Soil and groundwater can become contaminated from natural sources or numerous types of human activities. Residential, municipal, commercial, industrial, and agricultural activities can all affect the environment. Contaminants may reach soil and groundwater from activities such as:
- Sources on the land surface, such as releases or spills from stored industrial wastes
- Sources below the land surface but above the water table, such as septic systems or leaking underground petroleum storage systems
- Sources beneath the water table, such as injection wells.
Some substances found naturally in rocks or soils, such as iron, manganese, arsenic, chlorides, fluorides, sulfates, or radionuclides, can become dissolved in groundwater. Some substances may pose a health threat if consumed in excessive quantities; others may produce an undesirable odor, taste, or color.
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- Airport / Port
- Auto Repair
- Dry Cleaner
- Industrial Facility
- Oil Field
- Service Station
- Tank Farm
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Napa and Sonoma Valleys and Central Coast, California
Many types of activities occur on agricultural properties. The most obvious chemicals of concern from agricultural land use are pesticides, which include insecticides, herbicides, fungicides, rodent poisons and some other kinds of poisons.
Because there are thousands of potential pesticides, there is no single test for pesticides in soil or groundwater. The site history must be investigated to find out what types of pesticides may have been used. Pesticides can enter the environment in multiple ways such as:
- Pesticides applied to plants can seep into soil during rainfall and migrate into an underlying aquifer
- Runoff from rain falling on an area treated by pesticides can carry the pesticide so surface water sources (ditches, creeks, ponds, etc.)
- Pesticides may have been applied directly to lakes or wetlands for control of aquatic weeks, insects, or fish.
- Pesticides can move into air (either by volatilizing or with wind-blown dust) and migrate to surface waters
- Unused pesticides can be illegally dumped down a drain.
Pesticide mixing areas are often “hot spots” of contamination. Fact sheets providing more information about specific pesticide chemicals and their uses are available from the National Pesticide Information Center at: http://npic.orst.edu/npicfact.htm
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Airport / Port
Airports and sea ports typically occupy very large parcels of land and provide facilities for the transfer of cargo and people. These facilities include many types of operations that could impact soil and groundwater. Some common operations around ports include:
- Fuel storage (undergound and above ground)
- Chemical storage
- Rail yards
- Bus facilities
- Machine shops
- Maintenance yards
- Auto rental companies
- Automotive repair facilities
- Electrical generating stations
Typical contaminants present at ports and airports include petroleum hydrocarbons, chlorinated solvents, polycyclic aromatic hydrocarbons, perfluorochemicals (used in fire-fighting foams), metals, and pesticides.
Featured Project > Auto RepairSee all Projects
Automobile repair activities may result in accidental spills or intentional dumping of chemicals into soils. Junk vehicles may also be a source of these chemicals or other contaminants, depending on their condition and how and where they are stored. Many contaminants could be associated with these activities such as:
- Petroleum products such as gasoline and diesel fuel
- Polynuclear aromatic hydrocarbons (PAHs) particularly from motor oil
- Solvents like trichloroethylene (TCE)
- Used tires and rubber products
- Metals from used engine oil, which may contain chromium, lead, molybdenum, or nickel from engine wear
- Used batteries, which may release lead or mercury.
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Industrial waste clarifiers are used by manufacturers to prevent solids and oils from entering the municipal sewer system. They are typically multi-chamber concrete structures that are installed below grade. Clarifiers will intercept an industrial waste stream before connection to a sanitary sewer line. As wastewater passes through the clarifier, solids will settle to the bottom and oil will float. A service company will periodically remove the oil and solids for disposal or treatment at an offsite facility.
Clarifiers can be sources of contamination when other substances, such as chlorinated solvents or metals, are present in the waste stream. Solvents will migrate through concrete or rubber seals and impact subsurface soil and groundwater.
