Herb Levine EPA Region IX

Transcription

1 Opportunities to Integrate New Tools such as MBT and CSIA into Existing Policy and Guidance for Selection, Design and Performance Monitoring of Remedies at Chlorinated Solvent Sites Herb Levine EPA Region IX

2 Overview Introduction Review of EPA policy Ideas for integrating advanced tools into policy Use of advanced tools for remedy selection and performance monitoring Summary Case Study

3 Characterization and remedial evaluation best based on converging lines of evidence of chemical, geochemical and microbiological data. Advanced tools complement current analytical techniques.

4 EPA Policy on Use of MNA OSWER Directive P, April 21, Major tenets: protection of human health and the environment by remediation and restoration to beneficial use, prevention of groundwater migration; source control and long term performance monitoring required

5 Natural Attenuation Processes Reliance on natural attenuation process to achieve site specific remediation objectives in a reasonable time frame. NAP includes physical, chemical, or biological processes that reduce mass, toxicity, mobility, volume or concentration of contaminants.

6 Natural Attenuation Process NAP include these in-situ processes: biodegradation, dispersion, dilution, sorption, volatilization, radioactive decay, chemical or biological stabilization, transformation, or destruction of contaminants. EPA prefers those processes that degrade or destroy contaminants.

7 Demonstrating MNA through Site Characterization MNA decisions should be thoroughly and adequately supported with site specific characterization data and analysis. Site characterizations require quantitative knowledge of source mass, groundwater flow, contaminant phase distribution and partitioning, rates of biological and non-bio transformation and an understanding of how all these factors vary with time.

8 Demonstrating MNA through Site Characterization Three tiered approach recommended. More detailed information is collected to provide confidence on estimates of attenuation rates and remediation timeframe. 1. Historical groundwater data that demonstrate a clear trend of decreasing mass and/or concentration over time.

9 Demonstrating MNA through Site Characterization 2. Hydrogeologic and geochemical data that can be used to demonstrate indirectly the type(s) of NAP at the site, rate of contaminant reduction to site RAOs. Characterization data may be used to quantify the rates of sorption, dilution or volatilizations or to demonstrate and quantify the rates of biological degradation.

10 Demonstrating MNA through Site Characterization 3. Data from field or microcosm studies which directly demonstrate the occurrence of a particular natural attenuation process and its ability to degrade the contaminants of concern.

11 Demonstrating MNA through Site Characterization For Tiers 1 and 2 e.g. indirect measurements use EPA guidance on determining decreasing mass and/or concentrations over time Performance Monitoring of MNA Remedies for VOCs in Ground Water, EPA/600/R-04/027 April 2004 Provides guidance on developing monitoring well networks,evaluating concentration trends and transects for mass flux calculations.

12 Demonstrating MNA through Site Characterization Tier 3, e.g., direct measurements of field data and microcosm/microbiology includes the MBT(s) and CSIA presented by previous speakers. Existing EPA policy allows for application of these tools. Consider CSIA and/or MBT a direct measurement of field data.

13 Performance Monitoring with MBT and CSIA Similar analysis for location, number and frequency as described in Performance Monitoring for VOC Remedies in Ground Water. Locations should be chosen where biodegradation products have been observed. Number of samples can be less that those for geochemical and contaminant analysis. Frequency should be often enough to include in decision documents.

14 Implications and Decisions from Using MBT and CSIA Traditional data sets may indicate declining trends but not why. Are contaminants being destroyed or diluted? If contaminants are being destroyed what are the mechanisms and can they be monitored directly?

15 Implications and Decisions from Using MBT and CSIA CSIA provides definitive data proving destruction independent of concentration. MBT can identify the microbial mechanisms responsible for degradation. Both can be used effectively to characterize sites and provide insight during performance monitoring.

16 Recommendations Molecular Biological Tools and Compound Specific Isotope Analysis are powerful tools providing insight from the site characterization stage through to remedy performance monitoring. Can aid with important site decisions such as are contaminants degrading?, what are the destruction mechanisms?, is MNA sustainable over time?

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18 Case Study Work Plan Review The objective of the work plan is to describe the data collection (locations and frequency) and analysis methods to be used in a natural attenuation evaluation for groundwater at the site. The evaluation is intended to determine whether natural attenuation by degradation processes is occurring in the groundwater plume.

19 Case Study Work Plan Review Rationale for the Study Groundwater extraction, treatment, and discharge is the interim remedy for the site. Results from the groundwater monitoring program suggest that natural attenuation may be occurring in the PCE plume. Groundwater data collected from the site since 2001 suggests that PCE has been degraded totrichloroethene (TCE) and that TCE has been degraded to 1,2- dichloroethene (1,2-DCE) at some wells.

20 Case Study Work Plan Review Table 1-1 lists the wells on the site at which TCE and 1,2-DCE have been detected with PCE. It is important to determine what and to what extent natural attenuation processes may be assisting in remediating the groundwater plume.

21 Case Study Work Plan Review Sources. Halford s Cleaners is the source of the PCE plume at the site. PCE and sewer water were released on the site property and most likely from the sanitary sewer downstream from the cleaners. Migration Pathways. PCE originating from Halford's Cleaners may have migrated in the subsurface, dissolved in soil vapor, dissolved in groundwater, and/or as a separate, undissolved PCE liquid.

22 Case Study Work Plan Review Migration in Groundwater. The PCE plume originating from Halford's Cleaners was identified because it migrated to a municipal water supply well, Muni-11, located 1,000 feet northwest of the source area(figure 1-2).

23 Case Study The EPA Protocol (EPA, 1998) will be used to screen the site for evidence of biodegradation. However, identification and quantification of bacterial species will also be performed on groundwater samples from wells were favorable geochemical conditions are identified. The bacterial species to be evaluated are those known to biodegrade chlorinated ethenes. These include: Dehalococcoides ethenogenes, Dehalobactor, Desulfomonas, Desulfitobacterium,, and methanotrophic bacteria.

24 Case Study..Work Plan Review Isotopic Behavior During Degradation, To demonstrate a change in isotopic ratios of 35Cl/37Cl and 13C/12C, samples will be collected upgradient, near the source area and downgradient along the axis of the contaminant plume for quantifying the mass of carbon and chlorine stable isotopes. Quantifying the masses of isotopes of two different compounds (in this case carbon and chlorine) can help to distinguish the mechanism for degradation/transformation and help identify the source of contamination when multiple sources are present.

25 Case Study Work Plan Reivew DQOs for MBT and CSIA include: Recent and historical groundwater monitoring data collected during the monitoring program since 2001 and the proposed 2012 natural attenuation sampling. Recent and historical groundwater flow directions determined from piezometric surfaces from the monitoring program. Concentrations of PCE and any daughter products and natural attenuation parameters.

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29 Case Study Conclusion Site fails Tier 1, no degradation products occur at site, conclude that degradation is not happening. Take home message, evaluate Tiers 1 & 2 before considering MBT or CSIA