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With some residents alarmed at seeping water, the Southeast Louisiana Flood Protection Authority-East voted July 17, 2008 to hire an outside consultant to review the U.S. Army Corps of Engineers’ assessment of the problem at the repaired breach site on the 17th Street outfall canal in New Orleans.
Since at least the end of 2007, the Corps has been monitoring two seepage spots located near where the I-wall at the 17th Street Canal failed and within the length of a 690-ft. replacement stretch of T-wall construction that was built according to the recommendations of Corps-sponsored forensic investigative team, the Interagency Performance Evaluation Task Force.
“The seepage is occurring approximately 250 ft. north of the south end of the new T-wall construction, which is longer than the actual breach site,” says Richard Pinner, chief of the geotechnical branch of the Corps New Orleans District. “We think water is leaking through the T-wall monolith joints or the steel sheetpile interlocks. We think it is minor, not causing movement of materials, and that the wall is structurally sound.”
Public outcry and questions of their own about the integrity of the T-wall construction at that location precipitated the SLFPA-East’s move to conduct a peer review of the Corps findings. “There are some nervous residents, as anybody could understand,” says Tim Doody, SLFPA-East president. Normally, the Corps would pay for the review process, and “they were agreeable and happy to go through the process,” Doody says.
However, when Doody asked fellow board member Larry McKee, civil engineer, to oversee the process, they determined that if the board paid for and conducted the review independent of the Corps, it would expedite things and “provide us and the general public with a greater degree of confidence.”
The SLFPA contacted the American Society of Civil Engineers and American Council of Engineering Companies to compile a list of potential consultants. “It took us quite a while to get a list of names that met my requirements — those who haven’t done extensive work with the Corps, have geotechnical experience, and are well-respected in their field,” Doody says.
Tiny flags mark two areas of seepage, several yards from the levee toe.
At the July 17 meeting, the full board agreed to conduct the review independently, with an initial cost of $20,000 approved. Following a July 29 meeting with the Corps to determine the scope of work thus far, the authority plans to engage consultants to review the Corps’ findings within a 45-day schedule.
Epsie Hennesy, a 17th Street Canal resident who also fought a Corps tree and fence removal now under way on the same levee, appealed to the authority to postpone that program until the SLFPA-East gets the results of the independent peer review of the seepage. “It is imperative that the board forbid any more work during the most active part of the hurricane season until an independent study is completed,” Hennesy says. “The levee will not have time to heal from the destructive nature of the work before the onset of an active hurricane season.”
“We like the independent stance the board is taking, and we hope you will continue in this direction,” says Luke Ehrensing, who participated in the National Science Foundation’s review of the seepage and offered to share any of its findings. He says he has also been asked by frequent Corps critic Robert Bea, a University of California at Berkeley civil engineering professor, to endorse the levee board’s decision. “Bob Bea asked me to come and make a few comments and give you an atta boy for going ahead with the independent investigation of the seepage on the 17th Street Canal,” Ehrensing says.
“We are not trying to be trend-setters,” Doody says. “We are trying to regain some confidence and, honestly, we are trying to get to the truth and determine whether or not something needs to be done there. Because there is no third-party involved, and they will report directly to us, we will get control of the process and can set deadlines ourselves.”
Residents in rebuilt homes adjacent to the breach site worry if the new T-walls are structurally sound
At the canal wall, Boh Bros. Construction Company of New Orleans constructed a cofferdam and remediated the mass of sandbags that had been used to fill the breach, as well as other foreign material that migrated there with the floodwaters. In December 2007, the seepage prompted the Corps to once again contract Boh to remediate some sand and rip rap in the area and backfill with clay, Pinner says. “We removed small stone and pervious sand that allowed water to seep up from the canal,” he says. The Corps conducted salinity tests, found the water to be brackish (partly salty), and determined it must be seeping from the outfall canal. Still, the Corps has determined that the seepage does not pose any threat to the structural integrity of the T-wall construction at the site.
“We do have some piezometers out there in the marsh material and deep sand strata,” Pinner says. “There may be seepage through organic clays. Any T-wall is not waterproof. We design for seepage. Those T-walls are on 110- to 90-ft. long steel, H-piles,” he says. “That wall is structurally sound.”
The Corps planned to install more piezometers at the site and was considering installing French drains, slurry trench walls or sand layers to handle the seepage, Pinner says.