Preassessment screen-preliminary identification of resources potentially at risk.

§ 11.25 Preassessment screen—preliminary identification of resources potentially at risk. (a) Preliminary identification of pathways. (1) The authorized official shall make a preliminary identification of potential exposure pathways to facilitate identification of resources at risk. (2) Factors to be considered in this determination should include, as appropriate, the circumstances of the discharge or release, the characteristics of the terrain or body of water involved, weather conditions, and the known physical, chemical, and toxicological properties of the oil or hazardous substance. (3) Pathways to be considered shall include, as appropriate, direct contact, surface water, ground water, air, food chains, and particulate movement. (b) Exposed areas. An estimate of areas where exposure or effects may have occurred or are likely to occur shall be made. This estimate shall identify: (1) Areas where it has been or can be observed that the oil or hazardous substance has spread; (2) Areas to which the oil or hazardous substance has likely spread through pathways; and (3) Areas of indirect effect, where no oil or hazardous substance has spread, but where biological populations may have been affected as a result of animals moving into or through the site. (c) Exposed water estimates. The area of ground water or surface water that may be or has been exposed may be estimated by using the methods described in appendix I of this part. (d) Estimates of concentrations. An estimate of the concentrations of oil or a hazardous substance in those areas of potential exposure shall be developed. (e) Potentially affected resources. (1) Based upon the estimate of the areas of potential exposure, and the estimate of concentrations in those areas, the authorized official shall identify natural resources for which he may assert trusteeship that are potentially affected by the discharge or release. This preliminary identification should be used to direct further investigations, but it is not intended to preclude consideration of other resources later found to be affected. (2) A preliminary estimate, based on information readily available from resource managers, of the services of the resources identified as potentially affected shall be made. This estimate will be used in determining which resources to consider if further assessment efforts are justified.