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tSOIL VAPOR EXTRACTION PILOT STUDY REPORT San Joaquin County Montgomery Ward Auto Service Center Public Health Services Department 5400 Paellie Avenue Stockton, CA Site Code 2163 ' All the variables on the right hand side of the equation are known except for the sloe B P P Y estimating the slope from the graphs of vacuum versus time, soil permeability can be ' estimated It is important to note that the graphs used to estimate the slope must confirm to the following requirements ' -Data points used in the graph must be from monitoring points that are within the ROI of an extraction well -Data points should be measured immediately after starting up a VES Once a VES is run for sometime, the values reach steady state and no change will be observed unless the ' system is shut down to allow conditions to equilibrate -Data points from multiple types of monitoring points should not be combined, e g data points from soil vapor probes and passive wells should be treated separately They may yield different results r -Data points should, in general, conform to a trend If they do not, it indicates possible problems with the monitoring point and those data should be examined carefully -Data points should be measured during a fixed flow rate and vacuum Additionally, multiple vacuum extraction rates can be used to determine soil permeability for variable vacuum pressure However, if such tests are to be performed consecutively, the tests should be performed in order of increasing vacuum pressure (i a first test should be for lowest Ivacuum pressure, next one for the next higher vacuum pressure and so on) Figure 20 to Figure 22 shows vacuum vs time at all the soil vapor probes using three different extraction scenarios Figure 20 shows data when VEW-1A was used as an extraction well, Figure 21 shows data for VEW-113 as an extraction well and Figure 22 shows data when both VEW-lA and VEW-113 were concurrently used as extraction wells Selected data (that confirm to the previously stated guidelines) from these data sets are plotted on semi-log plots in Figure 23 to 25 Note that Figure 23 shows data from two different vacuum pressures which suggest two distinct slopes Best fit straight lines were fitted to each of these slopes Using the calculations presented earlier, the soil permeability calculated from each of these Igraphs are as follows Extracting from VEW-lA at 280 SCFM (Figure 23) Observation Slope Soil Point (In WC) Permeability (Darcies) SP-2 34 495 SP-3 39 432 I SP-4 26 647 SP-8 19 886 Extracting from VEW-lA at 225 SCFM (Figure 23) Observation Slope Soil Point (in i WC) Permeability (Darcies) SP-2 63 215 SP-3 59 229 SP-4 52 260 SP-8 36 386 Project No 1232 - 12 - ENVIRONMENTAL AUDIT, INC a