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FOG Control Program Manual <br />sizes GGIs based on the number of drainage fixture units within the FSE connected to <br />the grease waste line. The FOG Control Program Manager will also consider the <br />potential for large grease interceptors to become septic (which may create nuisance <br />odors and corrosive conditions) due to excessively long retention times. Thus, the Code <br />will be utilized with the following general considerations: <br />1) If the California Plumbing Code sizing calculation exceeds 1,500 gallons, the FOG <br />Control Program Manager will use utilize his/her best judgment based on other <br />factors at the FSE (e.g., cooking equipment, menu, frequency of use of the <br />drainage fixture units) to determine the final size of the interceptor. <br />2) The floor of the interceptor should not be too deep to allow for proper cleaning <br />and/or the interceptor should not be larger than 3,000 gallons for most <br />installations. <br />3) An FSE calculation of 375 to 750 gallons should require an interceptor of 750 <br />gallons. <br />4.4.2.2 Maintenance Requirements <br />The City requires that GGIs be cleaned (pumped) out completely as required to maintain <br />the GGI's efficient operation and prevent excessive accumulation of floating FOG and <br />settled solids. A complete pump -out means that all of the contents of the interceptor <br />are removed and no liquids are returned to the interceptor unless specific permission <br />has been granted in writing by the City (Appendix N, Pumping Frequency Variance <br />Request Form). Some GGIs may need to be pumped out more frequently than once <br />every 90 days if the accumulation of floating FOG and settled solids exceeds 25% of the <br />overall capacity of the interceptor (i.e., 25% rule). <br />4.4.3 HYDROMECHANICAL GREASE INTERCEPTORS <br />A hydromechanical grease interceptor (HGI) (also known as a grease trap) is a flow - <br />based grease interceptor that is usually installed in ground or above ground, inside or <br />outside of the facility, and has a typical capacity of less than 250 gallons. FSEs generally <br />prefer HGIs over gravity grease interceptors (GGIs) because HGIs are less expensive to <br />install, can fit in smaller spaces, and can be easier to maintain. A typical conceptual HGI <br />design is illustrated in Figure 4-3, Conceptual Design of a Typical Hydromechanical <br />Grease Interceptor. <br />19F-195 14 <br />