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PUBLIC HEALTH ASSESSMENT
IMPERIAL REFINING COMPANY
ARDMORE, CARTER COUNTY, OKLAHOMA
EPA FACILITY ID: OK0002024099

Prepared by:

Superfund Site Assessment Branch

Division of Health Assessment and Consultation

Agency for Toxic Substances and Disease Registry

Table of Contents

Purpose and Health Issues

Background

Site Description
History
Demographics
Land and Natural Resource Use

Data Used
Evaluation Process
Imperial Refining Company Exposure Pathways and Contaminants of Concern

Waste Piles Pathway
Surface Water Pathway
Sediment Pathway
Soil Pathway
Biota Pathway
Physical Hazards

Potential Exposure Pathways

Well Water Pathway
Air Pathway

Child Health Initiative
Health Outcome Data
Community Health Concerns

Conclusions

Recommendations

Public Health Action Plan

Site Team

References

Appendix A. Explanation of Evaluation Process

Screening Process
Evaluation of Public Health Implications
Non-Cancer Health Effects
Calculation of Risk of Carcinogenic Effects

Appendix B. Exposure Pathways for Imperial Refining Company Site

Appendix C. ATSDR Plain Language Glossary of Environmental Health Terms

LIST OF TABLES

Table 1. Waste Source Contaminants Above Soil Comparison Values

Table 2. Surface Water Contaminants Above Comparison Values

Table 3. Sediment Contaminants Above Soil Comparison Values

Purpose and Health Issues

Imperial Refining Company was proposed for the National Priorities List (NPL) on May 11, 2000 and listed on July 27, 2000. The Agency for Toxic Substances and Disease Registry (ATSDR) is required by Congress to conduct public health assessments on all sites proposed to the NPL. In this public health assessment, ATSDR evaluates the public health significance of the Imperial Refining Company site. ATSDR has reviewed available environmental data and community health concerns to determine whether adverse health effects are possible. In addition, this public health assessment recommends actions to prevent, reduce, or further identify the possibility for site-related adverse health effects.

Background

Site Description

This site description comes in part from the Removal Assessment Report (May 1999) and the Site Inspection Narrative Report (July 1998) [1,2]. The Imperial Refining Company (IRC) site is located just northeast of Ardmore, Oklahoma. It covers approximately 80 acres on either side of Highway 142 about 50 yards north of the overpass crossing the Atchison, Topeka, and Santa Fe railroad tracks. The legal description of the property is the SE1/4 of the NE1/4 of Section 20, and the SW1/4 of the NW1/4 of Section 21, Township 4 South, Range 2 East, Carter County, Oklahoma. Initial site investigations only covered about 55 acres of the property, located northwest of the railroad tracks.

The IRC property is well vegetated with trees and moderate underbrush, except in several impacted areas which are covered with asphalt- or tar-like wastes. At least one waste area also contains several abandoned, partially crushed 55-gallon drums. The drums are rusty and appear to be empty. An intermittent stream and several wetlands areas are found on the property. Ponds on the site could have been highway fill "borrow pits" or reservoirs during operation of the refinery. The site is bounded by undeveloped property to the south and east. A small business, an active refinery, and a small residential area with about a dozen houses are located north of the site, and west of the property are several treatment lagoons for waste water from the active refinery. Access to the site is not restricted.

History

Imperial Refining Company was a crude oil refinery which operated on the site from 1917 to 1934, when it declared bankruptcy. All tanks and storage equipment were dismantled by 1948. The tank bottom materials were apparently dumped out onto the site soils during the dismantling. Although the property has changed ownership several times since the tanks and storage equipment were dismantled, there is no clear evidence of further operations occurring on the site.

Demographics

Figure 1 shows demographic information for the population of the area surrounding the Imperial Refining site. About 2250 people live within a one-mile radius of the site. The population within a one-mile radius of the site is mostly Caucasian (70%), African-American (14%), and American Indian (13%). According to the site assessment report, there are approximately 130 workers and residents within 200 feet of contaminated areas. Ardmore is a city of 26,000 to 28,000 people. [2]

Land and Natural Resource Use

The land surrounding the site is mostly rural or industrial. There is a small residential area of about a dozen houses approximately 200 to 300 yards north of the site. During a visit to the site area, evidence of hunting- a deer blind and tree stand- just north of the site was observed. Members of the public interviewed during a public availability session on the IRC site confirmed that hunting is common on the site. They also indicated that people fish in the ponds on the site, especially during the summer, and that children no younger than 10 to 12 years old are known to play on the site.

