Soil contamination is caused by the presence of man made chemical alterations in naked ground. This type of contamination typically results from the rupture of underground storage tanks, application of pesticides, percolation of contaminated surface water, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals.
It is almost always directly correlated with the degree of industrialization and intensities of chemical usage. Large urbanized, heavily populated areas are also a source of contaminated biosolids or treated sewage sludge which contain not only human fecal matter but many of these same chemical contaminants washed through the system over the years. Philadelphia has a single sewer system which means everything from rainwater to toilet flushes to industrial residue all goes to the same place. Yuck.
Given Philadelphia’s rich industrial past it is an issue that takes on a particular importance for us, more so those, such as our own communities, who live in some of the most heavily post industrial sections of Philadelphia. The past has unfortunately left behind many chemical remnants, the very ingredients that went into the light to heavy industry that formed the nucleus of Philadelphia’s once thriving business past. Heavy metals forged locomotives, petroleums drove the freight lines, ships built of metals like lead, cadmium and zinc.
The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil and soil dust, vapors from the contaminants, and from secondary contamination of water supplies within and underlying the soil. Many local residents have been witness to the level of activity involved in the clean up of contaminated sites. Mapping of contaminated soil sites and the resulting cleanup are time consuming and expensive tasks, requiring extensive amounts of geology, hydrology, chemistry and computer modeling skills.
How does this relate to our common gardening experience? Does this mean it is unsafe to grow tomatoes in your side yard or to bring cut flowers into the house that came from Grandma’s in Port Richmond? No, but you should know what’s in your environment so you can be safe and healthy.
There are resources for getting your soil tested regardless of where you live. Penn State Extension Offices and University of Massachusetts offer a variety of testing some of which may make more sense for your situation. You might want to have a test run for lead to test safety, salinity or organic matter if you know the soil is safe but want to test it’s fertility.
Growing above ground in raised beds is always an option as is growing in an assortment of everything from old sneakers (talk about contaminated) to unused kiddie pools. Don’t try to take on remediation yourself unless you have a strong back, deep scientific and financial resources and a way of removing the soil that is there. Moving your problem to someone else’s yard is not the answer. Leave that to the professionals who have multiple technologies available to them-including phytoremediation – ironically the use of plants to pull the contaminants out of the soil, restructure them and release them into the air. But then what to do with those contaminated plants?
Cleanup or remediation is analyzed by environmental scientists who utilize field measurement of soil chemicals and also apply computer models for analyzing transport and fate of soil chemicals. There are several principal strategies for remediation:
- Excavate soil and take it to a disposal site away from ready pathways for human or sensitive ecosystem contact. This technique also applies to dredging of bay muds containing toxins.
- Aeration of soils at the contaminated site (with attendant risk of creating air pollution)
- Thermal remediation by introduction of heat to raise subsurface temperatures sufficiently high to volatilize chemical contaminants out of the soil for vapour extraction. Technologies include ISTD, electrical resistance heating (ERH), and ET-DSPtm.
- Bioremediation, involving microbial digestion of certain organic chemicals. Techniques used in bioremediation include landfarming, biostimulation and bio-augmentating soil biota with commercially available microflora.
- Extraction of groundwater or soil vapor with an active electromechanical system, with subsequent stripping of the contaminants from the extract.
- Containment of the soil contaminants (such as by capping or paving over in place).
- Phytoremediation, or using plants (such as willow) to extract heavy metals