Thursday, January 28, 2010

Contamination of Groundwater

Though it is was widely believed in the past that groundwater was protected from contamination, this is not true. Obvious contamination sources, such as landfills, lagoons, and other waste facilities are easily identified. Sources not so easily recognized as potential contamination sources include agricultural, industrial, and mining operations, and naturally occurring processes such as salt water intrusion. While it is quite common to dispose of waste by burying it, in doing so, we have at times opened the route of contamination for ground water. Once buried, some wastes are forgotten and become more difficult to locate as time passes. Waste disposed of in surface dumps also poses a threat, especially when rainwater or snowmelt seeps down through it into the groundwater. Because groundwater in many geologic formations moves slowly, a contamination problem can remain undiscovered for years or decades before the contamination plume reaches a well (or other outlet) where it is discovered. Fractured rock formations which tend to be groundwater rich in places like Virginia, are particularly susceptible to groundwater contamination. Public water supplies are routinely tested; however, private wells are only tested at the discretion of the owner. (Though the department of health recommends regular testing of private drinking wells, it is not required. In addition, when home owners test their drinking water they routinely only test for coliform- bacterial contamination.)

Remediating groundwater contamination is difficult and expensive. Often, treatment of contaminated groundwater is also expensive. The best approach is to prevent the contamination of groundwater. There is not a comprehensive estimate of ground water contamination costs for Virginia. An example of the magnitude of costs associated with groundwater contamination can be obtained from a review of the underground storage tank program. Between 1990 and 1998 the Virginia Department of Environmental Quality reimbursed tank owners $67 million for remediation of ground water contamination. These reimbursement costs do not include the costs borne by the tank owners or costs associated with remediation activities where responsible parties could not be identified. Gasoline floats on groundwater and is only somewhat soluble, it is introduced as a point source of contamination and thus, it is relatively easy to capture and clean up. The costs associated with other types and sources of contamination would be enormous.

Sources of groundwater contamination

Leaks and spills of petroleum products. Contamination of groundwater by petroleum products from leaking fuel tanks (both heating oil and gas and diesel fuel tanks), pipelines, and spills and releases. After World War II it became common practice to bury fuel tanks in the ground. No one thought about what would happen over time when these tanks rusted and began to leak creating a slow and steady source of contamination. In the late 1980’s the states began to regulate underground storage tanks, USTs. Virginia began a program to register, regulate and cleanup USTs and their contamination in 1989 and has spent over $67 million in the effort to cleanup contamination from USTs. As the backlog of historic contamination is cleaned up and the more protective regulations reduce the future contamination, USTs are becoming a smaller threat in the future. Motor oil can also pose a threat to groundwater. It is estimated that over 4 million gallons of used oil are disposed of improperly by do it yourself oil changer in Virginia each year. Improper disposal especially pouring it out on the ground or sending it with household waste to the sanitary landfill can impact groundwater.

Military installations have historically used solvents as degreasing agents for machinery and equipment, disposed of waste on site, have had underground pipelines associated with fueling operations, and fuels storage systems. These have often been large quantity operations and can result in significant impact to groundwater especially where the aquifer is unconfined.

A landfill is a site where trash and garbage are disposed of. Historically, mixed waste was simply buried and this resulted in contaminated leachate impacting groundwater. Leachate is the liquid formed when rainwater and snowmelt filter or percolate through buried refuse. The liquid formed by dissolving waste is the leachate. If the leachate is not captured and treated it can contaminate groundwater. Many of the old hazardous waste disposal sites have turned into CERCLA (Superfund) sites. Currently there are 26 federal NPL sites in Virginia including the 2008 Sterling CERCLA site. It is reported that a quarter of CERCLA sites are old landfills.

Under the federal Resource Conservation and Recovery Act (RCRA) definitions and regulations were created for sanitary landfills, a site where sold waste is disposed on land without creating public health or safety hazards. Landfills now required a clay or synthetic liner, and the compacted waste must be caped at the end of each day with soil, monitoring wells to check for groundwater contamination are required for active and closed sanitary landfills. These days, landfills usually contain household waste. Each person in the US creates and average of 4.5 pound of trash daily. It is important that hazardous materials are not disposed of with the regular household trash, and are instead properly recycled.

Onsite Sewage Disposal Systems
Cesspools, which directly disposed of untreated sewage wastewater into pits, are no longer permitted in Virginia. These days only septic and alternative onsite sewage systems (AOSS) are permitted in Virginia. Proper location, density, and maintenance of septic systems is necessary to ensure that the AOSS and soil can absorb wastewater from the system and remove the contaminants and disease causing bacteria before it can impact the groundwater. Home owners must also be careful not to dispose of insecticides, herbicides, solvents, paints, drugs or other chemicals in their sinks and toilets. Septic systems and AOSS are not designed to remove these substances and they will pass directly to the groundwater. Currently, there are Emergency AOSS regulations awaiting the Governor’s signature.

Agricultural activities can cause degradation of the groundwater. Excessive use of fertilizers and pesticides or improper application or disposal of these substances can contaminate groundwater. Shallow groundwater can also be impacted by runoff of pesticides and improper well construction. In addition, improper management, storage and disposal of animal waste from manure piles, animal waste lagoons and feedlots (which are not common in Virginia) can contaminate groundwater with biological contaminates and nitrate. Suburban pesticide use and surface runoff can also have significant impacts on groundwater. Excessive use of herbicides and pesticides on ornamental gardens can contribute to runoff and ground infiltration of pesticides. Injecting termite control chemicals directly into the soil surrounding all houses needs to be rethought and pest control planned and appropriately handled.

In southwestern Virginia coal mining can impact groundwater. Acidic ground water caused by the coal mining can be a serious problem. Below ground mining can intersect a groundwater aquifer and introduce contaminants into the aquifer. Tailing ponds used to dispose of mining waste can be a source of groundwater contamination. Mining is often associated with acidic impacts to groundwater.

Finally, coastal areas can be affected by saltwater intrusion caused by heavy pumping of the groundwater, a decrease in recharge or an increase in sea level. When the artesian layer of groundwater is pumped beyond its recharge rate, saltwater will rush flow in to fill the void. This is a growing problem in the Tidewater region of Virginia. Groundwater levels in the Tidewater region of Virginia’s coastal plain are continuing to decline. Impacts from groundwater withdrawals are propagating along the fall line into the coastal plain and have the potential to interfere with wells in these areas. Given current groundwater declines, the entire coastal plain aquifer system must be managed to maintain a sustainable future supply of ground water.

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