ARCHIVED REPORTS XR0006582 - Laserfiche WebLink

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concerning the Lincoln Center investigation from him or his consultants After review of several quarters of monitoring data it became apparent that some type of ground water removal was needed for migration control . Offsite monitor wells (MW5, MW6 , MW7 and MW10) were periodically showing increases in gasoline range hydrocarbons, most notable the BTEX' s . With the installation of two additional down gradient monitor wells (MW11 and MW12) the extent of the gasoline range plume was defined, with MW11 being below detection limits and MW12 displaying minor amounts of benzene 5 . 3 ug/L, toluene 1 . 9 ug/L and xylenes 2 . 1 ug/L. For a short period of time we were periodically (twice weekly) purging wells MW1, MW2, MW3 , MW8 and MW10 (2 to 27 gallons per well) with vacuum lift; removing water from the top of the aquifer at these wells . The wells that were purged contained significant gasoline range hydrocarbons Purging was initiated on December 1, 1992 and was ceased on August 30, 1993 when we were notified by Wickland that a representative of Lincoln Center voiced a concern to Wickland Properties that this activity might exacerbate the Lincoln Center ground water problem The periodic purging of selected wells was chosen due to the unlikelihood of influencing the Lincoln Center plume and the need to perform some type of ground water removal for migration control This activity was capturing and controlling the down gradient movement of the gasoline range plume until it was discontinued This is evident with the decrease in contaminant levels in MW12 from December, 1992 until September 1993 , at which time the levels again started to increase, see Table 1 Vapor extraction does have some influence on migration control, so it is important to have the vapor extraction system operate as much as possible The REMOX system has maintained, for the most part, better than 70% operation On a scheduled site visit on December 22 , 1993 , the WEGE technician found the system off. At that time a San Joaquin County PHS/EHD staff member was conducting a site visit and informed the technician that the equipment was probably turned off due to the Lincoln Center problem The equipment was left off until a letter dated December 30 , 1993 from San Joaquin County PHS/EHD clarifying that the communications between PHS/EHD staff and WEGE technician was misconstrued. WEGE continues to screen for the Lincoln Center plume . 1, 2, - dicholoroezhane (DCE) , zrichioroechylene (TCE an'" tetrachloroethylene (PCE) in the vapor stream. These have not been detected and results of ground water analyses utilizing EPA Method 624 on monitoring wells MW1 and MW6, collected on September 29, 1993 , were below detection limits . The San Joaquin County Health letter dated February 18, 1994 listed three items they wished addressed. Item 3 of this letter recommends that we additionally analyze the ground water using EPA Metod 601 at the next quaterly ground water sampling As you 3