These instructions are mostly taken from The New Orleans Residents’ Guide To Do It Yourself Soil Clean Up Using Natural Processes, published by the Meg Perry Healthy Soil Project (2006). The handbook includes great info for general soil cleanup, condensed here for space reasons.
Step 1: Soil evaluation and testing
Research historical contamination on/near the property using city/county records, aerial photographs, building permits, Sanborn fire insurance maps, property deeds, and EPA databases. Get your soil tested by a local agricultural extension or by UMASS Amherst.
Step 2: Soil preparation
If the soil is dead or compacted begin by aerating the soil. Pierce the soil with a garden fork or shovel but don’t turn the soil because this may bring toxic substances to the surface. If grass or other plants are already flourishing you may not need to aerate the soil. Wear at least a paper respirator when working if it’s dusty. Then spray compost tea to increase the amount of beneficial bacteria.
Compost tea: Fill a 5 gal. bucket with non-chlorinated water. (Let city tap water sit out over night to let chlorine volatilize. If your area uses chloramine, like the East Bay, add some citric acid to break it down.) Put an aquarium bubbler in the bucket to aerate the brewing tea. Suspend 1 cup of worm castings or aerobic compost in the water in an old stocking and squeeze it gently. After an hour, add 1/4 cup of food: molasses, humic acid, or fish hydrolase (ideally a mixture). Let the brew bubble for 24-36 hours, not longer or it will go anaerobic and smell! Apply it to damp soil within 4 hours before it goes bad, using a watering can or sprayer.
Step 3: Treating for High Levels of Metals like Lead and Arsenic
Different soil conditions are needed for the removal of metals such as lead (cationic metals) and metals such as arsenic (anionic metals)–that is, they cannot both be removed at once. Soil must be acidic (low pH) for removal of lead and other cationic metals. Soil must be basic (high pH) for removal of arsenic and anionic metals. This means that if you have both lead and arsenic in your soil, you will need to remove the toxins in several steps, rotating between acidic soil conditions and basic conditions.
Start first with the metals that are most highly concentrated. If both arsenic and lead are present, with higher concentrations of lead, for example, lower the pH and plant lots of sunflowers and Indian mustard to absorb lead. When these plants are fully-grown harvest them and throw them away. The next crop of Indian mustard should be in beds of high pH to treat for arsenic. Raising the pH to extract arsenic will also help immobilize lead.
Lead, Antimony, Barium, Cadmium, Copper, Mercury, Thallium, Zinc (cationic metals):
When trying to extract this group of heavy metals, lower the pH level by adding coffee grounds, organic sulfur or pine needles. The best lead absorbing plants are Indian mustard and sunflowers. Indian mustard will also uptake selenium, cadmium, nickel, and zinc. Sunflowers will also uptake cadmium and zinc. Plant seeds as directed, covering the area thoroughly; water and tend normally. When plants are grown spray compost tea around each plant a week before harvesting because this makes metals available to be absorbed by plants. Harvest and carefully discard in plastic bags that will go to the dump or be treated as toxic waste. Do not eat the mustard greens!
Arsenic and Chromium (anionic metals):
Grow Indian mustard in more basic conditions. Use thinly spread Phosphorous in some organic form such as bat guano or agricultural lime to raise the pH.
Step 4: Retesting and Repetition
Retest soils after each harvest or as often as you can. It is impossible to predict how long this will take because of ever-changing soil conditions; it will probably require many repetitions.
Personal Health and Safety:
Avoid direct contact with sediment. Touching sediment with bare hands, getting it in your mouth or eyes, or breathing the dust could be hazardous. Do not bring young children into contaminated areas, where they might touch sediment and then put fingers into their mouths.
Grow mostly fruiting crops (peas, beans, tomatoes, peppers, eggplant, squash, cucumbers, corn, etc.)–these are safest because most plants don’t store toxins in their fruits. Avoid eating the roots, stems or leaves of plants if your soil has high toxin levels. Do not plant greens–broccoli, kale, mustard greens, spinach and lettuce are some of the common greens that take up toxins. Cabbage is the safest of leafy crops.