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r RECEIVED J U L 19 111 Mr. R.R.Zielinski ENViRONM��EALThi 02320 0075 PER ES MW-1,MW-4 and MW-5 were used as vapor extraction wells during the test. These wells were Installed to depths ranging between 45 and 50 feet SGS. Each well was constructed with 20 feet of 4-inch-diameter, 0.020-Inch slotted well-screen, which extends through the subsurface clays and Into the tower silts and sands. Ths water table beneath the site has decreased approximately 8 feet since the Installation of the wells thus leaving between 10 to 12 feet of open screen that allowed for soil venting. Eight to ten feet of the open screen is confined within the upper clayey soils,leaving between 2 to 4 feet of open screen wlthin the lower silts and sands above the water table. Vapor extraction lines laid horizontally beneath the existing Food Mart building during remodeling of the station(referred to as VP),were also tested- MW-2.MW-3 and MW-9, in addition to the extraction wells,were used as vacuum monitoring points to aid in determining a radius of Influence from the applied vacuum at the extraction wells. SOIL VAPOR EXTRACTION TEST RESULTS The results of vacuum measurements taken during the soil vent pilot test are recorded In Table 3 (Attachment B). All the monitcoring wells used as extraction wells consistently required high vacuum pressures(60 to 70 Inches of water). MW-1 and MW-5 recorded the greatest Influence on surrounding welts; MW-4 had limited influence. Vapor extraction from the VP lines underneath the Food Mart building did not record any influence on any of the surrounding wells;it most likely drew vapors through the planter box area iii front of the building. The radius of Influence was graphically determined for each measured condition from a log-normal plot of drawdown versus distance(Attachment D). The radius of Influence was defined as the distance at which measured vacuum would be 0.1 inch of water. The radius of Influence ranged between 42 to 61 feet at flow raies ranging from 10 to 63 cfm, The average radius of Influence was 50 feet. The results are summarized in Table 4(Attachment 8). Because the vapor extraction points are cross-screenc-d through the upper clay and lower silts and sands,vapors may have been preferentially drawn from the capillary fringe In the lower sands. Therefore the determined radius of influence may not be representative of the conu+tlons In the upper clay zone. The vapor extraction wells and vacuum monitoring wells are spaced 30 to too from one another. Based on the results, including a factor of safety of 2,a flow rate of 20 cfm will produce a radius of influence of 25 feet In extraction wells which are screened In the lower sands. The hydrocarbon concentrations In vapor collected on May 21, 1991 from MW-5 and MW-4 are 150,000 and 71.00.17 pg/l,respectively. Copies of the complete laboratory reports and chain-of-custody manifests are In Attachment E, Please contact Groundwater Technology's West Sacramento office if you have questions or c . moarding this quarterly report, C:'�,mm71 Sincerely, GROU14DWATER TECHNOLOGY, INC, ( No 4422 MARTIN J. ©STENDORF t: JOHN E. BOWER E.K.SI Senior Project Geologist Environmental Geologist California Re MJfl/JE3/EKS:rc Project Manager Geologist,No. 4422 � Attachments •3 Gltoti`t)%tiitTt:f{ TFCIINOLO 4:INC.