Headquarters TCE Plume

The Headquarters (HQ) TCE Plume, located beneath the current Town Center near 2nd Avenue and Quebec Street migrated to the northwest from its source area between former Buildings 383 and 385 (Location  Map).  The source of the HQ TCE Plume appears to have been leakage from an oil/water separator at former Building 404 to a storm sewer that runs along the southeastern side of 1st Place, between former Buildings 385 and 382.  During the removal of the oil-water separator in 2001, TCE was detected in a sample of the separator contents but was not detected in the surrounding or underlying soil.  It was believed that leakage from junction vaults in the sewer system may have occurred resulting in the release of TCE to the environment.

In the source area of the HQ TCE Plume, the highest dissolved-phase TCE concentrations occurred in groundwater within bedrock.  The source area occurred over an erosional bedrock high where the water table historically fluctuated above and below the bedrock-alluvium contact.  West of the suspected source, the plume entered the Cherry Creek paleochannel, a major alluvial paleochannel incised in the top of the bedrock surface.

Potassium Permanganate (KMnO4) injections completed in the HQ TCE Plume include a KMnO4 treatability study (LAC, October 2006) and two different rounds of KMnO4 injections that occurred in 2004 and 2009.  Injections occurred in more than 100 points; over 27,000 pounds (by weight) of KMnO4 were injected into the saturated alluvium and bedrock intervals.

As illustrated in the HQ Plume Map from July 2018, all TCE concentrations are below the on-base site-specific standard of 11 µg/l. Accordingly, FOSET Parcel #3 was closed under Paragraph 50 of the First Consent Agreement No. 01-08-07-02.