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Soils And Urban Agriculture:

Land Use and Contaminants tableexcerpted by Jack Kittredge from the EPA publication “Brownfields and Urban Agriculture” and from “Using Historical Records to Assess Environmental Conditions at Community Gardens” by Robert Hersh and from “Toolbox for Sustainable City Living” by Scott Kellogg and Stacy Pettigrew

Overview

Across the country, communities are adopting the use of urban agriculture and community gardens for neighborhood revitalization. Sites ranging from former auto-manufacturers, industrial complexes, and whole neighborhoods, down to small individual lots, including commercial and residential areas, are being considered as potential spots for growing food.

Redeveloping any potentially contaminated urban property (often referred to as brownfields), brings up questions about the site’s environmental history and the risks posed by a proposed reuse. At this time there are no definitive standards for soil contaminant levels that are safe for food production. EPA has long-established soil screening levels for contaminated site cleanup, but these threshold-screening levels usually serve as a starting point for further property investigation and do not factor in plant uptake or bioavailability.

How clean is clean for gardening activities.

Clean-up and reuse of any contaminated site is based on risk assessment and exposure scenarios – the levels of contamination present and how a person can be exposed to that contaminant, based on the intended reuse. These criteria for residential, commercial and industrial reuse are based on potential exposure: length of time spent on the site, types of activities performed on the site, and potential contamination pathways such as inhalation, ingestion, or possible skin contact with contamination.

Step-By-Step Guidelines

The following process proposes a series of questions you need to ask and the information you need to gather in order to make decisions while implementing an urban agriculture project. This model may be applied to any urban agriculture project on any brownfield site, and may be of value for other reuses where contact with soil may be higher, such as parks or recreational areas.

The previous use of the property and those surrounding it will be the major deciding factor on how cautious you should be before gardening. The more historical information learned about a site’s previous uses, the more informed decisions can be made during garden development.

We can infer possible types of contamination based on the previous use of the property. For example, residential areas may have unsafe concentrations of lead where the presence of older housing stock or structures indicates lead-based paint was present. Industrial areas may be high in heavy metals such as cadmium, mercury, chromium and arsenic. Heavy metals are elements, the basic building blocks of matter. They cannot be broken down any further by regular natural processes. If left alone, heavy metals present in soils remain indefinitely. Excessive exposure to heavy metals can result in a number of negative health effects, including organ damage, birth defects, and immune system disorders.

Phytoremediation and compost remediation are the bioremediation methods most commonly used to treat heavy metal contamination. Phytoremediation accumulates metals in certain metal-loving plants that are then removed and disposed of elsewhere. Compost binds up metals with organic molecules in the soil, reducing the percentage that is absorbed by plants or human tissue.

Molecular contaminants are made up of molecules: elements bound together in different ways to create substances with varying chemical properties. Some molecular contaminants found in soils are pesticides (dieldrin, chlordane, glyphosate), fuels (diesel, gasoline), and byproducts of industry (PCBs, dioxin). Polycyclic aromatic hydrocarbons (PAHs), a group of chemicals formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, can be found at former residential properties as well as commercial and industrial properties from fires or combustion processes. PAHs stick to soil particles and are found in coal tar, crude oil roofing tar, wood smoke, vehicle exhaust, and asphalt roads. Sites previously used for parking may have high concentrations of petroleum from leaking oils and fuel, and gas stations may have had leaking underground storage tanks that can cause contaminated groundwater and soils, or poor indoor air quality. Even greenspace or agricultural uses may have hotspots from over-fertilized ground, pesticides, or animal feed spills.

Mycoremediation, bacterial remediation and compost bioremediation are the most appropriate methods for treating molecular contaminants. The natural metabolic processes of bacteria and fungi are capable of breaking the molecular bonds of contaminants, making them into benign components which they then use as food. These processes occur naturally over time, but the rate of degradation can be accelerated by adding beneficial organisms to a site and providing the proper habitat and nutrients.

Sanborn mapIdentify Previous Use — What is the history of your proposed site?

