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

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). If a limited removal of several dozen cubic yards were attempted in these high concentration areas it would likely not create a large change in the Exposure Point Concentrations (EPC) used in the Risk Assessment because these calculations are based on the arithmetic mean and not the maximum values found. Because a partial removal would have limited effect on the EPC, it would in rum have little effect on the overall risk results.

Some exceptions with high radium-226 levels exist prior to the RI studies, which were conducted in an earlier investigation by Radiation Management Corporation in 1982 (NUREG/CR-2722). This report often derived soil concentration using a field measurement technique using in-situ gamma-ray spectroscopy which is subject to larger error than current EPA protocols for laboratory analysis (e.g. PVC-11 at 13,000 picoCurie/gram and Base 5 Surface at 19,000 picoCurie/gram Bi-214/Ra-226). Exposure Pathways

Table 1 summarizes the cancer risks associated with radioactive material exposure as shown in the Baseline Risk Assessment for the West Lake Landfill. The total risk from All Routes is the sum of the Soil Ingestion, Inhalation and Direct Radiation risks. These risk values are based on the increased risk over a lifetime. The results indicate that the majority of risk is from Direct Radiation, i.e. external gamma exposure, of which over 90% is from radium-226 and its decay daughters for the Future Area 2 scenarios. Additionally, all Future scenarios include the calculated increase in radium-226 concentrations that will be present in 1,000 years. It's important to note that a 3E-4 lifetime risk corresponds to approximately 15 millirem per year of radiation dose (residential scenario)^, therefore the Storage Yard Worker at a 4E-4 risk has the potential of an increased radiation dose of approximately 91 millirem per year (corrected for exposure duration) as compared with other exposure levels in Table 2.

Table 1. Summary of Risks for Future Receptor Scenarios Evaluated in the West Lake Operable Unit 1 Baseline Risk Assessment171 Scenario Soil Ingestion Inhalation Direct All Routes Radiation Area 1 6E-5 1E-5 2E-6 5E-5 Grounds Keeper (1 in 16,700) Area 2 2E-4 1E-5 3E-6 2E-4 Grounds Keeper (1 in 5,000) Area 1 Storage Yard 1E-4 NE NE 1E-4 Worker (1 in 10,000) Area 2 Storage Yard 4E-4 NE NE 4E-4 Worker (1 in 2,500) "NE" - No exposure anticipated because a complete exposure pathway does not exist

The Grounds Keeper is assumed to be an employee who brush hogs in Areas 1 and 2 three days per year, eight hours per day, for 6.6 years of employment.

The Storage Yard Worker is assumed to be a full time employee (250 days per year for 6.6 years) that works in an adjacent building but spends 1 hour per day on a paved section of Areas 1 and 2. External Gamma

Overland Gamma and Borehole Measurements

An overland gamma radiation survey was conducted by McLaren/Hart based on a walkover scan at one-meter height that generated 56,736 data points. The survey was conducted with a sodium iodide 2"x2" detector. The maximum reading in Area 1 was 235 microR/hour (0.235 milliR/hour), and the maximum reading in Area 2 was 2,174 microR/hour (2.174 milliR/hour)181.

Radiation detectors used for environmental measurements similar to the West Lake Landfill often employ solid crystalline sodium iodide scintillation detectors because of their high efficiency for detecting gamma radiation. Typical background measurements range from 1,000 to 10,000 counts per minute depending on the size of the crystal in the detector, for example a Ludlum model 44-10 2"x2" sodium iodide detector will have a sensitivity of approximately 900 counts per minute for each microR/hour of exposure. A typical background rate of 5-10 microR/hour corresponds to a 4,500 to 9,000 counts per minute background range.

The radiological logging of boreholes during the RI investigations used a I"x4" sodium iodide detector'3'. Because their volumes are equal, the detector used in the borehole measurements will have a similar sensitivity as the Ludlum Model 44-10's 2"x2" detector. Therefore a borehole reading of 1,000,000 counts per minute would correspond to 1,100 microR/hour, or 1.1 milliR/hour. However, the geometry in a borehole is much different than a reading taken at three feet above the surface as the overland gamma survey was performed. Higher readings in a borehole are expected because the detector is physically closer to the contaminated material and because it is completely surrounded by the contaminated media.

