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`_~ COLORADO DEPARTMENT OF H1iALTH, Water Quality Control Division Summary of Rationale - Page 5. Permit No. CO-0042439 V. FACILITY EVALUATION: B. Lift Stations: One lift station exists is the system ahead of the treatment works. This station pumps all of the collected wastewater to the treatment works and hour meters in the station are utilized to calculate influent flows based on calibration of the pump flow rates. The lift station has two submersible pumps rated at I75 gpm (250,000 gpd) each. Th.e wetwell volume Ss 2,600 gallons with an additional 5,000 gallons of volume available in the sewer lines at high level. A visible light at the lift station is used as a high level alarm. C. Treatment Facility: 1. History and Description: The original site application was submitted in 1974 for a 0.025 MGD treatment facility to serve this district. In October, 1975, plans were subsequently reviewed on a 0.010 MGD extended aeration, activated sludge plant with a lined polishing pond to discharge to a percolation pond. The mechanical plant was installed but never used. A lift stat:Lon was installed and pumped all raw sewage directly to the polisltigg pond which was used as a facultative stabilization pond. In 1988, the district began making plans to obtain full approval of the stabilization pond for treatment and apply for a discharge permit since the percolation ponds were found to be tributary to the Los Pinos River. A site application amendment and disch-srge permit application were submitted in the spring of 1989. Flow and BOD monitoring began in 1988 and subsequently indicated that the single pond would not meet the 180 day detention time requirement and that the effluent limitation for BODS and percent removal requirement, which would be applicable upon issuance of a permit, were not consistently being met. The district was slow in providing any design data for the facility, and when finally submitted in early 1990, the district's plan for treatment by a single cell stabilization pond was rejected by the division. The district then submitted a plan far a phased aerated lagoon system with the first phase being approved by the division during the summer of 1990. A flow diagram of the first phase, aerated lagoon system is shown in Figure 3 of the permit. The facility consists of the existing lift station, a new aerated pond with subsurface aeration„ the existing polishing pond, a tablet chlorinator, a chlorine contact tank, dechlorination, and an effluent weir.