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I I I I I I I I I I I I I I I II I I I I 1. A subdrain system using a lift station (pump) 2. A subdrain system using gravity flow The two methods were evaluated based on the criteria of engineering constraints, construction methods and costs, and operation and maintenance costs. Overall, a subdrain system with a lift station would be more expensive to construct, operate, and maintain than a gravity system. A subdrain system using gravity flow would serve the purpose of lowering the groundwater levels, and would require less maintenance and would have essentially no operating cost once constructed. Based on the above considerations, a subdrain system using gravity flow was selected as the recommended plan of improvement. The outfall to the subdrain system would be on the right bank of the "Vega Ditch" (existing ditch parallel to Vega Street) on the south side of Gaspar Street. The elevation of the outlet pipe would allow free draining of the subdrain system during times of normal flows in the ditch. A flap gate would be installed on the outlet pipe to prevent water from backing up in the subdrain and to prevent small animals from entering the pipe. In addition to the subdrain system, there are several other aspects to the project that were investigated. They are as follows: · Rehabilitation of the Montez Ditch · Capping of artesian wells . Extension of the "Vega Ditch" · Construction of a closed conduit from the existing subdrain outlet to the "Vega Ditch" · Inspection and maintenance of drainage facilities VII. RECOMMENDED PROJECT PLAN Subdrain System The Colorado Water Conservation Board in cooperation with the Natural Resource Conservation District recommends that a gravity flow subdrain system be installed for the Town of San Luis, Colorado. The selected plan is a gravity subdrain system consisting of 3,890 feet of 10" perforated singlewall PVC with sock, 415 feet of 12" solid PVC, 6 manholes, 4 cleanouts, and an outfall structure with a flap gate. 10