PUBLIC HEALTH ASSESSMENT
Plutonium 239 in Sewage Sludge
Used as a Soil or Soil Amendment in the Livermore Community
LAWRENCE LIVERMORE NATIONAL LABORATORY, MAIN SITE (U.S. DOE)
LIVERMORE, ALAMEDA COUNTY, CALIFORNIA
Potential off-site exposure to plutonium 239 (Pu 239) in sewage sludge released from the Lawrence Livermore National Laboratory (LLNL) to the Livermore Water Reclamation Plant (LWRP) has been identified as a specific community concern.This public health assessment will address that concern by evaluating the public health implications of potential radiological doses from exposures to the Pu 239-contaminated sludge. In order to evaluate the public health implications of the historical distribution of Pu-contaminated sludge to the Livermore community three specific questions are addressed: 1) What concentrations of Pu 239 in sludge would produce doses of public health concern? 2) Were the concentrations of Pu 239 in the sludge distributed to the public by LWRP greater than the levels of potential health concern? 3) Do the available data provide an adequate basis for this public health assessment?
Doses of public health concern are defined as the human intake of Pu 239 (or other radionuclides) via ingestion, inhalation, or external exposure at levels that are capable of causing adverse health effects, such as cancer, other illnesses, or death. The ATSDR minimal risk level (MRL) of 100 mrem/year (above background) is used as a basis for determining radiological doses of public health concern. No adverse health effects have ever been documented from radiological doses of 100 mrem/year or less (above background). The average background radiation dose throughout the US is about 360 mrem/year. The MRL represents a dose of less than 1/3 of normal background.
Several sources of historical monitoring data are available to assess the historic concentrations of Pu 239 in sludge produced at the LWRP. These data include gross alpha concentrations in LLNL effluent to the LWRP, gross alpha concentrations in both digester and processed sludge, and Pu 239 concentrations in soils of disposal areas for contaminated sludge. Past studies have evaluated the potential radiological doses from exposure to Pu 239-contaminated sludge. These studies have assumed different exposure scenarios, including LWRP workers responsible for tilling and spreading the contaminated sludge, residents living adjacent to the sludge disposal area, children playing in sludge-contaminated areas, and adults gardening in and consuming food crops grown in contaminated-sludge soils.
The Pu 239-contaminated sludge, released from the LLNL to the LWRP, and distributed to the Livermore community represents a completed exposure pathway. The route or process of human uptake of the Pu 239 occurs via incidental ingestion and inhalation during the use, transport, or handling of the sludge, or the soil where the sludge was placed, or ingestion of vegetation grown in the sludge-amended soil. The calculation of radiological doses from a long-lived isotope such as Pu 239 is very complex due to the partitioning, retention, and decay of the isotope and each of its decay products within the environment and the different organs in the human body. For this health assessment, radiological doses from exposure to the Pu 239 contaminated sludge are calculated using RESRAD 6.2.1.
A soil Pu 239 concentration (100 percent sludge cover) of 816 pico Curies per gram (pCi/g; 1 pCi=1x 10-12 curies; averaged over an entire exposure area or residential yard) is required to produce a dose of 100 mrem/year, as calculated using RESRAD. This calculation includes health-protective exposure factors and includes ingestion of soil and garden crops, inhalation of dust, and external exposure. This calculation also assumes that the contaminated area covers an area of acre to a depth of 6 feet, of the area is unvegetated, and of the resident's food is grown on the contaminated area. Considering that it would take 108 pick-up truck loads of sludge to cover a 1/2 acre lot (to a 3 inch depth), such an exposure scenario, although possible, is very unlikely.
A nearly complete historical record of LWRP gross alpha concentrations for the period of 1960 through 1973 (analyzed by the California Department of Public Health; CDPH) indicates that maximum digester sludge concentrations were less than 300 pCi/g (monthly average values). The average monthly gross alpha concentration of digester sludge measured by LLNL was 606 pCi/g (June 1967; average of digesters 1 and 2). The CDPH digester sludge values show two distinct peaks corresponding with the 1964 and 1967 release episodes (297 pCi/g and 258 pCi/g, CDPH data, respectively). Gross alpha concentrations of LLNL effluent into the Livermore sewer system show the same peaks and provide supplementary data for those periods during which digester concentrations were not collected or analyzed. Collectively, the measured digester sludge data and the LLNL analyzed effluent data indicate that the 1964 and 1967 release episodes represent the worst-case sludge concentrations.
As the concentrations of Pu 239 in processed sewage sludge following the 1964 episode of maximum digester sludge concentration were less than 816 pCi/g, it follows that the maximum Pu 239 concentrations in sludge were below levels of health concern. Although sludge concentrations following the 1967 event are not available, processed sludge gross alpha concentrations following the 1964 release (297 pCi/g digester sludge values) were approximately 60 pCi/g. This indicates that digester sludge gross alpha concentrations are considerably reduced during the treatment process. As processed sludge is further milled and mixed before disposal, it is expected that processed sludge concentrations would be additionally reduced before distribution to the public.
Several areas where contaminated sludge was placed have been sampled for Pu 239 concentrations. These areas include Big Trees Park, residential yards of former LLNL employees, and a test garden on the LLNL facility. Maximum Pu 239 concentrations of these locations were less than 2 pCi/g. Although the initial sludge concentration of most of these areas is unknown, sludge and soil sampling at the LLNL test garden indicated that Pu 239 concentrations in applied sludge are reduced by a factor of more than 5 in the resulting soil. This indicates that tilling and mixing of applied sludge will additionally reduce residential soil Pu 239 concentrations.
Assuming that the available gross alpha concentrations in LWRP sludge and LLNL sewer effluent are a reasonable substitute for direct Pu 239 measurements, the available data clearly indicate that the Pu 239-contaminated sludge does not result in radiological doses of public health concern. Monthly nuclide specific and gross alpha monitoring data for 1973 indicate that gross alpha concentrations overestimate Pu 239 concentrations. Consequently, the use of gross alpha concentrations as a proxy for Pu 239 concentrations is a health protective assumption.
