Why Soil Remediation?

Backyard farms, community gardens, parklands, rail trails and dozens of other creative repurposings of land are transforming our landscape. Many of these changes involve introducing agricultural activities where they had not existed for many years. In the past decade the number of community gardens in the US incereased from 6,000 to 18,000, and the trend is accelerating. But as more of us come to live in cities, or try to bring into production land that has had previous contaminating uses, we need to be more thoughtful about avoiding toxic chemicals, heavy metals, or other man-made problems in our soil.

This issue is an attempt to survey the topic of Soil Remediation and report on groups that are in the trenches (literally, in some cases) dealing with contaminated ground and the current methods – in some cases physical barriers, in other cases planting in containers, some using plants to accumulate or microbes to detoxify contaminants, others applying humic substances to immobilize them – for making soil usable again.

Those of us blessed with rural farm locations and healthy soils may not think twice about how fortunate we are to have such gifts. But even pristine environments now sometimes suffer spills and dumpings, so it behooves us to be aware of how easily healthy soil can turn toxic. Also, reading about how much time and effort is necessary to repair tainted land should make us all more grateful for the miracle of living, active soil that we can so easily take for granted.

Some wise person once observed that the only thing standing between humanity and starvation is a few inches of biologically active topsoil. It is humbling to think that most of what we do as farmers and gardeners is tend forces that we don’t really understand, letting the knowledge bound up in seeds and soil sustain us. We hope that you enjoy this issue and it energizes your appreciation of these mundane miracles.

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


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.


Assessing Urban Impacted Soil for Urban Gardening


F E3 Garden Zone DepthUrban gardening is gaining momentum in North America. Urban gardening can provide broad health, environmental, social and economic benefits.

Often the land available for increasing the urban land base for community gardening are lands that are vacant, abandoned, or previously used for purposes other than food production. Despite a growing interest to garden on these lands, previous and current activities on or next to these sites might have resulted in con-tamination of the soil.

This guide is a decision-support tool used to identify areas that may be contaminated but could be suitable for food production and to identify appropriate ex-posure reduction actions based on the condition of the site.

T E1 Table of Land UseStep 1 – Establish a Level of Concern
The initial step of the guidance is to assess the likelihood that the soil quality for a garden may be of concern due to contamination from past activities. The appropriate Level of Concern is identified by conducting a site visit and researching the land use history to determine if various indicators are present.

A site visit is conducted by walking through and inspecting the site thoroughly. The site is walked through and checked for indications of illegal dumping or burning of garbage. The soil is turned over with a shovel in the areas intended for gardening and checked for soil staining (discoloration, usually dark patches) and odors (chemical and gasoline smells).

A site history is researched by searching available city records and asking local neighbors for information about the past and current use of the site and adjacent properties.

Each indicator is associated with a level of concern. The indicator of greatest concern defines the level of concern for the site as a whole. The table to the upper right lists the various indicators, the appropriate Level of Concern, and the recommended next steps for the garden site.

For sites that have been characterized as Medium Concern, go to Step 2. For all other gardens, go to Step 4.

Step 2 – Sample and Test the Soil
If the planned garden on a Medium Concern site is larger than 13 by 13 ft, the soil should be tested to determine the concentrations of soil contami-nants. The cost of a raised bed garden of this size is less than soil sampling, thus it is not cost effective to conduct soil testing for gardens that are smaller than this size. We recommend that small gardens in the Medium Concern category go to Step 4. For larger gardens, the depth of soil to be sampled is 0 to 40 cm.

We developed the above streamlined list of contaminants of concern (COCs) for the Medium Concern sites. The cost to analyze each composite sam-ple for all the parameters listed is approximately $250. The number of required composite samples is determined by the size of the garden. For a community garden 1 to 2 samples covers 225 to 450 m2, respectively. The average community garden is 280 m2. Thus, most community gardens will require 2 samples at a cost of approximately $500.

Contaminants of Concern for Medium Concern garden sites

Contaminants of Concern for Medium Concern garden sites

If the indicators identified during the site visit and site history suggest that the soil might be contaminated by other soil contaminants not on our stream-lined list of COCs, then the site should be treated as a site of High Concern (Go to Step 4).

Step 3 – Interpret the Soil Tests
In Step 3, the Exposure Reduction Tier for the garden is determined by comparing the soil concentration of each COC with the Soil Screening Values (SSVs) on page B-8.
The SSVs define the three risk levels, and are used to interpret the soil test data as follows:

• If the concentrations of all of the COCs are below the respective SSV 1, then the site requires Tier 1 Exposure Reduction;

• If the concentration of any COC is above the SSV 1 but does not exceed the SSV 2, then the site requires Tier 2 Exposure Reduction; or,

• If the concentration of any COC is above the SSV 2, then the site requires Tier 3 Exposure Reduction.

Urban Gardening Soil Screening Values (mg/kg)

Urban Gardening Soil Screening Values (mg/kg)

Step 4: Mitigate the Risks
There are many simple and inexpensive actions gardeners can easily take to reduce their exposure to urban soil contaminants depending on the risk level for the site. The illustration on page B-8 summarizes the recommended exposure reduction measures for the gardens that are required for Tier 1, 2 or 3 Exposure Reduction.

Existing Gardens
Through regular gardening practices gardeners already do many of the activities outlined in Tier 1 and 2 Exposure Reduction risk levels. For example, gardeners add soil and organic matter to their gardens on an annual basis to improve the yield of their garden. These behaviours, year after year, re-sult in a reduction in both the concentration and bioavailability of soil contaminants. In addition, gardeners turn over their soil at least twice a year, aer-ating their soils and exposing deeper soil to sunlight (two mechanisms that degrade and reduce organic soil contaminants). These practices over many years significantly reduce the concentration and the bioavailability of soil contaminants.

