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FDetention ime=2 000 gal proposed second tank capacity x 1-0 20¢o°i volume toss to sma a/scum accumulation) 1.5 (Peaking Factor)x 1,000 gpd e= 1.1 days. ule of thumb,the capacity of large volume tankage should be equal to approximately 5 times the ADF. Therefore,the two tanks can theoretically manage between 800 gpd(4,000=5 = 800 gpd)and (800+ 1,000)= 1,800 gpd with sufficient HRT. Higher acceptable ADFs(toward 1,800 gpd), may be achieved by periodically(preferably every 6 mos.) inspecting the tanks for sludge/scum accumulation and pumping the tanks if necessary. This pump-out interval of 6 mos. has been extrapolated from the equation found in Small and Decentralized Wastewater Management Systems, pg. 321. The second criterion for the determination of maximum use is the next limiting factor encountered, and that is the filter bed leachfield. The disposal area soils are highly permeable,to such a degree that the introduction of peat material must be incorporated as a mitigation factor. An average of the calculated soil acceptance rates stated in the Report is 0.85 + 1.2 gallons/ft2/day 2= 1.0 gallons/ft'/day. The filter bed area has been calculated to be 1,200 sq. ft using the EHD Calculation Requirements for Commercial Septic Systems guidelines. Therefore,the filter bed should initially accept 1,200 gals/day,which is roughly one- half between the minimum and maximum septic tank criterion(800 - 1800 gpd). The Long Term Acceptance Rate(LTAR)must also be considered. When percolative capacity slows to unacceptable rates due to advanced biomat formation,the 100%reserve replacement area must be activated. The third criterion for maximum use is the Water Use Computation Factor(WUCF)from the EHD Sewage Standards and the Estimated Waste/Sewage Flow Rates from the California Plumbing Code(CPC). The WUCF lists day workers at schools/offices at 30 gallons/person/day and 15 gallons/person/day,for Industrial Buildings with no cafeteria. The CPC lists a factor of 20 gallons/employee/day. Additionally, given contemporary plumbing requirement standards for low-flow fixtures,a point-of-use can be considered to be 2 gallons/person/use. In conclusion,taking the proposed filter bed with an initial 1,200 gallons/day acceptance rate as the primary limiting factor, divided by the WUCF conservative factor of 15 gallons/person/day for industrial buildings since the property is zoned Industrial,we find the proposed septic system to be installed on the subject property will theoretically manage 80 people per day. This determination is contingent upon several factors that must be adhered to such as pump-out intervals, replacement area activation, checking for fixture leakage, etc. Nitrate loading calculations for an on-site population of 80 people per day reveal a loading concentration of 7.3 ppm as nitrate-nitrogen (NO,-N)or 32.5 ppm as nitrate(NO,). The Attachment illustrates these calculations to derive the nitrate loading from the maximum population of the property along with the contribution of the on-site residential structure. The total nitrate-nitrogen potential originating from the subject property is 9.7 ppm,which under the Maximum Contaminate Level (MCL)of 10 ppm nitrate-nitrogen(NO,-N). 1 trust this document provides the requested information. If there should be any questions or comments, please contact me. Qtotessioo Respectfully submitted, s4aorV. Cho, o CH SNEY CON LILTING q q y No.75479 e Don Che ey, PE t Registered Civil Enginee #C75476 ria Civil Attachment:Nitrate Loading Calculations �e of Calif°t9 Page 2 of 2 Chesney Consulting