STUDY NUMBER ; 10.3 



ORGANIZATION ; University of Montana (UM) 



TITLE OF STUDY ; Groundwater Use and Management; A Sole Source 

 Aquifer Study, Missoula Valley, Montana 



CONTACT ( S ) ; William Woessner - University of Montana - Geology 

 Department, Missoula - 243-2341 



OBJECTIVE ; Evaluate the long-term quantity, quality and avail- 

 ability of the natural groundwater system in the Missoula Valley; 

 begin a long-term monitoring program and develop a predictive 

 tool to evaluate the consequences of current and future ground- 

 water management practices. 



DURATION ; 1985 - 1987 



CURRENT STATUS ; In the summer of 1983, the City of Missoula's 

 Rattlesnake Creek water supply system was closed because of gi- 

 ardia contamination. The city now relies solely on groundwater 

 for their drinking water. Approximately 7.6 billion gallons 

 of water are withdrawn annually from the underlying aquifer. 



The Missoula Valley Aquifer is directly connected to the 

 land surface with only sporadic layers of silt and clay to protect 

 it from downward infiltrating pollution. Improperly installed 

 septic tanks and the "French Drain" system of storm water disposal 

 utilized by the City of Missoula are major sources on contamin- 

 ation to the aquifer. 



This study is monitoring withdrawals from and discharges 

 into the Missoula Valley Aquifer by: 1) conducting surface water 

 discharge rates on the Clark Fork and Bitterroot Rivers, 2) mea- 

 suring water level changes at six monitoring wells, and 3) eval- 

 uating the discharge rates of two storm water drain systems and 

 three septic tank disposal fields. Water quality parameters 

 are also being collected at all monitoring sites. 



FUTURE ACTIVITIES ; The above monitoring program will continue 

 for two years. At that time, a numerical groundwater model will 

 be developed to predict the effects of existing and proposed 

 development and disposal practices on the aquifer system. 



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