Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Remediation® Conference

Monday, November 3, 2008 : 1:30 p.m.

Field Screening for PCB DNAPL Using Laser-Induced Fluorescence (LIF) to Detect Commingled Aromatic Hydrocarbons

Wayne C. Hardison, PE, Ban N. Aragona, CHMM and Justin J. Johnson, Haley & Aldrich of Michigan Inc.

This investigation uses rapid optic screening tool (ROST™) laser-induced fluorescence (LIF) technology to delineate the extent of a dense non-aqueous phase liquid (DNAPL) composed of polychlorinated biphenyls (PCBs) with a mixture of polycyclic aromatic hydrocarbons (PAHs).  ROST™/LIF technology uses an ultraviolet laser to induce fluorescent response in PAH compounds and is widely used in the environmental industry to delineate the extent of petroleum hydrocarbons in the subsurface.    Although PCBs do not fluoresce under ultraviolet light, the commingling of PAH compounds allows for the application of ROST™/LIF technology to delineate the extent of DNAPL in the subsurface.  Laboratory tests conducted to assess the feasibility of ROST™/LIF show that the PAH compounds commingled with the PCBs will fluoresce when exposed to ultraviolet light and produces a waveform unique to the DNAPL. 

 ROST™/LIF is typically used as a down-hole detection tool and is advanced into the subsurface with a truck-mounted cone pentrometer testing (CPT) rig. For this investigation, several factors prevent down-hole screening including the potential for DNAPL to adhere to ROST™/LIF probe and producing false positives; and the potential for recurring refusals by the CPT rig in the coarse anthropogenic fill unit.  Therefore, soil samples are continuously collected at 5-foot intervals and screened ex situ for the presence of DNAPL with the ROST™/LIF. 

 ROST™/LIF screening allowed for rapid delineation of DNAPL at the Site.  Results were verified through close visual inspection of the soil samples for the occurrence of DNAPL.  DNAPL was observed in a number of soil samples and as several distinct physical states: liquid phase, semi-solid phase, and trace phase.  ROST™/LIF detected DNAPL in all three of these physical states and distinguished it from other petroleum impacts.  Results of this investigation show ROST™/LIF provides an effective real-time field screening method for the detection of PAH compounds commingled with PCBs.

Justin J. Johnson, Haley & Aldrich of Michigan Inc. Justin J. Johnson is an environmental geologist for Haley & Aldrich of Ann Arbor, Michigan. He has a BA degree in geology from Gustavus Adolphus College (2002) and a MS degree in geological sciences from Michigan State University (2007). Mr. Johnson has been working as a geologist since 2004 and specializes in conducting environmental investigations at industrial sites including manufacturing facilities, former manufactured gas plants, and railroad yards.


Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Remediation® Conference