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r7Theo primary design factors for the mitigation of nitrate loading from this project are: 1.) Howomestic irrigation water in combination with effluent disposal water must be supplied to maintain lawn vigor, correlated with evapotranspiration, and 2.) How much nitrogen can be assimilated by the Fescue lawn grass, which must be planted. The following volumes are calculated: WATER DEMAND FOR FESCUE LAWN GRASS P=Precipitation for the Manteca Area(gals/year) I=Domestic Lawn Irrigation(gals/yr) E=Effluent Disposal Volume(gals/yr) ETo=Reference Evapotranspiration(gals/yr) Values and Assumptions: P=Precipitation in this locale is 11.68 inches per year, determined in Table 3 = 11.68 in/yr x 27,152 gals/ac-in x 750 sf filter bed(0.0172 ac)=5,455 gals/yr. I=The loamy sand soil structure under the proposed filter bed can hold approximately 1.5 inches of available water per foot of soil at field capacity(See Brady and Oster). Rooting depth of Fescue lawn grass, which must be planted,can easily reach four ft. Consequently,6.0 inches of water(1.5"/ft x 4 ft=6") within this soil profile depth must be available from a combination of effluent and domestic irrigation. The lawn growing season when irrigation is needed is primarily February through October. At an average water-use rate of 0.25 inches of water applied daily for this 214 day period, 53.5 inches of water will have been applied,which corresponds with the daily,monthly and yearly ETo particularly for May through August: I= 53.5 inches/yr x 27,152 gals/ac-in x,750 sf filter bed(0.0172 ac)=24,985 gals/yr. E=Effluent disposal volume for the proposed second unit dwelling is calculated to be: .225 galsADF,x 365 dpy=82,125 gals/yr ETo=The yearly average evapotranspiration(ETo)as illustrated in Table 3,total 53 inches: 53 inches/yr x 27,152 gals/ac-in x 750 sf filter bed(0.0172 ac)=24,752 gals/yr. From the water volume data presented, it appears that the effluent water volume may supply most of the j lawn grass irrigation demand. ETo theoretically cancels domestic irrigation demand,although supplemental lawn irrigation will be needed under heavy demand. NITROGEN DEMAND FOR FESCUE LAWN GRASS The lawn grass uptake of effluent nitrogen is determined as follows: The EHD directive from the Regional Water Quality Control Board 2012 OWTS Policy, as stated, is "to meet a 50%reduction in total nitrogen when comparing the 30-day average influent to the 30- day average effluent." Although the nitrate loading calculations on Page 7 demonstrate a Resultant (NR) average concentration of nitrate-nitrogen in recharge water of 18.8 ppm,this concentration takes into consideration the primary residence,theoretical rainfall and soil denitrification influences. i Page-9- Chesney Consulting