Oilmont: Wetland 



Climatic setting. The net annual precipitation balance for the 

 Oilmont site (from the MAPS database) is -27 inches, placing 

 Oilmont toward the more intensely evaporative end of the range for 

 the sample sites. Monthly average precipitation for the Sunburst 

 8E climatic station shows a broad summer peak with a maximum in 

 June. Since the mid-1970 's, the 3-year running average of annual 

 precipitation for the Sunburst station was mainly at or above the 

 mean for the period of record. Data for 1993 and 1994 were not 

 recovered for this station; regionally, 1993 totals were well above 

 the average and 1994 totals were below average. 



Geologic setting. The Oilmont site is underlain by calcareous till, 

 lying just north of a prominent end moraine marking a late 

 Pleistocene glacial advance. Shorelines and bottom sediments 

 observed under desiccated conditions consist of zoned chemical 

 precipitates and weakly cemented beach sand and gravel. 



Bedrock underlying the till is described as an unspecified 

 formation of the Colorado Group. The site is near the apex of the 

 Kevin-Sunburst structural dome and in the midst of the (producing) 

 Kevin-Sunburst oil field. 



Hydrologic type. The Oilmont wetland is a saline playa drained by 

 a culvert under higher water conditions , and lacking surface 

 drainage under low water conditions. Surface drainage, when it 

 occurs, is to another small wetland basin to the west. 



Basin characteristics. The Oilmont wetland has a small 

 contributing basin and a low ratio of catchment area to wetland 

 surface area. The wetland basin has a very flat, shallow cross- 

 section; the maximum water depth (controlled by the outlet culvert 

 crossing beneath the north-south county road) is estimated to be 

 less than three feet. The drainage of this basin has been altered 

 by road construction, especially by the berm upon which the east- 

 west road to Oilmont is constructed. The existence of this berm 

 appears to impound local runoff in the sampled wetland at the 

 expense of other small playas, once connected, south of the road. 

 Observations by local residents support this inference. 



Water chemistry. At the time of sampling in June of 1994, water 

 in this wetland was a "eusaline" sodium sulfate brine with notably 

 low bicarbonate and carbonate concentrations . In September of 

 1994, there was no surface water at this site. Mineral equilibria 

 indicate that at the time of sampling, the water column was 

 substantially oversaturated with carbonate species and near 

 equilibrium with gypsum. 



Orthophosphorous and total phosphorous concentrations at the 

 Oilmont wetland were in the upper third among hydrologically 

 similar sites. Nitrate and ammonium concentrations were both low. 



