Factors influencing groundwater inflows in a newly constructed cross-strike tunnel, eastern Massachusetts; 1, Lineaments and subsurface structures

Lineaments derived from three platforms; 1:250,000 Side-Looking Airborne Radar (SLAR) images, 1:58,000 Color Infrared (CIR) and 1:80,000 Black and White aerial photographs (BW), were compared to water bearing structures (n = 99) within a 9 km, 70 to 90 meter deep, east-west tunnel being constructed in eastern Massachusetts. Lineaments were drawn by three observers during two independent trials to produce 18 sets of lineaments (n = 9137) covering approximately 1,000 km (super 2) centered over the tunnel. All lineaments for each platform were compared. Three or more overlapping lineaments (azimuths within 5 degrees and within 1 mm at the scale of the imagery) define a single coincident lineament. This analysis generated three sets of coincident lineaments (n = 794), of these 37 cross the tunnel. Buffers were placed around the coincident lineaments at a distance of 1 mm from the center of the lineament at the scale of the platform (e.g. 250 m for the SLAR image). The Mann-Whitney U test was used to determine if the median flow from all tunnel structures which underlie the lineament buffer zones is significantly greater than that of all structures outside of the buffer zones. Results indicate that median flow (11,000 l/day) from structures located within the buffer zones of the BW are significantly greater at the 90% confidence level than the median flow (5,500 l/day) of structures located outside the buffer zones. No significant differences in flow were found for the other two platforms. Subsurface structures that parallel coincident lineaments (all platforms) and occur within the buffer zones have higher median flow (10,500 l/day) than those structures outside the buffer zones (6,600 l/day). However, this difference is significant at the 70% confidence level. These results suggest that, in some instances, a thorough lineament analysis can predict water-bearing subsurface structures in poorly exposed, glaciated, metamorphic terrain that has a high degree of suburban development.