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Diesel Impacted Soil Removal Report May 2010 California Army National Guard Armory Lodi, CA OTIE also evaluated the known depth to first groundwater in the vicinity of the site to determine how much of a potential threat to ground water the single sample exceedance of the Table A ESL might represent. Data available through the CVRWQCB's Geotracker database indicated that depth to first groundwater at two locations within one-half mile of the site in Lodi(40 North Main Street and 221 West Church Street)ranged from approximately 54 to 67 feet bgs during the November-December 2009 timeframe.Although depth to groundwater data are not available specifically for this site,the data available for these two sites appear to accurately reflect the significant depth to first groundwater typical of the area. In recognition that the ESLs for TPH-D in soil were developed based on leaching potential by the SFRWQCB,where depth to first groundwater is typically considerably shallower than noted above for the Central Valley in general, and for the Lodi area specifically, it follows that the ESL for soil in the Bay Area may be significantly more stringent than is appropriate for soil from a similar depth in this portion of the Central Valley. Another consideration is the proximity of the two floor samples (LODI-SO-10 and LODI-SO-11)to each other(approximately 18 inches). This proximity was,by design, a deliberate spacing to bias confirmation soil sampling toward the area of the highest pre-characterization sample measurement. Because the two samples differed significantly(2.2 versus 140 mg/kg,respectively),with the former being generally consistent with the remainder of the confirmation samples, it can be argued that the 140 mg/kg result is an outlier and not representative of overall soil conditions following excavation activities. A final consideration in evaluation of the single elevated floor sample is consideration of the floor sample with respect to the initial soil conditions found in the pre-characterization soil sampling. The single floor sample(LODI-SO-11) at 140 mg/kg was collected approximately 30 inches below the initial pre- characterization sample which had 13,000 mg/kg TPH-D at a depth of approximately 6 inches. Given that the fuel spill reportedly caused a release of TPH-D at the surface of the soil,these data indicate that there has been a vertical attenuation of TPH-D by nearly two orders of magnitude across 30 inches of soil. Roughly speaking, it is reasonable to assume that the continued attenuation of TPH-D will occur such that the concentration of TPH-D will be reduced to less than 100 mg/kg within the next few inches of soil.