Using Compound Specific Isotope Analysis (CSIA) as a Line of Evidence for MNA at a UST Petroleum Site

Transcription

1 Using Compound Specific Isotope Analysis (CSIA) as a Line of Evidence for MNA at a UST Petroleum Site

2 What is CSIA? It is an analytical method that can measure the ratios of stable isotopes. It is not biological.

3 How is CSIA used in the environmental arena? To determine if organic compounds are degrading.

4 Stable Isotope Atoms with the same number of protons, but a different number of neutrons. Source:

5 Stable Isotope Atoms with the same number of protons, but a different number of neutrons. Source:

6 How Stable Isotope Ratios are Measured Source: USEPA 2008

7 Reporting Measured Values (δ) δ 13 C ( ) = ( 13 C/ 12 C) sample ( 13 C/ 12 C) std ( 13 C/ 12 C) std X 1000 The value is reported as δ. Expressed relative to an international standard Reported as δ 13 C for Carbon Multiplied by 1000 because the value is so small Reported as parts per thousand or per mill

8 Degradation of an Isotope Source: Michael Hyman, Ph.D., 2011

9 Why the need for CSIA? Reductions in contaminant concentrations may be due to dilution or dispersion The sample collected may not be representative of the plume of contamination

10 Case Study Site Background Photograph by Stantec Consulting, 2008 The site is located in Sylvester, Georgia. It currently operates as a gas retail station with 1 3,000 gallon gasoline tank. A release was reported in January 27, 1998.

11 Site Lay Out Characterization Results Plume was defined. Highest benzene concentration was 20,000 µg/l. No free product Thirteen private wells within a ½ mile radius On site private well Pump & Treat, MPE/AS initially proposed. Additional Complications Remediation efforts limited by restrictions on radius of influence imposed by railroad. No alternate public water supply Source: Stantec Consulting

12 Arguments for NFA Conduct EFR Event to reduce benzene concentrations Moved outside private well Monitored benzene concentrations results showed trending downward Perimeter GWM wells all BDL CSIA used as additional line of evidence

13 Results of CSIA Sampling Events Results of δ 13 C data from the October 2, 2013 sampling event. As contaminants move along the plume line, the δ 13 C increases from in the upgradient well (MW 7) to in MW 23 which is approximately 169 feet downgradient. Results of δ13c data from the July 9, 2014 sampling event. As contaminants move along the plume line, δ 13 C increases from in the upgradient well (MW 8) to in MW 4R (97 feet downgradient). MW 23 and MW 26D were undetermined because benzene concentrations were too low (<0.50 µg/l).

14 The Scientific Method still works!

15 Quality Assurance Project Plan (QAPP) QAPP is required before environmental samples are collected There isn t enough information available to develop a QAPP for CSIA

16 QA/QC Recommendations (Resources) A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants using Compound Specific Isotope Analysis (CSIA), USEPA, 2008 ITRC (Interstate Technology & Regulatory Council) Environmental Molecular Diagnostics, New Site Characterization & Remediation Enhancement Tools. EMD 2. Washington, D.C.: Interstate Technology & Regulatory Council, Environmental Molecular Diagnostics Team.

17 Regulatory Approval Process for CSIA Involve the regulator as early as possible Arrange for a meeting to discuss proposed sampling Prepare a draft work plan for the initial meeting The draft work plan is not intended to be a document that requires forty (40) man-hours to complete

18 Regulatory Approval Process for CSIA

19 Undine E. Johnson Underground Storage Tank Management Program To learn, read. To know, write. To master, teach.