Feasibility Study/Corrective Action Plan (FS/CAP)
Prior to proceeding with remediation of a site, a Feasibility Study (FS) is performed, and a Corrective Action Plan (CAP) prepared. These are required by both the State UST Cleanup Fund (for leaking underground storage tank (LUST) sites) and local/regional regulatory agencies. The FS evaluates the appropriateness and cost-effectiveness of a number of remediation alternatives. The CAP provides details of implementation and monitoring of the remediation alternative selected for the site. If the remediation alternative requires detailed design specifications that were beyond the scope of work for the CAP, a Remedial Action Plan (RAP) is prepared.
Verification monitoring coincides with and follows remediation and may include sampling and analyses of soil and/or groundwater to verify that contaminants are being, or have been, reduced to acceptable levels. Verification monitoring may continue periodically for a year or more.
Remedial Action Plan (RAP)
Generally, EC&A establishes the remediation alternative that is most likely to be effective and meet regulatory agency criteria by performance of a Feasibility Study (FS), where a number of remediation alternatives are evaluated. When the type of remediation has been decided, we prepare a Corrective Action Plan (CAP) that describes construction, installation and operation criteria. For some alternatives a Remedial Action Plan (RAP) that provides even greater detail is needed. When the CAP/RAP has been reviewed and approved by the regulatory agency and in the case of UST sites, the State UST Cleanup Fund, EC&A may subcontract with a vendor or equipment manufacturer to perform a pilot test at the site. If the test indicates that the alternative is effective for remediation, we employ the subcontractor to proceed with construction of the specific remediation unit, for example an oxygen producing and sparge unit or nutrient producing and injection unit. EC&A then proceeds to acquire the appropriate permits for installation and operation of the unit.
Representative Remediation Methods
High Vacuum Dual Phase Extraction
High-vacuum dual phase extraction (HVDPE) uses a high-vacuum system to remove various combinations of contaminated groundwater, free-phase hydrocarbons and soil gas vapor containing fuel hydrocarbons (FHCs), from the unsaturated and saturated zones. HVDPE systems are a combination of traditional soil vapor extraction (SVE) and high vacuum groundwater extraction units. Unlike typical SVE and pump and treat systems, HVDPE systems apply a high vacuum capable of generating vacuums up to 29″ of mercury (Hg). The high vacuum is generated by a liquid ring blower capable of generating air flow in the range of 300 to 450 cubic feet per minute (cfm).
The HVDPE system uses a propane powered thermal oxidizer for vapor-phase abatement. The thermal oxidizer burns off the hydrocarbons vapor stream at a temperature of approximately 1,600 degrees Fahrenheit. When vapor concentrations drop below 6,000 parts per million by volume (ppmv), the system can be converted to an oxidizer using a catalytic cell membrane. When switched to catalytic mode, the system oxidizer can operate at a much lower temperature typically between 600-800 Fahrenheit. This decreases the use of propane by roughly 60 percent, thereby, making incineration more cost effective as the more concentrated stream of contaminants can be handled by a smaller incinerator.
HVDPE is often selected because it can be very effective in the removal of contaminants in layered fine-grained soils, with an intrinsic permeability of target soils and groundwater media of greater than 10-12 cm/sec. The application of the HVDPE also maximizes the effectiveness of the SVE component by lowering the water table and therefore increasing air-phase permeabilities in the vadose zone. HVDPE is very effective in the removal and treatment of petroleum hydrocarbons, including BTEX, diesel and kerosene compounds.
Extracted liquids and vapor are treated and collected for disposal. Typically, extraction wells are installed at approximately 20 to 25-ft intervals within the source area and screened in the zone of contaminated soils. The system lowers the water table around the wells, making more of the formation accessible to vapor extraction.
Additional information and photographs of the process and equipment can be accessed at the vendor’s website at http://CalClean.com.
Air Sparging/Soil Vapor Extraction
Air sparging (AS), or pumping air into soil/groundwater through wells in and/or around a contaminant mass can facilitate remediation in several ways. Oxygen in the air will combine with and cause the volatile organic compounds (VOCs) to volatilize, thereby reducing the contaminant mass; it may also enhance the activity of an existing nutrient population in soil, that is actively reducing VOCs; or the air can be used to contain and/or mobilize the contaminant mass. A typical AS system would have an air compressor attached to a manifold that directs airflow to a number of wells. The air flows through pvc piping to the bottom of the wells where it exits and enters the surrounding soil. The air spreads out as it rises toward the ground surface, volatilizing the VOCs that are contacted.
