Laypeople can be forgiven, but I don’t know why architects are so often shocked by how long sitework takes (and for that matter, shocked by how quickly a superstructure is erected, and shocked by how long systems take to install, and shocked by how long interior finishes take to complete). . . You’d think that after the first few buildings, it would sink in, but alas. Building on a contaminated site requires extreme patience while waiting for subsurface mitigation. Our options, generally from fastest to slowest. . .
Offsite soil washing: running water over the soil offers a fast (one month) option for small contaminations or small sites, because we can quickly load three dump trucks with soil and bring them to a plant that is ready to wash the soil before returning it to the site. We can build on washed soil. Soil washing is not generally cost-effective unless the soil is very polluted, or we have few fine silt or clay particles in the soil, or we are in a hurry. Gravel is easier to clean with watery mixtures than fine particles like silt and clay, which turn to mud when washed.
Capped site: fast option for sites where we will not be constructing something that penetrates the soil over the cap. We can build a parking lot on a capped site, but it's difficult to build a structure on a capped site and still ensure that the membrane will not be interrupted and rain will not seep down into the fallow soil. Soil capping doesn't remove the contaminated soil, but rather "sweeps it under the rug," directing rain around the polluted patch of ground with a membrane as a kind of underground umbrella.
Onsite soil washing: often the fast option for large sites. We'll rent and erect equipment capable of washing the soil and position it near the soil to be washed. Click here to see what that looks like. Soil washing generally is expensive and generally only addresses certain types of contaminants in certain types of soils, so it remains a relatively rare option.
Bioremediation: Injecting pollution-eating bacteria into the ground takes longer to clean the site (about six months) but bioremediation is usually far cheaper than soil washing, can remediate more different types of contaminants than soil washing, actually gets rid of the pollution (unlike capping), and unlike capped sites, we can use bioremediation and then build on top of the soil after it's clean.
Vapor extraction: sucking out the polluted gasses from underground. Takes about the same amount of time as bioremediation (maybe a bit longer, about a year. . . all of these estimates obviously depend on how contaminated the site is, how large the contaminated area is, and what the actual contaminant is). Like bioremediation, vapor extraction is relatively inexpensive, useful for a wide range of contaminants, and we can put a building on top of the site after its clean. Unlike bioremediation, vapor extraction doesn't work below the water table where the soil is always saturated.
Phytoremediation: We plant species that naturally take up pollutants in their roots. Obviously, this takes by far the most patience—many years’ worth.
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