ARCHIVED REPORTS_XR0003102 - Laserfiche WebLink

Home Browse Search

Mr. Marty Hartzell Page 6 of 10 computed for each well b fitting a straight line to the lotted data and interpolating the radial P Y g g P rP g distance at which the cut-off vacuum (1% of the applied vacuum) is observed on the straight line. For this series of tests, the ROI was evaluated using the direct distances from well screen to well screen. These distances ranged from approximately 12 feet (Valla to VWlb) to approximately 19 feet (VW1 to VW2). The apparent induced vacuums were consistently between 1% and 2.5% (0.6 to 1.1 inches of water) during the tests conducted with wells VW1b and VW2 as the test well. However, the induced vacuum was generally below 1% (generally <0.5 inches of water) when vacuum was applied to well Valla. Ground Zero assumes that an induced vacuum of 1% of applied vacuum, and no less than 0.5 inches of water, should be sufficient to induce subsurface airflow within the zone of influence, depending on the soil type. It appears from the data that the radius of influence should be approximately 20 to 25 feet from wells VWlb and VW2, but somewhat less from well Valla. Projected Vapor Flow Rate and Gasoline Removal Rate The VET was conducted to determine if soil vapor extraction would be an effective method to remediate soil contamination associated with the former gasoline USTs. The approximate extent of gasoline hydrocarbons in soil beneath the site is depicted on Figure 3. • Based on the test results, the effective radii of influence for the wells is estimated to be approximately 2025 feet which should provide lateral coverage of the area of gasoline impacted soil. However, the relatively low concentrations of gasoline constituents (700-720 ug/1) in soil vapor samples collected from well VWlb, which is completed within the zone of highest documented soil contamination, j suggests that the primary mode of vapor removal within this zone is via diffusion due to the low permeability of the soil zone (silt/clay). Thus the mass loss rate will be limited by the rate of diffusion of contamination from the less permeable silt zone to the more permeable sand zone. Vapor flow rates measured during testing were plotted against the respective applied vacuum (Figure 4). Straight lines were fit to the data in accordance with Darcy's law which predicts a linear relationship between flow and pressure differential. The plots were then used to predict flow under assumed operational conditions of applied vacuums of 60 inches of water and 80 inches of water. In our experience at other sites this is the practical range of vacuum under which a vapor extraction system can operate efficiently. At 60 inches vacuum we would expect wells Valla to flow at a rate of approximately 35 cfm. Approximately 45 cfin each could be anticipated from wells VWlb and VW2. At a vacuum of 80 inches of water, the respective flow rates would be approximately 45, 60 and 60 cfin, respectively. Utilizing the analytical data from the test, the combined initial hydrocarbon removal rates from the three wells would be approximately 15 pounds per day at 60" of vacuum or approximately 20 pounds per day at 80" of vacuum. However, due to the close proximity of residences, it is anticipated that a treatment system could only be operated a maximum of 10 hours per day. Thus initial hydrocarbon removal rates would likely be closer to 6-8 pounds per day. Hydrocarbon removal rate calculations are a:Mr.GROUNDZE�Sol�ezUkyotu.VE'MPT aoc