Environmental remediation is the process of reducing contaminants in environmental media such as groundwater, surface water, soil, or other ground types. The contaminated media may be removed and cleaned of pollutants offsite. This is often seen at sites such as gas stations or dry cleaners, where spills have taken place. This approach, often called a “dig and dump,” is a quick way to get a parcel of land pollutant free. The cost associated with removing contaminated media and backfilling with clean soil can add up very quickly. Therefore, this is a solution typically limited to a contaminated area that has a small geographical footprint. If there is a building on site, then the building would need to be removed to exhume the contaminated media underneath it. If this is not an option, means of in-situ remediation would be required to remove the contamination under the building.
Contaminated sites are a challenge, as pollutants can be carried by groundwater for a long distance and can therefore extend past the property. Plumes of contamination can in fact extend through many parcels of land, potentially affecting different landowners. In these cases, again, the only course of action may be in-situ remediation.
Remediation systems typically contain screened wells and/or trenched lateral perforated pipe, which is used to collect contaminated groundwater that is then treated on site above ground. Another common practice is the installation of injection wells. Depending on the site, injectables may include bioremediation agents, in-situ flushing agents, in-situ chemical agents, steam, air sparging or treated water. These may be vertical or horizontally placed wells (or a combination of both).
The first consideration is the installation of screened or perforated pipe. The use of a mud rotary rig to install vertical screens can be problematic if the well is not developed properly. The bentonite filter cake lining the borehole well should be removed completely so that groundwater can pass into the screen. If injection wells are installed, it is equally as important to make sure that no remnants of the filter cake is left. To aid in the removal of bentonite from the borehole wall, a contractor can use specialty products such as a bentonite thinner or a specialty well rehabilitation chemical designed solely to remove remnant bentonite. These products are used during well development and are surged through the screened area, allowing them to penetrate the formation and break down any remaining bentonite.
If injection or collection wells are installed horizontally using a horizontal directional drilling rig, the utilization of bentonite muds is strongly discouraged. It is very difficult to remove or break down the bentonite slurry that remains in the annular space. A natural, biodegradable fluid should be used in place of bentonite. This fluid will provide the drilling contractor with the properties required to complete a successful bore and is easily broken down afterward by injecting a liquid enzyme breaker. Contractors can get these specialty products from bentonite suppliers.
Remediation systems are often on site for long periods. In order for these systems to be effective, they must be maintained to ensure they continue to operate at the capacity expected.
Remediation systems are often on site for long periods. In order for these systems to be effective, they must be maintained to ensure they continue to operate at the capacity expected. Once in service, injection or extraction wells are very susceptible to mineral encrustations and mineral bacteria buildup. Battling biofouling and mineral encrustation may be a continual process. Mineral scale is formed by the presence of excess carbonates, magnesium and iron. These deposits will be accelerated by high screen flow velocities. Biofouling is a common natural occurrence and is often an issue in conjunction with mineral encrustation. It is the occurrence of microorganisms interacting with metals and minerals. An easy and cost-effective method for controlling mineral encrustation and biofouling is the utilization of well rehabilitation products. Using a wire brush inside the screen is effective to start to breakdown the encrustation and remove the slimy mineral bacteria. Follow this by injecting and surging a wetting agent in order to soften and loosen encrustation by increasing surface tension. This will open up fissures and cracks and penetrate the hard mineral buildup. The wetting agent should then be purged.
Screens that are primarily clogged by bacteria can then be treated using a chemical biofouling agent. It is best to surge this type of product through the screen over a period of 12 to 24 hours. If the pH of the water starts to rise during treatment, more product can be added. This is a chelating agent, which aids in removing suspended and dissolved particles. Once the pH becomes neutral, the product is used up. The next step is to inject a well rehabilitation chemical that can remove scale. This should be surged for 12 to 24 hours in order to break down and remove mineral encrustation. The mechanical movement produced by the surging ensures that problematic mineral deposits are dissolved and removed. Upon completion of this process, the pH should be monitored until it is neutral or the same as before treatment began. To end the process, it is recommended to shock chlorinate the well. Well rehabilitation chemicals are available from bentonite manufacturers and should be certified to NSF/ANSI 60 standards.
These same products are very useful to clean and maintain pump-and-treat remediation systems including dual-phase extraction systems, oil/water separators and air strippers. The chemicals are circulated through the system and break down mineral and bacteria buildup. Regular maintenance such as this ensures that the remediation equipment is running at its full capacity. This regular maintenance also reduces the risk of the equipment breaking down. This is very important when the remediation equipment may be located in hard-to-access areas and issues may not be noticed for long periods.
In-site environmental remediation is only as effective as the equipment used and the condition of the subsurface screens, perforated pipe, sumps, piping, fittings and tubing. They are dynamic systems that often run 24-7 for long periods. Utilizing the proper drilling fluids and well development chemicals during installation of the system is essential to ensure that the system is working properly to begin with. Once running, a regular maintenance program utilizing well rehabilitation chemicals to keep well screens and remediation equipment clear of biofouling can reduce headaches and avoid costly breakdowns.