COMPLIANCE INFO_1992-1993 - Laserfiche WebLink

Home Browse Search

Mr. Robert Grauli.ch Page 6 not necessarily the worst imaginable, but the most reasonably likely mismanagement that may occur. In order to assess the risk posed by the ash and determine whether that risk is acceptable or not, it was necessary to evaluate it in light of conditions of management (and mismanagement) . Risk is evaluated by comparing an anticipated exposure under anticipated or assumed conditions to a known or accepted "safe" level of exposure. Two different unit risk levels have been developed. The first was formulated by Drs. Brantner and Klein of the Toxicology and Risk Assessment Section of the Toxic Substances Control Program of the Department. The unit risk level was determined to be 3.55 x 10"5 (µg/m3)''. The second was formulated by the Office of Environmental Health Hazard Assessment of the Department for use by the California Air Pollution Control officers Association (CAPCOA) in the implementation of the California Air Resources Board's Air Toxics "Hot Spots" program (AB 2588) . This second unit risk level was determined to be 2.9 x 10'4 (14g/m3) '1, an order of magnitude greater than the Brantner and Klein value, and therefore more conservative. Using accepted modeling techniques, it is possible to estimate airborne concentrations of the respirable particles at the point of human exposure. The estimated airborne respirable concentration is then compared to the concentration which would exceed the "acceptable" risk level, i.e. , the unit risk divided into 1 x 10'6. Airborne concentrations of respirable crystalline silica were estimated as a function of wind velocity. Estimation of the airborne concentration of respirable crystalline silica, and subsequent exposure, was based on modeling techniques employed by the Department and the U.S. Environmental Protection Agency (EPA)4. Although evaluation of wastes is usually confined to the evaluation of the waste under reasonably expected mismanagement conditions, in this case it was felt that evaluating the waste using "worst anticipated" adverse conditions would be beneficial, at least in an initial estimation of risk. Estimates were made using the following assumptions: a. 25 miles per hour (12 meters/second) average annual wind speed; 3A unit risk level is defined as the increment of risk associated with the exposure of a receptor to a specified unit of an identified substance. 4The methods recommended by the Department are found in the California Site Mitigation Decision Tree Manual (1986). The methods recommended by EPA are found in "Screening Procedures for Estimating the Air Quality Impact of Stationary Sources" (EPA Document No. 4504-88-010, 1988).