SITE INFORMATION AND CORRESPONDENCE_2004-2014

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Mr. Maurice Benson July 8, 2008 Page 2 Comments 1) Page 1-13, Section 1.5.5; DTSC infers from the section that a benchscale test of the native soils at site P-5A was not conducted to assess both the potential for the conversion and mobility of naturally occurring metals such as arsenic in the soil, or the potential interference from other background metals in the soil matrix with the EHC. DTSC recommends that a benchscale test be performed on a representative soil sample taken at depth prior to the injection of the EHC slurry. 2) Page 1-13, Section 1.6, Hydraulic Fracturing; The injection of water under pressure (notching process) in order to create the necessary fractures or horizontal voids in the subsurface in combination with the slurry injection (11,000 gallons water) would also create a hydraulic flushing of the contaminants, potentially interfering with the engineering controls created by the operating extraction wells. Please describe in the work plan how Defense Enterprises Support San Joaquin California (DESJC) intends to mitigate the potential mobility of TCE to areas that are uncontaminated, less contaminated, or outside the hydraulic influence of the extraction well network. 3) Page 1-14, Section 1.6.3, Hydraulic Fracturing; Describe in the work plan how DESJC intends to ensure the hydraulic fracturing does not propagate along the natural fissures or cracks in the soil matrix, leading to non-uniform fractures, or fractures that would extend along a pathway not intended for treatment therefore affecting the effectiveness of the EHC contact with contaminants. 4) Page 2-2, Section 2.1.5, third sentence; The section states that two dual-nested monitoring wells will be installed in the target area to monitor groundwater both pre- and post injection of EHC. According to this section, one nested well will be installed approximately seven feet from the injection borehole with the second nested well "...located five feet downgradient and outside the radius of fracture (ROF)." The description of the well location is unclear, and leads one to interpret that the second nested well is only five feet downgradient of the first well, inside the ROF of approximately 20 feet, contradicting Figure 2-1. For clarity and consistency with Figure 2-1, the sentence should be restated as "One dual- nested well will be located downgradient, five feet outside the ROF." 5) Page 3-2, Section 3.4, Hollow-Stem Auger Drilling; DTSC recommends that continuous core samples of the area targeted are completed and analyzed pre- and post EHC injection to correlate the lithology with CPT data, but also assess initial soil concentrations of volatile organic compounds and background metals.