Trihydro has supported more than 100 environmental projects at a Texas refinery since 2017. Among these projects, Trihydro was tasked with the closure of an existing hazardous waste landfill. This involved removing out-of-service equipment, stormwater channel design and construction, stabilizing and grading an adjacent slope, and designing and overseeing the installation of a 3.5-acre landfill cover system.
The site had originally been a double-lined, hazardous waste surface impoundment that was converted into a nonhazardous waste landfill. The refinery used the remaining headspace for the storage of remediation-related waste materials (mainly hydrocarbon-impacted soil). The client asked Trihydro to assist with the landfill closure because it was nearly at capacity. It was also producing leachate, which drained into sumps that had to be pumped multiple times a week, causing significant costs and health and safety risks. Moreover, the existing stormwater outfall was unstable and eroding the adjacent slope.
The closure process included an alternatives analysis; the removal of out-of-service equipment such as piping, tanks, and electrical equipment; the design of a stormwater channel to divert runoff around the landfill; adjacent slope grading and stabilization; repairs to the existing bottom liner; the design and construction of the final cover system; and closure certification.
Before completing the cover system design, Trihydro used Unmanned Aircraft Systems (UAS) to collect aerial photography and topographic survey data of the landfill. The UAS survey, which collects data about every square inch, provided a much more detailed picture of the site compared to conventional survey approaches.
To address long-term operations and maintenance costs and challenges the client had experienced at other landfill caps—including revegetation and mesquite tree infiltration—our team took an innovative approach to the cover system design by using ClosureTurf®. The team worked closely with our client and another consultant to submit a Class 3 permit modification for approval of the modified cover system design. This effort included several submittals and meetings with the Texas Commission on Environmental Quality (TCEQ), which ultimately approved the use of ClosureTurf® in the landfill cover system—a first for TCEQ at the time.
In addition to developing design plans and specifications, Trihydro undertook planning, coordination, and management of the project, including meetings with the client to discuss project timelines, the contracting and bidding approach, and preparation for construction. Project coordination included weekly status calls with the Trihydro team and client, as well as ongoing management of project work.
Our team solicited bids for cover system installation and quality assessment and quality-control scopes of work, hosted a pre-bid meeting, reviewed bids, and selected contractors in coordination with the client. We provided construction oversight and general contracting for the cover system installation. After completing the cover system installation, Trihydro prepared design plans and specifications, managed and provided oversight for, and contracted the installation of a perimeter fence around the closed landfill.
Trihydro submitted a closure certification report for the completed project that was approved by TCEQ. The landfill closure addressed both the slope stability concerns and costly leachate problem.