Milltown Reservoir 



The Milltown Reservoir Superfund site is located at the 

 confluence of the Clark Fork and Blackfoot River, approx- 

 imately five miles upstream from Missoula, Montana. This 

 hydroelectric facility was built in 1906 and is currently 

 owned and operated by the Montana Power Company. The dam has 

 served as a trap for an estimated 120 million cubic feet of 

 arsenic and heavy metals laden sediments (Woessner et al. 

 1984) resulting from past mining and milling operations in 

 the headwaters of the Clark Fork. 



During a routine sampling in May 1981, the DHES-Water 

 Quality Bureau discovered that four wells serving 33 homes in 

 the community of Milltown were contaminated with arsenic. In 

 1983, the Milltown Reservoir area was listed as a Superfund 

 site, and DHES entered into a cooperative agreement with EPA 

 in July 1983 to conduct an RI/FS at the site. DHES hired the 

 University of Montana (UM) to do the initial studies, and by 

 December 1983, reservoir sediments had been identified as the 

 likely source of ground water contamination (Woessner et al. 

 1984) . Construction of a new well and distribution system 

 was started in November 1984 and was operational in June 

 1985. Subsequent sampling from homes on the system revealed 

 that about half the homes tested had hot water arsenic levels 

 above the drinking water standard. Replacement of hot water 

 heaters and, in some cases, hot water lines solved the 

 problem, and Milltown residents now have an uncontaminated 

 water supply. 



In April 1985, a continuing RI/FS for the Milltown 

 Reservoir site was initiated. DHES selected Harding Lawson 

 Associates (HLA) as contractor. The RI was expanded to 

 include a more detailed hydrogeologic evaluation downgradient 

 of the reservoir, and the FS was' to address long-term 

 remedial action. A review of the RI/FS draft reports 

 submitted by HLA in fall 1985 indicated a change of scope, 

 and supplemental work was performed in the 1986 field season. 

 After a review of the draft data report (August 1986) and 

 draft FS report (November 1986) , DHES determined that HLA had 

 not fulfilled the terms of its contract. The Feasibility 

 Study Agreement with HLA was terminated in February 1987. 



RI/FS activities at the Milltown Reservoir site were 

 minimal during most of 1987 and early 1988 while negotiation 

 for a contract settlement with HLA proceeded. DHES also 

 attempted to obtain the original documentation it needed to 

 validate the data collected by HLA. In May 1988, DHES 

 contracted with Camp, Dresser and McKee (CDM) , to perform the 

 data validation, complete the FS, and conduct a downstream 

 screening study. Field activities for the downstream 

 screening study are underway. CDM is currently developing a 



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