Existing gardens on lands that are in the Low Concern category should continue to use Tier 1 Exposure Reduction measures. Existing gardens in the Medium Concern category should use Tier 2 Exposure Reduction measures, with the exception of avoid or restrict growing produce. There is no need to test the soils. Existing gardens in the High Concern category should follow the soil testing indicated for Medium Concern sites.

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

Providence’s “Sidewalk Ends Farm” Brings Back Urban Soil

Farmer Tess Brown-Lavoie talks about compost and soil remediation at a CRAFT workshop. Attendees enjoyed a tour of the ‘greens factory’ and learned how to grow a never-ending supply of salad and arugula through biointensive production and succession planting.

Farmer Tess Brown-Lavoie talks about compost and soil remediation at a CRAFT workshop. Attendees enjoyed a tour of the ‘greens factory’ and learned how to grow a never-ending
supply of salad and arugula through biointensive production and succession planting.

Three young women turned their love of gardening into a thriving farm business. After college Fay Strongin, and sisters Laura Brown-Lavoie and Tess Brown-Lavoie, did not seek desk jobs but instead decided to start farming on an abandoned lot just minutes from busy downtown Providence, in Rhode Island.

The future farmers searched every side street in ever-increasing circles, seeking an open lot. They researched lot ownerships at city hall and reached out to landowners. “It took a lot of detective work and repeated efforts to connect with the owner of the abandoned lot on Harrison Street that became Sidewalk Ends Farm,” Tess said. The three sought a written multiyear lease, but faced communication challenges with the landowner. The farm team eventually secured verbal permission from the lot owner to farm the land for a year.

Harrison Street neighbors said there had been a rundown house at number 47 until it was torn down in the 1970s. Invasive vines and brush had completely taken over the lot. As the team began clearing away the brush, they found building debris, concrete and rubble in the cellar hole. Like many abandoned lots, this one had become the neighborhood’s dumping ground. The farmers found bottles and broken glass near every fence line.

Ever the optimist, Laura was confident the neighbors would stop dumping trash over the fence once they saw the land producing food.

City Farming Concerns

Tess Brown-Lavoie, Fay Strongin and Laura Brown-Lavoie at  Sidewalk Ends Farm in Providence, RI with their latest salad plantings

Tess Brown-Lavoie, Fay Strongin and Laura Brown-Lavoie at
Sidewalk Ends Farm in Providence, RI with their latest salad plantings

Suspecting the Harrison Street lot soils might contain toxins, heavy metals or lead, the farmers conducted thorough soil tests before beginning site preparations in September 2011. The front of their chosen lot had building debris from the original house — including lead paint chips. To mitigate risks, Tess said the team shoveled and carried all the “OK” topsoil from the back of the property to cap or cover the tainted soil at the front. Soil test results after moving the soil were in the acceptable range for growing food and raising animals.

As an added protection, the farm team installed thick layers of bedding over a liner before setting up a brightly colored chicken pen near the front fence for everyone to see. When refreshed, the used bedding helps feed the active compost pile. The chickens enjoy eating excess farm vegetables.

A series of raised beds were constructed from gleaned lumber and wood scraps, used pallets and other recycled materials. These beds were filled with 8” – 10” of fresh soil and rich compost before planting with shallow-rooted annual herbs. The farm’s Portable Wash Station doubles as a CSA pick-up station. It is located near the front fence and water supply. The lot front also contains a fire circle and woodchip-covered gathering area.

To protect nearby children from possible soil-born lead dust, woodchips cover all soil surfaces in the lot front.

Some deep-rooted crops accumulate minerals from well below the soil surface and can offer excellent nutrition. If grown in tainted soils, however, they can accumulate toxins. To minimize risks, Sidewalk Ends Farm grows shallow-rooted, short-season crops like salad greens and annual herbs.

Compost & Organic Matter

The first fall the three farmers splurged on truckloads of high quality compost from Smithfield Peat <www.smithfieldpeat.com>. Additional material was gathered and added all winter long (leaves, coffee grounds, etc.) and blended with a broad fork in the spring before the seeds and transplants went in. Since then, the farmers have produced and used their own compost from a variety of local inputs. Farmers collect food scraps from their CSA customers, local restaurants and coffee shops.

Taking advantage of urban closeness, these farmers encourage their neighbors to add to the farm’s active compost pile. Fun, informative signs help remind families how to compost. Fay said: “Composting helped us connect with our neighbors even more than growing food.” The neighbors now have an excuse to visit the farm regularly. Their random evening visits minimize potential theft. Neighbors are happy to reduce their trash hauling needs and to see their kitchen scraps recycled into next year’s salads.

“The farm neighbors get composting. We have a network of fertility,” said Tess when she described a recent bike trip where a driver pulled over and tossed her banana peel into Tess’s bike cart of food waste.

Fay is very enthusiastic about her farm-made compost. She said, “Compost is the key to our soil fertility because the only time this land is fallow is when it is frozen!”

Old carpet squares and flattened cardboard boxes marked paths at first. Now shredded leaves and burlap coffee sacks gleaned from a nearby café keep weeds down between rows of salad greens at the back of the lot.

The farmers repeat their soil tests annually and are happy to report the organic matter keeps rising. Sidewalk Ends Farm’s lead and heavy metals levels continue dropping towards undetectable levels.

Organics & Carbon Footprint

The Cranston Armory Farmers Market at the corner of Parade and Hudson Streets is just two blocks away from Sidewalk Ends Farm. CSA members pick up their shares at the farm. The farmers use bikes with trailers to deliver produce or collect food waste.

Adding organic matter increases carbon in the soil. Biking and selling locally has decreased food transportation miles and further lowering carbon dioxide emissions while increasing local food security.

Water Challenges

When the house at 47 Harrison Street was demolished in the 1970s, city water pipes were disconnected. Hooking up city water without a building proved too challenging, so the Sidewalk Ends Farm crew developed a creative solution with their neighbors. Hoses connected to neighboring buildings provide irrigation and wash water in return for a weekly CSA share (spring – fall) and a weekly loaf of fresh bread (winter months).

