PARENT SESSION
IP08 - Population Modeling Ecological Risk Assessment
Chair: Kapustka, Lawrence1, 1 5010 SW Hout Street, Corvallis, WA, USA
Co-chair: Landis, Wayne2, 2 516 High Street, Bellingham, WA, USA
8:00 AM to 12:00 PM - Tuesday, 19 November 2002
Room Room 150 G
(IP66) THE OREGON EXPERIMENT: A PRAGMATIC APPROACH TO POPULATION-LEVEL RISK ASSESSMENT.
Hope, Bruce*,1, Fuji, Taku2, 1 Oregon Department of Environmental Quality, Portland, OR, USA2 Hart Crowser, Inc., Lake Oswego, OR
ABSTRACT- In 1997, Oregon enacted an amended statute and associated rules that require protection of ecological receptors at the population level for all plants and animals not listed as threatened or endangered. Oregon's regulatory model for population risk assumes that an unacceptable risk occurs when there is a greater than 10 percent chance of less than or equal to 20 percent of the total local population receiving an exposure greater than the toxicity reference value (TRV). Conversely, risk is acceptable when either (a) chance of exposure exceeding the TRV is less than 10 percent regardless of the fraction of the population exposed or (b) chance of exposure exceeding the TRV is greater than 10 percent for an individual but less than 20 percent of the local population is exposed. This case study illustrates how Oregon's population-level procedure was used to develop site-specific groundwater remedial action objectives for resident aquatic populations at a site in Northwest Oregon, where an upland petroleum pipeline released gasoline-range hydrocarbons (TPH-G) into soils and groundwater immediately upgradient of the Tualatin River. The goal was to proactively establish a remedial action objective that would equate to an acceptable risk level for populations of aquatic receptors potentially threatened by future groundwater discharges to the river. The population-level RAO selected was a 10% dilution of the water-soluble fraction of pure product. This RAO was above fish population EC20 values or Tier II secondary chronic values but generally lower than lowest chronic values. These RAOs are below but close to Oregon's freshwater acute criteria, which are set at a LOEL because of insufficient data to develop criteria. That Oregon's population-based RAOs are closer to an actual effect level than to no-observed-adverse-effect or other conservative protective levels is consistent with the expectation that not all individuals be protected.
Key words: population-level risk, binomial joint probability model, population risk regulation, Oregon