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' street right-of-way corridor which exists within the Rockridge service area. The gravity collection sewer/conventional pumping station alterna- tive will be investigated in this report. A second alternative is the use of a low-pressure pump collection system. This system makes use of the existing septic tanks which would ' continue to function as storage receptacles for sludge on the tank bottom and scum on the top of the tank. With this system, a pump and ' pump chamber are suspended from the top of the septic tank and the liquid is drawn from the middle zone of the existing septic tank and pumped into a series of manifolded force mains to a central collection or discharge point. Each house would have its own pump installed in its own septic tank. A requirement of this alternative is that each ' septic tank be totally water tight or the constant leakage of ground water into the septic tank will cause the pumping system to operate ' continuously and pump large quantities of ground water into the treat- ment plant. Since all of the septic tanks are quite old and it is isuspected that they all leak substantially, it would be necessary to remove and replace each of the 375 septic tanks. Even with this measure, ' the high ground water table would establish a major realistic source of concern as to whether the new septic tanks would be, and remain, water tight. Because of these reasons, it was decided not to further ' explore this alternative. The third alternative is the installation of a grinder pump and ' pump chamber for each of the 375 dwelling units with each grinder pump discharging into a small sized manifolded.system of force mains. These small force mains would discharge at a point or points along the 6" ' and 18" existing force mains which run by, or cross through, the Rockridge ' project service area. Construction which would require excavation of the existing limestone could be avoided by installing each grinder pump and chamber within the septic tank which is presently in place ' for each of the 375 dwelling units. The lid of the existing septic tank would be removed, the contents of the septic tank pumped out and ithe existing septic tank back-filled with sand material. The grinder pump and pump chamber would be installed within the back-filled sand ' material and the existing 4" lateral from the house connected to the grinder pump chamber. A system of small force mains would be constructed i -4-