Generally, soil vapor extraction (SVE) is used in conjunction with AS. SVE is also a system that is set up to access the subsurface through wells that are attached though piping in trenches to the extraction system. SVE can be effective by extracting soil vapor from a contaminant zone, but is generally more effective if the vapor is being mobilized by AS. SVE is also intended to capture VOCs, thereby preventing them from escaping into the atmosphere from the ground surface. AS/SVE can be very effective in soil and groundwater remediation, but it is not capable of extracting groundwater and would not be as effective as other types of remediation if free product was present. A typical system can destroy up to 40 pounds of hydrocarbons per hour. These are stationary, un-manned systems.
Ozone & Hydrogen Peroxide Injection
This type of soil and groundwater remediation involves the use of an ozone generator that creates the ozone, which is pumped from a manifold through teflon tubing to the bottom of wells that have been installed specifically for its subsurface distribution. As with AS, the ozone gas is delivered through an injection well and spreads out vertically and laterally through the vadose zone and saturated zone. Volatilizing of the VOCs occurs rapidly as part of a REDOX reaction oxidizing the target VOCs, producing carbon dioxide and water. Depending on soil and groundwater conditions in the area, hydrogen peroxide may also be injected. The hydrogen peroxide facilitates the outward migration of the ozone, thereby, enhancing its remediation capability, and as a liquid enters the soil as a concentrated remediation source. The hydrogen peroxide is injected through PVC piping in the wells and is injected at the top of the aquifer to maximize mixing with the ozone.
The addition of hydrogen peroxide increases the REDOX reaction creating a very strong oxidizing groundwater condition that allows for a greater mass transfer of available dissolved oxygen for ongoing bio-activity outside the core of the solute plume. The hydrogen peroxide also acts as a surfactant (detergent) at the groundwater interface where absorbed-phase contaminants are present. Hydrogen peroxide combined with oxygen injection or ozone has proven effective in treating heavy range hydrocarbons such as diesel and kerosene spills.
Passive In-Situ Bioremediation
This method of remediation is used when it is learned that soil and groundwater already contain the appropriate amount and type of naturally occurring nutrients, to actively remediate the contaminants, without the use of additional enhancement products and/or activities. This form of remediation would most likely be used in instances where there are no nearby sensitive receptors, or they are far enough away that the plume of contaminants represent no significant threat of an impact. This method may also be employed where the amounts of contaminants present are small and chances of remediation prior to impacting a sensitive receptor are remote at best.
Pump & Treat
Pump-and-Treat Technology is a method of extracting groundwater and removing the contaminants it contains prior to discharging it. Pumping depresses the groundwater level leaving residual contaminants sorbed to the soil. When the groundwater is allowed to return to its normal level, contaminants sorbed onto soil become dissolved. This is the most common form of groundwater remediation. Pump-and-treat systems remove groundwater contaminated with a variety of dissolved materials, including VOCs, SVOCs, fuels and dissolved metals.
Nutrient Injection / Reductive Dechlorination of HVOCs
Reductive dechlorination is a microbially mediated reaction, whereby a chlorine atom on the chlorinated solvent is replaced by a hydrogen atom. Enhanced reductive dechlorination involves modifying the natural conditions in a groundwater system in order to create a state that is more conducive to degradation of chlorinated solvents. This process involves the use of an organic carbon source to facilitate the biological depletion of oxidizing compounds, resulting in an extremely reductive environment (oxygen deficient). The reducing environment allows for the biological transformation of complex solvents into non-toxic breakdown products.
To create an anerobic environment, the aquifer(s) must be supplied with a source of organic carbon in the form of dilute carbohydrate or a protein liquid mixture. Typically, the reagent to be injected into an aquifer as the “food source” is cheese whey, molasses, corn syrup or vegetable oil. These types of substrates are cost-effective, highly soluble and innocuous amendments for groundwater.
An advantage of enhanced reductive dechlorination is that the carbohydrate/protein mixture can be cost effective Virtually no system maintenance is needed after injection events other than groundwater sampling and monitoring to evaluate HVOC concentrations and groundwater conditions. Groundwater monitoring is generally less expensive than that for ozone and hydrogen peroxide injection because it is not necessary to analyze for ORP-sensitive chemicals. Additionally, underground delivery piping, generator and injection panels, onsite storage of chemicals and an enclosure are not required. Typical injection treatment involves a pickup truck and treatment trailer with a mixing vessel, diaphragm pump and pressure hoses. Enhanced reductive dechlorination does not create a potential human health risk from exposure to oxidizing agents.
