Freezeout Lake 



Climatic setting. The net annual precipitation balance for 

 Freezeout Lake is -27 inches, toward the more strongly evaporative 

 end of the range shown by sites in this classification. Monthly 

 average precipitation for the Choteau climatic station shows a 

 pronounced June maximum. Annual totals for this station show the 

 3-year running average below (often well below) the long-term 

 average throughout most of period from 1970 to 1990. The total 

 precipitation in 1992 (the year prior to sample collection) was 

 almost 4 inches below the long-term average, while the 1993 total 

 exceeded the long-term average by over 4 inches. 



Geologic setting. The Freezeout Lake basin is underlain by a 

 seguence of glaciolacustrine silt and clay deposited toward the 

 western limit of the extensive Glacial Lake Great Falls, and by 

 the Late Cretaceous Marias River Shale, Telegraph Creek Formation 

 and Two Medicine Formation. Permeable terrace gravel deposits 

 underlie some upland areas. 



Hydrologic type. Freezeout Lake and the surrounding ponds make up 

 a complex of diked and managed water bodies receiving irrigation 

 return flows from the Greenfields Division of the Sun River 

 Irrigation Project. Peripheral ponds drain to Freezeout Lake 

 proper through regulation structures. Managed outflow occurs via 

 Priest Butte Lakes to the Teton River at times of high streamflow. 

 Water levels are manipulated to meet water storage objectives in 

 the lake system and water quality objectives in both the lake 

 system and the Teton River. 



Basin characteristics. Freezeout Lake occupies the lower 

 elevations of a broad, low-gradient depression altered by diking, 

 ditching and transportation corridors. The catchment to wetland 

 area ratio is relatively low, but a large fraction of the inflows 

 to the lake system are irrigation return flows imported from 

 outside the natural drainage basin. Water depths are shallow 

 (maximum depth estimated to be 10-12 feet) and portions of the lake 

 system are surrounded by low-gradient salinated flats. 



Water chemistry • At the time of sampling, water at the WET21 site 

 was mildly alkaline, "oligosaline" and sodium sulfate in character. 

 Equilibrium calculations indicate near-saturation with calcium 

 carbonate species and substantial oversaturation with respect to 

 dolomite. With respect to sample sites in the same classification, 

 WET21 ranked mid-range in ammonium and total organic carbon 

 concentrations, relatively low in orthophosphorous concentration 

 and relatively high in total phosphorous. 



Within it class, the arsenic and copper concentrations ranked raid- 

 range and the boron concentration was near the high end of the 

 range . 



Chemical history. Several samples were collected by the U.S. 



