1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 7 901 NORTH 5TH STREET KANSAS CITY, KANSAS 66101 MAR - 0 2008 MEMORANDUM SUBJECT: Review of Radiological Conditions, West Lake Landfill FROM: Chuck Hooper, CHP Air Planning and Development Branch • THRU: Becky Weber, Director Air & Waste Management Division TO: John B. Askew, Regional Administrator 111 Superfund Site History In April, 1942, the Manhattan Engineer District (MED) contracted with the Mallinckrodt Chemical Works (MCW) of St. Louis, Missouri for large-scale uranium refining and processing as part of the atomic weapon's development of World War II. Several processes were used at MCW to extract uranium from the various ores and feed forms that arrived at MCW with the main goal of extracting as much of the uranium from the ore as possible. The MCW was not a facility that "enriches" the fissile isotopes of uranium; it simply extracted and produced uranium metal. The uranium produced still had a natural ratio of uranium isotopes (U-238 at 99.2745%, U-235 at 0.720%, and U-234 at 0.0055%), of which only uranium-235 is considered fissionable. Most of the constituents of an ore, even a high-grade pitchblende ore, are non-uranium metals and elements, because of this several steps are required and many waste residues are created that are not of value for uranium production. After the ore was milled and dried it was digested in nitric acid, a sulfuric acid step followed and a precipitate was formed that contained high levels of radium and lead, this residue was referred to by MCW as K-65. Ownership of K- 65 residue was retained by the supplier because potentially valuable elements were retained in the residue. Because of this the K-65 was always stored separately from other residues and was placed in drums. Later the K-65 residues were shipped to the Lake Ontario Ordnance Works. Another residue referred to as AJ-4, barium sulfate residue, was created when barium carbonate slurry was added when the ore had high levels of sulfates. The sulfate precipitates of this step also included trace amounts of uranium, radium and thorium. This residue was loaded into dump bins and transferred to the airport site and dumped on the ground because it was insoluble in water and regarded as fairly immobile. Later this barium sulfate residue was returned to MCW and an additional sodium carbonate leach process was added to help extract more uranium from the residue. This leached barium sulfate residue was then returned to the airport storage site. In 1966 the airport storage site was sold by the Atomic Energy Commission to the Commercial Discount Corporation of Chicago who in turn transported the leached barium sulfate residue and other process residues that still retained some uranium to the nearby Latty Avenue site. In 1969 the Cotter Corporation, with a facility in Carion City, Colorado, bought the Latty Avenue residues and for the next four years shipped residues to Colorado with the principal exception of 8700 tons of leached barium sulfate. In a 1974 investigation the Nuclear Regulatory Commission determined that in 1973 Cotter Corporation had disposed of the approximately 8700 tons of leached barium sulfate residues mixed with 39,000 tons of top soil at the West Lake Landfill[2]. The West Lake Landfill used the residues and topsoil mixture as a landfill amendment where it was mixed with landfill debris and trash in two distinct areas at West Lake Landfill. This currently makes up Operable Unit 1; Area 1 (-10 acres) and Area 2 (~30 acres)[3]. Area 2 generally has higher concentrations of radionuclides, and higher comparative risk estimates, than Area 1. Nature of Contamination References from MCW records indicate that although the leached barium sulfate was lower in radioactivity and radium/radon than the K-65 residue, it still warranted surveys and precautions such as dosimetry to be worn by workers at the airport storage site. Thorium-230 Additionally, when the NRC conducted studies at the West Lake Landfill they observed that although uranium was in relatively low concentrations, the levels of thorium-230 were elevated from 5 to 50 times higher than radium-226[4]. As a comparison to the Remedial Investigation (RJ) Report'31, the ratio of thorium-230:radium-226 from all samples above reference levels in Area 2 resulted in a ratio of 11:1, consistent with NRC investigations. The increase in thorium-230 is likely a result of the uranium processing as precipitates came out of the nitric acid solution at different rates. This would have altered the normal secular equilibrium that built up over millions of years. Because thorium-230 levels are elevated with respect to