Lake Thibadeau Northeast 



Climatic setting. The net annual precipitation balance for the 

 Lake Thibadeau Northeast site (from the MAPS database) is -26 

 inches, at the upper end of evaporative intensity for sample sites 

 of the glaciated plains. Mean monthly precipitation for the Havre 

 climatic station shows a pronounced June maximum. Annual 

 precipitation totals for the Havre station show an apparent 

 periodicity with a period of 5 to 7 years. From 1987 to 1990, the 

 three-year running average was below the average for the period of 

 record; from 1991 through 1993, the running average met or exceeded 

 the average for the period of record. In 1993, the year prior to 

 sampling, total precipitation exceeded the average by about 5 

 inches. 



Geologic setting. No satisfactory geologic mapping of this site 

 was discovered in a search of published resources. Small-scale 

 geologic mapping shows the area to be underlain by the Late 

 Cretaceous Bearpaw Shale. The site is within the extent of 

 Pleistocene glaciation, and Bearpaw Shale outcrops in the area are 

 probably underlain by calcareous, poorly permeable till; no 

 description of surficial sediments was discovered, however. 



Hydrologic type. The wetland area sampled is an artificial 

 impoundment of an intermittent first-order stream. Contour closure 

 suggests that the site may been a wetland prior to the construction 

 of the impoundment, though no documentation of the site history is 

 available. The impoundment has an outlet structure, but the 

 frequency and duration of outflow are not known. The dilute water 

 chemistry exhibited at the time of the DHES sampling suggests 

 recent surface water discharge and flushing of the impoxindment . 



Basin characteristics. The catchment is a low-gradient upland basin 

 with a moderate catchment to wetland area ratio. The depth of the 

 small, elongate basin is unknown but probably does not exceed 10 

 feet based on topographic considerations. Another impoundment 

 upgradient from the sample site probably influences the duration 

 and timing of inflow to the sample site. 



Water chemistry. At the time of sampling, the WET40 site contained 

 highly alkaline, dilute water of calcium/sodium-bicarbonate 

 composition. Mineral equilibria indicate over-saturation with 

 carbonate phases. Ammonium, phosphorous (total and 

 orthophosphorous ) and total organic carbon concentrations all rank 

 mid-range with respect to other sample sites in the same 

 classification. The arsenic concentration was moderate for sites 

 of the glaciated plains, and the boron concentration was the lowest 

 for any site in this class. Copper and iron concentrations, on the 

 other hand, ranked near the high end for sites in this class. Lead 

 was present at the detection limit, and most other trace elements 

 were reported below detection. 



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



