3
Contamination Sources and Source Control

Radioactive or chemically hazardous wastes disposed onsite at the Los Alamos National Laboratory (LANL) constitute the sources of contamination that are the subject of this chapter. The Laboratory has conducted onsite disposal of its wastes since the early 1940s. Disposal methods include the discharge of liquid effluents into canyons and the emplacement of solid wastes, mainly on mesa tops.1

Identifying and controlling contamination sources is essential for groundwater protection. Controlling a source of aqueous waste (e.g., an “outfall”)2 could involve treating that waste to remove contaminants or reducing or stopping the discharges. Controlling solid waste could involve ensuring that it is emplaced in such a way that it cannot release contaminants or, if necessary, recovering the disposed waste, repackaging it, and possibly shipping it offsite.3

This chapter addresses three questions regarding sources that were posed in the committee’s statement of task:

  1. What is the state of the Laboratory’s understanding of the major sources of groundwater contamination originating from Laboratory operations and have technically sound measures to control them been implemented?

  2. Have potential sources of non-Laboratory groundwater contamination been identified?

  3. Have the potential impacts of this [non-Laboratory] contamination on corrective-action decision making been assessed?

The committee’s short answer to the first question is yes for liquid sources and no for solids. Liquid waste discharges are generally eliminated or controlled. LANL’s data indicate that former liquid discharges were the sources of contamination currently found in groundwater. However, solid wastes and contaminants deemed by LANL to have less near-term potential to impact groundwater have received much less attention than the liquid sources and are not well understood, especially in terms of source inventories.

The committee’s short answer to the second question is a qualified yes. The short answer to the third is no, because LANL is only beginning to determine corrective actions under the Consent Order. This aspect of decision making was not discussed with the committee.

More detailed elaborations of these answers are provided in this chapter.

LANL’S SOURCE PRIORITIZATION

LANL is systematically investigating contaminant sources and the nature and extent of migration from them under a prioritized sequence that is directed by the Consent Order (see Chapter 2 for a description of the Order). These sources range from solid waste disposal sites in dry areas, to sanitary waste treatment plants, to radioactive waste treatment facilities. LANL’s Site-Wide Environmental Impact Statement identifies operating facilities as “key” or “non-key” depending on their potential to cause significant environmental impact (LANL, 2004a).

At the committee’s request, Birdsell et al. (2006) provided a summary of contaminant sources that LANL considers to be the most significant, including locations of liquid waste outfalls and disposal areas for solid wastes. LANL’s criteria for selecting these as the most significant sources include the following:

  • A large contaminant inventory,

  • A natural or anthropogenic aqueous driver (e.g., rainfall, facility effluent, alluvial groundwater) that

1

Discharges of gaseous effluents are not considered in this report.

2

An outfall is an intended point of discharge of wastewater into the environment. LANL outfalls are permitted by the EPA under the National Pollutant Discharge Elimination System.

3

The term waste package refers to the solid waste itself, its container, which may be simply a metal drum or may be more elaborately designed, and additional barrier materials inside or around the container if they are used.



