EAST MULTNOMAH COUNTY GROUND WATER CONTAMINATION
GRESHAM, MULTNOMAH COUNTY, OREGON
Appendix 1 - Figures 1, 2, 3, 4, and 5
Appendix 2 - Community Relations Plan East Multnomah County Groundwater Contamination Site
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Health Comparison Values
Health comparison values for ATSDR public health assessments are contaminant concentrations that are found in specific media (e.g., air, soil, and water) and that are used to select contaminants for further evaluation. The health comparison values were developed by using the most conservative assumptions (i.e., worst case). For example, soil health comparison values are developed for children who exhibit pica behavior. Soil ingestion in pica children greatly exceeds the soil ingestion rate for the normal population. The most conservative (lowest concentration) health comparison value was selected to be used in the Environmental Contamination and Other Hazards section. For example, Cancer Risk Evaluation Guides (CREGs) are usually selected for compounds identified as possible human carcinogens. Health comparison values used in the Environmental Contamination and Other Hazards section of this public health assessment are described below.
CREGs are contaminant concentrations estimated to cause no more than one excess cancer in a million (10E-6) persons exposed over a lifetime. CREGs are calculated from U.S. Environmental Protection Agency's (EPA's) cancer slope factors.
The Lifetime Health Advisory for drinking water (LTHA) is developed by the EPA. The LTHA is a lifetime exposure level specific for drinking water (assuming 20% of an individual's exposure comes from drinking water) at which adverse, noncarcinogenic health effects would not be expected to occur. When health comparison values are not available for other environmental media (i.e., soil and air), the LTHA is used to calculate a comparison value by factoring in the different ingestion or inhalation rates.
A Minimal Risk Level (MRL) is an estimate of daily human exposure to a chemical (in milligrams per kilogram per day) that is unlikely to cause an appreciable risk of deleterious effects (noncarcinogenic) over a specified duration of exposure. MRLs are based on human and animal studies and are reported in the ATSDR Toxicological Profiles for acute (< 14 days), intermediate (15 to 365 days), and chronic (> 365 days) exposures.
EPA's Reference Dose (Rfd) is an estimate of the daily exposure to a contaminant that is unlikely to cause adverse health effects. However, Rfds do not consider carcinogenic effects.
Environmental Media Evaluation Guides (EMEGs) are based on ATSDR's MRLs and factor in body weight and ingestion or inhalation rates. Reference Dose Media Evaluation Guides (RMEGs) are the same as EMEGs except that they are based on EPA Rfds.
The derivations of CREGs and MRLs are presented in the ATSDR Toxicological Profile for each
of the selected contaminants. The EMEGs and RMEGs are derived by the procedures outlined in
the ATSDR Public Health Assessment Guidance Manual. The LTHAs and Rfds are developed by
EPA and the derivation information can be obtained from the EPA.
| Appendix 4, Table 1 - Environmental Contaminants Detected Above Health Comparison Values at the Boeing Company Facility, Multnomah County, Oregon (7-5) | ||||||
| Contaminant | Range in Soil (mg/Kg) | Comparison Value for Ingestion (mg/Kg)* | Range in the TGA Groundwater (µg/L) | Range in the TSA Groundwater (µg/L) | Comparison Value for Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.4 | 8 | <0.4-10 | <0.4-2.2 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.4 | 1 | <0.4-720 | <0.2-16 | 0.06 | CREG |
| Cis-1,2-Dichloroethylene | <0.4 | 600 | <0.4-7,200 | <0.2-49 | 70 | LTHA |
| Tetrachloroethylene | <0.4 | 10 | <0.4-500 | <0.4-9.3 | 0.7 | CREG |
| 1,1,1-Trichloroethane | <0.4-4.7 | 11 | <0.4-39,000 | <0.2-58 | 200 | LTHA |
| Trichloroethylene | <0.4 | 60 | <0.4-8,400 | <0.4-520 | 3 | CREG |
| Vinyl Chloride | <0.4 | 0.04 | <0.2-13 | <0.2 | 0.2 | EMEG |
| * - See Appendix 3 for a description of the comparison values and their sources.
mg/Kg - milligrams of contaminant per kilogram of soil. µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. TSA - Troutdale Sandstone Aquifer. |
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| Appendix 4, Table 2 - Environmental Contaminants Detected Above Health Comparison Values at the Cascade Corporation Facility, Multnomah County, Oregon (8-14) | ||||||
| Contaminant | Range in Soil (mg/Kg) | Comparison Value for Ingestion (mg/Kg)* | Range in the TGA Groundwater (µg/L) | Range in the TSA Groundwater (µg/L) | Comparison Value for Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.4-33 | 8 | <0.5-13 | <0.5 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.4-1.6 | 1 | <0.5-25 | <0.5 | 0.06 | CREG |
| Cis-1,2-Dichloroethylene | <0.4-10 | 600 | <0.5-33,000 | <0.5-35 | 70 | LTHA |
| Tetrachloroethylene | <0.4 | 10 | <0.5-830 | <0.5-6.4 | 0.7 | CREG |
| 1,1,1-Trichloroethane | <0.4 | 11 | <0.5-270 | <0.5-0.6 | 200 | LTHA |
| Trichloroethylene | <0.4-5.5 | 60 | <0.5-35,200 | <0.5-130 | 3 | CREG |
| Vinyl Chloride | <0.4 | 0.04 | <0.5-106 | <0.5 | 0.2 | EMEG |
| * - See Appendix 3 for a description of the comparison values and their sources.
mg/Kg - milligrams of contaminant per kilogram of soil. µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. TSA - Troutdale Sandstone Aquifer. |
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| Appendix 4, Table 3 - Environmental Contaminants Detected Above Health Comparison Values at the Swift Adhesives Facility, Multnomah County, Oregon (15-17) | ||||||
| Contaminant | Range in Soil (mg/Kg) | Comparison Value for Ingestion (mg/Kg)* | Range in the Perched Groundwater (µg/L) | Range in the TGA Groundwater (µg/L) | Comparison Value of Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.6 | 8 | <0.5-5 | <0.5 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.6 | 1 | <0.5-430 | <0.5 | 0.06 | CREG |
| Cis-1,2-Dichloroethylene | <0.6 | 600 | <0.5-91 | <0.5 | 70 | LTHA |
| Tetrachloroethylene | <0.4-14 | 10 | <0.5-25 | <0.5 | 0.7 | CREG |
| 1,1,1-Trichloroethane | <0.6-120 | 11 | <0.5-140 | <0.5 | 200 | LTHA |
| Trichloroethylene | <0.6-14 | 60 | <0.5-33 | <0.5 | 3 | CREG |
| Vinyl Chloride | <0.6 | 0.04 | <0.5 | <0.5 | 0.2 | EMEG |
| * - See Appendix 3 for a description of the comparison values and their sources.
