Shown in Figure below is a groundwater contour map. The 2^nd figure is local str

ID: 1710507 • Letter: S

Question

Shown in Figure below is a groundwater contour map. The 2^nd figure is local stratigraphic column determined by drilling. The mean hydraulic conductivity of the upper aquifer is 150 ft day, and the effective porosity is 25%. Someone accidently spilled gasoline at site B about 10 years ago. (a) Briefly describe the possible occurrence and fate of gasoline contaminants, and your design for a network of monitoring wells to define the extent of the dissolved plume. This would include how many wells, where located, how deep, what design. You can put dots on the map to show the locations of the wells on the picture. (b) Clearly for a spill like this the location of the wells is critical. Explain ways to help determine where these wells should be located. (c) What other investigation work needs to be done in addition to the monitoring through the wells?

Explanation / Answer

Fuel spills and leaks pose a serious threat to human health and environmental quality. One gallon of gasoline can contaminate up to 1 million gallons of water. Cleanup of fuel-contaminated soil and water can be extremely difficult and expensive. It is best to take precautions to ensure that spills or leaks do not occur.

All types of petroleum are mixtures of toxic chemicals that, if not recovered, pose health threats in drinking water wells if they percolated into the ground water.

Petroleum can kill aquatic life and wildlife if it reaches surface water through a storm sewer.

Fuel Handling

Small spills during fueling are bound to happen. Although fuel evaporates rapidly at the land surface it also readily seeps into the soil. Local geology and soil type determine how quickly fuel may reach groundwater supplies or runoff to nearby streams or lakes. Once in the groundwater, fuel contamination is often difficult to clean up. Even small spills or leaks in the same place over time are a potential threat to water resources. The cumulative results of many small spills over time can lead to big problems. To protect water resources from fuel spills, take care to reduce any potential leaks and spills during fuel transfers. Always supervise fuel transfers from storage tanks to equipment, replace leaking or defective nozzles and use a can to catch any dripping that may occur after shutting off the fuel nozzle. Enforce a no smoking rule at the fuel handling and storage facility. Keep fuel pumps and nozzles secure from children and vandalism, and label each pump or nozzle as to the type of fuel dispensed.

Recommendations on Locating an AST to Protect Ground and Surface Water.

Locate fuel tanks as far as reasonably possible from wells. Generally, you should try to locate a new tank downslope and at least 250 feet from your well. Avoid areas with porous, corrosive or wet soils or sites that contain abandoned drainage tiles or previously disposed waste materials. Also avoid designated flood plain areas or areas where the water table is close to the surface. The tank should not be in contact with bare soil. All tanks should be be within a secondary containment system with sufficient holding capacity for the contents of the existing tank (or largest tank for multiple-tank facilities) plus a 10% freeboard.

As the spill has already reached water and bottom of ground:

Again, most of the petroleum can usually be recovered by using a sorbent. Use dry straw, grass, corncobs or other natural material that will float. Remove contaminated sorbent straw or grass with a rake and thin-spread it so biodegradation can take place. Synthetic sorbent pads or booms are more efficient and effective. “Oil only" sorbent pads or booms will absorb oil and repel water, float on top of the water and are easily retrievable. With the State/local PCA's approval, small amounts of contaminated sorbents can be burned in training fires. (Use Oil Absorbent Sweep to absorb broad sheens or surface oil spills off water.)

Wells should be located where there is minimum effect caused by gasoline which can be examined by the gasoline measuring instruments.

References:

1.http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2201&context=extension_curall

2. http://www.dawginc.com/fuel-spill-cleanup-ar21