California Human Health Screening Levels
Conceptual Site Model
Defense Energy Support Center
Defense Energy Support Center-Americas West
Defense Fuel Support Point
Defense Logistics Agency
Department of Toxic Substances Control
Granular activated carbon
General Services Administration
Groundwater treatment system
Human Health Risk Assessment
Kinder Morgan Energy Partners
Light non-aqueous phase liquids
Methyl tertiary-butyl ether
National Pollutant Discharge Elimination System
Offsite Chemicals Cleanup Subcommittee
Office of Environmental Health Hazard Assessment
Restoration Advisory Board
Risk-Based Corrective Action
Regional Water Quality Control Board
Soil Vapor Extraction
Total petroleum hydrocarbons
Volatile organic compounds
Water Replenishment District of Southern California
An aquifer is a rock or sediment unit that is wet and capable of transmitting significant quantities of water. Several aquifers, including the Exposition Aquifer, underlie the Norwalk Tank Farm site.
An aquitard is a rock or sediment unit that is wet but greatly slows the movement of water.
A chemical found in fuel. A known cancer-causing agent.
The breakdown of organic substances affected by microorganisms.
The use of biological mechanisms to destroy, transform, or immobilize environmental contaminants to protect potential sensitive receptors.
An air compressor is used to inject air into the groundwater below the groundwater level. This helps to volatilize, or turn into vapors, the chemicals that are dissolved in the groundwater. It also provides oxygen for the growth of bacteria. The bacteria eat the dissolved hydrocarbons, breaking them down into non-hazardous components. This process is called bioremediation.
Similar to biosparging, but air is injected into the soil above the groundwater to help facilitate bioremediation.
Usually, a vertical hole drilled into the ground from which soil samples can be collected and analyzed to determine the presence of chemicals and the physical characteristics of the soil.
The direction in which groundwater flows. Generally to the northwest in Norwalk.
Engineered bioremediation performed to clean up, and eventually close, a contaminated site.
Free Product/Groundwater Recovery
Groundwater recovery wells reach down underground to remove groundwater and free product (fuel floating on top of the groundwater). The recovered free product and groundwater are sent via piping to the treatment system. Also known as total fluids recovery.
Concentrations of water trapped in or moving through fractures, cracks, cavities, and pore spaces under the ground. Groundwater beneath the Norwalk site is found at 25 to 35 feet below ground and is not used for drinking water.
Health Risk Assessment
A study done to see if chemicals at a site pose a risk to human health; if steps should be taken to reduce human exposure; and if the public should be monitored.
Extraction and monitoring wells are normally drilled vertically. A horizontal well has the advantage of providing a large area of groundwater capture for a lower overall cost.
Light Non-aqueous Phase Liquid. Liquid that is lighter than water and floats on top of the water column.
Methyl tertiary-butyl ether. A fuel additive used to reduce smog.
Monitored Natural Attenuation
When natural processes, such as bioremediation, are used to achieve cleanup goals. Cleanup takes place without human intervention, but the progress is monitored on a predetermined schedule.
A well two to four inches in diameter with a removable cover that is drilled and constructed in a way that allows water samples to be taken and groundwater conditions to be evaluated. While wells are drilled, soil samples of the drill cuttings are often taken and analyzed for chemical compounds.
1,2-dichloroethane. A lead-scavenger that used to be added to fuels; also commonly used as an industrial cleaning agent and for pest and weed control. A known cancer-causing agent.
Use of plants to remediate contaminated soil or groundwater.
Small diameter wells used to measure groundwater levels.
Plumes are formed when fuel floats on or is dissolved in groundwater. Movement of groundwater causes the plume to spread.
A technology that uses strategically located wells from which groundwater is pumped. The groundwater is treated to remove benzene and fuel products and then passed through granular activated carbon to remove 1,2-DCA. Vapors produced during this process are treated before they are released.
The process of cleaning up contaminated soil and groundwater to levels that are acceptable to the regulatory agencies and that protect public health and safety as well as the environment.
Soil Vapor Extraction
Fuel vapors are removed from the soil by applying a vacuum which extracts them out through a series of underground wells. The vacuum removes vapors from the free product and removes hydrocarbon vapors created during the biosparge process. The vapors are sent via piping to the treatment system.
Total petroleum hydrocarbons. TPH is a measure of the amount of a given petroleum product, for example, gasoline, jet fuel, diesel, motor oil, or lubricants.
Volatile Organic Compounds. Organic liquids, including many common solvents, that readily evaporate at temperatures normally found at ground surface and at shallow depths.