Valley News -

By Joe Naiman

MWD to replace Lake Mathews wastewater system, upgrade Disaster Recovery Facility


Last updated 6/1/2018 at 3:48pm

The Metropolitan Water District of Southern California has authorized the final design to replace the wastewater system and upgrade the Disaster Recovery Facility at Lake Mathews.

The district voted May 8, to authorize the final design work for the wastewater system replacement and Disaster Recovery Facility upgrade, appropriated $890,000 for the work, found the replacement of the wastewater system categorically exempt from California Environmental Quality Act review and found that the previous CEQA review exemption for the Disaster Recovery Facility upgrades needed no further analysis or determination.

In the late 1930s, MWD built the Colorado River Aqueduct which runs from Parker to Lake Mathews, and MWD’s Colorado River supply is distributed from Lake Mathews. The reservoir’s original construction included installation of an on-site wastewater system which serves bathrooms and kitchen facilities at the Lake Mathews maintenance buildings, administrative offices and repair shops. The wastewater system was expanded in the 1960s.

The 1,600-square-foot masonry building with a steel roof used for the Lake Mathews Disaster Recovery Facility was originally a storage building and now houses electrical switchgear, telecommunications hardware, information technology servers and associated equipment, which creates off-site backup to ensure the continuation of MWD information technology functions in the event of a disaster which disables the information technology system at MWD’s headquarters building in Los Angeles. The facility also supplies power to the Lake Mathews Administration Building and to the lake’s junction shaft.

The wastewater system consists of three components: community septic tanks and leach fields, collector lines to convey wastewater from Lake Mathews facilities to the septic tanks and sewer laterals to convey wastewater from individual buildings to the collector lines. Solid waste in the septic tanks settles to the bottom of multiple chambers, before undergoing biological treatment before being removed by pump trucks at regular intervals, and the liquid effluent is dispersed through perforated pipes into subsurface soils in the leach fields. The system includes five community septic tanks and approximately 6,000 feet of collector lines and sewer laterals.

Although the wastewater system has been given regular maintenance, its age has led to incidents of slow-draining sinks and toilets, broken and clogged pipes, septic tank backups, and clogged leach fields. In the early 21st century municipal sewer service was extended to the area, and MWD staff recommended that the on-site septic tank treatment be discontinued and that the wastewater system be connected to the Western Municipal Water District sewer system. A nearby Western sewer main includes a connection point which was specifically installed for potential Lake Mathews future use, and that connection can accept wastewater by gravity flow from all of the Lake Mathews facilities.

In May 2017 MWD’s board authorized the preliminary design process while appropriating $350,000 for that phase which developed design criteria based on projected future wastewater flows and current codes, initiated the permitting for the sewer connection, conducted field investigations and potholing to locate utilities, designed a preliminary layout of the collection system, prepared environmental documentation and developed a cost estimate.

The actual work will replace the existing wastewater collector lines, laterals and manholes at Lake Mathews, connect the new lines to the existing facilities and to the Western sewer main and abandon the existing septic system. The final design phase will include potholing and surveys of existing utilities, preparation of drawings and specifications, local agency permitting, value engineering, development of a construction cost estimate and receipt of bids. GeoPentech will conduct the potholing and utility surveys while MWD staff will perform all other activities with the exception of the third-party value engineering whose expense is small enough that the MWD general manager can issue a contract without board approval.

The $610,000 budgeted for the wastewater system replacement final design work covers $314,000 for preparation of the drawings and specifications, $92,000 for permitting, bidding and project management, $85,000 for the GeoPentech utility investigations, $36,000 for the third-party value engineering assessment and $83,000 for contingency. The final design work is expected to be complete by February 2019.

A seismic assessment of the Disaster Recovery Facility was conducted in 2013 which indicated that the building could be damaged during a major earthquake. The structure is also approximately eight feet from the edge of a 50 foot high slope. The crest of the slope has eroded over the years and could undermine the Disaster Recovery Facility building’s foundation unless the slope is stabilized. The fire suppression system is undersized for the building’s current use.

The planned upgrades include structural strengthening of the roof connections, bracing of the interior walls, slope stabilization at the building’s perimeter, upgrading the fire suppression system, installing an electronic access system so that a local fire department can enter the structure and installing a new drainage line. The MWD board approved the preliminary design phase in December 2016 while appropriating $250,000 for that phase which covered geotechnical investigations, preparation of conceptual layout drawings, development of a construction cost estimate and preparation of environmental documentation.

The final design activities include obtaining local agency permits, preparing drawings and specifications, developing a construction cost estimate and advertising a competitive bid package. MWD staff will perform all of those activities. The $280,000 appropriated May 8 will cover $168,000 for design and preparation of drawings and specifications, $88,000 for permitting, bidding and project management and $24,000 for contingency. The final design phase for the Disaster Recovery Facility upgrades has a December 2018 estimated completion date.

Joe Naiman can be reached by email at [email protected]


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