What’s the Story of Soil in My City?

This blog post was written by Elizabeth Wilkes as part of the Spring 2018 UGA Urban Ecology class.

Why Urban Soil Matters

Soil is the basis for human life, supporting the life of plants which form the foundation of ecosystems. This fact can be easy to forget in the context of a city dominated by concrete and asphalt. Beneath roads, buildings, parking lots, and other impermeable surfaces in urban areas, dirt still exists, but most likely in a heavily-compacted, and potentially contaminated state, with minimal to no organic matter. Why bother thinking about the soils in your city, then?

Even if you spend most of your time inside buildings, the stability of the ground beneath buildings can determine how long the built environment lasts.  With increased development, the risk of overall subsidence, sinkholes, and landslides often goes unnoticed. Intense bursts of rainfall can wash away the little soil that does exist. Beyond these inherent risks in developed areas, people seek to cultivate soils for food production, create ornamental gardens and parks for recreation, or otherwise reinstate plant life in a given area — and functioning, healthy soil is necessary for any of these goals. However, urban soils are likely to be contaminated with pollutants.

In this climate change epoch, real-time events can drastically alter soil toxicity levels on a rapid timeframe. If your community experiences a disaster such as a hurricane, previously “locked-away” toxins might leak or become volatile because of storm damage. Take Hurricane Harvey from fall 2017 for example – the massive flooding which followed 60 inches of rainfall, or 33 trillion gallons of water in totality across the region, engendered unprecedented amounts of petroleum, coal, and other industrial wastes. Compared to previous disasters of similar scope, recent reports indicate that agencies have had difficulty keeping up on this occasion. It is in your best interest to stay vigilant about changes in soil quality, as neither state or industry entities responsible may be fully informed during these tumultuous times.

Once contaminated, soils can significantly affect human health outcomes. Heavy metals, including lead and arsenic, are among the most frequently occurring contaminants. This is partly because they can be present in the soil naturally, but at high concentrations they can pose dire threats to human health.  Heavy metals and other potentially toxic elements can make their way into the body via absorption (e.g. direct contact through touch), ingestion (e.g. small children accidentally eating while playing outside), or inhalation (e.g. breathing in floating particles). Other ways you can get exposed include via drinking water and eating plants that were grown in contaminated soils. Beyond the usual suspects, in recent studies, factors like radioactive elements and poorly drained soils have been causally linked to instances of infant mortality and some cancers (Oliver 2008).

Just as watersheds can be dramatically altered in urban areas, so can soils – and they are just as worthy of your attention.

Image Credit: USDA-NRCS

How Dirt Gets Dirty: From Bedrock to [Living] Soil

Soils are anything but static — in fact, all of the earth’s landforms have been shaped over time by destructive and constructive processes, namely erosion and deposition. For soil to form in the first place, a dynamic process involving physical, biological, and chemical processes is required.  Pedogenesis is a term used to describe the development of soil. Soil gradually erodes from larger, original rocks known as parent material, and this material determines which type of soil is eventually formed. Other primary soil formation factors include local topography (i.e. shape, elevation, and direction), climate, plants, animals, and microorganisms, and how much time has passed. What makes urban soils especially challenging to classify is that they are developed from a variety of materials caused by human activity, called technosols, which would not otherwise occur in nature – and sometimes over a rapid timeframe. Exploitation of resources, often concentrated in urban centers, can accelerate or completely modify soil dynamics. Areas in cities that were previously set aside for industrial uses, known as brownfields, often exhibit the highest levels of contamination, and might be already set aside and identified by government agencies. Residential sites pose additional hurdles when information is scarce.

Image Credit: Duke University Superfund Research Center

How to Discover Land Use History

It can be challenging to know how the land was used previously, but this information is just as essential to understanding soil conditions as preset-day land use and proximity to nearby pollution sources. Many of the worst environmental disasters have occurred because people did not sufficiently document or understand how the land was altered prior to most recent acquisition (e.g. covered, buried landfills or dump sites). This is especially common during periods of rapid population growth associated with economic booms, when large parcels of land are needed quickly to provide additional housing and facilities.

There are several places you can turn to find out more about your city’s land use history – internet search engines are your first best bet. One City of Atlanta resident assigned to this task in a watershed course researched the backstory of place-names, including road names, to learn more about the area. For example, English Avenue, as it turns out, was named after James English, a former Mayor of Atlanta and prominent businessman, primarily responsible for running a brick factory using forced convict labor before becoming a banker. The legacies of his resource use and abuse are still present in the neighborhood today, as the bricks still constitute much of the stormwater infrastructure, and remnants of the manufacturing process and formerly brick roads are now buried; impacts may also still be seen in the places where clay was mined for the purpose of creating the bricks.