Farm animals, including cows and horses, were observed in the fields near the site. Various types of wildlife, including sensitive species, live on the site [2].

The intermittent stream that runs through the north side of the site joins Sand Creek, which flows towards the northeast for approximately four miles until it joins Caddo Creek [1]. These downstream creeks are used for wastewater discharge by the active refinery north of the site and by the city of Ardmore.

No domestic groundwater wells are located within a one mile radius of the site [2]. According to state officials, Ardmore's municipal water system supplies drinking water to people living in the residential area north of the site.

Discussion

Data Used

Two sets of data have been collected to characterize the Imperial Refining Company site. On May 20, 1998, Oklahoma Department of Environmental Quality (DEQ) sampled waste sources (surface samples analyzed were from 0 to 6 inches in depth), surface water, and sediment (0 to 6 inches in depth) on the site as part of the Site Inspection [2]. On February 23 and 24, 1999, contractors for the Region 6 Superfund Technical Assessment and Response Team (START) collected waste source samples at the site as part of a Removal Assessment [1].

The data collected were part of the initial characterization of the wastes and highly impacted areas of the site. While this data gives useful information about site contaminants, it does not fully describe all the exposure pathways of potential concern. The conclusions reached in this document are based on the data available at the time and may be modified based on the results of additional samples that will be collected during the remedial investigation process.

Evaluation Process

The process by which ATSDR evaluates the possible health impact of contaminants is summarized here and described in more detail in Appendix A. ATSDR uses comparison values to determine which chemicals to examine more closely. Comparison values are concentrations of chemicals in the environment (air, water, or soil) below which no adverse human health effects should occur. Exceeding a comparison value does not mean that health effects will occur, just that more evaluation is needed.

If the level of contamination at the site is greater than the comparison value, further evaluation will focus on identifying which chemicals and exposure situations could be a health hazard. Child and adult exposure doses are calculated for the exposure scenario of interest. The exposure dose is the amount of a contaminant that gets into a person's body. These exposure doses are compared to appropriate health guidelines for that chemical. Health guideline values are considered safe doses; that is, health effects are unlikely below this level. If the exposure dose for a chemical is greater than the health guideline, then the exposure dose is compared to known health effect levels identified in ATSDR Toxicological Profiles. If the chemical of concern is a carcinogen, the cancer risk is also estimated. These comparisons are the basis for stating whether the exposure is a health hazard.

Imperial Refining Company Exposure Pathways and Contaminants of Concern

The following sections describe the various ways people could come into contact with contaminants at the Imperial Refining site. Each of these is known as an exposure pathway. A summary of the possible exposure pathways is given in Appendix B. If it is unlikely for anyone to be exposed to contaminants in a given pathway, then that pathway will not be evaluated further for human health risks.

Waste Piles Pathway

Several impacted areas on the site are covered with black, asphalt- or tar-like waste material; these will be referred to as source areas. People trespassing on the site for hunting, fishing, or other purposes could come into direct contact with these contaminants. People could get particles of the material on their skin, or they might accidentally eat or breathe in the particles.

To be conservative, our initial screening assumed that people will contact the source areas as much as they would the soil. Table 1 lists the contaminants that were found in the wastes on-site at levels above soil comparison values.

Table 1. Waste Source Contaminants Above Soil Comparison Values

Next, exposure doses were calculated for the contaminants of concern in Table 1. The worst case was assumed to be a ten-year-old (36.3 kg average [3]) contacting the maximum concentration of each contaminant all day for 52 days out of the year (once a week). The exposure dose estimated through this procedure was compared with health guideline values and toxicological information for the contaminant of concern. For evaluating the risk of cancer, we assumed adults weighing 70 kg would be exposed to the maximum concentration of each contaminant for 52 days a year for a lifetime (70 years). The following sections describe this evaluation for the contaminants of concern from Table 1.

