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C I J r 1� I operation and maintenance guidance. The difficulties associated with transporting two phases, liquid and gaseous, greatly complicate the design procedure. The valve boxes often corrode, causing numerous and continued malfunctions. Standby power and system malfunction reporting devices are often inadequate or nonexistent. In order to keep the vacuum systems operational, highly skilled electronics technicians are required. A much higher degree of maintenance is required on vacuum sewers than on alternate types of sewers. It was felt that such a commitment of new skilled manpower would be unacceptable to the County. 6.2.3 PRESSURE SEWERS A pressure sewer system consists of two major elements: the onsite pressurization facility and the pressurized sewer main. There are two alternative types of pressure systems: the septic tank effluent pump (STEP) system, and the grinder pump (GP) installation. The STEP system utilizes a septic tank for pre-treatment and pumps the effluent into the pressurized collection system. The GP system pumps household wastes directly from an underground storage tank into the pressurized collection main. Pressure sewers can be more cost-effective than gravity sewers in an area with a low population density and a high water table or where special geologic formations make conventional sewer construction impractical. The Rockridge Study Area is subject to a high-water table and is situated on a one to two feet thick layer of limestone just two to three feet below the ground surface which makes dewatering particularly difficult. However, the study area is well developed with population densities exceeding 8 persons per acre. 6.2.4 NO -ACTION ALTERNATIVE The no -action alternative would consist of property owners within the study areas continuing to use septic tanks for wastewater disposal. Although no IRC. VB4 6/4/87 6-2