Natural Attenuation or Passive In-Situ Bioremediation
Natural attenuation is a passive remedial process that depends on indigenous microorganisms to process, degrade and dissipate the petroleum constituents in soil and groundwater. The plume of FHCs in groundwater is monitored to ensure continued cleanup, but no mechanical remediation is implemented. As part of this process, the groundwater system would have to contain a natural supply of nutrients (electron acceptors) for microbial activity and the degradation of target contaminants. This would be in the form of molecular oxygen and other nutrients including nitrate, phosphorous, sulfate and iron. FHCs are generally biodegradable as long as indigenous microorganisms have an adequate supply of molecular oxygen, nutrients and biological activity is not inhibited by toxic substances.
In-situ Biosparging Augmented with Nutrient Injection
AS also referred to as bio-sparging, is an in-situ groundwater bioremediation technology that encourages growth and reproduction of indigenous microorganisms present to enhance biodegradation or organic constituents in the saturated zone. In-situ bioremediation can effectively remediate FHCs dissolved in groundwater and adsorbed onto the aquifer matrix. Short chain, low-molecular-weight water soluble constituents are degraded more rapidly and to lower residual levels than are long-chain less soluble contaminants. It has been shown that both TPHg and benzene are highly susceptible to natural degradation via aerobic activity.
Bioremediation generally requires a mechanism for stimulating and maintaining the activity of these microorganisms. The injection of air at low pressure into the saturated zone, has been shown to produce enhanced biodegradation of FHCs in locations where sufficient nutrients are present for the appropriate microorganisms to flourish.
The supplementation of in-situ bioremediation with nitrate injection has two primary functions. First, nitrate serves as a nutrient (electron acceptor) in the maintenance and stimulation of ongoing metabolic processes of the indigenous microbes.
Without the addition if nutrients, low levels of nitrogen and phosphate could potentially limit the biodegradation process. Salts of nitrate and trace amounts of phosphate (ammonium nitrate and/or potassium nitrate, augmented with phosphate) can be added to the groundwater system to provide sufficient nutrient mass to facilitate biodegradation.
The costs of installing and operating an AS system is substantially lower than other groundwater extraction systems in similar circumstances. The equipment is less complex and regulated wastes are not produced.
On properties where the contaminant impacted soil is accessible with a backhoe and/or excavator, it is sometimes more cost-effective to remove and dispose of the soil, and to the degree possible the impacted groundwater (usually pump, treat & dispose). Removal of this “source” material, essentially ends the migration of the contaminants into groundwater and can lead to rather quick site closure, at locations where other existing conditions continue to reduce remaining concentrations.
This type of remediation is particularly effective at locations where fuel hydrocarbons (FHCs) have been released, but MTBE is not present. On properties where the FHCs contained MTBE, or the release(s) involved dry cleaning solvents, it may be necessary to follow up with additional remediation directed specifically at groundwater.
Generally, this is a “special circumstance “ remediation alternative that is not acceptable by regulatory agency personnel for most sites. Encapsulation suggests complete containment, but may just involve the placement of a cap over the impacted materials and subsurface barriers intended to prevent the migration of groundwater through a site. The cap may be asphalt and/or concrete and the subsurface barriers could be sheet piling, clay-filled trenches, etc. This method of remediation can be effective in situations where the contaminant(s) are localized and can by this method, be prevented from impacting human health or the environment. Relatively small amounts of FHCs are frequently left in soil at release sites that are capped to prevent rainwater from penetrating the contaminant mass. Higher concentrations may also remain in-place if capped and otherwise do not represent a threat of an impact to human health or the environment.
A less common remediation method that involves immobilizing (fixing) contaminant(s) in-place. This would generally involve mixing the contaminated material with a kind of substance that would hold it in-place and prevent the contaminants from migrating.
Remediation System Design & Development
EC&A’s experience in remedial engineering and geology covers a wide range of project types and includes the following areas of expertise:
Remediation System Design and Permitting
Remediation System Installation, Operation and Maintenance
Contaminant Transport/Groundwater Modeling
Remedial Action Plans (RAP)
The RAP provides detailed specifications for the installation and operation of the remediation alternative selected during the FS. Commonly, a RAP is only needed where a remediation alternative is complex enough to require installation and operation specifications. It is a detailed description of the tasks required to implement the proposed remediation alternative.
EC&A has a State contractor’s license. Its primary use is to allow us to hire, and supervise the activities of subcontractors. EC&A uses subcontractors for construction of remediation systems and removal and disposal of ASTs and USTs. Our contractor’s license also allows us to serve as the general contractor for the investigation of sites, construction of remediation systems and other remediation activities required by our clients; and the removal and disposal of USTs or ASTs. Therefore, we can offer turnkey project services.