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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report 3 Contamination Sources and Source Control Radioactive or chemically hazardous wastes disposed onsite at the Los Alamos National Laboratory (LANL) constitute the sources of contamination that are the subject of this chapter. The Laboratory has conducted onsite disposal of its wastes since the early 1940s. Disposal methods include the discharge of liquid effluents into canyons and the emplacement of solid wastes, mainly on mesa tops.1 Identifying and controlling contamination sources is essential for groundwater protection. Controlling a source of aqueous waste (e.g., an “outfall”)2 could involve treating that waste to remove contaminants or reducing or stopping the discharges. Controlling solid waste could involve ensuring that it is emplaced in such a way that it cannot release contaminants or, if necessary, recovering the disposed waste, repackaging it, and possibly shipping it offsite.3 This chapter addresses three questions regarding sources that were posed in the committee’s statement of task: What is the state of the Laboratory’s understanding of the major sources of groundwater contamination originating from Laboratory operations and have technically sound measures to control them been implemented? Have potential sources of non-Laboratory groundwater contamination been identified? Have the potential impacts of this [non-Laboratory] contamination on corrective-action decision making been assessed? The committee’s short answer to the first question is yes for liquid sources and no for solids. Liquid waste discharges are generally eliminated or controlled. LANL’s data indicate that former liquid discharges were the sources of contamination currently found in groundwater. However, solid wastes and contaminants deemed by LANL to have less near-term potential to impact groundwater have received much less attention than the liquid sources and are not well understood, especially in terms of source inventories. The committee’s short answer to the second question is a qualified yes. The short answer to the third is no, because LANL is only beginning to determine corrective actions under the Consent Order. This aspect of decision making was not discussed with the committee. More detailed elaborations of these answers are provided in this chapter. LANL’S SOURCE PRIORITIZATION LANL is systematically investigating contaminant sources and the nature and extent of migration from them under a prioritized sequence that is directed by the Consent Order (see Chapter 2 for a description of the Order). These sources range from solid waste disposal sites in dry areas, to sanitary waste treatment plants, to radioactive waste treatment facilities. LANL’s Site-Wide Environmental Impact Statement identifies operating facilities as “key” or “non-key” depending on their potential to cause significant environmental impact (LANL, 2004a). At the committee’s request, Birdsell et al. (2006) provided a summary of contaminant sources that LANL considers to be the most significant, including locations of liquid waste outfalls and disposal areas for solid wastes. LANL’s criteria for selecting these as the most significant sources include the following: A large contaminant inventory, A natural or anthropogenic aqueous driver (e.g., rainfall, facility effluent, alluvial groundwater) that 1 Discharges of gaseous effluents are not considered in this report. 2 An outfall is an intended point of discharge of wastewater into the environment. LANL outfalls are permitted by the EPA under the National Pollutant Discharge Elimination System. 3 The term waste package refers to the solid waste itself, its container, which may be simply a metal drum or may be more elaborately designed, and additional barrier materials inside or around the container if they are used.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report occurred concurrently with and/or subsequent to the contaminant release, Contaminants that tend to move with the aqueous driver (“mobile” contaminants), and Release into a canyon (as opposed to emplacement on a dry mesa top). In addition to the Birdsell et al. (2006) summary, the types, amounts, and locations of waste releases to the subsurface are included in numerous references (Del Signore and Watkins, 2005; Katzman, 2006; LANL, 2003, 2004a,b, 2006a, 2007a; Rogers, 2006a,b). Liquid Discharges LANL presented data indicating that the major sources of contaminants affecting the groundwater beneath the Pajarito Plateau were past (“historic”) liquid discharges from radioactive treatment plants, sanitary treatment plants, high-explosives machining operations, and other outfalls; see Color Plate 3. Most of these discharges were neither treated nor regulated, and substantial amounts of contaminants were released to the environment; see Table 3.1. Recently LANL has made a significant effort to reduce its liquid discharges. From 1993 through 2006, the number of outfalls was reduced from 141 to 17. Of the 17 currently operating outfalls, LANL TABLE 3.1 Key LANL Outfalls and Approximate Contaminant Quantity Released Source Number (see Color Plate 3) Source Name Location Canyon (Watershed) Operation Period of Operation Approximate Water Volumes Released (m3) Main Chemical Contaminants Released Main Radionuclide Contaminants Releaseda Contaminants Detected in Deep Ground Water 01-002 / 45-001 Combined outfall at TA-1 and TA-45 Acid Canyon (Pueblo Canyon) Radioactive wastewater treatment 1944−1964 600,000 Perchlorate − unknown Nitrate ~ 100,000 kg Tritium ~ 58 Ci Sr-90 ~ 27 mCi Pu ~170 mCi Tritium, perchlorate 02-004(a) Omega West Reactor Upper Los Alamos Canyon Research and ca. 1970−1993 2,000 to 4,000   Tritium 70 Ci (maximum) Tritium 21-011(k) SWMU 21-011(k) DP Canyon (Los Alamos Canyon) Industrial wastewater outfall 1952−1986 200,000 Perchlorate − unknown Nitrate > 20 kg Tritium > 55 Ci Pu ~ 36 mCi Sr-90 ~ 5 mCi Cs-137 ~ 250 mCi Am-241 Tritium, perchlorate, nitrate Outfall 001 TA-3 Power Plant, Former TA-3 Wastewater Treatment Plant, Sanitary Wastewater System (SWWS) Sandia Canyon Cooling towers and sanitary wastewater 1950−present > 10,000,000 Chromium ~ 26,000 to 105,000 kg (ca. 1956−1972) Tritium ~ 30 Ci accidental release with sanitary waste (ca. 1969−1986) Chromium, tritium 16-021(c)-99 260 Outfall Cañon de Valle (Water Canyon) High explosives machining 1951−1996 340,000 to 1,500,000 RDX 15,000 to 64,000 kg None High-explosives (RDX) Outfall 051 TA-50 − 1 Effluent Canyon (Mortandad Canyon) Radioactive wastewater treatment 1963−present 1,400,000 Perchlorate − 800 to 1200 kg Nitrate ~ 200,000 kg Tritium ~800 Ci Sr-90 ~ 470 mCi Pu (239,240) ~ 0.2 Ci Pu (238) ~0.1 Ci Cs-137 ~ 2.1 Ci Am-241 ~ 0.2 Ci Tritium, nitrate, perchlorate aNote that tritium releases here are reported as original releases rather than decay-corrected. SOURCE: Donathan Krier, LANL.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report considers that only two, the outfall in Technical Area-50 (TA-50) and the current sanitary wastewater system (SWWS) outfall, are significant contamination sources according to the criteria listed above. The Radioactive Liquid Waste Treatment Facility (RLWTF) located at TA-50 has been LANL’s only source of liquid radioactive waste discharges since 1986. The facility collects and processes waste from over 1000 generating points sitewide. Liquid wastes from the RLWTF go to the TA-50 outfall, which discharges into Mortandad Canyon. Modernizing the RLWTF in 1999 substantially reduced the concentrations of actinides being released (Figure 3.1a). Tritium concentrations in the effluent were curtailed in the early 1990s (Figure 3.1b). These are real and substantial reductions because the volume of water discharged decreased from over 20 million liters per year in 1990 to just under 10 million liters per year in 2004. The release of radioactive contaminants from TA-50 continues but has been below the discharge limits stipulated by the Department of Energy (DOE; Del Signore and Watkins, 2005). Contaminant releases into Mortandad Canyon thus appear to have been controlled. Nonetheless, the substantial amount of water still being discharged at the TA-50 outfall may itself serve as a continuous aqueous driver to move previously released contaminants deeper into the groundwater. LANL is currently evaluating a plan to eliminate all effluent releases from the RLWTF at TA-50. Emplacements of Solid Wastes Potential sources of groundwater contamination are not limited to liquid effluents. Solid wastes4 include a large amount of radioactive material that is disposed of in the subsurface and present substantial uncertainties in the amount of contaminants that could eventually migrate to the groundwater. The committee encountered a number of terms applied to areas of the site where solid wastes are emplaced or that have been contaminated. The term “solid waste management unit” (SWMU) refers to any area from which DOE determines there may be a risk of release of contaminated materials, irrespective of whether the area was intended for the management or disposal of such materials. Areas where there was only a one-time spill are not considered to be SWMUs, but rather are included in the category of “area of concern” (AOC). An AOC is any area, which is not a SWMU, that may have had a release of hazardous waste or hazardous constituents. DOE also uses the generic term “potential release site” (PRS) in referring to areas from which contaminants have the potential to migrate into the environment, but not necessarily to contaminate groundwater. LANL uses a more restrictive term “material disposal area” (MDA) to designate specific areas used between 1945 and 1985 for the disposal of radioactive and hazardous wastes. MDAs are generally near-surface disposal facilities located on mesa tops; see Color Plate 4. The waste is usually buried in unlined pits or shafts. Given the variety of nomenclature, estimates of the number of solid waste emplacements or contaminated areas appear to converge around 1000. LANL (2007a) counts 829 SWMUs and AOCs that are in the process of being investigated, need investigation, or are pending a decision from the New Mexico Environment Department (NMED). Birdsell et al. (2006) identify 25 MDAs and 902 PRSs—478 of the PRSs are confirmed or suspected radiological sites and the remaining are non-radiological. A Notice of Intent (NOI) to sue LANL for violations of the Clean Water Act (Western Environmental Law Center, 2006) refers to SWMUs, AOCs, and PRSs collectively as “stormwater sites.” The NOI states that an original estimate of the number of stormwater sites was 2093. According to the NOI, 688 of these sites received No Further Action status by NMED, leaving 1405 to be dealt with. LANL considers that 9 of its 25 MDAs have a significant potential to contaminate groundwater with radionuclides. Of the nine MDAs considered significant, the inventory for two is “unknown” (see Table 3.2). For MDA G, the tritium inventory according to Table 3.2 is about 3.6 million Ci, which is far larger than the tritium discharged from any of the liquid outfalls. A large amount of Pu-239, about 2300 Ci or 39 kg, is reported to be in MDA AB. The presence of large amounts of radioactive materials in unlined pits in the MDAs is an issue. Although the mesa tops are generally considered to be dry, this is not true year-round. Standing water has been observed in unlined pits in several locations, including MDA AB (CCNS, 2007; Levitt et al., 2005). This contact of precipitation and runoff with stored waste materials implies that a fraction of the contaminants are subject to leaching and subsequent migration. The extent of this leaching is not known (CCNS, 2007). Overall, LANL estimates 40-60 percent of the SWMUs have been sampled; however, information about the total mass of contaminants for the SWMUs has not yet been compiled (D. Katzman, statement at the committee’s workshop, August 2006). Although LANL is still in the process of characterizing most solid waste disposal areas, the committee was not shown data to substantiate the claim that waste has not migrated from the SWMUs. Evaluation of all sites is scheduled for completion by 2015 (Birdsell et al., 2006). LANL has given generally lower priority to understanding and controlling its solid waste emplacements than its liquid waste discharges. While LANL presented a clear 4 The Resource Conservation and Recovery Act defines solid waste as any garbage, refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility, and other discarded material, including solid, liquid, semisolid, or contained gaseous material, resulting from industrial, commercial, mining, and agricultural operations and from community activities. See http://www.epa.gov/epaoswer/hotline/training/defsw.pdf.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report FIGURE 3.1a Actinide (Pu-238, Pu-239, Am-241) concentrations in effluent from the RLWTF. Releases of actinides have decreased significantly after upgrades to the facility in 1999. The concentration units of picocuries per liter (pCi/L) are 1000 times smaller than those in the figure for tritium below. These actinides have much longer radioactive half-lives than tritium, so they are usually of greater concern for groundwater protection. SOURCE: Del Signore and Watkins, 2005. FIGURE 3.1b Tritium concentrations in effluent from the RLWTF. The concentrations are in units of nanocuries per liter. A nanocurie is 10−9 curie. SOURCE: Del Signore and Watkins, 2005.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report TABLE 3.2 Nine of 25 Principal Material Disposal Areas at LANLa Material Disposal Area (MDA) Location (Technical Area) Period of Operation Key Radionuclide Inventory A 21 1944-1978 Pu ~ 701 Ci Am ~ 1.5 Ci B 21 1945-1952 Pu ~ 6.22 Ci Sr-90 ~ 0.285 Ci Cs ~ 0.005 Ci T 21 1945-1986 Pu ~ 182 Ci Am ~ 3740 Ci U ~ 6.9 Ci U 21 1948-1976 Unknown (Am, Cs, Pu, tritium, Sr, U) V 21 1945-1961 Unknown (Am, Cs, Pu, Sr-90, U, tritium) AB 49 1959-1961 Pu ~ 23,000 Ci (includes ~ 20,600 Ci of Pu-241, which has a 14.4-year half-life, and ~ 2300 Ci of Pu-239, which has a 24,000-year half-life) U ~ 0.246 Ci C 50 1948-1974 Tritium ~ 20000 Ci Sr-90 ~ 21 Ci U ~ 25 Ci Pu ~ 26 Ci Am ~ 145 Ci G 54 1957-1997 (parts remain active today) Am ~ 2360 Ci Cs ~ 2810 Ci Tritium ~ 3,610,000 Ci Pu ~ 16,000 Ci Sr-90 ~ 3500 Ci U ~ 124 Ci H 54 1960-1986 Tritium ~ 240 Ci Pu ~ 0.0267 Ci U ~ 75.2 Ci aThe Technical Area (TA) in which each is located is shown on Color Plate 4. SOURCE: Birdsell et al., 2006. rationale for doing so, dealing with these solid wastes will become technically more challenging and economically more demanding as time progresses. Over time, waste materials will degrade and become more vulnerable to leaching. Contaminants will migrate away from the wastes, thereby contaminating an increasingly larger volume in the subsurface. One way of considering this issue is: If the mesa tops were proposed for disposal of these materials today, what types of assessment and engineering controls would be required? The answer to this question can help guide LANL’s future efforts to manage its MDAs and SWMU contaminated areas. Non-LANL Sources Groundwater constituents that are unrelated to LANL operations include those from off site anthropogenic sources and from the natural geologic environment (background). The Laboratory is aware of several non-LANL sources of anthropogenic groundwater contamination, including runoff from roads and paved areas in the town of Los Alamos, pesticide applications in the headwater areas of the Santa Fe National Forest and Los Alamos, and low levels of radionuclides from atmospheric fallout (LANL, 2004b). The Los Alamos County wastewater treatment facility in Pueblo Canyon is a source of nitrates and other constituents typical of treated municipal wastewater. This source releases treated effluent into alluvial sediments that are known to contain LANL-derived contaminants. LANL (2006a) lists the facility as a “key source” of deep groundwater contamination with nitrate. LANL’s Groundwater Background Investigation Report provides a detailed description of background concentrations

