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distribution pipe; sizing is based on percolation test result for one 36-inch test hole, with corresponding soil acceptance rate of 0.311 gpd/ft2 (per SWRCB OWTS Policy, 2012); 5.96-ft vertical separation distance from bottom of filter beds to the local water table is indicated. • Future Reserve area: 100%reserve(expansion)area designated on plans Comments: 1. Overall Capacity. The wastewater system is of conventional design for a limited wastewater flow, based on a fixed number of toilets,urinals and sinks (48) and the assumption of each toilet/urinal being used once per hour,ten hours per day. Based on a typical average of three restroom uses per worker per workday,this would equate to a workforce of approximately 160 people in the facility. While the proposed building may be used and operated with this number of employees,the overall size of the buildings would allow a much greater occupancy. Under greater(allowable) occupancy wastewater generation volumes could easily increase beyond the capacity provided in the proposed wastewater facilities. In order to anticipate and provide appropriate adjustment for possible future increases in activities/occupancy, I recommend the following: a. Identify a contingency plan including additional area for future expansion of wastewater treatment and disposal facilities, demonstrating sufficient capacity to accommodate the maximum reasonable use/occupancy of the buildings. b. Implement an on-going monitoring program to measure and record actual wastewater flows on a monthly or quarterly basis for comparison with system design capacity and assumptions. The information would be used in the future to determine if and when measures should be taken to expand the wastewater system capacity. 2. Extremely Deep Tank and Sewer Installation. The proposed depth of installation for the four septic tanks, surge/dosing tank and effluent sewer lines are extremely deep, especially along the west side of the building. The tank inverts for septic tanks#1 and#2 are 11.7' and 14.2' below grade(rim elevation), respectively,putting the entire tank below the water table. Similarly,the invert of the proposed surge/dosing tank will be about 15' below grade and fully within the local groundwater. This will be highly problematic for numerous reasons: • Difficult and unsafe access to the tank for inspection, cleaning,maintenance and repair; manufacturer(Orenco) should confirm that appropriate maintenance of septic tank effluent filters can be provided under the proposed design; • High risk of chronic groundwater infiltration into the tanks at pipe connections and access risers, which could flood and put the system into seasonal or chronic failure; • Depth of soil cover over tanks may exceed allowable limits; 1 to 6 feet of cover is indicated in details for concrete tanks; manufacturer review and approval will be necessary. 2