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Welcome to the Soil section. This page contains the most current information about soil contaminant testing for urban gardens, examples of testing and remediation techniques, and additional resources.
NOTE: Because urban farming is a relatively new area for most government agency regulation, many jurisdictions have either not addressed soil safety or are in the planning stages of outlining soil testing rules. Given that, the information here can be used both for self regulation by urban gardeners and as recommendations for soil testing legislation. If you know of soil safety guidelines or requirements established by municipalities, counties, states or government agencies, please add that information here with the Rule and reference cited. Thank you!
- 1 Guidelines for Soil Safety Assessment
- 2 Guidelines for Soil Testing
- 3 Guidelines for Soil Remediation
- 4 Preventative Methods and Best Practices
- 5 Examples of Urban Garden Soil Remediation
- 6 Index of Existing Soil Safety Requirements by Location
Guidelines for Soil Safety Assessment
Potential sites for urban gardening may have previously been used for industry or other purposes that could leave substantial amounts of toxic substances in the soil. For this reason a thorough analysis should be conducted to determine if soil contains hazardous waste or chemicals This analysis should include the site’s proximity to buildings, vehicular traffic, industrial sites or other potential sources of contamination. The EPA (Environmental Protection Agency) recommends beginning your site assessment with an investigative stage: interviewing neighbors and previous landowners and conducting a site visit will help obtain site history and current conditions. Additionally, since sources of soil contamination can also be off-site, similar information about surrounding properties (particularly if they are commercial/industrial uses) should also be considered. An area analysis will reveal proximity to prior spills, leaks, and prior or current sources of air pollution that can affect soil safety.
After completing a site assessment, a soil test should be conducted. Using information about site history and surrounding conditions that suggest the presence toxic substances, one can look specifically for those contaminants that are most likely present based on the common source of the contaminant. For example, referencing Table 1 below, a site with history of petroleum spills would indicate likely presence of PAH’s, benzene, toluene, and xylene.
Common Sources of Contamination
|Paint (predating 1978)||Lead|
|High Traffic Areas||Lead, Zinc, PAH’s|
|Treated Lumber||Arsenic, Chromium, Copper|
|Burning Waste||PAH’s. dioxins|
|Coal Ash||Molybdenum, Sulfur|
|Sewage Sludge||Cadmium, Copper, Zinc, Lead, PBT’s|
|Petroleum Spills||PAH’s, benzene, toluene, xylene|
|Commercial/Industrial||PAH’s, petroleum, solvents, Lead, other heavy metals|
|Pesticides||Lead, Arsenic, Mercury (historical use), chlordane and other chlorinated pesticides|
Source: Heinegg et al., 2000
Information regarding the health effects of particular contaminants is available through the Agency for Toxic Substances and Diseases Registry (ATSDR) (http://www.atsdr.cdc.gov/) and the EPA (http://www.epa.gov )
Most Common Toxic Substances
DDT, DDE, DDD
Polycyclic Aromatic Hydrocarbons (PAH’s)
See ATSDR www.atsdr.cdc.gov
Guidelines for Soil Testing
The most common toxic substance screening a garden should be tested for is lead. This is extremely important if children are going to be involved in the garden project. The concern is the child’s direct exposure to the soil. An individual touching the soil, breathing the dust or eating the soil can expose himself to a toxic level of lead. Testing of the soil is imperative if children will be involved. One should know that lead occurs naturally in the soil between 7ppm-200ppm (parts per million), therefore one should contact his local Extension Office or State EPA to obtain naturally occurring levels in your area. Nevertheless, differing governmental agencies have set their own standard for permissible lead levels:
- The FEPA Lead Levels are 400 ppm. See: 40 CFR Part 745.65 Jan. 2001
- The State of California Environmental Health Office uses 80 ppm
- California Department of Toxic Substance Control uses 1000 ppm
- California Department of Health uses 400 ppm
- California Water Board uses 200 ppm
The National Lead Information Center concluded 23% of homes built prior to 1980 have soil levels which exceed 400 ppm and 3% of homes exceed 2000 ppm. Until a set standard for protocol is enacted to regulate the quality of soil as a medium, each organization or individual must decide for itself/himself which level it will allow for its garden if direct planting is implemented.
Lead Safety Resources
- E.P.A. Guidelines for Lead
- San Francisco Dept of Health Guidelines for Lead
- Lead Issues in Urban Garden Raised Beds testing of raised beds.
