HYDROGEOLOGIC CHARACTERIZATION OF A MOUNTAINTOP SEEPAGE LAKE IN CENTRAL CONNECTICUT

Lake Louise sits within a saddle depression on top of Talcott Mountain in central Connecticut. The lake has an area of 7000 m² and occupies 15% of the depression, with the remainder being wetland. Field and air photo data suggest that the lake once occupied the entire depression. Lake water depth reaches a maximum of 7m. There are no surface flow channels into the lake, so water is supplied by groundwater flow, direct precipitation, and local surface runoff. The lake has a spill point of 162.8 m elevation at which water exits along a small channel to a waterfall that feeds Lucy Brook. Channel flow out of the lake occurs only during periods of high rainfall.

The location of the lake is due to a unique set of geological conditions. The depression is at the foot of a roche moutonnée formed by the Holyoke basalt immediately to the north, and is interpreted to be a result of glacial scouring of weaker sandstones and siltstones of the Jurassic Shuttle Meadow Fm. that lie between the more resistant overlying Holyoke basalt and the underlying Talcott basalt. The three units, which strike 010°and dip 15° to 20° SE, comprise the hydrologic structure. The upper Talcott basalt is characterized by nonsystematic columnar jointing, and apparently has little vertical hydraulic conductivity as it serves as a low permeability boundary layer. The Shuttle Meadow Fm. is a fractured aquifer that exhibit two bed normal joint sets: 007°±11° and 292°±7°. The Holyoke basalt is also characterized by nonsystematic columnar jointing, but LiDAR-based DEM data reveal well-developed km-scale brittle structures (faults?) at the surface oriented 355° and 025°. These structures, along with systematic joint systems, may facilitate groundwater flow in a N-S direction. We are uncertain if the saddle is the ultimate groundwater discharge area, or if it is just a flow through point.

The lake has seen minimal anthropogenic impact. Water quality is excellent, with a pH of 6.32, alkalinity of 25 mg/L, conductivity of 33 µS, and nitrate, phosphate, and chlorine levels all undetectable. Secchi disk transparency is 1.3 m, indicating eutrophic conditions. The low conductivity implies a relatively short period of rock-water interaction and supports a relatively fast flow through of water. This study serves as a baseline for continued monitoring of the lake.