Urban Setting

No one says it is too quiet or boring at Sidewalk Ends Farm. Regular drive-by and open window “concerts” keep things lively. The herbs, flowers and greens seem to thrive with neighborhood music.

The farmers named their chickens for their favorite musicians, radio hosts and writers: Aretha, Berry, Goodman & Gonzales and Mary Wollstonecraft.

Sidewalk Ends Farm has brought back 1950s-style neighborhood closeness. People routinely lean over the fence and chat with their neighborhood farmers and each other. The chickens are very social and they love attention from visitors.

Land Security

In 2013, the three farmers used online crowd sourcing to raise just about enough money to buy the property when it came up for a tax auction. The landowner came in at the last possible minute and paid the back taxes owed. The farmers continue their negotiations with the landowner. For now, they have an agreement to farm there next year. A lot of effort has gone into making this site viable and safe to farm. Should these farmers have to move, the safe, fertile soil would remain.

Planning well, the farmers planted herbs and flowers in portable, repurposed containers like milk crates, 5-gallon pails and olive drums. Perennials and deep-rooted herbs thrive in these tall containers with site-made compost and have no risk of absorbing possible soil contaminants.

Goals & Results

To keep this farm viable, every inch of growing space needs to deliver two to three crops per year. The back lot uses bio-intensive planting patterns of tight, staggered rows to increase outputs in small spaces. As soon as a crop is harvested, any crop residue is quickly moved to the active compost pile. That same day, 1” to 2” of finished compost is spread and forked into the bed to provide organic matter and fertility. New seeds or transplants are then installed. Soils do not sit bare and exposed to wind or erosion.

Since 2011 Sidewalk Ends Farm has supplied greens and produce to a 20-member CSA and restaurants through the Little City Growers Co-Op <www.farmfresh.org/food/member.php?fn=272>. Their CSA shares are comparable to half shares from other farms; this fits the needs of city dwellers with their small kitchens, refrigerators and families.


The workshop was followed by a Young Farmer Nights  potluck supper and storytelling around a fire.

The workshop was followed by a Young Farmer Nights 
potluck supper and storytelling around a fire.

Sidewalk Ends Farm covered or capped their urban soils with fertile compost and clean soils. By selecting shallow-rooted crops, they grow safe, healthy foods for themselves and their CSA customers. By placing a liner under their chicken pen, they protect the chickens from scratching too deep.

Larger farms may not have the financial resources to move or replace soils on a big scale. Another soil treatment option is to use accumulator plants for phytoremediation. Growing specific plants on tainted land can help cleanse soils for future agricultural use. Various plants and microorganisms can degrade, tie up or even remove toxins from the soil.

Some plants can accumulate heavy metals like arsenic (sunflower and Chinese brake fern), cadmium (willow), common salt (sugar beet and barley) and radioactive elements (sunflowers). Other transgenic plants and microorganisms target mercury, selenium, petroleum and PCBs.

High levels of soil organic matter help tie up many heavy metals, making them unavailable to plants, preventing leaching and reducing toxic dust.

Toxic dust becomes airborne when soils are disturbed during removal and hauling. Bare infertile subsoil remains. Onsite treatment significantly reduces costs and the carbon footprint of hauling contaminated soils to hazardous waste facilities. In situ treatment significantly reduces exposure risks to neighboring children. Phytoremediation and urban agriculture can also prevent toxins from blowing or leaching onto surrounding properties or into ground water aquifers.

Plant Selection

According to “The Use of Plants for the Removal of Toxic Metals from Contaminated Soil” by Mitch Lasat, root exudates and symbiotic microorganisms help plant roots tolerate and absorb metals. Soil toxicity levels will affect typical plant biomass. High biomass crops create higher disposal costs. Lasat recommended site managers select plants with root system depths that match the depth of soil contamination.

Lasat reported that some species of maize tolerate and absorb high levels of Cadmium (Cd) but cannot tolerate high levels of Zinc (Zn). Maize and Indian mustard (Brassica juncea) show some promise for extracting Lead (Pb) from soils when synthetic chelates are applied after normal biomass levels are reached. According to Lasat, moderate Lead accumulators include Asiatic dayflower (Commelina communis), common ragweed (Ambrosia artemisiifolia), nodding thistle (Carduus nutans) and hemp dogbane (Apocynum cannabinum).

Lasat suggested acidic soils allow greater metals uptake. Caution is required as soluble lead can quickly leach below root zones. After plants remove sufficient metals, lime can be applied in preparation for new plantings. Early lime applications could tie up remaining metals and prevent further phytoremediation. Lasat reported that phosphorus could increase biomass but inhibit metals uptake, particularly lead.

Phytoremediation crops should be rotated and planted with modest spacing for highest effectiveness, according to Lasat.

If plants are grown directly in known toxic soils, the plants should not be eaten. After the plants have absorbed or tied up toxins, the plant biomass should be removed to a hazardous waste facility.

Lasat reported that some or all of the cost of hauling away toxic biomass might be recouped by recovering certain valuable metals like Copper, Nickel and Zinc. These metals may be captured (at licensed “phyto mining” facilities) through burning the biomass.

Some phytoremediation projects may take as long as 15 years to clean up soil. So far, most studies have been short term. Lasat recommended additional research be conducted on spacing, soil fertility amendments and metals recovery processes and opportunities.

To learn more about Sidewalk Ends Farm, see their Facebook page <www.facebook.com/pages/Sidewalk-Ends-Farm/213101742058011> or Sidewalk Ends Farm <www.farmfresh.org/food/farm.php?farm=3209> website. To arrange a visit to Sidewalk Ends Farm at 47 Harrison St, Providence, RI, email <laura.brown.lavoie@gmail.com> or call 617-817-6598.



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


–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.



  • 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!


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.


Phytoremediation:  Using Plants to Clean Up Soils

Thlaspi caerulescens, or alpine pennycress, is a small, weedy member of the broccoli and cabbage family. It accumulates metals in its shoots at astoundingly high levels.

