CONTRA COSTA COUNTY SIERRA-CRETE TASK FORCE HUMAN HEALTH RISK ASSESSMENT OF SIERRA-CRETE

Transcription

1 CONTRA COSTA COUNTY SIERRA-CRETE TASK FORCE HUMAN HEALTH RISK ASSESSMENT OF SIERRA-CRETE Volume V. Exposures to Current and Future Residents During Road Maintenance Prepared by: ENVIRON International Corporation Marketplace Tower 6001 Shellmound Street, Suite 700 Emeryville, California Prepared for: Contra Costa County Sierra-Crete Task Force* * The Contra Costa County Sierra-Crete Task Force includes representatives from the Contra Costa County Health Department, Contra Costa County Public Works Department, Contra Costa County Office of the County Administrator, Contra Costa County District V Office, Contra Costa County District III Office, California Department of Toxic Substances Control, California Department of Health Services, Central Valley Regional Water Quality Control Board, the Cities of Antioch, Brentwood, Oakley, and Pittsburg, DuPont, and other interested parties. February 28, 2003

2 HUMAN HEALTH RISK ASSESSMENT OF SIERRA-CRETE i Preface Contents Background Organization of this Report Acronyms and Abbreviations Page iv iv v vii Volume I. Introduction and Overview Introduction and Background Task Force Interest in Dioxins Summary of Environmental Testing Overview of the HHRA Methods Summary and Conclusions Volume II. Exposures to Current and Future Residents Living Along Streets Where Sierra-Crete was Used as a Road Base or Sub-Base Summary Conceptual Exposure Model Relevant Environmental Data Exposure Pathways and Assumptions Results and Interpretations Volume III. Exposures to Current and Future Children Playing on Streets Where Sierra-Crete was Used as a Road Base or Sub-Base Summary Conceptual Exposure Model Relevant Environmental Data Exposure Pathways and Assumptions Results and Interpretations Volume IV. Exposures to Current and Future Road Utility Maintenance Workers Summary Conceptual Exposure Model Relevant Environmental Data Exposure Pathways and Assumptions Results and Interpretations

3 Volume V. Exposures to Current and Future Residents During Road Maintenance 1 Summary 1 Conceptual Exposure Model 3 Relevant Environmental Data 3 Exposure Pathways and Assumptions 5 Results and Interpretations 6 ii Volume VI. Exposures to Past Road Construction Workers Summary Conceptual Exposure Model Relevant Environmental Data Exposure Pathways and Assumptions Results and Interpretations Volume VII. Exposures to Past Trespassers at Former Road Construction Sites Summary Conceptual Exposure Model Relevant Environmental Data Exposure Pathways and Assumptions Results and Interpretations Volume VIII. Environmental Evaluation Summary Conceptual Approach Screening Model and Assumptions Theoretical Levels in Surface Water Theoretical Levels in Fish Conclusions Volume IX. Supporting Technical Information East County Environmental Data Hazard Identification for Dioxins Overview of Methods for Calculating Theoretical Exposures and Health Risks Methods for Calculating Theoretical Exposures to Road Surfaces Methods for Calculating Theoretical Exposures During Road Maintenance Methods for Calculating Theoretical Exposures During Road Construction Uncertainties References

4 Volume X. Appendices A. Contra Costa County Task Force September 2002 Sampling and Analysis Plan B. Summary of Road Surface Sampling Conducted by the Contra Costa County Task Force in September 2002 C. Summary of Dioxin Testing Results on Roads in the Cities of Antioch, Bay Point, Brentwood, Oakley, and Pittsburg D. Spreadsheet Risk Assessment Calculations for the Road Surface Scenario E. Spreadsheet Risk Assessment Calculations for the Road Maintenance and Utility Repair Scenario F. Spreadsheet Risk Assessment Calculations for the Road Construction Scenario G. Dioxin: Environmental Occurrence, Exposure, & Effects on Human Health, Fact Sheet iii List of Tables Table 1. Summary of results used to evaluate theoretical exposures to dioxin TEQ WHO97 in Sierra-Crete by to residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or subbase material. Table 2. Summary of the highest concentrations (mg/kg) of metals in Sierra-Crete used to evaluate theoretical exposures to residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or sub-base material. Table 3. Theoretical lifetime average daily dose (LADD) of dioxin TEQ WHO97 and metals to an adult resident living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or sub-base material. Table 4. Theoretical average daily dose (ADD) of dioxin TEQ WHO97 and metals to adult and children residents living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or sub-base material. Table 5. Theoretical incremental cancer risks posed by exposures to dioxin TEQ WHO97 and metals by adult residents living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or subbase material. Table 6. Theoretical non-cancer hazard indices posed by exposures to dioxin TEQ WHO97 and metals by adult and child residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or sub-base material. List of Figures Figure 1. Conceptual exposure model describing the exposure pathways by which an adult or child might be exposed to Sierra-Crete during road utility maintenance.