No single data set is adequate for making the above public health determinations. There is not a consistent time series of Pu 239 or gross alpha concentrations in processed sludge. Similarly, there are gaps in the digester sludge measurements, and the LLNL effluent data do not provide specific levels of sludge contamination. However, collectively, the available data do provide an adequate basis for public health assessment. The trends in the different data values support and reinforce the individual data sets. Additionally, the health protective assumptions used in calculating doses provide additional assurance for the health conclusions. The following conclusions are based on our current knowledge of radiation health effects and the data reviewed and evaluated in this health assessment:
- Pu 239 from LLNL was released to the Livermore sewer system and resulted in the contamination of LWRP sludge which may have been distributed to the Livermore community resulting in areas of above background soil concentrations of Pu 239.
- Using health protective exposure assumptions, radiological doses from maximum measured concentrations of digester sludge are below levels of health concern. This evaluation assumes that digester sludge gross alpha concentrations represent Pu 239 concentrations and that digester sludge is spread uniformly over an entire residential yard. Pu 239 concentrations of processed sludge distributed to the Livermore community are estimated to be more than 10 times lower than digester sludge concentrations.
- The available data and evaluations provide an adequate basis for these public health conclusions. Any additional sampling data will be subject to the same types of uncertainties as existing historical data.
Based on the above conclusions, the historic distribution of Pu-contaminated sewage sludge is determined to be no apparent public health hazard. No apparent public health hazard means that while exposure may have occurred, or may still be occurring, the resulting doses are unlikely to cause cancer, other illnesses, or death. As the potential maximum radiological doses from exposures to Pu 239-contaminated sludge are below levels of health concern, ATSDR has no recommendations concerning additional soil sampling in areas of known or unknown sludge distribution. Because the community may still have unresolved concerns about this issue, ATSDR offers the following recommendations:
- Develop and present educational materials, based on the information included in this public health assessment, to the Livermore community.
- Continue current monitoring of Pu 239 (and other contaminant) concentrations in LLNL effluent and the LWRP sewage treatment system (as stipulated by existing discharge permit requirements).
SECTION 1: INTRODUCTION AND ENVIRONMENTAL PATHWAYS
The Lawrence Livermore National Laboratory (Livermore Site; hereafter referred to as LLNL, is a multi-program research facility owned by the U.S. Department of Energy (DOE) and operated by the University of California. The LLNL is a science, technology, and engineering facility with a special focus on nuclear weapons research and development. Other areas of research include arms control and treaty verification control technology, energy, the environment, biomedicine, the economy, and education (DOE 1992).
LLNL was placed on the Superfund National Priorities List (NPL) in 1987 on the basis of volatile organic compounds (VOCs; trichloroethylene, tetrachloroethylene, chloroform, 1,1-dichloroethylene, and others) in monitor wells and nearby drinking water wells (LLNL 1990). The Agency for Toxic Substances and Disease Registry (ATSDR) is required to conduct a public health assessment of all facilities proposed for the NPL.
During the course of the LLNL public health assessment process, potential off-site exposure to plutonium 239 (1) (Pu 239) in sewage sludge released from the LLNL to the Livermore Water Reclamation Plant (LWRP) was identified as a specific community concern (CDHS, in review). In response to this concern, ATSDR has prepared this public health assessment to determine if exposure to Pu 239-contaminated sludge could have occurred at concentrations likely to result in adverse health effects.
Processed sewage sludge from the LWRP was distributed for use as a soil amendment to municipal agencies from at least 1958 until 1976 and to the public from at least 1958 until 1973 (CDHS 2002). The LLNL facility has been discharging wastewater to the LWRP since at least 1959. Contaminant concentrations in effluent releases (including Pu 239) from LLNL to the municipal sewer system have been regulated by federal discharge limits and/or state and local permit requirements with related compliance monitoring since at least 1959 (LRL 1960-1970).
Radiological releases from LLNL to the sewer system during this period occurred as both routine low-level discharges and several higher concentration episodic events, which have resulted in Pu 239 contamination of the sludge processed and distributed by the LWRP. Although LLNL has monitored their sewage effluent since at least 1959, there has not been regular monitoring of the processed sewage sludge. Additionally, permit requirements, discharge limits, monitoring and reporting procedures have changed over time, which creates difficulties in interpreting Pu 239 concentrations in sludge during this time period. These changes, along with a lack of direct monitoring of processed sewage sludge have created concerns in the Livermore community about potential exposures to the Pu 239-contaminated sewage sludge that may have been used as a soil amendment for public and private properties.
In order to evaluate the public health implications of the historical distribution of Pu-contaminated sludge to the Livermore community, three specific questions must be addressed: 1) What concentrations of Pu 239 in sludge would produce doses of public health concern? 2) Were the concentrations of Pu 239 in the sludge distributed to the public by LWRP greater than the levels of potential health concern? 3) Do the available data provide an adequate basis for this exposure assessment and the resulting public health conclusions? Doses of public health concern are defined as the human intake of Pu 239 (or other radionuclides) via ingestion, inhalation, or external radiologic exposure at levels that are capable of causing adverse health effects, such as cancer, other illnesses, or death.
With regard to the Pu 239 concentration required to produce a dose of public health concern, in 1976, Lawrence Radiation Laboratory (now known as LLNL) staff published a study evaluating the use of Pu-contaminated sludge as a soil conditioner for food crops (Myers et al. 1976). Although the radiation dose estimated in that study is well below a level of health concern, it is possible that historic Pu 239 concentrations in LWRP sludge were higher than those used to estimate doses in the Myers et al. (1976) study. This document evaluates the historic monitoring data using a current exposure assessment model to determine if the concentrations of Pu 239 in sludge could have reached levels of public health concern.
Specifically, this public health assessment will evaluate whether potential maximum Pu 239 concentrations in sludge following the 1964 and 1967 episodic releases could have exceeded the concentration necessary to produce a dose of public health concern. Specific analytical measurements of Pu 239 (and Americium 241; Am 241 (2)) concentrations in the LWRP sludge during the 1967 to 1969 timeframe are currently not available. However, there are time-specific gross alpha data, which can provide limits on the potential maximum Pu 239 concentrations. This document will use that data to estimate the potential maximum Pu 239 sludge concentrations for the 1960-73 timeframe (including the assumptions underlying those estimates) and compare those concentrations with a concentration capable of producing a radiological dose of public health concern (question 1, above).
