Published online 16 August 2005
Published in Vadose Zone J 4:789-797 (2005)
DOI: 10.2136/vzj2004.0171
© 2005 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
SPECIAL SECTION: LOS ALAMOS NATIONAL LABORATORY
Comparison of the Water Balance of an Asphalt Cover and an Evapotranspiration Cover at Technical Area 49 at the Los Alamos National Laboratory
Daniel G. Levitta,*,
Matthew J. Hartmanna,
Kenneth C. Kisiela,
C. W. Criswellb,
P. Dwain Farleyc and
Candace Christensena
a Energy and Environmental Engineering Division, Apogen Technologies, Inc., 1350 Central Avenue, 3rd Floor, Los Alamos, NM 87544
b Risk Reduction and Environmental Stewardship—Remediation Services, Los Alamos National Laboratory, P.O. Box 1663, MS M992, Los Alamos, NM 87545
c Risk Reduction and Environmental Stewardship—Environmental Characterization and Remediation, Los Alamos National Laboratory, P.O. Box 1663, MS H865, Los Alamos, NM 87545
* Corresponding author (daniel.levitt{at}apogentech.com)
Received 2 December 2004.
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ABSTRACT
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Two different types of waste covers, an asphalt cap and an evapotranspiration (ET) cover, have been used to contain a contaminated site at Technical Area (TA) 49 at the Los Alamos National Laboratory (LANL). In 1961, a 2.5- to 20-cm-thick asphalt cap and gravel and clay cover was constructed to isolate contamination of surface soils associated with subcritical hydronuclear safety experiments conducted at TA-49 between 1959 and 1961. The asphalt cap remained in place for 37 yr until 1998 when it was replaced with an ET cover. Cracks and subsidence features in the asphalt cap were periodically filled during that time. The thickness of the ET cover is 2.1 m at its center, tapering to zero thickness at its edges. The ET cover is instrumented with three neutron logging access tubes, and four time domain reflectometry (TDR) probes, and covered by a galvanized steel mesh bio-intrusion layer. Soil moisture monitoring was conducted immediately after the removal of the asphalt cap in 1998, and continuously since 1999 within the ET cover, providing a unique comparison of the performance of these cap and cover types at a semiarid site. Soil moisture monitoring results indicate that the soils within and beneath the ET cover have been drying since its installation, and infiltration of precipitation and snowmelt has been minimized. The replacement of the asphalt cap with the ET cover has significantly decreased shallow subsurface moisture contents. With continued growth of vegetation and increased transpiration, the site should continue its return to native conditions where net infiltration and associated groundwater recharge rates are <7 mm yr–1.
Abbreviations: CH, Core Hole • ET, evapotranspiration • LANL, Los Alamos National Laboratory • MDA, Material Disposal Area • PRSs, Potential Release Sites • TA, Technical Area • TDR, time domain reflectometry
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INTRODUCTION
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IN 1959 THROUGH 1961, subcritical hydronuclear safety experiments were conducted at TA-49 at LANL. Hydronuclear experiments were conducted in 1- or 2-m-diameter shafts at depths ranging between 9 and 33 m, with the majority of the tests conducted at a depth of 17 m. Test shafts were drilled, test materials were placed at the bottom of the shafts, shafts were backfilled with sand or local crushed tuff, tests were detonated, subsidence in shafts was backfilled, and cement caps were poured over the test shafts. The diameter of the affected detonation zones is believed to be <6 m. Most test shafts were drilled on 8-m grid spacing in four main areas within TA-49. The area within TA-49 where the test experiments were conducted is now referred to as Material Disposal Area (MDA) AB. The areas within MDA AB where the underground experiments were conducted are referred to as Areas 1, 2, 2A, 2B, 3, and 4. These Areas are also referred to as Potential Release Sites (PRSs) (LANL, 1992; Levitt et al., 2003). Refer to Fig. 1
for the location of TA-49 and LANL within New Mexico, and refer to Fig. 2
for the locations of the Areas and PRSs within TA-49.
