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C,eolegWA TecktcusInc Page 2 Groundwater Monitoring Report Project No 770 2 January 17,2003 ' 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site The site exhibits a primarily silty/clayey geology with minor sand layers/lenses, pebbles, ' black organics and iron staining occasionally present The water table well groundwater elevation on September 13, 2002 averaged --40 33 feet mean sea level (MSL) or —64 feet below grade surface (bgs) This represents a decrease of approximately 3 79 feet since the June 2002 momtonng event Groundwater gradient calculations indicate that the flow in the water table wells was S 15°E with a slope of 0 017 ft/ft ' The groundwater gradient in the deeper aquifer monitored by wells MW-104, 105 & 106 was S84°E with a slope of 0 0019 ft/ft ' Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A Water table well gradient direction is shown on Figure 2A, and deep well gradient direction ' is illustrated in Figure 2B The historical water table gradients are illustrated in Figure 3A & 3B Groundwater Gradient Rose Diagrams for Water Table and Deep Wells, respectively The site displays highly variable shifts in groundwater direction Vertical Groundwater Gradients Under vertical groundwater flow conditions, the water level in a monitoring well is a ' function of the length of the well screen and its depth or vertical position in the aquifer As with horizontal flow conditions, the diameter of the well or piezometer is immaterial The following procedure is used to calculate vertical groundwater gradient • Determine vertical distance between the two measuring devices by the distance from the mid-point between the top and bottom seal of the deep well (MW-105) and the mid- point between the groundwater elevation and the bottom seal in the shallow well (MW- 5) • Measure the head in both wells used in the calculations ' • If the lateral distance between the well pair is greater than a few feet, then calculations must be made to correct the down-gradient piezometric head to account for the sloping ' water table between the wells The calculation considers the slope of the water table and the distance in a down-gradient direction between the two wells used in the calculations Figures 2A & 2B show the location of the well clusters, MW-5/105 and MW-6/-106, used for calculating vertical groundwater gradient in this report Table 1 includes Summary of Water Level and Gradients Water Table Wells, Table 2 includes Summary of Water Level and Gradients Deep Wells, Table 3 shows the calculated vertical gradients, and Table 6 1