Thlaspi caerulescens, or alpine pennycress, is a small, weedy member of the broccoli and cabbage family. It accumulates metals in its shoots at astoundingly high levels.

Phytoremediation is the use of green plants to remove pollutants from the environment or render them harmless. Current engineering-based technolo-gies used to clean up soils — like the removal of contaminated topsoil for storage in landfills — are very costly and dramatically disturb the landscape. But the “green” technology of using plants to take up heavy metals and radioisotopes can, in certain situations, provide a more economical approach and one that is less disruptive as well.

Certain plant species — known as metal hyperaccumulators — have the ability to extract elements from the soil and concentrate them in the easily har-vested plant stems, shoots, and leaves. These plant tissues can be collected, reduced in volume, and stored for later use. In addition, of course, while acting as vacuum cleaners these unique plants must also be able to tolerate and survive high levels of heavy metals in soils — like zinc, cadmium, and nickel.

We are at the early stages of identifying and learning about the transport and tolerance mechanisms of these plants. One for instance, Thlaspi caer-ulescens, or alpine pennycress, is a small, weedy member of the broccoli and cabbage family and thrives on soils having high levels of zinc, nickel, cobalt and cadmium. Researchers have been studying the underlying mechanisms that enable T. caerulescens to accumulate excessive amounts of heavy metals.

Plants Which Can Clean Up Various Contaminants

Plants Which Can Clean Up Various Contaminants

It apparently possesses genes that regulate the amount of metals taken up from the soil by its roots and deposited at other locations within the plant. These genes govern processes that can increase the solubility of metals in the soil surrounding the roots as well as the transport proteins that move metals into root cells. From there, the metals enter the plant›s vascular system for further transport to other parts of the plant and are ultimately depos-ited in leaf cells.

Thlaspi accumulates these metals in its shoots at astoundingly high levels. Where a typical plant may accumulate about 100 parts per million (ppm) zinc and 1 ppm cadmium, and would be poisoned with as little as 1,000 ppm of zinc or 20 to 50 ppm of cadmium, Thlaspi can accumulate up to 30,000 ppm zinc and 1,500 ppm cadmium in its shoots, while exhibiting few or no toxicity symptoms.

Whereas in normal plants zinc transporter genes, for instance, appear to be regulated by the zinc levels in the plant, in Thiaspi some sort of mutation has enabled these genes to stay maximally active at all times, independent of zinc levels until they are raised to very high concentrations.

Fortunately, zinc, nickel, cobalt and cadmium are metals that can be economically extracted from the shoots of Thiaspi, providing a viable process for removing these metals as soil contaminants. The crop would be grown as hay, and the plants cut and baled after they’d taken in enough minerals. Then they’d be burned and the ash sold as ore. Ashes of alpine pennycress grown on a high-zinc soil in Pennsylvania yielded 30 to 40 percent zinc — which is as high as high-grade ore.

Phytoremediation and Radioactivity

Phytoremediation has also shown promise as a means of dealing with radioactive elements. For soil contaminated with uranium, studies have found that adding the organic acid citrate to soils greatly increases both the solubility of uranium and its bioavailability for plant uptake and translocation. Cit-rate does this by binding to insoluble uranium in the soil. With the citrate treatment, shoots of test plants increased their uranium concentration to over 2,000 ppm — 100 times higher than the control plants.

The radioactive element cesium-137, with a half-life of 32.2 years, was released during the cold war by aboveground nuclear testing. Large land areas are now polluted with radiocesium and the costs of cleaning up just Department of Energy sites in the United States with engineering technology has been estimated at over $300 billion.

Amaranthus retroflexus is highly effective in removing radiocesium from soil.

Amaranthus retroflexus is highly effective in removing radiocesium from soil.

Fortunately, phytoremediation is an attractive alternative to these approaches. Studies showed that the primary limitation to removing cesium from soils with plants was its bioavailability. The form of the element made it unavailable to the plants for uptake. But now it appears that the ammonium ion is effective in dissolving cesium-137 in soils. This treatment increases the availability of cesium-137 for root uptake and significantly stimulates radioac-tive cesium accumulation in plant shoots.

And one plant species, a pigweed called Amaranthus retroflexus, has been found to be highly effective in removing radiocesium from soil. Researchers were able to remove 3 percent of the total amount in just one 3-month growing season. With plantings of two or three crops annually, the plant could clean up a contaminated site in less than 15 years.

Aluminum Tolerance in Acid Soils

Aluminum is the third most abundant element in the Earth’s crust and is a major component of clays in soil. At neutral or alkaline pH values, aluminum is not a problem for plants. In acid soils, however, a form of aluminum — Al+3 — is solubilized into a soil solution that is quite toxic to plant roots. Well over half the world’s 8 billion acres of arable land suffer from some degree of aluminum toxicity, including 86 million acres in the US.

Arabidopsis thalianaStudies have found that, in aluminum toxicity, the root tip is the key site of injury, leading to inhibited root growth, a stunted root system, and reduced yields or crop failures from decreased uptake of water and nutrients. In some plants, however, aluminum triggers the release of protective organic ac-ids from the root tip into adjacent soil. When released, these acids form a complex with the toxic aluminum, preventing the metal’s entry into the root. Wheat and corn, for instance, tolerate aluminum by excluding the metal from the root tip.

Researchers looking for better aluminum tolerance are studying Arabidopsis thaliana, or thale cress, a diminutive, weedy member of the mustard fami-ly. Mutants have been found which are quite aluminum tolerant and those mutations are being analyzed for genes conferring aluminum tolerance. It should then be possible to improve the tolerance of relatively aluminum-sensitive crop species, such as barley, or to further enhance the tolerance of existing aluminum-tolerant germplasm.