During the drilling of a new test shaft in 1960, transuranic materials were encountered from an adjacent shaft, resulting in contamination of surface soils. The area of contamination, within Area 2, was covered by a cap of clay and gravel in the spring of 1961. Then to prevent erosion, the cap was covered with a 2.5- to 20-cm-thick asphalt cover in the fall of 1961. Years later it was discovered that the asphalt cap had adversely affected the water balance of the site by allowing infiltration through cracks and a collapsed area of the cap, and by greatly reducing ET. In addition, some ponding probably occurred on the asphalt cap because natural drainage was reduced by the elevated edge of the cap. In 1975, many cracks and a large collapsed area (1.8 by 0.9 m wide and 0.9 to 1.2 m deep) of the asphalt cover were discovered. It was also discovered that Core Hole 2 (CH-2), a 5-cm-diameter, 155-m-deep cased borehole (originally drilled for hydrogeologic characterization) located in the center of Area 2, contained about 15 m of standing water. It was suspected that the cracks and the collapsed area in the asphalt cover allowed focused infiltration of water into CH-2. In 1976, the asphalt cap was repaired, but more cracks and standing water were again found in CH-2 in 1979, 1980, and 1991 (LANL, 1992; Rofer et al., 1999). In 1994, two 46-m-deep boreholes (49-2906 and 49-2907) were drilled through the asphalt cover to evaluate the subsurface conditions below the depths of the shafts and to augment the existing moisture monitoring holes at MDA AB (LANL, 1992). An aerial photograph of the asphalt cover, taken in 1998, is shown in Fig. 3
. The circular collapsed area can be seen close to the center of the asphalt cover. The collapsed area encompassed the location of CH-2.
In 1998, the asphalt cap was removed. Boreholes CH-2, 49-2906, and 49-2907 were removed and grouted, and an ET monolayer cover was constructed with three neutron logging access tubes for manual moisture monitoring and an automated soil moisture monitoring system using four TDR probes. During removal of the asphalt cover, a large zone of soil with elevated moisture contents was encountered on the northeast corner of the site. The elevated moisture contents were suspected to have resulted from lateral movement of moisture that had accumulated beneath the asphalt cap, probably within the old gravel and clay fill materials (LANL, 1999). Soil moisture measurements were taken immediately after the removal of the asphalt cover in 1998, and continuously since 1999 within the ET cover, providing a unique comparison of the performance of these cap and cover types at a semiarid site (LANL, 1999; Levitt et al., 2003).
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SITE DESCRIPTION
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Los Alamos National Laboratory is located in north-central New Mexico, and TA-49 is located on Frijoles mesa on the southwestern boundary of LANL (Fig. 1). The mesa is relatively flat and has a vadose zone comprised of 285 m of volcanic tuff (Bandelier tuff) over 74 m of alluvial fan sediments (Stimac et al., 2002). The soil thickness on the mesa is generally 1 m or less and can be classified as a sandy loam. In general, the thickness of the soil cover is closely related to topographic slope; the soil thins out rapidly from the crown of the mesa to the edge of the mesa (Weir and Purtymun, 1962). Intermittent occurrences of the El Cajete Pumice layer can be found beneath the surface soils and within the Bandelier tuff. Storm water runoff and erosion are minimal at TA-49. There are no perennial sources of water at or near the site, with no established runoff channels. Any surface water movement occurs as sheet flow during strong rainfall events or rapid snowmelt (LANL, 1992).
TA-49 is located at an elevation of approximately 2130 m above sea level in a semiarid, temperate mountain climate. The average annual precipitation at TA-49 is 45 cm. This includes both rainfall and snowfall liquid equivalents (Bowen, 1990).
The regional aquifer is located approximately 360 m below the surface of Frijoles Mesa. Volumetric water contents within the volcanic tuff are usually quite dry and range between 5 and 10% (Weir and Purtymun, 1962; Abeele et al., 1981). Gravimetric moisture analysis was performed on core samples from a 213-m-deep borehole within TA-49 in 1993 and 1994. Results indicated moisture contents of approximately 11% in near-surface soil and fill material, with a rapid decrease to 1 to 4% within the upper tuff unit (Stimac et al., 2002). Hydraulic properties for crushed tuff are reported for TA-54, located approximately 5 km from TA-49. The saturated volumetric water content for crushed tuff is reported to be approximately 38.3% (Hollis et al., 1997). The saturated water content for El Cajete Pumice is not reported, but is believed to be quite high (
70%) because of its low bulk density. Hydraulic properties for alluvium are not reported, but a large range in hydraulic properties is expected based on the degree of disturbance by human activities (Hollis et al., 1997).
