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3. Replacement with Vacuum Collection System: System Description — A vacuum collection system entails connection of each house service to a dedicated collection chamber from which a vacuum system transfers the collected sewage to a central location via vacuum. A layout of the system is shown in Figure 3. Similar to the gravity flow system, electric service is only required at the central vacuum station. The conceptual design of the vacuum sewer system is based on approximately one (1) collection chamber for four (4) homes. The final number of collection chambers will be determined based on the cost effectiveness of lateral (service) line length versus the cost of additional chambers. It is assumed the collection chambers would be located along the back easements, near the adjoining property lines. Each home would connect tv uic cha2i2ber "witii ail o-lllbh PVI, (SDR 35) service. Thus service will nun trom the existing house sewer connection, near the existing pump chamber, to the new collection chambers. These 8 -inch services provide system storage, in addition to the storage in the collection chambers. The vacuum system will consist of 3" through 8" PVC (SDR 21) pipe laid in a saw- tooth pattern to a single vacuum station, centrally located. As shown in the proposed layout, two separate loops to the station are proposed to minimize vacuum runs. One loop will service the north portion of the community while the other will service the south portion. The station includes the vacuum pumps, chamber, and sewage pumps for transfer via force main to a connection point in the existing gravity or force main system. An emergency generator and automatic transfer switch will be installed at the site to maintain operation during power outages. A bio -filter will be installed with the vacuum station to minimize odors through the system vent. The station will be housed above ground to avoid problems during flooding. Likely Construction Cost — $3,500,000 Table 3 depicts the cost breakdown used to estimate the cost of this alternative. In order to develop the cost estimate for this alternative, the following assumptions were made: • 8 -inch diameter service connection per home • One collection chamber for each of four homes • 15% cost premium for possible rock excavation and existing obstructions • Grade in the area is essentially flat • Annual average daily wastewater flow estimated as 300 gpd per connection • 3.7 -peak factor was used to estimate the design flow • The cost includes 20% for contingencies and administrative • The cost includes 10% for engineering and planning fees Page 5 of 7 F\UWitics\=W -ENGINEER G\Pmjev;- Ulilay Cmmrunlon Pm UVRC- Rockridge5ewer FE Miiigv ion UCP a 2521WBW Enginecering RepoAhch Memo Rockn'dgc -Vacuum Option doc