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 RAB’s last meeting was a virtual meeting on April 20, 2021. RAB information is available here: Restoration Advisory Board (RAB).

The Army is hosting a RAB/public meeting on July 20, 2021, at 7:00 p.m. CST. Rather than the normal cleanup update, this meeting will be focused on cleanup at Round Lake. The Army has prepared a Proposed Plan to document the preferred alternative of those evaluated in the Feasibility Study for Round Lake. This meeting is being conducted virtually to maintain social distancing and protect the health of the community during the Coronavirus Disease 2019 (COVID-19) public health emergency.

The Army will also be hosting an open house on July 20, 2021, from 10 a.m. until 3 p.m. at the Minnesota National Guard Facility – Arden Hills Army Training Site (AHATS). Army personnel (as well as other government agency representatives) will be on hand to answer any questions about the Proposed Plan to address contamination in Round Lake. Poster stations will be set up in the AHATS gymnasium at 4761 Hamline Ave N in Arden Hills with some of the same information to be presented at the RAB meeting later that evening. Handouts will be available in print. We encourage community members to attend the open house to have their questions answered in person. Please call (651) 282-4420 for directions.

The Proposed Plan Public Comment Period is open from July 9 – August 13, 2021

NOTE: Open house attendees will be required to adhere to all National, Regional, and State COVID-19 mandates and guidelines in place at the time of the Open House.

Both the open house and RAB meeting are open to the public. Anyone interested in or wanting information about the TCAAP cleanup activities for Round Lake is invited to attend.

You will be able to provide your comments orally at the end of the July 20 RAB meeting (for the record). You may also provide your comments in writing any time before August 13 (the end of the public comment period) by:

  • Filling out a comment form and dropping it off at the open house on July 20 between 10 a.m. and 3 p.m.
  • Sending your comments in writing by email to:
  • Sending your comments in writing by mailing to:
    U.S. Army Environmental Command,
    2455 Reynolds Road, Mailstop 112
    ATTN: AMIM-AEC-M/Albrecht
    JBSA Fort Sam Houston, TX 78234-7588

The RAB meeting will be held on MS teams. Following the RAB meeting, the Army will accept oral comments on the Proposed Plan for Round Lake. You do not need to download the MS Teams software to participate; you can access the meeting through your web browser. 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.

Immediately following the meeting, after all questions have been answered, the Army will accept oral comments. If you are submitting oral comments, you do not need to submit written comments. If you are submitting written comments, you do not need to submit oral comments. If you submit written comments by email you do not need to mail the comments. If you drop off your written comments at the Open House, you do not need to email or mail them.

The meeting agenda, fact sheet about the proposed plan, copy of the Proposed Plan and Remedial Investigation/Feasibility Study, July RAB presentation about the Proposed Plan, Open House Meeting information, and information about providing your feedback on the Army’s proposed plan, can be downloaded below before the meeting. Draft minutes from the April 20, 2021 meeting are also available for review and feedback.

NOTE: Additional documents related to the Round Lake remediation are available on the Resources Page.

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 is currently working on plans 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 or 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.

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 Army is working to optimize the two treatment facilities at OU1 and OU2.  The New Brighton Contaminated Groundwater Recovery System at OU1 and the Source Groundwater Recovery System at OU2 are being evaluated to increase contaminant removal  from groundwater.  Implementation of these optimization efforts are planned for summer 2021.

The Army hosted a stakeholder meeting (teleconference) on April 21, 2021 to provide a project update (presentation). The next stakeholder meeting will be held in September 2021. These meetings are more technical in nature than the RAB meetings but often discuss the same topics.

The Army worked with EPA, MPCA, MDNR and USFWS to finalize the Supplemental Remedial Investigation/Feasibility Study and Proposed Plan to address contamination in Round Lake (known as TCAAP-31) which is affecting benthic organisms in the lake but does not pose a risk to human health. A public comment period is open until August 13 for the community to provide input to the Army on the Proposed Plan.

Where can I get more information?

Any questions or concerns may be directed to the: