Quote
Discovering Brister’sSpring
Does Walden Pond Produce outflow seepage that feeds Concord’s Mill Brook?
Background:
The “Final Report of a Study of Trophic Level Conditions of Walden Pond” Prepared for the Mass. DEM by Bay-state Environmental Consultants dated April 1995 did not address that question but did provide interesting related data including the following partial quotes:
“Walden Pond is a 60 acre kettle-hole lake with a normal pool elevation of 158 feet.
The lake has a deep basin (102 feet) at the western end and a shallower end near the boat ramp and bathing beach, see fig.3.1-2.”
The topography is quite variable with numerous small depressions typical of a pitted glacial outwash created by retreating and stagnating ice sheets. The largest portion of the depicted watershed lies to the north and is entirely underlain by sandy glacial outwash derived sub soils.”
… Previous reports concluded that groundwater in the immediate area of the Concord landfill flows to the north towards Fairyland Pond and not towards Walden Pond (to the south). .. Groundwater seepage data from the BEC study indicates strong in-seepage along the northern edge of Walden Pond. Therefore, a significant area north and some east, but not including the landfill area, was assumed to be included in the subsurface watershed.”
The surface watershed and the estimated subsurface watershed for Walden Pond are depicted in figure 3.1-3.”
The subsurface watershed is largely framed by the MBTA railroad tracks to the west, route 2 to the north, and route 126 to the east and south.”
South and west of Walden Pond is a relatively large wetland system known as Heywood Meadow (figure 3.1-3). This wetland system has an outlet at its southern end which flows to the west beneath the railroad embankment. The wetland system is fed by groundwater inflow and a small intermittent stream on the east side. Suspected outflow seepage areas in Walden Pond include Deep Cove, Long Cove, and Little Cove which may, in part, been shaped by spring sapping (long term geologic “erosion” due to groundwater outflow).”
The relatively short separation distance (200 m) between the pond and the wetland area and the differential (potential head) in the elevation of open water in each system (Walden Pond , El. 158 ft; Heywood Meadow El. 150 ft) strongly suggests a subsurface hydrologic connection through the sandy subsoil.”