mg/Kg - milligrams of contaminant per kilogram of soil. µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. |
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| Appendix 4, Table 4 - Environmental Contaminants Detected Above Health Comparison Values Downgradient of the Cascade Corporation and Boeing Company Facilities, Multnomah County, Oregon (5-14) | |||||
| Contaminant | Range in the Columbia Slough Surface Water (µg/L) | Range in the TGA Groundwater (µg/L) | Range in the TSA Groundwater (µg/L) | Comparison Value for Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.2 | <0.2-1.6 | <0.2 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.2-23.9 | <0.2-50 | <0.2 | 0.06 | CREG |
| Cis-1,2-Dichloroethylene | <0.2-1.3 | <0.2-70 | <0.2 | 70 | LTHA |
| Tetrachloroethylene | <0.2-0.2 | <0.2-23 | <0.2 | 0.7 | CREG |
| 1,1,1-Trichloroethane | <0.2-28.8 | <0.2-950 | <0.2 | 200 | LTHA |
| Trichloroethylene | <0.2-23.3 | <0.2-570 | <0.2-57 | 3 | CREG |
| * - See Appendix 3 for a description of the comparison values and their sources.
µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. TSA - Troutdale Sandstone Aquifer. |
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| Appendix 4, Table 5 - Environmental Contaminants Detected Above Health Comparison Values Downgradient of the Cascade Corporation Facility, Multnomah County, Oregon (8-14) | |||||
| Contaminant | Range in Spring Water (µg/L) | Range in the TGA Groundwater (µg/L) | Range in the TSA Groundwater (µg/L) | Comparison Value for Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.5 | <0.5-2.8 | <0.5 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.5 | <0.5 | <0.5 | 0.06 | CREG |
| Cis-1,2-Dichloroethylene | <0.5-1,200 | <0.5-13,000 | <0.5-210 | 70 | LTHA |
| Tetrachloroethylene | <0.5-50 | <0.5-120 | <0.5-25 | 0.7 | CREG |
| Trichloroethylene | <0.5-1,000 | <0.5-15,000 | <0.5-410 | 3 | CREG |
| Vinyl Chloride | <0.5 | <0.5-106 | <0.5 | 0.2 | EMEG |
| * - See Appendix 3 for a description of the comparison values and their sources.
µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. TSA - Troutdale Sandstone Aquifer. |
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| Appendix 4, Table 6 - Environmental Contaminants Detected Above Health Comparison Values Downgradient of the Swift Adhesives Facility, Multnomah County, Oregon (15-17) | ||||
| Contaminant | Range in the Perched Groundwater (µg/L) | Range in the TGA Groundwater (µg/L) | Comparison Value for Ingestion (µg/L)* | Comparison Value Source* |
| 1,2-Dichloroethane | <0.5 | <0.5 | 0.4 | CREG |
| 1,1-Dichloroethylene | <0.5-13 | <0.5 | 0.06 | CREG |
| Trichloroethylene | <0.5-57 | <0.5 | 3 | CREG |
| * - See Appendix 3 for a description of the comparison values and their sources.
µg/L - micrograms of contaminant per liter of water. TGA - Troutdale Gravel Aquifer. |
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| Appendix 4, Table 7 - Environmental Contaminants Detected Above Health Comparison Values in Residential Wells, East Multnomah County Groundwater Contamination National Priorities List Site, Oregon (5-17) | |||
| Contaminant | Range in Residential Wells (µg/L) | Comparison Value of Ingestion (µg/L)* | Comparison Value Source* |
| Tetrachloroethylene | <0.5-3 | 0.7 | CREG |
| Trichloroethylene | <0.5-105 | 3 | CREG |
| * - See Appendix 3 for a description of the comparison values and their sources.
µg/L - micrograms of contaminant per liter of water. |
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| Appendix 5, Table 1 - Completed Environmental Exposure Pathways at the Proposed East Multnomah County Groundwater Contamination National Priorities List Site, Oregon | ||||||
| Pathway Name | Point of Exposure | Route of Exposure | Exposed Population | Time of Exposure | Contaminants of Concern | Estimated Exposure Population |
| Residential Drinking Water Wells | Drinking Water | Ingestion, Inhalation, Skin Contact |
People Who Obtain Drinking Water from Wells near the Boeing Company and Cascade Corp. Facilities | Past, Current, Future |
Trichloroethylene & Tetrachloroethylene |
Less Than 1,076 |
| Appendix 5, Table 2 - Possible Environmental Exposure Pathways at the Proposed East Multnomah County Groundwater Contamination National Priorities List Site, Oregon | ||||||
| Pathway Name | Point of Exposure | Route of Exposure | Exposed Population | Time of Exposure | Contaminants of Concern | Estimated Exposed Population |
| Future Groundwater Migration | Drinking Water | Ingestion, Inhalation, Skin Contact |
People Who Obtain Drinking Water from Well Downgradient of the Areas of Contamination | Future | Any of the Chlorinated Organic Solvents Listed in Appendix 4 | 750,000 |
| Worker Exposures | Work Place During Waste Disposal | Ingestion, Inhalation, Skin Contact |
Workers at Boeing, Cascade, and Swift Adhesive | Past | Any of the Facility-Specific Chlorinated Organic Solvents Listed in Appendix 4 | Unknown |
| Subsurface Soil | When the Subsurface Soils are Disturbed | Ingestion, Inhalation, Skin Contact |
People Nearby During Soil Excavation | Past, Current, Future |
Any of the Chlorinated Organic Solvents Listed in Appendix 4 | Unknown |
| Air | People Living Near the Boeing Company Facility | Inhalation | People Living near the Boeing Company Facility | Past, Current, Future |
1,1,1-Trichloroethane | Unknown |
| Surface Water | Shepard Spring, Taggart Spring, & Columbia Slough |
Ingestion, Inhalation, Skin Contact |
People Who Recreate in These Bodies of Water | Past, Current, Future |
Any of the Chlorinated Organic Solvents Listed in Appendix 4 | Unknown |
| APPENDIX 6, TABLE 1 - COMPARISON OF ESTIMATED EXPOSURE DOSE TO HEALTH GUIDELINES FOR INGESTION1 | ||||
| CONTAMINANT | EXPOSURE PATHWAY | HEALTH GUIDELINE | SOURCE | HEALTH GUIDELINE EXCEEDED BY EXPOSURE DOSE |
| Trichloroethylene | Residential Wells | 0.7 mg/Kg/Day2 | IMRL3 | NO |
| Tetrachloroethylene | Residential Wells | 0.01 mg/Kg/Day2 | Rfd4 | NO |
| 1 - An explanation of how exposure doses are calculated can be found after this Table.