This document will also evaluate information related to the radio-toxicity of plutonium. Specifically, this assessment will summarize the health effects studies from plutonium exposures, the doses at which those health effects occurred, and compare those doses with various Pu 239 soil concentrations and soil screening values.
The question of whether the available data provide an adequate basis for this public health assessment (question 3, above) presents a significant challenge in collecting and interpreting historical data. The currently required practices of data collection, analytical methods, quality assurance, and data management cannot be assumed for samples collected and analyzed 30 to 40 years ago. Rather than trying to impose those current requirements on the historic data, the evaluation of data adequacy for this assessment will focus on whether disparate data sets lead to similar and consistent interpretations. If different data sets produce similar results and support consistent conclusions, this assessment will conclude that the available data adequately measure past and current exposure conditions and provide a satisfactory basis for the public health evaluation.
The premise of this public health assessment is that Pu 239 concentrations in sludge following the 1964 and 1967 releases represent worst-case conditions. If estimated maximum doses from exposure to contaminated sludge from the worst-case conditions are below levels of public health concern, it follows that doses from all lesser exposures are also below levels of public health concern. Available monitoring data will be further evaluated to determine if sludge concentrations following the 1964 and 1967 releases do indeed represent worst-case conditions. Limitations and assumptions underlying the available data and exposure models will be noted.
The LLNL site is in southern Alameda County, California, and approximately 40 miles east of San Francisco (Figure 1). The LLNL is about three miles east of the central business district of the City of Livermore but directly abutted by residential properties to the west, commercial and industrial properties to the north, agricultural and residential land to the east, and the Sandia National Laboratory to the south. LLNL also operates the LLNL Site 300 near Tracy, California (about 12 miles east of the main site). Operations and potential contaminant releases of the Site 300 will be addressed in a separate public health assessment.
The LLNL main site, including a buffer zone acquired in 1989, covers an area of approximately 821 acres in the southeastern portion of the Livermore Valley. In 1942, the U.S. Department of the Navy acquired 681 acres of agricultural and ranch land to establish the Livermore Naval Air Station. Although the original use of the Naval Air Station was for flight training, by October 1944, aircraft assembly, repair, and overhaul were conducted at the Livermore NAS. From 1945 until the Livermore NAS was deactivated in 1946, extensive aircraft repair and assembly occurred at the site. The site was occupied by the Atomic Energy Commission (AEC) in 1950 with formal transfer of the property in 1951. The AEC, its successor agencies and ancillary entities have occupied the site for defense-related research. In 1952, the site was established as a separate part of the University of California Radiation Laboratory. In 1971, the Livermore site became the Lawrence Livermore Laboratory, and in 1979 was renamed by Congress as the Lawrence Livermore National Laboratory. LLNL is operated by the University of California under contract with the U.S. Department of Energy.
In 1992 DOE published the "Final Environmental Impact Statement and Environmental Impact Report for Continued Operation of the Lawrence Livermore National Laboratory and Sandia National Laboratories, Livermore". This document includes a detailed statement of LLNL operations and facilities. The information from that report outlining LLNL operations and facilities will not be reproduced here, but will be referenced as appropriate to define environmental releases and potential community exposures to chemical and radiological materials.
Background and Previous Studies
In order to assess the potential concentrations of Pu 239 in sludge processed by the LWRP, it is necessary to have a basic understanding of how a wastewater treatment plant operates. In an activated sludge system, such as the LWRP, wastewater enters the system through a series of screens where large debris is filtered. Primary treatment consists of gravitational separation by skimming of floating materials and settling of heavier particles and sediment. Primary treatment removes 45% to 50% of the waste materials in the initial plant influent. Solid materials from the primary separation step are pumped into the sludge digesters where bacteria break down and decompose the sludge (referred to as digester sludge). Water that has passed through the primary sedimentation tanks still contains significant amounts of waste materials in dissolved or very fine solid forms. This water undergoes secondary treatment by exposure to microorganisms that consume the waste material and convert it into biomass. This biomass is filtered from the water and is also pumped to the digesters as sludge.
Although waste solids remain in the digesters for approximately 28 days, new and re-processed sludge is pumped into and out of the digesters on a daily basis (J Dupont, personal communication; 7/09/02; also see Appendix 2). Digester sludge produced from the digester process is pumped into drying beds or lagoons where water can further evaporate from the wet sludge. The sludge lagoons and/or drying beds accumulate sludge from the digesters for periods of 1 to 5 years (hereafter referred to as dried or processed sludge). After drying, the remaining solid, dried sludge is transported to disposal areas, mixed with soil to enhance drying, and historically, provided to the public for use as a fertilizer or soil amendment.
Plutonium has a very low solubility in water. This means that very little of the Pu 239 present in the sewer effluent from the LLNL will occur in a dissolved form, but is much more likely to occur as a solid particle or adsorbed onto a solid particle. Within the LWRP, Pu 239 will rapidly accumulate with the solid materials in sludge. As both gross alpha and isotope specific monitoring of the liquid effluent released from the LWRP are typically non-detections (Pu 239 is below the detection limits of the analytical procedure), it follows that the Pu 239 entering the treatment plant remains in the sludge.
Figure 1. This map shows the LLNL within Livermore community and population characteristics surrounding LLNL facility. These population characteristics are not specifically related to potential sludge exposures (see the following section).
Past and ongoing monitoring reports document the plutonium releases to the LWRP and concentrations in the processed sludge. Although there are no historic isotope-specific data documenting the past Pu 239 sludge concentrations following the 1967 release, there are data which can be used to put an upper limit on the possible concentrations. Following the May-June 1967 release of plutonium to the LWRP, LRL staff initiated an enhanced sampling effort at the LWRP. Some results of that sampling effort are reported in a letter and attached memorandum from D.C. Sewell (LRL) to E.C. Shute (U.S. Atomic Energy Commission) dated August 22, 1967 (included as Appendix 2).
