SR0082543_SSNL - Laserfiche WebLink

Home Browse Search

Revised November 4, 2020 BGG Job No. G164.01 an agricultural worker; this rate was used for the nurdery employees. The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and sizing of the septic system should utilize the San Joaquin County Environmental Health Department On-Site Wastewater Treatment Systems Standards which incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed herein. The nitrate as nitrogen (N) concentration for non-showering employee use is estimated to be 85 mg/L (US EPA, 1980). This value was used in calculations for the nursery employees. No contributions from crop irrigation or soil amendments are considered for the Hantzsche/Finnemore method.It is reasonably assumed that the irrigation and soil amendments would be applied at close to agronomic rates for a net balance of plant irrigation and nutrients. The following tables present the calculated maximum average daily flow for the site and weighted average concentrations: Table 1 —Average Daily Flow Calculation Use Units Rate Subtotal Reduction' Average Daily Flow Employees full-time 50 15 gal/employee 750 gpd 5/7 535.7 gpd Total 535.7 gpd 1 Reduction factors convert calculated flow into average daily flow over a one-year period; 517 converts for anticipated weekday operations. Table 2—Weighted Avera a Concentration Calculation Use Average Daily Flow Estimated Waste Weighted Average Water Quality Product Employees 535.7 gpd 85 mg/L-N 45,535.7 gpd-mg/L-N full-time Totals 535.7 gpd 45,535.7 gpd-mg/L-N Weighted Average 45,535.7 gpd-mg/L-N/535.7 gpd= 85 mg/L-N Concentration: Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate(NO3)in the wastewater and release nitrogen gas(N2)to the atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain field may undergo a reduction between 10 percent to 25 percent. Soils with higher clay content,moist soil conditions,high pH,and organic material denitrify by about 25 percent,and soils with high sand content and fast percolation rates tend to denitrify at a lower rate of about 10 percent. A typical denitrification factor of 15 percent was estimated for the site due to the presence of cemented hardpan lenses below 4 feet deep at the site. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the proposed project to groundwater. The scenario utilizes the variables discussed previously,which represent the estimated conditions and uses associated with this project. The following table presents a summary of the assumptions for the nitrate loading calculation for the site. BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-I Hsin Orchids Pagel