5 Preface iv Background In early 2002, DuPont, using an independent qualified laboratory, established that Sierra-Crete contained trace levels of dioxins. Sierra-Crete is a structural road-base material that was manufactured at the former DuPont facility located in Oakley, California, between 1988 and During that period, Sierra-Crete was sold commercially to construction companies and used as an aggregate base or sub-base material beneath asphalt during the construction of approximately 36 miles of roads, and a few parking lots in East Contra Costa County, California. In April 2002, trace levels of dioxins were detected in white and dark stains that appear on road surfaces along cracks in asphalt pavement in a significant but small percentage of roads where Sierra-Crete was used. Upon making this discovery, DuPont shared the results of environmental testing conducted in April/May 2002 and a human health risk assessment (HHRA) completed in June with the Contra Costa County Health Department and the California Department of Toxic Substances Control (DTSC). The risk assessment report titled, Human Health Risk Assessment of Sierra-Crete, provided a conservative estimate of the nature and extent of the health risks associated with potential pathways of exposure by road construction workers and residents. The environmental sampling and HHRA were performed in accordance with both United States Environmental Protection Agency (U.S. EPA) and California DTSC guidance. Using the data generated from April/May 2002 environmental sampling in the City of Antioch, the June 2002 HHRA concluded that the use of Sierra-Crete during the construction of roads did not pose a significant health risk to road construction workers. Further, exposure to dioxins on white and dark stained and unstained road surfaces in residential neighborhoods in the City of Antioch where Sierra-Crete was used did not pose a significant health risk to residents. For both road construction workers and residents, the theoretical health risks posed by potential exposure to dioxins through dermal, inhalation, and incidental ingestion pathways were within regulatory limits. To further evaluate and verify the information provided by DuPont, the Contra Costa County Health Department convened a Sierra-Crete Task Force (Task Force) under the direction of Health Department Director Dr. Wendell Brunner. The Contra Costa County Sierra-Crete Task Force included representatives from the Contra Costa County Health Department, interested residents, Contra Costa County Public Works Department, Contra Costa County Office of the County Administrator, Contra Costa County Counsel s Office, Contra Costa County District V Office, Contra Costa County District III Office, California DTSC, California Department of Health Services, Central Valley Regional Water Quality Control Board, the Cities of Antioch, Bay Point, Brentwood, Oakley, and Pittsburg, DuPont, and other interested parties. The purposes of the Task Force were to: 1. Evaluate the technical methods and assumptions used by DuPont in the June 7, 2002 HHRA; 1 The June 7, 2002 human health risk assessment and addenda can be found on the Internet at and

