The Washington State Department of Transportation responded last week to residents’ concerns about the arsenic levels in the old State Route 520 bridge.

The post, written on Oct. 3 by WSDOT Media and Construction Communications Manager Steve Peer, states the level of arsenic in the old bridge’s concrete was tested in 2015 and 2016.

“The 2015 test, which determined the molecular composition of the concrete, identified an above-normal level of arsenic,” the post states. “This test was performed to determine if the concrete was suitable for recycling.

“The 2016 test was designed to assess if the level of arsenic and other elements from the old bridge’s hardened concrete could leach into the environment if the concrete were placed in a landfill. This second test, called a Toxic Characteristic Leaching Procedure (TCLP), is the EPA-approved analysis used by Public Health Seattle & King County for determining whether to allow disposal at Reserve Silica, a special landfill for inert materials. The TCLP result for arsenic was 0.2 parts per million — well below the EPA’s regulatory standard of 5 ppm for disposal.”

No further details about the 2015 test are given in the blog post, but when talking to the Reporter, Peer said the level of arsenic found in the first test was 50 to 65 ppm, results that concerned residents who live around Lake Washington, where the demolition of the old bridge is taking place.

Peer stressed that the 2016 test result is key because it indicates the amount of arsenic that could actually be released into the environment.

“What’s present (50 to 65 ppm from 2015 test) and what could leak out into the environment (0.2 ppm from 2016 test) are two different things,” he said. “When it’s encased in concrete, the amount that could potentially harm the environment is minimal.”

The blog post includes a link to a report detailing the environmental protocols followed during the current bridge removal and demolition work. The procedures are “designed to achieve no discharge of contaminants or materials that would violate water quality standards during bridge construction and demolition,” the report states.

The demolition of the old bridge is scheduled to be completed in November and is currently 70 percent complete.

“We’re working to make sure things are done right,” Peer said. “We know there are a lot of eyes watching this.”