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Step 4: Risk Assessment Work Plan

​Facilities choosing to perform a Level 3 or 4 risk assessment are required to submit a Risk Assessment Workplan. Level 1 and 2 risk assessments only require a Modeling Protocol that includes a thorough discussion of exposure locations and exposure scenarios.

Yes. A combined Modeling Protocol and Risk Assessment Work Plan will be accepted, and is preferred by DEQ. Please be sure to clearly define each required submittal in the document (i.e., include as separate chapters or sections).

​Yes. DEQ has developed a crosswalk between state-level zoning classifications and recommended exposure locations for use in a CAO Risk Assessment. Facilities may deviate from these recommendations with appropriate documentation from local land use authorities, such as the applicable city or county zoning authority requirements.

Acute risk should be evaluated everywhere that people 'normally congregate' for several hours in a day [OAR 340-245-0020 (22)]. For example, roadways, sidewalks, and railways do not need to be assessed for acute exposure since people are not expected to remain in one location for several hours. However, transit stations and stops, parks, golf courses, stadiums, and swimming pools are examples of locations where people might remain in one spot for several hours.

One criterion to use when determining if an area should be considered for acute risk exposure is 'are there reasonable circumstances where the public may spend 2 or more hours in this location?'; if the answer is yes, the location should be evaluated for acute risk.

DEQ does not recommend using tax lot boundaries when assigning exposure locations. Tax lots can be smaller than the useable property due to right of way areas. CAO requires zoning to be used when assigning exposure locations. 

Risk does not need to be evaluated on roadways or railways (other than at train stations and bus stops) that are close to a facility, as those are locations in which people would not normally congregate. However, modeling receptors that fall on roadways or railways must be included in the modeling grid to ensure completeness and accuracy of the modeling results. When reporting the final risk results of the highest risk by exposure scenario, risk at these locations may be omitted. For exposure locations far from a facility (such as on a 500 m modeling grid), do not exclude locations that happen to fall on a roadway or railway, as these locations are meant to be a general representation of the community and the underlying landuse/zoning (such as residential or commercial).


Typically people will not spend more than two hours at a small cemetery. However, if larger cemeteries have caretakers or other workers, acute risks should be evaluated (in addition to worker exposure).


Farmland may be considered an acute exposure, unless there is worker exposure that occurs for longer than an acute exposure. For instance, there are some farming practices that require workers to remain in a single field for a full workday, for a full season. Another example is a livestock area that requires workers to be present every day. In these cases, a worker exposure scenario would be more appropriate than a farm in which a worker may only be present a few hours a day for a few days a year. A residence on farmland must be evaluated for residential exposure. Please consult with DEQ with specific questions.

Areas zoned residential but no houses are built

The default option for any area zoned for residential use is to evaluate residential exposure. Residential risk represents the most conservative risk estimates due to the frequency and length of exposure. A facility may request to reclassify the residential zone to another exposure type such as worker or acute if there is no current residential land use in that area- see section “What if the land near my facility is not currently being used in a manner consistent with zoning map" below.

A large nature reserve

A large nature reserve that allows public access should be evaluated for acute exposure.


Parks should be evaluated for acute exposure as it is reasonable to assume that people will normally congregate for extended periods of time.

Jails and Prisons

Both jails and prisons should be evaluated for worker exposure. Given the more limited exposure duration in jails, residential exposure does not need to be evaluated. Prisons with inmates present for one year or more should also be evaluated for residential exposure. 

Future Urban Development

Areas Zoned “Future Urban Development" are defined as “holding zones inside Metro UGB - planned for future residential or nonresidential uses." The most conservative exposure location assignment for these types would be residential. DEQ recommends working with local land use authorities to determine if an urban development plan is in place that would better categorize the future land use. If this area will not be evaluated for residential risk, the facility may be required to provide annual documentation that the area has not had homes built or in development. If the facility evaluated this as a residential exposure, annual documentation would not be required.

​​If the land use near a facility is currently being used in a manner different than the zoning, you have the option of requesting that the chronic exposure locations be reclassified in the risk analysis to represent the current use. For example, if land surrounding a facility is zoned to allow for a residence or business but there is currently no established home or business at these locations. In this situation, the following is required [OAR 340-245-0210(1)(a)(F)]:

  • The approved locations must still be included in the model and acute noncancer risk must be evaluated in these locations.

  • The facility must submit annual reports demonstrating that the land use is unchanged.

  • If the annual report indicates that land use has changed, the facility must re-evaluate risk consistent with the current land use.

Please note, any occupied residence must be assessed as residential regardless of actual zoning classification – e.g., in the case where homes were permitted to remain in locations where local zoning has been revised to only allow future commercial development.

To request a change to underlying zoning, the facility must complete the AQ521 Form and the AQ522 Table.

Yes. Receptors not assigned as exposure locations (e.g., that fall on roadways or railways) should be included as modeling receptors for completeness and accuracy of the modeling results.

​While RBCs themselves are set in rule and cannot be altered, a Level 4 risk assessment allows for approved modifications of exposure frequency and duration. These updated exposure assumptions can be incorporated to calculate risk in a Level 4 risk assessment, if approved by the DEQ.

Toxicity equivalents (TEQs) are a convenient way to calculate risk for a chemical class where toxicity of individual compounds can be related to one of the most toxic members of the chemical class. For CAO, the approach for presenting TEQ risk depends on the class, but in general, DEQ recommends evaluating all congeners individually if possible as this will provide the most representative emissions profile and allows for confirmation of the risk calculations.

Polycyclic aromatic hydrocarbons (PAHs). The best approach is to evaluate PAHs individually because this is most representative. It is also the best way for DEQ to confirm the calculations. As a summary of risk, benzo[a]pyrene TEQs can also be calculated and compared with RBCs for total PAHs, because total PAH RBCs are based on benzo[a]pyrene carcinogenicity. Summing concentrations of PAH chemicals to get a total PAH value without consideration of TEQ is highly conservative, and not recommended.

Regardless of the approach used for cancer effects, benzo[a]pyrene must also be evaluated individually for noncancer health impacts.
Dioxins (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans). Similar to the approach for carcinogenic PAHs, evaluate dioxin congeners individually so that DEQ can confirm the calculations. As a summary of risk, a total dioxin TEQ (equivalent to the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin) can be compared to the PCDD/PCDF TEQ RBCs.

Polychlorinated biphenyls (PCBs). Evaluate PCBs as both total PCBs and as dioxin-like congeners. Similar to the approach for dioxins, the dioxin-like PCB congeners should be evaluated individually so that DEQ can confirm the calculations. As a summary of risk, a total dioxin-like PCB TEQ (equivalent to the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin) can be compared to the PCB TEQ RBCs.

Cleaner Air Oregon frequently asked questions for facilities 

The frequently asked questions (FAQs) on this page are provided to answer common questions about completing air toxics risk assessments for the Cleaner Air Oregon program, and ensure consistency across assessments. As the Cleaner Air Oregon process evolves, DEQ will update this page with common questions or unique scenarios. If there is a question you would like to see answered or have feedback on a response below, please contact us at

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