Operable Unit 2 (OU2) - Landfill Zone

OU2, also known as the landfill zone, is an approximate 74.5 acre parcel in the south-central portion of Lowry. The site is bounded by Alameda Avenue on the south, Westerly Creek Flood Control Dam and associated wetlands to the north, AMLI Apartment Complex to the west, and Westerly Creek to the east. The landfill was historically used for the disposal of base-related waste and associated construction debris primarily from training activities conducted at the former Lowry AFB. Disposal occurred from approximately 1948 until 1986. Waste was disposed in discrete trenches at the site and backfilled with soil.  Disposal of debris and rubble on the surface of the landfill appears to have occurred from 1981 to 1986 and between 1989 and 1992 during the construction of Westerly Creek Flood Control Dam. 

Investigations at OU2 began in 1983.  A list of environmental investigations conducted at OU2 are listed below. 



OU2 Environmental Investigation Chronology



Air Force
IRP Phase 1 records search
IRP Phase II Confirmation/Quantification Stage 1 – included groundwater sampling at landfill
SRI for the landfill zone
Focused Feasibility Study
Proposed Plan
Long-Term Monitoring for Radiological Parameters
OU2, Former Lowry Air Force Base, Colorado
Privatization - LAC
August 2002
Preliminary Closure Plan for OU2
Phase 2 CAP
Landfill Closure Report
Post-Closure Monitoring – 30 Year
Initiated 2006
Additional Radiological monitoring


A remedy was selected under the CERCLA process in 1998. The selected remedy implemented includes:

  • A low permeability soil cap
  • Groundwater, surface water, and gas monitoring
  • Institutional controls (deed restrictions and State Environmental Covenant)

Any future change in land use must be approved by the U.S. Air Force and CDPHE.

Construction of the soil cap at OU2 began in 2004 and was completed in March, 2005.  The use of this site is currently restricted to open space/non-irrigated.  The approved remedy includes a requirement for post closure cover maintenance and gas, surface water, and groundwater monitoring for 30 years.  

As part of the maintenance plan, the landfill is inspected routinely to maintain:

  •  the integrity of the cap
  •  surface conveyance structures
  • soil vents and probes
  • the fence surrounding the landfill

Monitoring of groundwater, surface water, and soil gas is performed in accordance with a schedule approved by CDPHE in the most recent Addendum to the Phase 2 CAP for OU2.

Gas Monitoring

Methane gas is produced when organic material breaks down in an oxygen-depleted environment, like a  landfill.  When the concentration of methane builds up it can be potentially explosive.  When a landfill is capped, methane can not move as easily through the cap and has the potential to accumulate.  The purpose of the gas monitoring is to ensure that methane gas concentrations in the subsurface soil do not exceed the lower explosive limit (LEL) of 5% methane. Twenty seven aboveground monitoring probes, located in the western and southern portion of the OU2 landfill, were installed to monitor methane gas. The soil gas probes are being sampled in accordance with a schedule approved by CDPHE.

Groundwater and Surface Water Sampling

The purpose of the groundwater and surface water sampling is to monitor water quality and to detect potential contamination originating from OU2.  The monitoring network  includes 9 groundwater monitoring wells and 3 surface water sample locations along Westerly Creek.  Groundwater and surface water samples are collected based on a CDPHE-approved schedule and are analyzed for metals, VOCs, and radionuclides (gross alpha and gross beta). Through July 2018, 23 post-closure sampling events have been conducted.  Final versions of the latest monitoring report is provided in the reference page under OU2 references.  Older reports are available in the Administrative Record.  Two rounds of groundwater monitoring have included additional radiological analysis, as requested by the CDPHE.  The two rounds with additional radiological analysis were conducted in February and April 2007.  After evaluation of the data, CDPHE approved the additional analysis and closed out the requirement for further investigation of landfill radiological groundwater and surface water sampling.  The radionuclides, gross alpha and gross beta, will continue to be sampled as part of the groundwater and surface water monitoring program.

Property Ownership

In December 2005, the Air Force transferred ownership of the land encompassing OU2 to IRG Redevelopment I, LLC.  Since 2006,  IRG Redevelopment I, LLC and its development partner, Lowry Vista, LLC, have been working on potential redevelopment for the landfill.  IRG Redevelopment and Lowry Vista have begun discussions with CDPHE, the Air Force, the City and County of Denver, and the public, seeking a change to the current land use to allow for mixed-use, a combination of residential and commercial/retail use.  Current information is provided  on the Lowry Vista Fact Sheet