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MATERIALS AND METHODS
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After the asphalt cap was removed, the underlying fill (clay and gravel) was regraded to promote storm water runoff and eliminate ponding. Above the clay and gravel fill (old cover materials), a layer of crushed tuff was placed and compacted (new cover material). The final surface consisted of approximately 15 cm of topsoil, seeded with native shallow rooting grasses, overlain with a thin layer of gravel and a galvanized steel mesh bio-intrusion barrier. The final cover thickness of the new cover of topsoil and crushed tuff (from cover surface to original ground surface level) ranges from 2.1 to 0 m. The topsoil was hand-seeded with a mixture of native grasses, including 40% blue grama [Bouteloua gracilis (Kunth) Lag. ex Griffiths], 40% western wheatgrass [Agropyron smithii Rydb. (basionym)], and 20% annual ryegrass (Lolium multiflorum Lam.). After seeding, the site was covered with a thin layer of gravel to increase erosion protection and protect the seed from animals and act as a mulch to enhance germination. The steel bio-intrusion layer is made of 11-gauge steel with 1.25-cm openings and was installed primarily to prevent gophers (Thomomys talpoides) from digging through the cover (LANL, 1999).
After installation of the ET cover, three neutron access holes (designated 49-10046, 49-10047, and 49-10048) were drilled and cored through the cover so soil water contents could be monitored. These boreholes range in depth from 3.4 to 4.3 m, and total depth is located just below the contact of soil or fill with weathered volcanic tuff (LANL, 1999). The geologic stratigraphy encountered during drilling and coring of these three boreholes immediately after construction of the ET cover is shown in Fig. 4 . Water contents were found to be lowest in the new ET cover material (crushed tuff) and the clay rich soils of the old cover (10–25%), and higher within crushed tuff and the El Cajete Pumice layers of the old cover (25–60%). The El Cajete Pumice was encountered at two of the three boreholes. Photographs of the ET cover are shown in Fig. 5 and 6
. These photographs were taken 2 Sept. 2004, approximately 6 yr after construction and seeding of the cover.
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Fig. 4. Stratigraphy and soil water contents encountered during coring of the three boreholes through the evapotranspiration (ET) cover in 1998. The green lines indicate original ground surface and "1998 Cover Material" refers to the ET cover installed in 1998. Layers between the 1998 cover material and original ground surface are the remnant layers from the pre-1998 cover.
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Fig. 6. Photograph of ET cover taken 2 Sept. 2004. Neutron logging Borehole 49-10048, PVC protection for wires from TDR West station, and the galvanized steel bio-intrusion mesh can be seen in the photograph.
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During the construction of the ET cover, TDR probes were installed within the cover material at two depths at two locations (Table 1, Fig. 7)
. The TDR probes (model CS615, Campbell Scientific Inc., Logan, UT) were wired into a Campbell Scientific data logger (model 23X) for automated measurements. The TDR probe wires were placed in PVC casing between the monitoring location and the data logger to prevent rodent damage to the wires. The calibration equation used to convert raw voltage measurements into volumetric water contents was taken from the CS615 users' manual. Volumetric water contents are measured with the four TDR probes twice per day. At the western location, TDR probes were buried at depths of 15 and 183 cm. At the eastern location, TDR probes were buried at depths of 15 and 305 cm. At both locations, the shallow probe was buried in a horizontal position at the base of the topsoil layer while the deep probe was buried in a vertical position. At both locations the deep probe was buried in a vertical position because this only required excavation of a borehole using a hand auger rather than requiring a larger excavation for installation of the 30-cm-long probes. At the western location the deep probe was buried in soil, while at the eastern location the deep probe was buried in the El Cajete Pumice layer. The shallow probes were installed in ET cover materials, so initial data do not represent natural conditions. Deeper probes were installed in preexisting geologic media, so they better represent the results of site improvements compared with the shallow probes. The TDR probes and an onsite precipitation gauge allow for characterization of the ET cover's performance in response to precipitation events.
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Fig. 7. Aerial photograph of Area 2 showing locations of the neutron logging boreholes, the two boreholes sampled in 1994 (49-2906 and 49-2907), CH-2, the four TDR probes, and the extent of the bio-intrusion barrier.
