low with respect to all sample sites, and most other trace elements 

 analyzed were below detection limits. 



CheBical history. Brush Lake has a record of field and 

 quantitative water chemistry analyses related to investigations of 

 the Clear Lake aquifer system and to the dynamics of ground-water 

 supported evaporative lakes. Specific conductance measurements 

 dating back to 1984 show an overall range from 5360 to 6140 

 microsiemens/cm with a relatively well-mixed, near-homogeneous 

 water column during summertime conditions. Monthly time-series 

 water quality sampling conducted in 1984 and 1985 has not yet been 

 analyzed. Brush Lake is believed to have been perennial throughout 

 it's Holocene history. 



Sediments. Sedimentation in Brush Lake is dominated by authigenic 

 tufa and marl formation, in part mediated by biological activity. 

 Detrital sediments are a relatively minor component of the system. 

 However, the WETll sampling site is along a relatively exposed, 

 winnowed shoreline and allogenic detrital material may be over- 

 represented in this sample relative to other littoral areas. 

 Extractable calcium and magnesium concentrations in the percent 

 range would be expected from different shoreline settings. 



Extractable arsenic was reported at the second-highest 

 concentration for this sample site classification. Boron, iron, 

 manganese and zinc were reported at concentrations near the lower 

 end of the ranges shown for this site classification. Most other 

 trace elements were below detection limits. Arsenic exceeded mean 

 soil concentrations for the western U.S. by a factor of about 2. 