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report of chemical constituents. The report defines background as “natural groundwater occurring at springs or penetrated by wells that have not been contaminated by the Laboratory or other municipal or industrial sources and that are representative of groundwater discharging from their respective host rocks or aquifer material” (LANL, 2006b, p.v). Sidebar 3.1 describes typical steps in groundwater sampling and analysis. Chapter 5 gives the committee’s assessment of LANL’s data quality procedures. The background report contains detailed information about the chemical analysis (inorganic, organic, stable isotope, radionuclide) of 208 groundwater samples from 12 springs and wells considered background. The major cations (calcium, magnesium, sodium, potassium) and anions (bicarbonate, chloride, fluoride, sulfate) as well as silica were detected in essentially all samples, i.e., frequencies of 98 to 100 percent of the samples, as would be expected for typical groundwater in the area. Trace metals—that would be considered “pollutants” if originating from an anthropogenic source—were detected over a wide range of frequencies— for example, arsenic (in 5 percent of the samples), cadmium (3 percent), chromium (48 percent), lead (15 percent), uranium (100 percent), and zinc (44 percent). Radionuclides at very low concentrations were detected in a relatively small percentage of the background samples, for example, americium-241 (16 percent), plutonium-238 (5 percent), and plutonium-239/240 (5 percent). LANL attributed these results to either fallout or, since many statistical “non-detections” were reported, instrument noise (LANL, 2006b).5 Gross alpha-radioactivity was detected in 76 percent of the samples with very little variation in concentration among sampling locations, indicative of naturally occurring uranium. Tritium was detected in all background samples and is interpreted as global fallout. Background activities of tritium were measured in excess of 30 pCi/L in the alluvial groundwater, <2 pCi/L in the perched aquifer, and <1 pCi/L in the regional aquifer. Strontium-90 was not detected in any of the samples. By presenting a detailed assessment of the background concentrations of contaminants at the site, LANL (2006b) is an important step in establishing a baseline for future remediation work at LANL. Little about non-LANL sources was presented during the committee meetings, however, indicating that LANL may not consider them especially important in its groundwater investigations. Although the Consent Order requires LANL to identify and assess non-LANL sources, it is not clear if such assessment of sources will have an effect on the corrective action decision (NMED, 2005, Section XI.F). SIDEBAR 3.1 Description of a Typical Groundwater Analysis LANL acquires samples from groundwater monitoring wells in alluvial, perched-intermediate, and regional aquifer zones; water supply wells; springs; and surface water base flow stations. Samples to measure contaminants from offsite sources or determine the natural background are taken from locations that are clearly up gradient from possible areas that may contain contamination from LANL operations. Field data collection procedures generally follow guidelines of U.S. Geological Survey water sample collection methods and industrial standards common to environmental sample collection and field measurements, including the collection of field blanks and field duplicates and the use of trip blanks. Sample collection, preservation, and measurement of field parameters for groundwater are conducted according to standard operating procedures and quality procedures. For the majority of analyte suites, both filtered and unfiltered samples are collected. Chemical analyses of water samples use commonly accepted analytical methods required under federal regulations such as the Clean Water Act and approved by the Environmental Protection Agency. Statements of work for contract analytical services include specific requirements for analyzing groundwater samples. A typical suite of parameters measured for a groundwater monitoring sample includes parameters measured in the field and those measured in analytical laboratories. Field parameters collected are pH, turbidity, specific conductance, dissolved oxygen, temperature, and oxidation-reduction potential. Analytical laboratory suites include 25 metals, hexavalent chromium, organics (volatile and semivolatile compounds pesticides, polychlorinated biphenyls, high-explosive residues, and dioxins or furans), radionuclides (gross alpha, gross beta, isotopic uranium, strontium-90, and tritium), and general inorganics (major ions, total dissolved solids, trace anions, silica, nitrogen species, total Kjehldahl nitrogen, perchlorate, and total organic carbon). SOURCE: Ardyth Simmons, LANL. MIGRATION FROM SOURCES: GEOCHEMISTRY The significance of a source depends on the hazard posed by the contaminants themselves (amount, toxicity, persistence), the volume of waste disposed, the size of the disposal area, and perhaps most importantly, the likelihood that the contaminants might move from the source into the groundwater. Packaging of solid waste is usually considered a primary barrier against migration; liquid discharges have no such barrier. In either case, however, once in the geologic media (e.g., the soil or rock material surrounding the source) migration depends on the chemical interactions between the contaminants and the geologic media in the presence of water. These interactions determine if the contaminant will 5 An instrument sometimes returns a reading that indicates the presence of a contaminant at a level that is near the limit of its ability to detect the contaminant. If the result cannot be corroborated by additional measurements or by other methods, it is usually considered to be a false positive or non-detection. Assessing the statistical significance of analytical data is discussed further in Chapter 5.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report move freely with the water or be substantially retained by geologic media along the flowpath. Chemical and physical interactions among some contaminants and the geologic media can cause them to adhere or “sorb” onto the media; see Sidebar 3.2 and Figure 3.2. Contaminants may sorb to a greater or lesser degree depending on their chemical form (speciation) and the nature of the geologic media. The radionuclides cesium-137 and strontium-90, and the actinide elements such as plutonium, are examples of contaminants that can strongly sorb onto geologic media, and hence their migration tends to be significantly retarded in the subsurface environment. There are instances, however, when species sorb onto small particulates or colloids, which can be transported by water, as noted in Sidebar 3.2 and discussed later in this section. Other contaminants are much more soluble in water and do not sorb as readily onto solids or other media. These contaminants are mobile and move at about the same velocity as the groundwater. Examples of non-sorbing contaminants include chromium (as chromate, CrO42−), nitrate (NO3−), perchlorate (ClO4−), tritium (as tritiated water), and some high explosives (e.g., RDX).6 Contaminant Species in the Subsurface LANL has long recognized the presence of radionuclide and chemical contamination in groundwater beneath the site. According to Birdsell et al. (2006), the combined conditions of a large, mobile inventory with a topographically focused water source are sufficient to drive non-sorbing contaminants through the thick unsaturated zone to the regional aquifer on the time scale of a few decades. While it is not surprising that the more mobile contaminants have been detected in the regional groundwater, their concentrations are much attenuated from the concentrations detected in the shallower subsurface. Table 3.3 shows the frequencies of detections of contamination in the alluvial, intermediate, and regional groundwater. The mobile contaminants chromium, nitrate, perchlorate, tritium, and RDX have moved downward from the alluvium where they were discharged from various outfalls. With the exception of tritium, there are few data to suggest that radioactive contaminants have migrated downward from the alluvial groundwater. Other than RDX, the non-radioactive contaminants occur naturally and have measured background values for the alluvial, intermediate, and regional groundwaters (LANL, 2007b). Some of the detections reported in the table may be below background values. For some species that occur naturally (e.g., chromium, uranium), determining the amounts added from anthropogneic sources is difficult. Measurement of isotopic ratios is a primary way of determining this difference. Contaminant Migration Graphical representations of LANL’s sampling data for plutonium and tritium contrast the general tendencies of these contaminants to migrate with groundwater and indicate how they are distributed across the site. Color Plates 5a,b compare plutonium measured in the shallow soils versus plutonium in the deep regional groundwater. They show that most plutonium is currently located in the shallow surface soils at the canyon bottoms. LANL has attributed its few sporadic detections of plutonium in the regional groundwater to “false positives” (Phelps, 