LAMORINDA WEEKLY | Town takes safety measures regarding new Rheem sinkhole

During a special session of the town council, held prior to the regularly scheduled meeting on April 24, the council members voted unanimously to approve a resolution authorizing the appropriation of $80,000 from the General Fund Reserve to Department 730 Storm Drain Maintenance. This authorization provides the initial technical support necessary to protect improvements to Moraga's storm drain infrastructure and ensure the health and safety of its citizens.

According to the staff report, the town was notified of a depression in a landscape planter near a streetlight pole on March 26 at the Rheem Boulevard and Center Street intersection. Concerns arose about potential problems affecting the town's storm drain system that runs approximately 25-feet below.

The property owners were advised by the town to take precautions to avoid the risk of health and safety hazards, including draining the 500-gallon underground oil tank on the Moraga Star gas station property to prevent possible seepage into Laguna Creek which flows through the storm drain culvert; removing the nearby streetlight pole to prevent it from potentially falling and injuring someone; and securing the surrounding area to prevent passersby from getting too close to the site.

Almost 10 days later the depression appeared to be a minor concern compared to an approximately 2-foot by 5-foot sinkhole that appeared on the property adjacent to the initial issue. Based on an inspection, it was determined that water, dirt and debris are entering into the corrugated metal pipe, below the property, that extends roughly 500-feet under the Rheem Shopping Center.

The town has kept regular contact with the property owners by stressing the urgency of the situation and offering technical support toward repairs keeping in line with those made during the 2017 sinkhole restoration process just across the street.

The Rheem Shopping Center property owner's contractor inspected the culvert on April 19, along with their engineering team, only to discover that approximately 20 feet of CMP under the sinkhole had been crushed. Reaching the same conclusion as the town, the contractor agreed that the voids in the pipe should be filled and the pipe should be lined.

Three days later, the property owners shored up the 20-foot section of crushed pipe to prevent a collapse.

Inspectors recommend a prephase to relieve pressure on top of the crushed pipe by excavating the soil above. The shape of the pipe must be restored and reinforced before filling any voids and lining the pipe.

While the town has made it clear that the property owners are responsible for repairs to the storm drain pipes on their property, the town continues to offer technical support. Town staff is gathering qualified consultants, many of whom were involved with the 2016 Rheem Sinkhole, to provide that support.

To date, $19,652.20 has been spent in providing technical support for the property owners. The $80,000 appropriation will cover that and provide additional funding for the next few weeks until a plan has been developed. The $1.65 million reimbursement to the General Fund for the Temporary Canyon Bridge is expected to restore the town's General Fund Reserve level to 50 percent of operating expenditures by June 30 and is enough to cover the initial emergency response.