Agenda - 11-19-1985 - Laserfiche WebLink

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A . A F Mr. Ken R. Thompson Page -2- May 15, 1985 . The proposed ordinance significantly improves the capability of the Upper Eno system to provide a safe water supply during droughts. • ( If all water systems would have drawn water to their full capacity during recent years, the three water supply reservoirs on the Eno would have been completely drained. This would, of course, have ..' created a dire emergency for northern orange County. The only reason this did not happen is that Orange Water and Sewer Authority purchased 4 only a fraction of the maximum contracted amount. Also, the Orange-Alamance Water System and the Town of Hillsborough did not withdraw to their full capacity. In our opinion, a water management ;- plan should be implemented if a complete water resources disaster is • to be avoided. If the approach using the ordinance fails, a •, s solution could be sought under the provisions of GS 143, Article 21, part 2. .7, •- Immediate consideration should be given to the adoption of a plan, with the understanding that as more information becomes available, : adjustments can be made. With the features outlined in the draft ordinance, the raw water system has limits on overall yield based on assumed withdrawals. For a sustained continuous withdrawal, and with the ordinance in effect, the gross yield of the Lake Orange system is only 2.6 MGD at the normal stage which would be reduced in line with 4 the withdrawals column of Table 2, on page 7. The model indicates • that this yield can be sustained over the period of record with only t-- , =4 one failure.* There are operating and storage adjustments that can be made to insure that there is no failure at the 2.6 MGD withdrawal rate. - . The overall yield figure could be increased if the OWASA would limit their withdrawal to specific amounts during specified periods. For instance, a 1.5 MGD withdrawal during September and October. In 'e any event, until additional storage or sources are made available, limits on use should be established for this limited resource. In the case of the Upper Eno River (the Eno River in Orange County) , for continuous withdrawal conditions, an initial withdrawal limit of 2.6 MOD should be considered (except when there is significant spill at. -; Ben Johnson Dam) . ,! In reviewing recent withdrawal data and supplemental . source , availability, a limit of 0.5 MGD for the Orange-Alamance system and 2.1 MGD for the Hillsborough system and their customers might be • appropriate. Excess needs of the Orange-Alamance system could probably be supplied from the Mebane-Graham-Burlington network. This network could also supply some water to Hillsborough and OWASA through the existing 6-inch connection or through a larger line that could be installed, which would further connect the Orange-Alamance and •Hillsborough systems. An assessment of how the water resource system would respond, using the ordinance and the above limits and assumptions, is shown in Annex A to this letter. As discussed above, changes on withdrawal times and limits will. change the model results. We would be pleased i! to further discuss the technical aspects of the system operation with r;! you at anytime. Also, as mentioned above, there are a few It' modifications to the operation and storage that would tend to increase vt the yield during stress periods, that should be explored. it' • k *A failure is the complete depletion of the usable storage 4, in Lak,..