Dry cleaning is a clothes cleaning process that uses a chemical solvent instead of water. From the late 1800's to the early 1900's, dry cleaning was performed using petroleum-based solvents such as turpentine, kerosene, benzene, gasoline, Stoddard solvent, and mineral spirits. After the turn of the century, chlorinated hydrocarbons became preferred because of low flammability. Typical chlorinated hydrocarbons used for dry cleaning have included carbon tetrachloride, trichloroethene, Freon 113 and tetrachloroethene (also known as perchloroethene, PCE, or perc). By the 1950s, PCE became the primary solvent used for dry cleaning.
PCE is a liquid at room temperature, but readily evaporates into the air and is also called a volatile organic compound (VOC). PCE in liquid form can migrate through unsealed concrete floors and concrete or asphalt parking lots. The same properties that allow PCE to migrate through concrete floors also allow it to migrate through soil and rock once it is in the natural environment.
There are two primary human health risk concerns associated with the release of PCE to the environment:
- PCE dissolves in ground water and can move rapidly away from the original spill area. The presence of PCE in ground water creates a risk to human health, even at very low concentrations, if the contaminated ground water is used as a source of drinking water.
- PCE evaporates from contaminated soil and ground water and can migrate up through the soil to the air. If there are buildings above the area of contamination, PCE can migrate into the indoor air of the buildings. The PCE in indoor air creates a health risk when breathed by humans.
Colorado Department of Public Health and Environment, 2006. Dry Cleaner Remediation Guidance Document, March.
State Coalition for Remediation of Drycleaners, 2009. Chemicals Used in Drycleaning Operations, July.
Featured Project > Industrial FacilitySee all Projects
Industrial facilities can release many types of contaminants to the environment depending on the type of industry and the specific procedures used on site. A brownfield is defined as “a property, the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant.” Cleaning up and reinvesting in these properties increases local tax bases, facilitates job growth, utilizes existing infrastructure, takes development pressures off of undeveloped, open land, and both improves and protects the environment.
If commercial or industrial manufacturing activities have occurred on or near the property, it is essential to research what chemicals might have been used for a specific activity. The level of contamination will depend on many factors, such as the type of chemical, the material and waste management procedures, and the length of time the chemical was used. Some of the many sources of soil and groundwater contamination include metals plating, electrical component fabrication, fuel or chemical storage, automobile or machine repair, furniture refinishing, treated lumber, pesticides, fertilizers, landfills, septic systems, fires, and lead-based paint.
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Municipal solid waste landfills accept nonhazardous wastes from a variety of sources, such as households, businesses, restaurants, medical facilities, and schools. Many municipal landfills also can accept contaminated soil from gasoline spills, conditionally exempted hazardous waste from businesses, small quantities of hazardous waste from households, and other toxic wastes. Industrial facilities may use their own captive landfill (i.e., a solid waste landfill for their exclusive use) to dispose of nonhazardous waste from their processes, such as sludge from paper mills and wood waste from woodprocessing facilities. Hazardous waste landfills accept toxic, reactive, and corrosive wastes from industrial facilities.
Landfill leachate is generated by the decomposition of waste. Leachate contains numerous constituents including dissolved metals (e.g., iron and manganese), salts (e.g., sodium and chloride), and common anions and cations (e.g., bicarbonate and sulfate). Leachate concentrations are typically much greater than concentrations present in natural groundwater systems. Leachate can contains hazardous constituents, such as volatile organic compounds and heavy metals . Wood-waste leachates typically are high in iron, manganese, and tannins and lignins. Leachate from ash landfills is likely to have elevated pH and to contain more salts and metals than other leachates.
Oil and gas drilling may cause environmental impacts to surrounding soil and groundwater. Drilling wastes can include hydraulic fluids, pipe dope, used oils and oil filters, rigwash, spilled fuel, drill cuttings, drums and containers, spent and unused solvents, paint and paint washes, and sandblast media. Wastes associated with drilling fluids include oil derivatives (e.g., such as polycyclic aromatic hydrocarbons (PAHs), phenols, cadmium, chromium, copper, lead, mercury, nickel, and drilling mud additives (including contaminants such as chromate and barite).