Arsenic

No health effects are expected from current exposure to the arsenic detected in the waste piles on the site. The estimated exposure dose for arsenic was found to be thirty times smaller than the chronic oral minimal risk level (MRL) for arsenic [4]. The MRL, an ATSDR health guideline value, is a dose of a chemical that is unlikely to cause an adverse, noncancerous health effect.

Arsenic has been shown to cause cancer, based on human studies [4]. However, based on the low levels of arsenic in the source areas and the low exposure doses, the chance of an increased risk of cancer from this exposure is negligible.

Lead

Exposure to lead in the source areas on this site is not likely to result in health effects. This is based on the maximum levels of lead detected and the assumption that older children only occasionally play or trespass on the site. If young children (less than 6 years old) had daily contact with the waste piles, the lead could pose a health hazard. However, it is very unlikely that a small child would be playing on the waste piles long enough to ingest appreciable amounts of dirt. Older children (and adults) are less vulnerable to lead in the soil than small children because they generally ingest less soil and less lead is absorbed into their bodies [5].

In general, the level of lead in a person's blood is a good measure of recent exposure to lead and also correlates well with health effects. If we use the most protective correlation between blood lead levels and soil concentration found in epidemiological studies (0.0068 g/dL per PPM) and the maximum lead concentration measured in soil, then a person exposed to this soil could increase their blood lead levels by 4.9 g/dl [5]. The Centers for Disease Control and Prevention (CDC) considers children to have elevated lead levels if the amount of lead in the blood is 10 g/dl or above. However, some studies have indicated that levels of 10 g/dl and less in children's blood may be associated with small decreases in IQ and slightly impaired hearing and growth. Any increase in blood lead level from exposure to the Imperial Refining site is likely to be much smaller than the 4.9 g/dl value. This is because the exposure to the whole site is infrequent, a child probably would not play exclusively on the waste piles, and the maximum concentration of lead was used to make our estimate.

Animal data indicate that lead is a probable human carcinogen [5]. However, the animal studies were based on very high doses of lead and are difficult to compare to low level environmental exposures, such as at Imperial Refining. Since there is no cancer slope factor for lead, it is not possible to quantitatively evaluate carcinogenic risk.

2-Methylnaphthalene

The estimated exposure dose for 2-methylnaphthalene was found to be more than two hundred times lower than the chronic oral MRL for 1-methylnaphthalene, a compound expected to behave like 2-methylnaphthalene [6]. No health effects are expected from this exposure.

Polycyclic Aromatic Hydrocarbons (PAHs)

The remaining contaminants from Table 1 are considered together as polycyclic aromatic hydrocarbons (PAHs). These individual PAHs often occur together in the environment, and many have similar toxicological effects and environmental fate [7]. PAHs are a group of chemicals that are formed during the incomplete burning of coal, oil, wood, or other organic substances, such as tobacco or charbroiled meat. They can also be found in crude oil and creosote. Low levels of PAHs are found throughout our environment in the air, water, and soil.

At the Imperial Refining site, adults or children who come into contact with the waste piles may get additional PAHs into their bodies by accidentally eating the soil (oral exposure) or by getting the contaminated soil on their skin (dermal exposure). Unlike some other compounds such as lead, significant amounts of PAHs can be absorbed through a person's skin. Breathing in PAH-contaminated dust from the site does not appear to be a significant source of exposure at this point, since the tar-like waste in the source areas is not crumbling into small particles.

For non-cancer health effects, the exposure doses were calculated from the maximum levels of PAHs (listed in Table 1). These estimated exposure doses for this site are over a thousand times smaller than effect levels seen in animal experiments on various PAHs. Therefore, no noncancer health effects are expected for ingestion of or dermal exposure to PAHs from the source areas, assuming the current infrequent use of this site.

There is evidence that some PAHs may cause cancer in humans. This evidence comes primarily from occupational studies of workers who were exposed to mixtures of PAHs as a result of their involvement in such processes as coke production, roofing, oil refining, or coal gasification. The associated cancer occurred predominately in the lungs, following inhalation exposure, and in the skin, following dermal exposure. Certain PAHs have also been shown to cause cancer in animals.

