SURFACE SOIL CONTAMINATION
EASTERN MICHAUD FLATS CONTAMINATION
POCATELLO, BANNOCK COUNTY, IDAHO
The Eastern Michaud Flats Contamination NPL site is located west of Pocatello, Idaho (1-3). Two manufacturing facilities, FMC Elemental Phosphorus Plant and Simplot Don Plant, are located on the NPL site (see Appendix A, Figure 1 for location map).
The FMC facility, FMC Elemental Phosphorus Plant, covers an estimated 1,189 acres and adjoins the western boundary of the Simplot Don Plant (2). Approximately 560 people are employed at the FMC Elemental Phosphorus Plant. Elemental phosphorus production at the facility has changed little since the plant operations began in 1949. Phosphate-bearing shale is shipped to FMC via the Union Pacific Railroad during the summer months. Ore cannot be shipped during the winter months because the ore tends to freeze in the rail cars. Therefore, the ore is stockpiled at the facility. Ore from the stockpiles is processed in four electric arc furnaces. The furnace reaction yields gaseous elemental phosphorus in addition to by-products, some of which contain radiological components. The elemental phosphorus is subsequently condensed to a liquid state and eventually shipped off-site. Approximately 1.5 million tons of ore are processed at the plant annually. The disposal of by-product waste material at and around the facility has resulted in slag piles covering large areas of land. In addition, air emissions (fugitive and direct discharges) from the facility have contributed to the environmental contamination associated with the Eastern Michaud Flats Contamination NPL site (1).
The Simplot Don Plant covers approximately 745 acres and adjoins the eastern property boundary of the FMC facility (2). Around 460 people work at the Simplot Don Plant. The plant began production of single superphosphate fertilizer in 1944. In 1954, the facility began producing phosphoric acid. The phosphoric acid is presently produced by using a wet (aqueous) process. Formerly phosphate ore was transported from the mines to the facility via rail. As of September 1991, the Simplot plant receives phosphate ore through a slurry pipeline. The phosphate ore slurry is processed at the Simplot Don Plant in phosphoric acid reactors and then further processed into a variety of solid and liquid fertilizers. The plant produces 12 principal products, including five grades of solid fertilizers and four grades of liquid fertilizers. The disposal of by-product waste material (e.g., gypsum) at and around the facility and air emissions (fugitive and direct discharges) from the facility have contributed to the environmental contamination associated with the Eastern Michaud Flats Contamination NPL site (1).
Both facilities are not located near any large populations centers. The nearest residence is approximately one mile north of the facilities (1-3). The plant boundaries are fenced. Representatives of FMC and Simplot have told ATSDR that trespassers are rarely found on their facilities. In addition, the land directly across US 30 from the plants is predominantly owned by either FMC or Simplot (see Appendix A, Figure 2). Deed restrictions to prevent future residential development have or will be placed on the properties across from the plants. Currently some of the land across US 30 is used for a drag racing strip (the old airport runaway) and for a softball/baseball field (on Simplot property).
During the Remedial Investigation (RI) for this NPL site, an extensive surface soil sampling and analysis program was undertaken (2). Composite samples of the raw materials and major waste products were taken. Surface soil samples were taken at various locations throughout the facilities. In addition, surface soil samples were taken off the facility properties (16 equally spaced transects with samples collected at regular intervals within a three mile radius). Supplemental samples of surface soil north of the facilities were also collected.
Tables 1, 2, and 3 summarize the results of the RI. The highest surface soil contamination was
found at the two plants. The highest surface soil contamination found beyond the FMC or
Simplot facility fence lines was on the land directly across US 30 from the plants (the land is
presently owned by either FMC or Simplot) (2). The pattern of surface soil contamination found
beyond the FMC or Simplot facility fence lines is coincident with the prevailing wind patterns
(i.e., the highest contamination was found northeast and northwest of the facilities). In addition,
the surface soil contamination decreases with distance from the facilities (2). Analytical results of
samples taken from residential areas are either at or below background levels or comparison
values (i.e., there is no site-related contamination at levels of health concern within residential areas).
There are two separate groups of people who may come in contact with site-related contaminants (the general public including children and workers at the FMC and Simplot facilities). Each of these groups' potential for exposure to site-related contaminants and potential for adverse health effects will be discussed separately.
For the following reasons, it is very unlikely that children or the general public would come in contact with site-related surface soil contamination for a sufficient amount of time (a significant portion of a lifetime continuously -- 20 years) to result in any adverse health effects: no residences are located next to the two facilities, people rarely trespass onto the facilities, those people who do trespass are at the facilities for only short periods of time, and that analytical results of surface soil samples taken at some distance from the facilities indicate that there is no surface soil contamination at levels of health concern within residential areas. In addition, people who attend or participate in the drag racing and softball/baseball activities directly across the street from the two facilities are unlikely to come in contact with a significant amount of surface soil contaminants. None of the contaminants found at or near the drag strip or the ball field are high enough to cause acute health effects (health effects that may occur after only a brief contact with contaminated surface soil).
Workers at the two facilities are the only people who may come in contact with a significant amount of surface soil contamination. There is very little vegetation covering the soil at the facilities (this is not an uncommon situation for these type of facilities). Therefore, the surface soil contamination is mobile and available for people to inhale or ingest (wind blown dust and direct transfer to clothes and hands).