2 - mg/Kg/Day is milligram of contaminant per kilogram of body weight per day. 3 - IMRL is ATSDR's intermediate minimal risk level. 4 - Rfd is EPA's reference dose. 5 - The environmental concentrations that were used to calculate the exposure doses are presented in the Public Health Implications section of this public health assessment. |
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Calculation of Exposure Dose from Ingestion of Drinking Water
The exposure doses for ingestion of drinking water were calculated in the following manner. The maximum concentration for a contaminant was multiplied by the water ingestion rate for adults (2 liters/day) or children (1 liter/day). This product was divided by the average weight for an adult, 70 kilograms (kg) (154 pounds), or for a child, 10 kg (22 pounds). A qualitative summary of these results can be found in the table above. The environmental concentrations that were used to calculate the exposure doses are presented in the Public Health Implications section of this public health assessment. The doses were calculated by the methods outlined in the Agency for Toxic Substances and Disease Registry Public Health Assessment Guidance Manual.
Calculation of Risk of Carcinogenic Effects
Carcinogenic risk from the ingestion of drinking water were calculated through as follows. The exposure doses for ingestion of drinking water calculated as described previously were multiplied by the EPA's Cancer Slope Factor for the contaminants of concern (28). The result represents the maximum risk for cancer after 70 years of exposure to the maximum concentration of the contaminant (see the discussion of the contaminant concentration in the Public Health Implications section of this public health assessment. Cancer Slope Factors were available for tetrachloroethylene and trichloroethylene (TCE).
The actual risk of cancer is probably lower than the calculated number. The method used to
calculate EPA's Cancer Slope Factor assumes that high dose animal data can be used to estimate
the risk for low dose exposures in humans (36). The method also assumes that there is no safe
level for exposure (37). There is little experimental evidence to confirm or refute those two
assumptions. The method computes the 95% upper bound for the risk, rather the average risk,
which results in there being a very good chance that the risk is actually lower, perhaps by several
orders of magnitude (38).
Appendix 7 - Response to Public Comments
Appendix 7 - Response to Comments Received during the Public Comment Period for the East Multnomah County Groundwater Contamination Public Health Assessment, Multnomah County, Oregon
The Public Health Assessment for the proposed East Multnomah County Groundwater Contamination National Priorities List (NPL) site was available for public review and comment from January 3 through February 17, 1995. The Public Comment Period was announced in The Oregonian and The Outlook newspapers. Copies of the public health assessment were made available for review at the Rockwood Public Library and the Gresham Regional Library. In addition, the public health assessment was sent to nine persons or organizations. Approximately 450 fliers announcing the Public Comment Period were also provided to local citizens.
During the Public Comment Period, the Agency for Toxic Substances and Disease Registry (ATSDR) received comments from two individuals, a neighborhood association, the Rockwood Water People's Utility District, the City of Portland Bureau of Water Works, the Boeing Company, the Cascade Corporation, the Oregon Department of Human Resources, and the Oregon Department of Environmental Quality (ODEQ). The comments and ATSDR's responses are summarized below. The comment letters can be requested from ATSDR through the Freedom of Information Act.
Comment: Several editorial comments were submitted for ATSDR's consideration.
Response: ATSDR incorporated the editorial comments where appropriate.
Comment: It was mentioned in your report ("East Multnomah County Groundwater Contamination" - December 7, 1994) on page 5 that approximately 55 families are served by these wells. Please note, however, that the number of homes using this water is 45 for West Interlachen Corp., 92 for Interlachen Inc., and 12 for Blue Lake Co-op. The total is 148 currently.
Response: Thank you for providing this information. The public health assessment will be revised to include this information.
Comment: Our groundwater resource is extremely valuable and currently very susceptible to contamination. What is needed immediately is a very strong regional plan to protect this resource. There is no management plan of any kind for our dual lake area by a single agency or group of agencies. Populations are moving into the lake area and the demand for groundwater will increase as will the surface water pollution.
Response: ATSDR is not a regulatory agency and does not have the authority to require or recommend that regional groundwater plans be developed. We will forward your comment to the U.S. Environmental Protection Agency (EPA) and ODEQ.
Comment: It is mentioned on page 5 of the ATSDR report that the Troutdale Gravel Aquifer (TGA) and the Troutdale Sandstone Aquifer (TSA) discharge to some extent into the Columbia Slough and Fairview Lake. Do you know the source of that data and the name of the accompanying report? We have many families that swim and boat in both lakes each summer and may experience contact with the water from these aquifers. It would seem most appropriate to test the lakes due to the exposure pathway and residential use.
Response: The reference is Landau Associated, Inc., Phase II Investigation, Boeing Portland, June 21, 1993.
It is unlikely that any of the groundwater contamination has entered the lakes because the groundwater contamination has not migrated under a significant portion of the lakes (please see Appendix 1, Figure 2). Therefore, it would not be appropriate to sample the lakes at this time.
Surface water samples have been taken from the Columbia Slough. The analytical results for those samples are discussed in the public health assessment and the possible exposure pathway is discussed on page 15 of the Public Comment Release Public Health Assessment.
Comment: We agree with your conclusion on recommending that a cancer survey be done. In 1991, two representatives of Interlachen Inc. reviewed the medical records of Providence Hospital in Portland. It was discovered that due to lack of funding, no central cancer registry was in place for Oregon. Each hospital does their own registry and no mechanism is in place to pool information. Because of the need for a cancer survey we feel that our participation and involvement with ATSDR at this opportune time would be advisable. We, therefore, fully support the cancer survey that you are recommending.