In order to estimate the increased risk of cancer from this group of PAHs, a relative potency approach has been developed for carcinogenic PAHs based on benzo(a)pyrene, the most studied PAH compound [7]. Using the maximum concentration of PAHs found at the site and assuming weekly contact with the contaminated source areas over many years results in an estimated low to moderate increase in the risk of cancer. This is likely an overestimate of the current cancer risk because of the conservative (i.e., protective) exposure assumptions we used. Also, people are not expected to frequently contact the maximum concentration every time they are on the site. When more sampling data are available for the Imperial Refining site, we can make a better estimate of the average concentration of PAHs that a person may contact in the soil and source areas.

If the use of the site changes in the future and people have increased exposure to the PAHs in the waste piles, then the risk of developing cancer will increase. ATSDR recommends limiting additional exposure by restricting access to the site until the site is remediated.

Surface Water Pathway

Water from surface runoff, streams, and ponds on the site comes in contact with the waste material. No use of this water for drinking water purposes was identified, but people who hunt, fish, or otherwise trespass on the site may accidentally ingest some of the surface water or get it on their skin.

A limited number of surface water samples (4) were collected during the site investigation. As shown in Table 2, one contaminant (chloroform) was present above the drinking water comparison value in these samples.

Only one of the four samples detected chloroform; the positive sample was taken from a wetland on the western central portion of the site. Estimated exposure of a ten-year old child (36.3 kg average [3]) who accidentally ingests this surface water 52 times a year (once a week) is more than ten times lower than the minimal risk level [8]. Health effects are not expected to occur due to exposure to chloroform at this level. Chloroform is a probable human carcinogen. However, the calculated increased cancer risk from exposure to the highest level of chloroform in Table 2 is negligible.

Sediment Pathway

People who hunt, fish, or otherwise trespass on the site may accidentally ingest some of the sediments from the ponds or streams on the site or get them on their skin. To be conservative, our initial screening assumed sediments would be contacted like soil particles. Table 3 lists the eight contaminants that were found at levels above soil comparison values in the sediments on site.

Table 3. Sediment Contaminants Above Soil Comparison Values

Next, exposure doses were calculated for the contaminants of concern in Table 3. The worst case was assumed to be a ten-year-old contacting the maximum concentration of each contaminant for about half a day for 52 days out of the year.

For this scenario, the exposure doses estimated for sediment are at least ten times smaller than exposure doses estimated for the source areas. The estimated exposure doses are well below the MRLs for arsenic and PAHs. At these concentrations, the increased risk of developing cancer is very low. Therefore, no health effects are expected from exposure to the sediment.

Soil Pathway

People trespassing on the site for hunting, fishing, or other purposes could come into contact with soil contaminated by the source areas. People could get soil particles on their skin, or they might accidentally eat or breathe in the soil. There is no data on contaminant levels in soil at this time; only the source areas have been sampled. It is assumed that the soil contamination is no greater than source area contamination. However, it is possible that not all source areas have been discovered, and additional soil contamination may exist. Therefore, any potential impact to public health cannot be determined until further investigation and/or additional sampling is conducted.

Biota Pathway

Hunting and fishing takes place on the site. Hunters, fishers, and their families may consume animals and fish that may have bioaccumulated contaminants from the wastes and sediments on the site. No data on contaminant levels in fish and animals from the site have been collected. There was little vegetation growing directly on the source areas, and it is therefore unlikely that animals could accumulate appreciable amounts of contaminants through eating vegetation. Based on the sediment data available, it is unlikely that fish would be affected to a large degree by contaminants. However, further characterization of the site may indicate that testing of fish tissue is warranted.

Physical Hazards

The site contains physical hazards which warrant restricting access. The rusted, partially crushed drums could have sharp edges, and areas with large quantities of broken glass were observed. A complete site characterization has not been performed as of the writing of this report, so other materials on site may also pose physical hazards.

Potential Exposure Pathways

Well Water Pathway

Contaminants from the source areas could infiltrate into the groundwater beneath the site. If people used this groundwater for drinking, they could be exposed to contaminants. According to the Site Inspection Report [2], there are no private drinking water wells within one mile of the site. This pathway will not be evaluated further because the current information indicates that no one is drinking groundwater near the site. If the well survey to be performed in conjunction with the remedial investigation shows wells have recently been installed near the site, we will evaluate this pathway at that time.

