Integrated multi-scale characterization of ground-water flow and chemical transport in fractured crystalline rock at the Mirror Lake Site, New Hampshire

Shapiro, Allen M.; Hsieh, Paul A.; Burton, William C.; Walsh, Gregory J.

doi:10.1029/171gm15

Cited by 31 publications

(23 citation statements)

References 31 publications

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“…For example, at dimensions of 10-100 m, bedrock fractures can support very high flow velocities, but at dimensions of 100-1000 m or more, flow velocities diminish rapidly, due to a bottleneck effect of intermittent low-conductivity fractures (4,34). Fractures that are low conductivity may contain MTBE or similar contaminants for long periods of time.…”

Section: Resultsmentioning

confidence: 99%

Methyl tert-Butyl Ether (MTBE) in Public and Private Wells in New Hampshire: Occurrence, Factors, and Possible Implications

Ayotte

Argue

McGarry

et al. 2008

Environ. Sci. Technol.

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Methyl tert-butyl ether (MTBE) concentrations g0.2 µg/L were found in samples of untreated water in 18% of publicsupply wells (n ) 284) and 9.1% of private domestic wells (n ) 264) sampled in 2005 and 2006 in New Hampshire. In counties that used reformulated gasoline (RFG), MTBE occurred at or above 0.2 µg/L in 30% of public-and 17% of private-supply wells. Additionally, 52% of public-supply wells collocated with fuel storage and 71% of mobile home park wells had MTBE. MTBE occurrence in public-supply wells was predicted by factors such as proximity to sources of fuel, land use, and population density, as well as low pH and distance from mapped lineaments. RFG use, land-use variables, and pH were important predictors of private-well MTBE occurrence. Variables representing sources of MTBE, such as the distance to known fuel sources, were not significant predictors of MTBE occurrence in private-supply wells. It is hypothesized that private wells may become contaminated from the collective effects of sources in high population areas and from undocumented incidental releases from onsite or proximal gasoline use. From 2003 to 2005, MTBE occurrence decreased in 63 publicsupply wells and increased in 60 private-supply wells, but neither trend was statistically significant.

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Section: Resultsmentioning

confidence: 99%

Methyl tert-Butyl Ether (MTBE) in Public and Private Wells in New Hampshire: Occurrence, Factors, and Possible Implications

Ayotte

Argue

McGarry

et al. 2008

Environ. Sci. Technol.

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“…In one study, the CZ was found to be thicker in strongly fractured crystalline rocks where fractures provide pathways for water to invade the bedrock, initiate weathering, and provide rapid bedrock drainage (Owen et al, 2007). Moreover, the flow of subsurface water is strongly influenced by parallel fractures (e.g., Shapiro et al, 2007), reinforcing the importance of understanding landscape-scale fracture patterns in crystalline bedrock (van Golf-Racht, 1982). The controls on water flow through saprolite are poorly understood, though some studies have found a zone of high hydraulic conductivity near the saprolite/bedrock boundary (e.g., Boisson et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Mapping Inherited Fractures in the Critical Zone Using Seismic Anisotropy From Circular Surveys

Novitsky

Holbrook

Carr

et al. 2018

Geophysical Research Letters

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Weathering and hydrological processes in Earth's shallow subsurface are influenced by inherited bedrock structures, such as bedding planes, faults, joints, and fractures. However, these structures are difficult to observe in soil‐mantled landscapes. Steeply dipping structures with a dominant orientation are detectable by seismic anisotropy, with fast wave speeds along the strike of structures. We measured shallow (~2–4 m) seismic anisotropy using “circle shots,” geophones deployed in a circle around a central shot point, in a weathered granite terrain in the Laramie Range of Wyoming. The inferred remnant fracture orientations agree with brittle fracture orientations measured at tens of meters depth in boreholes, demonstrating that bedrock fractures persist through the weathering process into the shallow critical zone. Seismic anisotropy positively correlates with saprolite thickness, suggesting that inherited bedrock fractures may control saprolite thickness by providing preferential pathways for corrosive meteoric waters to access the deep critical zone.

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“…Transmissivity of individual fractures typically varies over many orders of magnitude (Novakowski et al 1999;Shapiro et al 2007). Relatively few fractures can control a majority of the groundwater flow and advective contaminant transport, producing convoluted flow paths and spatially complex distributions of contaminants (NRC 1996;Shapiro et al 2007;NAS 2015). Additional complexities arise from the rock matrix, which has pore space into which contaminants can diffuse.…”

Section: Introductionmentioning

confidence: 99%

Bioremediation in Fractured Rock: 1. Modeling to Inform Design, Monitoring, and Expectations

Tiedeman¹,

Shapiro

Hsieh

et al. 2017

Groundwater

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Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower-permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture-dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high- and low-permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured-rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.

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Integrated multi-scale characterization of ground-water flow and chemical transport in fractured crystalline rock at the Mirror Lake Site, New Hampshire

Cited by 31 publications

References 31 publications

Methyl tert-Butyl Ether (MTBE) in Public and Private Wells in New Hampshire: Occurrence, Factors, and Possible Implications

Methyl tert-Butyl Ether (MTBE) in Public and Private Wells in New Hampshire: Occurrence, Factors, and Possible Implications

Mapping Inherited Fractures in the Critical Zone Using Seismic Anisotropy From Circular Surveys

Bioremediation in Fractured Rock: 1. Modeling to Inform Design, Monitoring, and Expectations

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