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from the last soundings The hydraulic gradient of the water table has changed slightly The original <br /> direction of flow gradient was South 75 degrees East, and on 10/19/98 it was almost due East The <br /> 4/l/99 gradient is down slope North 80 degrees East with S=0 002 The 9/09/99 soundings show <br /> the down slope gradient to be North 79 degrees East with S-0 0016 Soundings for this event place <br /> the down slope gradient at North 83 degrees East with S=0 0023 Pump rates for purging continue <br /> to be between 1 0 gpm and 2 0 gpm <br /> WATER SAMPLE ANALYSIS FINDINGS <br /> In general, monitoring well samples taken on 12/21/99 tested lower in 1,2-Dichloroethane <br /> compound concentrations than did the samples taken on 9/9/99 (see BTEX & PURGEABLE <br /> HALOCARBONS summary) Analysis by EPA Test Method 8260A was not repeated,as the 4/l/99 <br /> samples were non-detect The MW-3S is only monitoring well with BTEX compounds This is a <br /> change from the last event (9/9/99) <br /> The last sampling event of 9/9/99 may have produced a set of water samples that were not <br /> representative or an error was made in analysis The samples of 9/9199 did not follow the trend of <br /> previous events or did not match the findings of this event (12/21/99) <br /> CONCLUSIONS <br /> BETX compounds in the MW43S remain near the same concentrations as the last sampling event <br /> This monitoring well is receiving the highest impact of all the wells due to TANK#1 (the <br /> Stoddard's Solvent tank), which is up gradient and Northwest of MW#3S <br /> • Chlorine compounds are present in low concentration in all but MW#4S In general, Halocarbon <br /> concentrations in all water samples are somewhat lower than the last testing period Only MW-3S <br /> exceeds National Primary Drinking Water Regulation for 1,2-Dichlorethane The present 5 8 ug/L <br /> is considerably lower than 28 ug/1 found in the sample of 6/11/98 <br /> RECOMMENDATIONS <br /> The author recommends that all monitoring wells be sampled in the first quarter of 2000 to expand <br /> and reinforce the present monitoring well data It is recommended that a closure study be made in <br /> preparation for a request for closure <br /> Please contact this office at 209/368-9381 if any questions arise from this report <br /> Respectfully submitted, <br /> yQ�� � <br /> Foot ngi ring W S75 <br /> x P � <br /> Q r p? <br /> Ervin Rifenburg, CE <br /> • cc Mrs Helen Higgins, 3461 COVELLO CIRCLE <br /> CAMERON PARK CA 95682 <br /> 2 <br />