Although arsenic, beryllium, and lead were found above comparison values, it is unlikely that adverse health effects would occur because the highest levels of contamination were found at discrete areas (e.g., lead was only found in one sample above comparison values). It is unlikely that workers would ingest enough contaminated soil or inhale enough contaminated dust over the amount of time required to result in any adverse health effects (e.g., 100 grams of contaminated soil per day for several years) (4-6). It is important to note that the comparison values used to develop Tables 1, 2, and 3 assume that upon ingesting contaminated soil or inhaling contaminated dust, 100% of the contaminant is absorbed into the body. However, scientific literature clearly demonstrates that less than 50% of the ingested metal contaminants associated with soil (i.e., arsenic, beryllium, and lead) are absorbed into the body (4,5,6). In addition, comparison values have built-in safety factors which lower the values by 100 to 10,000 times below concentrations known to cause adverse health effects in animals or humans. The actual amount (dose) of site-related arsenic, beryllium, and lead (excluding any exposures directly related to job duties) that a worker may ingest or inhale is below that which has been observed to cause adverse health effects in humans or animals.
Fluoride was detected above the comparison value for surface soil (35,000 milligrams of fluoride per kilogram of soil [mg/kg]) at both facilities. The maximum concentration found at the FMC and Simplot facilities is 221,000 mg/kg and 123,000 mg/kg, respectively (2). According to the EPA Risk Assessment for this NPL site, the average fluoride surface soil concentration at the two facilities is 16,868 mg/kg (7). Assuming that a 70 kilogram (kg) adult ingests 100 milligrams (mg) of soil per day (incidental ingestion by hand to mouth activities and the clearing of contaminated dust particles from the respiratory tract) and that 100 percent of the fluoride is bio-available, the exposure dose to a worker ranges from 0.32 milligrams of fluoride per kilogram of body weight per day (mg/kg/day), worse case situation, to 0.0241 mg/kg/day, an average situation. These doses are below the levels of exposure shown to have resulted in adverse human health effects (0.48 mg/kg/day -- increased non-vertebral fracture rate in osteoporotic women) (8). Therefore, it is unlikely that any adverse human health effects would occur because of exposure to site-related fluoride.
Cadmium was detected at very high levels at the facilities (particularly at the FMC facility -- upwards of 5,110 mg/kg with an average of approximately 740 mg/kg) (2). Although EPA has designated cadmium as a probable human carcinogen via inhalation (Group B1 --occupational and animal studies indicate that inhaling cadmium fumes or aerosols could result in an increased risk of lung cancer ), it is doubtful that workers exposed to cadmium contaminated surface soil would inhale a sufficient amount of cadmium into their lungs that would result in an increased risk of lung cancer. The particle sizes of surface soil are probably too large to be deposited into the lung (the inhaled soil dust would either not enter the lungs in the first place or would be removed from the lungs by the various filtering and clearing mechanisms that function in the human body).
However, workers may ingest a significant amount of cadmium contaminated surface soil (either by hand to mouth habits or via the clearing of inhaled soil dust from the respiratory tract). The worst case theoretical dose (assuming a 70 kg person ingests 100 mg of contaminated soil per day, 100% bio-availability, and 5,110 mg/kg of cadmium in the surface soil) indicates that a worker could receive as much as of 0.0073 mg/kg/day of cadmium. A worker exposure of 0.001 mg/kg/day could occur if the average concentration of cadmium found at FMC is used. These theoretical doses are above the minimum risk level (MRL) of 0.0007 mg/kg/day established by ATSDR (9). The ATSDR MRL is based on a lifetime (greater than 20 years) threshold for proteinuria (proteins found in the urine because of damage to the kidneys) caused by dietary cadmium intake in residents of cadmium-polluted areas of Japan. The current average dietary intake of adult Americans is approximately 0.0004 mg/kg/day and smokers receive an addition 0.0004 mg/kg/day from cigarettes (9). Based upon these fact, workers who smoke may already be exceeding the threshold for chronic cadmium-related kidney damage. Smoking workers employed at FMC for 20 years or more and who ingest cadmium contaminated surface soil may be at increased risk. The workers of particular concern are those that perform most of their duties outside (i.e., slag and maintenance workers -- <50 workers) (2,7).
Elevated levels of radiation (gross alpha, beta, and gamma) have been detected in surface soil at both facilities (2). The highest levels of radiation are associated with the slag and gypsum. Usually only a few workers may come in contact with or near the slag and gypsum. These waste materials are generally handled via mechanical means (i.e., slurry pipeline and frontend loaders with enclosed cabs at Simplot, frontend loaders and haul trucks with enclosed cabs at FMC) (2,7). These material handling procedures tend to shield the worker from radiation and reduce the amount of radioisotopes that the worker may ingest or inhale. Gamma radiation exposure studies conducted at both facilities indicate that the workers are not being exposed to an excessive amount of gamma radiation (2). Depending upon work practices (e.g., amount of dust generated and personal protection devices use) and personal hygiene habits (e.g., how often hands are washed), slag or gypsum pile workers may inhale or ingest surface soil containing elevated gross alpha and beta radiation. This may increase the cancer risk of slag or gypsum pile workers (<50 workers) (10,11).
The surface soil contamination at the facilities is a potential reservoir of contaminants that could migrate into groundwater or surface water. Therefore, it may be prudent to remediate surface soil contamination in order to protect groundwater and surface water resources even though the surface soil contamination may not be at levels that pose a public health concern.