Response: ATSDR appreciates your support for the recommendation that cancer health statistics for the area of this NPL site be evaluated if the data are available. If the data are available, the cancer health statistics would only be conducted for the parts of Multnomah County impacted by the groundwater contamination. If the drinking water in your neighborhood has not been impacted by the groundwater contamination, your neighborhood would not be included in the recommended evaluation. ATSDR only recommended the cancer health statistics evaluation to see if it can be determined whether the groundwater contamination may have impacted the health of people exposed.
Comment: We support the other recommendations by ATSDR for the Public Health Action Plan mentioned on pages 22 and 23 of the Public Comment Release Public Health Assessment.
Response: ATSDR appreciates your support.
Comment: My husband and I feel satisfied that ODEQ, Boeing, and Cascade are doing all that can be done to rectify the problem. Therefore, we don't support the idea that this area ought to be finalized as a Superfund site. We feel confident that the test wells will no indicate contaminant movement towards our wells.
Response: Your satisfaction with the remedial efforts to date is noted. ATSDR does not determine whether a site is finalized on the NPL (a.k.a., Superfund). EPA decides whether a site should be finalized on the NPL. ATSDR will forward this comment to EPA.
Comment: My husband and I would be interested in the results of a statistical cancer survey done of this area. This contamination has existed for quite some time, undetected, and although our wells appear to contain healthy drinking water now, and probably have all along, we think a cancer study would shed more light on the issue of possible cause and effect between this groundwater contamination and the cancer deaths over a period of years in our neighborhood.
Response: ATSDR appreciates your support for the recommendation that cancer health statistics for the area of this NPL site be evaluated if the data are available. If the data are available, the cancer health statistics would only be conducted for the parts of Multnomah County impacted by the groundwater contamination. If the drinking water in your neighborhood has not been impacted by the groundwater contamination, your neighborhood would not be included in the recommended evaluation. ATSDR only recommended the cancer health statistics evaluation to see if it can be determined whether the groundwater contamination may have impacted the health of people exposed.
Comment: Page 1, Paragraph 2. Is it documented that the trichloroethylene (TCE) and tetrachloroethylene (PCE) concentrations have increased over time to their present levels?
Response: Because lower concentrations of TCE and PCE are found down gradient of the sources and generally the higher concentrations of the contaminants are found close to the sources, ATSDR believes that it is documented that the TCE and PCE concentrations have increased over time.
Comment: Page 2, Paragraph 2. The text states,"...the Agency for Toxic Substances and Disease Registry...concluded that the proposed... Site is a public health hazard (past, current, and future). ATSDR representatives made this determination because one contaminated drinking water well is being used by two households." Isn't another reason that exposure has occurred in the past?
Response: No. As discussed in more detail in the main text of the public health assessment, it is the continued use of this well that presents the public health hazard. If these individuals were to discontinue the use of the contaminated well, ATSDR believes that the potential for adverse health outcomes to occur would not be significant even though these individuals were exposed in the past.
Comment: As the range and level of contamination generally cannot be predicted, specific reference to the single well in the last two sentences of this paragraph should be deleted.
Response: Because higher concentrations of the contaminants were found up gradient from the well discussed in this paragraph, ATSDR believes it is appropriate to indicate that the contaminant concentrations in this well are likely to increase. ATSDR does not make any predictions as to how high the contaminant concentrations may increase in the public health assessment.
Comment: Fatigue has also been associated with high level TCE exposure.
Response: The public health assessment has been changed accordingly.
Comment: Page 4, Section C: Through direct retail sales within the City of Portland and wholesale agreements with surrounding jurisdictions, approximately 750,000 persons in the Portland metro area rely on the City's well field as both a regular (summer peaking) source of water in conjunction with the Bull Run Watershed, and as an emergency (standby) source of drinking water. The reason the wells have not been used at full capacity is because the City was requested not to do so by both EPA and ODEQ. In 1992 the City imposed significant water use curtailment requirements in order to comply with these requests. These curtailment requirements would have been unnecessary had the wells been available.
Response: The public health assessment has been changed accordingly.
Comment: Page 7, Section A.1: The Boeing Company is so far remediating only the upper, unconfined aquifer, TGA. Boeing has done nothing to remediate the on-site or off-site contamination of the TSA in which some of the City's wells are located. It is the contamination in this aquifer that poses the most direct threat to the City's wells.
Response: The public health assessment has been changed accordingly.
Comment: Page 8 Section A.1: Similar to the comment above, Cascade has not initiated remediation of the on-site or off-site contamination of the TSA. While the report is correct in stating that contamination has migrated into the two upper aquifers, the report does not state the condition of the deepest aquifer, the Sand Gravel Aquifer (SGA), thus giving the impression that it is clean. In actuality, no investigations have been done in the SGA, so it is not possible to state whether it is uncontaminated. The results of a recent pump test of the SGA have shown that pathways exist between the TSA and the SGA.
Response: The public health assessment has been changed accordingly.
Comment: Page 13, Section B.1: Contrary to the statement in the first paragraph of this section, several of the City's wells in the Blue Lake Aquifer (BLA) are being used as a drinking water supply, primarily because the natural hydrology in and around the BLA seems to protect those wells from contamination. The reason the rest of the wells are not now used as a drinking water supply is because of concerns about the contamination. The City would like to see its well field restored to full operation, including its expansion potential, as soon as possible.
Response: The public health assessment has been changed accordingly.
Comment: Appendix 1, Figure 2: I am enclosing what I believe to be a more accurate map of the contamination located in the TGA and TSA. The "possible TSA plume" on the revised map is based on appearance of contaminants in an initial sample but failure to confirm them in an second, follow-up sample.
Response: ATSDR has obtained a more accurate map from ODEQ. This map replaces Figure 2 in the public health assessment.
Comment: ODEQ concurs that the residents from two homes who may be drinking contaminated groundwater from their private well might have a low increased risk of developing cancer. ODEQ offered bottled water to these residences in 1990 and our offer was refused.
Please note that ODEQ is currently working with Cascade corporation to provide more permanent solutions of alternate water supplies for those parties currently receiving bottled water. ODEQ's goal is to eliminate other exposures from inhalation and dermal contact which could result from showering or other domestic use of contaminated groundwater.
