ARCHIVED REPORTS XR0007791 - Laserfiche WebLink

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Ill 1195 M11 48 WFM Laptop FAX William F McClenney RG REA Paye 4 of 5 I& Robert Huntley 11 January 1995 Page 3 The re-sampling effort took place on 22 December 1994 On 27 December 1994, RFA received the TPHg/BTEX analytical results This sample was reported to contain ethylbenzene at a concentration of 0 31 ug/L (reporting limit of 0 30 ug/L) and total xylenes at a concentration of 0 74 ug/L (reporting limit of 0 60 ug/L) The primary Maximum Contaminant Linut (MCL) used by the Califonua Department of Health Services(CA-DOHS)for ethylbenzene is 680 ug/L with the Federal MCL reported to be 700 ug/L In the case of total xylenes, the CA-DOHS MCL is 1,750 ug/L and the Federal MCL is 10,000 ug/L Therefore both results from MW4 are well below both the state and Federal MCLS All other analytes were reported to be below their respectrve method reporting limits CONCLUSIONS At this point in time,it is possible to draw the following conclusions from the available data • there appears to be no detectable impact from either diesel or gasoline range hydrocarbons in the soil samples collected above the capillary fringe in MW4 This would tend to place this location outside of the presumed location of the known gasoline fuel leak located west of MW4, • an as yet unknown material, which may have been tentatively identified as motor oil in the capillary fringe soil sample, and which may also be related to the odors described by personnel present during well development and sampling activities, appears to be present either in groundwater or in a clayey layer found near the water table surface At present there is no . definitive connection between the odors detected m well development and sampb ng purge waters and the material identified in sample SMW-46 5, though there would appear to be such a connection, o analytical results compared with groundwater gradients calculated from each well sampling episode indicate that the samples withdrawn from MW4 appear to indicate that the downgradiem extent of groundwater impact has been defined Well MW4 appears to be on the very detectable edge of groundwater impact, but not on a consistent basis as evinced by the two samp1mg/arWytical events conducted over a 16 day interval, • organic lead analyses in both soils and groundwater extracted from MW-4 failed to detect the present of this material This suggests that organic lead is not present at this location. This evidence is not definitive as to the possible ongm of the gasoline impact as it appears to have been obtained outside of the presumed location of the soil bound plume and apparently on the"feather" edge of the groundwater impact More data will be necessary to formulate a conclusion as to ongin of both plumes At this point in time, no further downgradient exploration for the extents of groundwater impact would appear to be warranted On that basis, we propose completing the report of installation of MW4 as a PIER report after receipt of the remaining analytical data We do not advise further downgradient well installations to chase the downgradient extent of the gasoline fuel groundwater impact.