6 2. Perform additional environmental sampling in the Cities of Antioch, Bay Point, Brentwood, Oakley, and Pittsburg to further understand and evaluate the occurrence of dioxins on stained road surfaces and in Sierra-Crete ; v 3. Prepare an updated HHRA that incorporates all of the available information pertaining to the use of Sierra-Crete in East Contra Costa County and further evaluates the potential for exposure and adverse health impacts on road workers and residents; and, 4. Provide recommendations to County and State authorities on actions that will protect public health and assure the continued well-being of residents in East Contra Costa County. Organization of this Report This document represents the final Sierra-Crete HHRA. It incorporates changes as a result of technical comments received on the June 7, 2002 HHRA from several members of the Task Force, as well as new information on the use of Sierra-Crete in East Contra Costa County and environmental sampling conducted in September The core of this document are six volumes that present the exposure and risk assessments for each of the six human exposure scenarios included in the HHRA. The intent is to provide all of the relevant information in each volume in a relatively straightforward manner that will assist the lay reader with understanding the significance of the environmental test data and results of the HHRA. Additional and more technical information that may be of particular interest to experienced risk assessors has been relegated to the last volume of the HHRA. Also included is an environmental evaluation as well as a number of supporting appendices. A synopsis of these volumes is as follows: Volume I Introduction and Overview The information provided in Volume I includes a description of the use of Sierra-Crete in East Contra Costa County and a summary of the results of extensive environmental sampling conducted in February and April/May by DuPont and September 2002 by the Contra Costa County Task Force. Volume I also includes an overview of the methods used to perform the HHRA and a summary of the results of the HHRA. Volume II through VII Exposure and Risk Assessments Volumes II through VII present the individual HHRAs for each of five different potentially exposed populations residents, children, road maintenance and utility workers, road construction workers, and road construction site trespassers. Each volume contains a non-technical summary of the assessment, a discussion of the relevant environmental data and the methods and assumptions used to calculate theoretical exposures. Each volume also includes a discussion of the exposure results, theoretical cancer and non-cancer health risks, a comparison to U.S. EPA s estimate of the typical background intake of dioxins from various environmental sources, and a brief discussion of the uncertainties in the assessment. Volume VIII Environmental Evaluation The information provided in VolumeVIII addresses the potential for dioxins on road surfaces to migrate to groundwater or to nearby creeks, reservoirs, and the San Joaquin River. The results of soil, surface water, and sediment sampling are presented in conjunction with a discussion of the results of screening models used to estimate

7 environmental levels. The evaluation includes consideration of uptake by fish and comparisons to levels reported in fish from Contra Costa County s San Pablo Dam Reservoir and San Francisco Bay. vi Volume IX Supporting Technical information The information in Volume IX includes additional supporting information describing the environmental sampling data set used to derive the exposure point concentrations used in the HHRA and the mathematical equations associated with the different exposure pathways that were considered. The volume also includes a brief review of the scientific information regarding the hazards posed by dioxins and a discussion of the uncertainties inherent in the HHRA process. Volume X Appendices Additional information, including the environmental data set from sampling conducted in September 2002 and risk assessment equations, are presented as appendices to this report.

8 Acronyms and Abbreviations vii ASTM atm ATSDR BAAQMD BCF BW Cal/EPA CARB o C CDI Cl Cl 2 cm CRWQCB DHHS DL DTSC e.g. EPC ft ft 3 g GC-ECD GC-MS HEAST HHRA HI HQ Hr i.e. IARC IRIS kg L LADD lb LOQ MCL µg Microgram Me x Cl y Metal chlorides mg Milligram mg/day mg/kg mg/kg-day mm M 2 M 3 NA ng ND American Society for Testing and Materials Atmosphere Agency for Toxic Substances and Disease Registry Bay Area Air Quality Management District Bioconcentration Factor Body weight California Environmental Protection Agency California Air Resources Board Degree Celsius Chronic daily intake Chloride Dichloride Centimeters California Regional Water Quality Control Board U.S. Department of Health and Human Services Detection Limit California Department of Toxic Substances Control For example Exposure point concentration Feet Cubic Feet Gram Gas Chromatography/Electron Capture Detector Gas Chromatography/Mass Spectrometry Health Effects Assessment Summary Tables Human health risk assessment Hazard index Hazard quotient Hour That Is International Agency for Research on Cancer Integrated Risk Information System Kilogram Liter Lifetime average daily dose Pound Limits of Quantitation Maximum Contaminant Level Milligram per day Milligram per kilogram Milligram per kilogram per day Millimeter Square Meter Cubic Meter Not Applicable Nanogram Not Detected

9 NR NTP OCDD OCDF OPP PAH Pb PCBs PCDDs PCDFs PEA pg PM ppb ppm ppmv pg pg/cm 2 ppt ppt/v QA/QC RfC RfD RT SAB sec SF SFRWQCB sq TCDD TCDF TEF TEQ TiCl 4 TiO 2 TRI UCL 95 U.S. EPA USFDA VOC WHO yr 2,3,7,8-TCDD Not Reported National Toxicology Program Octachlorinated dibenzo-p-dioxins Octachlorinated dibenzofurans Office of Pesticide Programs Polycyclic Aromatic Hydrocarbons Lead Polychlorinated Biphenyls Polychlorinated Dibenzo-p-dioxins Polychlorinated Dibenzofurans Preliminary Endangerment Assessment Picogram Particulate Matter Parts Per Billion Parts Per Million Parts Per Million (Chapter Basis) Picograms Picograms per square centimeter Parts Per Trillion Parts Per Trillion (Chapter Basis) Quality Assurance/Quality Control Reference Concentration Reference Dose Residence Time Science Advisory Board Second Slope Factor (also Cancer Potency Factor) San Francisco Regional Water Quality Control Board Square 2,3,7,8-tetrachlorodibenzo-p-dioxin 2,3,7,8-tetrachlorodibenzofuran Toxicity Equivalency Factor Toxicity Equivalents Titanium Tetrachloride Titanium dioxide Toxics Release Inventory 95 percent upper confidence limit on the mean United States Environmental Protection Agency U.S. Food and Drug Administration Volatile Organic Chemical World Health Organization Year 2,3,7,8-tetrachlorodibenzo-p-dioxin viii