Of particular interest are the semi-annual and annual Lawrence Radiation Laboratory (LRL: prior name of LLNL) environmental reports for the years before and after the accidental Pu/Am release in 1967 (LRL 1960-70; LLL 1971-73). Before 1967, the reports indicate values of gross alpha concentrations of monthly sludge and liquid effluent samples. For 1965 and 1966 the gross alpha activities in dried sludge ranged from 17 to 60 picocuries (3) per gram (pCi/g). Liquid effluent samples (from the oxidation ponds or unspecified location) ranged from 7 to 26 pCi/liter.
In addition to the sewage monitoring data collected by the LLNL, the California Department of Public Health (prior name of California Department of Health Services; CDHS), Bureau of Radiologic Health historically conducted radiological monitoring of public sewage treatment facilities. Monthly data (gross alpha) from the LWRP around the time of the May 1967 accidental Pu 239 release indicate maximum digester sludge concentrations in May and June (1967) of 258 pCi/g and 229 pCi/g (respectively). This data set includes monthly gross alpha concentrations (4) of LWRP digester sludge from 1960 to 1969 (CDHS, 1960-1969). The available monitoring data will be presented and summarized in the following section on "Maximum Pu 239 Concentrations in LWRP Sludge."
A number of studies and monitoring reports have been conducted and published to assess the potential health effects from the distribution of the plutonium-contaminated sludge. These studies include the Myers et al. (1976) study that specifically evaluated the radiological dose produced by using Pu 239-contaminated sewage sludge as a soil amendment on a residential garden. This study includes direct measurement of Pu 239 concentrations in sludge, the sludge-amended soil, air during tilling operations, and in food products grown in the sludge-amended soil.
In addition to the Myers et al. study evaluating potential exposures to home gardeners, Balke (1993) conducted an evaluation of potential exposures to workers at the LWRP facility and to residents living directly downwind of the contaminated sludge disposal area. This study also included reviews of directly measured Pu 239 concentrations in contaminated sludge, soil from the contaminated sludge disposal area, and air directly downwind of the sludge disposal area. Fifty year radiological doses were calculated for residents living adjacent to the contaminated sludge disposal area and to a hypothetical LWRP worker that tractor-tilled the contaminated sludge for 520 hours per year for 50 years (the frequency of tilling operations is based on LWRP work schedule information).
Potential exposure to the Pu 239-contaminated sewage sludge was also evaluated in a health consultation (ATSDR 1999a) on "Plutonium Contamination in Big Trees Park." The "Evaluation of Radiation Dose" in this health consultation calculated the dose to a pica child (5) playing in the area of the maximum measured Pu 239 concentration (1.02 pCi/g) for 2000 hours per year (eight hours per day for five days per week for 50 weeks per year). The exposure calculation also used health protective assumptions about the plutonium particle sizes and solubility and determined that the estimated committed effective whole body dose would be less than 1 millirem per year (mrem/yr). MacQueen et al. (2002) indicate that a more realistic exposure assessment would use an average Pu 239 concentration from the Big Trees Park area rather than the maximum concentration from one sample. The resulting dose would be about 8% of the dose calculated using the maximum concentration.
Based on recommendations in the Health Consultation, additional sampling in Big Trees Park was conducted in 1998. The results of that additional sampling were reported in another Health Consultation (ATSDR 2000) and an LLNL report (MacQueen et.al. 2002). Both the sampling results and doses calculated from those samples are similar to those from the 1999 Health Consultation. In addition to the re-sampling of Big Trees Park, the 2000 Health Consultation (ATSDR 2000) reported some historical results of 1973 analyses of the yards of LLNL employees that had obtained and used LWRP sewage sludge. While the Pu 239/240 concentrations of those yards are below levels of health concern (maximum value of 1.8 pCi/g), the results do indicate that contaminated sludge was distributed to the Livermore community.
A variety of historical monitoring data is available to assess the historic concentrations of Pu 239 in sludge produced at the LWRP. These data include gross alpha concentrations in LLNL effluent to the LWRP, gross alpha concentrations in both digester and processed sludge, and Pu 239 concentrations in soils of disposal areas for contaminated sludge. Past exposure studies have evaluated the potential radiological doses to Pu 239-contaminated sludge. These studies have assumed different exposure scenarios, including LWRP workers responsible for tilling and spreading the contaminated sludge, residents living adjacent to the sludge disposal area, children playing in sludge-contaminated areas, and adults gardening in and consuming food crops grown in contaminated-sludge soils.
A release of a chemical or radioactive material into the environment does not always result in human exposure. For an exposure to occur, a completed exposure pathway must exist. A completed exposure pathway exists when all of the following five elements are present: 1) a source of contamination, 2) an environmental medium through which the contaminant may be transported to 3) a point or area of human exposure, 4) a route or process of human uptake (ingestion, inhalation, etc.), and 5) a receptor population. A potentially completed pathway exists when one or more of the above elements are missing or unknown, but available information indicates that exposure is, or will be likely. An incomplete exposure pathway exists when one or more the five elements are missing and available data indicate that human exposure is unlikely.
The Pu 239-contaminated sludge, released from the LLNL to the LWRP, and distributed to the Livermore community represents a completed exposure pathway. Although there are still questions about which specific individuals or municipal agencies may have received the sludge, the finding that Pu 239-contaminated sludge was distributed to the tree wells at Big Trees Park proves that the sludge has been placed in areas of human exposure. Also, because the distribution of sludge from the LWRP to the public was a standard practice, it is further assumed that contaminated sludge was similarly distributed to the Livermore community.
The route or process of human uptake of the Pu 239 would occur via incidental ingestion and inhalation during the use, transport, or handling of the sludge, or the soil where the sludge was placed, or ingestion of vegetation grown in the sludge-amended soil. Although the specific people who may have been exposed to the Pu 239-contaminated sludge are unknown, more specific information concerning the human uptake of the Pu 239 will be presented in the following section on exposure assessment.
