ARCHIVED REPORTS XR0010073 - Laserfiche WebLink

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i This option would require permits for air and water discharge and a pilot study would be necessary to evaluate the efficiency of both air and water discharge and radius of extent While one horizontal well is envisioned, more wells could be needed to achieve the needed extent of extraction Usually there is a limit of extraction of either vapor or dissolved contaminants until an asymptotic lirrut of concentrations removed are attained, and tins system is anticipated to have to run for at least eighteen months The existing groundwater monitoring wells would be used to monitor groundwater capture extent and dissolved contaminants Confirmation soil borings and soil sampling would be needed in the vicinity of Borings PB-10, 11, 13, 15, 16 and 19 to ascertain the reduction of vadose soil contaminants Option 3 Thus option is a "passive" approach in that it uses petroleum-degrading materials (either bacteria, oxygen releasing compounds or a combination) to degrade the plume in place This would be an enhanced natural attenuation approach, and would use materials selected as most appropriate following a small bench and data study for the type and quantity of materials to be used This would be accomplished by drilling the materials into the vadose soil, capillary fringe and aquifer following an assessment of the quantity and placement grid to be used based upon the observed concentrations reported herein The compounds would be placed in a manner to dissolve and migrate in the aquifer with . the natural gradient to the affected capillary and aquifer areas (that is, former tank pit, downgradient of the pit and around MW-9) Although only one occurrence of this was noted in quarterly monitoring, early investigations placed some contaminants at the site boundary An additional grid or lune of compounds would be placed on a line from MW-1 to MW-5 near the site boundary as a protection to possible off-site mugration of contaminants As this is a passive approach, the contaminant degradation would be dependent upon the groundwater velocity to deliver degrading materials, the efficiency of degradation, and affecting all the areas of interest It is initially anticipated that this approach would last from one to two years to allow for plume degradation Additional Boring for Deep Groundwater Sample The RWQCB and PHS-EHD have indicated that a deep groundwater sample is necessary to define the lower hnut of dissolved contaminants One boring will be advanced downgradient of the former tank pit to collect this sample As the site is known to have a severe flowing problem, a method will be used to collect samples below 30- to 40 feet Since drawing contaminants vertically during drilling due to flowing may be a problem, a conductor approach win be used to collect thus sample This method may use two sets of augers, cone penetrometer or a temporary conductor casing to case out the upper contaminants (to an estimated depth of at least 30 feet A sampling device will be advanced to collect the groundwater sample This sampling would be done at PHS-EHD request with any cleanup approach option Page 10