SITE INFORMATION AND CORRESPONDENCE

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October 11, 2010 L Messrs Altwies and Palma Page 2 of 4 Former Manna Pro Site 4004 S. EI Dorado Street, Stockton, CA There is no significant health hazard from impacted media, but there is an increased health risk of 7.1 in 100,000`due to the dissolved benzene concentration. Based on the above listed conclusions, GPE requested that the investigation of the site be officially closed. Although there are many excellent points presented by GPE, the EHD has some concerns, as noted 'below,-and cannot concur with the site closure request at this time. �1 This decision is subject to appeal.to the State Water Resources Control Board (State Water # Board), pursuant to fH&SC.Section 25296.40 ,(a) (1), (Thompson-Richter.Underground Storage k Tank Reform Act - Senate Bill 562). Please contact the State Water Board Underground Storage Tank Program at (916) 341-5752 or visit the State Water. Board internet website at htt JIlwww.waterboards.ea. ov/ust/cleanu etitions.html for information regarding the appeals ! process: The concerns of the EHD fallow: I Although.the EHD does close sites with residual :contamination left in place in both soil and groundwater, the very high concentrations of_ total petroleum hydrocarbons quantified as gasoline (TPiHg) and benzene still impacting groundwater, under active remediation,, are a significant concern. Note.that the high concentrations of dissolved benzene were reported by GRE to exceed the HERD Johnson-Ettinger vapor intrusion screening model. The methodology ufilized by GPE°to determine the time required for reduction of the dissolved + contaminant concentrations of TPHg.and benzene to 100.pg/L and 1 .pg/L, respectively, neither concentration being,a WQO, is'new to the EHD and,the EHD requires an authoritative guidance i document-to evaluate the method validity. if the methodology is valid, ,the time required (37 years for TPHg, 43,years for benzene), already lengthy, may be,an underestimate as the data for much of the last seven years was obtained during active remediation, not natural conditions. The actual time to achieve WQOs under natural conditions is likely to:be,significantly longer, and, in of the opinion.the EHD; will 'be excessive. The appropriateness of further remediation of impacted media on,your site is supported'by the recommendation'in the last Five-Year Review Letter, dated 23 August 2010, from the. .California State Water Resources Control. Board (SWRCB) Cleanup Fund (CUF) in which the,CUF="concurs with the San Joaquin County LOP that active remediation continue to achieve Water Qualify Objectives in a timely manner." i GPE states that virtually all of the impacted soil in the vadose zone was removed through, excavation and attributes the estimated 15,000 pounds of recovered hydrocarbon contaminants to the effects of the-SVE and IAS system-on groundwater and impacted soil in the saturated zone. This would be an unusual occurrence; SVE isnot normally considered to be an effective tool to address:impacted groundwater or soil in the saturated zone and the EHD has doubts that a significant portionof the sparged air was ever recovered by°the SVE system due to the site hydrogeological framework and the design of the SVEIIAS system. l ' The IAS'sparge points are nominally set at.the top of a fine grained soil unit that is overlain by a ` thick sand unit, which in turn is overlain by another fine-grained soil unit. The upper fine-grained unit is overlain by a second sand:unit, the lower portion of which is currently in the saturated [ zone. While air sparged through the sparge points may rise into and migrate through the lower sand unit, intuitively, it seems quite possible that the air will not have enough 'buoyant force to penetrate the overlying fine-grained unit due to a very likely significant decrease of permeability E in the fine-grained unit. The EHD is of the opinion that air that manages to get to the top of the Closure Request Response-Letter 1010