Arsenic, boron and iron concentrations ranked mid-range among sites 

 classified with WET47; most other trace element concentrations were 

 below reporting limits. 



Cheaical history- The previous known chemical sampling of Mallard 

 Pond (conducted in August of 1990) included specific conductance 

 measurements from three points on the pond perimeter, including 

 one site very near WET47, and analytical water chemistry for a 

 single sample collected on the opposite (western) shoreline. The 

 specific conductance measurements demonstrated a substantial cross- 

 pond gradient in salinity; specific conductance at the two sites 

 on the western shoreline was higher than that near WET47 (measured 

 3 days earlier) by a factor of 1.75. The WET47 sample was also 

 higher in specific conductance than the 1990 measurement collected 

 nearby, by a factor of 1.4. 



Although moderately higher in total dissolved solids, the 1990 

 sample from the western shore was substantially lower in calcium 

 concentration than was the 1994 DHES sample from WET47. The field 

 pH of the 1990 sample was reported as 9.48, very similar to the 

 laboratory value reported for the WET47 sample. Taken together 

 with the depressed mid-day dissolved oxygen concentration for the 

 WET47 sample, it can be inferred that the WET47 sample was 

 collected from an area of ground-water discharge where C02, 

 dissolved oxygen and dissolved carbonate phases had not yet 

 equilibrated with the surface environment. The 1990 data show that 

 this adjustment, along with evaporative concentration and 

 increasing specific conductance, occurs during circulation of lake 

 water from the upgradient (eastern, WET47) shoreline to the 

 downgradient (western) side of the lake. 



Sedinents. As with Brush Lake and other relatively dilute ground- 

 water fed lakes in the area, the water chemistry data described 

 above imply loss of calcium (as calcium carbonate) from the water 

 column as ground-water enters the lake environment. The high 

 calcium concentration reported in the sediment analysis presumably 

 reflects active marl formation as part of Mallard Pond's 

 sedimentary regime. 



Extractable arsenic, boron, iron and zinc concentrations rank low 

 to mid-range with respect to similarly classified sites. None 

 exceed the mean soil values for the western United States. 



