Lineaments; their value in assessing regional groundwater availability and quality in bedrock aquifers of glaciated metamorphic terrains; a case study

A lineament analysis was performed for Georgetown, Maine, a 44 km[sup 2] island community on the central Maine coast in order to evaluate the relationship between mapped lineaments and (1) outcrop fractures, (2) the productivity of 35 existing bedrock wells, and (3) groundwater quality determined from a sample of 87 bedrock wells. Lineaments were drawn by three observers using two scales of imagery (SLAR and 1:80,000 Aerial Photograph). However, the extent of the overlap is not uniform. Some lineament domains (165[degree]), although reproducible, exhibit no correlation with fracture fabric whereas other lineament domains (120[degree]) only show a correlation with fracture fabric in a very limited geographic area. The productivity of wells located on'' lineaments, particularly those that geographically overlap similar-trending fracture domains, are generally more productive than non-lineament wells. However, in this, other geologic factors exhibit strong influences on high productivity in bedrock wells. Bedrock type (amphibolite) is the dominant and only statistically significant influence on well productivity followed by depth to the water table (shallow depths), proximity to lineaments (specifically those that correlate geographically with outcrop fractures), topographic position, and proximity to surface water bodies, in order of decreasing importance. Groundwater chemistry is controlled primarily by bedrock type, topographic setting, structural position, and overburden type and thickness, and not by a well's position with respect to lineaments. In this particular area of Maine, lineament analyses are generally ineffective for characterizing bedrock aquifers over large regions when more obvious and simpler explanations for the variations in chemical character of groundwater and water-bearing properties of the bedrock appear appropriate.