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Title: FIELD INVESTIGATION OF THE DRIFT SHADOW

Abstract

A drift shadow is an area immediately beneath an underground void that, in theory, will be relatively drier than the surrounding rock mass. Numerical and analytical models of water flow through unsaturated rock predict the existence of a drift shadow, but field tests confirming the existence of the drift shadow have yet to be performed. Proving the existence of drift shadows and understanding their hydrologic and transport characteristics could provide a better understanding of how contaminants move in the subsurface if released from waste emplacement drifts such as the proposed nuclear waste repository at Yucca Mountain, Nevada. We describe the field program that will be used to investigate the existence of a drift shadow--and the corresponding hydrological process at the Hazel-Atlas silica-sand mine located at the Black Diamond Mines Regional Preserve in Antioch, California. The location and configuration of this mine makes it an excellent site to observe and measure drift shadow characteristics. The mine is located in a porous sandstone unit of the Domengine formation, an approximately 230 meter thick series of interbedded Eocene-age shales, coals, and massive-bedded sandstones. The mining method used at the mine required the development of two parallel drifts, one above the other, driven alongmore » the strike of the mined sandstone stratum. This configuration provides the opportunity to introduce water into the rock mass in the upper drift and to observe and measure its flow around the underlying drift. The passive and active hydrologic tests to be performed are described. In the passive method, cores will be obtained in a radial pattern around a drift and will be sectioned and analyzed for in-situ water content using a gravimetric technique, as well as analyzed for chemistry. With the active hydrologic test, water will be introduced into the upper drift of the two parallel drifts and the flow of the water will be tracked as it passes near the bottom drift. Tensiometers, electrical resistance probes, neutron probes, and ground penetrating radar may be used to monitor the change in moisture content/potential over time as water is released.« less

Authors:
;
Publication Date:
Research Org.:
Yucca Mountain Project, Las Vegas, Nevada
Sponsoring Org.:
USDOE
OSTI Identifier:
884923
Report Number(s):
NA
MOL.20060227.0032, DC#45889; TRN: US0603808
DOE Contract Number:
NA
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; CHEMISTRY; CONFIGURATION; ELECTRIC CONDUCTIVITY; FIELD TESTS; MINING; MOISTURE; MONITORS; NEUTRON PROBES; POSITIONING; PROBES; RADAR; RADIOACTIVE WASTES; SANDSTONES; SHALES; WASTES; WATER; YUCCA MOUNTAIN

Citation Formats

G.W. Su, and T.J. Kneafsey. FIELD INVESTIGATION OF THE DRIFT SHADOW. United States: N. p., 2006. Web. doi:10.2172/884923.
G.W. Su, & T.J. Kneafsey. FIELD INVESTIGATION OF THE DRIFT SHADOW. United States. doi:10.2172/884923.
G.W. Su, and T.J. Kneafsey. Wed . "FIELD INVESTIGATION OF THE DRIFT SHADOW". United States. doi:10.2172/884923. https://www.osti.gov/servlets/purl/884923.
@article{osti_884923,
title = {FIELD INVESTIGATION OF THE DRIFT SHADOW},
author = {G.W. Su and T.J. Kneafsey},
abstractNote = {A drift shadow is an area immediately beneath an underground void that, in theory, will be relatively drier than the surrounding rock mass. Numerical and analytical models of water flow through unsaturated rock predict the existence of a drift shadow, but field tests confirming the existence of the drift shadow have yet to be performed. Proving the existence of drift shadows and understanding their hydrologic and transport characteristics could provide a better understanding of how contaminants move in the subsurface if released from waste emplacement drifts such as the proposed nuclear waste repository at Yucca Mountain, Nevada. We describe the field program that will be used to investigate the existence of a drift shadow--and the corresponding hydrological process at the Hazel-Atlas silica-sand mine located at the Black Diamond Mines Regional Preserve in Antioch, California. The location and configuration of this mine makes it an excellent site to observe and measure drift shadow characteristics. The mine is located in a porous sandstone unit of the Domengine formation, an approximately 230 meter thick series of interbedded Eocene-age shales, coals, and massive-bedded sandstones. The mining method used at the mine required the development of two parallel drifts, one above the other, driven along the strike of the mined sandstone stratum. This configuration provides the opportunity to introduce water into the rock mass in the upper drift and to observe and measure its flow around the underlying drift. The passive and active hydrologic tests to be performed are described. In the passive method, cores will be obtained in a radial pattern around a drift and will be sectioned and analyzed for in-situ water content using a gravimetric technique, as well as analyzed for chemistry. With the active hydrologic test, water will be introduced into the upper drift of the two parallel drifts and the flow of the water will be tracked as it passes near the bottom drift. Tensiometers, electrical resistance probes, neutron probes, and ground penetrating radar may be used to monitor the change in moisture content/potential over time as water is released.},
doi = {10.2172/884923},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2006},
month = {Wed Feb 01 00:00:00 EST 2006}
}

