**Soil remediation involves cleaning up polluted soils**. There are many different ways to reduce exposure to contaminated soils, and remediation methods vary in how effective they are and how much they actually reduce the problem or simply move the problem from one place to another.
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## Approaches for remediating contaminated soil
Remediation approaches are tailored to each site and situation. Different approaches could be combined at the same time or used one after another. Some factors that will affect which remediation approaches are most appropriate for a site:
+ **What contaminants are present**: Inorganic contaminants like heavy metals (e.g., lead, arsenic)? Organic compounds like petroleum products?
+ **The level of contamination**: Low, moderate, or high concentrations of contaminants?
+ **The size and depth of the area**: A small part of a residential property? A community garden? A larger plot of land?
+ **And other factors**, like the environmental conditions of the area (e.g., if you want to use plants for phytoremediation techniques, will the plants have enough sunlight and water to grow?), and the amount of time and money you have available for remediation.
### Bioremediation
**How bioremediation methods work:**
Bioremediation methods use living things, like plants, fungi, and bacteria, to help reduce soil contamination. Some plants grown in contaminated soil can take up heavy metals into their roots and leaves, removing them from the soil. Some fungi and bacteria can break down organic contaminants in the soil into less toxic compounds.
For a comprehensive introduction to bioremediation, check out this excellent **[Bioremediation for Urban Gardeners factsheet](https://compost.bc.ca/wp-content/uploads/2020/09/19-Bioremediation_no-image.pdf) created by @DanielleS with the Healing City Soils** program out of BC, Canada. The factsheet covers: what bioremediation is, kinds of bioremediation and how they work on different contaminants, a list of plants for phytoremediation (bioremediation using plants), and a **decision tree to determine if phytoremediation is right for your site**. Plus much more. Most of the information in this section is informed by this fantastic factsheet.
**Some different strategies:**
#### Phytoremediation with living plants
_Image: Diagram of a plant taking up heavy metals. [Rona.fawzy19](https://commons.wikimedia.org/wiki/File:Phytoremediation_by_Phytoextraction.svg), [CC BY SA](https://creativecommons.org/licenses/by-sa/4.0/deed.en)_
Phytoremediation involves growing certain plants in soils containing heavy metals. The plants take up the metals into their tissues as they grow, removing them from the soil over time. This particular process is phytoextraction.
+ _**Ease of use**_: relatively accessible because it uses tools and skills that gardeners and farmers already have. It’s a slow process that requires plant maintenance.
+ _**Relative cost**_: lower than conventional approaches to remediation.
+ _**Suitability**_: varies for each site, but in general phytoremediation is more suitable for smaller scale areas (home gardens, small farms) with low to moderate heavy metal contamination at shallow depths (where plant roots can reach). Not as suitable for large sites, highly contaminated sites, or organic contaminants.
(From the [Bioremediation for Urban Gardeners factsheet](https://compost.bc.ca/wp-content/uploads/2020/09/19-Bioremediation_no-image.pdf))
#### Mycoremediation with fungi/mushrooms and bioremediation with bacteria
Involves growing certain fungi or bacteria in soils contaminated with organic compounds, like petroleum products and polycyclic aromatic hydrocarbons (PAHs). The fungi and bacteria break down the organic compounds into less toxic ones.
“...more research is needed so that protocols for community-scale myco- and bioremediation can be applied safely and effectively to repair contaminated soils.” (From the [Bioremediation for Urban Gardeners factsheet](https://compost.bc.ca/wp-content/uploads/2020/09/19-Bioremediation_no-image.pdf))
**IMPORTANT NOTE!**
Plants or fungi that have taken up soil contaminants need to be removed and disposed of safely. It may be hazardous waste if contaminant levels are high. The bioremediation factsheet linked above lists some options for disposal.
**Examples of projects:**
+ [BKBioReactor](http://elizabeth-henaff.net/BKBioReactor): here’s a project involving microbial remediation of sediment in the Gowanus Canal in Brooklyn.
