SR0081492 SSNL - Laserfiche WebLink

Home Browse Search

15 November 2019 AdvancedGeo AGE Project No. 19-4912 Environmental Page 10 of 14 9.0. IMPACT OF NITRATE TO GROUNDWATER Due to the planned residential use of the property and the potential for nitrate leaching into the groundwater from the proposed septic system, a nitrate loading analysis for the future use of the septic system is required by the EHD. 9.1. CURRENT OFF-SITE SOURCES OF NITRATE Septic systems and agriculture are sources of nitrates in the area of the site. The property is bordered by residential land, and is near agricultural land, which might provide a nitrate source. There are several residences within 1,000-feet of the site. 9.2. IMPACT OF RAINFALL CONTRIBUTION TO NITRATE LOAD The rainfall of the area has been estimated for the nitrate loading analysis. Deep percolation is estimated by calculating the average monthly rainfall and evapotranspiration of the site area. If average monthly rainfall exceeds average monthly potential for evapotranspiration (ETo) there is a potential for deep percolation without consideration for runoff. Average potential ETo was estimated from data obtained from the California Irrigation Management Information System (CIMIS) Manteca Station #70. Manteca Station #70 has been collecting ETo and precipitation data since January 2014. Deep percolation (average annual rainfall recharge) was estimated utilizing the monthly ETo and precipitation data collected from Manteca Station #70 between 2014 and 2018. The annual rainfall average for the area between 2014 and 2018 was 11.64 inches (CIMIS); the annual ETo average ranged from 0.96 inches in 2015 to 5.63 inches in 2014. The estimated deep percolation (R) was determined by calculating the average of the ETo between 2014 and 2018. The estimated deep percolation (R) is 3.64 inches (Appendix C). 9.3. CURRENT ON-SITE SOURCES OF NITRATE Septic systems, rainfall and agriculture (property to the west) are sources of nitrates (fertilizers) present on or around the property. There are currently no structures or septic systems on the subject property. 9.4. FUTURE ON-SITE SOURCES OF NITRATE The future site usage includes the addition of a 2,900-square foot residence with four bedrooms for residential use. Residential use includes showering/bathing, clothes washing, cooking, and hand washing. The reasonable or maximum usage of wastewater for the four-bedroom home is 140 gpd per bedroom for a total of 560 gpd.