10 Volume V. Exposures to Current and Future Residents During Road Maintenance Summary 1 In early 2002, DuPont, using an independent qualified laboratory, established that Sierra-Crete contained trace levels of dioxins a class of environmental contaminants that has been associated with health effects such as cancer. In April 2002, trace levels of dioxins were detected in stains that appear on road surfaces along cracks in asphalt pavement in some roads where Sierra-Crete was used. Upon making this discovery, DuPont shared the results of the environmental testing and a human health risk assessment (HHRA) with the Contra Costa County Health Department and the California Department of Toxic Substances Control (DTSC). Although the initial risk assessment showed no significant risks would be expected from exposures to the low concentration of dioxins, health effects have been associated with exposure to elevated levels of dioxins. The Contra Costa County Health Department convened a Sierra- Crete Task Force (Task Force) under the direction of Health Department Director Dr. Wendell Brunner to determine if the initial findings were correct. In a risk assessment, either the level of a chemical that people could be exposed to or the calculated health risk is compared to a safe level to determine if there is a health concern or not. It is important to note that the assumptions used in this HHRA are designed to ensure that potential health risks will not be underestimated, so that decisions made based on this assessment will be protective of public health. The following summarizes how the human health risk assessment was performed and presents the results of the evaluation for residents living adjacent to a road maintenance site. The results of this final risk assessment confirm the earlier conclusions that there are no significant risks for residents who are exposed to Sierra-Crete during road maintenance in East Contra Costa County. Who is potentially exposed and how? The evaluation looked at how residents potentially could come in contact with Sierra-Crete during road maintenance. Both children and adults were considered. To determine how these residents might be exposed, a conceptual model was developed. The conceptual model is a tool for identifying and describing the ways in which residents might be exposed to Sierra-Crete. In this case, only two primary exposure pathways were identified the inhalation of airborne dust particles generated by excavation equipment during road maintenance and utility work activities, and swallowing of inhaled dust particles that are too large to reach the lungs and instead deposit in the mouth. How much might residents be exposed? The results of testing of 27 samples of Sierra-Crete collected from beneath pavement in East Contra Costa County indicated that the representative concentration of dioxins in Sierra-Crete was 293 picograms (trillionths of a gram) dioxin TEQ WHO97 2 per gram of Sierra-Crete. Although 2 Dioxin concentrations are typically described in terms of toxicity equivalents (or TEQ WHO97 ) relative to the most toxic form of the dioxins, regardless of which specific dioxins are present in an environmental

