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Bert E. Van Voris -4 - 25 February 2005 Supervising Engineer wastewater in a lined reservoir,but Musco did not equip the reservoir with the requisite liner. Musco has stated it removed the lenses of sandy soils encountered during the excavation of the dam,but the presence of these sandy lenses indicates the soil forming the indent of the reservoir site likely also has sandy lenses and this was not addressed during construction. The addendum does not consider biological attenuation as the likely cause of the low nitrogen concentrations in MW-16. Appendix E of the addendum states free carbon dioxide that seeps into groundwater can release calcium,magnesium, sodium, and bicarbonate alkalinity, and,by doing so, increase IDS. Carbon dioxide generated from the decomposition of organic waste constituents in the vadose zone(and groundwater) will have a similar effect. The addendum should provide technical information(e.g., calculations and supporting assumptions) estimating the anticipated concentration of free carbon dioxide in the reservoir's wastewater instead of stating that the aerators will remove the concentration to insignificant levels. The addendum suggests that the increased concentrations in calcium,magnesium, and alkalinity in MW-16 are attributable to dissolution of these constituents from soil due to increases in groundwater elevations. Similar increases in groundwater elevation have occurred in MW-15, which is immediately adjacent to the reservoir, yet monitoring data does not indicate that impounded wastewater is influencing the quality of groundwater in this well. Despite the increase in groundwater elevation in this well, the concentrations of calcium, magnesium, and alkalinity in MW-15 have remained essentially unchanged. In summary,the addendum does not provide sufficient technical documentation that the impoundment of wastewater in the reservoir is not releasing decomposable and salinity waste constituents to groundwater. Further, it does not document that the released concentrations do not unreasonably degrade groundwater. Monitoring for dissolved iron and manganese in MW-16 appears warranted to evaluate the extent to which organic overloading may be occurring in groundwater. Economic Considerations The addendum indicates that lining the reservoir or installing treatment to reduce BOD levels to 20 mg/l upstream of the reservoir will cost millions of dollars and"cause Musco to significantly curtail or cease operations completely,"6 which would result in the loss of about 300 jobs and impact a total of about 1200 members of the work force. Comment: Details of the derivation of treatment and reservoir lining costs, and on Musco's purported inability to pay for these improvements, are necessary for the Regional Board to evaluate Musco's claim that its implementation of either of these measures would cause Musco to significantly curtail or cease operations entirely. 'Page 5-1