Navy digs up petroleum contamination in rare cleanup action

Cleaning up petroleum contamination in soil and groundwater is pretty straightforward.  It is usually accomplished by one or more tried-and-proven methods that rely on inserting PVC pipe into the contamination zone for treatment.  But multiple efforts outside the sprawling Building 5 hangar complex on West Tower Avenue at Alameda Point failed to reduce contamination to regulatory goals.  In August 2020, after almost two decades of investigation and treatment efforts, the Navy resorted to a rarely used option of digging up all of the soil down to the water table and hauling most of it away.

Building 5 was the location of the Navy’s plane refurbishing and overhaul facility where thousands of civilians worked.  It was known as the Naval Air Rework Facility.  Before an airplane was moved into the hangar, it underwent de-fueling, flushing out fuel lines and cleaning various components with products akin to paint thinner.  This preparatory work was the source of the contamination in the soil and groundwater near the big hangar doors.

In 2011, after a decade of drilling investigative wells and trying to plot out the extent of the contamination, the Navy proceeded with a two-phase cleanup plan that they assumed would lead to successful cleanup.  The first phase of the plan involved pumping air into the contamination zone and simultaneously vacuuming out the petroleum hydrocarbon vapors into a tanker truck.  A total of 63 injection, extraction, and monitoring wells were created.  The vapor extraction event accomplished its goal, which was to reduce petroleum concentrations to the point at which a neutralizing chemical could finish the active remediation effort.

During the second phase the following year, the neutralizing chemical compound designed to break up the remaining petroleum product was injected.  The compound is called an oxidizer because it turns petroleum products into carbon dioxide and water.  The active ingredients were sodium persulfate and hydrogen peroxide.  Water testing via monitoring wells immediately after the injections showed that the chemical treatment achieved its goal.  But follow-up monitoring showed the petroleum concentrations were starting to go back up.  The only explanation for the numbers going up is that they did not treat a large enough area and that nearby petroleum was migrating.

This data led to a new round of investigative monitoring.  More monitoring wells were drilled and testing conducted between June 2016 and March 2018 in order to better delineate how wide the petroleum contamination was.  But rather than perform more in-ground treatments, the Navy opted instead to take the extraordinary step of digging up the entire area in August.

Twenty percent of the soil was clean enough to use for refilling the pits.  The other 80 percent had low enough concentrations of petroleum residue that it qualified as non-hazardous waste.   Some 222 truckloads of soil was hauled to two non-hazardous disposal sites in Solano County.  One of the facilities, the Potrero Hills Landfill, generates forty percent of the electricity for homes and industry in Suisun City from biogas at the facility.

The pits have been backfilled with clean soil on top of a layer of crushed rock and repaved.

The Navy will perform semiannual monitoring of the soil and groundwater for the next three years to assure that the goals are achieved.

As is the case with many petroleum cleanup sites, the last incremental amount of contamination is left to naturally occurring bacteria in the ground to break it down into harmless compounds.  The process is referred to as natural attenuation.  Getting to “zero” through active treatment is almost impossible.  Most soil and groundwater cleanup involves a series of treatments, each one setting the stage for the subsequent treatment.

As an interesting side note, during the natural attenuation phase, success is not measured by testing for the amount of petroleum or counting bacteria in water samples under a microscope.  Instead, a half dozen water quality parameters are measured.  Success or failure is inferred by everything else going on in the contamination zone.  For example, dissolved oxygen in water is used by bacteria in the biodegradation process.  Therefore, declining dissolved oxygen is a good indicator that the remaining petroleum hydrocarbon is being broken down by bacteria into harmless carbon dioxide and water as planned.

The Building 5 complex covering almost one million square feet is still owned by the Navy.  It has never been available to the city for leasing, due to the extensive cleanup activities in and around the complex.  The Navy has leased out parts of it for a movie production and for fixing one of the jet monuments.  With cleanup nearly complete, it is expected that Building 5 will be suitable for transfer in about two years.

More photos from the Navy –