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C406g1cal r'etluua t4c Page 2 Groundwater Monitoring Report Project No 770 2 R September 24, 2003 commercial and residential wells near the Marci parcel and the influences from these wells are the probable cause for the groundwater direction fluctuations 1 1.0 GROUNDWATER MONITORING ' Lt 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 groundwater monitoring schedule was modified to include monthly depth to groundwater measurements in 2002 This was ' necessary to better define the gradients that have varied greatly in the past The water table well groundwater elevation on April 28, 2003 averaged —38 15 feet mean sea level (MSL) or --62 feet below grade surface (bgs) For the May 23 event, the water table well groundwater elevation decreased to an average of—39 37 feet MSL or —63 feet bgs On June 18, 2003 the average depth to groundwater in the water table wells was again approximately 63 feet bgs and elevation averaged —38 84 feet MSL The second quarter first experienced a drop and then a rise in groundwater elevation A net decrease of 0 12 feet in groundwater elevation was recorded between the March and June 2003 sounding events Groundwater gradient calculations indicate that the flow in the water table wells was S52°E with a slope of 0 00t ft/ft on April 28, 2003 On May 23, 2003 the water table well gradient was S58°E with a slope of 0 003 ft/ft, and on June 18, 2003 it was S26°E with a slope of 0 001 ft/ft The groundwater gradient in the deeper aquifer monitored by wells MW-104, 105 & 106 was also calculated for the three sounding events On April 28, 2003 the deeper aquifer gradient was S74°W with a slope of 0 0068 ft/ft, on May 23 it was S77°W with a slope of 0 0063 ft/ft, and on June 18 it was S85°E with a slope of 0 0012 ft/ft ' Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A Water table well gradient directions are shown on Figure 2A, 3A & 4A for the April, May and June 2003 events, respectively Wells MW-4 and MW-5 are excluded from the ' contouring due to anomalous values that contort the contours in the central portion of the site The deep well gradient directions for the same events are illustrated in Figures 213, 3B and 4B, respectively The historical water table gradients are illustrated in Figure 5A & 5B Groundwater Gradient Rose Diagrams for Water Table and Deep Wells, respectively The site's shallow aquifer displays highly variable shifts in groundwater direction It is noted that groundwater f direction has been predominantly to the southeast since additional wells were installed in May 2002 The deeper aquifer flow had been consistently to the east for the previous seven