Soil

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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!

Guidelines for Soil Safety Assessment
Site Analysis

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.

See Soil 101: the East Bay Urban Agriculture Alliance’s guide to soil safety here.

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   

Common Source

Contaminant

 Paint (predating 1978)  Lead
 High Traffic Areas  Lead, Zinc, PAH’s
 Treated Lumber  Arsenic, Chromium, Copper
 Burning Waste  PAH’s. dioxins
 Manure  Copper, Zinc
 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
Aluminum
Ammonia
Arsenic
Asbestos
Benzene
Cadmium
Chromium
DDT, DDE, DDD
Formaldehyde
Lead
Mercury
PolychlorinatedBiphenyles(PCB’s)
Polycyclic Aromatic Hydrocarbons (PAH’s)
Toluene
Trichloroethylene (TCE)

See ATSDR www.atsdr.cdc.gov

Guidelines for Soil Testing
Lead 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
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.

Additional Guidelines

Soil Testing Instructions
Soil Testing Labs
Guidelines for Soil Remediation
Remediation Protocol

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.
  •  Non-Remediation
Summary of Physical Remediation Techniques
Excavation Geotextiles Soil Washing Soil Vapor Extraction
Access Yes  Yes  Yes  Yes
 Cost  Low  Low  Moderate  High
 Timeframe  1 season  1 season  1 season  1 season
 Effectiveness for Urban Agriculture  1  2  1  1
Environmental Effects Energy use;
Air pollution;
Disposal
Energy use;
Air pollution;
Disposal
Energy use;
Air pollution;
Disposal
Energy use;
Air pollution;
Disposal

Source: Heinegg et al., 2000

Summary of Bioremediation Techniques
 Microbial  Phyto  Fungal  Compost
 Access  Yes  Yes  No  Yes
 Cost  Low  Low  N/A  Low
 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
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

Healthy Soils for Urban Gardens    

Guidelines for Trace Element Contamination

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.

Index of Existing Soil Safety Requirements by Location

CALIFORNIA

Berkeley

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

San Francisco

Department of Public Health investigates and requires a lead testing of 400 ppm or less. The Department can enforce remediation.

Source: Department of Public Health Rules on Soil Testing

 

COLORADO

Wheatridge

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

 

LOUISIANA

New Orleans

Large Scale Community Farming requires soil testing.

Source: New Orleans Code

 

MARYLAND

Baltimore

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.

Sources: Planning Publication, Baltimore City Code

 

MASSACHUSETTS

Boston

The Boston Redevelopment Program has prepared a draft proposal on how Boston should address the soil testing requirement.

Source: Planning Publication

 

MICHIGAN

Detroit

No testing is required by the City.

Source: City Planning 313-224-6380

 

MINNESOTA

Minneapolis

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.

Sources: Land Stewardship Project, Planning Publication

 

NEW YORK

State

Department of Environmental Quality Soil Cleanup

Source: Soil Cleanup Objectives

 

OHIO

Cuyahoga County

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

Franklin County

Must submit soil test for specified contaminants. If do not meet standards must use raised beds.

Source: Zoning Resolution

Shaker Heights

A soil test is required for both contaminants and nutrients.

Source: City Planning, 216-429-8200, Community Garden Permits

Cleveland

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

Akron

The city provides the plots and completes all soil testing.

Source: City of Akron Permit Process

Dayton

Recommends testing and is in the process of changing requirements.

Source: City of Dayton, 937-224-9654

 

OREGON

State

Commercial or Small Urban Farm must complete Questionnaire and if contamination is suspected, a plan must be devised for mitigation.

Source: Oregon Dept of Agriculture Policy Manual

Portland

The Department of Environmental Quality does not require soil testing but it is recommended.

Source: Portland zoning code

 

PENNSYLVANIA

Pittsburgh

Soil testing is encouraged but not required.

Sources: Pittsburgh Department of Planning, Pittsburgh Urban Garden Handout

 

TENNESSEE

Nashville

No testing is required by the city but may need to meet Health Department.

Source: City Planning 615-862-7150

 

VIRGINIA

Richmond

City owns properties so conducts testing for garden groups.

Source: Richmond Garden Rules

 

WASHINGTON

Seattle

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

 

WISCONSIN

Milwaukee

All planting must be done in raised beds with uncontaminated soil. Milwaukee requires raised bed construction with a minimum soil depth of 12 inches.

Source: Planning Document, Permitting Process

 

INTERNATIONAL EXAMPLES:

NETHERLANDS

Amsterdam

Soil testing is required.

Source: Farming the City

 

Acknowledgements of Contribution:

Patti Mielziner