PFOA SURFICIAL MAPPING IN BENNINGTON, VT

Surficial mapping, well logs/borings analyses & assessment of bedrock recharge potential at 1:12,000 was done for the VT Survey to provide a knowledge base that includes determination of geomorphic history. Lithology & structure established a pre-glacial landscape with a trellis to rectangular drainage with pronounced NNE-SSW & E-W elements & an antecedent Walloomsac valley that cuts across structures & lithologies. A deep, N-S pre-glacial Furnace Brook valley developed along the base of the Green Mountains.

The area beneath the ChemFab site along Paran Creek consists of a variably permeable fluvial sequence of sand, gravel & silt that represents 2-3 distinct fluvial terrace packages of probable Holocene origin. Infiltration through these sediments to rock is not restricted by any impermeable till. Infiltration to rock through the washed-eroded till along the valley walls is similarly unrestricted by the overburden. This valley reach has no preserved Late Pleistocene sediments due to incision as Glacial Lake Bascom lowered with a small glacial lake breakout flood from Shaftsbury to the north. Early through middle Holocene sea level rise likely resulted in aggradation of these multiple fluvial terrace packages.

The area beneath the old landfill is underlain by ice contact sand & gravel & also by minor till. Additional stratigraphic data are needed to understand pathways of waste migration into rock in the landfill vicinity. There may be a complex stratigraphy preserved beneath the old landfill area due partly to its position in the lee side of the Hale mountain bedrock ridge. Older work included recovery of organic matter dated >56K years.

The prospect of a thick overburden sequence preserved in the pre-glacial Furnace Brook valley & the likelihood some of this sediment is permeable sand & gravel indicates there are pathways for contaminants to infiltrate to rock here that may not be slowed by any impermeable till. However, the stratigraphy is incompletely known along Chapel Road & a more complex stratigraphy may be preserved. Well log data indicate the presence of a viable overburden aquifer that should also be evaluated during investigations of the old landfill area in order to better understand the nature & extent of this unconfined sand & gravel aquifer.