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GROUNDWATER REMEDIATION
TECHNOLOGY OVERVIEW

TABLE OF CONTENTS

GROUNDWATER PUMP AND TREAT
AIR SPARGING
VAPOR EXTRACTION SYSTEMS
DRAWDOWN PUMPING
SURFACTANT ENHANCED RECOVERY
BIOREMEDIATION USING OXYGEN RELEASE COMPOUND

BIOREMEDIATION USING HYDROGEN RELEASE COMPOUND

GROUNDWATER PUMP AND TREAT

Groundwater pumping is a component of many pump-and-treat processes.The primary objectives of groundwater pumping include the removal of dissolved contaminants from the subsurface and containment of contaminated groundwater to prevent migration.

The first step of any remediation project consists of defining the remedial action objectives to be accomplished at the site. This involves gathering enough background information and field data to assess remedial requirements and possible cleanup levels. The first determination is whether cleanup or containment will be the most appropriate remedial action. If cleanup is chosen, the level of cleanup must be determined. If containment is chosen, groundwater pumping is used as a hydraulic barrier to prevent off-site migration of the contaminant plumes.

The next step consists of the design and implementation of the groundwater pumping system, based on data evaluated in setting the goals and objectives. The criteria for well design, pumping system, and treatment are dependent on the physical site characteristics and contaminant type. Actual treatment may include a train of processes such as gravity segregation, air strippers, and carbon systems tailored to remove specific contaminants.

Another step of any groundwater extraction system is a groundwater-monitoring program to verify its effectiveness. Monitoring the remedial system with wells and piezometers allows the operator to adjust the system in response to changes in subsurface conditions caused by the remediation.

The final step is determining the termination requirements. Termination requirements are based on the cleanup objectives defined in the initial stage of the remedial process. The termination criteria are also dependent on the site-specific aspects revealed during remedial operations.

Groundwater pump and treat technologies may include one or more of the following processes:

Liquid-phase carbon vessels:
Air stripping towers
Oil/water separators
Addition of caustic chemicals
Clarification
Filtration
UV/ oxidation

AIR SPARGING

Air sparging (or air injection) can be an effective method of accelerating remediation of groundwater and soils contaminated with volatile/semi volatile organic compounds. Air injection wells are strategically placed in the saturated and unsaturated zones and connected to a blower that is capable of supplying compressed air to the subsurface zone of impaction. As the air bubbles from the sparging well(s) are released into the groundwater, they travel upward through the saturated zone allowing dissolved organic compounds to partition into the advective vapor phase. When the vaporized organic compound bubbles reach the vadose zone, a vapor extraction system is able to remove the hydrocarbons.

By increasing the dissolved oxygen concentrations in the saturated zone, biological degradation of the organic compounds can be enhanced thereby decreasing the duration of remediation. The oxygen promotes the aerobic biodegradation of organic compounds by indigenous microorganisms in the soil and groundwater. The oxygen is introduced under pressure at a flow rate capable of sustaining aerobic biodegradation within the treatment zone. Certain conditions may prohibit an effective air sparging system, such as low permeability soils (clays) or a lack of nutrients (bioremediation).

VAPOR EXTRACTION SYSTEM INSTALLATION

In-situ vapor extraction systems (VES) include a variety of processes from vapor extraction wells to skid-mounted VES. Vapor extraction wells are typically connected using 2- to 4-inch diameter schedule 40 PVC piping (conveyance piping) and routed (either below or above grade) to the VES. The well conveyance pipes are connected to a PVC header collection manifold. Each well is equipped with a ball valve to isolate the vapors extraced from individual wells; a sample port for influent vapor concentration monitoring; and one flow element for monitoring flow rates in individual wells. A magnehelic vacuum gauge is installed at the header collection manifold to measure vacuum rate.

The impacted air stream, together with the entrained moisture and dust, is extracted from the impacted soil to the VES by induction by the vacuum blower. Blowers are capable of pulling a minimum of 200 scfm. The system components include a knockout drum for collection of entrained moisture; a vapor treatment system consisting of granular activated carbon (GAC) vessels; catalytic oxidation or thermal oxidation (depending on contaminant concentrations/type); a flow meter; and vacuum, temperature, and pressure gauges. A sample port is installed at the effluent vapor treatment system for collection of vapor samples to determine air emission concentrations to ensure compliance with air emission standards.

DRAWDOWN PUMPING

Pump drawdown nonaqueous-phase liquid (NAPL) recovery systems are designed to pump NAPL and groundwater from recovery wells or trenches. Pumping removes the water and lowers the water table near the extraction area to create a cone of depression. The cone of depression in the vicinity of the extraction well produces a gravity head that pushes the flow of NAPL toward the well and, in turn, increases the thickness of the NAPL layer in the well. Each foot of groundwater depression provides a driving head equivalent to a pressure difference of 0.45 psi. In most cases, the production of a cone of depression will increase NAPL recovery rates.

