ARCHIVED REPORTS XR0000879 - Laserfiche WebLink

Home Browse Search

I � N All samples were extracted using the tube with check valve pump system with exception of EW-1, IR,2R,and 3R. Purge rates were+/- .5 g.p.m. on monitoring wells 1, 2, 3, 7S,and 8S. Monitoring wells 1 R and 3R had poor recharge and grab samples were collected with a bailer. Monitoring well 2R was dry. Monitoring wells 5,6,8D,and 9 were purged at 1 g.p.m. EW-1 was purged at 10 g.p.m. with a submersible pump.The physical properties of the groundwater can be found in the Del-Tech Field Report, which is attached and part of this report. Replacement well MW-2R was found to be dry on the date of this sampling event. The remaining monitoring wells were sampled for analysis. The original monitoring wells(MW-1,MW-2,MW-3) were used to establish the groundwater elevation and hydraulic gradient. All samples were transported under chain of custody to Sherwood Labs of Hilmar, California for analysis by EPA method SW8020F. Samples were transported under chain of custody from Sherwood to Castle Analytical Labs for analysis by EPA Method 8260FA for oxygenates including 1,2-DCA and EDB. All water sample analysis and groundwater elevations are summarized in the attached tabular recap sheet. Copies of the original laboratory data sheets from this sampling event are also attached and are a part of this report. Findings It is apparent from the test results that the samples for 8S and 8D were switched. It is expected that 8D would be non-detect and that 8S would have values in the hundreds to thousands. This . correction is noted by hand on the original test results. The groundwater elevation at time of monitoring was about 0.15' lower than the last monitoring event. MW-1 now has the highest concentration of the monitoring wells with gasoline contamination of TPHg at 138,000 ppb,which is higher by 3 1,000 ppb from the last sampling event. EW-1 had a concentration of TPHg of 174,000, which is 48,000 ppb lower from last quarter. The groundwater hydraulic gradient was calculated at S=0.004 with the down slope in the North/Easterly direction,which is the normal site gradient for summer/fall. The gradient is determined by the first ground water elevation data of MW-1, MW-2, and MW-3 (see a site map attached). Analysis for oxygenates during this event indicates the presence of both MTBE and/or 1,2 DCA in moderate amounts in MW-1,MW-2,MW-3,MW-5, MW-7, MW-8S, MW-8D and EW-1. MW-1 had the highest concentration of both MTBE at 950 ppb, and 1,2 DCA at 410 ppb, and EW-1 had the highest concentration of EDB at 300 ppb. (see attached recap sheets). Conclusions The long term monitoring history indicates that natural attenuation is reducing the concentrations by about 10% per year. The quarterly fluctuations in concentration are driven by the eye of the plume oscillating with changes in the groundwater levels. Recommendations The author recommends that monitoring well sampling be continued on a quarterly basis with 3