2007; also see Chapter 5). Color Plates 6a,b compare the distribution of tritium in the shallow alluvial groundwater and the regional groundwater at the LANL site. In contrast to the current distribution of plutonium, tritium is prevalent in the groundwater system and not concentrated in surface soils. Most of the tritium is found in the shallow groundwater, with attenuated values observed in the deep regional groundwater. These observations are consistent with LANL’s conceptual models of pathways for contaminant migration, which are discussed in Chapter 4. As noted previously, water can transport contaminant species sorbed onto colloids (e.g., McCarthy and Degueldre, 1993; Ryan and Elimelech, 1996). Colloids are ubiquitous, naturally occurring or anthropogenic organic or inorganic particles, typically smaller than 1 micron in diameter, that remain suspended in water (Stumm, 1992). Studies have shown that colloids have a large range in concentration in natural waters, ranging from 0.0002 to 200 mg/L (McCarthy and Degueldre, 1993). Colloidal transport of plutonium in both surface water and groundwater has been documented at DOE sites, including Rocky Flats and the Nevada Test Site (Kersting et al., 1999; Santschi et al., 2002). Recently iron oxide colloids were shown to transport plutonium at the Mayak site in Russia (Novikov et al., 2006). Colloidal transport of plutonium was invoked for plutonium detected in alluvial groundwater samples collected from Mortandad Canyon, but the conclusions remain controversial (Penrose et al., 1990; Marty et al., 1997). The distribution of plutonium in shallow soils along canyon floors downgradient of the outfall locations, illustrated in Color Plate 5a, is indicative of transport by surface runoff, probably as colloidal and particulate matter. Storm events remobilize contaminated sediments and transport them downgradient. Stormwater runoff and erosion after the Cerro Grande fire in spring 2002 moved considerable amounts of soil and other materials, including contaminants, toward the Pueblo de San Ildefonso and the Rio Grande (Alvarez and Arends, 2000; LANL, 2005b). Chromium provides another example of how geochemistry can affect the mobility of important contaminants. 6 Chemically 1,3,5-trinitroperhydro-1,3,5-triazine, RDX is an explosive used in military and industrial applications. This chemical and its degradation products are typical of the high-explosive residues that are found in some areas of LANL groundwater.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report SIDEBAR 3.2 Chemical Factors that Affect the Migration of Contaminants in the Environment The hydrology, geology of the surrounding environment, water chemistry, and chemical composition of the contaminants all influence the ability of contaminants to migrate in the subsurface. The geochemistry (or chemical and physical characteristics) of contaminants controls their transport behavior in the environment, determining their aqueous speciation, solubility, sorptivity, oxidation/reduction behavior, and the extent of their transport by colloids. The composition of a given groundwater is derived from its chemical interaction with the surrounding rock and can be approximately described by pH, redox potential (Eh), ionic strength, and cation/anion composition. As the groundwater flows through different subsurface media, the chemistry of the groundwater can change and the aqueous speciation, solubility, sorptivity, and oxidation state of the contaminants may also change. Solubility The solubility of a contaminant is the maximum amount that can dissolve in a given quantity of solution at a specified temperature and pressure. Thus, a contaminant that has a high solubility for a given groundwater composition readily dissolves and may be highly mobile. In contrast, a contaminant with a low solubility will not appreciably dissolve. Contaminants that have a high solubility in groundwater at the site include chromium, nitrate, perchlorate, tritium, and high explosives (e.g., RDX) (LANL, 2005a; Birdsell et al., 2006). Calcium, sodium, and bicarbonate are the dominant major ions in the groundwater beneath the site (LANL, 2005a). Dissolved carbonate forms complexes with trace metals and influences the metals’ solubility and ultimately mobility in the subsurface. For example, a change in the pH or carbonate alkalinity of the groundwater will affect uranium’s aqueous speciation and either increase or decrease its solubility and sorptivity. Sorption Sorption refers to removal of an ion or molecule from solution due to its adhering to a solid material. In general, it does not imply a mechanism for that removal. The term sorption is often used to describe a number of surface processes including adsorption, ion exchange, and co-precipitation. Adsorption implies that ions or molecules are removed from solution and deposited on the surfaces of solids by chemical or physical binding. Chemical binding (sometimes referred to as chemisorption) suggests strong binding that is often irreversible because it is the result of a chemical bond between the ion and the surface. Another sorption process, ion exchange, results from the physical interchange of ions associated with a solid and ions in solution; this reaction is generally reversible. Physical binding is much weaker and is the result of van der Waals forces. Other processes such as precipitation/co-precipitation may also play a role in the removal of ions or molecules from solution. Sorption is a convenient term to use in transport modeling because it relates to the overall process of removing contaminants from migrating fluids without addressing the underlying mechanistic reactions. If precipitation is the actual mechanism involved, using a sorptive-type retardation model would not be appropriate. Certain minerals present in the subsurface, such as iron oxides, manganese oxides, clays, and zeolites, have a high sorption capacity for contaminants. Cesium, americium, plutonium, and strontium are contaminants that strongly sorb to these minerals as well as to organic carbon present in the water and soil. Although sorption is typically considered reversible, the sorption of contaminants acts to significantly retard their movement or, at the least, disperse the contaminant into a larger volume of water. Oxidation States The oxidation state of an element is defined by its charge. The oxidation state of an element is important in determining its aqueous speciation and reactivity in solution. For example, solutes such as uranium, plutonium, sulfate, nitrate, and chromate tend to be mobile under oxidizing conditions but can precipitate or sorb under reducing conditions. Water chemistry primarily determines which oxidation states dominate and which species are more prevelant. The behavior of U and Pu is strongly dependent on the redox potential of groundwater. At higher Eh values, the higher oxidation states of plutonium [Pu(V) and Pu(VI)] are more stable. Lower Eh values favor the lower oxidation state of Pu(IV). In general, contaminants in their higher oxidation states are more soluble in groundwater and, therefore, are more mobile than in their reduced state. Complexation Ligands present in groundwater, such as humic and fulvic acids, CO32−, and SO42−, can form strong aqueous complexes with actinides. The ligands act to stabilize anions in groundwater and enhance the concentration of anions in groundwater. For example, the presence of carbonate in groundwater has been shown to complex U resulting in an increase in the solubility of U in groundwater. Colloids Transport of contaminants in groundwater occurs as both dissolved solutes and as colloids. Colloids are naturally occurring particles, defined as ranging in size from 0.1 to 0.001 micrometer. Colloids are found in nearly all surface water and groundwater and are formed as a result of weathering of rocks, soils, and plants. Because they are small, colloids can remain suspended and are readily transported with groundwater. Colloids are a concern as a transport mechanism because contaminants that sorb strongly to the organic or inorganic aquifer matrix can also attach to suspended organic and inorganic colloids and migrate with groundwater. At the site, colloids may include natural material (silica, clays, organic matter, and Fe and Mn oxides) and possibly solid phases associated with the treated Laboratory discharge.