Bioremediation of Contaminated Soil

Bioremediation is defined as the use of biological processes to degrade, break down, transform, and/or essentially remove contaminants or impairments of quality from soil and water. Bioremediation is a natural process which relies on bacteria, fungi, and plants to alter contaminants as these organisms carry out their normal life functions. Metabolic processes of these organisms are capable of using chemical contaminants as an energy source, rendering the contaminants harmless or at least making them less toxic. This paper summarizes the general processes of bioremediation within the soil environment, focusing on biodegradation of petroleum hydrocarbons. The effect of soil conditions on rate of biodegradation of hydrocarbons is addressed. Further, limitations and potential of both ex situ and in situ bioremediation as viable alternatives to conventional remediation are explained and addressed.

Many substances known to have toxic properties have been introduced into the environment through human activity. These substances range in degree of toxicity and danger to human health. Many of these substances either immediately or ultimately come in contact with and are sequestered by soil. The emerging science and technology of bioremediation offers a method to detoxify contaminants. Bioremediation has been demonstrated and is being used as an effective means of mitigating:

  • Bacteria of the Pseudomonas genus. Different members of the genus are able to metabolize such chemical pollutants as polycyclic aromatic hydrocarbons, toluene, cyanide, carbazole, morphine and carbon tetrachloride.

    Bacteria of the Pseudomonas genus. Different members of the genus are able to
    metabolize such chemical pollutants as polycyclic aromatic hydrocarbons,
    toluene, cyanide, carbazole, morphine and carbon tetrachloride.


  • halogenated organic solvents
  • halogenated organic compounds
  • non-chlorinated pesticides and herbicides
  • nitrogen compounds
  • metals (lead, mercury, chromium)
  • radionuclides

Bioremediation technology exploits various naturally occurring mitigation processes: natural attenuation, biostimulation, and bioaugmentation.

  • Bioremediation which occurs without human intervention other than monitoring is often called natural attenuation. This natural attenuation relies on natural conditions and behavior of soil microorganisms that are indigenous to soil.
  • Biostimulationalso utilizes indigenous microbial populations to remediate contaminated soils.Biostimulation consists of adding nutrients and other substances to soil to catalyze natural attenuation processes.
  • Bioaugmentationinvolves introduction of exogenic microorganisms (sourced from outside the soil environment) capable of detoxifying a particular contaminant, sometimes employing genetically altered microorganisms.

During bioremediation, microbes utilize chemical contaminants in the soil as an energy source and, through oxidation-reduction reactions, metabolize the target contaminant into useable energy for microbes. By-products (metabolites) released back into the environment are typically in a less toxic form than the parent contaminants. For example, petroleum hydrocarbons can be degraded by microorganisms in the presence of oxygen through aerobic respiration. The hydrocarbon loses electrons and is oxidized while oxygen gains electrons and is reduced. The result is formation of carbon dioxide and water. When oxygen is limited in supply or absent, as in saturated or anaerobic soils or lake sediment, anaerobic (without oxygen) respiration prevails. Generally, inorganic compounds such as nitrate, sulfate, ferric iron, manganese, or carbon dioxide serve as terminal electron acceptors to facilitate biodegradation.

Three primary ingredients for bioremediation are:

1) presence of a contaminant,

2) an electron acceptor, and

3) presence of microorganisms that are capable of degrading the specific contaminant.

Generally, a contaminant is more easily and quickly degraded if it is a naturally occurring compound in the environment, or chemically similar to a naturally occurring compound, because microorganisms capable of its biodegradation are more likely to have evolved. Petroleum hydrocarbons are naturally occurring chemicals; therefore microorganisms which are capable of attenuating or degrading hydrocarbons exist in the environment. Development of biodegradation technologies of synthetic chemicals such as DDT is dependent on outcomes of research that searches for natural or genetically improved strains of microorganisms to degrade such contaminants into less toxic forms.

Microorganisms have limits of tolerance for particular environmental conditions, as well as optimal conditions for pinnacle performance. Factors that affect success and rate of microbial biodegradation are nutrient availability, moisture content, pH, and temperature of the soil matrix. Inorganic nutrients including, but not limited to, nitrogen, and phosphorus are necessary for microbial activity and cell growth. It has been shown that “treating petroleum-contaminated soil with nitrogen can increase cell growth rate, decrease the microbial lag phase, help to maintain microbial populations at high activity levels, and increase the rate of hydrocarbon degradation”. However, it has also been shown that excessive amounts of nitrogen in soil cause microbial inhibition. Walworth et al. (2005) suggest maintaining nitrogen levels below 1800 mg nitrogen/kg H2O for optimal biodegradation of petroleum hydrocarbons. Addition of phosphorus has benefits similar to that of nitrogen, but also results in similar limitations when applied in excess.

All soil microorganisms require moisture for cell growth and function. Availability of water affects diffusion of water and soluble nutrients into and out of microorganism cells. However, excess moisture, such as in saturated soil, is undesirable because it reduces the amount of available oxygen for aerobic respiration. Anaerobic respiration, which produces less energy for microorganisms than aerobic respiration and slows the rate of biodegradation, becomes the predominant process. Soil moisture content “between 45 and 85 percent of the water-holding capacity (field capacity) of the soil or about 12 percent to 30 percent by weight” is optimal for petroleum hydrocarbon degradation.

Soil pH is important because most microbial species can survive only within a certain pH range. Furthermore, soil pH can affect availability of nutrients. Biodegradation of petroleum hydrocarbons is optimal at a pH of 7 (neutral); the acceptable range is pH 6 – 8.

Temperature influences rate of biodegradation by controlling rate of enzymatic reactions within microorganisms. Generally, speed of enzymatic reactions in the cell approximately doubles for each 10˚ C rise in temperature. There is an upper limit to the temperature that microorganisms can withstand. Most bacteria found in soil, including many bacteria that degrade petroleum hydrocarbons, are mesophiles which have an optimum temperature ranging from 25˚ C to 45˚ C. Thermophilic bacteria (those which survive and thrive at relatively high temperatures) which are normally found in hot springs and compost heaps exist indigenously in cool soil environments and can be activated to degrade hydrocarbons with an increase in temperature to 60˚ C. This finding “suggested an intrinsic potential for natural attenuation in cool soils through thermally enhanced bioremediation techniques”.

