Geothermal energy is a powerful, clean, and renewable source, but it still presents environmental challenges requiring careful attention. For example, operators have to contend with the possibility of soil and groundwater contamination and direct issues like erosion and slope instability that come with geothermally and seismically active terrain. This chapter will focus on the practical applications of geomembranes in environmental remediation and soil stabilization.
Remediating Contaminated Soil
One of the primary environmental concerns in geothermal projects is the risk of soil and groundwater contamination. Despite best efforts, spills or leaks of geothermal fluids, drilling fluids, or other chemicals can occur during project development and operation. Since these fluids often contain dissolved minerals, heavy metals, or other contaminants, they can seriously harm soil and water quality if they escape into the environment.
Soil Contamination from Spills and Leaks
Contaminated soil is a serious problem for a few reasons. First, rainwater can leach contaminants into groundwater or surface water bodies, which can have far-reaching effects. However, contaminants can also be directly absorbed from the soil and into plant life. This is a significant concern because once those contaminants are in plants, they can quickly enter the food chain, affecting larger wildlife and potentially even human health. Clearly, prompt and effective remediation is essential to minimize the spread of contamination and restore the affected areas - water is just one part of the equation.
Geomembrane Applications for Containment
Wherever soil or groundwater contamination occurs, or when there’s simply an identified risk, impermeable, chemically-resistant geomembranes can keep contamination from spreading and even simplify cleanup efforts.
One key strategy is to create containment cells in response to a spill or existing contamination. A containment cell can be rapidly created by excavating as much contaminated soil as possible. However, since removing every trace of contamination is impossible, a geomembrane liner is placed within the excavation to prevent liquids from passing through the residual contaminated soil and leaching into groundwater supplies. Once lined, the cell can be filled with clean soil, although the contaminated soil is often returned for on-site treatment.
Managing Leachate
When containment cells are used, geomembranes are used in building leachate collection and treatment systems. When affected soil is returned to the cell for on-site treatment, rainfall can drain through it, producing highly contaminated leachate. Collection systems are installed to capture and divert the liquids as they pass through the soil, preventing them from spreading further and reaching groundwater. Geomembranes line the collection channels and ponds to keep the leachate contained.
Similar collection systems are used for managing contaminated stockpiles and long-term remediation systems.
Erosion Control and Slope Stabilization
While the potential for contamination is the most pressing concern, geothermal projects can also face significant challenges produced by the nature of geothermal formations. The rugged terrain, tendency for seismic activity, and altered hydrology often produce unstable ground and soil. The instability can trigger landslides, rockfalls, debris flows, and other dangerous slope failures.
In fact, geothermal activity can weaken rock and make it more susceptible to failure, increasing surface weathering and erosion. Erosion can strip valuable topsoil, damage critical infrastructure, disrupt project operations, and pollute aquatic ecosystems by overloading local waterways with sediment.
Geomembrane Applications for Erosion Control and Stabilization
Geomembranes are often installed alongside geotextiles and geogrids as part of an integrated system.
Silt Fences
Geomembrane silt fences are deployed in patterns designed to trap and slow sediment-laden runoff in areas with disturbed soil or high runoff volume. By slowing water flow, the silt fences help sediment settle instead of being carried off into nearby waterways.
Slope Protection
When erosion is a concern on slopes, geomembranes can be used with rock armoring or other stabilization techniques to protect the underlying soil from erosion caused by rainfall or runoff.
Geomembrane Liners on Slopes: In some cases, geomembranes cover slopes directly to shed water and prevent it from infiltrating the soil and triggering erosion. This strategy is often favored on steep slopes or when sediment runoff could threaten sensitive areas.
Addressing Potential Heavy Metal Contamination
While heavy metals can be broadly considered a subset of soil contamination, their unique characteristics and the specialized remediation techniques they require warrant a more detailed discussion.
Most hydrothermal fluids naturally contain heavy metals such as arsenic, mercury, lead, and others, based on the geological composition of the reservoir. While geothermal energy production is generally considered cleaner than fossil fuels, the high toxicity and persistence of heavy metals pose a significant and enduring environmental threat.
Heavy metal contamination can come from several sources within a geothermal project, including geothermal fluids brought to the surface for heat transfer. Waste materials like geothermal brines, sludge, and scale also contain high concentrations of toxic metals, which present a threat even in long-term storage. Since there is a risk of spills or leaks during virtually any operational stage, the risk of heavy metals escaping into the environment cannot be ignored.
Geomembrane Applications for Preventing Contaminant Migration
Geomembranes are the core of solutions for preventing heavy metals and protecting the environment from contamination.
Impermeable Barriers
Advanced geomembranes are capable of containing fluids and waste laden with heavy metals and preventing them from leaching into soil and groundwater. This ability is essential for lined reservoirs, impoundments, and waste storage facilities.
Vertical and Horizontal Barriers
Geomembranes can be configured to create vertical and horizontal barriers for controlling the direction of contaminant flow. Vertical barriers, such as cutoff walls, direct the lateral migration of contaminants, while horizontal barriers can prevent downward leaching.
Containing Contaminated Areas
In cases where heavy metal contamination has already occurred, geomembranes are used to encapsulate or contain the contaminated areas to prevent pollutants from spreading.
Specialized Remediation
Geomembranes can be used to create carefully controlled environments for specialized remediation techniques such as chemical stabilization or in-situ vitrification (where an electrical current melts contaminated soil and rock into a glasslike substance).
Looking Ahead
The next chapter will dive deeper into geomembranes’ material properties and performance, exploring how they can withstand extreme geothermal environments over time.
