Remediation Approaches Overview
With over 25 years of remediation projects under our belt we know that a one size remediation technique does not work on every site. On any given property requiring remediation, a variety of approaches should be considered so that both the cost and effectiveness of each approach can be weighed against the project objectives. Sometimes soil removal, soil blending and chemical injection can all be used to perform a remediation. As counter intuitive as it may sound, the goal of some remediation projects is not to cleanup a site 100% but rather to reduce contaminant mass and allow natural attenuation to increase. Multiple options should be always be considered.
By definition the word remediation refers to the removal or cleaning of a given media that has become contaminated or cleaning of a given media that has become contaminated or impacted with a contaminant or pollutant. Environmental remediation deals with the removal of the contamination found in media such as soils, groundwater and air.
The most common form of soil and groundwater contaminants are those that are impacted by petroleum-based products such as heating oil, diesel fuel, gasoline and kerosene. Hydrocarbon contamination from heating oil, diesel fuel and tanks (USTs), that over time leak. A lesser known but also prevalent form of contaminants are polyaromatic hydrocarbons (PAH). Contaminants such as petroleum hydrocarbons tend to spread through soil by diffusion and convection over time. Diffusion is a molecular transport that is driven by differences in concentration. Convection is a means of molecular motion where the driving force is provided by a fluid such as rain or wind (environmental conditions). Water will pick up pollutant particles as it soaks into the earth and carry them further from the initial spill, thus enlarging the plume. How far and fast petroleum compounds spread in the ground depends on a wide variety of factors and are site specific as geology can change drastically across even small sites.
Step 1 Driver for Remediation
Not all contamination is required to be remediated. An oil tank can leak and you can prove that petroleum levels are within acceptable levels, thus negating the need for remediation. For a site to require remediation you must have a drive such as soil contamination above permissible limits.
If you have no data indicating that you require remediation, then you have no driver. We find that many removed oil tanks do not require remediation, but rather investigation. This contradicts what many property owner's are told when they have an oil tank removed. Often time the tank removal company will say that soil remediation is required from a leaking removed tank, when in actuality a much cheaper alternative is available. /my-oil-tank-leaked-what-do-i-do-now-copy
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Step 2 Delineation
If you have laboratory analysis indicating exceedances of a compound then you have a driver to remediate. Any area that is contaminated, must first be delineated (defined) so that the horizontal and vertical extent of the contaminated area is known. Delineation is always your first step as people who say they just know when looking at say a removed leaking tank, are not looking out for the best interests of the property owner.
You cannot accurate estimate the cost to remediate without knowing the size of the area requiring remediation.
So the question that needs to be answered is how large or small of an area will require remediation. To determine the extent further investigation of the discharge is necessary. This is completed by advancing soil borings both within the known source area (to determine vertical extent) and around the perimeter of this location to determine the horizontal extent. This develops a form of 3D model of the extent of contamination, and then a plan can be developed to remediate the contamination. In addition to determining the extent of the soil contamination, depth to groundwater is also determined.
Remediation Technologies and Approaches
Remediation approaches are varied and can be classified in two distinct areas. One being in-situ, or on-site/in ground, and the other being ex-situ, or off- site. The choice of either remedial approach is contingent on a number of factors including contaminant plume size, concentration, geology and physical site conditions.
Ex-situ remediation consisting of excavating a contaminated area and transporting it to an off site location for treatment ensures a more thorough remediation and is by far the most common and effective approach. Off site facilities may consist of a thermal desorption facility where the soils are heated to thermal levels that cause the contamination to be burned off, which remediates the soils of their petroleum contamination. These thermally desorbed (remediated) soils can then be reused. Soils may also be taken to landfills for disposition.
In-situ remediations are limited by site conditions as the contaminants must fight gravity and surface. These environmental limitations force in-situ remediation to fall into three primary categories: soil washing, soil venting, and chemical injection. In-situ remediation employs two primary methods, which are the transportation of the pollutants (contaminants) out of the ground or the forced chemical degradation of the contaminants.
Bioremediation is the biological breakdown of complex chemicals (contaminants) into simpler constituents. Chemicals and bacteria can be set into the subsurface soils to break down the contaminants. Many sites already have a natural degradation of contaminants occurring by either aerobic (with oxygen) and anaerobic (without oxygen) with naturally occurring bacteria. Bioremediation typically tries to enhance this natural breakdown by enhancing the subsurface conditions to increase either form of chemical decomposition. The bacteria will break down complex chemicals into CO2 and smaller chemical constituents. The down side of this approach is that bioremediation is a fairly slow process which may take years to complete. Adding oxygen or nutrients into the environment for the bacteria will help enhance conditions for greater bacteria colonies, but subsurface geology can limit or enhance the proper conditions required for bioremediation.
Chemical Injection - Oxidation
Chemical transport can be motivated by electrical fields set in the subsurface, such as an anode and cathode placed within the area of contamination to create an electrical field. Basic science contends that contaminants may be polar and have a slight charge, and that they can be pulled by electro-magnetic forces toward a terminal with an opposite charge. This allows the contamination to congregate to the terminal. The terminal and surrounding soils can then be excavated and transported off site for processing. Chemical injections can be completed by installing injections point with mobile GeoProbe DPT Units.
Chemical oxidation technologies have evolved over the past several years and has proven to be an effective approach to treat organic contaminants including high concentration source area in the saturated and vadose (located above the water table) zones. Chemical oxidation can utilize a two-part process such as RegenOx. This process utilizes a solid alkaline oxidant that employs a sodium per-carbonate complex with a multi-part catalytic formula. The product is delivered as two separate applications; both are injected into the subsurface via dedicated points (monitoring wells) using drilling equipment. The catalyst (Part B) is installed first at a low concentration and followed by a clear water chaser equal to 1.5-3 times the well borehole volume. The oxidant (Part A) is then installed followed by a clear water chaser equal to 1.5-3 times the well borehole volume. Once in the subsurface, the combined product produces an effective oxidation reaction comparable to that of Fenton’s Reagent without a violent exothermic reaction. This allows the use of chemical oxidation around subsurface utilities that might otherwise be damaged by chemical oxidation with exothermic reactions. Chemical injection can help breakdown chemical contaminants to levels that are below regulatory limits.
In "soil washing," fluids like water or other chemicals are pumped in to force the pollutants out of the ground. Liquids that dissolve the pollutant are chosen. Many pollutants, however, aren't easily solvated, or are only soluble in caustic chemicals, limiting the applicability of in-situ washing. A typical example is trying to clean a greasy pan with cold water, the alternate use of hot water and detergent accomplishes the task much more thoroughly.
Soil venting is similar to soil washing, except that it employs gases instead of liquid to transport the pollutant out of the subsurface. This is very effective for volatile organic compounds which can be extracted from the subsurface by pumping air into bore holes while sucking it out of other holes or horizontally placed pipe. Subsurface soil conditions such as soil density has an obvious influence on the distance between the holes that are effective and economical. Hot air can be used to increase the vapor pressure of a compound, thus forcing the contaminant to volatize more readily.
Curren Environmental has experience in the various remedial approaches available today. Regardless of the remedial approach, the ultimate goal of all remedial approaches is to clean up environmental contaminants to levels that are below regulatory limits. Curren Environmental has the expertise and personnel to evaluate your environmental problem and discuss the various approaches.