Tailings fppm) 



Buried Soil fppm) 

 53 (geom mean) 

 58 (max) 



98 (geom mean) 

 336 (geom mean) 



As expected, these data show greatly elevated concentra- 

 tions of metals in the tailings. Metal levels in the 

 underlying soils are generally several times higher than 

 typical geochemical background values, indicating that 

 enrichment via leaching is occurring. 



MultiTech also collected some samples of the bluish 

 surface salts that form on the floodplain surface in some 

 areas during the summer. These samples contained 7 to nearly 

 10 percent total copper and 2 to 3 percent total zinc. 



Brooks (1988) recently conducted a detailed investiga- 

 tion of the distribution and concentration of metals in 

 sediments and water in the upper Clark Fork floodplain. The 

 study area included about two miles of floodplain near 

 Racetrack Creek. The author mapped the floodplain sediments 

 using aerial photos and data obtained from cores, trenches, 

 and augering. Soil samples were collected at various 

 distances from the river to determine mineralogy, grain size, 

 and lateral distribution of metals concentrations. Water 

 movement into the vadose zone was measured at selected sites 

 with suction lysimeters. Sandpoint piezometers and augered 

 wells were used to measure water levels and collect water 

 samples from the alluvial aquifer. 



By examining stratigraphic profiles of floodplain 

 sediment, Brooks delineated three major periods of mine waste 

 deposition: 1) pre-mining, represented by coarse sand and 

 organic overbank deposits under reducing conditions; 2) syn- 

 mining, characterized by transition sediments and tailings 

 deposits under oxidizing conditions; and 3) post-mining, 

 distinguished by grass-bound topsoil. 



In areas contaminated by tailings deposits, the author 

 documented enriched concentrations of cadmium, copper, 

 manganese, and zinc in sediments and porewater and arsenic 

 in ground water. Mechanisms that chemically distribute 

 metals between particulate and dissolved phases are mainly 

 dependent on the redox conditions and on the pH of the 

 system. Thus, changes in redox conditions or fluctuations in 

 pH could create a potential source of metals and arsenic to 

 local ground water and surface water systems (Brooks 1988) . 



3-43 



