Experts in engineering and seismology on Tuesday told the City Council a more complete study and risk assessment should be done before the Metropolitan Transportation Authority makes a final decision on the route of the Westside Subway Extension.
"More studies are needed to justify selection of station location and tunnel alignment," according to a presentation by Piotr Moncarz, project manager for Exponent. "A quantifiable measure of risk should be made using a risk-based methodology for each station option."
Exponent's analysis is a peer review of an October 2011 safety assessment by MTA consultants who compared the possibility of placing a subway station on Santa Monica Boulevard or Constellation Boulevard in Century City. The Constellation Boulevard stop would entail running a subway tunnel beneath as well as residences and businesses located in the city's western vicinity.
"Based on the findings reported in the Metro-sponsored reports and supporting review comments, momentum seems to be building against construction of a station on Santa Monica Boulevard based on perceived fault rupture hazards," Exponent said in its report. The company, however, noted potential dangers with both possible locations.
"It is Exponent’s view that the alternative Constellation Boulevard station, while generally in a more favorable location with regards to faulting issues, is instead faced with potential methane gas hazards that could represent at least as great a hazard to the public as the faulting hazards associated with the Santa Monica Boulevard station."
Moncarz and seismology expert Phillip Shaller highlighted several key concerns about the thoroughness of the MTA-commissioned study at the council study session. These concerns included:
- Questionable assessment of active earthquake faults near the proposed tunnel alignments;
- "Undocumented oil well castings" from a potential slew of abandoned metal oil well shafts under the high school that could significantly hinder tunnel drilling;
- The Metro study's "limited consideration of soil settlement" after tunneling and how that could impact overlying buildings and infrastructure.
Moncarz also pointed to 2009 MTA documentation indicating a potentially dangerous pocket of methane gas along the Constellation route, and he noted the failure of Metro's consultants to properly assess the level of risk associated with tunneling in such a location. Moncarz said the Metro report contains assumptions that dismiss concerns about possible danger that aren't backed by thorough ground testing or quantifiable risk assessment methodology.
In response to Exponent's critique, Metro CEO Arthur Leahy sent a dated Feb. 7 to council members and City Manager Jeff Kolin. Leahy countered, "It should be noted that the subway has operated for nearly 20 years in a methane gas area in downtown Los Angeles without incident."
The final environmental impact report of the MTA's plans, upon which the agency will base its final decision of the route, will be released later this year, according to Leahy.