- Center for Disease Control
- Ohio Lead Prevention
- Wisconsin Dept of Health Services Lead Program
- Iowa Lead Program
- E.P.A. Lead Program
- Center for Environmental Health
- Kansas Lead Prevention Program
- Alameda County California Lead Prevention Program
- Boston Lead Prevention Program
- Suffolk County New York Lead Prevention Program
- Massachusetts Lead Poisoning Analysis
- Pennsylvania Lead Prevention Program
- Minnesota Lead Prevention Program
- Oregon Lead Prevention Program
- Western New York Lead Prevention Program
- New York State Lead Program
- Colorado Lead Prevention Program
- Maryland Lead Prevention Program
- Alabama Lead Prevention Program
- Soil Testing Issues for School Gardens
- Oregon State Soil Guidelines;University of Davis Soil Guidelines
Soil Testing Protocol
Unfortunately there is no one set standard for Soil Screening Levels (SSL’s) for urban gardens set by the Environmental Protection Agency either at Federal or State levels, only an interim guideline. The only current standards to follow are set by the FEPA for Superfund Sites or Brownfields which are converted to Residential Use or for Agricultural use. Several cities have addressed the issue of soil contamination testing when an urban garden is located on city-owned property. Chicago uses raised beds only and Baltimore requires the organization or individual to file a soil test and any remediation plans before a permit is issued. And while Seattle, Indianapolis, and San Francisco recommend soil testing, they do not require it. Notwithstanding, the Department of Health could issue a citation if it is found that the garden’s soil exceeds the minimum lead levels and a child is harmed or could be harmed by exposure to the site. Contact your local EPA office for information regarding free soil testing through the EPA’s Brownfield Program. The Agency also has a remediation grants program to assist in the clean up of a site. In Indianapolis the Felege Hiywot Center was funded by the Brownfield Assistance Remediation Program.
Soil Testing Guidelines
After a thorough investigation of the previous use and proximity to potential contamination, two different soil sample collection methods are recommended, depending on the site itself:
- If you are in a low risk area take samples approximately six inches under the topsoil from multiple locations in the garden site. Mix the samples together and provide three samples to the testing agency. A recommended test panel should include pH, organic matter, nutrients, composition test for heavy metals, organic pathogens and asbestos.
- If your site is a known Brownfield or otherwise severely contaminated, the soil should come from at least 12-24 inches and the groundwater should be tested. Several colleges and universities have prepared guides on soil contamination and testing.
Soil Testing Instructions
- Purdue University Soil Sample Testing
- Soil Video
- Soil Sampling and Analysis
- Soil Sampling Video You Tube
- NSW Corporation Soil Sampling Testing
- Purdue University Horticulture and Soil Sampling
- Cornell University Soil Sampling Requirements
- Maryland Cooperative Extension Soil Sampling Guidelines
- Texas Plant and Soil Lab
- E-How for Soil Sampling
- Spectrum Analytic Soil Sampling Procedures
- Ontario Guidelines for Soil Testing
- University of Wisconsin Soil Lab Testing Procedures
- soil sample testing procedures
Soil Testing Labs
- U. Mass Amherst Soil Testing Lab
- Envirotech Private Lab for Soil Testing
- Accenvironmental Lab
- U. North Carolina Lab
- Missouri Testing Lab
- City Directory of Soil Testing Labs
- Cornell University Testing Lab
Guidelines for Soil Remediation
If the soil test results conclude contamination beyond a safe level for a known toxic substance, several different remediation methods exist.
- Excavation: as simple as hauling the contaminated soil to a regulated landfill.
- BioRemediation: the use of living organisms, primarily microorganisms, to degrade the environmental contaminants into less toxic forms. It uses naturally occurring bacteria and fungi or plants to degrade or detoxify substances hazardous to human health and/or the environment.
- Phytoremediation: the use of vegetation for in situ treatment of contaminated soils, sediments, and water.
Summary of Physical Remediation Techniques
|Excavation||Geotextiles||Soil Washing||Soil Vapor Extraction|
|Timeframe||1 season||1 season||1 season||1 season|
|Effectiveness for Urban Agriculture||1||2||1||1|
|Environmental Effects||Energy use;
Source: Heinegg et al., 2000
Summary of Bioremediation Techniques
|Timeframe||1 yr||2-5+ years||N/A||1 season|
|Effectiveness for UA||2||2||3||2-3|
|Environmental Effects||Potential metal toxicity||Disposal of toxic plants||Potential metal toxicity||None|
Source: Heinegg et al., 2000
Soil Remediation Resources
- Soil Remediation Products
- Soil Remediation Service Provider
- Soil Remediation for Explosives
- Water and Soil BioRemedation
- Soil Reclamation and Remediation
- North Carolina Procedures for Oil Contamination Cleanup
- Environmental Science Paper on BioRemdiation
- APEC Corporation PhytoRemediation Analysis
- PhytoRemediation Methods
- Ecological Engineering Remediation Methods
- USDA PhytoRemediation Analysis
- United Nations Remediation Methods
- University of Montana BioRemediation Methods
- Hydrogen Peroxide Remediation Method
- Salt Contaminated Soil Remediation
- Lead Remediation with Corn
- Phytotechnology Remediation Methods
- How to Design a Raised Bed Video
Preventative Methods and Best Practices
- Wash all produce prior to consumption in a solution of water/soap or vinegar. Discard older, outer leaves of leafy vegetables.
- Don’t use Leaves or Carbon Material from areas near busy streets to make compost
- Mulch all walkways to avoid dust or splashback onto plants
- Don’t grow near buildings where lead levels will be the highest. Locate plantings, especially leafy crops, as far away as practical from streets. As much as 75 feet would be good. Utilize barriers, such as walls, fences, and hedges, to help to block automobile exhaust and dust from coming into the site from streets and roads
- Do Continued testing of soil even if in raised beds (see study by the Massachusetts Geological Society of America.)
