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SEPTIC TANK SIZI NG CALCULATIONS The following criteria are used to estimate the Average Daily Flows (ADF) originating from each of the four referenced locations. From Uiese ADF criteria, septic tank size can be calculated for each location, which can then be totaled to estimate the size of a large receiving tank. ' The max/nrum number of people within a particular location(e.g.,Crush Office Building) and the number of restroom -fixtures serving that location is analyzed first. The maximum number of people will only occur during harvest, approximately three months out of any given year. Consequently, the septic tank must be sized to account for this anticipated maximum ADF. This maximum number of people is correlated with the SJC EHD Water Use Computation Factor Table,found in [ the Section 6.1.15 of the 1✓Ig1) Sewage Standards_ For Industrial Buildings with no rood cafeteria, a € value of 15 gal/person/day is assigned. To further assess potential water use, a"worst-case scenario during harvest time" is calculated whereby all restroom fixtures are used every 10 minutes, or six times per hour,24 hrs per day. These two values are then averaged to obtain an ADF. Secondly, the SJC EHD Sewage Standards equation is used for computing tank capacity,which is found in Section 6.1.14_ A Base Tank Capacity (BTC)of 1,200 gals is added to the ADF obtained to arrive at a tank capacity. Thirdly, the following Pump-out Interval equation is used to estimate the needed volumetric capacity for a commercial septic tank: 2.8(ADF)x P.F. The equation used assumes a three-year septage pump-out interval, although longer interval factors may be used which leads to much larger tanks. The three-year interval factor of 2.8 is used, along with the calculated ADC, multiplied by a Peaking Factor(PF) of 1.5,which is applicable for commercial systems. The value from the above EHD equation for tank capacity, is then averaged with the Pump-out Interval equation. Fourthly,the tank size obtained above is then correlated with a Detention Time equation in which the Factors oftank size, scum/sludge accumulation,ADF and the PF are used to verify that the tank size calculated will produce a detention time(hydraulic residence time)of at least one day. From this equation, the tank size can be adjusted to meet the minimum requirement of one day. The following calculations, as described above,are presented for sizing the septic tanks for each of the four referenced locations: CRUSH OFFICE BUILDING 25 people/2 shifts during harvest=50 people 10 people/ 1 shift during harvest= 10 people 50 f 10=60 x 15 gals/person/day= 900 gpd Crush Office Mens's Restroom Fixtures: Toilets= 1.5 gals/flush x 6 flushes/hr x 24 hr/day=216 gpd x 2ftoilets=432 gpd Urinals=0.5 gals/flush x 6 flushes/hr x 241ir/day= 72 gpd Crush Office Women's Restroom Fixtures: Toilets= 1.5 gals/flush x 6 'flushes/hr x 24 hr/day=216 gpd x 2 toilets=432 gpd Page 3 of 7 " Chesney Consulting