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",041Cal rat A cs IAC Page 9 Groundwater Monitoring Report Project No 723 2 August 31,2004 ' Recommendations ' 1 Continue quarterly groundwater monitoring 2 On November 20 - 26, 2003, three multi-chamber wells were installed at the site Each well has a maximum of four intervals that can be sampled The deepest interval (MW- 308) in CMTTM well MW-8/108/108/308 should be sampled to determine the vertical limit of the plume in the down gradient direction This action has been scheduled for the ' third quarter of 2004 3 The lateral extent of the groundwater plume is undefined down gradient of CMTrM well MW-81108/108/308 A limited site investigation should take place to define the down ' gradient extent of the plume This should consist of direct push probe drilling methods such as CPTTM to collect discrete groundwater samples rather than installing additional monitoring wells ' 4 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 5 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 ' ugA) 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 CMTTM well MW-108 is screened (4") at 52 feet bgs and it contains 6,010 ug/l 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 limit (0 5 ug/1) This suggests that the Shell facility has an MTBE problem not related to the subject site 4.0 LINHTATIONS 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