Case Study: Confirmation of TarGOST Laser-induced Fluorescence DNAPL Delineation with Soil Boring Data. TarGOST Technology: How Does it Work?

Transcription

1 Case Study: Confirmation of TarGOST Laser-induced Fluorescence DNAPL Delineation with Soil Boring Data Marc B. Okin Sean M. Carroll William R. Fisher Dakota Technologies, Inc. Randy W. St. Germain The International Symposium & Exhibition on the Redevelopment of Manufactured Gas Plant Sites April 6, 2006 Reading, England TarGOST Technology: How Does it Work? Developed & operated by Dakota Technologies, Inc. TarGOST = Tar-specific Green Optical Screening Tool Based on laser-induced fluorescence specific to PAH molecules, the primary component in MGP related tars, oils (DNAPL) Rapid pulses of green laser light (approximately 10 ns) are emitted into the ground 20 to 50 times per second (20-50 Hz) 1

2 TarGOST Technology: How Does it Work? 4 optical channels record energy released from PAH molecules following excitation Geoprobe - mounted TarGOST unit Note: Maximum probe depth is limited by the equipment on which TarGOST is mounted (have gone up to 60 ft BGS using Geoprobe / CPT) Software screen output TarGOST Technology: How Does it Work? Response time and amplitude contribute to the fluorescence signature of the DNAPL In the absence of PAH molecules, green light is rapidly reflected and recorded by the first optical sensor (blue peak) Nearly continuous readings (2-cm intervals) produces thorough coverage Approximately 45 minutes per 30-foot probe (~ 300 ft/day) 2

3 TarGOST Offers Unique Advantages over Traditional Approaches Rapid pace enables dense data collection Real-time data produces smart & flexible field approach Data product: spatially dense semi-quantitative Vertically continuous Results in fewer mobilizations, reduced uncertainty, reduction in long-term investigative costs and generates no investigative-derived waste Case Study: Site Overview What We Understood: Prior Conceptual Site Model Geology: Fill / alluvium / glacial till River located adjacent to Site (thought to sit on top of alluvium surface) Prior investigation results: DNAPL present in monitoring wells & suggested in onsite soil borings Off-site DNAPL presence suggested; however delineation elusive using conventional methods 3

4 Prior Conceptual Site Model A Former canal Former MGP Plant Superior Street B Gas Holders {Note: Larger holder was remediated in 1995} St. Mary s River 100 feet 5x vertical exag. 10 feet Fill Sandy till Alluvium Visible NAPL Significant Staining / Sheen Staining / Odor No visible impacts Silty till Sand lens Silty till Sand Silty till Investigation Scope TarGOST delineation: 70 probes on land (CPT rig, 8 days); 53 in River from small barge (Geoprobe, 4 days) Field geologist directed investigation and used GPS to capture position Soil borings/monitoring wells: some used for confirmation of TarGOST results Core sampling using large-diameter Geoprobe sampler: Conducted at impacted locations Cores submitted for fluorescent photography 4

5 Fluorescent Core Photography Light-end LNAPL 13 to 15 feet deep Heavier DNAPL oil 26 to 28 feet deep Note: Fluorescent photography performed by PTS Laboratories, Santa Fe Springs, CA Results - Summary DNAPL Delineation: Thicker DNAPL zones on-site (near historical operational structures); Thinner stringers in permeable zones fingering outward from source areas Observed multiple fluorescence signatures: Lighter fraction (More mobile?) Two DNAPL types 5

6 Investigation Results Revised Conceptual Site Model 6

7 Results: Source Area DNAPL Delineation NOTE: = Estimated glacial till surface Results: DNAPL Delineation Adjacent to Holder Foundation Along riverbank NOTE: = Estimated glacial till surface 7

8 River Sediment TarGOST Results Near shore: DNAPL seams of varying thickness Mid-river: thin DNAPL seam Maximum reading: 1118%RE at 12 FT NOTE: = Estimated glacial till surface DNAPL Signatures 8

9 DNAPL Signatures Red MGP oil Analysis of TarGOST Performance TarGOST provided rapid, real-time DNAPL delineation Results correlate well with observational & analytical data Data density provides good understanding of extent Real-time nature enhances efficiency (reduces chance of re-mobilization) Very effective for conceptual site model development & refinement 9

10 Conclusions TarGOST has a place in the arsenal of tools for DNAPL Assessment Build other investigational phases around TarGOST results (use soil borings to define vertical extent) Best used as First shot at hot-or-not DNAPL delineation to identify problem areas. Can be effective in middle of assessment phase fill data gaps (as it was in this investigation) * Understand limitations of TarGOST range of vision : Gasoline, solvent impacts will not be detected using TarGOST. THANK YOU FOR YOUR ATTENTION Dakota Technologies, Inc. 10