SU0009787 SSNL - Laserfiche WebLink

Home Browse Search

E. SURFACE WATER INFORMATION Storm water management is proposed to be an on-site retention basin. Since the groundwater directional flow may be toward the Stanislaus River, percolating rainwater from this basin into the top aquifer mixing layer may create a dilution effect to the down/cross gradient percolating septic system effluent. Groundwater dilution effects can only be truly discerned with groundwater monitoring and modeling. According to a scientific paper authored by Shaw and Turyk(1994),reduction of nitrate concentrations in groundwater can occur primarily through dispersion, or by percolating rainwater recharge. Climatic Data: Rainfall versus Evapotranspiration NLS§3.2.,/It is generally and scientifically accepted that when precipitation exceeds evapotranspiration (Eto), deep percolation of surface rainwater may occur. Evapotranspiration refers to water evaporation that takes place both at the soil surface and transpiration by plants,and is defined as water loss from a large field of 4-to-7 inch tall, cool-season grass that is not water stressed. The following Table illustrates rainfall and evapotranspiration for the Tracy area,the closest station. Precipitation data was obtained from the Soil Survey of San Joaquin County. The conservative"2 years in 10" data was used and not the "average rainfall"data. Evapotranspiration data was obtained from the California Irrigation Management Information System(CIMIS): TABLE 3 PRECIPITATION AND Eto DATA FOR TRACY, CA Month 2 Years in 10 will have more Eto Average Potential Deep precipitation than: (in/mo) Percolation(in/mo) (in/mo) (in/day) January 2.93 1.55 0.05 1.38 February 2.21 2.24 0.08 March 2.38 3.72 0.12 April 1.51 5.10 1 0.17 May 0.71 6.82 0.22 June 2.09 7.80 0.26 July 0.28 8.68 0.28 August 1.05 7.75 0.25 September 0.84 5.70 0.19 October 1.06 4.03 0.13 November 2.10 2.10 1 0.07 December 2.38 1.55 0.05 0.83 TOTALS in. 13.18 57.0 ------ 2.21 5