Contaminants can adsorb to soil particles, rendering some contaminants unavailable to microorganisms for biodegradation. Thus, in some circumstances, bioavailability of contaminants depends not only on the nature of the contaminant but also on soil type. Hydrophobic contaminants, like petroleum hydrocarbons, have low solubility in water and tend to adsorb strongly in soil with high organic matter content. In such cases, surfactants are utilized as part of the bioremediation process to increase solubility and mobility of these contaminants. Additional research findings of the existence of thermophilic bacteria in cool soil also suggest that high temperatures enhance the rate of biodegradation by increasing the bioavailability of contaminants. It is suggested that contaminants adsorbed to soil particles are mobilized and their solubility increased by high temperatures.

Soil type is an important consideration when determining the best suited bioremediation approach to a particular situation. In situ bioremediation refers to treatment of soil in place. In situ biostimulation treatments usually involve bioventing, in which oxygen and/or nutrients are pumped through injection wells into the soil. It is imperative that oxygen and nutrients are distributed evenly throughout the contaminated soil. Soil texture directly affects the utility of bioventing, in as much as permeability of soil to air and water is a function of soil texture. Fine-textured soils like clays have low permeability, which prevents biovented oxygen and nutrients from dispersing throughout the soil. It is also difficult to control moisture content in fine textured soils because their smaller pores and high surface area allow them to retain water. Fine textured soils are slow to drain from water-saturated soil conditions, thus preventing oxygen from reaching soil microbes throughout the contaminated area. Bioventing is well-suited for well-drained, medium, and coarse-textured soils.

In situ bioremediation causes minimal disturbance to the environment at the contamination site. In addition, it incurs less cost than conventional soil remediation or removal and replacement treatments because there is no transport of contaminated materials for off-site treatment. However, in situ bioremediation has some limitations:

1) it is not suitable for all soils,

2) complete degradation is difficult to achieve, and

3) natural conditions (i.e. temperature) are hard to control for optimal biodegradation.

Ex situ bioremediation, in which contaminated soil is excavated and treated elsewhere, is an alternative.

Ex situ bioremediation approaches include use of bioreactors, landfarming, and biopiles.

  • In the use of a bioreactor, contaminated soil is mixed with water and nutrients and the mixture is agitated by a mechanical bioreactor to stimulate action of microorganisms. This method is better suited to clay soils than other methods and is generally a quick process.
  • Landfarming involves spreading contaminated soil over a collection system and stimulating microbial activity by allowing good aeration and by monitoring nutrient availability.
  • Biopiles are mounds of contaminated soils that are kept aerated by pumping air into piles of soil through an injection system.

In each of these methods, conditions need to be monitored and adjusted regularly for optimal biodegradation. Use of landfarming and biopiles also present the issue of monitoring and containing volatilization of contaminants. Like in situ methods, ex situ bioremediation techniques generally cost less than conventional techniques and apply natural methods. However, they can require a large amount of land and, similar to in situ bioremediation, complete degradation is difficult to achieve, and evaporation of volatile components is a concern.

If the challenges of bioremediation, particularly of in situ techniques, can be overcome, bioremediation has potential to provide a low cost, non-intrusive, natural method to render toxic substances in soil less harmful or harmless over time. Currently, research is being conducted to improve and overcome limitations that hinder bioremediation of petroleum hydrocarbons. On a broader scope, much research has been and continues to be developed to enhance understanding of the essence of microbial behavior as microbes interact with various toxic contaminants.




Humic Substances in Environmental Remediation

Humic substances, a mixture of complex organic compounds that are usually separated into three fractions: humic acids, fulvic acids and humans, are generally seen as important components of soil and natural water. They are formed during humification of organic matter by soil microorganisms. Hu-mification is the chemical-microbiological process of transforming debris from living organisms into a general class of refractory organic compounds.

Humic substances account for 50 to 80% of the organic carbon of soil, natural water, and bottom sediments. They are typically derived on an industrial scale from natural deposits like peat and coal.

US Patent application 13/366,814, published in August of 2013, is for a process using humates to remove trichloroethene (TCE) and other chlorinated solvents from polluted aquifers. Traditional treatment methods utilize reagents that deplete oxygen and stimulate anaerobic degradation. While this is effective in removing TCE, it also converts the aquifer into a putrid reaction system and results in significant reduction in water quality. Microbially mediated chlorinated solvent degradation occurs naturally in aerobic groundwater systems, but at slow rates that allow the contamination to spread over large distances. Thus there is a need for a way to speed up the process of microbial activity. This occurs when significant amounts of natural organic matter in the form of humates are introduced to the aquifer. They stimulate the growth of the microbes, which is monitored using enzyme activity probes. More humates are added as necessary to maintain microbe activity.

US Patent application 13/366,814, published in August of 2013, is for a process using humates to remove trichloroethene (TCE) and other chlorinated solvents from polluted aquifers. Traditional treatment methods utilize reagents that deplete oxygen and stimulate anaerobic degradation. While this is effective in removing TCE, it also converts the aquifer into a putrid reaction system and results in significant reduction in water quality.
Microbially mediated chlorinated solvent degradation occurs naturally in aerobic groundwater systems, but at slow rates that allow the contamination to spread over large distances. Thus there is a need for a way to speed up the process of microbial activity. This occurs when significant amounts of natural organic matter in the form of humates are introduced to the aquifer. They stimulate the growth of the microbes, which is monitored using enzyme activity probes. More humates are added as necessary to maintain microbe activity.

Their peculiar feature is polyfunctionality, which enables them to interact in a variety of ways with both metal ions and organic chemicals. As a result, numerous studies have shown, humics are capable of altering both the chemical and the physical speciation of ecotoxicants and in turn affecting their bioavailability and toxicity. Hence humic substances hold great promise functioning as amendments to mitigate the adverse impacts of ecotoxicants and as active agents in remediation.

