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' • • <br />' <br />August 19, 1999 MEMORANDUM <br />993 -2057 <br />assessment for soil contamination is very low. The exposure assessment indicates that the <br />likelihood for mechanical leakage is medium, while the likelihood for corrosive leakage is <br />negligible. The mechanical leakage has occurred annually at other similar facilities, while <br />' corrosion leakage requires at 10 years of operation to reach a point where the pipeline and <br />fittings leak. Due to the five year life of the experimental mine, it is a negligible risk that <br />corrosion leakage would occur. The magnitude and duration of exposure for a mechanical <br />' leak will result in low exposure. The estimated volume of pregnant soda liquor is <br />estimated at 10 gpm for a maximum of 8 hours resulting in 4,800 gallons. Any greater <br />leakage would trigger alarms and the pipeline is visually inspected once every 8 hours. <br />Additionally, cameras will monitor most of the pipeline length. Pathways of exposure are <br />limited to the soils and vegetation directly contacted by the pregnant liquor. The pipeline <br />will be placed between two containment berms to control and collect any leakage. The <br />' topsoil resource will be removed and stockpiled for reclamation. The soil or foundation <br />material within the bermed area below the pipeline is part of the industrial disturbance and <br />represents a less significant environment at risk than native soils and vegetation in an <br />undisturbed area. The bermed area is graded to drain to the lined drainage collection pond <br />near the well field. The pathway for exposure is very low due to the drainage control and <br />' collection. The overall consequence assessment is low environmental consequences could <br />occur due to the low hazard and low magnitude and duration of exposure. However, the <br />overall risk characterization is controlled by the very low risk pathways, and the <br />environment at risk is contained within the industrial area. As a result the risk <br />characterization is described as very low. Proposed mitigation in addition to the <br />operational controls identified in the operating plan are presented on Table 1 and discussed <br />' in Section 9. <br />Operational errors resulting in accidental releases are the third failure mechanisms for the <br />' pipeline. As with the other failure mechanisms the hazard assessment indicates that soil <br />contamination is primary concern and ranges from very low to medium. The exposure <br />' assessment indicates that the likelihood is medium even with employee training and <br />adequate signage on valves and other controls. The magnitude and duration of exposure <br />should be medium due to the relatively rapid recognition of the release. The pathways are <br />' limited to the industrial within the bermed drainage and collection system. The <br />environment at risk is the industrial area around the pipeline valves and controls. The <br />overall consequence assessment is that very low environmental consequences will occur <br />' due to very low risk pathways for impacts to the environment at risk. The risk <br />characterization is described as very low due to the environment at risk and very low risk <br />pathways of exposure. Proposed mitigation in addition to the operational controls <br />' identified in the operating plan are presented on Table 1 and discussed in Section 9. <br />8.4 Process Plant <br />' Potential failure mechanisms at the process plant include spills due to upset conditions or <br />errors. Subsidence and groundwater and surface water contamination are considered to be <br />' \ \ GAI_DEN1\ PROJECTS \WP\99\2057\2057TM1.DOC Golder Associates <br />