Maps and Photographs — One of the most valuable sources of land use information is fire insurance maps made and published by the Sanborn Map Company. These maps are detailed and beautifully illustrated, and at a scale of 50-feet-to-one-inch they show building footprints, gas lines, underground storage tanks, pipelines, prevailing wind direction, railway corridors, and other information for some 12,000 U.S towns and cities starting in 1867 and continuing to the present. Perhaps the most important features to locate on these maps are the drains, where facilities released effluent that may have contained heavy metals, solvents, and other contaminants from production processes. No other published maps show such detailed urban land use information.

Historic Sanborn maps can be accessed in a number of ways. They are typically found in the archives and special collections of city halls or in public and university libraries. Most Sanborn maps have also been digitized by Environmental Data Resources, and can be searched online through latitudinal and longitudinal coordinates for a fee. See http://www.edrnet.com/environmental-services/sanborn-maps.

Changes in land use can also be detected through aerial and historic photographs. The oldest available aerial photography dates back to the 1920s, and the most common sources are the U.S. Geological Survey’s Urban Dynamic Research Program, state natural resources and transportation departments, and regional, county, and city planning agencies. In addition, there are numerous commercial aerial photography studios that have large archives, but their rates are high compared to government agencies.

New technologies, however, make it easier to access historical images. The “time slider” feature in Google Earth allows one to compare satellite images of a city’s built environment at different points in time. Currently Google Earth has made images available from the mid-1970s to the present, though the time period varies with location.

City Directories — City directories can also be used to research past uses of a property. They are not telephone directories, but rather indexes that provide a record of changes in property occupancy at specific addresses going as far back as the late 19th century in many cities. Starting with the most recent directory and working backward, it is possible to develop a list of business operations at single address over decades. One could determine, for example, that a vacant lot that looks suitable for a community garden was previously used as a gas station after having been an auto body shop, or a dry cleaners, or some other use that might have led to soil contamination. One can broaden a search to include business operations on nearby properties if there is reason to believe that contamination from these properties may have migrated onto the target site.

City directories are often overlooked in researching the historical uses of a property, but they show the dynamic nature of urban development—that is, the boom and bust cycles of urban history. They can identify how these broad changes played out at specific addresses. City directories can be found in many major public libraries, as well as state archives.

Environmental Databases — While no comprehensive list of contaminated properties is available, one can search a number of online environmental databases. For example, the Right-to-Know Network’s website—rtknet.org—provides access to site-specific information on chemical and oil spills, as well as the locations of illegal dumping, through the Emergency Response Notification System database (ERNS).

The RTKNet site also links to CERCLIS (Comprehensive Environmental Response, Compensation, and Liability Information System), an EPA-maintained database that contains information on preliminary assessments, potential and actual hazardous waste sites, site inspections, and cleanup activities at thousands of sites across the country. Similarly, EPA’s Resource Conservation and Recovery Act Information System (RCRIS), contains extensive data on hazardous-waste-handler permits and activities, which can be searched by address and or zip code. A wealth of environmental information can be found online at the state level through the state’s environmental protection agency.

Polk City Directory pageHistorical documents as well as environmental databases are key components of a site investigation. But in many cases, there may be limitations or gaps in the historical and regulatory record. One way to address these limitations is to find out about the property from persons who live nearby. Neighbors are likely to have a wealth of knowledge about a potentially contaminated site, particularly if the property was used for unregulated activities, such as midnight dumping, illegal auto repairs, etc. In addition, one can interview local planners, town historians, previous site owners, and others who have some connection with the property.

Perhaps the most critical step in the process is to walk through and inspect the site thoroughly. One often finds conditions not reflected in official records and photographs. The site can be checked for indications of illegal dumping or the burning of garbage. The presence of building rubble, old foundations, backfilled areas, and spots where subsidence has occured all indicate areas potentially requiring further assessment. The property can also be checked for soil staining and chemical and gasoline smells.