11 there are many different dioxins, the most toxic form was not present in any of the samples. The evaluation assumed that residents living adjacent to a road maintenance site were exposed to this representative concentration of dioxins. 2 In addition to dioxins, Sierra-Crete was tested for metals and other organic chemicals. With the exception of a few metals, the presence of other chemicals and metals in Sierra-Crete were below health-based residential soil criteria set by U.S. EPA Region IX 3. Nonetheless, the evaluation assumed that it was possible for residents to be exposed to the different types of metals found in Sierra-Crete. How was this evaluation performed? Using the environmental testing data developed for Sierra-Crete and taking into account how residents potentially could come in contact with Sierra-Crete, computer models were used to calculate average daily intakes of dioxins and metals through the exposure pathway. For the purposes of this scenario, residents living along roads where Sierra-Crete was used were assumed to be exposed to air particulate generated at a utility maintenance or repair trench in the road once per year for 30 years. From this intake, the potential health risks were calculated. The average intake also was directly compared to background intake levels from other sources of dioxin exposure (e.g., diet) to determine whether exposure to Sierra-Crete was a significant source of dioxin exposure. Health risks associated with chemical exposures are typically expressed as a theoretical or calculated excess cancer risk and as a hazard index for non-cancer effects. U.S. EPA has established that an excess cancer risk between 1 in ten thousand (10,000) and 1 in 1 million (1,000,000) is acceptable in the United States. For evaluation of non-cancer effects, the average daily intake of a chemical is compared to a level established by U.S. EPA or the State of California as being safe. When the average daily intake is less than the established safe level, the resulting ratio (the hazard quotient, or hazard index when all chemicals are added) for non-cancer effects is less than a value of one and exposure is considered to be not significant. Is exposure to Sierra-Crete a cause for concern? The results of this risk assessment indicate that exposure to dioxins in Sierra-Crete does not pose a significant increased cancer or non-cancer risk to residents living adjacent to a road maintenance site. The calculated cancer risk was five in ten million, which is below the acceptable risk threshold set by the State of California. The hazard index was below a value of one for both children and adults, indicating that non-cancer health risks are insignificant. In addition, the average daily intakes calculated for children and adults were approximately 0.001% of the U.S. EPA s estimates of the total average daily intake of dioxins from background sources typically encountered by the U.S. general population. In summary, residents living adjacent to a road where maintenance and utility repair occurs are not exposed to unacceptable levels of the constituents in Sierra-Crete. sample. The TEQ WHO97 method used in this assessment was developed by the World Health Organization (WHO) in 1997 and endorsed by both the U.S. EPA and California DTSC. 3 This statement refers to Preliminary Soil Remediation Goals, or more commonly referred to as soil PRGs, set by U.S. EPA Region IX headquarters located in San Francisco, CA. Soil PRGs are often used as a screening tool to evaluate organic chemical and metal levels in soil.

12 Conceptual Exposure Model 3 Road maintenance and utility repair activities involving the removal of asphalt and digging trenches into the road base or sub-base periodically occur on roads where Sierra-Crete was used. It is plausible, albeit unlikely, that residents could be exposed to Sierra-Crete associated with road excavation and trenching activities during the course of a typical 3-day road utility maintenance job. Direct contact with Sierra-Crete in an excavated trench is unlikely to occur because of the various protective measures typically practiced to prevent access to road trenches by individuals other than the road work crew assigned to the maintenance or repair activity. For example, temporary barriers are typically used during the workday to keep the pubic a safe distance from work zones and steel plates are always placed over open trenches at the end of the work day to prevent injuries and property damage. These barriers also reduce or eliminate the opportunity for direct contact with Sierra-Crete. The only plausible means by which an adult or child resident potentially may be exposed to Sierra-Crete are through the inhalation of particulate and incidental ingestion of particulate inhaled and swallowed during the period of excavation and trench work. The conceptual exposure model describing how an adult or child might be exposed to Sierra-Crete is presented in Figure 1. Figure 1. Conceptual exposure model describing the exposure pathways by which an adult or child might be exposed to Sierra-Crete during road utility maintenance. Primary Source Potential Release Mechanism Exposure Media Exposure Route Road Maintenance/ Utility Work Done on Roadbed Where the Roadbase or Subase with Sierra Crete is Disturbed Excavated Trench Suspension in Air by Wind or Equipment Disturbance Ambient Outdoor Air Inhalation of Respirable Particulates Ingestion of Particulates Inhaled & Swallowed The potential for exposure to Sierra-Crete during road maintenance was evaluated for both adults and children in accordance with California DTSC risk assessment guidance. The exposure model assumed a 30-year residential exposure period, which represents the reasonable maximum estimate of time a person lives in one residence. The first 6 years were modeled as child exposure and the remaining 24 years were modeled as adult exposure. Relevant Environmental Data The data set describing the concentrations of dioxin TEQ WHO97 in Sierra-Crete in samples collected from test roads at DuPont s former Oakley facility and from beneath roads in the Cities of Antioch, Bay Point, Brentwood, Oakley, and Pittsburg is summarized in Table 1. The concentrations of dioxin TEQ WHO97 in Sierra-Crete sampled from beneath roads at DuPont s former Oakley facility were reported in the June 2002 HHRA. In September 2002, additional Sierra-Crete samples were collected from beneath roads in the Cities of Antioch, Bay Point,

