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RMWD working on remediation of sewage spill

 

Last updated 9/20/2007 at Noon



The Rainbow Municipal Water District (RMWD) will be working to mitigate the effects of a 540,000-gallon sewage spill which occurred September 4.

“The work is underway. The flow of the sewer has been restored, so there’s no danger of repeated leakage there,” said RMWD interim general manager Gene Buckley.

The overflow occurred on the east side of Interstate 15 north of State Route 76. The sewer line, which was constructed in the 1960s, runs through the Horse Ranch Creek wetlands area. “The fact that it’s in a designated wetlands area is not good, but the fact that it’s not near residential homes is a good thing,” Buckley said.

The spill occurred more than half a mile away from the nearest residence and thus poses no risks for residents.

The wetlands setting also meant that on-site maintenance had been minimal. The blockage which caused the overflow was deemed to be the result of roots which had grown into the sewer pipes, and the 13 manholes within the wetlands area had not been accessible for maintenance purposes. Many of those manholes had been buried over time and were considered “lost.”

The sewer line had not been ignored completely by the Rainbow Municipal Water District. In 2004 district staff commenced work on a plan to build roads into the wetland area to access the sewer manholes. The cost estimate for that project in 2004 was $645,000. Before the project could be implemented, however, the RMWD board cancelled all capital projects in 2005, citing the need for funding to pay fines stemming from Department of Health Services violations.

“After we mitigate this problem now we have to go back and fix it,” district engineer Brian Lee said of the roadwork plan. “We have to reactivate the project that we stopped in 2005.”

Lee was not with the district at the time the capital projects were cancelled. The current cost estimate for that project has risen to $1,000,000.

On the night of September 4, RMWD staff noticed a reduced flow in a downstream lift station. “Once we know we’re not getting the water where it should be, we have to go out and find where it’s going,” Lee said.

The field operations staff found the blockage later that night. The roots had accumulated additional debris and had clogged up the sewage flow, sending it through a manhole cover and into the wetlands. “It goes through a point of least resistance, which is up and through the cover,” Buckley said.

“We had problems locating the clog,” Lee said. “The sewer line, being in a wetland, there’s no good access for it.”

The field staff eventually found the manhole where the leakage was occurring, but there was no access to bring a pumping truck or other equipment to the manhole. The staff went to a manhole upstream which was accessible and began pumping sewage into tankers.

The pumping continued through September 5, and on September 5 the district built a road approximately 200 feet long to reach the manhole where the sewage had overflowed. Enough blockage was removed by September 6 to allow the sewer line to run without overflowing, and the 12-inch vitrified clay pipe sewer line is currently 75 percent operational.

The Regional Water Quality Control Board and the county’s Office of Emergency Services were immediately notified. Because of the wetlands designation other agencies involved include the Army Corps of Engineers, the US Fish and Wildlife Service, and the California Department of Fish and Game. Because access to the manhole was constructed from Interstate 15, the California Department of Transportation was also involved.

The 540,000-gallon figure is an estimate, and the district is responsible for mitigating both the sewage spill impact and the impact from the constructed roadway. A special board meeting September 10 saw the authorization to award a contract to Willdan Engineering for up to $230,000 to assist with mitigation measures and the revised plan to build roads to access the manholes. Willdan has already been working with the district on the Morro Overflow Correction Project.

Actions, which may be required as part of the mitigation, include removal of all contaminated soil, replanting and rehabilitating the affected area of construction, and long-term maintenance of off-site mitigation areas.

“We are waiting for a response from the Regional Water Quality Control Board,” Lee said. “That response should give us our instructions on how we are to proceed with mitigating the sewer spill.”

The district may also be subject to fines for the spill. The maximum fine would be $10,000 per day of occurrence and $10 for every gallon not cleaned up, which would equate to a maximum possible fine of $5,410,000. The Regional Water Quality Control Board has the authority to levy the fine and can also reduce the fine if the district proactively works to clean up the spill. Potential fines may also be assessed by other agencies.

The district’s current mitigation actions are not guaranteed to reduce or eliminate a fine, but the mitigation efforts initiate the positive remediation attempts which are the district’s only control over the amount of the fine. District staff estimates a mitigation cost of $500,000 not including any fines, and district staff estimate that the work will likely reduce the fine to the $10,000 daily assessment.

In addition to the estimated $510,000 for remediation and $1,000,000 for the road construction project, the Rainbow board also approved having staff bring back a recommendation on rehabilitating the sewer lines once full access to the sewer is available. The rehabilitation would consist of exposing and raising existing manholes, cleaning the sewer line and clearing it of all debris, and slip-lining the sewer pipe and manholes with a PVC liner.

The slip-lining process can be done from one manhole to the next without digging up the entire sewer line, and the cost estimate is currently between $500,000 and $1,000,000, although no definite estimate can be provided until the manholes are all accessed and the sewer line is inspected.

In addition to constructing the access roads, the road project will also require an update of the original environmental impact report.

“We’re looking forward towards the future,” Lee said.

 

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