Determine Whether Previous Use is High or Low Risk to Site Soil and Water

Once you feel you have an understanding of the previous uses of the site, determine whether that use is high or low risk for agriculture reuses, the likely crops or garden design, and sample the site accordingly. As a rule of thumb, recreational or residential previous uses are typically lower risk while commercial and industrial uses can be considered higher risk.

Perform Sampling

Low risk previous uses like residential areas, green space, traffic corridors and parking areas generally have a narrow band of likely contamination that allows for a basic sampling strategy. High risk uses, like manufacturing or rail yards, open up the possibility of many types of contamination over a wide area of the site, and require a more rigorous sampling strategy.

Not all types of contamination will have the same effect on you as a gardener or on your crops. Research on soil metal chemistry and plant uptake has found that most metals are so insoluble or so strongly attached (i.e. adsorbed) to the actual soil particles or plant roots, that they do not reach the edible portions of most plants at levels which would compromise human health when eaten.

Manage Risks

Perform Clean-Up

If results indicate that the existing soil is not safe for gardening activities and you are planning to plant in-ground, remediation may be necessary. Techniques most applicable for agriculture projects include physical (excavation, installing geotextiles, soil washing or soil vapor extraction) or biological (microbial, phytoremediation, or application of soil amendments).

Many non-remedial options exist for sites with low levels of contamination, or sites with contamination exposure risks which can be controlled by planting above ground, including installing raised beds, gardening in containers, green walls or rooftop growing, and aquaponics.

Each remediation technique has unique benefits and drawbacks. Digging away the contaminated soil and disposing it in a landfill is the most effective technique for removing contaminants but can discard valuable topsoil. This is also the most expensive method, and replacing the contaminated soil with clean, non-industrial fill (that has been sampled for contaminants or has been certified as safe) can be cost-prohibitive to a non-profit gardener or community group. In-situ or on site remediation techniques or biological strategies may take multiple growing seasons or multiple applications, costly monitoring, and maintenance. Even remediation by amending with compost may be more involved than it sounds since composting needs to have preceded growing to create sufficiently healthy soil.

Construct physical controls

  • Build your garden away from existing roads and rail, or build a hedge or fence to reduce windblown contamination from mobile sources and busy streets.
  • Cover existing soil and walkways with mulch, landscape fabric, stones, or bricks.
  • Use mulch in your garden beds to reduce dust and soil splash back, reduce weed establishment, regulate soil temperature and moisture, and add organic matter.
  • Use soil amendments to maintain neutral pH, add organic matter and improve soil structure.
  • Add topsoil or clean fill to ensure the soil is safe for handling by children or gardeners of all ages and for food production. Your state or local environmental program, extension service, or nursery may be able to direct you to providers of “certified safe” soils, or to recommended safe sources for gardening soil.
  • Build raised beds or container gardens

– Raised beds help improve water drainage in heavy clay soils or low-lying areas. They also create accessible gardening locations for many users and allow for more precise soil management.

– Foot traffic should not be necessary in the bed, so the soil does not become compacted and soil preparation in the coming years is minimized.

– Your state or local city agency may recommend using a water permeable fabric cover or geotextile as the bottom layer of your raised bed to further reduce exposure to soils of concern.

– Raised beds can be made by simply mounding soil into windrows or by building containers. Sided beds can be made from wood, synthetic wood, stone, concrete block, brick or naturally rot-resistant woods such as cedar and redwood.

Begin Farming

Whether it is a long-term or an interim use, simply greening a once-blighted or vacant property and improving the soil structure has real effects on the economic and social value of land and community health. It can also reduce the runoff of urban soil, silt and contaminants into stormwater systems by allowing greater infiltration of rain into soils improved with added compost and soil amendments. The ability to grow food or horticultural crops such as flowers or trees on this newly greened area will produce multiple beneficial effects to those who may farm it. Healthy eating, increased physical activity, reduction of blight, improved air quality and improved quality of life are all nearly immediate health benefits from urban agriculture.