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report FIGURE 3.2 Some geochemical processes that can affect contaminant migration. A variety of chemical and/or physical processes can retard or halt the migration of contaminants along a hydrogeologic pathway, such as the fracture depicted here. While the general nature of these processes is understood, the committee received little quantitative data to confirm many of LANL’s assumptions about contaminant migration. Processes similar to those depicted in this figure may also operate around sampling points in monitoring wells. Such processes involving materials introduced in drilling the monitoring wells could interfere with the sampling of contaminants in groundwater (see Chapter 5). SOURCE: LANL, 2000. There are two chromium species that typically exist in the environment. The hexavalent species, chromate (CrO42−), is chemically toxic and mobile in the environment. Chromate is the prevalent form of chromium under oxidizing conditions. Under reducing conditions the trivalent oxide (Cr2O3), which has limited mobility and toxicity, predominates. The unexpected detection of chromium in 2005 initiated a major, ongoing effort to determine the amounts and location of the bulk of the contamination and develop plans for its remediation, as summarized in Sidebar 3.3. Committee Views on Geochemistry and Contaminant Migration As discussed in this section, geochemical interactions are important for contaminant migration. Like the hydrogeology, the geochemistry of the LANL site is quite complex. However, the committee received little evidence that LANL has sought to understand the geochemistry of contaminant migration at a level of detail comparable to the site investigations conducted under the Hydrogeologic Workplan. For example, the Synthesis Report (LANL, 2005a) that summarizes site characterization under the workplan is some 300 pages long but contains only a 50-page description of groundwater chemistry with no discussion of how this chemistry could affect contaminant migration. During the course of this study, few data were presented to the committee from laboratory experiments or field tests that would begin to quantify the general knowledge about geochemical effects on contaminant migration described in Sidebar 3.2 or to substantiate LANL’s general observations and assumptions about the geochemical behavior of sorbing contaminants that have been described in this section. REPRESENTATION OF SOURCE DATA LANL has amassed a very large amount of data on contamination sources. The committee struggled to comprehend so much information in spite of well-prepared presentations at the committee’s meetings and the workshop discussions. The Birdsell et al. (2006) report provided a useful initial summary of the sources LANL considers to be the most significant. Although limited in scope, the Birdsell et al. report is a good model for future reports. In the next three parts of this section, the committee gives its views about how LANL can not only provide more comprehensible summaries of contamination sources and their importance, but also demonstrate mastery of groundwater protection fundamentals to a broad audience of stakeholders.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report TABLE 3.3 Frequencies of Detections of Key Contaminants in LANL Groundwater Analyte Number of Analyses Number of Detections Frequency of Detections (percent) Chromium Alluvial UF (UF = unfiltered) 317 176 55.5 Chromium Intermediate UF 142 105 73.9 Chromium Regional UF 603 433 71.8 Chromium Alluvial F (F = filtered) 306 113 36.9 Chromium Intermediate F 108 65 60.2 Chromium Regional F 454 244 53.7 Perchlorate Alluvial UF 257 122 47.5 Perchlorate Intermediate UF 94 37 39.4 Perchlorate Regional UF 1058 334 31.6 Perchlorate Alluvial F 301 193 64.1 Perchlorate Intermediate F 136 75 55.1 Perchlorate Regional F 375 136 36.3 Nitrate Alluvial UF 169 127 75.1 Nitrate Intermediate UF 72 60 83.3 Nitrate Regional UF 422 352 83.4 Nitrate Alluvial F 261 245 93.9 Nitrate Intermediate F 107 94 87.9 Nitrate Regional F 395 295 74.7 Tritium Alluvial UF 301 217 72.1 Tritium Intermediate UF 170 127 74.7 Tritium Regional UF 869 205 23.6 RDX Alluvial UF 172 87 50.6 RDX Intermediate UF 96 29 30.2 RDX Regional UF 615 23 3.7 Tritium, Chromium, Nitrate, Perchlorate combined Intermediate UF 1044 642 61.5 Tritium, Chromium, Nitrate, Perchlorate combined Alluvial UF 478 329 68.8 Tritium, Chromium, Nitrate, Perchlorate combined Regional UF 2952 1324 44.9 Chromium, Nitrate, Perchlorate combined Alluvial F 868 551 63.5 Chromium, Nitrate, Perchlorate combined Intermediate F 351 234 66.7 Chromium, Nitrate, Perchlorate combined Regional F 1224 675 55.1 With Tritiuma       All Radionuclides Alluvial UF 1429 444 31.1 All Radionuclides Intermediate UF 787 137 17.4 All Radionuclides Regional UF 4158 231 5.6 Without Tritiuma       All Radionuclides Alluvial UF 1128 227 20.1 All Radionuclides Intermediate UF 617 10 1.6 All Radionuclides Regional UF 3289 26 0.79 Tritium is not analyzed on filtered samples       All Radionuclides Alluvial F 871 133 15.3 All Radionuclides Intermediate F 403 5 1.2 All Radionuclides Regional F 1068 6 0.56 aRadionuclides include americium-241, cesium-137, cobalt-60, iodine-129, neptunium-237, plutonium-238, plutonium-239/240, strontium-90, technetium-99, and tritium. SOURCE: Ardyth Symmons, LANL.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report SIDEBAR 3.3 Chromium Contamination in Groundwater at LANL Routine groundwater monitoring conducted in 2005 led to the identification of chromium contamination in regional groundwater at monitoring well R-28 located in Mortandad Canyon; see Color Plate 10. Chromium concentrations at that well have been between about 300 and 440 µg/L (ppb) exceeding the NMED and Environmental Protection Agency standards of 50 µg/L and 100 µg/L, respectively. Investigations are under way pursuant to the 2005 Consent Order between LANL and the NMED. Objectives of the investigation are to: Characterize the present-day spatial distribution of chromium and related constituents, Collect data to evaluate the geochemical and physical or hydrologic processes that govern chromium transport, and Collect and evaluate data to help guide subsequent investigations and remedy selection. Potential Sources of Chromium Contamination Multiple potential sources of chromium contamination have been identified including electroplating, photo processing, and use as a corrosion inhibitor in cooling-tower systems. The highest chromium usage is believed to be associated with the cooling-tower system in TA-03 at the head of Sandia Canyon, wherepotentially large amounts (potentially up to 37 lb/day) of chromate (Cr6+, the highly soluble, mobile, and toxic form of chromium) were released along with large volumes of water. Extent of Contamination in Regional Groundwater Chromium has been detected in the regional groundwater at concentrations above the background value of about 6.62 µg/L in three wells including R-28, R-11, and R-15. Studies show that the chromium is in the chromate form. Chromium in nearby water supply wells is within background. Quarterly sampling in monitoring and water supply wells is ongoing. Chromium occurs at relatively low concentrations (generally less than 15 µg/L) in surface water, shallow alluvial groundwater, and intermediate-depth groundwater beneath Sandia Canyon. The unsaturated zone between the surface and the deep groundwater at ~700-800 feet also shows low concentrations of chromium suggesting that much of the chromium might remain bound to sediment near the surface and/or has migrated through the unsaturated zone into the regional groundwater. The current (2007) phase of the investigation involves installation of a deep monitoring well (R-35) to further define the extent of chromium and to serve as a monitoring point relative to water supply well PM-3. A sediment investigation is also under way to determine how much chromium remains bound to sediments at the surface. SOURCE: Danny Katzman, LANL. Mass Balance Mass balance is a mathematical tool used throughout science and engineering to account for materials in a system—for example in the design and operation of a chemical plant or a refinery; see Sidebar 3.4. Applied to groundwater protection, developing mass balances would demonstrate LANL’s ability to account for contaminants released from its operations. LANL is aware of this and has begun to develop mass balances for contaminants around some sources (Birdsell et al., 2006). With appropriate acknowledgment of uncertainties (see the next section), mass balances would provide summary representations of LANL’s source and monitoring data that would allow verification by outside experts and enhanced understanding by all stakeholders. Identifying major uncertainties in the development of a mass balance can help guide future site investigations. As illustrated in Figure 3.3, sources are the inputs from which contaminants enter the soils, rocks, and water that constitute the hydrogeologic environment beneath the LANL site. Contaminants from a source may migrate along a pathway through the geologic media. The “control volume” enclosing the pathway is a conceptualization. In some cases where contaminants have migrated only a short distance from the source, it may represent the relatively small volume of soil or other media around the source that is contaminated. This is frequently true for solid sources disposed of in dry locations. Uncertainties in the mass balance will be due primarily to uncertainties in source inventory as discussed earlier in this chapter. In these cases, remediation options including source removal, containment, or no action can be evaluated as means to ensure groundwater protection. In other cases, contaminants may have migrated substantial distances from their source, and the control volume may encompass an entire watershed or more. Along with uncertainties in the source inventory, a mass balance for such a large volume will reflect uncertainties in the contaminant migration pathways, discussed in Chapter 4, and in the monitoring data, discussed in Chapter 5. In cases of extended migration, source removal will probably not be practical; instead, reducing flows of water that could move the contamination deeper into the subsurface, as LANL is

