ARCHIVED REPORTS XR0000882 - Laserfiche WebLink

Home Browse Search

contamination of TPHg at 144,000 ppb which is higher than 50,000 ppb of the last sampling event. The groundwater hydraulic gradient was calculated at S=0.004 with the down slope in the easterly direction, which is a change from the northeast direction of the normal site gradient. 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 1,2 DCA in moderate amounts in MW-1,MW-2,and EW-1. EW-1 had the highest concentration of both MTBE at 1500 ppb,1,2 DCA at 670 ppb, and EDB at 480 ppb. (see attached recap sheets). Monitoring well MW-8S appears to have recovered from the damage done by the demolition of the building on the property directly east of its location. TPHg has fallen from 5730 ppb on March 23, 2003, to non-detect during this event. This is most likely a result of the purging of the well during the last three sampling events. The extraction well EW-1 produced the highest concentrations of TPHg,MTBE, 1,2 DCA and EDB with TPHg at 227000 ppb compared to 196,000 ppb from the last sampling event. Conclusions The concentration of all contaminants of the spill are receding at a rate of about 25 % per year. There is a very active natural attenuation of the contaminates on this site. The lone exception is EW-1. This well has only been in use and sampled for three quarters and may not have produced enough data to determine if natural attenuation will effect this well as it has the others. The Redox is taking place in all the monitoring wells with the exception of MW-3 and MW-7S. EW-1 is positioned in the best location to remove the'highest concentrations of gasoline contamination in ithe sand aquifer between 50' and 60'below the surface. Recommendations The author recommends that monitoring well sampling be continued on a quarterly basis with analysis for TPHg, BTEX, and oxygenates. Work in Progress The present work plan calls for mobilization of a discharge tank and pump installation for the proposed pump test. This work will be started when the UST Fund is current on reimbursement for this site. At the present time, funds for the completion of this work plan are not available. Please contact Ervin Rifenburg of this office at (209)368-9381 if you have any questions on this report. �PpfESSfp CO *PJFEAf. Respectfully submitted, y AN LL' No.147 Foothil erin Ir- Ervin Ervin Rifenburg, �OFC Attachments: Groundwater Analysis Recap, Site Maps,Del-Tech Monitoring Report,Lab Reports cc: Michael D. & Sharon 4livarez, 436 W. Scotts Ave. Stockton, Ca. 3