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Ms. Victoria McCartney August 14, 2006 Page 3 of 5 • elevations are presented in Table 1 of the G-R Groundwater Monitoring and Sampling Report (Attachment 1). Calculated groundwater elevation data were then used to construct the groundwater potentiometric map(Figure 1 of the G-R Groundwater Monitoring and Sampling Report, [Attachment 1]). ' Separate phase hydrocarbons(SPH)were not observed during gauging of the monitoring wells. Groundwater elevations at the site ranged from 8.97 (MW-16) to 9.81 (MW-5) feet below mean sea level. ' Groundwater elevations across the site have decreased an average of 2.16 feet since the first quarter of 2006. The groundwater flow direction was generally to the southeast, as illustrated on the potentiometric map (Figure 1 of the G-R Groundwater Monitoring and Sampling Report, [Attachment 1]) and the ' horizontal hydraulic gradient ranged from approximately 0.002 to 0.004 feet per foot (fVft). The groundwater flow direction at the site has been predominately to the southeast since the second quarter of 2000 as depicted on the Groundwater Flow Direction Rose Diagram(Attachment 2). ' Groundwater Analytical A concentration map for TPH-G, benzene, and MTBE is presented as Figure 2 of the G-R Groundwater Monitoring and Sampling Report (Attachment 1). Analytical results for the quarterly groundwater monitoring event are presented in Tables 1 through 3 of the G-R Groundwater Monitoring and Sampling Report (Attachment 1). Maximum and minimum concentrations of the petroleum hydrocarbon ' constituents detected in the groundwater samples are presented in the table below: Frequency Range of of Detected Frequency of California Concentration of Constituent Detection Primary iJzceedances in uglL Above the Concentrations MCLS Exceedances (well ID) MDL' (in ug/L) TPH-G 4/11 65-9,800 TPH-D 10/11 57-1,800 TPH-MO 9/11 48-750 -- -- Benzene 4111 1-230 1 4111 95 (MW-15);4 (MW-7); 1 Y MW-8 230 MW-15D Toluene 3111 09-170 150 1/11 170 MW-15D ' Eth lbenzene 3/11 4-470 300 1/11 470 MW-1513 Total Xylenes 3/11 2-680 1,750 0111 MTBE 2/11 3-8 13 0111 TBA 2/11 8-13 -- -- -- DIPE 1111 1 -- -- -- 1,2-DCA 1111 3 0.5 1111 3 (MW-3 Notes: ' 1. MDL=method detection limit 2.ug/L=microgram per liter,equivalent to parts per billion(ppb) 3.MCL =maximum contaminant level Zl 0 ' Methanol, ethanol, ETBE anil yEDB were not detected at concentrations above the method detection limits (MDLs). Dissolved impacts appear to be primarily isolated to the area of the former underground storage tank (UST) complex on the southern portion of the property. Concentrations of petroleum ' hydrocarbons have continued to decline in monitoring wells MW-15 and MW-1D located in the former UST complex. Concentration versus time graphs for monitoring wells MW-7, -15 and MW-15D are . presented as Figures 1, 2 and 3, respectively, within Attachment 3. Dissolved troleum hydrocarbons in 025603054.doc , ' BLASLAND, BOUCK& LEE, INC. an ARCADIS company