Response: ATSDR appreciates ODEQ's concurrence regarding the potential cancer risk of the residents from two homes who may be drinking contaminated groundwater.
ODEQ's efforts to provide more permanent solution for people using bottled water will be noted in the Public Health Actions section of the public health assessment.
Comment: Page 3, 3rd paragraph. The surface impoundment at Boeing was located west of the main plant building.
Response: The public health assessment has been revised accordingly.
Comment: Page 4, Next to last paragraph. The Portland Water Bureau reportedly serves approximately 750,000 residents of Portland, Gresham, and other municipalities.
Response: The public health assessment has been revised accordingly.
Comment: Osbourn Spring is located southeast of Cascade.
Response: The public health assessment has been revised accordingly.
Comment: Page 5, last paragraph. There are four aquifers at the site. Three of these aquifers are used as drinking water sources. The shallow aquifer, called the TGA, is not currently used as a drinking water supply at or in the immediate vicinity of the site. An intermediate aquifer called the TSA is separated from the TGA by a clayey siltstone confining layer. The deep aquifer called the SGA underlies the TSA. Another silt and clay layer separates the TSA from the SGA. The BLA, located between Blue Lake and the Columbia River, abuts the TSA and SGA aquifers.
Response: The public health assessment has been revised accordingly.
Comment: Page 9, second paragraph. Please note that no monitoring wells have been installed at the Firestone facility discussed in this paragraph. Monitoring and/or private water supply wells down gradient of this facility have not shown any volatile organic compounds (VOCs) contamination. Based on the Swift Adhesives investigation and the spatial distribution of VOCs at Firestone, it is unlikely that the source of the detected VOCs at Firestone are from an upgradient source.
Response: The public health assessment has been revised accordingly.
Comment: Page 13, first paragraph. There are several other wells in use that have detected TCE below the maximum contaminant level of 5 micrograms per liter. It is also possible that mobile home parks may be using their wells for irrigation or water for swimming pools.
Response: The public health assessment has been revised accordingly.
Comment: Toxicologic Evaluation. ODEQ recommends that this section of the report consider the breakdown products of TCE, especially vinyl chloride which has been detected on occasion in monitoring wells. Vinyl chloride has not, however, been detected in water supply wells being monitored by ODEQ, Boeing, or Cascade Corporation.
Response: As indicated at the beginning of the Toxicological Evaluation section, only contaminants that people have been exposed to are discussed (i.e., completed exposure pathways). Because there is no evidence that people have been exposed to vinyl chloride or any of the other breakdown products, it would not be appropriate to include vinyl chloride in this section.
Comment: On page 5, the second word at the very top - It lists us as a "City". While we are a municipal corporation, we are a People's Utility District under Oregon Revised Statutes 261.
Response: The public health assessment has been revised to indicate that the water system is a People's Utility District.
Comment: The report's numerous speculative discussions of past impact on public health posed by the East Multnomah County Groundwater Site is outside the scope of the policies and procedures that prescribe how the agency is to prepare health assessments as provided for in 42 CFR Part 90. In particular, a "health assessment" is defined as:
"...the evaluation of data and information on the release of hazardous substances into the environment in order to assess any current or future impact on public health, develop health advisories or other recommendations, and identify studies or actions need to evaluate and mitigate or prevent human health effects."
Response: In order to determine the current or future impact a site may have on public health, ATSDR must try and determine whether people were exposed in the past, at what concentrations, and for how long. The possible health effects associated with a site will depend upon evaluating this type of information. The possible health consequences associated with exposure to a chemical substance depends upon the amount and length of exposure. In addition, some health consequences (e.g., cancer) could possibly occur after a latency period has passed (e.g., years) after exposure has stopped. Therefore, ATSDR must try to evaluate whether past exposures occurred at levels of public health concern.
Comment: The health comparison values for TCE and PCE are Cancer Risk Evaluation Guides (CREGs). CREGs are chemical concentrations estimated to cause no more than one excess cancer in a million persons exposed over a lifetime and are calculated from the U.S. Environmental Protection Agency's (EPA) cancer slope factors (CSFs). The EPA has withdrawn its CSFs for TCE and PCE from the Integrated Risk Information System (IRIS) for further review; therefore, CREGs are not calculable and should not be used in the report. Statements implying that ingesting groundwater containing TCE and PCE is associated with an increased risk of developing cancer should thus be deleted from the text.
Response: PCE is listed in IRIS as "Probable Human Carcinogen-Possible Human Carcinogen" (B2-C). In addition, both the International Agency for Research on Cancer and the Department of Health and Human Services list PCE as "Possibly Carcinogenic to Humans" and "Reasonably Anticipated to be a Carcinogen", respectively. TCE is listed in IRIS as a "Probable Human Carcinogen-Possible Human Carcinogen". Therefore, ATSDR believes that it is correct in concluding that:
"If the well is used to obtain drinking water over a lifetime (70 years) and the regional groundwater is not remediated, people ingesting the contaminated water from this well might have a low increased risk of developing cancer." (emphasis added)
The commentator is correct in pointing out that EPA has withdrawn the CSFs for TCE and PCE. The old CSFs were not used by ATSDR to develop the conclusion quoted above. This conclusion is based on the fact that various agencies have determined, at this time, that there may be a cancer risk associated with exposure to these compounds.
The CREGs for TCE and PCE were only used as a basis for evaluation of the groundwater monitoring data to determine which contaminants should be looked at more closely. As stated on page 7 of the Public Comment Release of this public health assessment, the presence of a contaminant on the lists in the on-site/off-site contaminant tables does not mean that either exposure to the contaminant or adverse health effects have occurred or will occur. Inclusion in the list indicates only that the potential for human exposures to the selected contaminants and the potential for adverse human health effects as a result of any exposures to the selected contaminants are discussed in more detail in later sections of the public health assessment. Even if ATSDR had not used the CREGs for TCE and PCE, both contaminants would have been selected for further evaluation because both contaminants are considered to be "Possible Human Carcinogens" (see discussion above).
Comment: Page 3, Paragraph 2, Last Sentence. The data for reliable evaluation of health statistics are not likely to exist because the area of past usage covers multiple municipal and county jurisdiction and does not conform to census delineation.
Response: There are various geographical mapping and data reduction techniques available which can overcome the problems identified in this comment.
