Soil Remediation Basics
Soil remediation is the process of by which previously contaminated land becomes useable again. Broadly speaking, there are two strategies used for soil remediation: clean-up technologies and stabilization.
Clean-up technologies reduce the amount of contaminant by either destroying or removing them. Stabilization technologies (also called containment) lowers the pollutant’s mobility and bioavailability. Both soil clean-up and stabilization can be done either in-situ or ex-situ and can be either physical, chemical or biological processes.
Hepure provides chemical and biological solutions for both in-situ and ex-situ applications for soil remediation. Selecting the best solution for soil remediation depends on the specific conditions and goals of your project.
Important Factors For Soil Remediation
Defining the Matrix: Soil type (e.g. % of sand, silt or clay), fractured rock or sediment, porosity, moisture content and the amount of heterogeneity.
Type of Contaminate: A good understanding of the contaminate or mix of contaminate in the soil matrix. General categories are Chlorinated Volatile Organic Compounds (CVOC), Petroleum Hydrocarbons, Metals, Inorganics, Pesticides, Polycyclic Aromatic Hydrocarbons (PAH), and the newest categories of PFOS and PFAS. Some contaminates may be addressed with a single technology (CVOC and Metals) where others will require different approaches (Inorganics and Pesticides).
Concentration of Contaminates: The concentration and mass of contaminate is very important. Many remedial methods work well with lower concentration and some with elevated concentration and/or free product.
Groundwater Level: Saturated and vadose zone soil may require different types of treatment to ensure enough contact and water for chemical reactions to occur. Remedial Goals: Understanding the goals is very important in selection of remedial alternative. Reaching TCLP standards would require a vastly different approach than removal for closure.
Matrix Chemistry: One of the most overlooked parameters is chemistry, specifically geochemistry. This refers to substances which normally would not be thought of as a contaminate but may interfere with implementation of remedial technologies. Soil matrix chemistry includes, major cations and anions, mineral content, pH, buffering capacity, ion exchange capacity, acidity, salinity, and ORP. The interaction of factors can be complex, such as precipitation of arsenic to arsenophyrite requires the correct pH and Eh conditions as well as the right iron and sulfate concentration which is dynamic depending on the surface reducing bacteria activity.
The factors discussed above are typically collected and documented in a detailed site assessment. Site assessments will address site-specific conditions as well as document the types of contaminates and potential sources of the release.
Decision Tree and Cost
A typical decision tree for soil remediation starts with the decision to treat on-site or off-site (e.g dig and haul). Depending on the size of the project considerable costs can be avoided by treating on-site. Saturated soils are typical treated in-situ, but vadose zone soils can be treated in-situ or ex-situ or a combination of both.
Injection Techniques: Saturated soils can be treated by using a variety of injection techniques depending on the amendment and the soil matrix. Traditional direct push techniques (DPT) can be used for soluble amendments and high permeable soil matrix. However, either solid amendment (e.g. ZVI or cellulose carbon) or low permeable soils may need a high pressure injection technique, such as hydraulic or pneumatic methods.
Soil Mixing Techniques: Soil mixing techniques are particularly appealing for shallow vadose zone soils (~0-25’bgs) because they can achieve consistent dispersal of amendment even in low permeability or heterogenous soils. The type of equipment will depend on the soil matrix, amendment(s), and depth of treatment. It can be done ex-situ (e.g soil piles) or in-situ. It may involve pug mills, soil shredder and specialize blending heads (See video). Soil mixing is often cheaper and more sustainable than traditional injection methods or dig and haul. Deeper vadose soils can be treated by soil mixing techniques; however, more specialize equipment and complicated support/shoring systems may be needed and will increase costs.
Each amendment addresses a contaminate or group of contaminates and may designed to be effective in a variety geological setting and geochemistries.
The product links provide a more detailed review of how each may be used. As you can probably tell, there’s a lot to keep in mind. Please contact us. We’ll help diagnose your issue and figure out your best course of action.
Source for figures:
Lombi, E., & Hamon, R. E. (2005). REMEDIATION OF POLLUTED SOILS. Encyclopedia of Soils in the Environment. Elsevier. https://doi.org/10.1016/B0-12-348530-4/00087-4