Air Pathway

Contaminants may volatilize from the source area, or particles may be transported as fugitive dust. People could breathe in these contaminants or get them on their skin. There is no data on air contaminants from the Imperial Refining site. Based on the current conditions at the site and the source area makeup, it is extremely unlikely that contaminants are being transported through this pathway. The main contaminants in the source areas are not very volatile, and the source areas do not appear to crumble into small enough particles to create dust.

Due to the age of the contamination, more volatile contaminants were probably released in the past. While people could have been exposed to these contaminants, the rural nature of the area suggests that exposure was not great or frequent enough to significantly affect people's health.

Child Health Initiative

ATSDR recognizes that infants and children may be more vulnerable to exposures than adults in communities faced with contamination of their air, water, soil, or food. This vulnerability is a result of the following factors:

• Children are more likely to play outdoors and bring food into contaminated areas.
• Children are shorter, resulting in a greater likelihood to breathe dust, soil, and heavy vapors close to the ground.
• Children are smaller, resulting in higher doses of chemical exposure per body weight.
• The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages.

Because children depend completely on adults for risk identification and management decisions, ATSDR is committed to evaluating their special interests at the Imperial Refining Company site as part of the ATSDR Child Health Initiative.

The major exposure route for children living near the Imperial Refining Company NPL site is ingestion of surface soil. Please refer to the appropriate section for discussion of the health effects that are possible for these children.

Health Outcome Data

The Superfund law requires that health outcome data be considered in a public health assessment. Health outcome data may include mortality information (e.g., the number of people dying from a certain disease) or morbidity information (e.g., the number of people in an area getting a certain disease or illness). In order to thoroughly evaluate health outcome data as it relates to a hazardous waste site, the following elements are necessary: (1) the presence of a completed human exposure pathway, (2) sufficiently high contaminant levels to result in measurable health effects, (3) sufficient number of people in the completed pathway for the health effect to be measured, and (4) a health outcome database in which disease rates for populations of concern can be identified.

The Imperial Refining site does not meet the requirements for including an evaluation of health outcome data in a public health assessment. While there are completed human exposure pathways at this site, the contaminant levels, exposures, and exposed population are not great enough to result in a meaningful measurement of health outcome data.

Community Health Concerns

On January 24, 2001, ATSDR had a public availability session in Ardmore. The meeting was attended by approximately 5 residents of Ardmore, as well as several officials from city, state, and federal organizations. The community voiced only one concern regarding human health in the area and it is summarized below:

Concern: About 3-4 years ago, during a summer night, a strong odor was coming from the area of the Imperial Refining site. It smelled like rotten eggs, but did not seem to be coming from the refinery treatment ponds (located west of the Imperial Refining site). Also at this time, a welding torch flared up, like there was something flammable in the air. This occurred about a quarter mile south of the site.

Response: Of course, at this point in time, it is very difficult to determine the true cause of the past odor. But we do use past information like this to help us evaluate site conditions and, when appropriate, direct future sampling efforts. Observations about the site are always appreciated.

A rotten egg smell usually indicates hydrogen sulfide in the air. Hydrogen sulfide is a colorless, flammable gas and is found naturally or may be produced from man-made processes. It is often the result of bacteria breaking down organic matter. This could occur in sewage treatment plants or in wetlands. Since hydrogen sulfide is found in crude petroleum, refineries may also be a source of this compound.

Because hydrogen sulfide gas is heavier than air, it is possible that the gas collected in a low area downwind of the source. People are very sensitive to hydrogen sulfide and can smell it at low concentrations (around 0.5 parts of gas per billion parts of air). At higher concentrations, it can be irritating to your eyes and throat or cause even more serious health problems. Since this situation was out in the open, it is unlikely that any gas present could build up to very high concentrations. The citizen reporting this odor did not describe any health problems resulting from it.

