Site Closure Strategy for Contaminants in Fractured Crystalline Rock Air Force Plant 6, Marietta, GA

Transcription

1 Site Closure Strategy for Contaminants in Fractured Crystalline Rock Air Force Plant 6, Marietta, GA Joint Services Environmental Management Conference May 21 May 24, 2007 Prepared by William Brown/ASC and Casey Hudson

2 Presentation Outline Site Background Conceptual Site Model Air Force and Regulatory Agency Positions Development of Site Closure Strategy Factors Effecting Closure Strategy Planned Corrective Actions Conclusions

3 Site Background Aircraft manufacturing since 1940s Approximately 720 acres within 3,300+ acre Dobbins Air Reserve Base RCRA permitted facility Extensive solvent plumes that extend offsite Stakeholders include AF, GA EPD, LM Aero, and neighboring property owners

4 Air Force Plant 6 Air Force Plant 6 Marietta, Georgia

5 AFP 6 and Dobbins ARB

6 Geology and Hydrology Two zones Unconsolidated overburden [fill, saprolite, and partially weathered rock (PWR)] Crystalline bedrock Groundwater occurs under unconfined to semi-confined conditions No confining layer Both zones are highly heterogeneous and anisotropic

7 Conceptual Geologic Setting

8 Contaminant Sources and Plumes Overburden TCE concentrations >600,000 µg/l in source area (DNAPL) >1,600 µg/l offsite Bedrock TCE concentrations >95,000 µg/l in source area (DNAPL?) >100 µg/l offsite (~100 bgs) Largest TCE plume > 3,000 ft long and >300 ft deep

9 Contaminant fate Site Risks Large TCE plume is stable Modeling indicates plume life >50 years Majority of mass onsite in the overburden Under current land use the only complete pathway is groundwater vapor intrusion hypothetical and indirect

10 Air Force Position Few treatment options for bedrock aquifer difficult to locate contaminants, treatment questionable, very expensive Prefer use of risk-based approach to develop cleanup levels Corrective actions limited by available funds

11 Regulatory Agency Position Agency Policy All groundwater in Georgia is a natural resource Therefore cleanup must achieve MCLs Agency expects offsite plume to reach MCLs within a reasonable time (e.g. <30 Yrs)

12 Development of Site Management Strategy Air Force wants to demonstrate good faith effort Source zone reduction Control offsite plume migration Air Force would use available funds for limited corrective action followed by MNA Build case for Technically Impracticability (TI) waiver in bedrock Gain stakeholder agreement with Air Force vision If necessary, revise Air Force vision to accommodate stakeholders Parties agree that corrective actions can/should be dynamic as more is learned

13 Source Area Target Treatment Zone

14 Project Execution Stakeholder Chartering RCRA Facility Investigations - 3 Phases and Risk Assessment Corrective Measures Study/ Corrective Measures Design Implement Source Area and Boundary Treatment Agency Acceptance of Short Duration Active Remedy followed by MNA and LUCs (TI) Interim Corrective Measures and Pilot Studies

15 Shaping Stakeholder Acceptance Stakeholder chartering Technical briefings DNAPL properties and migration in subsurface Fractured rock hydrogeology Behavior of plumes in fractured rock Regular status meetings (especially results of pilot studies)

16 Corrective Action Strategy Establish strategy at project inception with an understanding it may evolve Develop a thorough Conceptual Site Model and identify potential receptors Identify data gaps in Conceptual Site Model Use phased approach to both characterization and corrective actions Conduct peer reviews of procedures and results Define preliminary risk-based cleanup goals Pilot test candidate remedial technologies Early on seek stakeholder agreement to corrective action approach then sustain

17 Sustaining Stakeholder Agreement Thorough site characterization Contaminant mapping Aquifer testing Borehole geophysics Modeling (groundwater flow and solvent biodegradation rates) Evaluation of results from Interim Corrective Measures Pilot testing of remediation technologies

18 Current Cleanup Goals Long-Term Corrective Action Goals Reduce groundwater plume concentrations to MCLs via active treatment and MNA in < 30 years Source Area Short-Term Goal Treat source area contamination to reduce mass flux by 50% to shrink the plume and to facilitate MNA Boundary Area Short-Term Goal Reduce offsite contaminant migration by 70% to shrink the offsite plume and to facilitate MNA

19 Corrective Action Plan Limited aquifer restoration and long-term care Remedy elements: Source area treatment Control/minimize offsite migration Monitored Natural Attenuation Land Use Controls Sustain agency acceptance of MNA and LUCs Annual reports on corrective action effectiveness Hold 5-year reviews

20 Conclusions Plan project with site closure in mind Define vision for site management and obtain concurrence from stakeholders Charter and consistently involve stakeholders Develop comprehensive Conceptual Site Model and update with new data Evaluate potential cleanup technologies early; use pilot studies for critical evaluation Phase the work to manage budgets and modify approaches with new data Sustain stakeholder acceptance with regular updates and flexible approach

21 Acknowledgments Bill Brown/ASC - Remedial Program Manager and Co-Author Vivian Perez/AFCEE Contracting Officer Representative Mike Laney/LM Aero AFP6 POC CH2M HILL Project Team Co-Authors Sharon Schultz, Craig Sprinkle, and Dan Marion