Comment: Page 4, Sentence 1. The importance of the backup well field is not clear in the context. It is noted elsewhere the well field is generally downgradient from the contamination area. It is worth noting that five of the city's wells are screened in the BLA, which is not in contact with the TCE and is only weakly connected to the TSA.
Response: The public health assessment has been modified to clarify the location of the city wells and possible impact of the groundwater contamination on the city wells.
Comment: Page 4, Section B, Paragraph 3. Remediation and source reduction activities have also occurred at the Boeing and Cascade sites, including soil removal and groundwater extraction and treatment. The text should reflect this.
Response: The public health assessment has been modified accordingly.
Comment: Page 4, Section C, Paragraph 2. The demographics explanation is misleading. It should be specifically stated that only a few people in the area rely on groundwater as a primary drinking water source.
Response: The public health assessment has been modified to clarify the demographic information.
Comment: Page 4, Section C, Paragraph 2. We are unable to locate Richland in the Portland area.
Response: The public health assessment has been changed to indicate the Portland Water Bureau supplies water to three of the local water districts (Rockwood, Hazelwood, and Gilbert).
Comment: Page 5, Paragraph 4. Although Fairview Lake is recreationally used by local residents, recreational use of the Columbia Slough near Fairview Lake is accidental, as there is no developed recreational access. The slough is primarily used for irrigation.
Response: The public health assessment has been modified accordingly.
Comment: Page 5, Last Paragraph. The statement that groundwater flow in the three subject aquifers is "...predominantly to the north" overstates the actual information on groundwater flow in the area.
Response: The public health assessment has been modified to give more precise information on the groundwater flow in the three aquifers.
Comment: Page 6, Paragraphs 1 and 2. Evaluation of actual cancer risk (assuming TCE and PCE are carcinogens) is probably impossible. At levels of risk on the order of one in 100,000, only two to three cases would be reported in the entire Multnomah County population.
Response: In accordance with ATSDR guidance, the evaluation of cancer cases within a population near a NPL site is conducted not only when ATSDR can document that human exposures to carcinogens has occurred but also when the surrounding population indicates they are concerned about the rate of cancer cases in the area (i.e., Community Health Concern). During ATSDR's original site visit in 1993, the community indicated to ATSDR that they believe that the occurrence of cancer is elevated in the area.
Comment: Page 8 and 9, References to Tables 1 through 7. Each of these tables lists only the 1,2-dichloroethene (1,2-DCE) isomer, trans-1,2-DCE. Actually the predominant 1,2-DCE isomer detected is cis-1,2-DCE.
Response: The public health assessment has been corrected accordingly.
Comment: Table 4. This table refers to contaminants detected downgradient of the Cascade and Boeing sites, while Tables 5 and 6 specifically refer to contaminants detected downgradient of the Cascade and Swift sites, respectively. Should "Cascade Corporation and" be deleted from the title of Table 4?
Response: No. Groundwater monitoring data indicates that some of the groundwater contamination from Cascade has migrated under the Boeing facility, intermixed with the contamination from the Boeing facility, and migrated beyond the boundaries of the Boeing facility. Therefore, the contaminants detected are downgradient of both the Boeing and Cascade facilities.
Comment: Page 10, Section 3, Paragraph 1; Table 7 in Appendix 4. The second sentence should be deleted. According to Table 7 in Appendix 4, trans-1,2-DCE [sic] has not migrated into residential wells above it comparison value.
Response: The public health assessment has been modified accordingly.
Comment: Page 12, Paragraph 4. The estimate of the number of people potentially exposed should be substantiated. For example, was the estimated based on average household size, or were census data used?
Response: Information has been added to the public health assessment to substantiate the population estimate.
Comment: Page 13, Last Paragraph. Approximately 20 people use the aquifer as a primary water source. The way the sentence is written is misleading.
Response: The public health assessment has been modified to clarify this paragraph. However, the wells used by the West Interlachen Corp., the Interlachen Inc., and Blue Lake Co-op provide drinking water to 148 families. Therefore, more than 20 people use the aquifers as a primary water source.
Comment: Page 14, Section 2 - Worker Exposures. The ATSDR probably does have information necessary to calculate ambient target levels based on National Institute of Occupational Safety and Health (NIOSH) or other chronic exposure criteria. Such a calculation would indicate that levels from contamination sources or remediation are well below workplace standards.
Response: ATSDR's primary concern relating to worker exposures are associated with worker exposures to contaminated water from the industrial wells. As stated in the public health assessment, ATSDR does not have adequate information to estimate how extensive the exposures might have been (e.g., length of the time the wells were contaminated, concentrations of contaminants in the wells, and how the wells were used).
Comment: Page 16, Paragraph 2; Page 17, Paragraph 1; and Page 18, Paragraph 2. These paragraphs are contradictory.
Response: The public health assessment has been modified to avoid any contradictions.
Comment: Page 20, Paragraphs 1 and 2. The explanation here could be clearer and note that the worse case estimates show low potential, while actual exposure would be reduced due to both limited durations of exposure and lower average concentrations.
Response: As indicated within this section of the public health assessment, ATSDR believes that the exposures could have occurred for more than 10 years. We do not believe that this length of time is a limited duration exposure. Therefore, this part of the public health assessment has not been changed.
Comment: Page 23, Paragraph 1. The discussion on the TSA interim removal action should be updated, noting that the system was tested to evaluate its effectiveness for protecting the beneficial uses of the BLA.
Response: ATSDR has obtained the latest Community Relations Plan from the ODEQ. This plan summarizes the key activities that have taken place and that will occur at the site. The plan has replaced the summary originally in Appendix 2 of this public health assessment.
Comment: Appendices. The information provided in Appendix 3 (definitions of terms CREG, Reference Dose Media Evaluation Guide [RMEG], Lifetime Health Advisory [LTHA], and Environmental Medial Evaluation Guide [EMEG]) is not sufficient to verify the derivations of the comparison values in Appendix 4. Also, the discussion in Appendix 3 is unclear as to the hierarchy of preferences among these comparison values.
Response: The derivations of CREGs and Minimal Risk Levels (MRLs) are presented in the ATSDR Toxicological Profile for each of the contaminants. The RMEGs and EMEGs are derived by the methods outlined in the ATSDR Public Health Assessment Guidance Manual. The LTHA is developed by EPA.
The public health assessment has been modified so that it explains the hierarchy of preferences among the comparison values.