Exposure Comparison

Often the first reaction when dealing with a radiological issue is to compare the external gamma radiation readings with background or other familiar exposures such as the dose absorbed by the body from a medical x-ray image. There are two reasons why this is an inappropriate comparison. First, the external gamma dose is just one pathway that could create a potential health risk, ingestion and inhalation are other pathways for exposure to radioactive materials, and in certain circumstances they can be the primary driver of risk instead of the external gamma pathway.

Secondly, the comparison of a gamma radiation level at a radiological site against other common radiation exposures does not fully account for the setting (occupational exposure versus public dose limits), exposure duration (full time residential occupancy versus the less duration recreational use), land use, and even potential benefit that certain radiological exposures can have in nuclear medicine and diagnostic imaging. Medical exposures have a benefit that cannot be readily compared with occupational or natural background exposures. Nevertheless, Table 2 may help the reader have a better perspective of various exposures.

Table 2. Various Exposure Levels Example Exposure Rate Radium-226 Dose (millirem/year) (microR/hour) (picoCurie/gram) West Lake Landfill, Area 2 Future Storage 189 avg. in Area 2, all 2,174 max. 91 Yard Worker Under depths Current Conditions Background 5-10 ~1 360 Uranium Mining 100'stolow 1,000's Low 100's Na Overburden/Protore Ramsar, Iran High 600 avg. in elevated 8-2,000 1,030 max. Natural Background areas X-Ray Exam, Single Chest to Lumbar Na na 2-70 per exam Spine19] CT Chest191 Na na 800 per exam Angioplasty (Heart Na na 750-5,700 per exam Study) [9] NRC Occupational Na na 5,000 Limit NRC Public Limit from Licensed 2,000 na 100 Facility DOT Limit for Occupied Cab of 2,000 na 5,000 Transport Vehicle

A common range of background radiation exposure as read on portable radiation meters is approximately 5-10 microR/hour (at 8760 hours per year this amounts to -66 millirem/year). However, this only includes the cosmic and terrestrial sources of background radiation. Typical radiation survey instruments don't account for the internal dose from naturally occurring radionuclides present in our bodies (e.g. potassium-40), nor do they fully measure the dose from the inhalation of radon and radon decay products that contribute the majority of our background dose.

A summary of sampling results from waste rock and overburden from several abandoned uranium mining sites are presented in US EPA Technologically Enhanced Naturally Occurring Radioactive Materials From Uranium Mining, Volume 1: Mining and Reclamation Background. Uranium and radium concentrations and direct radiation readings of the protore (unreclaimed subeconomic ores) and overburden, i.e. waste that is left behind when the uranium ore has been mined, are presented in the report. These measurements vary from levels that are slightly elevated above background to levels in the hundreds of picoCuries/gram for uranium and radium. These waste materials left behind were not utilized because of their low uranium concentration and are likely to be lower than the "ore" material that was removed for processing. Gamma radiation readings also vary depending on the concentration of the material left behind but range from slightly elevated to hundreds of microR/hour to several milliR/hourll°J.

Some areas of the world have higher terrestrial background levels than others. One unusual area with naturally high radiation background occurs in Ramsar, Iran. The town of approximately 2000 people on the shores of the Caspian Sea has naturally high levels of radium due mainly from residues from mineral deposition from the many hot springs in the area. Exposure rates have been measured from 8 to 2,000 microR/hour, and soil sampling indicates levels of radium-226 as high as 1,030 picoCurie/gram (3.8E4 Bq/kg)mi.

The NRC occupational limit is 5,000 millirem/year. The public dose limit from a licensed facility is 100 millirem/year, with a limit of 2 millirem/hour.

