ARCHIVED REPORTS XR0009536 - Laserfiche WebLink

Home Browse Search

IFormer Manna Pro Site Page 13 Quaiteily Groundwater Monitoring Report ' & Monitoting Well Consttuctton Pi oject No 207 2 . June 2, 2000 1 5.0 DISCUSSION ' 5.1 Discussion of Data ' Deep Monitoring Well The first groundwater sample collected from the newly completed and developed well, MW-11 contained low levels of gasoline range petroleum hydrocarbons ' This data is, however, considered suspect The soil samples collected at the 55 and 69 foot levels did not contain detectable gasoline hydrocarbons, although the 96 foot sample did contain barely detectable levels of toluene and xylene The tSimulProbe water sample at 69 feet contained about 550 ppb of TPH and the 96 foot sample contained 150 ppb of TPH A sample of drilling mud was collected after thr drilling was completed and it contained 5 ppm of total gasoline hydrocarbons and 36 ppb of benzene I Taken in their totality, the data lead to the suspicion that the gasoline found in this water sample was a result of cross-contamination caused by mud filtrate invasion into the fine sand at the bottom of the well While drilling the mud is being continuously circulate d and any gasoline to the soil becomes entrained in the mud By the time the drilling was completed, the drilling mud had significant gasoline concentration As the working face of the boring is exposed during drilling, it is exposed to the mud, and the mud filtrate is free to enter into the soil to the extent that permeability will allow Regarding the water samples collected while drilling, the SimulProbe tool is driven ahead of the bottom of the boring In this case, that distance was about I 16 inches In order to allow fluid entry, the tool is retracted about 4 inches and the screen is exposed This means that the point of fluid entry lies dust 12 inches below the open bore hole which was filled with gasoline impacted drilling mud in I a hydrostatically somewhat overbalanced condition The mud may well have penetrated into the native soil sufficiently far to be collected in the SimulProbe sampling device as well as in the groundwater monitoring sample At this time, ' this is suggested as a possibility and not a conclusion Several additional quarters of monitoring will be needed to determine if the well water will "clean- up„ Based on the boring log and the sample results, it is clear that the bulk of the contaminant mass lies in the interval between 30 feet and 55 feet • r2937 Veneman Ave ,#B240 Geo-Phase Environmental Inc Phone (209) 569-0293 Modesto, CA 95356 Fax (209) 569-0293 I