New contaminate source discovered in Yorba Linda gas station cleanup will increase costs

A new contaminate source and residual hydrocarbon concentrations will increase the cost and lengthen the time required for remediation at the former gas station property between the Yorba Linda public library and Imperial Highway at the Lemon Drive intersection.

The library and the adjacent former gas station land is to be sold to In-N-Out for a fast-food operation, once the library moves to a Lakeview Avenue and Lemon Drive location in 2020.

Originally, the seven-year process to remove contaminates affecting groundwater under the city-owned property was set for final close-out at the end of this year, but now closure is not expected until late next year, noted a report from Assistant City Engineer Rick Yee.

And the project cost will jump $490,606 to $1,129,831 under the 2016 contract with Stantec Engineering, a Canada-based firm with offices in Irvine. Prior to an initial 2011 contract with Stantec, the city spent $540,000 to remove and dispose of contaminated soil.

Since 2011, some $2.5 million has been spent on remediation and groundwater monitoring at the site. The Orange County Transportation Authority paid $1.775 million, with the remainder coming from the State Underground Storage Tank Fund.

Of the $490,606 in additional costs, $320,000 is expected to come from state storage tank reimbursements and $170,606 from city reserve funds. The transportation authority says the latter can be deducted from money owed to the authority for purchasing the gas station land.

During the current remediation efforts, a new contaminate source was detected in the subsurface soil, according to Yee's report, which was reviewed at the most recent City Council meeting.

“Soil vapor concentrations at two monitoring wells suggest that diesel fluids are present on site and are believed to have been generated from a source other than the (former station) gasoline storage tanks,” Yee's report stated.

Also, while checks at 16 of 17 monitoring wells show “a reduction in contaminants below the required threshold for closure,” there is one monitoring location “with residual concentrations that warrants additional treatment to reach closure threshold levels,” Yee noted.

Work at the site is governed by the State Water Resources Control Board with local oversight by the Orange County Health Care Agency. After the city purchased the site in 2004 as a part of the Imperial Highway widening project, a Superior Court judgment required the city to clear up contamination, which had spread west under Imperial Highway toward a restaurant parcel.

The initial phase of site cleanup included the installation of equipment that removed floating gasoline from the groundwater, completed in 2011, with the past seven years devoted to an effort to remove the remaining dissolved gasoline mixed with the groundwater.

Since 2011, about 17,500 pounds of contaminant have been removed from the site, according to Yee's report.