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Treated Nater Disposal Typical methods of treated water disposal include recharging the groundwater to the aquifer, discharge to a sanitary sewer system or discharge to a surface drainage system. No sanitary sewer system is presently in place at the Sebastiani Vineyards/Woodbridge cellars site. Conveyance distances to the nearest surface drainege system are considered prohibitive and may require lengthy negotiations to obtain construction access and rights-of-way. Groundwater recharge has been selected as the treated water disposal method for this remedial action plan. Two alternatives for recharge are considered feasible for reintroduction of treated water to the local groundwater system. The primary approach to recharge will be a groundwater infiltration, gallery. Discussion of a contingency recharge option, groundwater recharge wells, is included for consideration in this remedial action plan. Infiltration Gallery A treated groundwater infiltration gallery is considered the most r, appropriate method for shallow groundwater recharge at this site. As shown on Figure 9, the infiltration gallery would be located approximately 75 feet northeast of the proposed soil and groundwater treatment facility. The infiltration trench would be located in an area which will be minimally affected by the proposed Sebastiani facility expansion. Groundwater recharge at this location would have no potential adverse effects on the groundwater controls established by the downgradient groundwater extraction system. As shown on Figure 11, the infiltration gallery would consist of a trench approximately 12 inches wide. Ideally, the trench would extend approximately 5 feet into the silty sand unit which is commonly encountered at about 16 to 18 feet below ground surface at the site. �. However, total depth of the trench may be limited due to soil stability. The length of the gallery trench has been determined based upon the projected infiltration capacity of the silty sand unit and the projected flow rate of treatment plant effluent. A plant effluent of 8 gpm was used to determine the proposed trench length. At 8 gpm (1.1,500 gallons per day) the trench would need to be approximately 12 feet long, However, a safety factor of 1.5 was used in designing the length of the infiltration gallery trench, resulting in an 18-foot long trench. The infiltration gallery trench would be backfilled from its total depth to approximately 18 inches below existing grade with clean, washed, rounded, 1/4- x 1/8-inch stream gravel, free of fine-grained sediments and 22