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report SIDEBAR 3.4 The Applications of Mass Balance Mass balance is an expression of the law of conservation of mass. It is one of several fundamental conservation laws (e.g., energy, momentum, electrical charge). Use of mass balance is ubiquitous in science and engineering to account for materials in a given system. The more important aspects and limitations of applying mass balance principles to LANL’s groundwater protection program are outlined below. The mass balance applies to essentially any material entity that can be identified and quantitatively measured, including radioactive and chemical species. Often mass balance is applied to groups of components that behave collectively as one component. The entity is chosen according to the needs of the problem. The mass balance applies to a specific region in space or “control volume.” The dimensions of the control volume are chosen according to the needs of the problem. The control volume does not have to be a single region in space, be in one phase (fluid or solid), or have a regular geometric shape. Choosing an appropriate control volume may be the most important part of the application of mass balance in accounting for contaminants at LANL; see Figure 3.3. The mass balance applies to a specific time increment or the time difference between the present and initial terms. Formally, mass balance is described by a time-dependent non-steady-state equation. For the purpose of this discussion, the equation can be written as: mass present in the control volume (determined by monitoring) − initial mass in the control volume (from the original source) = mass from non-LANL sources (natural or arising offsite) − mass output + mass reacted (altered or retained in the flowpath) The terms in this expression can be described and used as follows: The mass present in the control volume at any time after the initial time is determined from monitoring around the source(s) and asnecessary monitoring extended pathways, which must be known from site characterization. Uncertainty in this parameter arises from uncertainty in knowledge about the pathways (Chapter 4) and uncertainty in the sampling data (Chapter 5). The initial mass from original or indigenous sources is known or estimated from records of waste emplacements or discharges. This quantity can be from a single event or be a sum of events, including continuous discharge. The committee recognizes a good deal of LANL’s source data are incomplete or missing, which is a major source of uncertainty discussed earlier in this chapter. Mass from non-LANL sources such as naturally occurring contaminants (background) or from offsite origins is also determined by measurements discussed earlier in this chapter. This term of the equation is important because it may account for part or all of the mass of the contaminant detected in the control volume (term 2 above). There are clearly uncertainties in this term as well as the others. Mass reacted is the amount of the contaminant that is transformed along the flowpath. Some radioactive contaminants with relatively short half-lives may simply decay away at the source or along the pathway. For example, tritium has a half-life (t1/2) of about 12.5 years; for plutonium-241, t1/2 is about 14.4 years; and for strontium-90 and cesium-137, t1/2 is about 30 years. Geochemical, or in some cases biochemical, processes may immobilize or nearly immobilize a contaminant or change it to a non-hazardous form. The mass output represents migration of a contaminant out of the control volume into a previously uncontaminated area. If all the terms in the mass balance require estimation, which is clearly the case described here, the equation is used to check the consistency of the estimates. If the equation is satisfied, the mass balance is said to be closed for that entity and control volume. This application of mass balance, essentially a means by which LANL can succinctly display its knowledge and uncertainties of the amounts and locations of contaminants on the site, is the use envisioned by the committee. Reducing uncertainties identified in performing mass balance can help guide future work in LANL’s groundwater protection program. doing for the TA-50 discharges into Mortandad Canyon, may be more appropriate. The simple mass balance equation in Sidebar 3.4 provides only a snapshot at a given time. In this sense, mass balance provides no predictive ability. However, successive mass balances performed as additional monitoring data are acquired can provide estimates of the rate a contaminant is migrating from its source, accumulating in the vadose zone, and entering the regional aquifer if this is the case. Developing a mass balance for significant contaminants (those listed in the Consent Order and other regulations) is an important tool for LANL to demonstrate that contaminants from its operations are accounted for. LANL has sufficient data to begin constructing mass balances for simple systems where source quantities are reasonably well known and migration is limited, which is LANL’s current approach. These limited mass balances could then be integrated to describe larger areas as more knowledge is acquired from future work on defining source inventories and monitoring. Such future work is clearly indicated if knowledge to develop the mass balance of an important contaminant (e.g., chromium, plutonium) around a given source is lacking.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report FIGURE 3.3 Conceptualization of the migration of contaminants from their source through the hydrogeologic environment. In principle, one can use source inventories, release data, and sampling to determine, or estimate, a mass balance that accounts for the inventory of a contaminant that may reach an important water supply at some future time. The pathway represents all of the ways that a contaminant can move from input to output. SOURCE: Committee. By accounting for contaminants, mass balance is an important tool in planning remediation. While remediation by controlling or removing the source is typically the simplest, quantifying the buildup of contaminants that have moved outside their source into the vadose zone and intermediate aquifers can inform decisions for continued monitoring or active remediation along a pathway. Uncertainty Beginning with uncertainties in LANL’s source inventories described in this chapter, concepts of uncertainty reappear throughout this report. According to IAEA (1989) and NCRP (2005) nomenclature, uncertainty can be divided into Type A and Type B. Type A uncertainty reflects how well a property can be determined by measuring it. This type of uncertainty is generally estimated by repeated measurements of the property under investigation—repeated field or laboratory measurements of the hydraulic conductivity of intact rock would be an example of this kind of uncertainty. In technical terms, this type of uncertainty analysis deals with the variability about a mean estimate of a parameter or some other measurable feature of the system (stochastic variation), which is typically indicated with error bars or a plus/minus interval bounding the measurement. Type A uncertainty is encountered in all data collection and is usually addressed by a well-functioning quality assurance program and sample analysis plans. Chapter 5 provides the committee’s assessment of LANL’s data quality program. A second type of uncertainty is due to lack of knowledge about the system or a component of the system. Type B uncertainty is equally or perhaps more important than Type A at this stage of LANL’s groundwater protection program. Two examples of Type B uncertainty at LANL are the following: Source inventories—the radionuclide inventories for two (of nine) key MDAs listed in Table 3.2 are “unknown.” The currently unknown quantity of radionuclides in those MDAs includes Am, Cs, Pu, tritium, Sr, and U. Pathways for contaminant migration—there are alternative conceptual models that can account for currently available characterization data, as discussed in Chapter 4. These Type B uncertainties are difficult to express with error bars or bounding intervals. Type B uncertainties (based on lack of knowledge) usually dominate Type A uncertainties in environmental decision making, for example, for making a regulatory decision about the level of cleanup or the type of characterization that might be required. Type B sources of uncertainty led to the “surprise” discovery of chromium in the regional aquifer; see Sidebar 3.3. The committee does not mean to imply that Type B uncertainties cannot be addressed or reduced. LANL scientists have made significant progress in understanding

