Denver Federal Center Calibration Silo Removal Plan What are the DFC Calibration Silos? Installed in 1981 by Bureau of Mines Support minerals industry with public domain well logging tool test facility Three underground tanks with solid granite columns of known geophysical response Records not maintained of its use over the 30 year operating history Silos identified as Feature 1704 have several other associated wells including a 1970’s vintage calibration well gallery Removal action also includes USGS wells identified as Feature 616 also involved in property transfer area

Denver Federal Center Calibration Silo Removal Plan Why must the Silos be Removed? GSA is transferring property on the west end of the DFC for redevelopment consistent with the Master Plan process initiated in The Denver Regional Transportation District (RTD) has already commenced work on the West Corridor line that will run through the DFC in the area of the current silo installation. RTD will commence construction of the DFC West Corridor Station on the land just south of the Silos and needs the Silo area itself for construction staging. Construction standards require that developer must be able to excavate down at least 30 feet at site – this precludes closing silos in place. GSA is anxious to complete the property transfer agreements with RTD by no later than January Silos and associated wells must be removed for this to be completely executed.

Colorado Department of Public Health and Environment (CDPHE) Overseeing Removal In 1997 CDPHE issued an “Order on Consent” ( ) which requires GSA to assess and remediate, as necessary, ALL AREAS of contamination which have been identified through due diligent search. Order issued under State hazardous waste law authority. GSA commenced comprehensive RCRA Facility Investigation sampling which included units 1704 and 616 which encompass calibration facilities. CDPHE must approve a corrective action work plan regarding the closure of the Silos and wells to ensure remediation of contamination to appropriate State Standards. Liquid contents of Silos will be disposed of in a commercial industrial waste water treatment plant. USGS and GSA have demonstrated to CDPHE that Silos are contained units and have not impacted adjacent soil or groundwater environment. With the exception of one well at 616, anticipate that all wells can be closed in accordance with Colorado State Engineer practices. One well at 616 shows elevated vinyl chloride levels and preliminary discussions with CDPHE have recommended a slug treatment of potassium permanganate to oxidize contaminant. Denver Federal Center Calibration Silo Removal Plan

Removal and Property Disposition Evaluation GSA and USGS working collaboratively on site issues GSA will be managing real property transfer to RTD under its DFC Property Manager Role USGS is responsible for funding closure of Silos and has declared granite columns as unserviceable (personal) property - Form DI-103A GSA will issue RFP for demolition contractor to remove Silos and related wells – scope of work and contracting documents jointly prepared by both Agencies USGS has done extensive investigation as to preservation of the engineered granite for reinstallation in new calibration facility In discussions with two potential University partners, but technology transfer partnerships are looking more unlikely before removal must take place USGS HQ staff have been extremely helpful during the investigation/evaluation phase