Produced water (water that coexists with oil and gas in the formation and is recovered during well development) generation can be an issue during the drilling/development phase, although it usually becomes a greater waste management concern over the long-term operation of an oil or gas field because water production typically increases with the age of the production well. Regulations govern the disposal of this produced water; the majority of it is disposed of by underground injection either in disposal wells or in enhanced oil recovery wells.
Energy pipelines include liquid petroleum and natural gas pipelines. Liquid petroleum pipelines can carry crude oil, refined product, and volatile liquids. Crude oil transmission lines bring oil from producing areas to refineries. One of the largest is the Trans-Alaska Pipeline, which is 48 inches in diameter.
Refined product pipelines can carry gasoline, jet fuel, heating oil, and diesel fuel. They deliver product to fuel terminals with large storage tanks for distrution by tanker trucks. Major industries, airports, and power generation plants can be supplied directly by product pipelines. Volatile liquid lines contain light hydrocarbons such as ethane, butane, and propane.
Because pipelines are typically buried, soil will be directly impacted by a release. Subsurface releases to soil tend to disperse slowly and are generally located within a contiguous and discrete area, often limited to the backfill materials within the pipeline trench. In the event of a spill, a portion of the released materials would enter the surrounding soil and disperse both vertically and horizontally in the soil. The extent of dispersal would depend on a number of factors, including speed and success of emergency containment and cleanup, size and rate of release, topography of the release site, vegetative cover, soil moisture, bulk density, and soil porosity. High rates of release from the buried pipeline would result in a greater likelihood that released materials would escape the trench and reach the ground surface.
The vulnerability of groundwater aquifers is a function of the depth to groundwater and the permeability of the overlying soils. Depending on soil properties, the depth to groundwater, and the amount of petroleum released to the unsaturated zone, localized groundwater contamination can result from the presence of free petroleum and the migration of its dissolved constituents. Crude oil and petroleum products are less dense than water and would tend to form a floating pool after reaching the groundwater surface. The petroleum constituents that are soluble in water will form a larger, dissolved “plume.” This plume would tend to migrate laterally in the direction of groundwater flow. The flow velocity of dissolved constituents would be a function of the groundwater flow rate and natural attenuation, with the dissolved constituents migrating more slowly than groundwater.
Unlike chemicals with high environmental persistence (e.g., trichloroethylene, pesticides), the areal extent of the dissolved constituents will stabilize over time due to natural attenuation processes. Natural biodegradation through metabolism by naturally occurring microorganisms is often an effective mechanism for reducing the volume of crude oil and its constituents.
In 2016, there were approximately 563,000 underground storage tanks (USTs) in the U.S. that stored petroleum or hazardous substances. Until the mid-1980s, most USTs were made of bare steel, which could corrode and allow UST contents to leak into the environment. Faulty installation or inadequate operating and maintenance procedures also can cause USTs to release their contents into the environment. Since 1984, more than 1.8 million USTs have been closed.
Nearly all USTs regulated by the underground storage tank requirements contain petroleum. UST owners include marketers who sell gasoline to the public (such as service stations and convenience stores) and non marketers who use tanks solely for their own needs (such as fleet service operators and local governments).
The greatest potential hazard from a leaking UST is that the petroleum or other hazardous substance can seep into the soil and contaminate groundwater, the source of drinking water for nearly half of all Americans. A leaking UST can present other health and environmental risks, including the potential for fire and explosion.
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Aboveground storage tanks are commonly used to store petroleum products and other chemical substances. Many businesses and municipal highway departments store gasoline, diesel fuel, fuel oil, or chemicals in onsite tanks. Industries use storage tanks to hold chemicals used in processes or to store hazardous wastes.
Improper chemical storage, materials handling, and poor-quality containers can be major threats to soil and groundwater. Tanker trucks and train cars pose another chemical storage hazard. Each year, approximately 16,000 chemical spills occur from trucks, trains, and storage tanks, often when materials are being transferred. At the site of an accidental spill, the chemicals are often diluted with water and then washed into the soil, increasing the possibility of groundwater contamination