13 Oakley, and Pittsburg. Additional discussion of the data is provided in Volume IX of this document. 4 The dioxin TEQ WHO97 data from the February (10 samples) and September 2002 (17 samples) Sierra-Crete data sets were combined for the purposes of estimating potential exposures to road construction workers. Two samples collected in September 2002 were determined not to be samples of Sierra-Crete and were excluded from the combined data set. The combined data set used in the HHRA included 27 samples. Consistent with California DTSC guidance, a value of 293 pg dioxin TEQ WHO97 /g was used in the exposure models. This represents the 95 percent upper confidence limit (95UCL) on the arithmetic mean concentration of dioxin TEQ WHO97 in the combined Sierra-Crete data set. Table 1. Summary of results used to evaluate theoretical exposures to dioxin TEQ WHO97 in Sierra-Crete by to residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or subbase material. [1] Sierra-Crete Number of Samples 27 Total Dioxin TEQ WHO97 (picogram per gram) Minimum 66 Maximum 1,004 Arithmetic Mean th UCL on the Arithmetic Mean 293 * * Value used in the HHRA to represent the exposure point concentration. [1] The data set includes samples collected from beneath roads on DuPont s former Oakley facility in February 2002 and the Cities of Antioch, Bay Point, Oakley, and Pittsburg in September The combined data set includes 27 samples, and not 29 samples, because two samples collected in September 2002 were determined not to be samples of Sierra-Crete and, thus, were excluded from consideration in the HHRA. Analytical tests were performed by Alta Analytical Laboratory (El Dorado Hills, CA) using U.S. EPA Method 1613A. Total dioxin TEQ WHO97 was calculated using WHO (van den Berg et al., 1998) toxic equivalency factors. Congeners reported by the laboratory as non-detect were assumed to be present at 1/2 the detection limit. In addition to dioxins, Sierra-Crete was tested for metals and organic chemicals in two samples collected in September Semi-volatile organic chemicals (SVOCs) and polyaromatic hydrocarbons (PAHs) were not detected in Sierra-Crete. The highest concentrations of metals reported in Sierra-Crete were used to represent exposure point concentrations in the exposure models. The data are summarized in Table 2. Additional discussion of the data is provided in Volume IX of this document.

14 Table 2. Summary of the highest concentrations (mg/kg) of metals in Sierra-Crete used to evaluate theoretical exposures to residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or sub-base material. 5 Chemical [1] Sierra-Crete [1] All SVOCs Not Detected All PAHs Not Detected Metals (milligrams per kilogram) Antimony Not Detected Arsenic 2.3 Barium 490 Beryllium Not Detected Cadmium 0.49 Chromium, Total 720 Chromium, Hexavalent 290 Cobalt 16 Copper 20 Lead 7.2 Mercury Not Detected Molybdenum 10 Nickel 85 Selenium Not Detected Silver 8.5 Thallium Not Detected Vanadium 1,800 Zinc 33 [1] Analytical results from STL Denver Laboratory using U.S. EPA Method 8270C (semivolatile organic chemicals), U.S. EPA Method 8310 (polyaromatic hydrocarbons), and U.S. EPA Method 6010B, 7471, 6020 and 7199 (metals analysis methods). Results are reported in milligrams per kilogram (mg/kg) and represent the highest concentrations in two samples of Sierra-Crete. In addition to chemical measurements of Sierra-Crete, total suspended and respirable particulate measurements were collected at construction sites where Sierra-Crete was used as a base or subbase material prior to covering by asphalt. The results of measurements collected at the breathing zone of road construction workers during construction were used to evaluate the inhalation and indirect ingestion exposure pathways. In other words, particulate levels in air during road utility maintenance were assumed to be equivalent to the levels measured during road construction. Additional discussion of the data is provided in Volume IX of this document. Exposure Pathways and Assumptions The exposure model used to evaluate exposures to Sierra-Crete by residents during road utility maintenance included two exposure pathways: Inhalation of respirable particulates originating from excavation and trench activities; and, Ingestion of particulates inhaled and swallowed.