There is no way to precisely determine how many members of the Livermore community may have been (or are) exposed to soil with elevated concentrations of Pu 239 from LLNL-released and LWRP-processed sludge. There are anecdotal references to a logbook maintained by LWRP as a record of sludge distribution. If available, this logbook could provide a specific reference to who may have obtained and used sludge as a soil amendment. Despite extensive searches, this logbook has not been located.
In lieu of a quantitative estimate of the number of people potentially exposed to contaminated sludge, this evaluation will focus on the exposure conditions or scenarios that would lead to the highest doses or worst-case exposure conditions. Although it is not expected that any member of the Livermore community would include all of the conditions or exposures of the potential worst-case scenario, many Livermore residents could have been exposed to Pu 239-contaminated soil.
SECTION 2: COMMUNITY CONCERNS RELATED TO PLUTONIUM IN SEWAGE SLUDGE
Community health concerns about the LLNL-related contamination are summarized in a health consultation prepared by the California Department of Health Services (CDHS 2001). This health consultation describes the Site Team formed to prioritize community health concerns and lists the community health concerns regarding LLNL and the processes by which those concerns have been collected. Concerns about plutonium contamination of LWRP sewage sludge are repeated in several portions of the health consultation and are (as included in Appendix A of that document): "Residential distribution of plutonium contaminated sewer sludge from the Livermore Water Reclamation Plant" which is listed as an exposure concern and "Financing of plutonium testing in yards that received sewer sludge from the water reclamation plant" which is listed as a procedural concern. Evaluation of the distribution or exposures to plutonium-contaminated sewage sludge are not included in the Site Team Priority Concerns (Appendix B of the Health Consultation), but may be related to "Biomonitoring for plutonium" (item 9 of 9 in Appendix B).
In addition to the above specific concerns about plutonium in sewage sludge, there are a number of references to concerns about plutonium in Big Trees Park and other areas throughout the Livermore community. As it has been determined that the plutonium in Big Trees Park and other municipal properties is the result of distribution of plutonium-contaminated sewage sludge as a soil amendment (ATSDR 2000; MacQueen et.al. 2002) many of the concerns about plutonium soil contamination are directly or indirectly related to the distribution of contaminated sewage sludge.
In September of 1999, ATSDR conducted a public availability session at the Arroyo Seco Elementary School. The session was held to provide community members an opportunity to tell ATSDR representatives about any concerns they may have related to LLNL contaminants, specific health concerns, or issues related to the ATSDR's conduct of the public health assessment. Four ATSDR representatives listened to and took notes from 6 members of the Livermore community (about 30 people attended the session, but only 6 provided specific comments). Comments related to exposure to, and distribution of, the contaminated sewage sludge were presented to, and noted by, the ATSDR representatives.
In response to these concerns, CDHS formed a "sludge working group" (SWG) in March 2000 to develop a community-based process for addressing those concerns (CDHS 2002). The group, which met periodically in 2000 and 2001, consisted of representatives of state and local agencies and members of local and regional special interest groups. Most of the members of the SWG are also members of the Site Team (described above).
During a conference call with ATSDR representatives (July 30, 2002), members of the SWG described several specific concerns related to the Pu 239-contaminated sludge issue. These concerns include: an overall perception that there are insufficient data available for evaluating the public health issues related to historic sludge distribution and exposure, the SWG also had concerns about the use of the ATSDR minimal risk level (MRL) used to evaluate doses of public health concern, and the need to include potential doses to children as part of the exposure assessment in this document. Those concerns are explicitly addressed in this PHA.
The remaining portions of this public health assessment will address the community's concerns by providing estimated radiological doses from exposure to Pu 239-contaminated sewage sludge, compare the estimated doses with those that have caused sickness or death, and determine whether available monitoring and exposure data are adequate for evaluating potential public health effects.
Peer review and public comments on the public release version of this PHA are included as Appendix 3. This appendix also includes the ATSDR's responses to those comments which indicate how the final version was revised or why it was not revised.
SECTION 3: EXPOSURE ASSESSMENT OF PU 239-CONTAMINATED SLUDGE
As indicated in the previous section on "Background Information and Previous Studies" there have been several evaluations of the concentrations of Pu 239 in LWRP sludge and radiological dose estimates from exposure to the contaminated sludge. Several of the studies have used 2.5 pCi/g as a soil screening guidance value. The derivation and significance of this soil screening value will be discussed in the following section on "Public Health Implications". This exposure assessment will calculate radiological doses using a Pu 239 concentration of 2.5 pCi/g in the soil of a acre homesite (the EPA default exposure area).
The calculation of whole body and organ specific radiological doses from a long-lived isotope such as Pu 239 is very complex due to the partitioning, retention, and decay of the isotope and each of its decay products within the environment and the different organs in the human body. This complexity is resolved through the use of analytical models that track and sum the doses (or radioactive decays or relative risks) across the environmental pathways and through the human body. For this health assessment, radiological doses from exposure to the Pu 239 contaminated sludge are calculated using RESRAD 6.2.1 (ANL 2001). RESRAD is a computer model designed to estimate radiation doses and risks from RESidual RADioactive materials. RESRAD 6 (6) represents the sixth major version of the RESRAD code since it was first issued in 1989. RESRAD has been used for deriving limits for radionuclides in soil by the U.S. Environmental Protection Agency (EPA), the U.S. Army Corps of Engineers, U.S. Department of Energy (DOE; and its contractors), and the U.S. Nuclear Regulatory Commission (NRC).
The use of RESRAD 6 requires specification of several dozen parameters or use of default values for those parameters. The default values are used for all parameters except area of contaminated zone (1/2 acre) and average annual wind speed (3.89 m/sec). The above parameters were adjusted to agree with values recommended in the EPA Exposure Factors Handbook (EPA 1999) or area-specific meteorological conditions (average wind speed).
The RESRAD 6 dose calculation includes dose contributions from external gamma exposure, inhalation of dust/soil, food, milk, and meat ingestion, drinking water, and soil ingestion. Dose contributions from radon are not included.
