Final Draft - Wastewater Collection System Capacity Analysis Apprendix A April, 1999

Home Browse Search

Final Report City of Paris, Tezas Wastewater Collection System Capacity Analysis combinations of replacement and rehabilitation that results in the least cost for the scenarios evaluated. Derivation of Cost Estimates To develop the costs associated with replacement pipes, a table was developed which reviewed the open cut construction costs for several communities in Texas. The cost for each replacement section was based on the average depth of the segment and the replacement pipe diameter. These estimates are of a general order of magnitude and only a detailed pre-engineering study could recommend specific pipe diameters, depths and distances required to alleviate restrictions. Estimated diameter increases that were less than 6 inches were not considered in the estimates provided. Costs to rehabilitate the defects that were observed were prepared by ADS Environmental Services based on years of accumulated rehabilitation construction costs. It is important to note that none of these costs in this report include design and project administration costs. Results In general, the overall capacity of the system is good. There are a few areas that appear to have inadequate capacity even during dry weather. These are areas with extremely low slopes and include the downstream end of Basins 13 and 30. If there are many observed overflow and backup complaints during dry weather this is most likely related to local maintenance problems. Based on the Design Event and No Rehabilitation Scenazio, there are 279 line segments out of approximately 2500 that are predicted to have inadequate capacity. Of these only 87 line segments required upsizing by six inches or more. By performing rehabilitation in only the Top 5 basins this number is reduced to 62 pipe segments. The combined cost reduction is from $7.48 million dollars to $6.92 million dollars. Based on the four rehabilitation and replacement programs evaluated, the costs for each program was calculated and recommendations made for the lowest cost program which was the Top 5 program. In this scenario all defects should be repaired in the Top 5 basins. Reverse Slope Pipe Segments Note that in the investigation of the system, there were 22 pipes that were reported through a combination of GPS and field depth measurements to have adverse or reverse slopes. That is the downstream invert elevation is higher than the upstream elevation. Pipe segments in these configurations behave somewhat like siphons and aze likely to create maintenance problems. For these reasons, a listing of the pipes and their recommended sizes and costs are included following the Basin Summaries. The 15