Pumping may be accomplished with one or two pumps. In the single-pump configuration, one pump withdraws both water and NAPL. The dual-pump configuration uses one pump located below the water table to remove the water and a second pump located in the NAPL layer to recover the NAPL. A single-pump system reduces capital and operating costs by having simpler control systems and operation, but it produces a stream of mixed water and NAPL that must be separated.

SURFACTANT ENHANCED RECOVERY

The application of surfactant micelles or steam to the groundwater can facilitate the groundwater pumping process by increasing the mobility and solubility of the contaminants absorbed to the soil matrix. These material can also facilitate the entrainment of hydrophobic contaminants to allow removal and assures that multi-phase contaminants can be effectively removed. Surfactants can increase the contaminant mass removal per pore volume of groundwater flushing through the contaminated zone.

The implementation of surfactant-enhanced recovery requires the injection of surfactants into a contaminated aquifer. Typical systems use a pump to extract groundwater at some distance from the injection point. The extracted groundwater is treated ex-situ to separate the injected surfactants from the contaminants and groundwater. In order to be cost-effective, the design of the surfactant-enhanced recovery system is critical. Once the surfactants have separated from the groundwater, they can be re-injected into the subsurface. Contaminants must be separated from the groundwater and treated prior to discharge of the extracted groundwater.

BIOREMEDIATION USING OXYGEN RELEASE COMPOUND

Oxygen Release Compound (ORC) offers a passive, cost-effective approach to accelerating aerobic bioremediation. ORC is a patented formulation of magnesium peroxide that time-releases oxygen when hydrated in accordance with the following reaction:

MgO2 + H2O ----> 1/2O2 + Mg(OH)2

Oxygen is often the limiting factor for aerobic microbes capable of biologically degrading contaminants such as organic compounds. Without adequate oxygen, contaminant degradation will either cease or proceed by much slower anaerobic (oxygen-free) processes. ORC releases oxygen for six months to one year. Indigenous aerobic microbes flourish in the presence of the long-lasting oxygen source, accelerating natural attenuation of target contaminants, such as BTEX, diesel-range organics, MTBE, nitroaromatics (e.g., nitroaniline, nitrobenzene), chloroaromatics (e.g., chlorobenzene, pentachlorophenol) and certain chlorinated aliphatics (e.g., vinyl chloride, dichloromethane).

ORC is manufactured as a powder, and when mixed with water forms a slurry. The slurry is injected into the soil by direct-push equipment or as backfill in augered bore holes. ORC is available in "filter socks" that can be lowered into a well through zone of saturated contamination. Once it contacts the groundwater, the oxgen is released.

ORC applications are easy, flexible, and may be designed to meet a variety of remediation objectives:

1. Source Treatment: ORC slurry may be applied by injection, in and around the contaminant source area, to collapse the plume.

2. Oxygen Barrier: ORC applications can be configured to form a permeable "oxygen barrier" to control the leading edge of a migrating plume and to avoid potential downgradient risk and liability.

3. Excavated Tank Treatment: ORC may be applied across the floor of an excavation to eliminate over-excavation in pursuit of residual contaminants and to create a zone of remedial activity, which can manage new contaminant influx.

4. Localized Plume Remediation: Isolated areas of residual contamination can often prevent site closure. ORC provides a low-cost, passive system to significantly accelerate natural attenuation and achieve cost-effective site closure.

BIOREMEDIATION USING HYDROGEN RELEASE COMPOUND

Hydrogen Release Compound (HRC) is an innovative and unique product that is used to stimulate rapid degradation of chlorinated solvent contaminants often found in groundwater and soil. It has been applied to treat compounds such as perchloroethene (PCE) and trichloroethene (TCE) on sites across the US and has demonstrated breakthrough results. HRC has been shown to achieve rapid in-situ degradation of target compounds without the costs and disruption associated with complex engineered remediation systems and without the ongoing cost and liability of natural attenuation approaches. HRC is a proven, technically sound, and a very cost effective technology.

HRC is a proprietary, environmentally safe, food quality, polylactate ester specially formulated for slow release of lactic acid upon hydration. The HRC is simply applied to the subsurface via push-point injection or within dedicated wells. The HRC is then left in place, where it passively works to stimulate rapid contaminant degradation.

The process by which HRC operates is a rather complex series of chemical and biologically mediated reactions. Initially, when in contact with subsurface moisture, the HRC slowly releases lactic acid. Indigenous anaerobic microbes (such as acetogens) metabolize the lactic acid producing consistent low concentrations of dissolved hydrogen. The resulting hydrogen is then used by other subsurface microbes (reductive dehalogenators) to strip the solvent molecules of their chlorine atoms and allow for further biological degradation. When in the subsurface, HRC continues to operate in this fashion for a year, cost effectively degrading a wide range of chlorinated aliphatic hydrocarbons (CAHs) including common groundwater pollutants such as PCE, and TCE as well as their daughter products.