15 The potential for exposure to dioxins and metals was estimated for each exposure pathway using exposure equations consistent with U.S. EPA and California DTSC risk assessment guidance. For each equation, information and assumptions on the frequency and duration of exposure were based on the duration of the typical road maintenance and utility repair project. According to expert recollection, the typical utility maintenance job involving excavation of the road base or sub-base is 3 days. For the purposes of this scenario, residents living along roads where Sierra- Crete was used were assumed to be exposed to air particulate generated at a utility maintenance or repair trench in the road once per year for 30 years. Exposure assumptions pertaining to the inhalation of particulates in the air and incidental ingestion of Sierra-Crete particulate inhaled and swallowed were adopted from U.S. EPA (1997) guidance on selecting exposure factors for use in exposure models. Further discussion of the exposure models and assumptions used in the models is provided in Volume IX of this document. 6 Results and Interpretations Health risk estimates are derived by combining hazard data with exposure data. The results of the exposure assessment provide the exposure data in the form of the daily dose associated with potential exposures to chemicals by all pathways in an exposure model. A theoretical lifetime average daily dose (LADD) is calculated for chemicals known or suspected to cause cancer and represents the theoretical average daily level of exposure over a 70-year human lifetime. The average daily dose (ADD) represents the theoretical average daily dose received during any single day of exposure. The ADD is used to evaluate chemicals that may cause or induce adverse health effects other than cancer. The LADD and ADD dose estimates are then combined with the toxicity factors developed by U.S. EPA and the California Office of Health Hazard Assessment (OEHHA) to calculate a theoretical cancer risk or hazard potential. Cancer risk is typically expressed exponentially. For example, cancer risks are often described as 1 x 10-6 or as 1 in 1 million risk, which is the same as describing the risk of cancer as one additional cancer in 1 million people exposed. The larger the value of the negative exponent (e.g., 10-7 or 10-8 ), then the smaller is the theoretical cancer risk (e.g., 1 x 10-7 or 1 x 10-8 is the same as describing 1 in 10 million or 1 in 100 million people exposed). The U.S. EPA has established that an excess cancer risk between 1 in ten thousand (10,000) and 1 in 1 million (1,000,000) is acceptable. If the theoretical cancer risk in a risk assessment is less than 1 in 1 million, then risk is considered to be negligible. For evaluation of non-cancer health concerns, the risk is expressed as a hazard quotient (HQ). It is the ratio of the ADD to a safe level of exposure established by U.S. EPA or California OEHHA. The sum of HQs for each exposure pathway and chemical considered in an exposure model is referred to as a Hazard Index (HI). When the HI for non-cancer health effects is smaller than a value of one, then non-cancer risk is considered to be insignificant. The LADD dose estimates for adult residents are presented in Table 3. The ADD dose estimates for adults and children (0-6 years) using a 30-year residential exposure duration are presented in Table 4.

16 Table 3. Theoretical lifetime average daily dose (LADD) of dioxin TEQ WHO97 and metals to an adult resident living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or sub-base material. 7 Chemical Theoretical Lifetime Daily Dose (LADD; mg/kg-day) [1] Adult Resident Total Dioxin TEQ WHO x Arsenic 1.9 x Barium 4.0 x 10-9 Cadmium 4.0 x Chromium, total 5.9 x 10-9 Chromium VI 8.9 x Cobalt 1.3 x Copper 1.6 x Lead 5.9 x Molybdenum 8.2 x Nickel 7.0 x Silver 7.0 x Vanadium 1.5 x 10-8 Zinc 2.7 x [1] The total LADD represents the level of exposure predicted when exposures from each of the two exposure pathways considered in the exposure model are averaged over a 70- year average human lifetime. It is not appropriate to calculate an LADD for a 0-6 year old childhood exposure period. The 0-6 year old exposure period is, however, a part of the calculation of the adult LADD.

17 Table 4. Theoretical average daily dose (ADD) of dioxin TEQ WHO97 and metals to adult and children residents living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or sub-base material. 8 Chemical Theoretical Average Daily Dose (ADD; mg/kg-day) [1] 0-6 year Child Resident Adult Resident Total Dioxin TEQ WHO x x Arsenic 9.0 x x Barium 1.9 x x 10-9 Cadmium 1.9 x x Chromium, total 2.8 x x 10-8 Chromium VI 1.1 x x 10-9 Cobalt 6.3 x x Copper 7.8 x x Lead 2.8 x x Molybdenum 3.9 x x Nickel 3.3 x x 10-9 Silver 3.3 x x Vanadium 7.0 x x 10-8 Zinc 1.3 x x [1] The total ADD represents the level of exposure predicted when exposures from each of the two exposure pathways (i.e., inhalation and ingestion of particulate inhaled and swallowed) considered in the exposure model. The theoretical incremental cancer risks associated with exposure to dioxins and metals were calculated for adults using the LADD results shown in Table 3. In accordance with both U.S. EPA and California risk assessment guidance, cancer risks typically are not calculated for children. The theoretical incremental cancer risks calculated for adult residents are summarized in Table 5.