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To supplement the TDR data, eight neutron access holes surrounding Area 2 (2A-O, 2A-Y, 2B-Y, TH-1, TH-2, TH-3, TH-4, and TH-5) and the three boreholes through the Area 2 ET cover were neutron logged on a monthly basis from September 1999 until September 2002, after which they were monitored every 2 mo. The 2A/2B boreholes, TH boreholes, the 46-m-deep boreholes (49-2906 and 49-2907), and the CH-2 borehole were periodically neutron logged before 1998 using the same logging techniques as were used after 1998. Water content profiles were measured at 49-2906, 49-2907 in 1994, and at CH-2 in 1998, and represent moisture conditions beneath the asphalt cover. Water content profiles from the five TH boreholes represent undisturbed soil moisture conditions in the Frijoles Mesa. Water content profiles from the three 2A/2B boreholes represent disturbed soil moisture conditions because these boreholes were installed into unused test shafts that were backfilled with crushed tuff. The 2A/2B boreholes represent moisture conditions of disturbed soils after four decades of redistribution. Therefore, moisture conditions in the ET cover should eventually be equivalent to or drier than those in the 2A/2B boreholes. The locations of the four TDR probes and the 11 neutron logging access tubes described above are shown in Fig. 7. A summary of the boreholes used for water content measurements (by core sampling and neutron logging) is shown in Table 2.
Volumetric water contents were calculated using calibration equations from the neutron probe users' manual. Different calibration equations were used for the different casing types for the 2A/2B, TH, and ET cover casings. However, the same calibration equation was used for topsoil, clay layers, crushed tuff, and intact tuff for a given borehole. The 2A/2B boreholes were drilled through backfilled crushed tuff materials, the TH boreholes were drilled through thin soil and intact tuff, and the ET cover boreholes (49-10046, 49-10047, and 49-10048) were drilled through a thin topsoil layer, crushed tuff, thin clay layers, and in some cases, the El Cajete Pumice layer. Water contents provided by neutron logging in the El Cajete Pumice may be higher than actual water contents, but these measurements are adequate for comparing relative changes in water content with time.
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RESULTS AND DISCUSSION
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During the past 4 yr, volumetric soil water contents measured with the shallow (0.15 m deep) TDR probes in the ET cover have ranged from approximately 8 to 44%. The shallow TDR probe at the west site, which is upslope from the east site, measured maximum water contents of about 31% in the winter of 2000–2001, and lower maximums in subsequent winters and springs. The shallow TDR probe at the east site measured maximum water contents >40% during three of the past four winters and springs. These measurements indicate near-saturated to saturated soil conditions. The deep TDR probes measured water contents that remained fairly steady, with water contents at approximately 10% at the east site (in the pumice layer), and 16 to 17% at the west site (in soil). The exception to this was an increase in water content from 10 to 17% at a depth of 3 m at the east site in April 2004. This increase was in response to a period of sustained rainfall (8.3 cm in a 10-d period). However, water contents at this depth quickly returned to a residual water content of 10% within 2 mo. These data indicate that occasional pulses of infiltration can penetrate the entire depth of the ET cover following periods of high rainfall. These pulses may be mitigated or eliminated once vegetation on the ET cover has reached maturity. Although the vegetation appear to be quite mature in the photographs in Fig. 5 and 6, large bare areas are currently present and vegetative cover and rooting depth are expected to increase in the future. A time series plot of the water content measurements from the TDR probes, with cumulative precipitation, is shown in Fig. 8
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Fig. 8. Soil water contents from TDR measurements within the ET cover from April 2000 to October 2004 with monthly precipitation totals.
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Moisture content data collected from the neutron logging boreholes in the ET cover during the past 4 yr indicate a significant decrease in subsurface moisture due to the removal of the asphalt cover. The current moisture contents observed in these boreholes range from 12 to 22%, a decrease of as much as 48% volumetric water content (61% to 13%) from values measured just after removal of the asphalt cap. Figure 9
illustrates soil water contents from neutron logging measurements from CH-2, just before it was abandoned in 1998, soil water contents from core taken from the three boreholes in the ET cover as they were drilled in 1998, and the average 2004 (January–September) soil water contents from neutron logging measurements. These data indicate that the removal of the asphalt cap and installation of an ET cover has resulted in significant drying of the soil profile, particularly at depths of 1.5 to 3.0 m. The very large decreases in water content at depths of 1.5 to 3.0 m for Boreholes 49-1007 and 49-1008 indicate that the El Cajete Pumice layer has dried out significantly in the past 6 yr. It should be noted that the elevation of the CH-2 borehole was approximately 1.5 m below that of the ET cover surface, so the top of the water content profile from CH-2 begins 1.5 m below the ET cover water content profiles. It should also be noted that the calibration used for conversion of neutron counts to water content for CH-2 is not documented, and it is suspected that the water content measurements for CH-2 should be higher to be consistent with the water content measurements from the core samples in Boreholes 49-1006, 49-1007, and 49-1008. Therefore, the water contents measured at CH-2 in 1998 were multiplied by 2 and plotted in Fig. 9 (dashed line) because this profile is a close match to the core sample data.
