Ontario Nine Wetland 



Climatic setting. The net annual precipitation balance for the 

 Ontario Mine (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 WET59) 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 WET59 site in underlain by quartz monzonite 

 of the Boulder Batholith, near the contact with a mass of aplitic 

 intrusive rock underlying O'Keefe Mountain. Surficial deposits 

 are not shown on geologic maps of the immediate area and are 

 probably thin or absent. Historic mine workings drain to the 

 unnamed creek supporting the wetland. No specific information on 

 the nature of mineralization in these particular workings was 

 found. Sulfide mineralization is widespread in the area. 



Hydrologic type. The WET59 site is in a headwater riparian wetland 

 area supported by a small first-order stream receiving ground-water 

 discharge which is contaminated by acid mine drainage. 



Basin characteristics. The surface water catchment is small and 

 relatively steep; the wetland area is not definable at published 

 map scales. Ground-water delivered as mine drainage may possibly 

 originate outside the boundaries of the surface catchment. 



Water chemistry. The water sampled at WET59 is characterized by 

 obvious effects of acid mine drainage (AMD), including very low pH, 

 dominance of the anion makeup by sulfate, and elevated 

 concentrations of metals. Nitrate and ammonium concentrations were 

 below detection limits, the orthophosphate concentration ranked 

 mid-range in comparison to other Rocky Mountain sites. The total 

 organic carbon concentration was among the lowest in the sample 

 set. Arsenic, cadmium, copper, lead and zinc concentrations were 

 the highest among the Rocky Mountain sites. In the case of 

 cadmium, lead and zinc, WET59 showed the highest water-column 

 concentrations in the entire data set. 



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



Sediments. A very high concentration of extractable iron probably 

 reflects deposition of iron hydroxides precipitated from the water 

 column. Extractable arsenic and lead concentrations are the 



