Nov 26, 2013 - By Alejandra Silva, Staff WriterA consulting firm will conduct field work and sampling during the first week of December at the city-owned vacant lot at 420 E. Main St. in downtown Riverton, according to Wyoming Department of Environmental Quality representatives.
Stantec Consulting, of Salt Lake City, has been hired by the DEQ to do the work, which will be funded by the Brownfields Assistance program, a program established by the DEQ to help local governments conduct testing and cleaning to make contaminated areas serviceable.
Before it became city property, the downtown lot was home to a gasoline station and later a dry cleaning business. The city said it has paid more than $81,000 so far to demolish the former Daisy Cleaners building and perform asbestos removal. The DEQ's Storage Tank Program also removed fuel tanks and placed a soil vapor extraction and air spark system at the site to deal with petroleum contamination.
Kristi Dobra, a natural resource analyst from the DEQ's Lander office, told the Riverton City Council during its meeting Nov. 19 that the department is working closely with other groups to make sure no clean-up process is duplicated unnecessarily.
A report provided to the council said chlorinated solvents from the former dry cleaning operation were present in groundwater samples. The contamination "is suspected in soils though not yet confirmed with sampling," the report read.
Stantec Consulting will install two deep monitoring wells and collect groundwater samples from the new and previously installed monitoring wells. A soil gas survey also will be conducted on the site to find out if there are chlorinated solvent vapors. The results of this soil gas survey can direct the department to the location of the spill or leak that caused the contamination. Heavily contaminated soils also can be removed to a disposal site.
Dobra said solvents can evaporate easily, and groundwater contaminated with these solvents can vent vapors into the soils above, possibly creating vapor intrusion problems in nearby properties.
To determine if this has happened, Stantec Consulting will perform soil gas investigations on the properties at 418 E. Main St. and 421 E. Main St., Dobra said. Tests done by the DEQ Storage Tank program in the past showed solvents present in the groundwater. Recent results have shown lower levels of solvents, but because the results have been higher before, Dobra said it would be best to check if the groundwater has migrated toward the adjacent buildings. When this happens, there is a risk of vapor intruding into the indoor air through cracks in foundations and crawl spaces.
These investigations also would ensure there is no vapor intrusion on the vacant lot in case the city decided to place a structure there in the future, Dobra said. From there, a "remedial alternatives evaluation" will help direct the department with clean-up procedures.
"Right now we're just trying to figure out what kind of problems we have, if any," she said. "And the extent of those."
The department plans to provide the city with the data it compiles.
The causes of contamination could have been improper waste disposal into sewers or the soil, a leaking sewer line, or an accidental spill.
In a split vote in November 2012, the Riverton City Council decided to convert the vacant lot into a "green space" for the community, instead of a business or parking lot. The council members also discussed that when they applied for the Brownfields Assistance program, they were required to declare how they would use the lot.
However, those plans could change depending on what is found in the soil.
"We will come to you and say, 'these are the levels that are in the soils and this is what the appropriate use could be,'" said DEQ Brownfields Assistance program coordinator Vickie Meredith, adding that the council members could create a resolution to restrict the use of the space, if they chose to sell the lot to someone else.
"Our hope is that if there's some contamination in the soil in a very limited source area that we can pick it up and get it out of there, and then you guys don't have to worry about restricting the property or not," she said.
If the lot is more contaminated than the department expects, Meredith said remediation could conclude by the end of 2014. She added that while the work is being done, the lot could not be used as a parking lot as it is now.
Mayor Ron Warpness thanked the DEQ for presenting its initial plans.
"We're very anxious to learn the fate of that piece of property," he said. "It's a prime location in our community, and it's very important for us to do what we can for it."
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