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UNOCAL <br /> Page 2 <br /> shallow groundwater above the MCLS", but a definition of shallow groundwater is <br /> not provided. The Report Figures 6-1 and 6-2 show concentrations for NP1 and <br /> NP2 that are data from NPI-22 (screen interval 22-37 feet bsg) and NP2-22 <br /> (screen interval 22-47 feet bsg). This infers that the Report definition of shallow <br /> groundwater is that water above 50 feet bsg. Additional sampling and analysis <br /> of the shallow groundwater may confirm this statement. <br /> The Report Figure 6-3 is a conceptual model for the distribution of Benzene in <br /> groundwater and indicates the Benzene plume in groundwater at the 50 to 80 <br /> foot interval extends 230 feet from NP1 and in the interval below 108 feet bsg <br /> extends 190 feet from NPI. The Report also states that the vertical extent of <br /> impact is reasonably interpreted to be short due to the underlying low <br /> permeability zones and biodegradation. These concepts should be confirmed by <br /> further investigation including installation of additional monitoring wells screened <br /> in these intervals in the parking lot of the motel northeast of the site. <br /> In the discussion of the general water quality of the site the report states that the <br /> Total Dissolved Solids (TDS) reading for U5 on March 9, 1998 was anomalous. <br /> There was no further testing of the water from this well to support that statement. <br /> Table 6-1 in the Report shows that NP1-22, NPI-65 and NP1-111 exceeded <br /> basin plan objectives for specific conductance on February 5, 1999. Lab data to <br /> support this is not included, although conductivity readings were taken by the <br /> field technicians during purging of the wells. The table also shows that NP1-22, <br /> NP1-65 and NP1-111 exceeded the basin plan objectives for TDS on December <br /> 1998 without supporting lab data. This data should be submitted as an <br /> addendum to the report or the table should be corrected. <br /> The Report states that MTBE has not been detected at the site. MTBE has been <br /> detected in groundwater samples from U3 and U4 on different dates. Analysis <br /> for oxygenate compounds using EPA method 8260 has only been performed <br /> once. Additional analysis for oxygenates using this method should be <br /> performed. <br /> The discussions regarding the biogeochemical data which indicates that the <br /> groundwater contaminant plume is undergoing microbial biodegradation can be <br /> disputed. The Dissolved Oxygen (DO) reading was much higher in NP2-116, <br /> where there is groundwater contamination, than in wells where contaminants are <br /> not detected. Also the DO reading from NP1-65 with the highest concentration of <br /> contaminants is similar to those wells where contaminants are not detected. Iron <br /> levels in NP1-65 also were similar to the levels in those wells where <br /> contaminants are not detected. The sulfate level in NPI-65 is higher than in <br />