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1.1 This practice presents a method for delineating the subsurface presence of nonaqueous phase liquids (NAPLs) consisting of petroleum hydrocarbons, coal tars, and similar waste materials using an optical image profiler (OIP) system. The OIP probe is advanced into waste materials, soils, and unconsolidated formations using direct push (DP) methods. The OIP system provides data approximately each 15 mm (0.05 ft) of log depth to support high-resolution site characterization.

1.2 OIP logging is limited to wastes, soils, and unconsolidated formations that can be penetrated with the available direct push equipment. The ability to penetrate materials is based on carrying vehicle weight, density of soil/materials, and consistency of soil/materials. Penetration may be limited or damage to sensors or tooling can occur under certain ground conditions. DP tools are not designed to penetrate consolidated rock (Guides D6001/D6001M and D6282/D6282M, Practices D7352 and D8037/D8037M).

1.3 Units—The values stated in SI units are to be regarded as standard, however, inch pound units are indicated for information within parentheses as they are in common use for many users. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.

1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.

1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 Subsurface contamination of soil and groundwater by nonaqueous phase liquids and wastes of various hydrocarbons is widespread in the industrialized world. In 2004, the U.S. EPA estimated there were about 680 000 active underground storage tanks (USTs) in the United States. They also estimated that approximately 96 % of these contained petroleum products and more than 443 000 releases had been confirmed (3). This indicates that there are many facilities and locations where LNAPLs may be present in subsurface soil. Often, subsurface hydrocarbon contamination may consist of common petroleum oils or fuels (diesel, gasoline, jet fuel, etc.), or crude oil and associated wastes. However, creosote used at wood treating facilities (4) or coal tars generated at historical manufactured gas plants (5) and other similar waste materials are also of concern. These products and related wastes contain aromatic and/or PAHs that will fluoresce under certain wavelengths of incident light (6).

5.2 Laser induced fluorescence (LIF) (Practice D6187) was initially developed in the 1990s for the detection of many types of hydrocarbon NAPLs in subsurface soils (7). This system uses a laser mounted above ground with a fiber-optic cable to transmit laser light down-hole and out a sapphire window to illuminate the formation. Resultant fluorescent light is transmitted back up-hole with a second fiber-optic cable to a spectroscope system for analysis. These systems have been successfully deployed using both a cone penetrometer truck or with a direct push percussion probing machine to locate hydrocarbon NAPLs and associated wastes in the subsurface at many sites (8). Comparable systems for hydrocarbon detection using lasers are still available such as the UVOST and TarGOST systems (9).

5.3 The OIP system cannot directly detect dense nonaqueous phase liquids (DNAPLs) composed of chlorinated volatile organic compounds (CVOCs). However, if the CVOC DNAPL contains greases or oils from degreasing operations, they may be detectable with the OIP system. Alternate methods for detection of CVOC DNAPL include the dye-LIF system (10) and the MIP system (Practice D7352). The MIP system also can detect dissolved phase CVOCs and dissolved phase petroleum groundwater plumes (11).

5.4 In place of a large up-hole laser and associated fiber-optic cables, the OIP system uses a small UV LED or a small green laser diode down-hole inside the probe to illuminate the formation through a sapphire window to induce fluorescence. Additionally, a small CMOS camera mounted behind the sapphire window inside the probe is used as the detector for the emitted visible range fluorescent light (Fig. 1). The OIP has been successfully deployed under both cone penetrometer vehicles or with a direct push percussion probing machine to locate hydrocarbon NAPLs and associated wastes in the subsurface at many sites (2).

5.5 The CMOS camera takes images of the visible light fluorescence at approximately 30 frames per second (FPS) as the probe is advanced at approximately 2 cm/s. Images collected by the CMOS camera are sent to the instruments and computer system. The computer software analyzes the color in the pixels of the collected images. Pixels are analyzed for specific ranges of color typical of UV or green light induced fluorescence of hydrocarbons. The computer software determines the percent area in each image identified as hydrocarbon fluorescence.

5.6 To obtain better quality images at depths of interest, probe advancement may be halted. An icon on-screen enables the operator to acquire images when the probe is at rest in both UV and visible light or green and infrared light, depending on the probe used. These “still” images provide the operator with images of greater sharpness and clarity which are needed to observe the distribution of NAPL or formation color and/or texture (Fig. 3). The still images are saved at the depth acquired in the log file.

FIG. 3 Examples of Still Images

Examples of still images taken under UV light (A) and visible light (B) at the same depth with the OIP system while the probe is not moving. The product at this location was #2 fuel oil. Droplets, blebs, and ganglia of product are visible in both images.

5.7 The OIP system provides a real-time method to screen for NAPL at hydrocarbon contaminated sites. A graphical log is used to present a log of average percent area of fluorescence in the images, bulk formation EC, HPT injection pressure, and selected images (Fig. 2). Real-time data allow for adaptive planning in site investigations (12-15). The results from the OIP system can be used for identifying locations and specific depths for sampling or remedial actions.

5.8 Detection ranges for common fuels were assessed in a laboratory bench test (2). Clean silica sand with 10 % moisture was spiked with multiple concentrations of common fuel-related contaminants (gasoline, diesel fuel, crude oil) and tested on the OIP-UV system. The crude oil tested could be observed below a bulk concentration of 100 mg/kg, fresh on-road diesel fuel was detected near 200 mg/kg, and fresh gasoline was detected at about 300 mg/kg. These products were observed as free phase droplets at low bulk concentrations in the clean sand-water matrix in this bench test, not as dissolved phase compounds. Product weathering, biodegradation, and site-specific soil and moisture conditions can have an impact and can raise the minimum detection limit significantly.

5.9 While the OIP-UV system uses a 265 nm to 275 nm UV source that can induce fluorescence of BTEX (benzene, toluene, ethyl benzene, and xylenes), the CMOS camera is currently not capable of detecting UV range fluorescence produced by these analytes.

5.10 The OIP log data can be modeled in 2D and/or 3D with appropriate software programs. These models provide useful visualization tools for describing the distribution of hydrocarbon NAPL contamination and associated wastes across a site. Soil images, EC, and HPT results can be used to determine lithology and contaminant migration pathways (2, 11, 16).

5.11 The data obtained from application of this practice may be used to guide soil (Guide D6282/D6282M) and groundwater sampling (Guide D6001/D6001M) or placement of long-term monitoring wells (Practice D5092/D5092M, Guide D6724/D6724M, Practice D6725/D6725M).

5.12 The OIP system can be used to assess the effectiveness of remediation on sites contaminated with hydrocarbons and associated waste materials. OIP logs can be run following remedial actions to assess a reduction or elimination of hydrocarbon fluorescence. Soil images can also be used to identify depths of soil impacted by remediation fluids through changes in soil color with visible light images, or the presence of fluorescent tracer dyes mixed with remedial fluids injected in the subsurface.

5.13 The OIP system cannot detect dissolved phase hydrocarbons. The membrane interface probe (MIP) (Practice D7352) is often used in conjunction with the OIP or independently to log dissolved phase contaminant plumes associated with hydrocarbon NAPL contamination, associated wastes, or other volatile organic compounds.