- Improve Soil Conditions
- Thoroughly remove and properly dispose of refuse from urban garden sites before planting. Be especially vigilant for old painted wood, tires, galvanized metal, and batteries
- Always wash hands thoroughly after working or playing in urban soils. Thorough hand washing is especially important for children who are more susceptible to trace elements. Consider using gloves, especially for children
- Dilute pockets of higher than normal concentrations of trace elements by digging and spreading the soil over a large area in the garden or by adding additional, clean soil and thoroughly mixing it with the contaminated soil. It is generally not feasible to dig contaminated soil from the garden and dispose of it off site. Such soil would be considered toxic waste and strict rules and regulations govern its disposal
- Since most potentially hazardous trace elements are found in the upper one to two inches of uncultivated or undisturbed soil, it is always a good idea to cultivate soil deeply, to at least eight inches deep if possible, before planting to dilute the contaminated soil with clean soil below
- Maintain soil pH near 7, or neutral, and ensure phosphate levels are adequate
Examples of Urban Garden Soil Remediation
Soil is a major issue in Chicago, since most of the land in the city has been contaminated. Rather than building grow boxes to combat the problem, City Farm lays down a layer of clay soil (to adsorb contaminants and keep them from moving upward), then layers good garden soil on top of that. The Food Project in Boston tests soil once a year through the UMass Extension services. Lead levels continue to remain low. They use raised beds without frames with 2 feet of soil depth. In their new property, they have laid out geotextile to separate the new soil from the preexisting soil. Food Project sources their soil from several regional businesses.
- City of Chicago Resource Center Garden
- The Food Project Remediation Methods
- University of Illinois Study on Raised Beds vs. Non-Raised Beds for Soil Contamination
Index of Existing Soil Safety Requirements by Location
Proposed Amendment 23 C.16.030 and 23 F.04.00: Must submit soil test with lead levels under 300 ppm.
Source: Proposed Zoning Changes
Department of Public Health investigates and requires a lead testing of 400 ppm or less. The Department can enforce remediation.
City does not have jurisdiction so no regulation. All gardens have been on private property so have not had to address liability issue on public property.
Source: City Planning 303-235-2846
Large Scale Community Farming requires soil testing.
Source: New Orleans Code
Baltimore’s Draft Ordinance (as of September 2011) requires soil testing as an alternative to raised beds and the test results must be presented along with remediation strategies in order to obtain a use permit. Baltimore neither conducts nor permits soil testing on city owned land.
The Boston Redevelopment Program has prepared a draft proposal on how Boston should address the soil testing requirement.
Source: Planning Publication
No testing is required by the City.
Source: City Planning 313-224-6380
Minneapolis determines site suitability based on previous use. For example, highly contaminated sites known as brownfields are documented in a city database. Because urban agriculture projects are reviewed on a case by case basis as a Conditional Use (either through Administrative Review or the Board of Adjustments), City Planners are able to review the proposed site and determine the appropriateness of the site for farming for public consumption. The property owner is responsible for soil testing and it is not required as part of the ordinance. Stricter soil testing on city owned properties is being considered.
Department of Environmental Quality Soil Cleanup
Source: Soil Cleanup Objectives
If Ohio State University Extension is used as garden manager then soil testing is required to meet EPA Residential Guidelines.
Source: County Department of Planning 216-429-8200
Must submit soil test for specified contaminants. If do not meet standards must use raised beds.
Source: Zoning Resolution
A soil test is required for both contaminants and nutrients.
Source: City Planning, 216-429-8200, Community Garden Permits
Soil testing required contractually if requesting to lease or use Land Bank property owned by the City of Cleveland. The testing requires the lead levels be below the EPA standards for Residential Property.
Source: Land Bank, 216-664-4059
The city provides the plots and completes all soil testing.
Source: City of Akron Permit Process
Recommends testing and is in the process of changing requirements.
Source: City of Dayton, 937-224-9654
Commercial or Small Urban Farm must complete Questionnaire and if contamination is suspected, a plan must be devised for mitigation.
The Department of Environmental Quality does not require soil testing but it is recommended.
Source: Portland zoning code
Soil testing is encouraged but not required.
Sources: Pittsburgh Department of Planning, Pittsburgh Urban Garden Handout
No testing is required by the city but may need to meet Health Department.
Source: City Planning 615-862-7150
City owns properties so conducts testing for garden groups.
Source: Richmond Garden Rules
If a proposed farm is over 4,000 square feet, a Management Plan is required which is reviewed and approved by a city planner. The intention of the Management Plan is to consider the potential impacts and mitigation required for soil disturbing activity, use of agricultural chemicals, and noise and odor generating activities.
Sources: City of Seattle Planning: 206-684-3771, Planning Publication
All planting must be done in raised beds with uncontaminated soil. Milwaukee requires raised bed construction with a minimum soil depth of 12 inches.
Soil testing is required.
Source: Farming the City
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