 




Guide for Soil Testing in Urban Gardens

Materials NeededWe recommend testing the soil if the planned garden is on a Medium Concern site AND if the garden is larger than 13 X 13 ft. Testing the soil consists of tak-ing a soil sample, having it analyzed, and interpreting the results. It is not cost-effective to conduct soil testing for small gardens. This is based on estimates of the cost of soil testing versus building a raised bed garden.

Soil Sampling

Collect a representative soil sample of the site. A composite soil sample is made up of two or more combined sub-samples to represent an area of the garden. Use the following checklist to walk you through taking a soil sample.

Create a diagram and plan where you are going to take your soil samples:
• Make note of the name and address of the property
• Draw a line around your garden using pylons, tape or rope. The soil sample should be taken from the area that the gardeners use. A typical commu-nity garden will need only one or two soil samples. We recommend that a composite soil sample is taken every 10 x 10 to 15 x 15 m area (approxi-mately 50 x 50 ft). Starting at one corner of the composite soil sampling area, walk diagonally to the far corner and repeat, making an “X” pattern. Mark the location of a sub-sample approximately every 2.5 m (8 ft) using a pylon or some other marker. This is where you will take your sub-samples of soil that will make a sample. For gardens larger than half an acre, call 311 for help
• Note the location of the sub-samples on your diagram

Soil Sampling AreaSample the soil
• Strip off turf or other vegetation from the sub-sample spot
• Take shovel and dig into soil down to 40 cm (16 in) Place sub-sample soil into Bucket 1
• Break up and mix the sub-sample soil in Bucket 1
• Remove stones and visible debris
• Note the presence and type(s) of debris, smells, and staining in your field notes
• Transfer a trowel full of the mixed soil from Bucket 1 to Bucket 2
• Refill the hole with the remainder of the soil in Bucket 1, and replace the turf
• Repeat until nine sub-samples have been collected separately in Bucket 1 and transferred to Bucket 2
Create composite soil sample
• Mix the combined sub-samples in Bucket 2 to make the composite.
• Label sample bag with:
• name of site
• sample number
• sampling date
• name(s) of person(s) doing the sampling

• Transfer the mixed soil from Bucket 2 to the labeled sample bag
• Seal the sample bag and place it in a cooler with ice packs

Note: If you are creating more than one composite sample, all equipment should be washed with soap and water between the composite samples. There is no need to wash the equipment when taking sub-samples.

The laboratory will tell you how much soil you need. Typically, each composite soil sample is approximately 2 cups (2 small trowels of soil). Each la-boratory is different and prices change over time. You should expect to pay between $150 to $300 for each composite soil sample.

Soil Analysis

Purpose: Select a laboratory for the soil analysis and tell the lab staff what analyses you would like them to do.

Toronto Public Health has identified a list of the most likely contaminants present in Medium Concern sites. Use the following checklist to walk you through getting your samples analyzed.
Soil Analysis Checklist
1. Select a laboratory able to do the analysis
Find qualified labs in your area through:
• Yellow Pages (heading: Laboratories – Analytical & Testing)
• Internet search

2. Contact the Laboratory
Get in contact with your chosen lab several days before you take the samples to:
• Confirm price and turnaround time
• Obtain a chain of custody form. The chain of custody form provides information on you (the client), the samples, and the analyses that you want
• Tell the lab when you expect to deliver the samples
• Obtain instructions for handling the samples and delivering them to the lab
3. Fill out a Chain of Custody Form
Fill out the chain of custody form and keep the required copies with the samples
• Every lab’s form differs, but you will have to indicate that you want the soil tested for pH values, metals and PAHs. Write out the full name of each metal and PAH you want tested for
Contact the lab for advice if you have any difficulty with the form
Soil interpretation
• Ask the lab to interpret the soil samples according to the contaminants and the Soil Screening Values for urban gardening listed on page B-7
4. Deliver Samples to the Lab
The laboratory will provide instructions
Deliver or ship samples to lab within one day of sampling. Some laboratories will pick up the soil sample
Keep samples refrigerated or in a cooler between the time you take them and the time you deliver or send them to the lab




Lead in Urban Soils

Lead is a widespread problem in America’s urban areas. Years of driving with leaded gasoline, using lead paint on our houses, and running our water through pipes joined with lead solder have seriously contaminated our soils.