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Fig. 9. Soil water contents measured from ET cover core samples and neutron logging CH-2 (1998) and from neutron logging three boreholes in the ET cover (average of 2004 measurements).
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Neutron logging data indicate that the five undisturbed boreholes surrounding Area 2 (TH-1, TH-2, TH-3, TH-4, TH-5) have peak moisture contents between 10 and 20% at depths of 0.3 to 2 m (Fig. 10)
. This depth range corresponds to the thickness of soil covering the weathered tuff of the Tshirege Member of the Bandelier tuff. Moisture contents then drop rapidly, and stay relatively constant between 0 and 5% to total depth of the borehole (27–35 m) (Birdsell et al., 2005). Neutron logging data from the three boreholes representing disturbed but stable conditions (2A-O, 2A-Y, and 2B-Y) are also shown in Fig. 10 and indicate a similar trend to that measured in the undisturbed TH boreholes, except that water contents in the three 2A/2B boreholes are generally slightly wetter than in the TH boreholes. This is because the three 2A/2B boreholes were filled with crushed tuff (or sand) while the TH boreholes were drilled through native tuff, and because the 2A boreholes may have experienced ponding conditions while the asphalt cover was in place. Gravimetric sampling data from the two 46-m boreholes (49-2906 and 49-2907) are also shown in Fig. 10. These water content profiles were developed from samples collected during drilling of the boreholes in 1994, and the water contents are much higher than the 2A/2B and TH boreholes. Water content profiles from these two boreholes clearly indicate highly elevated water contents from just beneath the asphalt cover, then a steady decrease to water contents <10% at a depth of 20 m. The highest water content measurement of 57% at a depth of 2.2 m corresponds to a clay layer in the old (pre-1999) cover material.
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Fig. 10. Water content measurements (average of 1999–2004) from neutron logging the TH (undisturbed conditions) and 2A/2B (disturbed conditions) boreholes, and water content measurements from core samples collected in 1994 from Boreholes 49-2906 and 49-2907.
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Vertical fluxes were determined for Boreholes 49-10046, 49-10047, and 49-10048 in 1998 on the basis of chloride concentrations from core samples collected immediately after the removal of the Area 2 asphalt cover (Newman and Ludwig, 2000). Flux estimates determined from this study indicated a range of 0.6 to 1.3 cm yr–1. These values are similar to fluxes estimated beneath disturbed areas within TA 54, where fluxes ranged form 0.02 to 0.9 cm yr–1 (Newman et al., 1999). Fluxes determined for undisturbed mesa top localities within LANL range from –9.5 to 0.69 cm yr–1 (Rogers et al., 1996). The neutron logging data generally support the fluxes determined from chloride data for disturbed and undisturbed sites. The water contents measured during drilling of the two 46-m (49-2906 and 49-2907) boreholes in 1994 were the highest. Birdsell et al. (2005) matched a simulated flux of 60 mm yr–1 to the data from these boreholes. The original water contents from the ET cover boreholes were wetter than recent measurements, indicating relatively higher fluxes, while the recent water content data from ET cover boreholes is drier, corresponding to lower fluxes. The water contents from the 2A/2B boreholes (disturbed conditions) are generally drier than the ET cover water contents, but slightly wetter than the water contents from the TH (undisturbed conditions) boreholes. Infiltration rates were modeled for the TH boreholes and an infiltration rate of 0.1 mm yr–1 fit the water content data well for these boreholes (Birdsell et al., 2005).
The data clearly indicate that the ET cover design is performing better than the asphalt cover design, especially if recent profiles for 2004 in the three ET cover boreholes are compared with 1994 sampling data. However, more moisture monitoring data from the ET cover should be collected for this conclusion to be definitive. This is because the winter of 1997–1998 was an "El Nino" winter, with an average of approximately 54 cm precipitation for the 2-yr period of 1997 and 1998, while the 4-yr period of 2000 to 2003 was quite dry with an average precipitation of approximately 32 cm yr–1 (www.weather.lanl.gov). The average annual precipitation for the area is approximately 45 cm yr–1 (Bowen, 1990).
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CONCLUSIONS
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Soil moisture monitoring data provided by TDR and neutron logging measurements indicate that the ET cover is performing well at returning infiltrating precipitation and snowmelt to the atmosphere by ET, isolating soil contamination at a depth of approximately 2 m below the cover surface and the radiological inventory located approximately 19 m below the cover surface, and thereby mitigating deep percolation and possible mobilization of contaminants to the regional groundwater aquifer located at a depth of about 360 m below ground surface. If percolation from precipitation and focused infiltration reached the radiological inventory at a depth of 17 m while the asphalt cover was in place, that pathway has been mitigated with the installation of the ET cover, and any areas of elevated moisture content at depth should redistribute to drier areas in the subsurface. Although moisture conditions have not returned to those observed in stable disturbed or undisturbed areas, the neutron logging data indicate that the soils beneath the ET cover continue to dry. With continued growth of vegetation and increased transpiration, the site should continue its return to natural vadose zone conditions. Moisture monitoring activities should continue to ensure that the drying trend observed in the ET cover is due to the improved cover design rather than due to climatic conditions.
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REFERENCES
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- Abeele, W.V., M.L. Wheeler, and B.W. Burton. 1981. Geohydrology of Bandelier Tuff. Rep. LA-8962-MS. Los Alamos Natl. Lab., Los Alamos, NM.
- Birdsell, K.H., B.D. Newman, D.E. Broxton, and B.A. Robinson. 2005. Conceptual models of vadose-zone flow and transport beneath the Pajarito Plateau, Los Alamos, New Mexico. Available at www.vadosezonejournal.org. Vadose Zone J. 4:620–636 (this issue).[Abstract/Free Full Text]
- Bowen, B.M. 1990. Los Alamos climatology. Rep. LA-11735-MS. Los Alamos Natl. Lab., Los Alamos, NM.
- Hollis, D., E. Vold, R. Shuman, K. Birdsell, K. Bower, W. Hansen, D.J. Krier, P. Longmire, B. Newman, D. Rogers, and E. Springer. 1997. Performance assessment and composite analysis for Los Alamos National Laboratory Material Disposal Area G. Rep. LA-UR-97-85. Los Alamos Natl. Lab., Los Alamos, NM.
- Levitt, D.G., J.K. Hopkins, C.W. Criswell, K.C. Kisiel, D.L. Newell, and L.A. Woodworth. 2003. Site characterization and monitoring of Technical Area 49 at the Los Alamos National Laboratory. Proceedings of the Waste Management '03 Conference, Tucson, AZ. 23–27 Feb. 2003.
- Los Alamos National Laboratory. 1992. RFI work plan for Operable Unit 1144. Rep. LA-UR-92-900. Los Alamos Natl. Lab., Los Alamos, NM.
- Los Alamos National Laboratory. 1999. Interim measures report for Potential Release Sites 49-001(B), 49-001(C), 49-001(D), 49-001(G). Rep. LA-UR-99-2169. Los Alamos Natl. Lab., Los Alamos, NM.
- Newman, B.D., and D.E. Ludwig. 2000. Evaluation of near-surface hydrology of MDA AB, TA-49, Los Alamos National Laboratory: Interpretations based on chloride and stable isotope profiles. Draft Report. Los Alamos Natl. Lab., Los Alamos, NM.
- Newman, B.D., D. Newell, and M. VanEeckhount. 1999. Spatial variation in near-surface hydrologic behavior at TA 54, MDA G. Internal Report. Los Alamos Natl. Lab., Los Alamos, NM.
- Rofer, C.K., B.A. Martinez, M.B. Klein, G.K. Bayhurst, and I.R. Triay. 1999. Moisture accumulation under asphalt cover at radioactive waste-burial site. Pract. Period. Hazard. Toxic Radioact. Waste Manage. 3:10–17.[CrossRef]
- Rogers, D.B., B.M. Gallaher, and E.L. Vold. 1996. Vadose zone infiltration beneath the Pajartio Plateau at Los Alamos National Laboratory. New Mexico Geological Society Guidebook, 47th Field Conference, Jemez Mountains Region. NM Geol. Soc., Las Cruces, NM.
- Stimac, J.A., D.E. Broxton, E.C. Kluk, and S.J. Chipera. 2002. Stratigraphy of the tuffs from Borehole 49–2-700–1 at Technical Area 49, Los Alamos National Laboratory, New Mexico. Rep. LA-13969-MS. Los Alamos Natl. Lab., Los Alamos, NM.
- Weir, J.E., and W.D. Purtymun. 1962. Geology and hydrology of Technical Area 49, Frijoles Mesa, Los Alamos County, New Mexico. Administration Release Rep. USGS, Albuquerque, NM.
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TOP
ABSTRACT
INTRODUCTION
