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' GoIogcalTclntcl�uPage Groundwater Monitoring Report Project No 723 2 October 29,2004 ' 3 We recommend that interim remediation be considered before this plume migrates any further and the cost for cleanup continues to increase A feasibility study work plan for dual phase soil vapor and groundwater extraction was previously submitted to SJC PHS/EHD GTI's September 8, 2003 "Feasibility Study Work Plan - Dual Phase Soil Vapor and Groundwater Extraction Pilot Test" was approved by SJC PHS/EHD in their ' November 15, 2003 The pilot test was performed in late July 2004 4 The SJC/EHD records for the adjacent Shell gas station should be reviewed to determine the degree of co-mingling of the plumes beneath the subject and adjacent Shell Oil sites ' Mr Jeff Wong of the San Joaquin County Environmental Health Department (SJC/EHD) supplied GTI staff with a copy of a July, 2003 groundwater monitoring report for the Shell Service Station facility across N El Dorado Street The report indicates that the ' wells on the northern portion of the Shell site contain low levels of TPH-G (110 - 2,500 ug/1) Since these monitoring wells are 50 feet deep, it is likely that the subject plume is ' diluted in these wells and mixing with shallower clean water The CMTrm well MW-108 is screened (4") at 52 feet bgs and it contains 6,010-ug/1 TPH-G The Shell site report also indicates that the two wells in the southern portion of the site (near the existing USTs) have MTBE above the laboratory detection limits The two northern wells that lie along the subject site plume axis do not contain MTBE above the laboratory reporting linut (0 5 ug/1) This suggests that the Shell facility has an MTBE problem not related to the subject site Further delineation of the plume in this area may be warranted 4.0 LEMaTATI®NS This report was prepared in accordance with the generally accepted standard of care and ' practice in effect at the time Services were rendered It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that standards existing at ' the present time may change as knowledge increases and the state of the practice continues to improve Further, that differing subsurface soil characteristics can be experienced within a small distance and therefore cannot be known in an absolute sense All conclusions and ' recommendations are based on the available data and information. ' The tasks proposed and completed during this project were reviewed and approved by the local regulatory agency for compliance with the law No warranty, expressed or implied, is made