A welding torch flaring up could result from a number of conditions, including something with the welding operation itself. If an outside gas was the cause, it could be another naturally occurring gas, methane. Methane is also produced by bacteria breaking down organic material, such as in landfills or sewage plants. When large amounts of methane are produced, it can pose an explosive hazard if it collects in confined spaces. Methane is an odorless gas and is not otherwise considered toxic or harmful. For the situation described by the citizen, again, it is impossible for us to determine years later exactly what caused the flare up.

Conclusions

1. Based on the available environmental data and the limited use of the site, the Imperial Refining Company does not pose a health hazard to citizens at this time. This is categorized by ATSDR as "no apparent public health hazard". However, changing exposure scenarios, such as residential development of the site or the addition of a playground, could alter this conclusion.

2. The site is not sufficiently characterized regarding contaminant levels. Further information on contaminant types and levels in soils may modify the above conclusion.

3. There are physical hazards on the site.

4. Off-site contaminant migration has not been determined for the site.

Recommendations

• ATSDR recommends that contamination at the site be fully characterized. This should include measuring contamination in the soil, soil gas, shallow groundwater, surface water, and sediment. Based on the surface water and sediment findings, fish tissue sampling may be warranted.
• Until the site is fully characterized and to prevent injury from the physical hazards at the site, ATSDR recommends restricting access through such actions as fencing or posting. Proposed land uses should be reviewed for public health impact.
• ATSDR recommends that off-site migration of site contamination, if any, be characterized.

Public Health Action Plan

The Public Health Action Plan for the Imperial Refining Company NPL Site contains a description of actions to be taken by ATSDR at the site after the completion of this public health assessment. The purpose of the Public Health Action Plan is to ensure that this public health assessment not only identifies public health hazards, but provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. Included is a commitment on the part of ATSDR to follow up on this plan to ensure that it is implemented. The public health action to be implemented is as follows:

• A fact sheet on the site and the findings of this public health assessment will be developed and distributed to citizens living near the site.
• Additional environmental sampling results for the site will be reviewed as needed, and the possible public health implications will be evaluated.

ATSDR will reevaluate and expand the Public Health Action Plan when needed. New environmental, toxicological, or health outcome data or the results of implementing the above proposed actions may determine the need for additional actions at this site.

Site Team

References

• Ecology and Environment. Removal Assessment Report for Imperial Refining Company. Prepared for the U.S. Environmental Protection Agency, Region VI. Dallas, TX: May 1999.
  
  
• Oklahoma Department of Environmental Quality. Site Inspection Narrative Report. Oklahoma City, OK: July 1998.
  
  
• US Environmental Protection Agency. Exposure factors handbook. Washington, DC: US Environmental Protection Agency. Office of Research and Development. EPA/600/C-99/001: February 1999.
  
  
• Agency for Toxic Substances and Disease Registry. Toxicological profile for arsenic: update. Atlanta: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2000.
  
  
• Agency for Toxic Substances and Disease Registry. Toxicological profile for lead: update. Atlanta: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1999.
  
  
• Agency for Toxic Substances and Disease Registry. Toxicological profile for naphthalene: update. Atlanta: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1995.
  
  
• Agency for Toxic Substances and Disease Registry. Toxicological profile for polycyclic aromatic hydrocarbons (PAHs): update. Atlanta: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1995.
  
  
• Agency for Toxic Substances and Disease Registry. Toxicological profile for chloroform: update. Atlanta: US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1997.
  
  

Appendix A. Explanation of Evaluation Process

Screening Process

In evaluating these data, ATSDR used comparison values to determine which chemicals to examine more closely. Comparison Values (CVs) are the contaminant concentrations found in a specific media (air, soil, or water) and are used to select contaminants for further evaluation. CVs incorporate assumptions of daily exposure to the chemical and a standard amount of air, water, and soil that someone may inhale or ingest each day.

As health-based thresholds, CVs are set at a concentration below which no known or anticipated adverse human health effects are expected to occur. Different comparison values are developed for cancer and non-cancer health effects. Non-cancer levels are based on valid toxicologic studies for a chemical, with appropriate safety factors included, and the assumption that small children (22 pounds) and adults are exposed every day. Cancer levels are the media concentrations at which there could be a one in a million excess cancer risk for an adult eating contaminated soil or drinking contaminated water every day for 70 years. For chemicals for which both cancer and non-cancer numbers exist, the lower level is used to be protective. Exceeding a comparison value does not mean that health effects will occur, just that more evaluation is needed.

