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ARCADIS GERAGHTY&MILLER <br /> increased. Ultimately, these approaches utilize simplified models <br /> which are no less uncertain than the calculation methodology <br /> described above. <br /> Currently, there is no approach that can be considered more useful <br /> and viable for monitoring a resource medium than actually taking a <br /> sample of that medium itself. The approach presented in the work <br /> plan goes beyond predicting future impacts by providing the means <br /> (through the installation of a sampling point) of acquiring real-time, <br /> tangible data which demonstrates the water quality status of the site <br /> groundwater. <br /> It is the opinion of ARCADIS Geraghty and Miller that it is not <br /> necessary or appropriate to acquire saturated zone soil samples at <br /> this site in order to assess the current or future potential impacts to <br /> groundwater at the site. Groundwater samples, as previously <br /> collected at the site and proposed in this work plan, are a superior <br /> approach. <br /> However, in order to demonstrate UNOCAL's desire to cooperate <br /> and collaborate with SJCPHS, ARCADIS Geraghty and Miller will <br /> collect and analyze unsaturated zone and saturated zone soil <br /> samples at the sampling point proposed in the May 26, 1998 work <br /> plan according to the protocols described in Attachment A (also <br /> included in the May 26, 1998 work plan). Separate soil and <br /> groundwater samples will be simultaneously taken at 10-foot <br /> intervals, using the simulprobe technology, starting at ground <br /> surface down to total boring depth. Sampling will continue, as <br /> indicated in the May 26, 1998 work plan, to a minimum depth of 70 <br /> feet bgs and until two successive samples in a row contain no <br /> detectable concentrations of TPHg, BTEX, or MTBE. Below the <br /> first encountered water, samples will be taken at maximum of 10- <br /> foot intervals or at changes in lithology. Samples will be submitted <br /> to a California State Certified Laboratory under chain of custody <br /> and analyzed for the petroleum hydrocarbon constituents of interest <br /> as described in section A.6 of the Attachement to the work plan. <br /> SJCPHS <br /> Comment: In paragraph 5, your letter states, "The proposed soil boring should <br /> be located further south between U3 and UM." <br /> Response: It is agreed that UNOCAL can relocate the proposed <br /> boring/sampling points. <br /> SJCPHS <br /> 4 <br />