The East Bay Municipal Utility Department (EBMUD) is still searching for what caused two water mains to break, which led to two sinkholes in Alameda last week; one on Lincoln Avenue and one on Otis Drive.

EBMUD operates the water mains in Alameda. In an email to the Sun, EBMUD Senior Public Information Representative Andrea Pook said the utility company hasn’t yet found the exact cause of the breaks as crews were busy repairing the lines to get customers’ water service back on. EBMUD will conduct a thorough investigation to determine the causes.

The water main breaks were unexpected for EBMUD. EBMUD conducts a risk model to create a prioritized plan for pipeline replacement throughout their system. A recent study showed the pipeline on Lincoln, a cast iron pipe set in 1894, was in “surprisingly good condition.” The pipe on Otis Drive, a steel pipe set in 1964, also showed it was not in need of replacement.

“The two pipes that recently failed in Alameda were classified as a medium risk,” said Pook. As a result, EBMUD focuses its Pipe Rebuild resources on higher risk pipes in other areas of its water system.

EBMUD has 4,200 miles of water mains snaking under the Bay Area, including 192 miles of water mains in Alameda. The utility organization assigns risk grades to all pipes. According to Pook, of the 192 miles of pipes in Alameda, 1.7 miles has a D or F rating.

“Our goal is to have pipes last as long as possible, but unforeseen conditions can cause pipes to break before they are replaced,” said Pook. “Our Pipe Rebuild Program has been in place for several years, and we are significantly increasing the rate of our pipe replacement to address the challenges of aging infrastructure and to take advantage of the newest technologies and pipe materials.”

Pook said water mains in the Bay Area are of different ages, different types of materials and may go through areas with various conditions, including sandy soils subject to liquefaction as in Alameda. Even with the two breaks last week, water main breaks in Alameda are low compared to the rest of EBMUD’s service area. According to Pook, Alameda has five water main breaks per 100 miles of pipes per year, compared to 25 breaks per 100 miles in the rest of its service area.

In the last 10 years, EBMUD has installed 11.5 miles of pipe in Alameda. This includes both pipeline infrastructure renewals and system extensions.

Last week, two different sinkholes formed in Alameda after two water mains broke. The first sinkhole formed on Wednesday, Aug. 2, on the 2900 block of Lincoln Avenue. The sinkhole was reported around 6 p.m. The second sinkhole formed on Friday, Aug. 4, on the 1200 block of Otis Drive. In both instances, water service to multiple Alameda households were shutoff while EBMUD, the Alameda Fire Department, and the city's Public Works Department made repairs to water pipes and the road. Water service returned in both instances after a few days.