25F - AGMT - DELHI DIVERSION PROJECT

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Preliminary Design Report Addendum No.2 3.5 SEDIMENTATION AND DISCHARGE STORAGE CHAMBER The discharge storage chamber will provide approximately 140,000 gallons of storage for further sediment particles and storage volume to be pumped either to the surface reservoir located within the golf course or pumped directly into the sanitary sewer system for final treatment and disposal. The discharge storage chamber will consist of a 60,000 gallon concrete chamber followed by four precast reinforced concrete underground storage chambers, each with a dimension of 7' -8" by 14' by 50'. The RCB storage tank will provide an additional storage capacity of 80,000 gallons for dry- weather conditions. During the wet - weather condition, the water level in the storage chamber will be approximately 2 feet higher than the dry- weather condition, and will provide an effective storage volume of 75,000 gallon (for HRT calculation) and a total storage of 175,000 gallons. The calculated hydraulic retention time for the dry- weather conditions is 13 hours, which is conservative compared to a typical 28 hour sedimentation chamber design. The short HRT during maximum design flow conditions (100 cfs) indicates that sedimentation will not likely be effective during the high flow event. This suggests that the cleaning of sedimentation from dry- weather conditions should take place prior to the rainy season, to avoid flushing the sediments in the storage chamber. Table 3- 3 Sedimentation and Discharge Storage Chamber Design 3.6 PUMP STATION URS understands that the underlying land owner of the golf course has expressed concerns regarding water quality and its suitability for irrigation. If the golf course accepts the water quality for irrigation, a single pump station with proper control and a single motorized three -way control valve on the pump discharge pipeline will be able to deliver the harvested water to the golf course reservoir during the hours of 5:00 am to 12:00 pm. The pump on -off control will be based on levels in the receiving reservoir and the pump station wet well. The pump station will pump the harvested water to the sewer system during the hours of 12:00 pm to 5:00 am through the adjacent CMSD sewer connection. If the captured dry - weather flow can not be reused for golf course irrigation, alternatively it can be pumped continuously to the OCSD trunk main connections. The pump station will be a typical duplex station, each with a 300 gpm capacity submersible pump. The pump head varies for different pipe routing options and discharge points between 20 feet to 80 feet dynamic head. More details are provided in Section 4. LW 10 25F -142 Total Stora a Effective Volume HRT Dry- weather Condition 1 140,000 gallon 140,000 gallon 13 hours Maximum Flow Condition 1 175,000 gallon 75,000 gallon 1.7 minutes 3.6 PUMP STATION URS understands that the underlying land owner of the golf course has expressed concerns regarding water quality and its suitability for irrigation. If the golf course accepts the water quality for irrigation, a single pump station with proper control and a single motorized three -way control valve on the pump discharge pipeline will be able to deliver the harvested water to the golf course reservoir during the hours of 5:00 am to 12:00 pm. The pump on -off control will be based on levels in the receiving reservoir and the pump station wet well. The pump station will pump the harvested water to the sewer system during the hours of 12:00 pm to 5:00 am through the adjacent CMSD sewer connection. If the captured dry - weather flow can not be reused for golf course irrigation, alternatively it can be pumped continuously to the OCSD trunk main connections. The pump station will be a typical duplex station, each with a 300 gpm capacity submersible pump. The pump head varies for different pipe routing options and discharge points between 20 feet to 80 feet dynamic head. More details are provided in Section 4. LW 10 25F -142