Background concentrations of lead in agricultural soils average 10 parts per million. In urban soils, however, lead levels typically are much higher. The Centers for Disease Control estimate that some 21 million pre-1940s homes contain lead paint. When 125 inner city gardens were tested in Boston in 2000, 82% of them had lead levels above the reportable limit of 400 parts per million (ppm). We have banned leaded gas and lead in paint, but the element does not migrate easily nor is it taken up in plants or degraded by biological activity.

In Syracuse, New York soil sampling conducted by university researchers found high levels of lead and arsenic in five out of six community gardens in low-income and minority neighborhoods where residents grew much of their own fresh vegetables dfuring the summer months. The gardens were located on plots where abandoned homes had been razed. Lead paint from the demolished hhouses dontaminated the soil, and lead-rich exhaust from passing traffic built u in the soil over decades.

Where to Look for Lead

Visual assessments of painted structures help to identify areas around the property that are high risk for causing lead poisoning, but they cannot be used to confirm lead contamination of soil. You can look for deteriorated paint on all painted building components, especially any exterior walls, windows, or trim damaged from a roof or plumbing leak. Also look on surfaces that experience friction or impact like doors, windows, floors, and trim areas. In addition, look for chipped paint on the yard around the house. The next step will be to check if there are areas of bare soil or thin grass that are greater than 9 square feet. The special risk areas for soil are drip lines – within 2 feet of the house, play areas, gardens (in native soil) and uncovered walkways.

If the house/structure was built before 1978, and you see deteriorated paint or there is bare soil or thin grass in special risk areas, you should test your soil for lead. Testing is especially important if there are children under the age of six living in the house and if there is or will be a garden in native soil.

Soil Testing

Suggested Sampling Materials:

  • Gloves
  • 1-quart Ziploc-style bags (one per composite sample, usually 1-4 per yard)
  • Permanent marker (to mark bag)
  • Record Sheet, Map Sheet (see samples Appendix B and C)
  • Auger, shovel, trowel or similar tool
  • Rag or paper towels
  • If windy/risk of creating dust: Respirator (3M / HEPA filter)

Sampling Procedure:

Step 1 – Identify Potential Risk Areas

With input from resident and/or owner, identify areas that are most likely to be a risk based on the following high risk factors:

  1. High use, especially by children (play areas, gardens, walkways)
  2. Bare soil
  3. Proximity to house (especially the “drip zone” within 3 feet of the house, aka “drip line”)
  4. Visible chipping paint or known former structures

Choose the areas to be tested and mark them on a Map (optional), drawn in the context of the property, streets, and compass heading (mark North on the map). Give each area a sample name/number (ex. #1 = Drip line).

Step 2 – Collect Composite Samples

Within each possible risk area chosen, collect 6-8 samples (evenly spread out in the area) in this way:

  1. Make a hole with auger, shovel, trowel or similar tool. The hole should be thin and approximately 6 inches deep. Take some soil from each depth of the hole either by scraping the tool along the side of the hole, or poking out a column of soil from the core if using a bulb tool or something similar. Mark each hole with an “X” on the Map Sheet. Wear gloves and, if windy, respirator to prevent inhaling dust.
  2. Put all 6-8 soil samples in one bag, avoiding insects and large pieces of debris such as sticks, stones, bark, etc. Total soil should be approximately one cup. Wipe off sampling tool between composite sample sets (not individual samples).
  3. Label bag with sample name/number, address of site, name of organization and date.

DEPTH ANALYSIS: A useful tool to find out lead concentrations at different depths: take a separate sample from 2-4 different depths (for example: 1 inch deep, then 3 inches deep, then 6 inches deep).

Step 3 – Document Area. Complete the map and record sheet, making sure sample names/numbers match up and marking important structures, notes and other relevant details such as type of siding, use of spaces, etc.