radjum-226 it will, over time, create an increase in levels of radium-226 that will equal thorium-230'and thus increase the dose (or risk) in the long term, i.e. in thousands of years. Secular Equilibrium Equilibrium of a radioactive decay chain occurs when a fixed ratio between the activities of the daughter and the parent exists. This indicates that the daughter activity is decreasing with the half-life characteristic of the parent. On a graph of activity versus time the curves for the parent and daughter will be parallel when equilibrium is reached. If the half-life of the parent (80,000 years for thorium-230) is much longer than the half- life of the daughter (1,600 years for radium-226) then secular equilibrium is possible. It is called secular since the equilibrium is maintained for a long time due to the comparatively large half- life of the parent. For secular equilibrium to be achieved, sufficient time for the in-growth of the daughter must pass. This is generally considered to be seven half-lives of the daughter. Radium-226 and Radon-222 Radium-226 and the rest of the eight decay daughters in the uranium decay chain usually provide the bulk of potential risk from an external gamma radiation perspective. Radium-226 also adds a unique challenge in that it decays into radon-222, a colorless, odorless, noble gas that can escape from the soil matrix and cause an internal dose as an inhalation hazard. Radon-222 and its other naturally occurring isotopes produce the majority of our natural radiation background exposure. Radon exposure accounts for 200 millirem of the estimated 360 millirem per year of background radiation dose'5'. Figure 1. Uranium-238 Decay Chain 238U (4.51x10y) (2,47x1 Oy)| a ?3<W ex i r (1.17m) i r 234Th 230Th , (24.1d) K' ^ (8.0x10 y) Legend a \ r 238 y Rsdlorudkle 6 22 Ra 9 (1602y) (4,51x10 y) "HalHJo Radonudkies produced In less Shan one percent of the ia transformations ol Ihe parent are no) shown, T22{ ji (3.823:!) <JC ir 718 po ™PO | j?1°PC (3,05m; S* (ie4MS} J*\ (l3S.4d) 214 a RI 'a a I I 210RI ' n ir *mli P ,, Mm P l« 214pb / 210pb ' [286^ (26.8m) (21y) : (stable) Topsoil and landfill debris/trash mix Most of the barium sulfate residue was briefly returned to MCW and leached with sodium carbonate in order to remove additional uranium and then returned to the airport site. At this point MCW records indicate that there were 7 tons of uranium left within the total of 8700 tons of leached barium sulfate residues, and that radium-226 concentrations were approximately 3960 picoCurie/gram[1]. If the residues were dumped in the landfill in an unadulterated form then the soil sampling results should indicate levels at this approximate level. However, the NRC investigation in 1974[2] revealed that the 8700 tons of leached barium sulfate residues were mixed with 39,000 tons of topsoil (a 4.5:1 soil to residue mixture) and then delivered to the West Lake Landfill (this corresponds to a total volume of material of approximately 39,750 cubic yards at 1.2 tons/cubic yards -compacted). At some point this leached barium sulfate residue and topsoil was mixed with landfill waste at the landfill. Investigations from bore hole analysis in the Remedial Investigation (RI) Report^', and the conclusion reached by the NRC'4\ were that the residues were additionally mixed with landfill waste (e.g. wood, plastic, paper, wire, rubber, yard waste, shredded tires, glass, etc.) and that when the residue/soil was encountered without waste it was limited to one or two feet thick or less. Both of these reports estimate that the total volume of contaminated debris within the landfill now accounts for approximately 150,000 cubic yards. The 39,750 cubic yards of residue/soil from Latty Avenue was in turn mixed with trash at an approximate ratio of 3.8:1. If the original concentration of unadulterated leached barium sulfate residue of 3960 picoCurie/gram has been diluted with top soil at a rate of 4.5:1 and then a subsequent rate of 3.8:1 with landfill trash debris, then the average expected radium-226 level within the landfill would be approximately 232 picoCurie/gram for a homogenous mixture. The average radium-226 concentration in the larger Area 2 is 189 picoCurie/gram[3], which indicates that the original 8700 tons of leached barium sulfate residues were likely mixed with top soil and landfill debris at the approximate ratios given. A few soil samples show that there are some areas where the concentration of radium-226 approached this original level of 3960 picoCurie/gram, indicating that the material is not a completely homogenous mixture (WL-209 at 3,720 picoCurie/gram and WL-234 at 3,060 picoCurie/gram).