Q&A: What are the unique engineering challenges for San Francisco’s burgeoning downtown area?

706 Mission, San Francisco, CA

706 Mission, San Francisco, CA

Background Information

Langan Treadwell Rollo is performing engineering services for several new high-rise residential developments in downtown San Francisco: 706 Mission Street, Transbay Blocks 6/7 and Block 8, 201 Folsom Street, and 41 Tehama Street, among others. These projects address both the city’s lack of land space (only 7 miles wide by 7 miles long) and desire for smaller units (an estimated 38% of residents are single occupants). According to the San Francisco Planning Department’s 2014 Housing Inventory Report, the production of new housing has increased by 50% from 2013.

What makes all this interesting — and challenging — to an environmental scientist is these projects focus on sky-high vertical growth built on land that our ancestors extended horizontally.

Solutions to Challenges
As a result of the 1906 earthquake and subsequent fire and the preceding Gold Rush era, many of the new downtown developments exist on, or are close to, infill. Rubble, wreckage, old wharves and piers, and abandoned ships can be within these infills.

Boat

Remnants of an old ship found during an excavation in downtown San Francisco.

Given the nature of infill, we recognize that contamination and historical concerns will likely result in additional costs for soil handling and disposal. San Francisco’s infill is the reason why the city created the Maher Ordinance (Article 22A of the San Francisco Health Code), regulated by the city’s Department of Public Health (SFDPH). This city code mandates stricter protocols, including site history, soil sampling, and site mitigation, which SFDPH oversees and approves.

Another challenge we face when excavating is the discovery of potential artifacts. These areas within the excavation are then left undisturbed so archaeologists can investigate. While this process can delay a project, it can be quite interesting. During recent excavations, we encountered remnants of an old ship as well as a lighter boat that originated from New England. Our construction crews have discovered items of interest that were as deep as 60 feet below ground so they likely existed several thousand years ago. Some of these artifacts are now displayed in museums. This is why I like the more complex projects: the more challenges we face, the more fascinating these projects become.

Answer provided by Peter J. Cusack
Peter Cusack is an environmental scientist who has worked on San Francisco and other Bay Area projects for the last 26 years. He manages and implements hazardous waste characterization and remediation projects. His experience includes pre-acquisition site assessments, site investigations, underground storage tanks removal, Phase II investigations, soil and groundwater sampling and remediation, development of soil management plans, aquifer pumping tests, contractor oversight, and field inspection for numerous construction projects. His work is often done in coordination with our geotechnical practice. He has extensive experience in site investigations and regulatory agency interaction prior to new construction/development.