White Lake 



Climatic setting. The net annual precipitation balance for White 

 Lake derived from the MAPS database is -23 inches, toward the less 

 evaporative end for sites in this class. Based on analyses of 

 evaporation pan data, this is a considerable underestimate White 

 Lake's water deficit, and points out the need to view the MAPS 

 estimates only as relative indicators of net site precipitation. 

 Mean monthly precipitation for the Medicine Lake climatic station 

 shows a pronounced June maximum. Annual totals for this station 

 show apparent periodicity with a 5 to 7 year cycle. Throughout the 

 1980s, the 3-year running average remained below (often well below) 

 the long-term average, recovering in the early 1990s. In 1993 (the 

 year before sampling) precipitation exceeded the long-term average 

 by more than 1 inch. 



Geologic setting. White Lake occupies an ice-block depression 

 (kettle) on the margin of the late Pleistocene outwash sand and 

 gravel forming the Clear Lake aquifer. Surficial sediments within 

 the lake basin are dominated by authigenic sulfate minerals 

 precipitated from in-flowing ground water and fine-grained 

 glaciolacustrine sediments contrasting with the permeable sand and 

 gravel of the Brush Lake basin. Glacial sediments are underlain 

 at depth by the early Tertiary Fort Union Formation. 



Hydrologic type. White Lake is an ephemeral saline playa which 

 receives in-flowing ground water (depleted in calciiam through 

 carbonate precipitation in upgradient Brush Lake) and has 

 restricted ground-water outflow. White Lake lacks significant 

 surface water inflow or outflow. 



Basin characteristics. The shallow White Lake depression has a 

 minimal surface catchment beyond the playa surface; the lake's 

 water and solute budgets contrast with those of adjacent Brush Lake 

 due to distinct aquifer permeabilities, different lake geometries 

 and different influent water chemistry. The resulting lake water 

 chemistries are markedly different but genetically related as 

 components of a serial system of ground-water supported lakes which 

 responds to variations in aquifer head with changes in lake area, 

 volume and water chemistry. 



Water chemistry. White Lake contains highly alkaline "hypersaline" 

 sodium sulfate brine with very high ammonium concentration and 

 total organic carbon concentrations and exceptionally high 

 phosphorous concentration. Due to depletion through carbonate 

 precipitation in Brush Lake, the influent calcium concentration in 

 White Lake is very low and authigenic sedimentation is dominated 

 by mirabilite (Na2SO4*10H2O) ; mineral equilibria indicate slight 

 undersaturation with respect to mirabilite at the time of the DHES 

 sampling. 



The concentrated White Lake brine exhibited the highest arsenic and 

 second-highest boron concentrations of the sample set. The zinc 



