Road to Cleaner Water Leads to… a Road
PCBs found in 38-year old tar sealant
Tacoma’s work to protect the Foss waterway has revealed polychlorinated biphenyls, more commonly known as PCBs, in globules of old roadway sealant. While any source of pollution isn’t good news, there is a silver lining. This pollution has been found and can now be dealt with.
"Tacoma may be the only community in the nation capable of tracking down and pinpointing a pollution problem like this," said Environmental Services Director Mike Slevin. "We’ve got a team of environmental science superheroes wearing lab coats and climbing down manholes to help us solve these mysteries."
The pollutants that were found in the storm drainage system are coming from a tar-like seam sealant between the street’s asphalt and concrete curb and gutter. The sealant was placed when the road was reconstructed 38 years ago. It spans five residential blocks in east Tacoma on East 61st and 62nd streets between East I and K streets and East E Street between East 64th and East 65th streets. The sealant is intermittent and most has worn away, but City staff believe the remaining sealant is entering the storm system through a unique French drain-style drainage system under this section of roadway. The system was installed to deal with a high water table while the road was being constructed.
PCB pollution levels found in a few of the samples exceed limits set by the Toxic Substance Control Act. City staff have reported their findings to the Washington State Department of Ecology and the Federal Environmental Protection Agency and are working with those agencies to develop the path forward.
Dr. Teri Floyd, of Floyd|Snider Inc., the City’s consultant on cleanup issues along the Foss Waterway, notes that in her opinion, "there’s not a significant risk to public health because PCBs, even at these concentrations, are not acutely toxic to either humans or critters. The potential concern at these concentrations would be with long term ingestion or inhalation, which is simply not possible given the location of the PCB-containing sealant in the stormwater and roadway system. The cleanup levels for sediments in the waterway necessary to keep our fish healthy are much lower than those needed to protect people, because the fish accumulate the PCBs in their tissues over their lifetimes. We would not want these concentrations in Puget Sound, but they do not represent a risk to the public given their location."
This area’s storm drains ultimately enter the Thea Foss Waterway though downstream water samples register below PCB cleanup requirements. To address any potential resident impact, City staff are working with state and federal regulators to develop a plan to permanently address and remove the issue areas.
City staff began testing and tracking catch basin sediment samples in the Foss Watershed in 2002. Readings in this location were inconsistent, only showing comparably higher PCB concentrations in half of the samples taken over 10 years. In 2011, the City took the highly proactive step of cleaning storm system pipes to remove such legacy pollutants. However, in 2012 the elevated PCB levels were back, suggesting an active, rather than legacy, source. The City then extended its testing to individual inlets throughout an approximately 39-block area. Sediment results narrowed the City’s search to 33 inlets within 8 blocks. This summer, City staff were able to pinpoint the problem area through a series of borings and samples.
"We’ve done something that no one else has," Slevin said. "We’re using long-term and innovative approaches in ways that are making us a national leader. But it takes time. As we make more legacy pollution discoveries in the future, our work will ultimately help us and others to better understand how to protect Puget Sound and our waterways."