Environmental Remediation

Trihydro has experience with numerous types of active remediation systems. This includes ex situ pump and treat (P&T) with many types of treatment methods including granular activated carbon (GAC), ion exchange, air strippers, advanced oxidation processes (AOPs) that use hydrogen peroxide, ultraviolet (UV) light, and/or ozone to generate free radicals to treat recalcitrant organic compounds. For complex waste streams, multiple types of treatment units are used in series for increased efficiency. Trihydro has experience with soil vapor extraction (SVE) with GAC and catalytic oxidation used as treatment methods. Trihydro is also experienced with in situ active systems, including air sparging, biosparging, dynamic groundwater recirculation, heat-enhanced remediation, thermal remediation, hot water flushing, and ozone sparging. While the majority of these systems operate with grid power, we have also designed systems operating off of solar, wind, or diesel generators at remote sites.

Trihydro supports the entire project lifecycle for active remediation systems, beginning with scoping and design, and selecting the correct system for site-specific conditions. We work with clients and technology providers during the procurement phase and construction contractors during installation. In some instances, we retrofit existing equipment from a client’s portfolio of closed sites to allow the reuse of an existing system rather than the purchase of a new one. We and our contractors support startup/shakedown to confirm systems operate as intended and to remedy any unexpected conditions. We perform O&M to ensure systems operate reliably or coordinate local subcontractors who provide on-site O&M. We optimize systems by modifying operating conditions or durations to increase efficiency and lower costs. Lastly, we have shut down many systems, including attaining regulatory buy-in that remedy transition is appropriate and decommissioning system components.

Passive remediation systems implement the treatment process in an episodic manner, such as periodic reagent injections. Natural processes are then leveraged to continue to achieve some degree of treatment without continued active systems. Passive remediation systems rely on in situ processes, thus these two types of remediation are discussed together.

At Trihydro, we are well-versed in the benefits in situ and passive remediation systems can provide, and have extensive experience designing, constructing, monitoring, and optimizing these systems. Our experience includes the following technologies.

• In situ chemical oxidation (ISCO) using permanganate, persulfate, ozone, hydrogen peroxide, and combinations of these. We have self-performed injections and worked with specialty injection contractors. Our personnel have authored ISCO guidance documents (e.g., ITRC’s “Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater”, SERDP’s textbook “In Situ Chemical Oxidation for Groundwater Remediation”) and have given invited technical training on this topic (e.g., US Navy’s “In Situ Chemical Oxidation – Best Practices and New Innovations”). Trihydro has worked with research universities and commercial laboratories to perform bench testing to evaluate ISCO effectiveness in a laboratory setting.
• In situ chemical reduction (ISCR) using multiple formulations of zero valent iron (ZVI). This process is a sister process to ISCO in that the reactions are chemical (not biological) but the target contaminants become geochemically reduced during the process.
• In situ bioremediation (ISB) including aerobic processes and anaerobic processes. Each of these leverage the ability of microorganisms, typically bacteria, to degrade target compounds. ISB may consist of the addition of reagents to support native populations (termed “biostimulation”) or sometimes consists of the addition of highly specialized microbes that have been found at other sites (termed “bioaugmentation”). Aerobic ISB can be used to treat traditional compounds such as petroleum hydrocarbons, but also the emerging contaminant 1,4-dioxane. Aerobic ISB is typically mediated by injecting air (air sparging or biosparging) but can also be performed with specialized reagents (e.g., calcium peroxide or hydrogen peroxide) or oxygen emitters. Anaerobic ISB is typically applied to chlorinated solvents such as perchloroethene (PCE), trichloroethene (TCE), trichloroethane (TCA) and similar compounds. This process involves the delivery of a carbon source (i.e., food) and can sometimes benefit from the addition of bioaugmentation cultures that contain Dehalococcoides and other known dechlorinators. Trihydro has implemented anaerobic ISB at many sites using emulsified vegetable oil (EVO) and other simple substrates, including one of the largest anaerobic ISB sites in the world. Trihydro has also evaluated cometabolic bioremediation, where bacteria consume a secondary substrate (not the contaminant) and fortuitously create an enzyme that degrades the target compound. Cometabolic bioremediation offers promise for treatment of some emerging contaminants, such as 1,4-dioxane.
• Phytoremediation is the use of plants to remediate target compounds. Trihydro has implemented both pilot and large-scale phytoremediation for petroleum hydrocarbons, chlorinated compounds and 1,4-dioxane, and also for the on-site management of landfill leachate. Trihydro personnel have delivered technical training sessions on phytoremediation (e.g., US Navy’s “Phytoremediation: State of the Practice and New Advances”).
• Monitored Natural Attenuation (MNA) is a technology in which environmental monitoring is used to verify that natural processes are attenuating target compounds. This is typically performed by monitoring groundwater using multiple lines of evidence. These can include target compounds, geochemical conditions, redox conditions, microbial populations, and isotopic signatures. Trihydro has experience with each of these methods for petroleum compounds, chlorinated solvents, and emerging contaminants. MNA is often used as a polishing technology for lower concentration areas or after more active remediation. Trihydro has used quantitative evaluation of site conditions to successfully transition sites from active remediation and/or injection-based programs to MNA.
• Natural source zone depletion (NSZD) monitors the degradation of petroleum free product and residuals. Trihydro has used this passive approach to quantify the destruction of free product by measurement of carbon dioxide (CO2) flux with dynamic closed chambers, CO2 traps, nested vapor points used to calculate gradients, and isotopic signatures. NSZD data have been used to support remedy transitions to more passive systems or to demonstrate that natural processes are sufficient, avoiding the need for an active system. Trihydro personnel have authored multiple journal articles on NSZD.

Remediation process optimization (also called remedial process optimization, or RPO) is the deliberate process of evaluating and enhancing remedial programs. RPO’s ultimate goal is to achieve endpoints more quickly and at a lower cost. The data on which RPO is based are the as-built remedy (additional information always comes to light in environmental construction), actual operation and maintenance (O&M) requirements of the remedy, performance outcomes achieved, and costs. RPO has several general elements, each of which can result in improved system performance. Exit strategies are re-examined, both for individual remedy components and the remedy as a whole. The conceptual site model (CSM) is revisited and updated to account for actual data. O&M and monitoring strategies are considered with a critical eye to reduce cost or increase performance.

Trihydro’s personnel understand the value of RPO and have experience with implementation to maximize the performance that can be achieved. RPO has included retrofits and modifications to existing systems, such as pulsed operations, updates to Programmable Logic Controller (PLC) or Supervisory Control and Data Acquisition (SCADA) controls, and more efficient pumps or treatment units. Sampling programs have been modified to transition to low-flow or zero purge methods to allow sampling to happen faster and with less waste. Sampling frequencies have been reduced after demonstration of actual trends in existing data. Technology transitions have allowed our clients to move from active systems that are operating at asymptotic conditions to passive systems that are achieving comparable treatment outcomes. These elements of RPO collectively allow projects to continue to move forward toward site closure once they have entered the active remediation phase.