Ending threat of solvents in groundwater leaching into San Francisco Bay

Site 1 at the northwestern tip of Alameda Point was used as the principal disposal area for all waste generated at Naval Air Station-Alameda from 1943 to 1956.  This disposal area, which was once part of the Bay, was created by sinking pontoons and barges in the Bay and backfilling with dredge soil.

Disposal of cleaning solvents and petroleum products at one unlined pit within the landfill resulted in a groundwater plume that poses a threat of leaching into San Francisco Bay today.

In the 1990s the Navy installed an underground barrier system, called a funnel and gate permeable reactive barrier, to stem the flow of contaminants into the Bay.  It was not a permanent solution.  In July of this year the permanent solution began with the injection of neutralizing chemicals into the plume.

Protecting marine life

San Francisco Bay at Alameda Point western shoreline where threat of solvent leaching exists.

Most cleanup activities around the base are aimed at eliminating direct health risks to humans, such as from soil or from vapors that could enter a building.  In a few cases, the cleanup is focused first on direct impacts to marine life such as fish, which could in turn cause health problems for people who eat them.

The cleanup effort at the Site 1 plume is one of those cases.  This effort will keep toxins — solvents, petroleum products, and metals — from ever leaching into the Bay, being ingested by fish, and then consumed by humans.  The effort will also reduce unacceptable levels of vapors that are escaping directly above the plume.  The future use of the site will be restricted to open space recreational.

The process

July 2012 – Manifold system of hose lines that send oxidant chemicals to individual wells that go into the underground plume contamination area. Navy photo.

The chemical injection process, called In Situ Chemical Oxidation (ISCO), is accomplished by injecting oxidants (catalyzed hydrogen-peroxide and sodium persulfate) into the plume through injection wells.  “These oxidants produce short-lived reactions that directly destroy the targeted contaminants,” according to the Navy.  Groundwater tests will determine if further treatments are necessary.

Tanks of chemicals for neutralizing solvent plume. Shown as work area being set up in June 2012.

Treatments will continue until either the groundwater is clean enough, or the solvent and petroleum concentration has been reduced by 75%.  Once they get to 75% reduction, further injections are more or less a waste of money.  From then on, the contaminant concentration is low enough that the remainder will either degrade or disperse and dilute naturally without posing a risk to fish or humans.  This process is called natural attenuation and is often relied upon to finish the job when the bulk of contaminants are neutralized and treatment methods no longer yield effective results.

The groundwater plume is also contaminated with metals consisting of arsenic, copper, mercury, nickel, silver, and zinc.  The metals problem will, in theory, be taken care of when the solvents and petroleum products are eliminated.  This will cause the chemistry of the groundwater to change, which in turn will cause the metals to no longer remain dissolved in the water.  The metals will return to their solid state and remain where they are.  That’s the theory.

But to make sure it’s working, there will be a long-term groundwater monitoring program to make sure the metals aren’t moving.  If problems arise in the future, the Navy will have to come back and design a new remedy.  The Navy is responsible for the landfill’s contents staying in place in perpetuity.

Map of Site 1 disposal area with arrow from left indicating plume treatment area. Map also shows outlines of individual unlined pits that were used for disposal of waste. Half of the area is now covered by runway.

The Navy opted not to remove the landfill contents because of the $93 million price tag and because the risk of contaminant releases was deemed low.  A new set of environmental concerns associated with digging up and hauling away a landfill was also cited during the decision process.

The groundwater plume being treated is approximately 30 feet wide by 160 feet long, and it occurs mainly between depths of 5 and 10 feet below the ground surface.

Site 1 groundwater treatment work underway in July. San Francisco in background. Navy photo.

Delay on soil cover

All of 30-acre Site 1 will eventually be covered with soil and seeded with native grasses.  Work on the soil cover was delayed when the contractor discovered that the part of the landfill once used for burning waste was larger than expected.  The documentation has to go back through the review process, with a work plan for the soil cover hopefully prepared and ready to implement by 2014.