Livingston’s sewer system study continues
Polk County Enterprise, July 2007
LIVINGSTON -- The first step of a multi-phase sanitary sewer evaluation program was delivered to Livingston City Council members during the group’s June meeting. The manhole inventory report prepared by The Brannon Corporation details points that wastewater and storm runoff enters the sewer system.
The inventory also is the first step on the plan of action drafted by the City of Livingston to address 2004 flood events that caused an overflow at lift stations and manholes after two storms caused flow more than five times the average daily flow at the wastewater treatment plant.
The city’s plan of action is currently under review by the Texas Commission on Environmental Quality and approval is expected in the coming weeks, according to consulting engineer Kirk R. Bynum, P.E., project engineer for The Brannon Corporation.
The goals of the evaluation program include:
Reducing system failures and malfunctions;
Reducing energy usage;
Return of at least a partial amount of reserve capacity to allow for future development; and
Reducing the costs of wastewater treatment.
The first phase of the evaluation program is analysis of infiltration and inflow into the wastewater system Bynum’s report said.
Engineers believe that about 60 percent of the infiltration and inflow can be eliminated from the system through rehabilitation.
The measures necessary to achieve that level of rehabilitation are determined through surveys of wastewater flow, average annual rainfall in the area and actual precipitation measured in the city each month to anticipate the load the system should expect.
Engineers then gather data on the size, age, type and joint connections on existing collection lines; develop maps of manholes and the number and type of lift stations.
They also evaluate current maintenance procedures and excursions from the wastewater system permit.
During the field survey on lines and manholes, engineers determine the physical condition of the sewer lines, topography of the area, as well as streets, alleys and access to the manholes via above ground reconnaissance and inspection.
The study then conducts smoke testing and simulated rainfall events as deemed prudent to evaluate the system’s capacity to handle stormwater.
Testing personnel then clean and inspect sewer lines through closed circuit T.V. equipment and report problems observed and possible rehabilitative measures.
During the manhole inventory, inspection crews accounted for 653 of an expected 709 manholes and their GPS locations have been added to the city’s digital maps, Bynum’s report said.
There are 29 manholes recorded in field books that have no GPS location registered, according to Bynum.
Another 183 manholes are “hiding” under pavement or other obstructions and engineers expect to locate or disprove their existence during the next phase of testing.
The condition of the 653 manholes located is relatively good, Bynum’s report said.
Corrosion found within some of the manholes may indicate the presence of hydrogen sulfide gas in the system, the report said, but that level of gas production is not “overly problematic.”
The engineer’s preliminary opinion is that the City of Livingston’s system does tend to be impacted by inflow and infiltration; the inflow has a greater impact.
Notes on each manhole inspected showed that most items found were classified as a “5” on a scale from one to five, with one being the most serious.
Most of the items that received a 5 priority rating can be corrected during cleaning and additional inspection set for later phases of the plan.
Priority 3 items show signs of heavy corrosion or obvious leaks and should be repaired as the budget permits whereas priority 1 and 2 items should be corrected during the 2007-08 fiscal year, Bynum’s report said.
Of the 653 manholes, 17 need priority 3 repairs; nine were rated priority 2 and 13 priority 1 items.