data acquisition and spectral analysis on the platform.

1.3 This sensor responds to any material that fluoresces when excited with ultraviolet wavelengths of light, largely the polycyclic aromatic, aromatic, and substituted hydrocarbons, along with a few heterocyclic hydrocarbons. The excitation energy will cause all encountered fluorophores to fluoresce, including some minerals and some non-petroleum organic matter. However, because the sensor collects full spectral information, discrimination among the fluorophores may be distinguished using the spectral features associated with the data. Soil samples should be taken to verify recurring spectral signatures to discriminate between fluorescing petroleum hydrocarbons and naturally occurring fluorophores.

1.4 This practice is used in conjunction with a cone penetrometer of the electronic type, described in Test Method D5778.

1.4.1 The direct push LIF described in this practice can provide accurate information on the characteristics of the soils and contaminants encountered in the vadose zone and the saturated zone, although it does not make a distinction between dissolved and sorbed contamination in the saturated zone.

1.5 This practice describes rapid, continuous, in-situ, real-time characterization of subsurface soil.

1.6 Direct push LIF is limited to soils that can be penetrated with the available equipment. The ability to penetrate strata is based on carrying vehicle weight, density of soil, and consistency of soil. Penetration may be limited; or, damage to sensors can occur in certain ground conditions.

1.7 This practice does not address the installation of any temporary or permanent soil, groundwater, soil vapor monitoring, or remediation devices; although, the devices described may be left in-situ for the purpose of on-going monitoring.

1.8 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are for information only.

1.9 Direct push LIF environmental site characterization will often involve safety planning, administration, and documentation. This practice does not purport to address the issues of operational or site safety.

1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.