Gypsum is the major remediation amendment used for the remediation Of salt/hydrocarbon impacted soil.
There are three major impacts on soil and plants when salt water spills occur.
• Soil particles are dispersed which destroys aggregation
• Osmotic potential reduces the plants ability to up take water
• Ionic balance of the soil solution is impacted reducing nutrient absorption
The potential dispersion of a soil can be determined by the exchangeable sodium percentage (ESP). Soil dispersion results in:
• Loss of soil structure
• Loss of pore structure
• Reduced air and water movement
• Reduced bioactivity
• Reduced nutrient transfer
• Increased water run off and erosion of soil
In the remediation process it is very important to treat the soil as soon as possible. Rain on the spill site before gypsum is added will increase the rate of soil dispersion.
Hydrocarbon spills impact soil by:
• Affecting soil physical structure by coating soil aggregates
• Affecting soil water holding capacity
• Reducing and diverting water infiltration into the soil
• Obstructing air and water movement in the soil matrix
• Reducing cation/anion ion exchange on soil aggregates
At low hydrocarbon concentrations, the impact on plants is due to the physical impact on soil structure. Soils contaminated with 1 to 2% hydrocarbon can be remediated with the normal salt spill remediation process. At hydrocarbon concentrations of 4% or greater, some direct toxicity to plants occurs. At hydrocarbon concentrations of 7%, direct toxicity to plants occurs. These actual hydrocarbon concentrations will vary depending on the type of hydrocarbon, type of soil and the species of plants. At hydrocarbon concentrations greater than 2%, additional remediation steps are required which are described in the remediation amendments section.
For Hydrocarbon spills gypsum can be added at 5 tons/acre before hydrocarbon washing is initiated.
The primary goal of remediation is to reduce the amount of soil dispersion caused by the Na+ ion. This is accomplished by adding calcium ions. Gypsum is a good source of Ca++ ions in the form of calcium sulfate (CaS04).
If it is determined that the soil contains >50% clay, a 20% increase in gypsum should be considered.
REGYP has supplied numerous petrol station remediation projects with gypsum.