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November 2013 MM k 1351 SANITARY SEWER FEASIBILITY STUDY & REPORT NORTH SEBASTIAN AREA LOW PRESSURE SEWER SYSTEM ALTERNATIVES Low pressure sewer systems generally utilize two (2) types; the grinder pump system and the septic tank effluent pump (STEP) system. The grinder pump alternative is a system utilizing small simplex or duplex package grinder pump station located on each sewer user's property. Residential users can use a simplex (1 pump) station but commercial and other non-residential users must use a duplex (2 pumps) station as required by FDEP. These small individual grinder stations periodically discharge the wastewater into a small diameter force main piping system typically located in the street rights-of-way. Unlike gravity sewer flow or the vacuum collection system alternative, both of which involve only a sewer lateral on the user's property the grinder pump system requires each sewer user to locate and install the package grinder pump station on their property and accept responsibility for the maintenance and operation of the pump station. The pump stations are furnished with grinder pumps that grind all solids into a slurry. Therefore, the force main system which conveys the wastewater to the various points of discharge can be designed using force mains as small as 2 - inch diameter. In addition, the small force main system can be constructed with approximately 36 - inches of cover and does not have to be constructed at a gradient. This reduces construction time as well as cost. Since the force main system must be constructed with water tight joints, it can be constructed in areas with a high groundwater table without concern for groundwater infiltration. H owever, localized flooding can result in inflow into the individual small pump station so they need to be located with tops above the flood elevation. A drawing showing a typical simplex grinder pump station and several pictures of a local pump station installation are included in the appendix of the report. Low pressure systems with grinder pump stations have been used in Indian River County and although they operate with reasonable success, there have been problems with regard to acceptance and satisfaction by the users. As an example, the majority of Indian River Drive in Study Area #1 is served by a low pressure system with users installing small package grinder pump stations to serve their residential and commercial properties. This system has been in operation since the early '90s, but expansion of the system to serve users between Indian River D rive and US'#1 has not occurred as anticipated. As stated previously, another low pressure sewer system alternative is the STEP system which utilizes small submersible standard (non -grinder) sewage pumps in a holding tank with controls. H owever, the septic tank remains in use to collect and store the wastewater solids and must be 15