It has been found that humic substances can enhance biotic and abiotic degradation of phenols, polyaromatic hydrocarbons (PAH) and pesticides in the aquatic environment. They are generally recognized to be responsible for the binding of major parts of the available metal ions in water and soil.

High adsorption capacity, high ion exchange capacity and environmental compatibility makes humic substances an attractive material for environmen-tal remediation. The results of biochemical studies indicate that humates can detoxify organic and inorganic inhibitors of biological processes. Humates also enhance biodegradation of toxic organic substances (phenols, formaldehyde, mineral oil) thus making their treatment more efficient. The results of chemical studies demonstrate that humates can be successfully used for immobilization of heavy metals (copper, iron, manganese). Thus humates can potentially be used as a filling material for barrier walls to prevent transport and bioavailability of heavy metals in soil.

The complexity of even simple molecules like this humic acid illustrate the diversity of ways it can attract and bind with metallic ions or complex carbohydrates and petrochemicals.

The complexity of even simple molecules like this humic acid illustrate the diversity of ways it can attract and bind with metallic ions or complex carbohydrates and petrochemicals.

The ability of humic substances to act as chelating agents for metal ions is well-documented. The particular effect that humic substances have on che-latable metals in hazardous wastes depend upon the following factors:
· the nature of the humic substances, particularly on their fulvic and humic acid content
· the chemistry of soil or water environment with respect to acidity-alkalinity and oxidation-reduction
· the presence of competing species (e.g. cyanide that compete with humic ligands for metal ions)

There are very few reports on practical applications of humic substances in environmental remediation. Most of them utilized humates to remove met-als from water or immobilize heavy metals in soil. Pilot scale applications of humates for removal of petroleum products from groundwater have also been reported.

Humates are found in various geological deposits and wetlands,  and sold primarily for agricultural purposes.

Humates are found in various geological deposits and wetlands,
and sold primarily for agricultural purposes.

Recent studies have been initiated on the application of humates in environmental remediation. The studies included biochemical and chemical tests with various heavy metals and organic pollutants. The initial results of the studies indicate that humates can detoxify organic and inorganic inhibitors of biological processes and enhance biodegradation of toxic organic substances (phenols, formaldehyde) as well as detoxify and immobilize phenols, ammonia and heavy metals (copper, chromium, iron, lead, manganese, nickel and zinc). The removal of phenol, formaldehyde and phosphorus by humates was found substantially higher in biological treatment as compared to chemical treatment. The removal of heavy metals was also higher in biological system but the difference was not as dramatic as for organic pollutants.

Grain Husbandry and Wide Spacing

‘Wheat’s worst enemy is another wheat plant.’ 1869

The beneficial results of wide spacing in grain crops are great indeed! Here in our own backyard, the Heritage Grain Conservancy conducted SARE-funded organic wheat trials at UMass and at partnering farms over four years from 2008 to 2012. Not only did we trial and select hundreds of almost-extinct landrace wheats for local adaptability, but we conducted spacing trials to compare the health and yield of landrace and modern wheats at various spacings.

The fields were cover cropped the season before, enriched with minerals and under sown with clover to suppress weeds. Wheat seeds were spaced 12”, 10”, 8”, 6” and 4” apart in 3 replicated plots. After analysis of the results at the end of the season, we discovered that wider spacing produced higher yield and more robust plants with less disease, especially in the heritage wheat plots.

Awaken Wheat’s Potential through Wide Spacing

Awaken Wheat’s Potential through Wide Spacing

The results of our trials are as follows:

12” – (5 lbs per acre) – Extensive tillering with large 10” long, fat seed heads, almost no disease, but also about 25% of the seedheads were short and stunted. The plant kept growing and putting out new tillers until it was mature. 12” spacing is excellent for seedsaving of the dominant seed heads to generate robust new strains. Extensive root systems reached out to lower levels of soil, finding moisture that enabled the plant to survive drought, and anchoring it during periods of heavy rainfall. No lodging occured.

10” – (7.5 lbs per acre) – Less tillers, slight balancing out of the large to small seedhead proportions.

8” – (11 lbs per acre) – The optimal spacing for field production with evenly sized heads, minimal disease and highest yield/seed weight.

6” – (20 lbs per acre) – The wheat plants were shorter with fewer seed heads.

4” – (40 lbs per acre) Wheat plants were at least a foot shorter, lacked access to sunlight due to crowding and had the highest level of fusarium due to lack of air flow. Greatest lodging.

To understand the significance of these results, it is important to know that heritage (landrace) wheats produce extensive tillers in fertile soil, however modern wheats are bred for few tillers and short stubby roots so that they do not collapse (lodge) under intensive agrochemical applications.

Landrace wheat at 12” spacing produces over 40 tillers per plant. Each clump grows from one seed.

Landrace wheat at 12” spacing produces over 40 tillers per plant. Each clump grows from one seed.

Modern wheat did not put out additional tillers at any spacing and were lower yielding at the wide 12” to 8” spacing than the heritage wheat. Under the modern spacing of 75 lbs per acre (30 seeds per square foot), the disease level was similar to the 4” spacing of heritage wheat. Seedheads were consistently the smallest. Woody stalks on short stocky modern plants prevented lodging and the root systems was the smallest of all. There is about 500% greater leaf surface area in the heritage wheats. The heritage wheats are powered by sunlight, but the modern wheats, bred with less leaf surface area and stubby roots, are dependent on synthetic fertilizers to survive and are powered by petroleum.

Wide spacing promotes extensive roots systems for better nutrient uptake, developing roots more fully, enhancing nutrient uptake, nourishing taller plants for increased photosynthesis that imparts richer flavor. Taller plants with greater photosynthesis have richer flavor and more phytonutrients.

Climate resilience and fertility trials of heritage vs modern wheats

Ancient emmer and einkorn exhibited stable higher yields and robust resilience under stressed conditions, whereas the modern wheat had the lowest yields and weaker plants. The heritage wheat was more resilient than the modern but less resilient than the ancient hulled wheats.