From the government, USDA offers several databases of soil information, and the EPA offers EJSCREEN, a mapping tool for locating disproportionately polluted sites, are worth perusing (reference Module 5 for more information about this resource). Sometimes these resources might not be “zoomed-in” enough for your purposes. Start talking to neighbors and older residents to learn about what buildings and operations used to be located near you. Consult your local library and city or town planning department to access archives to discover what existed in previous decades and centuries. If you suspect there might be a hazard near the site of interest, it is worthwhile to conduct an official soil test. See image below for a visual of how to conduct a test on site.

Image Credit: Virginia Department of Health, via Food Well Alliance


How to Test Soil + Locate Local Resources

Extension services offered by land-grant universities in your home state are a good place to start. Many soil testing services offered are agriculturally-oriented, namely to test for basic nutrient levels (Nitrogen, Phosphorus, and Potassium), pH, and organic matter. Testing for possible contamination can be more difficult to track down, but it is still possible to do through private laboratories. These private labs may charge more per test, but public labs can sometimes offer financial support or facilitate group-purchasing rates. Check the links section below this blog to see what resources are available near you.

How to “Fix” Soil: Mitigation Strategies

One advantage of tackling problems from a systems mindset – “win-win” mitigation strategies are possible. Green infrastructure plans that integrate rain gardens and other vegetative features can help mitigate pollution flows into bodies of water and nearby soils. Sometimes, contamination is so great, that there is no other option but to completely replace the soil on a given piece of land, a process known as excavation. This is a most expensive and often cost-prohibitive route. Yet if there is sufficient financial support in the community, this can be a very effective action.

If you are particularly interested in urban agriculture, a frequent practice is to bring in compost from an outside source to add to raised beds. If you are intent on cultivating, regardless of the state of the preexisting soil, some important strategies to consider include: using raised beds; replacing or mixing new soil or compost with existing soil; improving drainage on-site; keeping soil pH as close to neutral as possible; and creating a barrier between the soil below and added soil using landscape fabric.

Commercial composting facilities are becoming increasingly common in and around major urban centers as people begin to understand the importance of reducing waste (especially food waste, as up to 40% of food in the United States is wasted). It is worthwhile to investigate what resource local NGO’s are offering – there are new projects and funding sources appearing all the time, as there has been a surge of interest in urban agriculture and soils over the last 3-5 years.

Here in Atlanta, Food Well Alliance sponsors an annual soil festival, where attendees can obtain free loads of compost and connect to other facilities that offer soil testing services. This year’s festival is coming up soon on May 5, 2018, and will include free on-site soil testing by “soilSHOP, hosted by the Georgia Department of Public Health, in partnership with the Agency for Toxic Substances and Disease Registry and the Environmental Protection Agency. The soilSHOP will offer free lead soil screenings with same-day results and explanations on screening outcomes and ways to reduce potential exposures to lead in soils while gardening or playing in yards” – more information on exhibitors here, and link to register here!

(Note that it may be helpful to reference the Watershed Basics module, where you can find a model describing the different disturbed and “natural” layers, and how topsoil is lost, in context of understanding the whole watershed. This explanation starts at 16:16 in the embedded video).


External Links:

Cornell Resource on Sources and Impacts of Soil Contamination: http://cwmi.css.cornell.edu/sourcesandimpacts.pdf

Cornell Guide to Soil Testing: http://cwmi.css.cornell.edu/guidetosoil.pdf

Urban Soils Backgrounder – North Carolina State University: https://www.ces.ncsu.edu/fletcher/programs/nursery/metria/metria05/m57.pdf

OSU Small Farms – Toxic Farm Soil:

Soil Contaminants in the Garden: Should I Be Concerned? Duke Superfund Research Center: http://sites.nicholas.duke.edu/superfund/files/2018/03/DUSRC-General-Contaminant-Fact-Sheet.pdf

Labs to send soils to test for total lead concentration (and more):


Guo, G., Zhou, Q., & Ma, L. Q. (2006). Availability and assessment of fixing additives for the in situ remediation of heavy metal contaminated soils: a review. Environmental monitoring and assessment, 116(1-3), 513-528.

Mulligan, C. N., Yong, R. N., & Gibbs, B. F. (2001). Remediation technologies for metal-contaminated soils and groundwater: an evaluation. Engineering geology, 60(1-4), 193-207.

Oliver, M. A. (1997). Soil and human health: a review. European Journal of Soil Science, 48(4), 573-592.

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