Technical Report:

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  • If proven, the concept of drift shadow, a zone of reduced water content and slower ground-water travel time beneath openings in fractured rock of the unsaturated zone, may increase performance of a proposed geologic repository for high-level radioactive waste at Yucca Mountain. To test this concept under natural-flow conditions present in the proposed repository horizon, isotopes within the uranium-series decay chain (uranium-238, uranium-234, and thorium-230, or {sup 238}U-{sup 234}U-{sup 230}Th) have been analyzed in samples of rock from beneath four naturally occurring lithophysal cavities. All samples show {sup 234}U depletion relative to parent {sup 238}U, indicating varying degrees of water-rockmore » interaction over the past million years. Variations in {sup 234}U/{sup 238}U activity ratios indicate that depletion of {sup 234}U relative to {sup 238}U can be either smaller or greater in rock beneath cavity floors relative to rock near cavity margins. These results are consistent with the concept of drift shadow and with numerical simulations of meter-scale spherical cavities in fractured tuff. Differences in distribution patterns of {sup 234}U/{sup 238}U activity ratios in rock beneath the cavity floors are interpreted to reflect differences in the amount of past seepage into lithophysal cavities, as indicated by the abundance of secondary mineral deposits present on the cavity floors.« less
  • X-ray absorption imaging experiments and measurements of inflow and outflow distribution provide quantitative and vistial evidence for capillary diversion around a drift and a drift-shadow effect. Test cells were constructed from volcanic tuff with either in-plane (one fracture parallel to the face of the test cell) or multi-fracture (with a grid of fractures perpendicular to the test cell) systems. Tracer solutions were dripped in the fractures at ports along the top of the test cell. Discharge along the bottom boundary and in the drift was monitored. Variables included flow rate and fracture aperture. X-ray absorption imaging allowed for visualization ofmore » flow paths through the system. Evidence for capillary diversion and drift shadow include: (1) very small (< 1 %,of inflow in most cases) measured discharge into the drift, (2) discharge less than expected under the drift and discharge greater than expected just beyond the drift, and (3) visualization of the tracer-solution flow path from above the drift, around the drift, and shedding beyond the drift. However, tracer was also observed in a natural fracture under the drift in one system. It is unclear whether these high concentrations are due to diversion around the drift and back under the drift or capillary spreading along the bottom boundary of the test cell. Future experiments will focus on using samples collected directly from Yucca Mountain and minimizing the capillary barrier effects along the lower boundary of the test cells. The implementation of the drift shadow effect, as supported by these experiments, could impact performance of the proposed Yucca Mountain repository.« less
  • No abstract prepared.
  • A drift shadow is an area immediately beneath an undergroundvoidthat, in theory, will be relatively drier than the surrounding rockmass. Numerical and analytical models of water flow through unsaturatedrock predict the existence of a drift shadow, but field tests confirmingits existence have yet to be performed. Proving the existence of driftshadows and understanding their hydrologic and transport characteristicscould provide a better understanding of how contaminants move in thesubsurface if released from waste emplacement drifts such as the proposednuclear waste repository at Yucca Mountain, Nevada. We describe the fieldprogram that will be used to investigate the existence of a drift shadowandmore » the corresponding hydrological process at the Hazel-Atlas silica-sandmine located at the Black Diamond Mines Regional Preserve in Antioch,California. The location and configuration of this mine makes it anexcellent site to observe and measure drift shadow characteristics. Themine is located in a porous sandstone unit of the Domengine Formation, anapproximately 230 meter thick series of interbedded Eocene-age shales,coals, and massive-bedded sandstones. The mining method used at the minerequired the development of two parallel drifts, one above the other,driven along the strike of the mined sandstone stratum. Thisconfiguration provides the opportunity to introduce water into the rockmass in the upper drift and to observe and measure its flow around theunderlying drift. The passive and active hydrologic tests to be performedare described. In the passive method, cores will be obtained in a radialpattern around a drift and will be sectioned and analyzed for in-situwater content and chemical constituents. With the active hydrologic test,water will be introduced into the upper drift of the two parallel driftsand the flow of the water will be tracked as it passes near the bottomdrift. Tensiometers, electrical resistance probes, neutron probes, andground penetrating radar may be used to monitor the change in moisturecontent and potential over time as water is released.« less