Vapor Intrusion Success Story: Colorado Department of - - PowerPoint PPT Presentation

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Dec 25, 2023 136 likes •256 views

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

SLIDE 1

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

SLIDE 2

1955 - CDOT commenced

peration 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

SLIDE 3

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

SLIDE 4

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

SLIDE 5

SLIDE 6

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

SLIDE 7

Source Zone P&T + ERD Performance (2003-2011)

Deep Zone Shallow Zone

SEPTEMBER 2007 SEPTEMBER 2007 SEPTEMBER 2009 SEPTEMBER 2009 SEPTEMBER 2011 SEPTEMBER 2011 SEPTEMBER 2003 SEPTEMBER 2003

SLIDE 8

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

SLIDE 9

Weight of Evidence Evaluation for Buildings Currently in Remediation Weight of Evidence Evaluation for Buildings Not in Remediation

SLIDE 10

Phased Confirmation Sampling Process

SLIDE 11

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