Twin Cities Army Ammunition Plant


Landscape with trees and water

Welcome to the website for the former Twin Cities Army Ammunition Plant (TCAAP). The former TCAAP is located in the city of Arden Hills in the northern portion of the Minneapolis – St. Paul metropolitan area in Ramsey County. It is surrounded by the cities of New Brighton, Arden Hills, Mounds View, and Shoreview, Minnesota. TCAAP formerly occupied a four-square mile area east of U.S. Interstate Highway 35W and north of Ramsey County Highway 96.

Previous manufacturing operations from 1942 to 1981 impacted soil, groundwater, sediment, and surface water, and the former TCAAP was placed on the National Priority List (NPL) in September 1983 and designated as the New Brighton/Arden Hills (NB/AH) Superfund Site. Cleanup at the former TCAAP is taking place under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) with the United States Army as the lead agency in coordination with the United States Environmental Protection Agency (U.S. EPA) Region 5 and the Minnesota Pollution Control Agency (MPCA).

The size of the former TCAAP has shrunk over time because of property ownership transfers and reassignment of control to the National Guard Bureau, Army Reserve, Ramsey County, and the City of Arden Hills. The remaining land (approximately 160 acres) is in the process of being transferred out of federal ownership.

Map showing Former Twin Cities
Army Ammunition Plant in Minnesota
Photograph of former manufacturing facility at the TCAAP​

Public involvement

The most recent TCAAP Restoration Advisory Board (RAB)’s meeting was a virtual meeting on Feb. 20, 2024. Additional RAB meeting information is available at Restoration Advisory Board (RAB).

The Army is hosting a RAB meeting on Sep 17, 2024, at 7:00 p.m. CST, to update the community on the latest status of cleanup at TCAAP. This meeting is being conducted in person with a virtual option for those unable to travel to the meeting.

The RAB meeting will be held in person and on MS teams. If you’d prefer you can also dial into a teleconference line. Please contact Kay Toye at (520) 903-4363 or email: for information on how to access the RAB meeting via internet or phone.

The presentation slides can be downloaded below before the meeting. Draft minutes from the Feb 22, 2024 meeting are also available for review and feedback.

The RAB meeting is open to the public. Anyone interested in or wanting information about the TCAAP cleanup activities is invited to attend.

If you are interested in serving on the RAB, please let us know.
Cathy Kropp, Environmental PA Specialist
Phone: 443-243-0313
More information about the RAB is available here.

Recent Updates

The Army will continue to monitor groundwater through sampling, and operate and fund groundwater treatment at New Brighton (known as OU1) and Arden Hills (known as OU2) until the levels are within state and federal standards for safe drinking water.

The Army has taken actions to optimize the two treatment facilities to ensure they are operating as efficiently and effectively as possible.

The permanent granular activated carbon Water Treatment Facility in New Brighton (OU1) and the TCAAP groundwater remediation system (TGRS at OU2), that were the primary treatment components of the original remedies, were not capable of removing an emerging chemical of concern (1,4-dioxane) to levels protective of public health. Therefore, the Army added a supplemental process to each system to treat 1,4-dioxane.  An explanation of significant differences (ESD) was published to document these changes and is available on the resources page.

Many actions have been performed to address affected soil and groundwater at the NB/AH Superfund Site, including source removal; groundwater treatment; capping; soil treatment with an in-situ volatilization system; and soil incineration. The groundwater plumes in Operable Unit (OU) 1 and OU 3 are monitored annually by a network of nearly 300 monitoring wells.

The Record of Decision(ROD) for Round Lake was fully signed by all parties on September 20, 2022.

Annual Performance Reports (APRs) and Five Year Review Reports are published by the Army to summarize the status of remedy implementation and to address remedy performance at the NB/AH Superfund Site. You may access the most recent APR and Five Year Review Report on the resources page

What’s Next?

The next stakeholder meeting will be held on Sep 17, 2024. These meetings are more technical in nature than the RAB meetings but often discuss the same topics.

The Army will fund and New Brighton will install a new drinking water supply well as part of the OU1 optimization. At OU2, the Army will complete abandonment of 40 monitoring wells, complete installation of three monitoring wells, optimize the monitoring well network, conduct risk assessment for more unrestricted land use, and conduct an engineering evaluation/cost analysis for the 135 Primer/Tracer area. The Army has completed optimization of the TCAAP Groundwater Recovery System (TGRS) for OU2, including constructing and operating  the Source Groundwater Recovery System (SGRS) and modifying the Boundary Groundwater Recovery System (BGRS). Together these two systems comprise the TGRS. The Army will continue annual groundwater monitoring of OU3.

The Army worked with EPA, MPCA, MDNR and USFWS to finalize the Round Lake Record of Decision (ROD), signed by all parties on Sep. 20, 2022. A summary outlining the comments/feedback received on the Proposed Plan and the Army’s responses is included with the ROD. The next meeting of the Round Lake Technical Working Group is TBD.

Where can I get more information?

Any questions or concerns may be directed to the: