APPENDIX F
DISSENTING STATEMENT ON ISSUES 1 AND 7

M.D. Mifflin

April 21, 1995

Overview

OPINION: Characterization studies at the Ward Valley Site failed to resolve the issue of deep percolation. Further, a history of both chemical and radioactive leachate at the water table at the Beatty facility, an analog of the Ward Valley Site, suggests inadequate documentation/understanding of the hydrologic processes in the thick vadose zones at both sites.

Arid-climate vadose zones are the least well-documented hydrologic systems of terrestial environments (and may prove to be the most deceptive as well). This Opinion disagrees with the Majority Opinion in its conclusions and recommendations for two of seven issues:

Issue 1:

The potential transfer of contaminants through the unsaturated zone to the ground water, and

Issue 7:

Potential interference of the raised trench design with revegetation and reestablishment of native plant community.

Issues 1 and 7 deal with the occurrence of water below the root zone that may percolate into the zone of emplaced waste and permit mobilization of contaminants through the formation of leachates. Issue 1 is related to vadose hydrologic processes that have been and are operating at the undisturbed site, and Issue 7 relates to processes that may operate when the site is used for waste disposal. Both issues relate to the role native vegetation in terms of infiltrated water and possible deeper percolation of water at the site. The Majority Opinion conclusions on Issues 1 and 7 are, in simple words, that the general knowledge and site databases indicate it is likely the vegetation root zones serve as efficient and effective barriers to deep percolation in the site area at the present time and that enough is known to reestablish vegetation to perform the same function on the trench covers.

The Majority Opinion discusses, in detail, the Ward Valley site databases with respect to strengths, weaknesses, and assumptions. Some additional observations are offered:

Saturated-Zone Water Samples and Analytical Utility: The pumped water samples at Ward Valley are vertically mixed samples due to the 14 meters of screened interval well design, and in all monitoring wells, the top of the screened interval is 5 meters or more below the static water levels. These pumped water samples, therefore, do not represent the uppermost saturated-zone water samples, but rather mixed samples of primarily deeper flow zones in layered sediments of



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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology APPENDIX F DISSENTING STATEMENT ON ISSUES 1 AND 7 M.D. Mifflin April 21, 1995 Overview OPINION: Characterization studies at the Ward Valley Site failed to resolve the issue of deep percolation. Further, a history of both chemical and radioactive leachate at the water table at the Beatty facility, an analog of the Ward Valley Site, suggests inadequate documentation/understanding of the hydrologic processes in the thick vadose zones at both sites. Arid-climate vadose zones are the least well-documented hydrologic systems of terrestial environments (and may prove to be the most deceptive as well). This Opinion disagrees with the Majority Opinion in its conclusions and recommendations for two of seven issues: Issue 1: The potential transfer of contaminants through the unsaturated zone to the ground water, and Issue 7: Potential interference of the raised trench design with revegetation and reestablishment of native plant community. Issues 1 and 7 deal with the occurrence of water below the root zone that may percolate into the zone of emplaced waste and permit mobilization of contaminants through the formation of leachates. Issue 1 is related to vadose hydrologic processes that have been and are operating at the undisturbed site, and Issue 7 relates to processes that may operate when the site is used for waste disposal. Both issues relate to the role native vegetation in terms of infiltrated water and possible deeper percolation of water at the site. The Majority Opinion conclusions on Issues 1 and 7 are, in simple words, that the general knowledge and site databases indicate it is likely the vegetation root zones serve as efficient and effective barriers to deep percolation in the site area at the present time and that enough is known to reestablish vegetation to perform the same function on the trench covers. The Majority Opinion discusses, in detail, the Ward Valley site databases with respect to strengths, weaknesses, and assumptions. Some additional observations are offered: Saturated-Zone Water Samples and Analytical Utility: The pumped water samples at Ward Valley are vertically mixed samples due to the 14 meters of screened interval well design, and in all monitoring wells, the top of the screened interval is 5 meters or more below the static water levels. These pumped water samples, therefore, do not represent the uppermost saturated-zone water samples, but rather mixed samples of primarily deeper flow zones in layered sediments of

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology highly varied permeability. Thus, the saturated-zone water samples used to establish analyses for C-14, 0-18, deuterium, tritium, and water chemistry did not sample uppermost saturation and cannot give useful results from the perspective of site area recharge. Constituents of water samples representing vertical profiles in the upper part of the saturated zone allow recognition of stratified young water in the saturated zone, the presence or absence in turn would argue for or against significant recharge in the general area of the site. Increased concentration of modem carbon in a prolonged pumped sample from MW-WV-1 suggests that some stratification of younger water may be present at the site. There is too little known of the processes within the vadose zone and locations of recharge in arid terrain systems to establish confident interpretations as to "age" of water on the basis of pumped mixed layer samples. Varying mixtures of very young and very old water or, if only long-distance lateral flow is involved, only relatively old water, cannot normally be recognized. Further, the designs of the existing monitoring wells are not ideal for early recognition of leachate plumes in the saturated zone because of the stratified nature and varied permeability of the sediments in the saturated zone. Uncertainty in Characterization Datasets: There are two Ward Valley site datasets that suggest that some deeper percolation and recharge may occur at the site: (1) the above background tritium values down to 30 meters in depth, and (2) the downward fluid potential gradient indicated by MW-WV-1 and MW-WV-2 water levels in the saturated zone. Soil moisture and chloride profiles indicate dry conditions and no percolation to below the root zone. Other Ward Valley site datasets also may be interpreted to permit some deep percolation by preferred or local paths, such as periodic water-level fluctuations, water-chemistry variations, high infiltration rates at the pit percolation test, high densities of normally deep-rooted plants, numerous small wash channels in the site area, a higher concentration of modem carbon in the longer-term pumped sample from MW-WV-1, the order of magnitude larger heat dissipation probe potentials than would be determined from the thermocouple psychrometers and soil moisture content data, and so forth. However, all of these datasets are not definitive for the question being asked: they are either extremely sparse, and/or often highly localized in some cases, ambiguous, or poor in quality or sampling design for the questions being asked, and therefore of uncertain utility with respect to confident documentation of the presence or absence of periodic pulses of infiltration (perhaps localized) and downward movement of water in the vadose zone. Soil moisture monitoring studies in arid climates normally document little or no moisture percolating to more than 2 meters (Wierenga, et al., 1991; Estrella, et al., 1993; Gee, et al., 1994; Scanlon, 1994; Nichols, 1987; Fisher, 1992). However, evidence for deeper percolation and preferred pathways raise uncertainty (Allison and Hughes, 1983; Baumgardner and Scanlon, 1992; Elzeftawy and Mifflin, 1984; Gee and Hillel, 1988; Natir, et al., 1994; Scanlon, 1992; Steenhuis, et al., 1994). Direct moisture profile monitoring (potential and changing water content) and laboratory moisture content determinations in the vadose zone are very limited in both time and space. Other datasets, such as soil chloride profiles and tritium, are integrating the constituents of interest over various time periods. Most subsurface datasets do not integrate the sample over lateral areas beyond the borehole with the exception of gas phase (tritium) samples, and thus may not detect preferred pathways or relatively narrow and localized zones or corridors of matrix flow. Nearly all boreholes are located at the surface to avoid ephemeral surface washes (boreholes are typically located to protect the monitoring equipment or borehole operation from surface-water

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology runoff events and associated losses). However, when channelized runoff occasionally occurs, it produces orders of magnitude greater infiltration per unit of time along narrow corridors as compared to incident precipitation, and many field experiments demonstrate that pulses of infiltrated water follow vertical pathways without lateral dispersion of more than one or two meters. Borehole-derived databases are biased to interfluve conditions for near-surface processes, and most sampled constituents are not suited to detect preferred pathway or highly localized percolation with the exception of pumped gas phase tritium. The significant tritium values at Ward Valley could be in error; however, they are the database of the vadose zone that has the best potential to document local deep percolation over a 40-year period, including areas beyond the boreholes. The following give insight into the problems of short-term and highly localized vadose zone borehole monitoring databases. Elzeftawy and Mifflin (1984) applied soil physics monitoring techniques (thermocouple psychrometers) in Nevada to study recharge. Generally, no annual recharge seemed to occur in areas with less than 25 to 30 centimeters of mean annual precipitation. However, on the Jean-Goodsprings alluvial fan south of Las Vegas, Nevada (10-15 centimeters of mean annual precipitation) within 4 meters of a relatively well-developed wash channel, a 50-meter deep borehole drilled dry in the alluvium was equipped with a series of paired thermocouple psychrometers from one meter to depth. After reading several months of stabilized large negative potential readings at all depths, a saturation from passed to full depth (50 meters) immediately after a short-lived, high-intensity precipitation event of greater than 12.7 centimeters (the site storage gage topped over). Several hours of flow occurred in the wash. At another installation (thermocouples at 1.5 meters) in the Las Vegas area (Kyle Canyon fan, 20 centimeters of mean annual precipitation) only dry steady readings were observed for several years. However, nearby, a house basement in a disturbed area (natural vegetation removed) is 3 meters below existing grade but above and greater than 40 meters from a local wash. In the 25 years since construction, the normally bone-dry basement, in dose contact with highly-developed calcrete layer (caliche), flooded once to a depth of 23 centimeters and drained in 48 hours. Infiltration apparently perched and flowed laterally on the calcrete layer to the basement area and up along the joints between the slab and walls toward the end of a 3-day series of heavy precipitation events (accumulated total of 23 centimeters). Beatty Facility Experience: At the U.S. Ecology Beatty, Nevada, radioactive and hazardous waste disposal facility, the climate, vegetation zone, hydrogeology, and basin setting are similar to the Ward Valley site. The general design for the proposed Ward Valley disposal facility is closely based on the Beatty disposal facility, and similarites are pointed out throughout the license application documentation. Water balance and soil profile chloride studies generally support the notion of no active recharge at the Beatty site in an area immediately adjacent to the site during the period of studies (Prudic, 1994; Fischer, 1992; Nichols, 1987). The monitoring well analytical records, however, indicate that leachates from radioactive and chemical waste have reached the water table since 1982 (CRCPD D-5 Committee, 1994; Adams, 1990; Johnson, 1990). Because of the mixed evidence (for and against deep percolation) at both sites and the close similarities of the sites and activities, the experience at the Beatty disposal facility offers insight into the vadose zone hydrology of the Ward Valley site. However, the Committee had difficulty obtaining documentary

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology records in a timely manner for the site and remains silent on the leachate evidence at the Beatty facility. Modeled Performance: The Ward Valley site numerical modeling demonstrates anticipated benefits of the vadose zone retention capacity for any leachate that might develop. There are two unresolved questions, however, associated with the modeling exercise: (1) The existing moisture contents are unknown (assumed) at the Ward Valley site for the lower 600 feet of the vadose zone (an important weakness of the model), and (2) the same leachate retention modeled at the Ward Valley site should also be operating at the Beatty facility, where about 300 feet of vadose zone is available as moisture retention reservoir for percolating leachate. Ward Valley has, perhaps, about twice as much mean annual precipitation and double the thickness of the vadose zone as the Beatty facility. The modeled retention appears to not have occurred at the Beatty facility, as the first documented evidence for leachate in the saturated zone was in 1982, 20 years after disposal operations began, and apparent occasional breakthroughs of leachate continue to occur through 1993. Preferred pathways are a good possibility at the Beatty facility; large volumes of generated leachate are the other. Deep Water Tables: There is a notion that deep water tables indicate little or no net recharge in arid terrains. A deep water table (thick vadose zone) may be related to a host of factors, the most important of which are a combination of limited availability of moisture for recharge in the region and the local transmissive characteristics of the terrain with respect to the overall configuration of the ground-water flow system (Mifflin, 1968). Vadose zone studies at Yucca Mountain (e.g. Fabryka-Martin, et al., 1993) highlight the above by demonstrating that an area with great depth to the regional water table (locally at over 400 meters) and similar climate to Ward Valley displays widespread evidence for some recharge (but the surface processes are still not fully documented). At Ward Valley, the deep water table is related to the general aridity of the region and flow-system configuration; absence of site-specific recharge should not be assumed on the basis of water-table depth. Soil Chloride Profiles: Soil chloride profiles probably do not represent more than apparent histories of matrix transport/fate of incident precipitation at the borehole site. The age interpretations are directly dependent on assumed rates of chloride input (very, very uncertain in arid basin settings with extensive local salt sources, playas, and histories of marked climate and hydrologic changes). A series of chloride profiles taken from interfluve areas across the ephemeral washes and along the thalweg of washes would be of great interest. Such data do not exist. If the salt bulges were to consistently persist below washes, this line of evidence would be more convincing and useful. Dry Drilling Technique Evidence: Other suggestive lines of evidence indicate deep percolation and associated recharge in basin environments of the Mojave Desert, but there is too little systematic data collection to establish how quantitatively important the basin recharge may be. In four undeveloped alluvial basins with known poor water quality in the Las Vegas area, dry drilling has been used in exploration for water supplies (Mifflin, unpublished field notes). Each basin explored by the drilling technique has produced suggestive evidence of localized recharge. Perching at depth (water produced during drilling above the level of stabilized static water levels) and uppermost (but of limited thickness) zones of low TDS water underlain by poorer-quality water has been noted. Such occurrences are interpreted as related to limited local recharge within

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology the basins. The same dry-drilling approach (dual-wall reverse circulation rotary techniques available since the mid-1970's) would have produced better-controlled water samples and cuttings for the Ward Valley characterization effort. Preferred Pathways: Desiccation fractures in silty and clayey sediments are well-documented in add and semi-arid basins, including the Mojave and Great Basin Deserts. Such fractures are the best candidates for preferred pathways of flow in the vadose zone environments; they are documented to perform such a role in near-surface environments. Each alluvial basin fill has undergone at least five major climatic changes from pluvial climates to more add climates during the Pleistocene, with attendant changes in positions of water tables, soil moisture conditions in the vadose zone, ground-water discharge and recharge relationships, and surface-water hydrology. Desiccation fractures and compaction faults attend the changing moisture contents in the fine-grained sediments. Earth fissures (Parker, 1963; Passmore, 1975; Patt and Maxey, 1978; Holzer, 1984; Mifflin, et al., 1991) are dramatic surface manifestations closely related to desiccation fractures, and most commonly are observed in areas where major declines in ground-water levels are taking place, usually in areas of heavy ground-water exploitation and attendant land subsidence; they also occur due to natural desiccation, often in playa areas. There is little question that, where earth fissures occur, very large volumes of ephemeral surface-water runoff pass to well below the root zone along preferred pathways. The hydrologic role the more deeply buried desiccation fractures may take is unknown. Pulsed breakthroughs of contaminants at the Beatty facility can be explained without calling upon large volumes of leachate production if there are local, vertically extensive features such as desiccation fractures, and rapid downward flow of relatively small volumes of leachate along the fractures. Without preferred pathways, very large volumes of leachate seem necessary, and Issue 7 is elevated to a very important, poorly investigated and unresolved issue, with respect to operational practices and trench covers. ISSUE 1 Opinion: The site characterization failed to establish reasonable assurance of vadose zone hydrology of the site area. Two site-specific databases suggest deep percolation (the vadose zone showing a profile of significant levels of tritium and a saturated zone downward gradient), whereas other databases from six boreholes suggest little or no deep percolation at the borehole sites. The Beatty facility monitoring record and the significant tritium profile at the Ward Valley site combine to suggest the vadose-zone hydrology is not understood at either site, and that leachate may form and reach the water table much more rapidly than anticipated in the license application for Ward Valley. Recommendations: Beatty Facility studies are urged because they will likely yield important insight into the uncertain vadose-zone processes that permit leachate migration and better focused data collection at the Ward Valley site. (1) The Beatty facility waste containment experience warrants very careful, in-depth review and study. The leachate signals in the analytical record from the monitoring wells at the Beatty facility need to be independently reviewed from several perspectives: monitoring well designs, sampling methodologies, sample management, and laboratory analytical procedures, all of which have the potential to influence concentrations of

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology indicators of leachates. (2) If radioactive and chemical leachates have traveled to the water table (as the records indicate and several agency reports conclude is the case), the independent review should expand to consider the relationships between facility design, operational practices, and leachate production. Trench closure techniques and current leachate production rates in open lined trenches are a critical part of the review. (3) If appropriate, the proposed Ward Valley site facility design, operation, monitoring, and closure plans should be reviewed and modified to minimize leachate production and downward migration. Additional, carefully focused databases may help establish "reasonable assurance" and better background databases for monitoring system design requirements if the Ward Valley site goes forward as a waste-disposal facility. The following is believed the most cost-effective (both in time and funds) approach to developing the databases for resolution of the deep percolation issue: (1) Borehole deviation surveys in MW-WV-1 and MW-WV-2 will demonstrate if MW-WV-2 deviates from vertical sufficiently (>3°) to produce the difference in water levels indicating a downward gradient in the saturated zone. (2) Additional boreholes for the vadose zone and uppermost saturated zone should be established by a dry drilling methodology that allows collection of moisture content cuttings and water samples throughout the vadose zone and several meters into the uppermost saturated zone. The dual wall reverse circulation rotary technique is cost-effective and useful for vertically controlled sampling in the 300 meter thick vadose zone and uppermost saturated zone. The methodology will produce cuttings in the vadose zone useful for the following analyses: C1-36, soil moisture contents, water extractions for tritium (later gas extractions for tritium and C-14 are possible), and water samples from the uppermost saturated zone for tritium, C-14, environmental isotopes, and gross water chemistry. The boreholes can be finished for either a vadose zone and/or uppermost saturation monitoring. The air used for the drilling medium should be tagged with a tracer (SF-6). The methodology is flexible, and short intervals of coring can be adapted to the sampling techniques. The actual drilling, sampling and completion is not time-consuming. Between one and two weeks would be required for each borehole. Most analytical and interpretive work on samples should be complete within six months of sample collection. The most cost-effective completion approach is to finish the boreholes as uppermost saturated-zone monitoring wells. ISSUE 7 OPINION: The Wilshire Group concern about revegetation of raised trench covers, considering the width, configuration, and climate, is shared because of the absence of documentation of required infiltration adequate to rapidly reestablish and maintain a plant community equivalent to the high-density natural desert plant community, and a potential for the capillary barrier design to cause deep rooting to, and perhaps below, the capillary barrier horizon. The Wilshire Group raised concern about revegetation of the raised trench covers. They thought the raised trench cover design would not allow runon from adjacent areas and limited reestablishment of vegetation may allow infiltration through the cap and erosion due to the lack of stabilizing vegetation (Wilshire, et al., 1993). The Majority Opinion, however, generally concludes that there is no problem due to the current level of understanding of desert vegetation.

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology Discussion: The success or failure of long-term waste containment rests on two premises: (1) little or no infiltrated water reaching the emplaced waste to form leachate, and (2) what little leachate that may be generated is retained in the thick vadose zone due to the moisture retention capacity of the vadose zone. Therefore, timely revegetation to high densities is of paramount importance to assure little or no percolation of water to the emplaced waste. A preliminary review of the trench cover and water balance literature suggests there is little or no documentation of the time and moisture required to reestablish the existing high-density vegetation and root-zone barrier on the raised trench covers in the Mojave Desert climate. The observations of Schlesinger, et al., (1989) and Schlesinger and James (1984) indicate surface-water runon is important, and the U.S. Ecology (1994) revegetated 25-year-old training dikes along I-10 (photographic evidence) may not be appropriate analogs of raised trench covers due to marked differences in configuration and surface-water availability. If revegetation to effective root barrier densities requires a decade or more, there is likely a very serious design problem that allows net accumulation of deeper percolation to accumulate on the capillary barrier at six meters. Gee, et al., (1994) have demonstrated up to 50% of precipitation may infiltrate in arid climates and percolate to greater depths under bare soil conditions. If two decades were to pass before an effective root barrier became fully established, and a net infiltration of 25% of mean annual precipitation occurred over the period, this amount equates to 4 to 5 meters of saturation above the capillary. barrier emplaced at 6 meters of depth. With the above scenario, the following would result: (1) roots would follow the moisture down due to the capillary fringe above perched saturation at the capillary barrier, and/or (2) flow breakthrough would occur in some parts of the capillary barrier or at least around the perimeter. The design purpose of the coarse capillary barrier layer within the trench cover is to prevent deeper percolation and limit the root depths. However, delayed revegetation might very well tend to encourage deep roofing, as well as eventually allow percolation of perching water into the waste horizon. Deep roofing phreatophytes, such as the mesquite of the local area, might become established if a near-surface capillary fringe were to develop. Recommendations: (1) The raised trench cover and associated capillary barrier design warrant careful experimental evaluation at representative scales, where both the raised design trench cover and a trench cover at existing grade with natural runon are monitored and evaluated. Water balance studies with soil moisture and potential monitoring to at least the waste emplacement horizon is necessary. (2) Leachate production and rates of revegetation of trench covers should be part of the review study at the Beatty facility. REFERENCES Adams, S.R., 1990. Historical environmental monitoring report, U.S. Ecology Low-Level Radioactive Waste Disposal Facility, Beatty, Nevada, U.S. Ecology, September 27, 1990, 71 pp. Allison, G.B., and M.W. Hughes, 1983. The use of natural tracers as indicators of soil-water movement in a temperate semi-arid region, Journal of Hydrology 602, pp. 157-173.

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology Baumgardner, R.W., Jr., and B. Scanlon, 1992. Surface fissures in the Hueco Bolson and adjacent basins, West Texas, University of Texas at Austin, Bureau of Economic Geology, Geological Circular 92(2), pp. 1-40. Beven, K., 1991. Modeling preferential flow, in Gish, T.J., and A. Shirmohammadi (eds.), Preferential Flow, Proc. of the National Symposium, American Society of Agricultural Engineers, St. Joseph, MI, p. 77. CRCPD E-5 Committee, October 1994. Environmental summary of the Beatty, Nevada Low-Level Radioactive Waste Disposal Site, Chapter 4, in Conference of Radiation Control Program Directors, Inc., Environmental Monitoring Report for Commercial Low-Level Radioactive Waste Disposal Sites, pp. 4-3 to 4-36. Elzeftawy, A., and M.D. Mifflin, 1984. Vadose zone moisture migration in arid and semi-arid terrain, Symposium on Characterization and Monitoring of the Vadose Zone, Symposium Proceedings, National Water Well Association, Las Vegas, Nevada, December, 1983. Estrella, R., S. Tyler, J. Chapman, and M. Miller, 1993. Area 5 site characterization project-report of hydraulic property analysis through August 1993, Desert Research Institute, Water Resources Center 45121, pp. 1-51. Fabryka-Martin, J., M. Caffee, G. Nimz, J. Southon, S. Wightman, W. Murphy, M. Wickman, and P. Sharma, 1994. Distribution of chlorine-36 in the unsaturated zone at Yucca Mountain: an indicator of fast transport paths, Focus '93 Conference, Site Characterization and Model Validation, American Nuclear Society, Las Vegas, Nevada, pp. 56-58. Fischer, J.M., 1992. Sediment properties and water movement through shallow unsaturated alluvium at an arid site for disposal of low-level radioactive waste near Beatty, Nye County, Nevada, U.S. Geological Survey, Water Resources Investigations Report 92(4032), pp. 1-48. Gee, G.W. and D. Hillel, 1988. Ground-water recharge in arid regions: Review and critique of estimation methods, Journal of Hydrological Processes 2, pp. 255-266. Gee, G.W., P.J. Wierenga, B.J. Andraski, M.H. Young, M.J. Fayer, and M.L. Rockhold, 1994. Variations in water balance and recharge potential at three western desert sites, Soil Science Society of America Journal 58, pp. 63-82. Holzer, T.L., 1984. Ground failure induced by ground-water withdrawal from unconsolidated sediment, in Holzer, T. (ed.), Man-Induced Land Subsidence: Reviews in Engineering Geology, vol. VI, Geological Society of America, Boulder, Colorado, pp. 67-105. Johnson, R.L., 1990. A review of organic contaminants in the unsaturated zone and groundwater zones at the Beatty, Nevada TSD Site, prepared for U.S. EPA, Region IX, Department of Environmental Science and Engineering, Oregon Graduate Institute, Beaverton, Oregon 97006, September 27, 1990, 8 pp. plus attachments. Mifflin, M.D., Adenle, O.A., and Johnson, R.J., 1991. Earth fissures in Las Vegas Valley, 1990 inventory, Section C, in Bell, J.W. and J.G. Price (eds.), Subsidence in Las Vegas Valley, 1980-1991, Final Project Report, Nevada Bureau of Mines and Geology, pp. C1-C30.

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Ward Valley: An Examination of Seven Issues in Earth Sciences and Ecology Mifflin, M.D., 1968. Delineation of ground-water flow systems in Nevada, Desert Research Institute, CWRR, Technical Report Services H-W, No. 4, 111 pp. Nativ, R., E. Adar, O. Dahan, and M. Geyh, 1995. Water recharge and solute transport through the vadose zone of fractured chalk under desert conditions, Water Resource Research, 31:2, pp. 253-261. Nichols, W.D., 1987. Geohydrology of the unsaturated zone at the burial site for low-level radioactive waste near Beatty, Nye County, Nevada, U.S. Geological Survey, Water Supply Paper 2312, p. 57 pp. Parker, Gerald G., 1963. Piping, a geomorphic agent in landform development of the drylands , in International Association of Scientific Hydrology, Publication No. 65, Berkeley, California, pp. 103-113. Passmore, Gary W., 1975. Subsidence-induced fissures in Las Vegas Valley, Nevada (M.S. Thesis), University of Nevada, Reno, Nevada, 105 pp. Raft, R.O., and G.B. Maxey, 1978. Mapping of earth fissures in Las Vegas Valley, Nevada, University of Nevada, Desert Research Institute Project Report 51, 19 pp. Scanlon, B.R., 1994. Water and heat fluxes in desert soils, 1. Field studies, Water Resources Research 30, pp, 709-719. Scanlon, B.R., 1992. Evaluation of liquid and vapor water flow in desert Soils based on chlorine 36 and tritium tracers and nonisothermal flow simulations, Water Resources Research 18, pp. 285-297. Scanlon, B.R., 1992. Moisture and solute flux along preferred pathways characterized by fissured sediments in desert soils, Journal of Contaminant Hydrology 10, pp. 19-46. Schlesinger, W.H., P.J. Fonteyn, and W.A. Reiners. 1989. Effects of overland flow on plant water relations, erosion and soil water percolation on a Mojave Desert landscape, Soil Science Society of American Journal 53, pp. 1567-1572. Schlesinger, W.H., and C.S. Jones, 1984. The comparative importance of overland runoff and mean annual rainfall to shrub communities of the Mojave Desert, Botanical Gazette 145, pp. 116-124. Steenhuis, T.S., J. Yves Pariange, and J.A. Aburime, 1994. Preferential flow in structured and sandy soils: Consequences for modeling and monitoring, in Wilson, L.G., L.G. Everett, and L.J. Cullen (eds.), Handbook of Vadose Zone Characterization and Monitoring, Lewis Publishers, Boca Raton, Florida, pp. 61-77. U.S. Ecology, Inc., 1994. Handbook of supplemental information to the National Academy of Sciences, October 6, 1994. Wierenga, P.J., R.G. Hills, and D.B. Hudson, 1991. The Las Cruces Trench Site: Characterization, experimental results, and one-dimensional flow predictions, Water Resources Research 27, pp. 2695-2705. Wilshire, H., K. Howard, and D. Miller, 1993. Memorandum to Secretary Bruce Babbit, dated June 2, 1993, 3 pp.

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