Ontario Creek Headwaters 



Cli»atic setting. The net annual precipitation balance for Ontario 

 Creek Headwaters (from the MAPS database) is -3 inches, placing the 

 site near the humid end of the range shown by the sample sites, but 

 mid-range for those in the Rocky Mountains. Mean monthly 

 precipitation for the Basin climatic station (at a much different 

 elevation than the site) shows a bimodal distribution, with a 

 primary June maximum and a secondary January peak. The three-year 

 running average of annual precipitation for the Boulder station 

 (also at some distance from WET58) shows values below the long-term 

 average for much of the 1980s and near or above the long-term 

 average for 1990-93, with precipitation in 1993 (the year of 

 sampling) almost 6 inches above average. [Water supply to the 

 Ontario Creek headwaters is probably supported mainly by winter 

 snowpack, however, which is not reflected in data from these low- 

 elevation stations.] 



Geologic setting. The Ontario Creek wetland is underlain by deeply 

 weathered glacial till interpreted as early Wisconsin in age. 

 Glacial deposits, which are probably very thin, overlie the 

 Cretaceous-aged Elkhorn volcanics and quartz monzonite the Boulder 

 batholith. Hydrothermal mineralization has encouraged extensive 

 prospecting and historic ore production at numerous nearby sites 

 along the Ontario Creek-Telegraph Creek divide. 



Hydrologic type. WET58 is a small headwaters site with 

 intermittent(?) surface water outflow and without channelized 

 inflow. Although ground-water relationships are not knovm, the 

 position of the wetland near a drainage divide suggests recharge 

 from the wetland to ground-water may occur. 



Basin characteristics. The Ontario Creek wetland is a shallow 

 basin with a small, low-gradient catchment and a low catchment to 

 wetland area ratio in comparison to other Rocky Mountain sampling 

 sites. No mines or prospects are known within the immediate 

 catchment, but some level of sulfide mineralization is probably 

 ubiquitous in the area. 



Water chemistry. The Ontario Creek wetland is acidic, extremely 

 dilute and calcium/sodium-sulfate in composition. Nitrogen and 

 orthophosphorous concentrations are very low, and the total organic 

 carbon concentration ranks mid-range in comparison to Rocky 

 Mountain sites. 



The copper concentration reported is very high, exceeded in the 

 site class only by sample sites with known mining impacts. Arsenic 

 and iron concentrations rank mid-range within this site class, and 

 lead was reported at the detection limit. 



Chemical history. No other chemical data from this site are known. 



Sediments. The extractable concentrations of arsenic and copper 