An exposure scenario is a quantitative description of the types of human behaviors and activities during which exposure to a contaminated material or substance might occur. A scenario description includes the frequency with which an exposure activity occurs, the duration of each episode of the activity, and the types of potential uptake, such as ingestion or inhalation that occur during each exposure activity. The exposure scenarios provide the basis for calculating a quantitative estimate of the amount of contaminated material someone may have taken into their body. The quantitative estimate of exposure is called the exposure dose and is usually expressed per unit time (day or year). The radiological doses presented in the following section are expressed as millirem per year (mrem/yr).
Previous studies have identified and evaluated several exposure scenarios. These scenarios include the evaluation of exposures that may have occurred from use of contaminated sewage sludge as a soil amendment to a residential garden, exposures to a LWRP worker conducting sludge land spreading operations, and a resident living directly adjacent to the area of land spreading operations. Collectively, these scenarios represent the activities and behaviors where direct contact and uptake of contaminated sludge is most likely and therefore present the highest potential for significant exposure. Although no specific individuals can be associated with each of these scenarios, each is likely to have occurred such that the exposure pathway will be considered to be complete for each scenario.
The most health protective exposure scenario is to assume that an entire residential lot or yard has been covered with contaminated sludge. In order to calculate an estimated exposure dose for this residential exposure scenario, it is necessary to make assumptions about the exposure factors during which exposure to contaminated sludge could occur. The basis for this scenario is a 1/2 acre residential lot with uniform contamination over the entire area to a depth of two meters (7). Exposure occurs for 350 days per year. The exposure factors include the frequency and duration of exposure activities, as well as the specific rates of contaminant uptake (e.g., breathing and ingestion rates) during those activities. The exposure factors used in estimating the integrated dose for this assessment are primarily RESRAD default values which are similar to values from the Exposure Factors Handbook developed by the U.S. Environmental Protection Agency (EPA 1999) or from the EPA Soil Screening Guidance for Radionuclides (EPA 2002).
All intake rates used in this assessment are based on lifetime doses (70 years) for long term (30 year) exposures. Exposure to the contaminated sludge areas is assumed to occur for a 30 year period for several reasons. It has been approximately 30 years since the sludge was distributed to the Livermore community, and 30 years is the 95th percentile of residential occupation of a home (EPA 1999). Seventy years is a commonly used timeframe to assess lifetime doses (EPA 1999). With long-lived radionuclides, such as Pu 239, exposure to radioactive decay in the body occurs long after intake has stopped.
In some cases it may be important to consider intake rates and behaviors of children if childhood activities lead to potentially higher doses. In this case, childhood activities would only occur for a limited portion of the overall 70 year exposure duration. Also, the Pu 239 dose conversion factors specifically include provision of body and organ weights that are corrected for aging and growth. Additionally, the exposure scenarios assume activities such as gardening and outdoor workers that have very high soil exposure and intake rates. Consequently, the high intake rates, the Pu 239 dose conversion factors, and long exposure durations are protective of any potential exposures to children and adults.
Table 1. The duration and intake rates for potential exposures to Pu 239-contaminated sludge spread uniformly over an entire residential yard and garden. All exposure frequencies and intake rates are RESRAD defaults and similar to values from the Exposure Factors Handbook (EPA 1999).
|
Exposure Factors |
Intake Rates and Durations |
| Ingestion of soil | 70 year rate- 100 mg/day for 70 years |
| Inhalation of fugitive dust | Inhalation rate of 24 m3/day (8400 m3/yr) One half of lot is unvegetated (bare soil) Air/soil concentration ratio is 1.0e-4 g/m3* 68% of time is spent indoors (on site) 32% of time is spent outdoors (on site) Indoor air loading is 40% of outdoor air |
| Ingestion of food grown in home garden | 160 kg/year vegetable and fruit ingestion rate 14 kg/year leafy vegetable ingestion rate One half of all produce consumed is grown in home garden |
| Exposure Frequency | 350 days per year for 30 or 70 years (~4 % of time is spent off site) |
|
* The air/soil concentration ratio is the average mass loading of the airborne contaminated soil particles in g/m3. The default mass loading (1.0e-4 g/m3) is a conservative estimate that takes into account short periods of high mass loading and sustained periods of normal activity on a typical farm (ANL 2001). |
|
Estimated Doses from Pu 239/240 Contaminated Soil
The results of the RESRAD dose estimations are presented in Figure 2. This chart shows the combined dose for all nuclides and all pathways as 0.31 mrem/year for a time period of 1 to 70 years. This dose estimate assumes that an entire residential yard and garden are contaminated with Pu 239 and Pu 240 at a combined average concentration of 2.5 pCi/g. Consumption of plants (food crops) accounts for about 65% of the total dose, soil ingestion about 26% of the dose, and inhalation of dust accounting for about 6% of the dose (Figure A-2).
Figure 2. The annual Effective Dose Equivalent (whole
body; EDE) from a residential exposure scenario to an average soil Pu 239/240
concentration of 2.5 pCi/g is 0.31 mrem/year. This scenario assumes of annual
fruit, vegetable, and grain consumption comes from a home garden. The relative
contributions of the Pu 239 and Pu 240 components do not affect the total dose
as those nuclides have identical dose coefficients. The relative Pu 239 and
Pu 240 composition shown in this figure and Appendix 4 are based on average
compositions of weapons grade plutonium (NAS 1995).
Note that the estimated Pu 239 dose (Annual Effective Dose Equivalent; EDE) is constant over a 70 year time period. The effective dose equivalent from year one is the same as that from year 70. The output of the RESRAD model run is included as Appendix 4. The public health implications of a radiological dose of 0.31 mrem/year are discussed in the following "Public Health Implications" section. Following sections will evaluate this dose assessment with different concentrations of Pu 239 including the estimated maximum concentration based on measured gross alpha concentrations.
