ARCHIVED REPORTS_XR0007882 - Laserfiche WebLink

Home Browse Search

1 16 Working To Restore Nature ' Report on Vapor Extraction Test January 29, 1993 Coca-Cola Former Distribution Facility, Stockton, California 5400601 recorded vacuum levels suggest that subsurface air flow occurs and is presumed to be sufficient for remediation Most radius of influence concepts assume that subsurface air ' continuously flows through homogeneous and isotropic soils and that short-circuiting effects are neglected This theory must be modified according to subsurface stratigraphy and based on the results of the vapor extraction test ' More specifically, air modeling studies suggest that the distance from the extraction well at which 1 % of the applied wellhead vacuum is measured, can be interpreted as the effective ' radius of influence (Chevron, 1991) This method is based upon theoretical model predictions which project that 90 % of the total air extracted from the well will flow through soils within the radius of influence when a 1 % cut off is used ' Using this 1% cut off method, the 1% cut off for extraction well VEW-1 was less than the distance to the nearest observation well VEW-3 VEW-3 is located about 24 feet from VEW-1 A plot of the data indicates that the effective radius of influence for VEW-1 at the I% cut off point is only about 10 feet Analysis of the preliminary vapor extraction test data from USTEC (USTEC, September 1991), supports this conclusion since their data appears to indicate an effective radius of influence of about 7 feet, using the 1% cut off method For extraction well VEW-3 the effective radius of influence appeared to vary between 20 ' to 40 feet, with an average of 30 feet The effective radius of influence for VEW-3 using observation wells VEW-2 and VEW-5 was about 20 feet, while it was about 40 feet for observation wells VEW-6 and VEW-S This indicates that subsurface stratigraphy is ' impacting the induced vacuum and that tighter soils appear to be present south and west of the former gasoline tank, and more porous soils north of the tank IThe estimated radii of influence for each of the eight existing vapor extraction wells are shown in Plate 5 based on the results of this investigation This radius of influence will be exerted primarily over the depth of the screened interval in each well, with the understanding that cleanup time will be more rapid in the more porous strata than in the more dense strata (ie such as clay) present in each well The estimated average effective radius of influence for each of the vapor extraction wells is estimated as follows VEW-1 = 10 feet, VEW-2 = 20 feet, VEW-3 = 30 feet, VEW-4 = 30 feet, VEW-5 = 30 feet, VEW-6 = 30 feet, VEW-7 = 20 feet, and VEW-S = 30 feet These estimates are shown in Plate 5, Estimated Effective Radius of Influence Some of these wells are screened significantly deeper than the vertical extent of the area of concern This is discussed in the following paragraph ' 131