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APPENDIX B Page 2 of 3 ■ Holly Commerce Center Michaels TI's, Formerly E&E Trading ■ Tracy, CA S I E G F R I E D For this project: W= 0.1.48 ac-ft/yr nW= 146 mg N/L d = 30% nb=Assumed 0.1 ppm, NO3-N R= Ri + R2 = Average annual rainfall in ac-ft/yr(see below for analysis) Total Site Area = 25.88 acres Annual Rainfall = 9.5in (per San Joaquin County Standard Drawing D-3) Total Runoff= 9.5in/yr x 25.88 acres x (1/12) = 20.49 ac-ft/yr R, = Portion of annual rainfall that is absorbed into leach field areas, landscaping less evaporation from paved surfaces. For the sake of this analysis it is assumed that the site is 10% pervious and that 1% of the runoff is retained in the pavement area and evaporated. The paved areas are approximately 50.7% of the site. R, _ ( 20.49 ac-ft/yr x 10%) - (20.49 ac-ft/yr x 1% x 50.7%) = 2.0488—0.1039 = 1.9450 ac-ft R2 = Portion of the annual rainfall that is captured by the basin and infiltrated, including any evapotranspiration. Although Attachment 1 suggests a month by month analysis this analysis has simplified the approach due to the fact that the County mandated storm water quality requirements dictate that the basin capture and treat the 85th percentile event and capture and treat at least 80% annually. Per the figure below from Appendix D of the California Storm Water BMP Handbook for New Development and Redevelopment for an impervious coefficient of 93% and a required capture rate of 80% the basin annually will capture approximately 70% of the total runoff and infiltrate it with a typical drawdown time of 48 hours. The basin will not be planted and will not have standing water during months when the ET rate is high, however for the sake of this analysis it is assumed that 5% of the water is lost to ET. R2 = 25.88 ac-ft/yr x (70% - 5%) = 13.3174 ac-ft R= R, + R2 = 1.9450 ac-ft/yr+ 13.3174 ac-ft/yr= 15.2624 ac-ft/yr Therefore: nr= Wnw(1-d)+Rnb/(W+R) _ ((1.48 ac-ft/yr x 146 mg N/L)x (1-0.30) + (15.2624 ac-ft/yr x 0.10 ppm))/(1.48 ac-ft/yr+ 15.2624 ac- ft/yr) = 9.1481 ppm as nitrate-nitrogen (NO3-N) amount falls below the 10ppm threshold Stockton San Jose Sacramento Modesto 3428 Brookside Rd. 111 N. Market St.,#300 900 Howe Ave.,#200 100 Sycamore Ave,#100 Stockton, CA 95219 San Jose, CA 95113 Sacramento, CA 95825 Modesto, CA 95354 t:209.943.2021 t:408.754.2021 t:916.520.2777 t:209.762.3580 F:\17projects\17017 Holly Sugar Industrial\Civil\Septic Sizing-Prelim\17017 Holly Commerce Center H&I Nitrate Loading Memo.docx