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Agenda Item:- Reports-3b Status : Informational • Minnesota Pollution Control Agency MAR 9 1984 Mr. Owen Mobley Twin Cities Army Ammunition Plant Arden Hills, Minnesota 55112 Dear Mr. Mobley: Thank you for your letter of February 23, 1983 in which you summarized the Army's conclusions from the Army's Toxic and Hazardous Materials Agency's (USATHAMA) year-long study of ground water contamination at the Twin Cities Army Ammunition Plant (TCAAP) in Arden Hills, Minnesota. My staff has reviewed the Army's conclusions and the data that you have provided us. The Phase I study that the Army just completed was intended to determine whether • TCAAP is a source of ground water contaminants, such as trichloroethylene and other volatile organic hydrocarbons, and whether these contaminants are migrating beyond the TCAAP's boundaries. The Army has answered both of these questions in the affirmative: "volatile organic hydrocarbon contamination sources are present on TCAAP," "contaminant migration from at least two (TCAAP) sources is occurring" and "contamination is moving outside of the (TCAAP) installation at the southwestern boundary. " (The source of these quotations is the February 23, 1983 l.etter from you to me. ) We agree with these conclusions. The Army has made a number of other conclusions, however, which are not supported by the data available at this time. You state in your letter that it is "unlikely" that the contamination sources present at TCAAP are the cause of the contamination found in the city of New Brighton wells. We think that that conclusion is premature and not supported by the data that are available. The Phase I study, of course, was not extensive enough to determine the effects of ' TCAAP contaminant sources on the New Brighton municipal wells. But contrary to the Army's speculations, the Army's Phase I data and other data collected to date do not preclude in any way TCAAP as a source of contamination of the . New Brighton wells. For example, the Phase I study indicates that contamination in the bedrock aquifer could migrate at a rate of nearly one-half mile per year. We also disagree with the Army's conclusion that more data are necessary before it can be determined whether TCAAP is contaminating the private wells immediately to the southwest. More data are always helpful, of course, but all data available point to the conclusion that TCAAP is indeed contaminating these • private wells. Phone: 612/296-7301 1935 West County Road B2, Roseville, Minnesota 551 13-2785 Regional Offices • Duluth/Brainerd/Detroit Lakes/Marshall/Rochester Equal Opportunity Employer 0