Denton Wastewater Collection System Asset Management Program Provides Cost Savings And Prioritized Approach For O&M And Rehabilitation

The City of Denton wastewater department has built a collection system asset management program step by step since the 1990’s. In early 90’s the GIS program was implemented to create an inventory of the collection system assets and create a geographical representation of the sewer lines, lift stations, force mains etc. The computerized maintenance management system (CMMS) was then implemented in the late 90’s to begin the digital work order, and inventory of field condition assessment of the collection system assets, complaint calls etc. During implementation of impact fees in 1998, the wastewater department purchased the Hydroworks later upgraded to Infoworks computer model for collection system master planning and capacity assurance. The results from this model drive the 5-year capital improvement programs for capacity, the 10-year impact fee CIP, and the model is also used to determine the impact of large proposed developments on the collection system.The CMMS database since the late 90’s is now substantial, and with the knowledge contained in it created the opportunity to implement the Water Environment Research Foundation (WERF) collection system prioritization system model SCRAPS (Sewer Cataloguing Retrieval And Prioritization System). The SCRAPS model houses an “expert system” and given the user’s input of existing pipeline data, the expert system uses the knowledge data base with its set of rules, to compute the probability that a pipeline may fail structurally, operationally, or hydraulically using Bayesian probability theory. Based on surrounding land use, estimated costs for reconstruction, and potential impacts to human & environmental health, SCRAPS computes the probability that consequence of failure of any sewer segment may be high. Using Probability & Consequence of Failure analysis, SCRAPS model then provides a numerical ranking from 0 to 100 for each pipe segment, highest being worst. Using this ranking, Denton has focused the use of available dollars to sewer segments most in need of attention, created a 1-year, 5-year, and 10-year sewer line cleaning program, and CCTV of high priority lines program. The implementation of the SCRAPS model provided the opportunity to create a digital database of the entire wastewater collection system using over 80 data points for each sewer line segment as input in the SCRAPS model.Having created a digital warehouse of data for each sewer segment with SCRAPS then allowed Denton to segway into a fully computerized asset management program. The wastewater department purchased the CapPlan Sewer model in late 2011 updated to Infomaster Sewer in 2013, and has now a fully functioning asset management program for rehabilitation, reconstruction of sewer lines. The model integrates the results of the SCRAPS model as input for priority ranking, CCTV PACP ranking, CMMS data on chokes, overflows, Infoworks output data on sewer line capacity etc. and then provides a complete program of prioritized CCTV, point repairs needed, rehab/reconstruction needed for sewer lines, and cost for each activity using the input unit cost values. This has allowed Denton to move further from the 50-year depreciation of collection system assets method of developing the rehab/reconstruction budget to a fully computerized, priority ranked system of rehab/reconstruction, resulting in substantial cost savings. This system allows for more focused use of scarce dollars for prioritized operation and maintenance proactively, and needed rehab/replacement of sewer lines based on CCTV, probability and consequence of failure.