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1 <br /> GENESIS ENGINEERING&REDEVELOPMENT <br /> Howard F. Hold, P.G. <br /> February 6, 2012 <br /> Page 2 <br /> Response: <br /> Figures 3 and A-1 have been revised to show the proposed sample locations. These <br /> locations were selected by overlaying a grid onto the property,to ensure broad and even <br /> sample coverage across the property. <br /> As to the justification for selection of this sampling location, looking at the topographic <br /> map of the general area(Figure 1),the area surrounding the Site generally consists of <br /> farmland, land being used for housing or commercial use, or land that, like the Site,has <br /> been filled in, as well as the dikes holding back the surface water. Since construction of <br /> dikes in the San Joaquin Delta early in the 20th century,the land has been put into <br /> intensive use. As a result, all of the land immediately surrounding the Site has been put <br /> to some kind of use, and much has been filled. The lack of fallow land, parks, or <br /> otherwise undisturbed land in the surrounding area makes the selection of an area for <br /> background soil sampling difficult, as all the land has been modified in some way. There <br /> is no area that has not been used for some purpose. That makes proximity to the Site; <br /> lack of industrial use and/or imported fill; and similarity in water table elevation the most <br /> controllable variables in selection of the background sampling location. <br /> The closest and most available land for background sampling that has similar conditions <br /> to the Site prior to landfilling is the farm area immediately east of the Site. Prior to <br /> landfilling,the Site was close to or below sea level, and surrounded by levees. Native <br /> soils beneath the drill mud fill are believed to be similar to those on the adjacent property <br /> to the east. <br /> RWQCB Comment: <br /> The sampling protocol in section 2.2.1 conflicts with the area presented in section 2.1. <br /> The discharger states: "Samples will be collected by driving a 6-inch long stainless steel <br /> sampling head into undisturbed soil. If any evidence of imported fill materials,waste, or <br /> contamination is encountered in any borings,then an alternative sampling location will <br /> be selected." Since this field is believed to have been farmed on a regular basis and it is <br /> unclear what the depth of the undisturbed native soil will be encountered, therefore the <br /> Discharger should explain how the material will be identified in the field as undisturbed <br /> background soil. <br />