There are a number of materials available to assist in Soil Remediation. This Tech Note provides Guidelines for material selection.
Soil remediation is a growing use for lining materials. In this application the liner is used to separate the contaminated soil from clean soils in the work area. For many years this was done with "6 mil" Polyethylene film, however as remediations begin to involve more complex chemicals, and take place over longer periods, more reliable lining materials are being requested.
What is Unique About Soil Remediation?
There are three basic types of soil remediation. Short term and long term, remediation, and contaminated soil storage. We define short term as soil remediation that will take less than 12 months between placing the first materials on the liner until the job is completed. Long term is where the soil remediation will take longer than 12 months, or if a permanent installation is required. Short term remediation projects often require an inexpensive, disposable lining material, while long term remediation requires secure, long term containment.
The second factor to consider in a soil remediation application is the presence and extent of the contamination. Usually the chemical concentrations occurring in the soils to be contained are quite low by lining standards. Levels of less than 1000 ppm are easily contained by materials which are typically suitable for use at 20% concentrations. Often the contaminants are locked into the soil structure so that movement of the contaminants does not occur easily. As a rule of thumb we use the presence, or absence of free liquid as our second decision factor in our lining selection.
The two major styles of soil remediation are short term, with no free liquid present, and long term, with accumulations of liquid water or other product to be expected over the life of the installation.
Short Term Soil Remediation
Short term containment with no free liquid present is the most common use for a soil remediation liner. In this application the liner is used to separate the contaminated soil from clean soils in the treatment area. The liner is there to provide easy cleanup after the remediation is complete, and to direct any liquid (typically run-off water, not free product) away from the clean underlying soils. After 3 to 12 months the remediated soil and the liner are removed to expose the clean soil below.
The OR RPE® lining material has been specifically designed for short term soil remediation applications. It is suitable for soil remediation applications involving hydrocarbons, as well as a wide range of inorganic and organic chemicals. OR RPE® consists of a high strength fabric coated on both sides with a low permeability, High Density Polyethylene coating. The extended chemical resistance of OR RPE® and its strength allow it to be used for most short term soil remediation applications. OR RPE® is supplied in large prefabricated panels so that field seams are not normally required. OR RPE® is not normally recommended for long term liquid containment. Please see the Layfield Plastics RPE® design guide for further information on OR RPE®.
Long Term Soil Remediation
There is an increasing use of liners for long term soil remediation applications. In long term applications the liner is required to contain liquids such as contaminated water or bio-remediation nutrients on a continuous basis for more than 12 months. In this type of application we need to actually design a liquid containment that will last the life of the facility. This type of design needs to select a lining material that will provide a positive liquid barrier. This barrier must then be installed and backfilled in a way that prevents damage to the liner during construction and also during the design life of the facility. Layfield Plastics usually recommends that a .75mm (30 mil) minimum thickness liner material be used for long term soil remediation. In hydrocarbon contaminated soils Arctic Liner® is an excellent choice, while in soils contaminated with inorganic chemicals, regular PVC is an suitable choice. Both Arctic Liner® and regular PVC can be easily installed and repaired, and are supplied in fabricated panels that do not normally require field welds. HDPE lining materials are also in common use for soil remediation in larger facilities but a minimum thickness of 1 mm (40 mil) should be used. Often a small soil remediation project is more economical with a prefabricated liner, while a larger facility (over 10,000 m2, 100,000 ft2) can benefit from an HDPE liner.
Use of soil remediation liners on heavily contaminated soils with free-running liquid contaminants should be designed as if you were designing a pond to contain the actual product. With hazardous materials this may involve more complex lining systems and would be governed by local regulations.
Soil Storage and Covers
Soil storage systems are used when the cost of soil remediation is such that only a portion of the contaminated area can be cleaned in any given budget period. The remaining contaminated soil is stored until the next budget period. Another use for soil storage is to stockpile contaminated soil until an economical treatment technology becomes available.
In soil storage, the design of the lining system needs to take into account the long term chemical resistance and permeation performance of the liner with the contaminants present. Since soil storage usually occurs with low level contaminated soils, the lining selection is usually simplified by the low contaminant concentration.
The liner should be designed and installed according to normal construction practice, with a carefully prepared base and backfill prior to stockpiling the contaminated soil.
Soil storage often uses cover materials to prevent the infiltration of water during the storage period. Water infiltration can cause movement of the contaminants, and in the worst case, flood the liner system causing contaminant release. Often the use of an effective cover system can reduce the reliance on the liner system and result in substantial cost savings. Layfield Plastics provides RPE® 15 cover systems that as large as 10,000 m2 (100,000ft2) in a single piece, with useful lifetimes of 3+ years. Please review the Layfield design note on RPE® lining materials in the Geomembrane Fabrication section for further information about RPE® cover materials.
Soil remediation is a rapidly developing field. Please contact your Layfield representative for the latest in information, and for typical uses of soil remediation liners in your local area.