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Clear Creek Management Area
What Do The Results Mean?
There was no combination of scenario, toxicity value, or visits per year that were below the EPA acceptable risk range of 1 in 1,000,000. Using the IRIS model, as shown in Figure 6, EPA’s risk estimations found that, with the exception of Scenario 3 Day Use Hiker, making five or more visits to CCMA per year over a 30-year period would put recreational users above the 10-4 risk range (1 in 10,000). Only Scenario 3 (Day Use Hiking) had risk calculations within the acceptable range. The highest IRIS risk estimations, 2 x 10-3 (2 in 1,000), were calculated using the 95% UCL exposure concentration for 12 visits per year for recreational Scenario 1 and 120 visits per year for worker Scenario 7 (SUV Patrol).
Figure 6 – Adult Cancer Risk, Scenarios 1 – 7: Mean and 95% UCL Exposures Using IRIS Unit Risk
Using the OEHHA model, even one visit per year for recreational scenarios 1, 2, 4, and 5, creates a risk that exceeds EPA’s acceptable range (Figure 7). The higher risks reflect the fact that the OEHHA asbestos toxicity value is 8 times higher than the value in IRIS. At the high end of the risk range, excess lifetime cancer risk estimations using the OEHHA model and the 95% UCL concentration indicate that recreational users riding motorcycles 12 weekends per year (Scenario 1), and workers performing SUV patrol duties at CCMA (Scenario 7) for 120 days per year during a 30-year career, could have as much as a 1 in 100 (1 x 10-2) chance of developing asbestos-related cancer. It should be noted that neither the IRIS nor OEHHA models are designed for very high exposure levels, so the absolute number calculated for the high-end risk has a higher degree of uncertainty than the numbers calculated for the lower exposure scenarios. However, the risks are still extremely high.
Figure 7 – Adult Cancer Risk, Scenarios 1 – 7: Mean and 95% UCL Exposures Using OEHHA Unit Risk
The Child/Adult estimations using the IRIS model found that five or more visits per year for Scenarios 1 through 4 was above the 10-4 risk range (Figure 8) and all visits were above the acceptable range using the OEHHA model (Figure 9).
Figure 8 – Child/Adult Cancer Risk, Scenarios 1 – 4: Mean and 95% UCL Exposures Using IRIS Unit Risk
Figure 9 – Child/Adult Cancer Risk, Scenarios 1 – 4: Mean and 95% UCL Exposures Using OEHHA Unit Risk
For the Child risks, which were calculated for a 12-year exposure from ages 6 to 18, less than five visits per year for Scenarios 1 and 2, one, five, and twelve visits for Scenario 3, and one and five visits per year for Scenario 4 were within the acceptable risk range using IRIS (Figure 10). Using the OEHHA model, only less than five visits per year for Scenario 3 Day Use Hiker was within the acceptable range (Figure 11).
Figure 10 – Child Cancer Risk, Scenarios 1 – 4: Mean and 95% UCL Exposures Using IRIS Unit Risk
Figure 11 – Child Cancer Risk, Scenarios 1 – 4: Mean and 95% UCL Exposures Using OEHHA Unit Risk
