Laserfiche WebLink
Soil Suitability Nitrate Loading Study <br /> Manteca Unified School District <br /> 5700 East Nile Ave.,Manteca,CA <br /> Page 9 <br /> A typical denitrification estimate of 15 percent was chosen based on the silty sands with low fines reported <br /> for the Site. <br /> 2.3.5 Calculated Mass Balance of Nitrogen Loading Considering all Potential Sources Identified <br /> A nitrate loading scenario was performed to assess the impact from the proposed project using the Hantzche <br /> and Finnemore formula/model. The scenario utilizes the variables discussed previously which represent the <br /> estimated conditions and uses associated with this project.Table 4 presents a summary of the nitrate loading <br /> calculation for the parcel. A copy of the nitrate loading calculation sheet is included in Appendix F. <br /> Table 4 <br /> Summary of Nitrate Mass Balance Analysis <br /> Concentration Effluent Leach Field Deep <br /> Parcel Size Design Average <br /> Parcel Result Concentration Percolation of <br /> Number (Nc)* in Acres Daily Flow (Nw) Denitrification Rainfall <br /> (A) (Q in gpd) (d) <br /> m L-N m L-N (R in inches) <br /> 1 25.4 1 15.36 1 6,378 1 35 15% 0.99 <br /> Notes: * Maximum contaminant level(MCL)for nitrate in drinking water is 10 mg/L-N; <br /> mg/L=milligrams per liter;gpd=gallons per day. <br /> Based on the nitrate loading balance calculation, nitrate levels for the proposed use is 25.4 mg/L, which is <br /> above the MCL of 10 mg/L for nitrate-N in drinking water. <br /> 2.3.6 Calculated Impact of Nitrogen Loading from Site Project to Down Gradient Wells, Rivers, <br /> Lakes, Etc. <br /> Based on the relatively flat topography of the site, we do not foresee percolating effluent affecting any <br /> surface water resources. <br /> 2.4 DISCUSSION OF NITRATE LOADING RESULTS RELATIVE TO PROPOSED <br /> METHOD OF WASTEWATER DISPOSAL <br /> 2.4.1 Total Nitrate Impact from Proposed Project <br /> The nitrate MCL set by the US EPA is 45 mg/L-NO3 or 10 mg/L-N.This report concludes that the proposed <br /> development of a multi-purpose building of 14,600 square feet, and a kindergarten classroom building of <br /> 4,500 square feet has a design capacity of approximately 6,378 gallons per day effluent into the proposed <br /> septic system. The actual usage will be considerably less when completed but will increase over time as <br /> additional students attend the school.The proposed development,if operated the design capacity,may result <br /> in an estimated nitrate load of 25.4 mg/L-N and, without mitigation, could cause long-term build-up of <br /> nitrate in groundwater above 10 mg/L-N. However due to existing degradation of groundwater documented <br /> in groundwater samples collected from Site wells,the shallow aquifer at the Site is not utilized for drinking <br /> water. <br /> One must consider that nitrate-NO3 concentrations in groundwater inflow from up gradient areas may also <br /> increase over time from other land uses such as agriculture and increased rural residential use. Nitrate in <br /> groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank <br /> waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. The proposed <br /> development is located within a shallow depth to ground water zone surrounded by septic use parcels in the <br /> ow 111*4. <br /> ilv CONDOR <br />