Comment: Appendix 1, Figure 2. The boundary of the TSA plume should be updated to account for TSA impacts in the western portion of the Boeing site. The eastern extent of the plume should also be modified to incorporate data from Cascade.
Response: ATSDR has obtained a more accurate map from the ODEQ. This map replaced Figure 2 in the public health assessment.
Comment: Appendix 6, Page 56, Paragraph 1. This paragraph states that doses were calculated for either adults and children. It should be specified whether the calculation were for adults or children. The exposure point concentrations should also be reported so the calculations can be verified.
Response: The concentrations used in the calculations are noted on page 16 of the Public Comment Release Public Health Assessment. As implied by the Appendix 6 discussion, both adult and child calculation were conducted.
Comment: Please change "Boeing Company of Portland" to "The Boeing Company" throughout the assessment.
Response: The public health assessment has been changed accordingly.
Comment: Page 1, Paragraph 1. The map (Figure 1) does not show the City of Troutdale. Is the City of Troutdale included in the NPL site? Is the City of Troutdale included in the Reynolds Aluminum NPL site?
Response: A portion of the City of Troutdale (western edge) is included in the proposed East Multnomah County Groundwater Contamination NPL site and a portion of the City of Troutdale is included in the proposed Reynolds Metals NPL site. The site boundaries for the two proposed NPL sites do not overlap. The proposed Reynolds Metals NPL site is located east of the proposed East Multnomah County Groundwater Contamination NPL site and is not located on the map (Figure 1). The public health assessment has been changed to indicate that only a portion of the City of Troutdale is included in the proposed East Multnomah County Groundwater Contamination NPL site.
Comment: Page 1, Paragraph 1. Can ATSDR be specific about the location of this well? Boeing understands that this well is located near N.E. 205th Avenue, downgradient of the Cascade facility. Boeing suggests that the location of this well be indicated on Figure 1 and/or Figure 2.
Response: This well is located downgradient of the Cascade facility east of 201st Avenue. This information will be added to the public health assessment.
Comment: Page 1, Paragraph 2. Cascade has been in operation since 1956; Boeing plant since 1963.
Response: The public health assessment has been changed accordingly.
Comment: Page 2, Paragraph 1. Apparently ATSDR would not conclude that the NPL site was a public health hazard if this well were not in use. ATSDR can only encourage, rather than require, abandonment of this well. Since the well owner/user apparently has a choice of whether to continue exposure, this does not seem an appropriate basis for determination of a current and future "public" health hazard.
Response: The fact that people make an informed decision about the health risk associated with a particular situation does not have any bearing in ATSDR's decision as to which hazard category to assign to a site. In addition, the number of individuals at risk has no bearing on ATSDR's determination. The ATSDR Public Health Assessment Guidance Manual states that a site should be classified as a "public health hazard" when there is evidence that exposures may result in long-term adverse health effects to any segment of the receptor population. We believe that the site is classified appropriately.
Comment: Page 4, Paragraph 1. It should be stated in this paragraph that the City of Portland backup supply wells have not and are currently not impacted by the groundwater contamination.
Response: The public health assessment has been changed accordingly.
Comment: Page 4, Paragraph 7. This paragraph may be misleading, as it seems to imply that everyone who obtains water from these large aquifers is potentially at risk from a plume located in only a portion of the aquifers. It also seems to overstate potential exposures because the ATSDR has only identified one well currently used for primary drinking supply in the area of the plume.
Response: The information provided in this paragraph is for background purposes. Because the City of Portland does obtain some of its drinking water supply from the affected aquifers, ATSDR believes this information is appropriate. However, ATSDR has added discussion to this paragraph to clarify the potential exposure risk.
Comment: Page 5, Paragraph 4. Discharge from the lower Columbia Slough to the Willamette River or other water bodies is not relevant to this assessment, since the lower slough is hydraulically isolated from the slough in the NPL area.
Response: The public health assessment has been changed to clarify this issue.
Comment: Page 5, Paragraph 5. Springs may historically have been used to water livestock, but have not been used for many years.
Response: The public health assessment has been changed accordingly.
Comment: Page 5, Paragraph 7. A plan view figure and one or two cross sections would help to make this discussion clearer.
Response: The public health assessment has been changed accordingly.
Comment: Page 5, Paragraph 7. The statement is not accurate as written, as the TGA does not discharge to Fairview Lake. Change to read: "...discharge to some extent to the Columbia Slough. The TSA may also discharge to Fairview Lake."
Response: The public health assessment has been changed accordingly.
Comment: Page 7, Paragraph 2. Base on the discussion in this paragraph, it appears that concentration data dating back to 1985 were compared to ATSDR health values. However, because interim remedial actions have been undertaken since that data(e.g., pump and treat activities), the most recent data collected (e.g., during the past 2 to 3 years), which are most representative of current site conditions, should be used compare to ATSDR health values.
Response: In order to determine what contaminant might have and/or could pose a public health concern, ATSDR compares all available concentration data to the health comparison values. As indicated in the next paragraph, the selection of a contaminant is only done to focus the discussion of the public health assessment. The determination as to what levels people were exposed to and for how long is presented later in the document.
Comment: Page 7 Paragraph 4, Line 31-33. This sentence should be deleted. Boeing's 1994 Administrative Order on Consent with EPA recognizes that the evaluation of the surface impoundment attributed groundwater contamination in the impoundment area to an on-site, upgradient source.
Response: The public health assessment has been changed accordingly.
Comment: Page 8, Paragraph 7. Available data indicate TCE concentration as high as 240 micrograms per liter in a sample taken on 4/4/90 and 410 micrograms per liter on 5/21/91.
Response: The public health assessment has been changed accordingly.
Comment: Page 10, Paragraph 1, and Appendix 4. Reference to "trans-1,2-DCE" seems incorrect. This isomer generally appears in trace amounts as opposed to the cis isomer which is commonly detected at higher concentrations.
Response: The public health assessment has been changed accordingly.
Comment: Page 10, Paragraph 2. Data presented cannot be appropriately evaluated without reference to aquifer, location (for up/down gradient determination), and data of sample collection.
Response: The references for this information is given in the first paragraph. All of the wells discussed in this paragraph are downgradient of source areas. The public health assessment has been modified to clarify this issue.
