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Thursday, July 05, 2012

Lagoon Project Contractors Prepare for Dewatering Phase to Commence

• Opponents Continue to Raise Water Quality and Habitat Questions


Demolition and construction on State Parks’ Malibu Lagoon Restoration and Enhancement Project slowed this week, as contractors wait for the last nesting birds to leave the area.
Bulldozers and backhoes were at work on Tuesday, removing mud from the channels in the western portion of the lagoon and piling it on higher ground where sycamores and willows once grew, to dry in the sun.
The outflow pipe for the project’s dewatering phase was installed this week.  Granite cobbles and geotextile cloth were deployed to control potential beach erosion.
The final dewatering plan for the project was released on June 25. State Parks District Superintendent Craig Sap assured the Malibu City Council that the city would have time to review the document. However, Malibu’s City Manager, Jim Thorsen, is currently on vacation.
Although the plan was only released on June 25, most of the first stage and part of the second stage outlined in the document has already been completed.
According to the dewatering plan, stage one includes: “1. Clear and grub…It is estimated that clearing and grubbing will take 3 days.  2. Installation of turbidity curtain, silt curtains and/or silt fence, which will be anchored as needed to prevent passage of fish from the main lagoon into the western channels (2 days). 3. Temporary dike construction will occur which will separate the western channels from the main lagoon (minimum 4 days). 4. Installation of treatment filtration system (3 days).”
Stage two entails: “1. Clear and grub in area where dewatering channels, basin, and berm will be constructed (3 days). 2. Building the temporary basin: the temporary basin will require similar treatment as the dewatering berm with regard to clearing the area of fish. The dewatering basin will be constructed in a dry condition or isolated and enclosed with turbidity curtains, silt curtains and/or slit fence prior to construction. The dewatering basin will be approximately 2,664,000 gallons.
“The dewatering basin is used to contain the dewatered water and has the capacity to hold more than 85 hours of pumped water at a rate of 1100 gallons per minute with treatment and discharge from the basin at 600 gpm. The estimated seepage rate for Area 1 is 1,104 gpm…
“4. Water is then pumped from the 20' x 20' X 8' sump area by two or more 4i diesel-powered pumps via two or more 611 pipes into the dewatering basin.
“ 5. Water will be transported from the dewatering basin to the treatment plant via two 411 pipes. 
“6. Water will be discharged from the treatment plant via a 611 pipe at the mean high tide line.
“7. Two 4-inch return pipes will be installed from the treatment system back to the dewatering basin for testing treatment system operations over a 48 hour period, before any treated water is discharged at the mean high tide line. At any time during dewatering, if the treatment system  does not properly operate partially or non-treated water will be returned to the dewatering basin while any repairs or replacement occurs.
8. Grading Area 1 in the western Lagoon will take place over 7 days.”
The plan includes the following contingency for water quality:
“If water quality objectives cannot be met via the proposed 600 gpm treatment system the contractor will immediately repair and/or replace any malfunctioning components to achieve proper operation. Water can be temporarily pumped into dewatering basins so that grading operations can continue. The dewatering treatment system is equipped with port valves which  allow Pure Effect to collect samples from each independent component to determine which, if any, components are malfunctioning. The treatment system is already designed with built in redundancy as there are two identical components for each stage of the treatment process
“If one of these components fail water can be routed through only one  side of the treatment system to facilitate repairs or replacement of components. This enables dewatering and treatment to occur while accomplishing any necessary maintenance or repairs.
“If water quality objectives still cannot be met via the proposed 600 gpm treatment system the contractor will cease discharge to repair the system and replace any malfunctioning components.
“If dewatering operations are forced to shut down the contractor will be required to test the system to ensure proper operations before any further discharge at the mean high tide line can occur.”
Project opponents continue to express concerns over whether the plan is adequate to prevent bacterial contamination in the Santa Monica Bay and at Surfrider Beach.
Critics also continue to take issue with the discovery of a Stevens meadow mouse, also known as a South Coast meadow vole,  a California Department of Fish and Game species of special concern that was recorded in a photograph taken after construction began on the lagoon project.
The small rodent, which has a distinctive grizzled coat, was not observed by project biologists Opponents state that the area where the vole was photographed is still intact and that the Department of Fish and Game should investigate before further construction takes place.
They question whether there may be other threatened species at the site that may also not have been noted before demolition began.
Dewatering is expected to begin later this week or early next week. The dewatering plan is available at the City of Malibu website:

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