TY - Generic T1 - Characterizing fractured crystalline bedrock aquifers using hydrostructural domains in the Nashoba Terrane, eastern Massachusetts T2 - Abstracts with Programs - Geological Society of America Y1 - 2006 A1 - Alex K Manda A1 - Stephen B Mabee A1 - David F Boutt KW - #StaffPubs KW - anisotropy KW - aquifers KW - BEDROCK KW - characterization KW - connectivity KW - crystalline rocks KW - eastern Massachusetts KW - fractures KW - ground water KW - heterogeneity KW - hydraulic conductivity KW - Hydrogeology 21 KW - massachusetts KW - Nashoba terrane KW - outcrops KW - physical properties KW - site exploration KW - United States KW - water wells AB - Fractured crystalline bedrock aquifers are good sources of potable water in many parts of the world. However, siting of highly productive wells in these rock units remains a challenging and expensive task because fracture development at the regional scale is both heterogeneous and anisotropic. Using low cost field data to define units of rock that have similar lithologic and fracture characteristics can significantly reduce time and energy spent on determining areas with better than average aquifer productivity. These physical characteristics that impart a particular hydraulic character on rocks are used to delineate regions with similar hydrologic characteristics called hydrostructural domains (Mackie, 2002). Hydrostructural domains are delineated from fracture characterization data that were collected from 79 outcrops located in the Nashoba Terrane of eastern Massachusetts. Information collected and used to delineate the domains include the number and distribution of fracture sets, types of fractures present or absent, the degree of fracture development, fracture intensity/density, fracture connectivity and rock type. Discrete fracture networks are generated from the fracture characterization data to simulate groundwater flow in the region. Conductivity of particular units is evaluated and compared to results from existing pumping tests obtained from the US Geological Survey. Preliminary results indicate that there is great value in utilizing fracture characteristic data obtained from surface outcrops to predict subsurface groundwater flow characteristics of fractured bedrock aquifers. Water managers, developers and decision makers are eager to know which areas are the most promising for encountering highly conductive zones in the subsurface. Collecting extensive structural data from surface outcrops, although not as accurate as drilling wells, is a cheaper alternative that could provide at least a rough estimate of the hydraulic properties of fractured rocks leading to effective siting of new water wells. Hydrostructural domain maps may pinpoint specific areas that have a high potential for wells to encounter highly conductive zones and could therefore be a powerful tool in transferring information from one site to another without having to repeatedly undertake extensive site characterization. JF - Abstracts with Programs - Geological Society of America PB - Geological Society of America (GSA) : Boulder, CO, United States CY - United States VL - 38 SN - 00167592 UR - https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_113075.htm IS - 77 N1 - Accession Number: 2007-032741; Conference Name: Geological Society of America, 2006 annual meeting; Philadelphia, PA, United States; Conference Date: 20061022; Language: English; Coden: GAAPBC; Collation: 1; Collation: 25; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 200709; Monograph Title: Geological Society of America, 2006 annual meeting; Monograph Author(s): Anonymous; Reviewed Item: Analytic JO - Abstracts with Programs - Geological Society of America ER - TY - Generic T1 - Implications of diurnal river fluctuations on mass transport in a valley-fill aquifer T2 - Abstracts with Programs - Geological Society of America Y1 - 2006 A1 - Brandon J Fleming A1 - David F Boutt A1 - Stephen B Mabee KW - #StaffPubs KW - aquifers KW - BEDROCK KW - clastic sediments KW - controls KW - diffusion KW - diurnal variations KW - drainage KW - drift KW - Eastern U.S. KW - Environmental geology 22 KW - floods KW - fluctuations KW - geochemical cycle KW - geologic hazards KW - ground water KW - measurement KW - mixing KW - models KW - Northeastern U.S. KW - numerical models KW - nutrients KW - pollution KW - processes KW - pumping KW - quantitative analysis KW - residence time KW - sediments KW - shallow aquifers KW - surface water KW - three-dimensional models KW - tracers KW - transport KW - United States KW - valleys KW - water pollution KW - water resources KW - water wells AB - Aquifers located in isolated stratified drift deposits in the northeastern portion of the US are extremely fragile and important groundwater resources. These aquifers, when restricted to bedrock valleys, are often strongly coupled to significant surface water drainage systems. In northwestern Massachusetts, surface water associated with the Deerfield River watershed is highly regulated by dams to protect against flooding and to generate hydroelectric power. Regular releases of water from these dams cause diurnal fluctuations in river stage. In a previous study performed by the USGS, measurements from two clusters of wells show a significant response to river stage fluctuations in the aquifer. Fluctuations in river stage and resulting changes in head levels in the aquifer cause a switch from a losing to a gaining stream. The flow reversals have implications for mass transport and nutrient cycling within the hyporheic zone. In this paper we investigate the physical hydrologic controls on mass transport in the shallow aquifer. Using a coupled groundwater flow and transport code, we built a quasi three dimensional transient numerical model to approximate the head changes in the aquifer caused by the stage fluctuations in the river. Flow velocities and residence times were estimated in the aquifer for a variety of flow conditions. The mixing process driven by the aquifer head changes were quantified in the proximity of the hyporheic zone and shown to significantly influence both vertical and horizontal flow velocities in a region close to the stream-aquifer boundary. The diurnal river stage changes also appear to influence farfield hydrologic conditions and potentially hydrologically isolate the river and hyporheic zone. To further investigate these mixing processes we applied a mass transport code with conservative tracers to the aquifer. Fluctuation of the river stage combined with the heterogeneous nature of the aquifer creates a pumping mechanism that creates excess mixing within shallow portions of the aquifer. Aquifer dispersivity and molecular diffusion both contribute to the anomalous mixing modeled in the shallow aquifer. Mixing driven by stream stage changes has important implications for nutrient cycling as well as contaminant transport in the shallow aquifer. JF - Abstracts with Programs - Geological Society of America PB - Geological Society of America (GSA) : Boulder, CO, United States CY - United States VL - 38 SN - 00167592 UR - https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_115285.htm IS - 77 N1 - Accession Number: 2010-061334; Conference Name: Geological Society of America, 2006 annual meeting; Philadelphia, PA, United States; Conference Date: 20061022; Language: English; Coden: GAAPBC; Collation: 1; Collation: 468; Publication Types: Abstract Only; Serial; Conference document; Updated Code: 201034; Monograph Title: Geological Society of America, 2006 annual meeting; Monograph Author(s): Anonymous; Reviewed Item: Analytic JO - Abstracts with Programs - Geological Society of America ER -