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' 470togkAl7eckxus kc Page 2 Groundwater Monrtormg Report ' Project No 724 2 April 25,2006 ' that a co-mingled plume is present and is sourced from the contaminated parcels to the northwest of the Morita Brothers site The CPT boring investigation in January 2006 supports this conclusion The groundwater samples obtained from over 150 feet east of the ' site from the Aurora Street CPT boreholes did not contain elevated levels of TPH-G that are present in borings along the southern edge of Charter Way The February 2006 monitoring ' event was the first in which no benzene was detected in the wells above the laboratory reporting limit of 0 5 ug/l The low levels of petroleum hydrocarbon that are found on site and immediately to the east of the site do not warrant corrective action 1 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site ' The site's monitoring wells are screened through various levels of the aquifer as shown in Figure 14 The wells' construction details are indicated in Table 7 ' Horizontal Groundwater Gradients Due to there being monitoring well sets at three different depth intervals (water table, intermediate & deep), three different horizontal gradients are usually calculated, one for each interval The calculated gradients for the February 2006 monitoring event are as follows Water table wells screened 25 to 50 ft bgs 0 0038 ft/ft flowing S50°E ' Intermediate wells screened 42 to 64 ft bgs variable variable Deep wells screened 65 to 80 ft bgs 0 0043 ft/ft flowing S20°E* *MW-104 was not utihzed for gradient deterrrunathon due to deeper well screen(87 5—90') ' Figures 2, 3 & 4 show the respective gradient directions for the shallow, intermediate and � deep wells, respectively The data for well MW-104 are omitted in Figure 4 contours due the ' well's deeper screened interval The groundwater flow direction was southeasterly for the water table and deeper aquifer intervals for this monitoring event The intermediate aquifer ' exhibited anomalous gradients with multiple directions present Figures 5A, 5B and 5C, Groundwater Gradient Rose Diagrams, illustrate the historical range ' of groundwater flow directions for the three respective horizons Tables 1, 2 & 3 in Appendix A contain the historical groundwater elevations and gradients for the shallow, intermediate and deep wells respectively 1 The average elevation of groundwater in the water table wells site was -2136 feet mean sea level (msl) This elevation represents an increase of 105 feet since the November 2005 monitoring event 1