Historic Research in Wide Spacing

regarding-seeding-rateFascinated by my ‘discovery’ of the value of wide spacing, I researched the matter and learned that 1800s grain research reported similar results in their trials, and promoted wide spacing of wheat. This important knowledge has been almost forgotten, as have the superior seeds. Our experiment results are confirmed by an experiment on wheat seeding rates published by the USDA in 1869 with Tappahannock (aka Red Lamas) wheat:

Landrace wheat at 12” spacing produces over 40 tillers per plant. Each clump grows from one seed.

  1. 14 lbs per acre planted / 3,456 lbs harvested / highest quality ever seen

Drilled September 22, 1868, on rich, well-drained clay soil, at the rate of one peck (14 lbs) to the acre. This rate yielded fifty-two bushels per acre. The grain was superior to any other wheat heretofore grown in the county. It weighed sixty-four pounds per measured bushel.

  1. 54 lbs per acre planted / 2,299 lbs harvested / superior quality

Broadcast on the same date on similar soil at the rate of one bushel per acre. This yielded thirty-eight bushels per acre, weighing sixty and one half pounds per bushel. It was superior to ordinary varieties.

  1. 108 lbs per acre planted / 873.75 lbs harvested / good quality

Broadcast on the same date on similar soil at the rate of two bushels per acre. It yielded at the rate of fifteen bushels per acre, each weighing fifty-eight and one fourth pounds per bushel. The grain was the same quality as the best summer varieties.

It will be noticed in this experiment that the lightest seeding rate not only produced the largest yield of grain, but also the finest quality and by far the heaviest in weight.

In 1868, Mr. J.P. Nelson sowed 11 lbs of wheat evenly on one acre. He reported, ‘The wheat grew luxuriantly beyond anything I ever saw, at least 40 stems each with good heads from one root.’ Although the seeding was excessively light compared to typical 50 lb rates of today, the yield was quite above average. A lighter seeding rate not only gave the largest yield, but the finest quality. ‘It was by far the heaviest in weight and had the least disease.’ Department of Seed. Washington DC, Frederick Watts, Commissioner of Agriculture. 1869

The recommended seeding rate in 1869 is consistent with the results of our research today. 11 lbs per acre is a spacing of about 8” between each seed. Specific seeding rate recommendations vary from variety to variety, therefore we advise that each farmer conduct on-farm trials to determine optimal seed rate for a variety according to his or her soil and fertility management practices, and to select for preferred traits.

Regarding seeding rate, Vilmorin, France’s master seedsman in the late 1800s, reports:

‘Among many experiments we have made on this subject, we will mention one that is conclusive. In a field of good soil under ordinary conditions of wheat culture, we planted a winter wheat in the month of October in four plots of equal extent. One of them that served as comparison, had 180 liters of seed per hectare (2.47 acres), while others received only half, the third and the sixth seed to the first, that is to say respectively 90, 60 and 30 liters. We found at harvest, the yield of straw and grain increased as the rate was more lightly seeded. Not only the performance of the last at 30 liters was the greatest, but the grain was the best and heaviest at the same volume. Later in season, it can be sown thicker. Size or fineness of grain must also be considered. Experience is the best as a guide, but it must be informed by thinking and reasoning.’

The seeding rate of wheat sown by one farmer cannot be a practical guideline for another unless the variety, soil and the time of seeding is the about same. Since kernels of wheat vary in weight and size, the number of grains in a pound will vary. A liter measures volume, so it is difficult to know exactly Vilmorin’s weight. Each variety has a difference density. Vilmorin’s recommended seeding rate for his variety is about 15 lbs per acre.

What is Heritage (Landrace) Wheat?

Landraces are pre-industrial domesticated plants or animals that have been maintained by traditional farmers in low-input, variable fields over generations so as to evolve a high level of local adaptability and survival mechanisms. In contrast modern cultivars are developed by scientific breeding with modern farming methods for conventional high-input farming. Landrace cereals, legumes and vegetables populations have been selected and saved by farmers for thousands of years since the dawn of agriculture. The popular definition of ‘heirloom’ as a variety that was grown over 50 years ago forgets the long history of our ancient landrace food crops. Landraces evolved long before industrial breeding for global markets favored uniformity, appearance and shelf-life.

Because landrace wheat was cultivated generations before the chemical soil amendments and pesticide spraying were introduced in the twentieth century, how do we grow them? What can we learn from the traditional wheat growing methods?

Good grain husbandry enhances the ecological dynamics between the interdependent soil, seed and human systems.

Living Soil enriched with compost and minerals in a rotation of vegetables and cover crops, gives wheat the balanced fertility it needs. A vital soil system nourishes larger roots that reach lower to find soil moisture to avoid heat stress and stabilize the plant in heavy rain. Robust plants get less disease.

Wider Spacing for Seed-Saving and Higher Yield – Awaken the full potential of the plant: Grow landraces and mixtures in living soil at 12” space (5 lbs/acre). Select a diversity of the healthiest fat seedheads to save for seed. Plant at 8” spacing (12 lbs/ acre) for field production. Broadcast clover in early spring to suppress weeds. Wide spacing nourishes deeper roots for better survival under drought, heat and rain extremes. Planting closer than 8” means fewer tillers, shorter seedheads, more disease and lower productivity.

Biodiversity and Seed-Saving – Selective seed-saving has been the responsibility of farmers since the dawn of agriculture. This knowledge, however, is almost forgotten.

Landrace wheats are genetically diverse populations selected by traditional farmers over millennia to be well adapted, and were grown in mixtures of diverse genotypes. As farmers rediscover the power of seed-saving at wide spacing, new climate-resilient locally-adapted landraces for organic farms can emerge. These are the seeds that can feed us as we face unprecedented climate weather extremes!

For heritage wheat seeds adapted to New England

organic conditions, see: growseed.org.

copyright 2014 Eli Rogosa,

Heritage Grain Conservancy