In June 1985, MultiTech undertook a reconnaissance-level 

 study of irrigated lands between Rocker and Gold Creek as 

 part of the Silver Bow Creek RI Agriculture Investigation 

 (MultiTech 1986) . Its objectives were to refine previous 

 estimates of the extent and severity of contamination and to 

 prepare a preliminary evaluation of the impact on irrigated 

 croplands, livestock, and human health and welfare. 



During the reconnaissance study, 38 soil samples were 

 collected at 16 sites from six areas (Figure 3-6) . At all 

 sites except the one near Gold Creek, soil samples were 

 collected both upgradient and downgradient of abandoned 

 irrigation ditches. Eighteen plant samples were also 

 collected at the 16 sites. Observations from this study 

 include (MultiTech 1986) : 



• Soil and plant metal levels were elevated more 

 frequently in the downgradient than in the upgrad- 

 ient sites. 



• Heavy metals contamination in upgradient soils 

 tended to be limited to the top six inches of soil, 

 whereas contamination commonly extended to 24 

 inches or more in downgradient soils. 



• Contamination of soils was more severe in Silver 

 Bow Creek and upper Clark Fork floodplain areas 

 than in irrigated terrace sites. 



• Vegetation growing on contaminated sites contained 

 elevated metal levels (particularly zinc) ; however, 

 concentrations were generally in the range that is 

 nontoxic to livestock unless such vegetation is the 

 only forage source. 



• Deposition of heavy metals and resulting increased 

 acidity from pyrite mineral oxidation was severe 

 enough in some areas to prevent vegetative growth. 



• The rural nature and remoteness of most of the 

 affected areas limited the risk to humans via 

 direct contact or ingestion of metals. 



• Airborne contaminants may have constituted some of 

 the soil's heavy metals burden at the two sites 

 closest to the Anaconda Smelter site. 



• Additional aerial photo interpretation of the study 

 area, aided by the field observation, supported the 

 original estimate of about 5,400 acres of obviously 

 affected land in Silver Bow, Deer Lodge, and Powell 

 counties. 



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