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Water Intrusion In BART Tunnels Creates Underground 'Rainforest'

SAN FRANCISCO (CBS SF) -- One of the many infrastructure problems BART officials are hoping to address if voters approve the $3.5 billion repair bond of Measure RR was illustrated in a recently released video that shows just how badly water intrusion is affecting the system's tunnels.

The video shot early Thursday morning after service had concluded was distributed by BART spokesperson Taylor Huckaby. The clip shows a maintenance car traveling down the tracks from the Civic Center Station before cutting to workers taking photos and film of the water leakage inside the tunnel.

The water is seen running down the walls and under the tracks in small rivulets in several different places. According to BART officials, the damp stretch of tracks has earned the nickname "the rainforest" from maintenance crews.

BART officials brought up water intrusion as one of the numerous issues the agency hopes to fix with the passage of Measure RR in an article posted to the BART website on September 19.

The article outlines the central issue of why the water intrusion affects the system's tunnel in San Francisco.

"Unlike the pricey real estate above, BART's tunnels in downtown San Francisco are below the water table. This means either seawater or freshwater constantly seek to convert the section of trackway between Embarcadero and 16th Street/Mission Stations into a flume ride," the article notes. "One might think tunneling underground would create a watertight environment, but downtown San Francisco isn't all rock—and not all rock is waterproof!"

While BART repair crews have been repacking areas of the tunnel with a waterproofing compound to keep the leaks from growing, the compound degrades fairly quickly. The article notes that the tunnel area is too large to be covered by a system of drains and pumps -- though there already are pumps installed at some of the bigger underground streams --and that draining too much from "the whole downtown area could cause Market Street to sink (or possibly collapse)."

In addition to undermining the structural integrity of the train tunnels, BART officials say the moisture from the underground water sources is also damaging the rails themselves as trains running over the damp tracks forces water into the steel, creating what are described as "micro fractures."

The article outlines a possible solution for the water intrusion, stating that BART engineers could use the naturally occurring, clay-like compound called bentonite for waterproofing. However, the waterproofing of miles of tunnel and the attendant repairs to track and electrical cabling will be expensive, which is why the major project is being touted as one of main "big-ticket repair items" that Measure RR would fund if passed.

While early polls showed the bond was likely to pass in San Francisco and Alameda counties, voters in Contra Costa County -- where the 2013 BART strike hit commuters the hardest -- were still up in the air.

A two-thirds majority is needed to pass the measure.

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