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.
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.
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.