Maximum Pu 239 Concentrations in LWRP Sludge
As previously stated there are no isotope-specific measurements of Pu 239 in sludge that may have been distributed to the Livermore community in the 1967 to 1970 timeframe. However, there is a relatively complete record of monthly gross alpha measurements of sludge from the LWRP digester for the 1960 to 1969 period (CDPH data; CDHS 1960-1969). In addition, there are measurements of gross alpha concentrations in sewer effluent leaving the LLNL facility, gross alpha concentrations in digester and dried sludge, and estimates of annual gross alpha releases to the sewer system from LLNL. Gross alpha concentrations from several of these data sources are plotted in Figure 3. The data underlying this chart are included in Appendix 5.
The gross alpha concentrations in Figure 3 span the years from 1960 to 1973 and include monthly, 6-month, and annual averages for sludge from the digesters and drying beds (dried sludge). The values plotted in Figure 3 represent gross alpha concentrations as picoCuries per gram (pCi/g) for dried sludge from the digesters or drying beds, pCi/Liter (pCi/L) for liquid effluent data, and Ci/year for annual releases to the sewer system (on the right hand scale). The annual release value for 1973 is the specific Pu 239 concentration; values for all other years are gross alpha concentrations.
Figure 3 shows several significant trends related to historic gross alpha concentrations in sewage effluent (from LLNL) and gross alpha concentrations in the digesters and drying beds. The most significant trend is that the 1967 Pu 239 release is consistently tracked by all of the data types and it is obviously the most significant short or long term release event. Figure 3 shows that the 6 month average sewer effluent data and the annual release data both track the monthly digester sludge values. This indicates that the semi-annual or annual data averages capture and record a short term event, such as the May-June 1967 Pu 239 release.
Note that the digester sludge value from June 1964 is the highest CDPH digester sludge value (296.9 pCi/g). Also note that the sewer effluent and annual release values do record a release event in the 1964 timeframe, but that the effluent spike is only about 1/3 that of the 1967 event. Another important trend from the 1964-1965 timeframe is the relationship between the elevated effluent release and digester sludge values and the subsequent increase in the dried sludge gross alpha concentrations. Dried sludge gross alpha concentrations increase about 8 to 12 months after the May-June 1964 digester and effluent spikes.
This time lag represents the processing time required for LLNL effluent to be processed through the treatment plant and for placement of the resulting sludge in the drying beds. It is also important to note that, because of the time lag and the mixing and dilution that occur in the sewage processing, the gross alpha concentrations in the dried sludge are much lower than the digester concentrations. The May-June 1964 digester spike reaches gross alpha concentrations of 297 pCi/g while the maximum drying bed sludge values are only 60 pCi/g with a 10-12 month lag period.
Digester sludge concentrations decrease over several months after a release event, such as the May-June 1967 Pu 239 release. As shown in Figure 3, it takes about 6 to 8 months for digester concentrations to return to pre-release values. From high concentrations of 258 pCi/g in May 1967 and 229 pCi/g in June, monthly values decline relatively rapidly with concentrations less than 100 pCi/g by October 1967 and less than 50 pCi/g by January 1968. This 6 to 8 month decline in digester gross alpha concentrations reflects the dilution process that occurs within the digesters.
In addition to the gross alpha concentrations measured by CDPH, LLNL also collected and measured gross alpha concentrations in sludge from the LWRP digesters (1 and 2) and from the oxidation pond. In the LLNL annual or semi-annual environmental reports (LRL or LLL 1960-73) these values are reported as 6 month or annual average values. LLNL has recently re-calculated the monthly values that underlie the annual or semi-annual reported values (McConachie personal communication, January 28, 2003). These values are included in Appendix 5. The LLNL measured digester concentrations are not plotted on Figure 3 because we currently have a limited number of data points for the time period. We will continue to evaluate these data as they become available.
For the 1967 measurements, the LLNL gross alpha sludge values (the average of digesters 1 and 2) are larger than the gross alpha concentrations measured by CDPH. The June 1967 value measured by CDPH is 229 pCi/g while the LLNL value for the same month is 606 pCi/g (digester 1 and 2 average). It is not known if these differences are due to the way the samples are collected and composited (such as a combination of digester 1 and 2 samples or the time period over which the samples are composited), analytical procedures, or a combination of these and other factors. Although there are consistent differences in the absolute values of these measurements, both data sets show similar peaks and trends over time. Following references to specific digester sludge values will state whether the measurements were analyzed by the CDPH or by the LLNL.
The distribution of these gross alpha data values indicates that the release of Pu 239 into the LWRP sewer system is documented by measurements of gross alpha concentrations in digester sludge samples, sludge samples from the drying beds, and LLNL sewer effluent data. Because the measurement of gross alpha concentrations entails counting all alpha decays, it necessarily includes a variety of radionuclides, such as uranium, thorium, radium, and other alpha emitters. If the analysis process is accurately measuring gross alpha concentrations, the resulting gross alpha measurements are a health-protective estimate of Pu 239 concentrations.
Figure 4 presents one year (1973) of monthly digester gross alpha concentrations (analyzed by LLNL) and the relative proportions of Pu 239 and Pu 238 in that sludge. This figure shows that, during 1973, the Pu 239 concentrations in the LWRP digester represented about 2% to 4% of the overall gross alpha concentration. The gross alpha measurements are not a specific measurement of Pu 239 concentrations because typical gross alpha measurements detect all alpha decays (within a specified energy range). Gross alpha measurements within the energy range used at LLNL includes isotopes, such as uranium 235 and 238 in addition to Pu 239. Because Pu 239 has a higher radio-toxicity than the other common alpha decay nuclides, assuming that all alpha decays occur as Pu 239, is a health protective estimation of the total radiological concentration.
During a specific release of Pu 239 (such as the May 1967 release), the relative concentration of the Pu 239 will increase. For the 1967 release, most of the increase in the gross alpha concentration was probably due to Pu 239. However, the baseline contribution from other alpha-emitting radionuclides will still be present, such that the gross alpha concentrations will be a health protective estimate of the specific Pu 239 concentrations.
