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0 0 <br /> Re-Manufacturing, Ltd. -5- 26 June 1991 <br /> Closure Plan <br /> 9. Water Work Corp. used the Designated Level Methodology with an attenuation factor <br /> of 100 and an MCL for lead of 50 µg/1 . Generally, to calculate protection of <br /> surface or ground water a contaminant level which is protective of the most <br /> sensitive beneficial use of the waters is used. If a detailed assessment of <br /> attenuation is not performed, Regional Board staff will generally assume an <br /> attenuation factor of 100 for sites where at least 30 feet of alluvial materials <br /> containing a significant clay content exist between the base of the landfill and <br /> the highest level of ground water. We are more concerned with the threat to <br /> surface waters, however, since only a single clay liner (cap) is proposed to <br /> separate the disposed hazardous waste from Mormon Slough. A much smaller <br /> attenuation factor under these conditions would appear to be our highest concern. <br /> How will this lack of attenuation be mitigated? The beneficial use of Mormon <br /> Slough would include the protection of freshwater aquatic life. The EPA National <br /> Ambient Water Quality Criteria to protect freshwater aquatic life varies with the <br /> hardness of the water between 0.07 and 25 mg/L for hardness ranges of 5 to <br /> 500 mg/L of CaCO„ respectively. <br /> 10. Ground water monitoring is proposed for one year after closure. Ground water <br /> monitoring, to some extent, is necessary throughout the post closure period. As <br /> stated in #7 above, the post closure period extends as long as the waste poses a <br /> threat to waters of the state. The extent of ground water monitoring can be <br /> somewhat minimized by using early detection vadose zone monitoring (e.g. <br /> lysimeters) for the presence of migrating fluids. Sections 2550 and 2556 of <br /> Chapter 15 also requires unsaturated zone (vadose zone) monitoring. <br /> 11 . In addition to the confirmation samples proposed, analyses for phenols (8040) , <br /> Total Extractable Hydrocarbons, Volatile Halocarbons (8010) and Volatile Aromatics <br /> (8020) should be included in the four areas of the impoundment floor, where <br /> borings were drilled on 24 August 1989. This is to either confirm or deny the <br /> presence of those constituents. <br /> Conclusion <br /> More detail is necessary in order for the plan to be approved and implemented. <br /> Construction drawings and specifications must be submitted. The above comments should <br /> be addressed and submitted to the Board as soon as possible so that the site <br /> investigation and closure of the impoundment can be expedited. Any changes in the <br /> proposed time schedule (specific dates) should also be submitted. <br /> HAR REVIEW <br /> The HAR addendum contained additional information to complete the HAR requirements of <br /> the TPCA. However, some of the HAR information was also included in the closure plan <br /> addendum. Our 19 February 1991 memorandum regarding the HAR included requests for the <br /> following: <br /> 1. One round of ground water quality sampling was conducted in November 1990. <br /> Additional ground water sampling was required for quality assurance and seasonal <br /> variation determination. A second round of samples was collected on <br />