'-?}?. U .; 0141603 



Data derived under conditions similar to those found in the 

 Helena Valley merited greater consideration than other data. For 

 example, a toxic soil level for wheat on calcareous loamy soils 

 was more applicable than a toxic soil level for cabbage on sandy 

 acid soils. The hazard levels presented in this document are thus 

 site specific for crops and conditions present in the Helena 

 Valley as much as allowed by the reviewed literature. In some 

 cases, a site specific evaluation was not possible. Site specific 

 conditions for the Helena Valley are presented in the following 

 section (1.4) . Once hazard levels were developed they were 

 compared to means and ranges of soil/plant chemical levels 

 measured in the Helena Valley and control sites. 



1.4 Site Description 



The Helena Valley is located in west central Montana and 

 trends in a west northwest direction. It is 35.4 km (22.1 mi) 

 long and 17.1 km (10.7 mi) wide. The valley is bounded on the 

 northeast by the Big Belt Mountains, on the south by the Elkhorn 

 Mountains and the Boulder Batholith, and on the west by mountains 

 forming the continental divide. Lower portions of the valley are 

 occupied by Lake Helena and Hauser Lake formed by dams on Prickly 

 Pear Creek and the Missouri River. Elevations range from 1,113 m 

 (3650 ft) mean sea level at Hauser Lake to 2,560 m (8,400 ft) in 

 the surrounding mountains. Geological materials on the valley 

 floor consist of quaternary and tertiary sediments that are 

 consolidated or poorly consolidated. Soils are moderately 

 calcareous and composed of silt and clay (Miesch and Huffman 

 1969). Typical soil series mapped in portions of the Helena 

 Valley are the Hilger, Martinsdale, Musselshell, and Sappington 

 series all of which contain horizons that are "strongly to 

 violently" effervescent (Soil Conservation Service 1977b) . Except 

 for an area in the immediate vicinity of East Helena surficial 

 soil pH values range from about 7.1 to 8.6 (EPA, 1986) Soil 

 profiles are poorly to moderately developed on both quaternary and 

 tertiary parent materials. The Helena Valley is semi-arid and 

 receives less than 25.4 cm (10 in) of annual precipitation. The 