18 Table 5. Theoretical incremental cancer risks posed by exposures to dioxin TEQ WHO97 and metals by adult residents living adjacent to a road maintenance or utility repair trench on a road where Sierra-Crete was used as a road base or subbase material. 9 Theoretical Cancer Risk Chemical Resident (Child + Adult) [1] Total Dioxin TEQ WHO97 2 x Arsenic 1 x Barium -- [2] Cadmium 2 x Chromium, total -- Chromium VI 5 x 10-7 Cobalt -- Copper -- Lead 1 x Molybdenum -- Nickel 2 x Silver -- Vanadium -- Zinc -- Cumulative Theoretical Cancer [3] 5 x 10-7 Risk [1] The California OEHHA cancer potency value for dioxins was used to calculate the theoretical cancer risk. It is not appropriate to calculate theoretical cancer risks for a 0-6 year old childhood exposure period. The calculation of cancer risks is appropriate only for evaluation of the full 30-year exposure period, which is the sum of exposures to the 0-6 year child and the 6-30 year adult exposure periods. [2] A -- indicates that the metal is not considered carcinogenic to humans by U.S. EPA or the State of California. [3] The cumulative total theoretical incremental cancer risk represents the sum of the theoretical incremental cancer risks associated with exposures to dioxins, arsenic, cadmium, chromium VI, lead, and nickel. As shown in Table 5, theoretical incremental cancer risks associated with exposures to dioxin and each of the metals were below 1 x 10-6 risk levels. The cumulative incremental cancer risk calculated by summing the incremental cancer risks associated with dioxin and each metal was approximately five in ten million (5 x 10-7 risk level), which is below the 1 x 10-6 risk level considered to be insignificant by U.S. EPA and the State of California. Theoretical non-cancer hazard indices (HIs) associated with exposure of adult and children residents to dioxins and metals were calculated using the ADD results shown in Table 4. Theoretical non-cancer HIs are summarized in Table 6.

19 Table 6. Theoretical non-cancer hazard indices posed by exposures to dioxin TEQ WHO97 and metals by adult and child residents living adjacent to a road maintenance or utility repair trench in a road where Sierra-Crete was used as a road base or subbase material. 10 Theoretical Hazard Index Chemical 0-6 year Child Resident Adult Resident Total Dioxin TEQ WHO Arsenic Barium Cadmium Chromium, total Chromium VI Cobalt -- [1] -- Copper Lead Molybdenum Nickel Silver Vanadium Zinc Cumulative Total [2] Hazard Index [1] A -- indicates that a non-cancer toxicity value has not been developed by either U.S. EPA or California OEHHA. In the absence of a toxicity value, an HI was not calculated. [2] The cumulative total non-cancer HI represents the sum of the HIs associated with exposure to dioxins and each of the metals for which toxicity values have been developed by U.S. EPA or California OEHHA. As shown in Table 6, theoretical non-cancer hazard indices associated with exposures to dioxin or metals were well below a value of one for both adult and child residents. The cumulative HIs for adult and child residents, which represents the sum of the HIs associated with dioxin and each metal, also were well below a value of one, indicating that non-cancer risks are insignificant. To further evaluate potential exposures to dioxins in Sierra-Crete, the ADDs calculated for adult and children were compared to U.S. EPA (2000b) estimates of the total average daily intake of dioxins from background sources typically encountered in the U.S. general population. According to U.S. EPA (2000b), the typical background intake of dioxins in U.S. adults is, on average, 59 pg dioxin TEQ WHO97 /kg BW/day (or, 5.9 x mg dioxin TEQ WHO97 /kg BW/day). A person s typical background daily intake of dioxins is the result of exposures to trace levels of dioxins commonly found in soil, air, and a wide variety of meat, dairy and other food products (U.S. EPA, 2000b). On average, adults and children living adjacent to a road utility repair or maintenance trench on a road where Sierra-Crete was used as a road base or sub-base material might have an incremental increase of approximately 0.001% above their typical average daily intake of dioxins from all other environmental and dietary sources.