USING TRIAD (AKA PROFESSIONAL JUDGMENT) TO TRACK A COMMINGLED PLUME

Transcription

1 USING TRIAD (AKA PROFESSIONAL JUDGMENT) TO TRACK A COMMINGLED PLUME Why Triad? can adapt as needed (and we ve needed) using professional judgment every step of the way literally thousands of decisions made in the course of this investigation see Our project involves TCE source identification within large study area, with commingled TCE/PCE plume Only PCE source has been identified Large (1-2MGD) Public Supply Wells impacted and others at potential risk Using Environmental Forensics CSIA & geochemical analyses to get good data without drilling to 500 feet Next steps - assess deeper contamination and localized hydrologic conditions identify the TCE source

2 Source Identification in the beginning All Inclusive First Search/EDR Report - blew out their computer Numerous previous investigations to review and evaluate Other site data EPA/USGS/State/County/Municipal sources Hundreds of potential data and TCE sources: Industrial parks and corridors, poorly closed landfills, Federal and State Superfund sites, Former Manufactured Gas Plant Site, Vapor Intrusion Legacy Sites, injection wells Now what? Well

3 While we often must rely on data collected by others, do not rely on interpretations by others. - NAVFAC We are here to talk about using professional judgment

4 GEOPROBE INVESTIGATION Started with three transects perpendicular to known OU1 TCE/PCE-dominant plumes along three major roads: Total of 41 sampling locations, Collected 136 depth-discrete water samples, Maximum 120 bgs reviewed by and agreed as being best plan to identify plume by EPA-HQ high resolution site characterization and optimization staff (uh huh) Minimal shallow TCE hits up to 3300 ug/l, some in double digits, 0.52, 0.65, 1.8 and 0.82 ug/l w/o pumping Clean, shallow ground water on Long Island? How CAN this BE?

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6 Conceptual site Model after geoprobe - what do we know now? Surprisingly pristine Upper Glacial Aquifer clean, oxygenated water to 120 ft bgs No reductive dechlorination in oxygenated shallow subsurface, no daughter products Geoprobe investigation shows contamination s gone deep - due to accretion, DNAPL source, large and/or long-term contaminant source, lack of degradation, mass induced recharge, extreme vertical gradient all of the above? Deep water supply well sampling and CSIA analysis shows VOC contamination is at bgs, with same, discrete (as in DNA-like match ) TCE source feeding a miles-long plume

7 WHAT IS CSIA? Compound-Specific Isotope Analysis (CSIA) is an environmental forensic analytical technique that allows you to identify distinct TCE and other contaminant sources, one TCE from another Looks at δ 13 C, δ 37 Cl, and δ 2 H stable isotopes 13C/12C ratio used in 1D -CSIA one isotope 13C/12C and 37Cl/35Cl used in 2D -CSIA two isotopes 13C/12C, 37Cl/35Cl and 2H/1H used in 3D -CSIA three isotopes think of 3D as a DNA fingerprint ZZZZZZZZZZZZZZZZ I know, but you need to know they do different things for you! See

8 WHAT CAN CSIA DO FOR YOU? 1D - d 13 C ratio only - evaluates degradation process along pathway and can identify same source as it degrades 2D - d 13 C and d 37 Cl ratios can determine process of degradation and can differentiate between sources from concurrent enrichment of both isotopes 3D - d 13 C, d 37 Cl and d 2 H ratios can determine TCE origin See Download%20Center/Zymax-Isotope-Forensic-Analyses pdf

9 Cost Allocation by 2D-CSIA PRP A: d 13 C = -30 d 37 Cl = -2 PRP B: d 13 C = -25 d 37 Cl = +3 Co-mingled Plume: d 13 C = -29 d 37 Cl = -1 Plume = 80% PRP A + 20% PRP B Calculated by 13 C: (-29)*1 = (-30)*A + (-25)*(1-A) Confirmed by 37 Cl: (-1)*1 = (-2)*A + 3*(1-A) A=80% A=80%

10 PRELIMINARY CSIA RESULTS TWO PLUMES, THREE LOBES, PLUS A DIFFERENT SUPERFUND SITE, JUST FOR FUN (but PLeASe DOn t take the StARting POintS LiteRALLY)

11 WHY GO DEEP? MULTIPLE LINES OF EVIDENCE!!! Besides the PWS CSIA Results showing contamination at feet bgs? Diving Plume Criteria Hydraulic: downward gradients due to sewer exfiltration, low hydraulic conductivity, Geological: Biogeochemical: plumes (former?) shallow

12 GO DEEP! MULTIPLE LINES OF EVIDENCE CONTRIBUTING FACTORS TO VERTICAL GRADIENT OUR ACTUAL PLUME DIVE APPEARS TO QUITE SEVERE, MAYBE FOOT PER FOOT? ACCRETION DUE TO RECHARGE DNAPL MOVEMENT IN SUBSURFACE

13 PUBLIC SUPPLY WELL MASS DISCHARGE CALCULATIONS Mass discharge calculations show huge dilution of VOCs in large (1M+ GPD) supply wells Preliminary results at one well indicate g/day (50 plus pounds) of VOCs moving into well at about 10 ppb total VOCs pumping 1.7 MGD, 24/7, for at least 20 years Category 9 Plume can only go one level higher, as per ITRC Morale is, there s a big difference when sampling pumping vs. monitoring wells. Even supply wells meeting MCLs can have large, continuing source impacts lasting for decades.

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16 NEXT STEPS AND 100S MORE PROFESSIONAL JUDGMENT CALLS TO MAKE Transducer study begins this month to gain better understanding of vertical and horizontal groundwater flow and seasonal change Additional data review and calculations - to assess mass discharge, define plume(s) gathering info on supply well pumpage rates, use patterns and VOC history now from public records More CSIA sampling and analysis to connect impacted supply wells at depth before drilling Strategic drilling (shallow and deep) and depth-discrete GW sampling to zero in on potential sources

17 WAIT - WHERE D THE BLUE PLUME GO? CSIA results from three months later indicate GW flow may have reversed (for now) and we are sucking a different plume into supply wells. All it takes is one huge well to start or stop pumping. But the blue plume (and its source) is still there. Go ahead, try and design a recovery system in this kind of dynamic environment.

18 LISA K. VOYCE MSENE/TOX HDR Project Manager/Associate/Risk Assessor One Blue Hill Plaza, 12 th floor PO Box 1509 Pearl River, NY Ext. 263 hdrinc.com And LSRPA Board of Trustees member Thanks for listening! Questions? Lots to think about