ARCHIVED REPORTS_XR0008213 - Laserfiche WebLink

Home Browse Search

procedures that can be used to assess the fate of chemicals in the environment and estimate environmental attenuation factors for specific waste constituents and site conditions. Detailed information on many environmental fate characteristics may prove difficult or impractical to obtain. Therefore, the analysis may be approached initially in a simplified manner,by using more easily obtainable information on some of the key characteristics and conservative assumptions about the remaining characteristics to approximate the minimum expected attenuation. For example,in the analysis of the threat posed to surface waters the lowest anticipated initial dilution of the waste or leachate into surface waters can be used as a measure of attenuation. If this type of simplistic analysis can clearly demonstrate that waste constituents cannot adversely impact water quality, then further and more detailed analysis may be unnecessary. If a simplified analysis gives inconclusive results or shows that the potential for water quality degradation may exist, the waste discharger may wish to obtain detailed information on heretofore undetermined environmental fate characteristics in order to refine the analysis In many cases, resources may not permit a detailed environmental fate analysis for the selection of attenuation factors. This is especially true where a discharger requires a preliminary idea of how a waste will be classified. For these cases it is proposed that a "generic" environmental attenuation factor be chosen in a manner similar to that used by DHS in the setting of hazardous STLCs. The CAM SOR 3 justifies the use of a 100-fold attenuation factor,based on studies conducted by Batelle Laboratories and EPA?-34 Both studies stress that the degree of attenuation of waste constituents depends on waste-and site-specific conditions,as discussed above. It is,therefore,impossible to select an attenuation factor that will be appropriate for all wastes constituents or all disposal sites and situations. Expected landfill-to-useable ground water attenuations cited by EPA range from one to 1,000-fold,based on mathematical models and actual field data. Both the Batelle and EPA documents selected a 100-fold attenuation factor to conservatively represent average attenuation of waste constituents as leachate moves to an underground source of drinking water; however,neither study provides detailed descriptions of which waste-and site-specific conditions are best approximated by the 100-fold factor. In selecting a "generic" environmental attenuation factor for purposes of deriving designated levels, the 100-fold factor should be used in those disposal situations which provide an "average" degree of natural protection for water quality from the discharge of wastes under reasonable worst-case conditions. An example of such an average disposal situation would be a landfill in the alluvium of the Central Valley with a significant depth (i.e.,greater than 30 feet) of soil containing appreciable and continuous clay or silty-clay strata between the base of the landfill and ground water. For sites that provide less than this "average" amount of water quality protection(e.g.,high ground water or more highly permeable geologic materials--sandy soils or fractured rock),a lower environmental attenuation factor,such as one(1)or ten (10)should be chosen. Where a very low degree of natural water quality protection may exist or for situations in which the mass Ioading of J waste constituents is likely to saturate environmental attenuation processes (e.g.,the . discharge of large volumes of a liquid waste to a surface impoundment continuously over many years in an area with moderately permeable soils), a factor of one (1)should be used. A factor of 1,000 may be appropriate in areas that provide a very high degree of water Page 32 Designated Level Methodology