Richard Bangert posts stories and photos about Alameda Point environmental issues on his blog Alameda Point Environmental Report https://alamedapointenviro.com/
Solvent Cleanup Completed at Point
Solvent Cleanup Completed at Point
A liquid solvent that is able to dissolve other substances can run, but it can’t hide from investigators, even 20 feet below ground. A toxic cleaning solvent called trichloroethane (TCE) was used to degrease metal parts in industrial operations at the Navy’s aircraft repair facility. When this solvent leaks into soil and groundwater, as it did in Building 5 at Alameda Point, the odorless vapors can cause cancer and other ill health effects to occupants of buildings above as it evaporates.
The actual process of cleaning up the contamination, while time-consuming, is not the real problem. The real challenge is finding it, measuring it, and calculating what the safe cleanup level is for future use of the building, in this case commercial.
The Navy has spent some 30 years, starting before the base closed, mapping the geology and groundwater flow, drilling wells, taking water samples, plotting the extent of contamination, creating 3-D models of the contamination, creating health risk models, and employing a variety of cleanup methods. In November 2020, the Navy reported that the air quality in Building 5, covering almost a million square feet, is now safe for future workers.
The cleanup process has employed three methods of removing the solvent. First, an isolated pocket of liquid solvent was pumped out. Second, both steam and high voltage electrodes in the ground were used to vaporize the bulk of the solvent and vacuum it out. The third method, called chemical oxidation, involves injecting chemicals to break down the remaining area of elevated solvent into harmless substances.
It is worth noting that the other common method of treating trichloroethane contamination, using bacteria, also known as bioremediation, produces the exact same harmless breakdown compounds as the chemical oxidation process. But that process, which is being used on a large solvent contamination area south of Alameda Point’s Site A new development, is much slower.
The reason the faster chemical-oxidation process was ruled out for that site is because there are numerous utility pipes for electrical, gas, water and sewer that crisscross the cleanup site. Injected cleanup chemicals would end up being diverted when they hit the various pipes and frustrate the even distribution of the cleanup chemicals. Bacteria, on the other hand, is already there and can spread on its own after injecting food sources like lactose and veggie oil, which the Navy has done.
While it took a long time for chemists to come up with the sophisticated three-chemical cleanup mixture used at Building 5, the chemicals themselves are surprisingly familiar names. Hydrogen peroxide is common in most medicine cabinets for topical use on skin. Sodium persulfate is common at pool supply stores for use as a pool or spa shock treatment to quickly get rid of algae. Chelated iron is common in pantries and garages as either a human health supplement or plant supplement.
Peroxide, persulfate, and iron each play a complementary role, allowing the mixture to remain stable and travel farther in the wet soil and to prolong the action of breaking down the solvent. Individually they would work but only for a brief period. The beauty of the chemical oxidation process is that it breaks down solvents like trichloroethane to simple hydrocarbons such as ethene and ethane. Ethene, also known as ethylene, is commonly used in agriculture as a food ripening agent.
The vacuum extraction method using steam, and then high-voltage steel beams that heated the soil and ground water to near boiling, were performed at Building 5 between 1999 and 2009.
The steel beam electrode method removed 99.9 percent of the amount needed to reach the goal. It was discontinued when it reached the point where the results were so tiny it did not justify the huge electric bill.
Bringing the job to completion was left to the chemical injection method. It was not until 2018 and 2019 that the three-chemical mixture was injected on four different occasions. A series of four water sampling events that followed showed the goals had been reached.
An elaborate quality control process for water testing was performed by an independent third-party validation company. The company evaluated duplicate field samples and other lab-prepared samples that would reveal any suspicious results in follow-up monitoring.
The odyssey of cleanup at Building 5 involving radium-226, petroleum products, and cleaning solvent is expected to be declared officially completed by the end of 2021, with transfer to the city expected in early 2022. Building 5 is across the street from Rock Wall Wine Company.