TY - Generic T1 - Field mapping and fracture characterization techniques predict groundwater preferential flow paths in fractured bedrock aquifers, Nashoba Terrane, MA T2 - AGU Fall Conference, 2005 Y1 - 2005 A1 - Alex K Manda A1 - Stephen B Mabee A1 - Hubbs, S. A. KW - #StaffPubs KW - aquifers KW - BEDROCK KW - characterization KW - fractured materials KW - fractures KW - ground water KW - Hydrogeology 21 KW - mapping KW - massachusetts KW - Middlesex County Massachusetts KW - movement KW - Nashoba terrane KW - patterns KW - preferential flow KW - recharge KW - reservoir properties KW - substrates KW - United States AB - A study examining the relationship between fracture characteristics and groundwater was undertaken in the crystalline Nashoba Terrane of eastern Massachusetts. The Nashoba Terrane, a fault-bounded, highly deformed sliver of Paleozoic igneous and metamorphic rocks, covers an area of 600 sq km about 50 km northwest of Boston. Increasing industrial development coupled with population growth place significant pressure on developers to provide sufficient potable water for the population. To aid water development and management, this study examined fracture characteristics at regional, quadrangle and wellfield scales. The regional-scale work involved recording over 4000 structural measurements from 80 outcrops in the terrane. Fracture information recorded at each data station included strike and dip, trace length, spacing, termination, and fracture type. Preliminary results show that hydrostructural domains can be defined from combinations of fracture characterization and rock types. These domains are used to conceptualize general groundwater flow patterns in the subsurface: steeply dipping fractures, such as partings parallel to foliation enhance recharge potential and impose strong flow anisotropy. A different character is observed if steeply dipping joints intersect sheeting joints. In this instance, both recharge and lateral flow will be enhanced and flow anisotropy will be reduced. The distribution and intensity of particular fracture sets varies as a function of rock type, proximity to major features and local stress states. Partings parallel to foliation are prevalent in gneissic rocks whereas sheeting joints are more common in igneous rocks. Common joints are the most prevalent fractures, present in all rock types across the entire terrane. Quadrangle and wellfield scale data can be used to validate the regional-scale conceptual models. A comprehensive well-yield database was created to test the proposed models. Over 500 water wells in the terrane were evaluated to determine regions with high and low yield. The findings were evaluated in terms of location with respect to newly defined hydrostructural domain maps at both regional and quadrangle scales. Application of these hydrostructural domains in field studies can be useful not only in characterizing fracture intensity and distribution, but can shed more light on the potential of intersecting subsurface zones that could be exploited for economic gain. JF - AGU Fall Conference, 2005 PB - American Geophysical Union : Washington, DC, United States CY - United States VL - 86 SN - 00963941 IS - 52, Suppl.52, Suppl. N1 - Accession Number: 2009-053313; Conference Name: American Geophysical Union 2005 fall meeting; San Francisco, CA, United States; Conference Date: 20051205; Language: English; Coordinates: N420800N424400W0710200W0715300; Coden: EOSTAJ; Collation: -1; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 200930; Monograph Title: AGU 2005 fall meeting; Monograph Author(s): Anonymous; Reviewed Item: Analytic JO - Eos, Transactions, American Geophysical Union ER - TY - JOUR T1 - A field study (Massachusetts, USA) of the factors controlling the depth of groundwater flow systems in crystalline fractured-rock terrain JF - Hydrogeology Journal Y1 - 2010 A1 - David F Boutt A1 - Diggins, Patrick A1 - Stephen B Mabee KW - #StaffPubs KW - aquifers KW - boreholes KW - crystalline rocks KW - eastern Massachusetts KW - fractured materials KW - fractures KW - ground water KW - hydraulic conductivity KW - Hydrogeology 21 KW - massachusetts KW - Nashoba terrane KW - permeability KW - porosity KW - preferential flow KW - shallow-water environment KW - substrates KW - United States AB - Groundwater movement and availability in crystalline and metamorphosed rocks is dominated by the secondary porosity generated through fracturing. The distributions of fractures and fracture zones determine permeable pathways and the productivity of these rocks. Controls on how these distributions vary with depth in the shallow subsurface (<300 m) and their resulting influence on groundwater flow is not well understood. The results of a subsurface study in the Nashoba and Avalon terranes of eastern Massachusetts (USA), which is a region experiencing expanded use of the fractured bedrock as a potable-supply aquifer, are presented. The study logged the distribution of fractures in 17 boreholes, identified flowing fractures, and hydraulically characterized the rock mass intersecting the boreholes. Of all fractures encountered, 2.5% are hydraulically active. Boreholes show decreasing fracture frequency up to 300 m depth, with hydraulically active fractures showing a similar trend; this restricts topographically driven flow. Borehole temperature profiles corroborate this, with minimal hydrologically altered flow observed in the profiles below 100 m. Results from this study suggest that active flow systems in these geologic settings are shallow and that fracture permeability outside of the influence of large-scale structures will follow a decreasing trend with depth. Copyright 2010 Springer-Verlag PB - Springer : Berlin - Heidelberg, Germany CY - Federal Republic of Germany VL - 18 SN - 1431217414350157 UR - http://link.springer.com/article/10.1007%2Fs10040-010-0640-y IS - 88 N1 - Accession Number: 2011-042136; Language: English; Coordinates: N420000N425000W0695500W0714500; Collation: 16; Publication Types: Serial; Updated Code: 201124; Illustration(s): illus. incl. 3 tables, geol. sketch map; Number of References: 58; Reviewed Item: Analytic JO - Hydrogeology Journal ER -