- In only 24 days from notice to proceed, and in difficult weather conditions, Ensero designed, constructed and commissioned a new water treatment plant (WTP), consistently achieving treatment goals for arsenic, cadmium, selenium and zinc.
- A permanent soil and groundwater remedy enabled full site release and ultimately facilitated redevelopment, creating nearly 1,000,000 ft2 of new built construction and an award-winning brownfields redevelopment project.
- Ensero’s groundwater and soil remedies enabled shut down of the active WTP after 4 years and eliminated the need for perpetual treatment and site maintenance.
- The entire program was completed in only 4.5 years and on-budget, under a fixed-price contract secured by a performance bond.
- On-site soil stabilization and reuse eliminated the need for and risk associated with off-site disposal.
The Globeville Smelter Site, formerly owned by ASARCO, operated from the 1870s through 2006, smelting and purifying lead, cadmium, and other specialty metals, and producing arsenic trioxide. Over a century of handling hazardous materials resulted in substantial environmental impacts, including elevated levels of lead, zinc, cadmium and arsenic in soil and groundwater. The site was listed on the National Priorities List (Superfund) in 1993. Following ASARCO’s bankruptcy, the State of Colorado (CDPHE) became a trustee for the site remediation, and selected Ensero as the lead environmental consultant and general contractor for site remediation.
The Ensero Solution
Ensero worked closely with the site redeveloper, EnviroFinance Group, to expedite cleanup for redevelopment and to maximize the square footage available for redevelopment under industrial standards. We designed and implemented remedies to treat heavy metal-contaminated groundwater and runoff, 13 acres of low pH soils, 17 acres of waste gypsum materials, and widely distributed soils high in arsenic.
Expedited redevelopment was made possible through Ensero’s innovative soil stabilization approach. Acid and metals contaminated soil was mixed with high pH gypsum, crushed site demolition slag and asphalt to create geotechnically stable fill with leaching potential below site-specific standards (per SPLP SW-846 Test Method 1312). The stable fill was placed, compacted, and then covered with clean soil to enable safe construction of buildings.
Ensero implemented comprehensive, site-wide in-situ groundwater remedies. We created subsurface sulfate-reducing conditions in the upland area to immobilize dissolved metals in groundwater and installed reducing permeable reactive barriers and reactive zones in the lowlands to precipitate metals in situ. Metals concentration in groundwater decreased to below maximum contaminant levels (MCLs) at the property line within 4 years.
After decommissioning the more than 20-year-old WTP, Ensero designed, constructed, and commissioned a new WTP to treat source area groundwater and runoff. The modernized WTP (designed, built, and commissioned within 24 days) included ferric iron coagulation for arsenic removal, lime coagulation for other metals removal (including iron, cadmium, lead, and zinc), and automated pH and turbidity control. Effluent consistently achieved treatment goals for arsenic, cadmium, selenium, and zinc, and was discharged to the Publicly Owned Treatment Works (POTW). Ensero operated the WTP in compliance with the permit requirements for 4 years (2011 to 2015), while completing the source area soil and in-situ groundwater treatments. The in-situ groundwater treatment was effective, eliminating the need for the WTP, and CDPHE granted permission to shut down and decommission the WTP in 2015.
Ensero’s site-wide remediation approach was so successful that site was delisted from the NPL in 2013 and allowed to transition to a state-led voluntary cleanup program, where it was completed with full regulatory release. Successful completion ultimately enabled redevelopment through an award-winning brownfields redevelopment project that created nearly 1,000,000 ft2 of new construction.
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