Post-Sampling Procedure:

Each lab requires different sample preparation and bag labeling. For labs that require dry samples, dry them by placing soil in sun on a piece of dark flexible material or newspaper in an area with little or no wind. Return to bag when dry, being careful not to mix up the samples. Debris can be removed at this stage as well. Send samples, with a list of samples, to soil testing lab. You may want to retain a “copy” of each sample in case of a lab or mail error.

Where can you send your soil samples?

One recommended lab for quick turn-around and inexpensive testing, useful if just the lead concentration is needed, is Environmental Health Services Lab: http://www.leadlab.com/

If you need more information about the soil composition in addition to the lead concentration you can contact your local extension service. One such recommended lab is University of Massachusetts Soil and Plant Tissue Testing Lab: http://www.umass.edu/soiltest/

Interpreting the Soil Test

Look for the “total concentration” or “total estimated lead” or similar number on the lab report. Results are measured in µg/g or mcg/g or most commonly: Parts Per Million: PPM.

0-400 PPM Recommended options:

The EPA deems these levels safe for gardening and play. At levels of 200 and above, some groups advise using compost amendment and/or phytoremediation.

400-2000 PPM Recommended options:

–Build raised beds or containers gardens for immediate gardening

–Phytoremediation

–Compost amendment (in addition to diluting toxic concentrations, studies have shown high phosphorus compost amendment reduces bio-availability of lead)

–Cover with 6 inches of clean soil, then stabilize or create a barrier using the following: perennial plants, wood chips, landscaping fabric, crushed stone, patio, stepping stones, etc.

2000+ PPM Recommended options:

Immediate Steps:

  • Get children who have come in contact with infected area tested (blood lead level tests done at most doctor’s offices and health clinics).
  • Block off or cover area.

Long-term Solutions:

–Some groups recommend permanent coverings (see above) for this level.

–Build raised beds or container gardens for immediate gardening

–Some groups recommend excavation or burying on site with proper safety precautions. This can be very costly, especially for disposal, and safety precautions are extensive.

Remediation

Phytoremediation

  • As densely as possible, plant hyper-accumulators, such as scented geraniums (others include mustard greens, Indian mustard, sunflowers, collards or spinach), to accumulate lead into the roots, stems and leaves of the plant. After the growing season, safely dispose of the plants (if you put into the municipal waste stream, ensure that your area has good lead protections on incinerators, landfills, etc.) Note: this technique is very slow, and depending on the lead concentrations and soil conditions remediation can take several growing seasons. It is advisable to combine these phytoextraction techniques with other lead-safe landscaping techniques in most cases.
  • Stabilize the soil by planting plants that grow soil-retaining root systems such as shrubs or ground-covers to reduce foot-traffic access and dust-creation. This process is call “biostabilization.”

Advantages of Phytoremediation:

  • Inexpensive
  • Does not disrupt ecosystems
  • Low-tech, accessible
  • Metals can be reclaimed

Disadvantages of Phytoremediation:

  • Remediation is confined to depth of roots
  • Leaching into groundwater is not prevented
  • Time consuming (studies suggest 300 ppm can be removed in 7 to 10 years)

Compost and Soil Amendments

  • Add 6-12 inches compost to your garden to dilute and bind up the lead.
  • You can reduce the amount of lead that is available to be absorbed into people’s bodies by adding phosphorus to the soil (in the form of rock phosphate) forming pyromorphite crystals.
  • Some cities and towns have free or inexpensive municipal composting programs.

Other Landscaping Techniques

Capping with clean soil: Add 6-12 inches of clean screened loam on top of contaminated areas, then stabilize the new soil. Stabilization techniques include bio-stabilization (lawns, perennial garden beds, bushes, spreading ground covers such as pachysandra) or installing a hardscape (patios, walkways, crushed stone / peastone beds with sturdy edging).