CVs used in this document are listed below:

Environmental Media Evaluation Guides (EMEGs) are estimated contaminant concentrations in a media where non-carcinogenic health effects are unlikely. The EMEG is derived from US Agency for Toxic Substances and Disease Registry's (ATSDR's) minimal risk level (MRL).

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrations that would be expected to cause no more than one additional excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors (CSFs).

EPA Soil Screening Levels (SSLs) are estimated contaminant concentrations in soil at which additional evaluation is needed to determine if action is required to eliminate or reduce exposure.

Evaluation of Public Health Implications

The next step is to take those contaminants that are greater than the comparison values and further identify which chemicals and exposure situations are likely to be a health hazard. Child and adult exposure doses are calculated for the site-specific exposure scenario, using our assumptions of who goes on the site and how often they contact the site contaminants. The exposure dose is the amount of a contaminant that gets into a person's body. The following is a brief explanation of how we calculated the estimated exposure doses for the Imperial Refining site.

Source Area Contaminant Ingestion

Exposure doses for ingestion of contaminants from the source areas were calculated in the following manner. The maximum concentration measured in the source areas, in mg/kg (or PPM), was multiplied by the soil ingestion rate for adults, 0.0001 kg/day, or children, 0.0002 kg/day. The multiplication product was divided by the average weight for an adult, 70 kg (154 pounds) or a ten-year old child, 36.3 kg (80 pounds). The resulting dose was then multiplied by a factor of 52/365, because the exposure was assumed to occur on average of once a week throughout the year.

Surface Water Ingestion

Exposure doses for surface water ingestion were calculated in the following manner. The maximum concentration for a surface water contaminant, in milligrams per liter (mg/L), was multiplied by an incidental surface water ingestion rate of 0.02 liters/day for adults or 0.01 liter/day for children. These ingestion rates are 1/100th of the EPA default drinking water rates. The multiplication product was divided by the average weight for an adult, 70 kg (154 pounds), or for a ten-year old child, 36.3 kg (80 pounds). The resulting dose was then multiplied by a factor of 52/365, because the exposure was assumed to occur on average once a week throughout the year.

Sediment Ingestion

Exposure doses for ingestion of contaminants from the sediment were calculated in the following manner. The maximum concentration measured in the sediment, in mg/kg (or PPM), was multiplied by one-tenth of the soil ingestion rate, 0.00001 kg/day for adults or 0.00002 kg/day for children. The multiplication product was divided by the average weight for an adult, 70 kg (154 pounds) or a ten-year-old child, 36.3 kg (80 pounds). The resulting dose was then multiplied by a factor of 52/365, because the exposure was assumed to occur on average once a week throughout the year.

Dermal (Skin) Exposure

Dermal absorption depends on numerous factors including the area of exposed skin, anatomical location of exposed skin, length of contact, concentration of chemical on skin, chemical-specific permeability, soil adherence, medium in which the chemical is applied, and skin condition and integrity. Because chemicals differ greatly in their potential to be absorbed through the skin, each chemical needs to be evaluated separately and is discussed as needed in the main body of the public health assessment. The assumed exposure frequency and duration for contact with the soil, sediment, and surface water is the same as used above for the ingestion route. The skin surface area and soil-to-skin adherence factors used in this public health assessment were taken from EPA's Exposure Factor Handbook ⁽¹⁾. Absorption factors and other chemical-specific factors were taken from the ATSDR toxicological profile for that chemical.

The calculated exposure doses are then compared to an appropriate health guideline for that chemical. Health guideline values are considered safe doses; that is, health effects are unlikely below this level. The health guideline value is based on valid toxicologic studies for a chemical, with appropriate safety factors built-in to account for human variation, animal-to-human differences, and/or the use of the lowest adverse effect level. For non-cancer health effects, the following health guideline values are used.

Minimal Risk Level (MRLs) - developed by ATSDR

An estimate of daily human exposure - by a specified route and length of time - to a dose o