Hydrogeologic analyses in support of the conceptual model for the LANL Area G LLRW performance assessment

Conference · Mon Apr 01 04:00:00 EST 1996

OSTI ID:212464

Vold, E L; Birdsell, K; Rogers, D; Springer, E; Krier, D; Turin, H J

The Los Alamos National Laboratory low level radioactive waste disposal facility at Area G is currently completing a draft of the site Performance Assessment. Results from previous field studies have estimated a range in recharge rate up to 1 cm/yr. Recent estimates of unsaturated hydraulic conductivity for each stratigraphic layer under a unit gradient assumption show a wide range in recharge rate of 10{sup {minus}4} to 1 cm/yr depending upon location. Numerical computations show that a single net infiltration rate at the mesa surface does not match the moisture profile in each stratigraphic layer simultaneously, suggesting local source or sink terms possibly due to surface connected porous regions. The best fit to field data at deeper stratigraphic layers occurs for a net infiltration of about 0.1 cm/yr. A recent detailed analysis evaluated liquid phase vertical moisture flux, based on moisture profiles in several boreholes and van Genuchten fits to the hydraulic properties for each of the stratigraphic units. Results show a near surface infiltration region averages 8m deep, below which is a dry, low moisture content, and low flux region, where liquid phase recharge averages to zero. Analysis shows this low flux region is dominated by vapor movement. Field data from tritium diffusion studies, from pressure fluctuation attenuation studies, and from comparisons of in-situ and core sample permeabilities indicate that the vapor diffusion is enhanced above that expected in the matrix and is presumably due to enhanced flow through the fractures. Below this dry region within the mesa is a moisture spike which analyses show corresponds to a moisture source. The likely physical explanation is seasonal transient infiltration through surface-connected fractures. This anomalous region is being investigated in current field studies, because it is critical in understanding the moisture flux which continues to deeper regions through the unsaturated zone.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 212464
• Report Number(s): LA-UR--96-369; CONF-960212--66; ON: DE96008161
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
FLOW MODELS
HYDRAULIC CONDUCTIVITY
HYDROLOGY
LANL
LOW-LEVEL RADIOACTIVE WASTES
PERFORMANCE
PERMEABILITY
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE FACILITIES
SITE CHARACTERIZATION
VOLCANIC ROCKS
WATER INFLUX