- Two aquifers in the Pittsfield area each have different depths and bedrock characteristics. A deep carbonate aquifer, on which the airport is located, is part of a system that supplies high-quality water to local and regional systems, including Croton Reservoir and the water supply for greater New York City. The other aquifer, composed of gravel from glacial sediments, has been directly affected by PCB contamination from the General Electric facility and its waste disposal sites. Though the overall contamination is now considered to be in remediation, groundwater impacts are addressed in joint GE / EPA clean-up activities in only a cursory manner.
- The two aquifers meet in western Pittsfield, where contaminant exchange may occur. Both aquifers contribute to the Housatonic River, which flows southward from Pittsfield through western Massachusetts and Connecticut (see the first map graphic in part 1 of this article series).
- The aquifer in the southwestern part of Pittsfield supplies groundwater to the only major branch of the Housatonic River headwaters that is not contaminated with PCBs. This high-quality aquifer resource acts as an active chemical filter and supplies water to communities in the vicinity of the Pittsfield Airport, including residents in Pittsfield who use groundwater wells for their domestic supply.
- No geotechnical development activity in the vicinity of Pittsfield, and especially at the airport because of its sensitive location, should be undertaken without study of potential impacts on the surface and groundwater system. Such construction could alter flow patterns, possibly leading to the complete loss of wetland areas and the release of additional PCB contaminants into the surface and groundwater system.
calcareous wetlands (sometimes known as fens) such as those to be affected by construction at the Pittsfield Airport, what is the likelihood of successful wetland replication and/or enhancement without prior detailed studies of their structure, origin, ecology and biochemical composition? Based on the documents at hand, we lack the data to support any answers or conclusions about the specific area at issue. Published evaluations in professional journals have generally reported unfavorable comparisons between the quality and function of constructed wetlands in comparison with their natural counterparts, even for sites in close proximity.
In addition, the continuity of surface and subsurface geology suggests that, where blasting and digging are planned in areas near these wetlands to provide fill for runway and safety areas, that removal of soils could lead to unanticipated results: the discovery or even creation of new springs, enhanced surface and subsurface outflow from the wetland areas, and even the complete drainage of valuable open-water and wetlands areas.
These wetlands, generally renowned for their biodiversity, are further distinguished by the underlying geology and the hydrogeologic conditions giving rise to seepage and springs at these particular locations. There is, however, little or no reference to such phenomena in much of the project documentation. It is evident from the aerial photography in Google Maps (see the map embedded in part 1 of this article series) that the original construction of the Pittsfield Airport occurred in wetland areas, but there is no indication in the project that this history and its impacts on the area may be relevant to planned construction. We must ask, what is the potential cumulative damage to the hydrologic system? If the planned construction proceeds, the rich ecology of these wetland areas and our opportunity to study the processes that generated these special areas could be lost entirely.
It is apparent that the location of airport construction relative to the locations of groundwater seepage and springs has not been determined. What are the potential consequences of building an airport runway on carbonate-dominated fill over, or even near, a groundwater spring? In carbonate aquifers, groundwater is known to dissolve the surrounding minerals to form cavities (karst geology), leading to caves and sinkholes if the ground surface is affected. These processes in a fill area can lead to progressive dissolution and wasting of soils, leading to added maintenance requirements (e.g. crack repair, repaving) and even the complete collapse of the runway above. The weight of an aircraft on the runway during taxi, takeoff or landing only adds to such danger.
The hydrology and geology of the area have been the subject of prior study: the USGS has issued a number of reports (1916, 1968, 1973, 1984, 1985, 1991, 1992, 1996, 1998a, 1998b, 1998c, 1999a, 1999b, and 2000) regarding the upper Housatonic surface waters and underlying geology and hydrogeology. However, regulatory assessments and the project permits are based on project documents that have referenced none of these sources. Hydrologic Atlas No. 281, a 1968 USGS report, includes numerous figures describing the fundamental physiography, geology, and hydrology (including water quality) of the Housatonic River basin. From that study, it is clear that one of the few areas left unaffected by PCB contamination from the GE facility was the Southwest Branch of the Housatonic, where the airport and these wetlands occur.
A deep carbonate aquifer underlies the upper Housatonic basin, but the surface aquifers vary in composition with location. In Pittsfield, the surface (alluvial) aquifer is dominated by glacial sediments; both the West and East Branches of the Housatonic occur in these conditions. The loose conglomeration of glacial deposits facilitates the transport of PCB contamination laterally and downward to the underlying carbonate bedrock. Upstream on the Southwest Branch, however, the deep carbonate aquifer is exposed at the surface, hence the occurrence of calcareous wetlands there but not farther to the east. While the hydrologic chemistry and hydraulic conductivity of the carbonate aquifer may differ from those in the surface deposits to the east, those differences would not prevent the exchange of contaminants at the geologic contact between the two aquifers.
USGS Ground Water Atlas of the United States, published in 1995 and now available on-line, shows that the carbonate bedrock formations underlying much of the upper Housatonic basin are contiguous with carbonate bedrock outcrops along the Hudson River basin in New York (see figure 85 at right, figure 99 below, and figure 101 on-line). It needs to be remembered that a surface watershed divide indicates the separation only of surface and shallow-soil water drainage, and then from the conditions described in the USGS studies it becomes clear that the water resources of western Massachusetts are connected beneath the Taconic Range to resources in southeastern New York, including some of the drinking water sources for New York City. In addition, the consistent grouping in USGS studies of the Housatonic River basin with the Connecticut River and Thames River basins to the east, from which extensive water supplies for Boston and other metropolitan areas are drawn, is a clue that significant connections exist there as well. It is well-known that the wetlands in the vicinity of Pittsfield share groundwater hydrology and chemistry with areas to the south, including conservation areas along Yokun Ridge (part of the Taconic Range) and numerous communities on the Massachusetts side of the drainage divide between the Hudson River and Housatonic River basins.