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quality protection or for constituents that are known to have a much greater than average <br /> degree of environmental attenuation. [Examples of such constituents are free cyanide in <br /> surface waters, copper,zinc, and DDT under common environmental conditions 12�.] <br /> Whenever sufficient site- and waste-specific data can be obtained, a more thorough <br /> analysis of environmental fate should be substituted for this "generic" attenuation factor <br /> approach. It is the responsibility of the waste discharger to provide this analysis. <br /> 3 3.2 Designated Levels for Liquid Wastes <br /> The Total Designated Level for a constituent of a liquid waste is calculated by multiplying <br /> the water quality goal by the environmental attenuation factor that takes into account <br /> reasonable worst-case site-and waste-specific conditions at the proposed place of waste <br /> discharge. <br /> Total Designated Level Water Environmental <br /> for constituent of a = Quality x Attenuation ill <br /> liquid waste (mg1l of waste) Goal (mgA) Factor <br /> Figure 11 presents an example of the disposal of a hypothetical liquid waste to an unlined <br /> surface impoundment In this example,the constituent of concern in the waste is arsenic <br /> and the potential threat to ground water is being considered. Ground water at this site has <br /> the potential for use as domestic supply. The Primary MCL for arsenic of 50µg/1 (0.05 <br /> i mg/1) has been chosen as the water quality goal, protective of this beneficial use. By <br /> environmental fate analysis, the soils between the base of the unpoundment and the <br /> highest anticipated elevation of ground water have been estimated to provide a minimum <br /> of"n"-fold attenuation for arsenic. The environmental attenuation factor is, therefore, _ <br /> - equal-to"n":The disposal of-tlus waste is proposed-to occur over atwo year period;thus, <br /> _the_attenuativ_ -processes-for-arsenic in.the soil-are not expected to become saturated.'The. <br /> Total Designated Level for arsenic in the liquid waste discharged to this hypothetical <br /> T - -impoundment is,-therefore,-equal to(0.05 x r1)-mg/1: If analysis of the waste shows that its <br /> dissolved arsenic concentration is equal to or greater than (0.05 x n) mg/l, the waste will <br /> not receive sufficient attenuation as it migrates from the impoundment to ground water- <br /> and the resulting concentration of arsenic in ground water may exceed the Primary MCL, <br /> thus impairing the beneficial use of the water for domestic supply. This waste should, <br /> therefore,be classified as a 'designated waste' and the impoundment should be required to <br /> meet Class 11 surface impoundment construction standards. If the arsenic concentration in <br />-- - --— - -the waste is below(0.05 xn)mg/l;tKe-ii agfe- dods not have the potential to degrade ground <br /> water quality and would be classified as an 'inert waste' for this site. (Obviously,a liquid <br /> waste may not be classified as a 'nonhazardous solid waste'.} <br /> If the arsenic concentration in the waste is close to but does not exceed (0.05 x n)mg/l, <br /> some impoundment construction requirements, such as a single clay liner,may be prudent <br /> to ensure that sufficient attenuation exists. This would be especially important if questions. <br /> exist about the representativeness of the waste sampling and analysis or if the waste <br /> characteristics are expected to vary significantly over the period of time that the discharge <br /> will occur. <br /> Designated Level Methodology Page 33 <br />