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05/26/2009 13:27 9518273 DOUGLAS KUNEY PAGE 10/14 d maximum i "full" level and an emergency spillway) should be provided between the settled embankment height and the bottom of the emergency spillway. StaQs� Larzoans Two-stage lagoons (Figure 2) require more total vol=e than saingla-stage lagoons, but effluent from they second stage will be of higher quality which is desirable when effluent is to be recycled for flushing buildings. le -effluent y be recycled from well-designed primary lagoons, flushing tar will contain fewer solids and disagreeable odors, will be less corx4mive, and the threat of disease transmission will be less when c a secotiI -stage lagoon, Two-stage lagoons provide of advaritages over single ana0r0biC 14900ns. HOWeVerr =1 poultry a0lications, more tbam two units in series is rarely benefit a1.. The first stage should be planned to contain the minim= design treatmoont. volume for an anaerobic unit,, and should be Maintained at a constant depth using an overflow device into the second stage, Design of the s nd-s ge will depend on intandad use. Four objectives orsecond-stage units are possible.: (1) source of water for flus 9`, (2) further treatment of wastes, (3) holding of effluent for land disposal, (4) a combination of the .i Exact design of second-stage, units for options 1 2, and 4. would beat be based on analysis of wastaimter which each unit will receive. This information will iarely be available for individual farm situations, *t a rule-of- thumb is ordinarily sufficient. A second-stage. lagoon should be made large enough to containl pouf st o e loaded into the total system (first and second-stages) betweenplanned irrigation times, plus a Minimum design volume of so percent of the first-stage unit. xinjaux water depth of second-stage la o d be 4 to 4 feet. This will encourage aerobic conditions, resulting in better qualityflushing water. All pumping for ix�rigation and flushing should be from the second-stage lagoon. The second-stacp unit my only be used for1holding overflow from e primary lagoon until it can be cobveniently irrigatedfor crop utilization. n such cises, the second unit should be as deep as practicalsiZ'ed to hold the total volum& of all wastes and runaff whiafi will enter the Gnti= system, including 84fetY margins. When feasible, contents a entire second-stage unitimay be restoved and applied to the land. Where lagoons are installed in high-water table areas,, contents should not be lowered below e existing water table to prevent die-tur:Iiing the physical and biological seal. I • i I 273 i