Jul. 10—The costly and yearslong process of removing petroleum pollution from the ground beneath and surrounding the county-owned state District Courthouse in downtown Santa Fe is almost over.
"The site is in the final stages of deeming it successfully cleaned up," state Environment Department spokesman Matthew Maez wrote in an email.
After a fraught site selection process, Santa Fe County officials got a nasty surprise in 2009 when they began construction of a new multimillion courthouse at the corner of Montezuma Avenue and Sandoval Street.
A massive plume of oil and gas pollution was detected beneath the site; it had seeped from leaky underground storage tanks of several gas stations located in the area between 1920 and 1970.
The discovery delayed construction of the new courthouse for more than a year, reduced a planned underground parking garage from two levels to one and contributed to costs increases on the project that drove the price tag from an original estimate of
$38 million to a final bill of
$63 million, including construction and remediation.
The courthouse opened in 2013.
In 2010, the gasoline plume was about 500 feet long and 150 feet wide, according to the Environment Department.
Maez wrote non-aqueous phase liquid, better known by the acronym NAPL, was gauged in monitoring wells "up to three feet thick approximately 30 feet below ground."
NAPLs are organic liquid contaminants that do not dissolve in or easily mix with water. They include oil, gasoline and petroleum products.
Once introduced, NAPLs tend to contaminate soil and groundwater for long periods of time and can be persistent organic pollutants.
But after years of remediation — much of it done from 2009 through 2015 — and monitoring that has continued since then, the project is nearing official completion.
Results of 2019 groundwater monitoring conducted via dozens of test wells scattered across several blocks between the Design Center to the south of the courthouse and the District Attorney's Office to the north show remediation efforts undertaken between 2009 and 2015 successfully removed gasoline which had leaked into the aquifer, Maez wrote.
Cleanup work continues in four "hot spots" which tested above acceptable levels for pollutants, including benzene, ethylbenzene and naphthalene in 2019, according to summary testing results provided by the Environment Department.
"The ongoing work that is being performed addresses the remaining groundwater contamination in order to meet New Mexico Water Quality Control Commission standards and obtain a No Further Action determination," which will signal the site has been successfully cleaned up and long-running monitoring could be discontinued, Maez wrote.
In addition, contractors will sample specific wells at the site every three months with the first quarterly groundwater monitoring report due in August 2022."
While the new courthouse
has enough air circulation to make air quality monitoring unnecessary, Maez wrote, there were concerns about air quality in the garage and District Attorney's Office building, so Santa Fe County monitored air quality at those sites.
The county's environmental consultant collected soil vapor samples from inside the District Attorney's Office in 2015.
Some contaminants were detected by the lab but were not above "vapor intrusion screening levels."
In April 2019, benzene and naphthalene were not detected in the air samples collected by a consultant for Santa Fe County. Ethylbenzene was detected in one of the three samples at extremely low levels, Maez wrote, "indicating that the remediation efforts are succeeding and people in the building are not at risk."
The Environment Department has spent about $4.9 million
for the project, of which
$4.3 million came from its Corrective Action Fund and $532,456 from American Recovery and Reinvestment Act of 2009 funds, Maez wrote.
Santa Fe County paid a little more than $5.9 million for remediation costs, county operations manager and constituent liaison Sara Smith wrote in an email Friday.