Infiltration and Inflow Correction & Hydraulic Modeling

Houston, Texas


Construction Cost: $11 million


Project Description: As prime consultant, Ratnala & Bahl, Inc. has a 3-year contract that is funded annually to provide the City of Houston with a staff to provide management required to oversee the SSES/PI effort in two service areas, make preliminary estimates for rehab, write scope of services and oversee design consultants performing rehab design to correct inflow and infiltration (sewer rehab).  Also responsible for hydraulic modeling of the wastewater collection system.  This effort includes updating the Cityís existing modeling packages to keep them current with existing technologies, analyzing the permanent flow meters and temporary meters for changes in flows and updating the existing system response and operational changes to real storm events by performing real storm event modeling for service areas in the City of Houston.  RBI is responsible for conversion of the existing hydraulic model from SWMM to ďstate-of-the-artĒ software, INFOWORKS. This effort also compares the overflows and surcharge violations from the model output with the excursion tracking systemís reports to identify the problem areas and to predict the future excursions at the same locations for similar storm events.


Services Provided:

Sanitary Sewer Rehabilitation: As a requirement to obtain permits, which allowed for the construction of wet weather facilities in three (3) wastewater treatment plant service areas, the City of Houston was required to confirm and correct the known inflow sources in these areas.  Therefore, the City of Houston included in RBIís contract the responsibility for SSES, which included smoke, dye water flood testing and CCTV of FWSD #23 and Northside Service areas.  Analyzed test results and CCTV and made preliminary recommendations and cost estimates to perform rehab and correct I/I. The work included management/oversight of the inflow/infiltration correction design performed by Consultants under contract to the City of Houston and the required annual reporting to the EPA and TNRCC on the progress to eliminate the inflow sources.  Two Consultants were responsible for the design of inflow and infiltration correction in two (2) treatment plant service areas, FWSD#23 and Northside/69th Street.  These two service areas comprise approximately 31% of the City of Houstonís wastewater collection system of 26 million linear feet of sewer ranging in size from 6" to 144" in diameter.

All 145 inflow leaks in FWSD#23 and Northside/69th Street service areas have been corrected.  Additionally, a contractor is presently completing the repairs to correct approximately 500 infiltration leaks in the FWSD#23 Service Area at a construction cost of approximately $1.7M.

Hydraulic Modeling: Converted the Cityís hydraulic models to User Query Model (UQM) for clients to view the modeling results.  Preprocessing programs are developed for data to link the model to City GIS and radar rainfall.

                                                                                                                              Smoke Test Leak


Service Area Modelers interpret, manage and analyzed the data generated by both permanent and temporary flow monitors and revised the hydraulic model flows and investigate possible solutions to those impacts.  Small lines analysis is also performed to identify any deficiency in capacity and propose a recommendation to alleviate any sanitary sewer overflows.  Technical assistance is provided to answer Requests for Information (RFI) from various departments of the City and design consultants working on City projects.  Real storm events are selected and NEXRAIN radar rainfall distributions are obtained for those storms.  Modelers also update the hydrologic characteristics of sub-basins contributing flow to the trunk sewers by using Houston Infiltration and Inflow Hydrograph Generation (HIIHG) program to generate hydrographs and compare them to the flow meters.  Finally the modelers run the design storm event to size the necessary facilities and to propose relief projects.

Our Mission
Is to develop a close working relationship with our clients to meet their engineering and architectural challenges professionally, ethically and cost effectively. Each client's need becomes Ratnala & Bahl, Inc. objective.
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