A 100,000 liter underground storage tank (UST) has leaked its entire contents into the surrounding subsurface....

  

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A 100,000 liter underground storage tank (UST) has leaked its entire contents into the surrounding subsurface. A portion of the spill remained hung up in the vadose zone due to negative pressures (matric potential), while the remaining amount came to float on top of the water table (groundwater surface) which is more than 10 meters below ground. Show a graphic that depicts this situation and complete the following calculations. Provide graphic depictions and annotated calculations to supporting your response as necessary. a) Several weeks after the event, contaminant geohydrologist investigators determined that at least some part of the spill was contained in a volume of soil in the vadose zone with approximate rectangular top and sides measuring 3 meters wide by 20 meters long at the ground surface, by 6 meters deep (measured from the visibly affected ground surface area). This volume contained gasoline suspended immobile in the vadose soil pores due to negative pore pressure conditions and surface tension. Using the 5% rule, the empirical rule introduced in class, what volume of gasoline (in liters) would be suspended in the vadose zone? Show your calculations and explain your assumptions. b) Based on your answer to a), how much gasoline might be expected to have reached the groundwater table likely to be found floating on the groundwater table surface 4 meters below the affected vadose zone? State the assumptions inherent in your calculation. Rule of thumb: On the order of 5% of the volume of the region which experienced NAPL transport will remain NAPL filled with residual product (Cary et al., 1989c). This is important for planning in soil clean up, as well as understanding how much of the product may have reached the upper aquifer. A 100,000 liter underground storage tank (UST) has leaked its entire contents into the surrounding subsurface. A portion of the spill remained hung up in the vadose zone due to negative pressures (matric potential), while the remaining amount came to float on top of the water table (groundwater surface) which is more than 10 meters below ground. Show a graphic that depicts this situation and complete the following calculations. Provide graphic depictions and annotated calculations to supporting your response as necessary. a) Several weeks after the event, contaminant geohydrologist investigators determined that at least some part of the spill was contained in a volume of soil in the vadose zone with approximate rectangular top and sides measuring 3 meters wide by 20 meters long at the ground surface, by 6 meters deep (measured from the visibly affected ground surface area). This volume contained gasoline suspended immobile in the vadose soil pores due to negative pore pressure conditions and surface tension. Using the 5% rule, the empirical rule introduced in class, what volume of gasoline (in liters) would be suspended in the vadose zone? Show your calculations and explain your assumptions. b) Based on your answer to a), how much gasoline might be expected to have reached the groundwater table likely to be found floating on the groundwater table surface 4 meters below the affected vadose zone? State the assumptions inherent in your calculation. Rule of thumb: On the order of 5% of the volume of the region which experienced NAPL transport will remain NAPL filled with residual product (Cary et al., 1989c). This is important for planning in soil clean up, as well as understanding how much of the product may have reached the upper aquifer.

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a Using the 5 rule 5 of the volume of the affected soil in the vadose zone will contain gasoline sus... View the full answer