Resolution No. 4793 - Laserfiche WebLink

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MWMC FACIUI'IES PLAN limited to prhna~y effluent diversion, which typically occurs only 1 or 2 weeks per year. The alternatives have nearly equal non-monetary ratings. Based on the analysis presented above, it is recom_mended that the WPCF prc~ceed with Alternative 1, conversion of the existing gaseous chlorine system to sodium hypoc~florite chlorination for both SE and PE diversion flows. Future Considerations and Recommendations At some h~ture time the WPCF will want to implement Level W reuse water on a relatively large scale and this will drive the expansion of the dis'refection system. Regulatory requirements for Level IV reuse water require either the construction of a new UV system or the addition of chlor~rte contact basins providing a 90 minute modal contact tLme. The requirement for a 90 minute modal contact th'ne using an industry accepted dispersion coefficient of 0.7 would require a total detention t~ne of 128 minutes, resul~g in extremely large chlorine contact basins. This will make the construction of a new UV facility much more cost-competitive with a new chlorine disinfection system. The recommended approach for disLrffecfion of bahare reuse effluent is to construct UV facihfies as reuse is implemented over the 20-year project life. The UV facilities would provide a reuse effluent with a 2.2 Mean Probable Number (MPN)/100 mL Total Coliform effluent on a 7-day median basis. A UV facility designed with this criteria would provide substantially more secondary effluent disinfection capacity at the lower dis~xffection requirement of 406 MPN/IO0 mL (this is for a single sample and is the criteria that would control secondary effluent disinfection design). Thus, a dLsinfection facility initially designed to provide reuse quality effluent could be used to provide disinfection of a much larger quantity of secondary effluent. In addition, the existing chlorine contact basins could easily provide the 90 minutes modal contact t/me required for Level IV reuse water using sodium hypochlorite diskffection. The recommended fiature approach to disinfection will be extremely flexible. 6.4 Effluent Disposal Alternatives Effluent reuse alternatives evaluated are based on application of Level II (secondary effluent) and Level IV (filtered) process water from the WPCF. Effluent quality influences the alternatives available for disposal. In general, effluent reuse alternatives were based on application of reuse to poplar trees, grass for hay, pasture, green spaces, and golf courses. Because of regional cl~rrate conditions, reuse alternatives are focused primarily on application during the dry season months of June through September. Regional crops uptake the greatest amok, mt of liquid during these months. Drivers for MWMC effluent reuse include: Develop public awareness and preference for reuse - Regulatory requirements related to temperature of effluent discharge to receiving waters Increasing biosol~ds (liquid and dewatered) loading rates to land application sites Filtration improvements identified in this Facilities Plan (see Section 6.2.6) will provide 30 mgd ot filtration capacity through the design period (2025). These improvements along with 626 MWMC_6.0_I~EV1 ~ DOC