The Department of Transportation (DOT) and NRC set the acceptable levels of radiation from packages for commerce. The maximum radiation reading on a labeled Yellow III package is 200 millirem/hour on contact and ten millirem/hour at one meter. For an exclusive use shipment the occupied position within the driver's cab is limited to 2 millirem/hour.

Conclusions

Although the radioactive material in the form of leached barium sulfate residues is not exactly typical of ore, overburden, or protore of most uranium mining areas, it is consistent with these from a radiological standpoint, with the exception that over time the radium concentration will increase to the levels of thorium-230. For these impacted areas at the landfill the thorium- 230 concentrations are elevated approximately 11:1 over radium-226. The Baseline Risk Assessment accounts for this in the Future exposure scenarios by increasing the radium-226 concentrations to levels that will be present in 1,000 years.

Sampling results indicate that the vast majority of radiologically impacted Areas 1 and 2 are at levels that do not indicate that the original leached barium sulfate residues transported to the landfill were dumped in one place, and that they were mixed irregularly throughout the landfilled material. Removing only a portion of the contaminated material, even in areas that are elevated above the average, would have a small impact on the risk because the Exposure Point Concentration used to calculate risk is based on the arithmetic mean and not a maximum concentration. While elevated count rates were measured in some areas of the landfill materials, limited removal in these areas would not necessarily reduce the overall risk to below acceptable levels without the need for further action.

Regardless of any other comparisons, the Baseline Risk Assessment provides the best assessment of a site's human health risk whether the contaminant is radioactive or not. The results of that risk assessment exceeded the acceptable risk range for a Future Grounds Keeper and Future Storage Yard Worker, therefore additional response action is necessary. The enhanced cover/cap system and other actions outlined in the Feasibility Study and Proposed Plan can be designed to reduce radiation levels at the surface of the landfill to acceptable levels for future worker scenarios, with the added benefit that radiation exposure for workers during the cover/cap installation are likely to be much less than if a partial removal of the residues were attempted. References

[1 ] Oak Ridge Associated Universities, Dose Reconstruction Team for NIOSH, Basis for Development of an Exposure Matrix for the Mallinckrodt Chemical Company St. Louis Downtown Site and the St. Louis Airport Site, St. Louis, Missouri (ORAUT-TKBS-0005, Revision 2, June 14, 2007); 8.6.2 Assumptions for Radioactive Source Terms, and Table A-4

[2] NRC NUREG-1308, Rev 1, Radioactive Material in the West Lake Landfill Summary Report (June 1988)

[3] Engineering Management Support, Inc, Remedial Investigation Report West Lake Landfill Operable Unit 1 (April 2000)

[4] Radiation Management Corporation, NRC NUREG/CR-2722 Radiological Survey of the West Lake Landfill St. Louis County, Missouri (May 1982)

[5] National Council on Radiation Protection and Measurements, Report No. 93, Ionizing Radiation Exposure of the Population of the United States

[6] OSWER No. 9200.4-18; Memorandum: Establishment of Cleanup Levels for CERCLA Sites with Radioactive Contamination (1997)

[7] Auxier & Associates, me, Baseline Risk Assessment West Lake Landfill Operable Unit 1, (April 2000); Table A.5-13

[8] McLaren/Hart Environmental Engineering Corp., Overland Gamma Survey Report West Lake Landfill Radiological Areas 1 & 2 (April 30, 1996)

[9] Health Physics Society Fact Sheet; Radiation Exposure from Medical Diagnostic Imaging Procedures

[10] US EPA, Technologically Enhanced Naturally Occurring Radioactive Materials From Uranium Mining, Volume 1: Mining and Reclamation Background; Appendix V. Radiochemical Data for Uranium Overburden and Waste Rock, Pit Lakes and Streams, and In Situ Leach Operations (EPA 402R-05-007, January 2006)

[11] Sohrabi, M., Esmaili, A.R.; New Public Dose Assessment of Elevated Natural Radiation Areas of Ramsar (Iran) for Epidemiological Studies (2002)

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