Drainage: All our suggested hardscaping techniques are water permeable (as opposed to paving, for example) but most require drainage to be taken into account, especially when capping with clean soil is used, as to not have the capped soil wash away. Lawns that are the low-points of the yard often require a buried drainage pipe (also called French Drain) which is installed by digging a trench with at least a 1% slope, lining it with landscaping fabric, installing a drain pipe (ideally a 4 inch rigid plastic perforated drain pipe, flexible corrugated pipe can be used but is harder to clean out), then surrounded by crushed stone, and covering with landscaping fabric to divert water from undesired areas (like towards foundations or low lawns).

Edging: usually the most challenging aspect of hardscaping work, especially in the case of lead-safe landscaping where disturbance of native soil must be minimized. Some digging to set edging (blocks, plastic edging, rot-resistant lumber) is often unavoidable, but the more you can use existing edges or build up clean soil to retain hardscaping base or material the better. For all projects that include digging, remember to call dig safe (dial 811), use respirators (3M HEPA filter), coveralls, boot coverings, and other dust prevention such as tarps and wetting soil before displacement.

Rain gardens: also a great design element that address drainage and flooding issues. More info on Rain Gardens here: http://www.raingardennetwork.com/build.htm

Raised Beds and Containers: See below on how to make raised garden beds. Container gardens are also a good immediate option for gardeners wanting to safely grow within one season. Get creative with your containers! Recycled bathtubs, bins, mini swimming pools make great container garden receptacle, as long as they have a way to drain excess water.

Construction Guide for Raised Beds

raised bedWant to grow this season and worried about your soil being contaminated or not good enough quality? You can make a raised garden bed for about $100 and fill it with fresh compost!

Materials Needed:

Wood: 4x4s in 3ft lengths or longer (our most common combinations: for 10ftx4ft bed that is approximately 1ft deep, we use six 10ft and three 8ft – cut in half – 4×4 timbers). Make sure to get naturally rot-resistant (black locust is great, cedar works) or alternatively pressure treated wood (ideally sodium silicate), especially avoiding those that contain Arsenic (most often in the form of Chromated Copper Arsenate – CCA) as you don’t want to be putting toxins near your food crops! Some use 2×6 inch boards, but we’ve found that, though less expensive, they have half the life span.

  • Spikes: These are 6inch long nails. 30 spikes needed for each one foot deep bed. You can also use 6 inch screws such as “timberlocks” with a strong power drill or using pre-drilled holes in the timbers.

Compost: (soil made from composted organic matter such as yard waste) Make your own from food/yard waste, purchase, or look for free or inexpensive municipal composting programs.

Landscaping Fabric: To create a barrier under the bed so that water can go through but the plant’s roots cannot. One small roll will be plenty, most hardware stores carry this.

Tools: Four-to-six pound sledge hammer for spikes, shovels for soil, scissors or utility knife to cut the landscaping fabric, gloves, eye protection and a circular saw if you need to cut the timbers to length.

Step-by-step Instructions:

  • Find a flat place that gets lots of sun. Gather materials (see above). Cut lumber and landscaping fabric to desired lengths.
  • Pin the landscaping fabric on the ground with fabric staples, then place the first level of boards on top in the shape and location desired. Notice how each piece of wood is touching the end of only one other piece (i.e. you do not want the end pieces touching the ends of both side pieces, etc.)
  • Hammer the spikes into the ends of the wood horizontally – connecting them to the other pieces in the rectangle – and four spikes into the ground to hold the fabric bed in place. For hills, it is recommended to use re-bar that go through pre-drilled holes in wood and are pounded into the ground at least 1 foot deep.
  • Lay the second layer remembering to rotate the wood so that no connection is directly above the one below it (see image above).
  • Hammer the second layer vertically down into the first layer with spikes every 2-3 feet. Some horizontal spikes into the ends of the timbers are useful to keep tight corners.
  • Repeat with a third layer, remember to rotate the layout again.
  • Fill the bed with soil.
  • Plant your organic vegetables!

Excavation

You can excavate very small gardens with extremely high levels of lead by replacing the top three feet of contaminated soil with compost and clean soil. Due to the high costs and intense labor of the excavation process, the opportunity to use this technique is very limited.