Geologic Stability and Hydrologic Isolation at the WCS ... Presentation - Geology.pdf · The WCS...
Transcript of Geologic Stability and Hydrologic Isolation at the WCS ... Presentation - Geology.pdf · The WCS...
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Geologic Stability and Hydrologic Isolation at the WCS Site, Andrews County, TX
Robert M. Holt, Dennis W. Powers, Gerry Grisak, John Pickens, Ed Hughes, Steve Cook and Clark Griffith
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The WCS site is One of the Most Characterized Sites in the U.S.
• 20,000 pages in reports to TCEQ related to the geologic and hydrologic conditions at the site
• These studies show that– The site has been and will
continue to be geologically stable– Radioactive and hazardous
wastes will be hydrologically isolated from usable water resources
• The following summarizes some important conclusions of these studies
Low-Level LicenseApplication
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Subsurface Characterization Activities at WCS Have Been Extensive
Approximately, 596 wells/soil borings, including:• 448 monitoring wells• Over 130 uncased soil borings• 18 instrumented boreholes
Numerous geologic/hydrologic investigations, including:• 15 major geologic studies• 18 major hydrogeologic studies • Nine geophysical investigations
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The WCS site is Geologically Stable
WIPP
Wink Sink
Jal Sink
San SimonSink
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The WCS site is Unaffected by Salt Dissolution
Rustler and Salado Formation Salt Beds Show Regional Continuity and No Changes Indicating Dissolution
A A’
B B’
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The WCS site is Unaffected by Salt Dissolution
CP-975 Core Slabs Show No Brecciation Above Salt or Mudstones Equivalent to Salt-bearing Beds
Upper Rustler anhydrite - unbrecciated
Upper Rustler mudstone –bedded at top
1583‐1593 ft depth 1643‐1653 ft depth
Middle Rustler anhydrite - unbrecciated
Mid
dle
Rus
tler
halit
e
BaseBase
Top Top
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The WCS site is Unaffected by Salt Dissolution Trench Study of Caliche - “V-shaped” Fractures Claimed As
Evidence of Dissolution
No “V-shaped” fractures found
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Two Hydrologic Units are Important to the WCS Site – The Dockum Group
Mudstones/Claystones – Ancient soils containing swelling clays
Siltstones/Sandstones – Discontinuous stream deposits
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Two Hydrologic Units are Important to the WCS Site – The OAG
Thin veneer of silts, sands, and gravels - Occupies erosional depressions on the Dockum Group
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The Dockum is a Low Permeability Medium
• 168 measurements of Dockum hydraulic conductivity (core and well tests) show: – Vertical effective hydraulic
conductivity of 1.2×10-9 cm/s (two orders of magnitude lower than required for a clay liner)
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Dockum Red Beds are Unsaturated
• 1,303 measurements of in situ water potential on core samples from 12 boreholes indicate unsaturated conditions
• No vertical flow from the surface to depth
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Water Flow in the Dockum is Slow Playa Observations -
• Water table conditions existed in the OAG under the playa for at least 18,000 years
• Currently ~ 7 feet of water in the OAG at the playa
• Borehole B-133 was drilled into the playa and sampled
• Water has only moved between 23 and 29 feet into the Red Beds in 18,000 years
• Water is very slow moving
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The OAG has Been Extensively Characterized
• 259 wells
• 157 dry wells
• OAG is only a few feet thick in near the WCS facilities and thickens to the north and south
• The average OAG thickness is 13.5 feet
• The average saturated thickness in the northern part of the facility is 2.7 feet
Thin
Thick
Thick
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The Base of the OAG is the Dockum
Top of Dockum is an ancient land surface that predates the OAG
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OAG water is Discontinuous and Controlled by Dockum Topography
These puddles accumulate, then dry out
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Summary
• The site is geologically stable• The site is hydrologically isolated • The site is ideal for disposal of hazardous, byproduct
and low-level radioactive waste