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._ �✓,"u� fix:..:-"' 4 � _ "ar., i?a*" v�- �,r�+ �"�. ^sem{`� c;: : .'�.:_"".,^ x - �°'� •� r' _ qZ� �:� � � �� A.-rt,. '� � . "� �'w,��s� * F tan' `+:�� °'i�:�e M 1 n RECEIVE,?,) JUL 19 !^91 lV tr'I j;J iVTJ %i EA E_Z�-I Mr. R.0 Zielinski toERi t ES 02320 0075 MWA.MW-4 and MW-5 were used as vapor extraction wells during the lest. The:3e Yells woro Installed to depths ranging between 45 and 50 feet BGS. Each well was constructed with 2^0 feat of 4-Inch-diameter, 0.020-Inch slotted well-rcreen, which extends t€.rough the subsurface clay; and Into the lower slits and sands. The water table beneath the site has decreased approximately a feet s!^ce the Installation of the � wells thus leaving between 10 to i2 feet of open screen that allowed for soil venting, Eight to tan feet of the open screen Is confined within the upper clayey Solis,leaving ketween 2 to 4 feet of open screen within the lower slits and sands above the water table. Vapor extractior,ilnes laid horizontally beneath the existing Food Me.t 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 F-the extraction wells. SOIL VAPOR EXTRACTION TEST RESULTS The results of vacuum measurements taken during the soil vent plat test are recorded In Table 3 (Attachment B). All the monitoring wells used as extraction :jells consistently required high vacuum pressures(60 to 70 Inches of water). MW-1 and MW-5 recorded the greatest influence on surrounding wells; MW-4 had limited Influence. Vapor extraction fror;.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 tho planter box area In front of the boding. The radius of influence was graphically determined for each measured condition from a log-normal plot o" drawdown versus distance (Attachment D). The radius of Influence was defined as the distance at whi,h measured vacuum would be 0.1 Inch of water. The radlus of Influeace ranged between 42 to til feet at slow rates ranging from 10 to&I cfm. The average radius of influence was 50 feet. The results are summarized in Table 4(Attachmet it B). r acause the vapor extraction points are cross-screened through the upper clay and lower silts and sands,vapors may have been preferentially drawn from the capillary fringe in the lower viands. Therefore the determined radlus of influence may not be representative of the conditions In the Lippe:clay zone. The vapor extraction wells and vacuum monitoring wells are spaced 30 to 1CG:ram one another. Based on the results, Including a fa-l-,.,of safety of 2,a Row rate of 20 cfm rill!produce a radius of Influence of 25 feet in extraction wells w'iiuh are screened In the lower sands. The hydrocarbon con;.entrations In vapor collected on May 21,1991 from MW-5 and MW-4 are 150,000 and 71,000 pg/l,respeoWely. Copies of the complete laboratory reports and chain-of-custody manifests ara In Attachment E. Please contact Groundwater Technology's West Sacramento office if you have questirms or c regarding this quarterly report. �p C, �4y1 a i Sincerely, / L6,6 v, h GROUNDWATER TECHNOLOGY, INC. 0" r No.4422 MARTINJ.bSTt NDORI= UU JOHN E. BOWER E. K. 5th tf td�FU�l� Senior Project Geologist Environmantal Geologist Callfarnia Re Project Manager Geologist, No.4422 MJO/JEB/EKS:rc Attachments a:GROUNDWATER TEc"NOLUCy,INc. .