Vapor Intrusion Success Story: Colorado Department of Transportation Materials Testing Laboratory Walter Avramenko Hazardous Waste Corrective Action Unit Leader Colorado Department of Public Health and Environment
1955 - CDOT commenced operation at facility 1993 - Department notified of solvent release from 3 USTs 1994 - Onsite ground water and soil systems operational 1995 - Compliance Order 1996 - Initial testing at homes around the MTL and residents notified of the presence of vapors 1,1-DCE Ground Water Plume
Residential Indoor Air Program Primary issues: 1,1-DCE and TCE • Temporary relocation of 12 residents • Installed Indoor Air Mitigation • Systems: - 14 apartment buildings - 12 townhomes - 22 single-family homes Converted to low-maintenance, • low-energy usage radon-style systems in 2010
Aerobic Biodegradation (AB) System and MNA (2001-2008) • Start-up January 2001 • Large-scale injection system via 82 hydrofractured injection wells, 3 treatment buildings • Dissolved methane and oxygen to support produced by methanotrophs cometabolically destroy COCs • System operation – Continuous injections initially – Switched to pulsed injections – 0.1 to 0.5 gpm per well • Remediation timeframe: 12 years
Enhanced ReductiveDechlorination (ERD) • AB System pace was not expected to meet treatment goals in the target timeframe/cost despite several efforts to optimize the system • ERD pilot testing (2005-2008) – Achieved anaerobic conditions in 10-12 months in the test area – Full dechlorination achieved at all test wells – ERD half-lives were approximately 1 ⁄ 5 those observed under AB • Full-scale ERD System (2008-2013) • Upgrades to automate injections at 78 wells • Injection volumes: 1,000 to 4,000 gal/well 2-4 times/yr • Dosage ranges between 1 and 3% molasses • Significantly lower lifecycle cost
Source Zone P&T + ERD Performance (2003-2011) Shallow Zone SEPTEMBER 2003 SEPTEMBER 2007 SEPTEMBER 2009 SEPTEMBER 2011 Deep Zone SEPTEMBER 2003 SEPTEMBER 2007 SEPTEMBER 2009 SEPTEMBER 2011
Indoor Air System Shutdown • 2005 Indoor Air Work Plan – process to determine if continued remediation warranted • Weight of evidence approach for selecting locations to do confirmatory sampling • 2005-2007: Initial round of system shutdowns – Confirmatory sampling conducted post-system shutdown – Two to four samples collected over the course of one year • 2012-2013: Final round of system shutdowns – All off-site locations well below indoor air goals
Weight of Evidence Evaluation for Weight of Evidence Evaluation for Buildings Currently in Remediation Buildings Not in Remediation
Phased Confirmation Sampling Process
Indoor Air No Further Action • Confirmation samples prove that remediation goals (1x10 -6 ) reliably achieved in buildings without active mitigation • August 2014: CDPHE issued No Further Action letter for Off-site Indoor Air Program • No mitigation and monitoring required in all off-site areas
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