COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

Diesel Impacted Soil Removal Report May 2010 California Army National Guard Armory Lodi, CA ■ Local Depth to First Groundwater. Although site-specific data are not available, CVRWQCB's Geotracker database indicated that depth to first groundwater at two sites within one-half mile of the site in Lodi ranged from 54 to 67 feet bgs in November-December 2009. Considering that the Interim Final ESLs are based on shallower groundwater conditions,the guidance level of 180 mg/kg for TPH-D may be viewed as conservative for the specific conditions at this site. ■ Horizontal Variability in Floor Soil Samples and Preponderance of Measurements Less than 10 mg/kg TPH-D. The two floor samples were collected approximately 18 inches apart,by design. Because the two samples differed significantly(2.2 versus 140 mg/kg)and because the 2.2 mg/kg TPH-D floor sample was consistent with the four additional side-wall samples which were all less than 6 mg/kg TPH-D, it is reasonable to conclude that the single elevated floor sample does not represent overall soil conditions. ■ Vertical Attenuation of TPH-D Concentration. 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 almost two orders of magnitude across 30 inches of soil. 5.2 Evaluation Discussion In consideration of the finding of one soil sample with a TPH-D concentration above the 100 mg/kg guidance level adopted for this removal action and based on insights provided by the CVRWQCB, OTIE evaluated screening levels established by the SFRWQCB for potential applicability to this site. Additionally,OTIE considered regional depth to groundwater data as well as site-specific conditions relating to the specific confirmation samples. The objective of these considerations, as addressed individually below,was to determine whether the confirmation sampling results reflected in Table 2 warrant further site removal actions. OTIE evaluated Interim Final ESLs established by the SFRWQCB in November 2007 and revised in May 2008. Specifically, OTIE referred to the ESL for TPH-D (middle distillates)under a commercial/ industrial land use presented in Table A—Shallow Soils (< 3 meters bgs), Groundwater is a Current or Potential Source of Drinking Water; and in Table B—Shallow Soils (< 3 meters bgs), Groundwater is not a Current or Potential Source of Drinking Water. The ESL for TPH-D in Table A is 83 mg/kg,which is below the concentration detected in confirmation sample LODI-SO-11. The ESL for TPH-D in Table B is 180 mg/kg,which is above the concentration detected in that confirmation sample. It is noted that ESLs are intended to aid in expediting the identification of potential environmental concerns at a site, and not necessarily as cleanup standards. Comparison of data to ESLs is one tool in determining the potential need for additional action at a site,but an exceedance of the ESL does not necessarily indicate that additional actions are required or appropriate. Whereas it is understood that the CVRWQCB considers all groundwater in the Central Valley to be a potential source of drinking water unless demonstrated otherwise,we believe it is important to take into consideration potential mitigating factors specific to the region and/or area. Pursuant to the ESL documentation, a groundwater occurrence may be excluded from consideration as a potential source of drinking water if TDS concentrations are greater than or equal to 3,000 mg/L, or if the water bearing unit is not sufficiently permeable to produce an average sustained yield of 200 gallons of water per day. Although no specific data relative to TDS concentrations or well yield exist for first groundwater at the site or in the immediate area of the site due to typical influences on shallow groundwater by historical agricultural activities in the Central Valley, it is possible that TDS concentrations are sufficiently high that the shallowest groundwater occurrence would not be considered a potential source of drinking water.