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report the major features and components of past waste disposal practices and the geologic system. Characterizing contamination sources and the hydrogeologic system cannot eliminate Type B uncertainty, but it can help both to reduce the uncertainty and to better estimate the level of uncertainty that remains. Uncertainty is a fundamental component of scientific knowledge. For LANL, the problem is not removed simply by acquiring additional data. Progress in the groundwater protection program will be an iterative process, for which increased knowledge may reduce uncertainty in some cases or increase the uncertainty in other cases. Better communication of uncertainty with the public and stakeholders could help support consensus-building efforts as the program advances. Relational Databases and Data Visualization LANL gave the committee a tremendous amount of analytical data in a variety of presentations and discussions, figures, and reports. Finding the most informative ways to use these data, for example to show source locations or the locations of contaminants detected in site characterization, is challenging. LANL could not readily display data to address questions that came up during the committee’s workshop discussions regarding sources. Based on this experience, LANL appears to have the need—and the opportunity—to find better ways to describe its accumulated knowledge. Relational databases allow one to more easily store and retrieve data, and can be very useful for managing data for analysis and visualization. The term relational database refers to the storage of data in a set of tables that are linked by a set of logical relations; this is different from the storage of data in a single spreadsheet or table, which can be inefficient. Results of interrogating a relational database can be displayed visually to provide an efficient means of conveying information. One such database is a part of the RACER program, a DOE-funded interactive relational database that allows easy visualization and analysis of large datasets.7 Produced by the RACER program, Figure 3.4 summarizes a large amount of tritium data in a way that is relatively easy to understand. The diagram shows the location of wells located along an A-A′ transect in Mortandad canyon, number of wells, location of the screened intervals, and a plot of tritium concentrations for each well at a given date. Tritium data for each well are plotted as concentration (pCi/L) (y-axis) versus time (1968-2000) (x-axis). The inset shows the location of the A-A′ transect. Such graphical relational databases are useful for making very large amounts of data understandable to both scientists and interested citizens. For example, the plots show that higher concentrations of tritium were detected in the shallow groundwater compared to groundwater collected from the regional aquifer. Data analyses that were below the detection limit (below Method Detection Limit and designated as U, see Sidebar 5.2) were not plotted. This plot is for illustrative purposes only as the RACER project is still being developed. FINDINGS AND RECOMMENDATIONS ON SOURCES General Findings The committee found that LANL has controlled its liquid waste discharges. According to information presented to the committee, contamination now found in groundwater, including the regional aquifer, most likely came from previous discharges of liquid wastes. Solid wastes and contaminants deemed by LANL to have less near-term potential to impact groundwater have received much less attention than the liquid sources and are not well characterized, especially in terms of source inventories. Remediation of these solid wastes (e.g., the MDAs) under the Consent Order has only recently begun and was not discussed with the committee. Based on LANL’s written reports, the committee judged that the Laboratory has a good understanding of non-LANL sources of contamination. Offsite anthropogenic sources are identified in the Integrated Groundwater Monitoring Plan for Los Alamos National Laboratory (LANL, 2006a, 2007b). The LANL Groundwater Background Investigation Report (LANL, 2006b) provides comprehensive data on naturally occurring contamination in the site’s groundwater. Detailed Findings and Recommendations The committee offers the following findings and recommendations to assist LANL in future work to understand and control its contamination sources, with emphasis on longer-term concerns that have not been addressed during the first portion of the groundwater protection program. Solid wastes (e.g., the 25 MDAs) and certain contaminants deemed by LANL to be essentially immobile (e.g., Pu) have the potential for impacting groundwater in the future. MDA AB in TA-49, which contains some 2300 Ci of Pu-239, is an example. The committee received little information that would provide assurance that these sources are well understood or well controlled. Recommendation: LANL should complete the characterization of major contaminant disposal sites and their inventories, i.e., complete the investigation of historical information about these disposal sites with emphasis on radionuclides and chemicals likely to impact human health and the environment. Selected sites should be characterized by field analysis when historical infor- 7 Information contained in the RACER database was provided by LANL, and it is publicly available in LANL’s Water Quality Data Base accessible at http://wqdbworld.lanl.gov.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report FIGURE 3.4 Visualization of tritium detected in wells along Mortandad Canyon. Tritium concentrations are graphed as a function of time at each sampling point. The diagram gives a sense of the location of sampling wells, the number of wells, and the depth at which tritium has been detected. Such visual aids are important for making very large amounts of sampling data understandable to both scientists and interested citizens. SOURCE: Risk Assessment Corporation. mation is insufficient to determine quantities of major contaminants disposed and to confirm the degree of migration that has occurred. LANL should devote greater effort to characterizing sources with significant inventories of contaminants (especially plutonium) that usually are strongly sorbing but still have the long-term potential to migrate in the presence of water. Priority for investigating sources is established by the Consent Order. This recommendation emphasizes the need to confirm assumptions that underpin the assignment of lower priority to “immobile” wastes. There are still large uncertainties in LANL’s estimates of the inventories of principal contaminant sources and their locations. Similarly, analyses are lacking to approximate the current locations of contaminants (which may have migrated from these sources) in the various hydrogeological units that constitute the LANL site and surrounding areas. Recommendation: For the major disposal sites, LANL should develop mass balance estimates of the quantities of disposed chemicals and radionuclides remaining in the surface soil and/or residing in the shallow alluvium, the vadose zone, and the regional aquifer.

