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B. SURFACE WATER INFORMATION Surface water consists of all other water sources originating on the surface of the project, other .- than septic system effluent. These sources include rainfall, surface runoff, domestic irrigation and stormwater retention. The San Joaquin County of Public Works - Isohyetal Map indicate 11 inches of rainfall to be the Mean Annual Precipitation in the area of the project. After project development, a percentage of the land surface will be impermeably covered with structures, concrete and asphalt. This will have an attenuating effect on the downward migration of nitrate molecules currently "in-transit" and on nitrate yet to be formed. These impermeable surfaces will be traded for potential point sources of nitrate: on-site septic systems, lawns, landscaping and retention basins. Domestic irrigation recharge can account for 250 to 1,500 gallons of water/day/residence during the spring and summer months (approx. 6 mos. out of the yr). Excessive lawn and landscape watering can lead to nitrogen leaching, and runoff to open areas and stormwater retention basins. C. WASTEWATER FLOW CALCULATIONS AND CHARACTERISTICS Domestic wastewater flows have been studied for decades with variable data published in the scientific literature. Wastewater flows will be managed by on-site septic systems. The total daily water use is a combination of household and personal uses, as itemized below: HOUSEHOLD PERSONAL USE 25 gal for laundry 2 gal for drinking and cooking 10 gal for dishwashing 3 gal for oral hygiene ` 5 gal for misc. use 14 gal for bathing 16 gal for toilet flushing/sink washing FLOW RATE in gals/home/day= 40 gals/household/day+(35 gaVperson/day x number of persons/home). Assuming the average household within the project will have 4 persons per house (husband, wife and two children), the daily wastewater flow rate can be estimated at: 40 gals + (35 gals x 4 people/home)= 180 gals/day for an average flow per resident of 45 gals. Although the residences will be built with water saving devises,the occupants will probably be of a higher income level. This normally translates into higher water usage for various reasons (e.g., indoor spas, increased entertaining, etc.). Therefore, as a safety factor, the total daily wastewater flow per house and average daily flow per resident will be increased 1.5x to 270 gals/house and 68 gals/resident, respectively. The peaking factor for individual residences on septic tanks will vary with the day of the week and usage. Peak hourly rates are normally associated with the discharge of clothes wash machines, dishwashers and shower/bath water. The ratio of the peak day to the average day can vary from 1.5 to>5, depending upon the time of the year and usage. 7 Valley A9 Research