Comment: Page 10, Paragraphs 5-6, and Page 11, Paragraph 1. This data should be deleted. The vast majority of the 1987-1991 Toxic Chemical Release Inventory (TRI) data presented regarding Boeing air emissions are irrelevant to the groundwater problem under analysis as they relate to manufacturing processes. Additionally, this data is irrelevant to the time period identified (pre-1986) for the occurrence of releases to groundwater.
Response: In accordance with the ATSDR Public Health Assessment Guidance Manual, TRI data should be presented. As indicated in the Potential Environmental Exposure Pathways subsection, it is possible that people are being exposed to 1,1,1-trichloroethane in addition to the drinking water exposures to chlorinated organic solvents. The paragraph noted by the commentator has been modified to indicate that TRI data can be used to determine if there are any additional exposure routes to site-related or similar contaminants.
Comment: Page 12, Paragraph 3. The last sentence of this paragraph is misleading and unnecessarily disquieting. The plume and groundwater flow have been well characterized and the maximum concentrations are known with reasonable certainty. The maximum concentration in the well cannot exceed the maximum concentration in the plume upgradient of the well.
Response: The public health assessment has been modified to indicate the concentration in the well is unlikely to exceed the maximum concentration in the groundwater plume upgradient of the well.
Comment: Page 13, Paragraph 4. This incorrect. The City of Portland pumped a portion of its well field for drinking water supply as recently as 1994.
Response: The public health assessment has been changed accordingly.
Comment: Page 14, Paragraph 3. If requested, data are available to estimate incremental exposure to stripping tower off-gases at the Boeing facility.
Response: As indicated in this sub-section, ATSDR believes that there is a potential for people to exposed to the off-gases from the stripping tower. The public health assessment has been changed to indicate that ATSDR does not believe that this potential exposure is significant.
Comment: Page 15, Paragraph 1. Although no ambient air samples were collected to assess the extent of human exposure, it should be noted, as described on page 9 of the ATSDR Public Health Assessment, that air monitoring at the facilities on site "did not detect any significant air contamination".
Response: Air monitoring at the facility may not be reflective of the ambient air conditions away from the facility because the ambient air discharges reported in the TRI may have been discharged at different heights and may not have migrated to ground level near the areas that were monitored (e.g., stack height and mixing zone conditions).
Comment: Page 15, Paragraph 4. This last statement is incorrect. Although the extent of exposure is likely to be low, recreational activities at the Columbia Slough do represent complete nonoccupational exposure pathways to site-related contaminants.
Response: The water contamination in the Columbia Slough appears to be located in one small part of the Slough. Because a person would have to be within that area and would have to inadvertently consume or inhale contaminants at this area, ATSDR believes it is appropriate to classify this as a potential exposure pathway.
Comment: Pages 16 through 18. The material presented here seems to unnecessarily raise potential for concern where none exists or can be supported by available data. This section (A.2) could be replaced with the first sentence of the first full paragraph on page 17 and the second full paragraph on page 18.
Response: ATSDR disagrees. One of the purposes of an ATSDR public health assessment is to provide the public with information concerning the possible health effects the contaminants may be associated with at the levels of exposure found at each site. The information cited by the commentator provides the latest information concerning TCE. As indicated in the text of this public health assessment, the results of the studies reviewed indicate that further investigation of low dose TCE exposures is needed.
Comment: Page 22. Recommendation #2 should be revised to reflect that not all wells are sole supply sources. A concentration at levels of health concern in one or more wells does not necessarily result in a water supply with concentrations at these levels if the water is blended with other non-contaminated water, which would almost certainly be the case with public supply systems.
Response: The recommendation has been modified to indicate that any well that would result in human exposures at or above levels of health concern should not be used as a drinking water supply.
Comment: Page 30, Figure 1. The map does not show all city wells within the mapped area.
Response: Figure 1 is a general vicinity map. It was never intended to show all of the city wells. A new figure has been added to the public health assessment which does show all of the city wells.
Comment: Page 31, Figure 2. The map incorrectly shows a TCE plume on portions of the Boeing site where the TGA is not present and where no TGA contamination has been detected. Supplemental figures are available to ATSDR on request.
Response: ATSDR has obtained a more accurate map from the ODEQ. This map replaced Figure 2 in the public health assessment.
Comment: Appendix 3, Page 42. It is unclear from the description provided on this page when a particular health comparison value is used over another.
Response: The public health assessment has been modified to clarify this issue.
Comment: Appendix 4. Some contaminants are listed in the tables even though they were not detected at levels of health concern.
Response: The tables have been modified so that only contaminants detected at levels of health concern are listed in each table.
Comment: Appendix 5, Table 2, Page 53. Shepard Spring and Taggart Spring are on private property and are not generally available for recreation. There is no known use of these surface water features for recreation.
Response: This table presents the potential environmental exposure pathways. People could possibly come in contact with the spring water while playing or walking across the property (e.g., recreating). Therefore, ATSDR believes it is appropriate to list these springs at this location.
Comment: Appendix 6, Pages 55 and 56. The exposure doses are not provided in this table for comparison.
Response: The exposure doses were calculated using the residential well sampling results. The
doses were calculated by the methods outlined in the ATSDR Public Health Assessment Guidance
Manual.
1. The National Toxicology Program in its Annual Report on Carcinogens classifies a chemical as a "known human carcinogen" based on sufficient human data. Its classification of a chemical as being "reasonably anticipated to be a carcinogen" is based on limited human or sufficient animal data.
2. IARC defines a class 1 carcinogen as a substance which studies in humans indicate a causal relationship between the agent and human cancer. Class 2 carcinogens are those reasonably anticipated to be carcinogens. For a 2A classification, there is limited evidence of carcinogenicity from human studies which indicate that a causal interpretation is credible, but not conclusive. A classification of 2B indicates that there is sufficient evidence of carcinogenicity from studies in experimental animals.
3. In EPA's classification scheme, a chemical is considered a class A or human carcinogen based on sufficient evidence from studies of humans. A substance is considered class B1 if there is limited evidence from human studies. B2 is used when evidence for carcinogenicity is inadequate or non-existent based on human studies, but sufficient based on animal studies.
4. Category I: The substance meets the definition of a potential occupational carcinogen in (i) humans, or (ii) in a single mammalian species.
Category II: The substance (i) meets the definition of a potential occupational carcinogen but the
evidence is suggestive.
