A Different Approach Using Passive Treatment or Remediation
Remote contaminated sites that are without power and are difficult to access create challenges for site remediation. In other cases, the water being treated needs only minor adjustment. These projects require a different approach, like passive treatment, that is less energy-intense and has lower operations and maintenance needs.
Passive remediation may be a good option to meet these challenges. The term “passive remediation” describes remediation that uses no external energy, has few moving parts, and runs with little on-going labor needs. ProAct uses passive treatment less than the more conventional, equipment-intensive technologies. Below are some of the ways ProAct has used a passive treatment approach.
In-line devices, such as polymer socks, baffles and settling chambers may be used to add treatment chemicals or reduce solids in a channel or pipe. While most of ProAct’s systems are active systems that use pumps to transfer water through various vessels and treatment equipment, ProAct has used in-line devices to address dissolved solids and adjust pH.
More often, ProAct uses its equipment to compliment a passive treatment system installed by others. ProAct is well-accustomed to coordinating with clients and other contractors in a team effort to clean up contaminated sites. Some of the types of passive treatment used by these other contractors are described below.
Types of Passive Treatments
Natural biological, chemical and physical processes can break down and attenuate contaminants. Passive treatment uses various physical means, chemical addition, or introduction of biological organisms to enhance these natural processes. In this way, passive treatment acts to cost-effectively reduce contaminant concentration, mobility, toxicity, or volume in soil or groundwater.
Natural attenuation of contaminants in soil and groundwater may reduce contaminants over time by sorption, volatilization, and biodegradation progressively. Using natural attenuation for remediation may only require access control, such as fencing, and on-going monitoring. Sometimes, allowing time for natural attenuation to occur may require surface or subsurface migration control.
Built-in filtration systems use geo-textiles, stone or other methods to capture solids. This may be needed when high solids are the sole concern. This may also be used when the contaminant is intermixed or adhered to the solid particles.
Phyto-remediation uses plants to pull contaminants from soils or water into the plant tissue. Sometimes this process alone changes the contaminant into a less toxic form. Plants that do not change the contaminants, but only incorporate them into the plant tissue may be left to stand, sequestering the contaminants. Other times, these plants may be harvested for disposal. Phyto-remediation is mostly used for heavy metal extraction, but can also be used to remediate organic compounds and salts.
In bio-remediation, certain micro-organisms use their metabolic processes to destroy or render contaminants less toxic. Microbes may be used to treat explosives, hydrocarbons, pesticides, and solvents. Microbes may be added to surface water, injected into groundwater or incorporated into soil. Soil amendment can enhance the remedial action of subsurface microbes.
In-situ fixation uses added chemicals to bind or encapsulate contaminants. When they are encapsulated or bound, they are unavailable for absorption by humans or other organisms. This is most frequently used for soil remediation.
Some passive remediation uses the natural movement of water to move contaminated groundwater through a treatment zone. Examples of such treatment zones include limestone beds and iron filing walls.
In complex passive treatment systems such as constructed wetlands, several of these processes may act simultaneously. In addition to phyto-remediation and bio-remediation, photo-chemical reactions may occur when UV light helps to breakdown a contaminant.
While passive approaches tend to be less expensive, because of the lack of additional power, these projects typically have relatively low flow rates. They may be too slow to meet regulator and client needs.
ProAct’s engineers consider cost, remediation speed, and site access when designing remediation systems. ProAct is well-qualified to take on the most complex project using active processes, but will apply the same professional standards to passive projects, as well. ProAct applies its “Teamwork” value when working with other contractors at a site to provide safe and professional remediation service.