It should be further noted that, as shown in Figure 3, maximum Pu 239 (or gross alpha) concentrations in digester sludge will overestimate the Pu 239 concentrations in the sludge lagoons or drying beds. The sludge lagoons receive sludge for periods of a year or more for drying and mixing. Consequently, short periods of high concentration sludge will be mixed with a much greater volume of lower concentration sludge. Therefore, use of the maximum gross alpha concentrations of monthly maximum values from the sludge digesters as an indicator of maximum Pu 239 concentrations in processed sludge is very health protective. Any sludge that may have been distributed to the public would have had significantly lower Pu 239 concentrations as indicated by gross alpha concentrations of dried sludge (Figure 3).
Although this evaluation of gross alpha and Pu 239 concentrations in LWRP sludge cannot provide specific Pu 239 concentration values for LWRP sludge, it does provide a reliable upper limit on what those concentrations could have been. The maximum sludge Pu 239 concentrations could not have exceeded the gross alpha value of 674 pCi/g (as measured by LLNL) in digester sludge samples and were most likely lower than 100 pCi/g.
Average values in soils to which the sludge was added would necessarily be lower than sludge values. In the Myers et.al. (1976) study, the addition of 13 cubic meters (17 cubic yards) of sludge, with an average concentration of 2.8 pCi/g, resulted in a soil Pu 239 concentration of 0.43 pCi/g over an area of 170 square meters (203 square yards or 0.042 acres). Thirteen cubic meters represents about nine pick-up truck loads of sludge (at 50 cubic feet or 450 pounds per load). Assuming an average sludge concentration of 250 pCi/g, 54 pick-up truck loads of sludge would raise the average Pu 239 concentration in a acre residential yard to less than 50 pCi/g (or 108 truck loads for a acre lot). Using a more likely average sludge Pu 239 concentration of 25 pCi/g, more than 540 pick-up truck loads would be required to raise the average soil concentration to 5 pCi/g. A more reasonable volume of 5 pick-up truck loads of sludge at a concentration of 25 pCi/g would raise the average concentration of a acre yard to less than 0.05 pCi/g.
Figure 3. Gross alpha concentrations of digester sludge (monthly average values),
effluent from LLNL, dried sludge from LWRP drying beds, and LLNL annual releases
to sewer system. Sludge values are in pCi/g, sewer effluent values in pCi/L,
and annual releases in Ci/year (right hand scale). Annual releases for 1973
are Pu 239 specific values; all others are gross alpha. Data underlying the
chart are listed and the sources are referenced in Appendix 5.
Alternatively, if the sludge is not mixed with existing soil as an amendment, but is used as a cover material, it would take 108 pick up truck loads (50 cubic feet per load) to cover a 1/2 acre lot with 3 inches of sludge. The resulting sludge Pu 239 concentration would not be diluted by mixing, but would be at the average sludge concentration. Note that the above RESRAD dose estimates assume a acre lot with uniform contamination to a depth of 2 meters (~7 feet). Each of the above sludge usage scenarios is unlikely, but possible. As there is no way to precisely estimate how much sludge may have been added to a garden or yard, the following dose evaluations will evaluate possible radiological doses from several possible concentrations of Pu 239 in sludge and residential soil. These concentrations include Pu 239 values measured in sludge and soil samples, and the maximum possible values derived from digester sludge gross alpha concentrations.
Figure 4. Relative contributions of Pu 239 and Pu 238 to gross alpha concentrations
in monthly digester sludge samples for 1973. Data are from the 1973 annual environmental
report (LLL 1973). Overall, the Pu 239 constitutes between 2% and 4% of the
overall gross alpha concentration. The largest component of the gross alpha
concentrations are probably uranium isotopes which were not specifically analyzed.
The relative contribution of plutonium isotopes during this period represents
baseline conditions. During a specific release episode, such as the May-June
1967 release, the relative plutonium contribution will be much higher while
the baseline contribution of uranium and other radionuclides remains the same.
Note that the gross alpha concentration and percent contribution are on different
scales and that the concentration scale is logarithmic.
1 Plutonium will be present as several different isotopes. Typical weapons grade plutonium consists of about 94% Pu 239 and about 6% Pu 240 with much lower percentages of Pu 238, 241, and 242 (NAS 1995). Standard analyses using alpha spectroscopy will not differentiate between Pu 239 and Pu 240. However the dose conversions factors for the Pu 239 and Pu 240 isotopes are equal so that differences in the relative abundance will not change the resulting dose estimates. Due to the much higher proportion of Pu 239, this document will refer to combined Pu 239/240 measurements as Pu 239. A glossary of technical terms is included as Appendix 1.
2 The releases may have contained an unknown proportion of Am 241. In typical weapons-grade plutonium, Am 241 comprises less than 1 % of the activity (NAS 1995) and does not have a significant contribution in the resulting dose. This assessment will focus on Pu 239 as the primary dose constituent.
3 The gross alpha concentrations are originally reported in disintegrations per minute per gram (dpm/g). Liquid effluents are presented as dpm per liter. Dpm is converted to pCi using the following conversion factors. 1 dpm = 60 dps; 1 dps = 1 Bequerel; 1 Bequerel = 27 pCi.
4 Although we have no information on the historic CDHS, Bureau of Radiological Health gross alpha analytical procedures, there is no a priori reason to doubt the validity or utility of their data. We are currently trying to determine their specific procedures.
5 A pica child is a 2-3 year old child with a craving for unnatural food such as soil or ashes. Although the prevalence of this type of behavior is unknown, the EPA recommends that pica ingestion rates only be used for acute (1 to 14 day) exposure assessments (EPA 1999).
6 The default Pu 239 dose coefficients in RESRAD 6 are based on ICRP Publication 67 (1993). Those dose coefficients have been updated by use of values from ICRP Publication 72 (1996).
7 A acre residential lot is used as the basis for comparison and dose calculation because it is the area used as an underlying assumption in the derivation of the US EPA Preliminary Remedial Goal (PRG) of 2.5 pCi/g for Pu 239. A two meter depth is used to approximate the "infinite slab" assumption underlying the EPA PRG. A more detailed evaluation of the assumptions underlying the development of the PRG is included in Appendix 6.
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