+ [Phytotechnology Project Profiles](https://clu-in.org/products/phyto/): a US EPA database of phytoremediation projects, detailing “information about relevant site background, the types of contaminants treated, the type of vegetation used, the mechanisms of phytotechnology, planting date, project size, location, cost, monitoring and performance results, and points of contact and references.”
+ "[Minnesota Develops Method To Recycle Petroleum-Contaminated Soil](http://onlinepubs.trb.org/onlinepubs/trnews/rpo/rpo.trn175.pdf)": a report from the Minnesota Department of Transportation describing a project where bioremediation followed up excavation of petroleum-contaminated soils, and cost significantly less than typical remediation methods.
**Additional resources:**
+ [Bioremediation](http://ei.cornell.edu/biodeg/bioremed/index.html): a brief introduction to bioremediation plus more resource links from the Environmental Inquiry program
+ [Citizen’s Guide to Phytoremediation](https://clu-in.org/download/remed/phyto2.pdf): a factsheet from the US EPA describing different types of phytoremediation, plus examples of cleanup sites across the US using various plants for phytoremediation on different contaminants.
+ Watson, N.M. [Mycoremediation: Studies in mycelium as an agent of bioremediation](https://ohiostate.pressbooks.pub/sciencebitesvolume2/chapter/3-6-mycoremediation-studies-in-mycelium-as-an-agent-of-bioremediation/). In _Environmental ScienceBites Volume 2_ by Lower B.H., Shaul T.R., Shaul K.A., and Weaver E.M.
+ Rhodes, C.J. 2014. [Mycoremediation (bioremediation with fungi) – growing mushrooms to clean the earth](https://doi.org/10.3184/095422914X14047407349335). _Chemical Speciation & Bioavailability_, 26:196-198.
### Physical methods for soil remediation
**How physical methods work:**
Physical methods reduce exposure to contaminants at a site by removing soil, broadly blocking access to it, or physically separating or trapping contaminants.
**Some different strategies:**
#### Excavation
Excavation involves digging up contaminated soil and moving it to a landfill or treating it offsite.
+ _**Ease of use**_: less accessible when it requires large equipment to dig up and transport soil.
+ _**Relative cost**_: high cost to dig up and dispose of contaminated soils. [Up to $260 USD per cubic meter](https://www.homeadvisor.com/cost/landscape/excavate-land/) of soil for excavation alone at a residential site.
+ _**Suitability**_: may be used for large, highly contaminated sites, e.g., Superfund sites.
#### Capping / Encapsulation
This method involves placing a physical barrier over contaminated soil and covering the barrier with clean topsoil.
+ _**Ease of use**_:
+ _**Relative cost**_:
+ _**Suitability**_: may be suitable for highly contaminated areas that need immediate containment; but this method doesn’t remove contaminants from the area.
#### Thermal desorption
This method removes hydrocarbon contamination (like petroleum products) by heating soil in a specialized low-temperature dryer. The heat evaporates the hydrocarbons off the soil, and then they’re collected and treated separately.
+ _**Ease of use**_: not accessible to most people as it requires specialized heating equipment at an offsite facility or in a portable unit for onsite use.
+ _**Relative cost**_: high cost at [up to $80 per cubic meter](http://onlinepubs.trb.org/onlinepubs/trnews/rpo/rpo.trn175.pdf).
+ _**Suitability**_: for high levels of hydrocarbon contamination. Its cost might limit this method to small volumes of soil.
**Examples of projects:**
**Additional resources:**
+ [Citizen’s Guide to Excavation of Contaminated Soil](https://www.epa.gov/sites/production/files/2015-04/documents/a_citizens_guide_to_excavation_of_contaminated_soil.pdf): factsheet from the US EPA
### Chemical treatments
**How chemical methods work:**
Uses specific chemicals to reduce contamination by binding to contaminants so they can be removed more effectively or breaking down contaminants into less toxic substances.
**Some different strategies:**
**Examples of projects:**
**Additional resources:**
## How do you know remediation is working?