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Plans and Practices for Groundwater Protection at the Los Alamos National Laboratory: Final Report Sitewide, LANL should perform a mass balance for hazardous and radioactive substances by assessing the types, quantities, and volumes of individual hazardous materials that have entered the site over the years.8 These analyses, with estimates of data uncertainties, should help LANL account for contaminant sources, releases, radioactive decay, and migration through the hydrogeologic system in a way that is transparent and understandable to all of its stakeholders. Surface water is an important pathway for transport of contaminants to the groundwater. Stormwater can remobilize contaminants that have been deposited in canyons and transport them downstream. The contaminants can enter the shallow groundwater away from their original source or be transported offsite. Recommendation: LANL needs to quantify the inventories of contaminants released in the canyons in order to understand their potential threat to groundwater. The sitewide mass balance of inventories of hazardous and radioactive substances should include the surface water transport pathway. LANL should continue to develop surface water and sediment monitoring programs. LANL should continue, and improve, its control of contaminants moving down the canyons to prevent further surface transport and redistribution offsite of both mobile and sorbing contaminants. Measures to control surface transport down canyons, including further reduction of aqueous discharges, removal of contaminated media, and appropriate use of barriers, are needed. The geochemistry of contaminant migration has not been studied at a level of detail comparable to the site investigations conducted under the Hydrogeologic Workplan. This is a gap in LANL’s current groundwater protection program. Recommendation: LANL should better integrate geochemistry into its conceptual modeling. Laboratory experiments and field tests, in addition to literature data, are necessary to substantiate LANL’s general observations and assumptions about the geochemical behavior of contaminants. LANL will continue to be an active DOE site with the potential for release of contaminants from its ongoing operations. Discharges and releases have been cut substantially at TA-50, the location of the site’s radioactive liquid waste treatment facility. Yet, its discharges will continue to provide a flow of water that will tend to remobilize contaminants already deposited in the canyons. Recommendation: LANL should continue to review all operations and reduce discharges and releases to the greatest extent practical. This includes efforts to minimize the disposal of solid wastes on mesa tops because waste disposal in those areas can pose a long-term threat to the regional groundwater. 8 When taking mass loss mechanisms into account (e.g., radioactive decay), this will identify the upper boundary of pollutant mass that may still exist at the site today.