ARCHIVED REPORTS_XR0011605 - Laserfiche WebLink

Home Browse Search

{ 2.3 Monitoring Well Development and Sampling „r f3 Monitoring Wells MW-8 through MW-12 were developed on August 31, 1998 bV removing 10 casing volumes using an above-ground, diaphragm pump. Field procedures for groundwater monitoring well development are presented in Appendix E. Well development data is presented in the field survey forms in Appendix F. Monitoring Wells MW-1 through MW-6 and MW-8 through MW-12 were sampled on September 3, 1998. The wells were purged of at least 3 well casing volumes while monitoring pH, specific conductivity, and temperature parameters at maximum intervals of two gallons before sample collection. Groundwater parameters were collected using a Aquacheck Model 51500 water analyzer meter with pH calibrated on a daily basis and specific conductivity and temperature calibrated on a weekly basis. Dissolved oxygen concentration was measured in each sample collected with a disposable bailer before and after purging each well using a YSI Model 55 meter that was calibrated on a daily basis. The samples were transported in an iced cooler to a state-certified laboratory with chain of custody procedures. Field observations during well sampling are presented in the sampling forms in Appendix F. 2.4 Groundwater Level Measurement and Well Surveying The top of casing of each well was surveyed by a licensed surveyor in reference to a City of Lathrop benchmark and relative to mean sea level. On September 3, 1998, the depth to groundwater in the wells was measured from the top of the well casing to the nearest 0.01 foot, using an electronic water level indicator. The survey data and groundwater elevations are presented in Table 1. The well elevation survey map is included in Appendix E, and the groundwater elevation measurements obtained on September 3, 1998 are shown on Figure 3. 2.5 Destruction of Monitoring Well MW-7 The SJCEHD required that Monitoring Well MW-7 be destroyed because it was paved over during improvement of a highway on-ramp . Well MW-7 was paved over between the September 1993 and January 1994 sampling events. The well was located, repaired, and sampled in February 1995,but was again paved over before the next sampling event. Before well destruction, a permit was acquired from the SJCEHD and an encroachment permit from the City of Lathrop. Copies of the permits are included in Appendix B. On August 16, 1998, MW-7 was destroyed by overdrilling to the total depth of the boring using an 8-inch-diameter hollow-stem auger. Well MW-7 was constructed using 2-inch-diameter PVC casing to a depth of 20 feet. After overdrilling and removing the well vault, the borehole was tremie grouted by inserting a 1-inch-diameter pipe to the bottom of the borehole and then filling with neat cement from the bottom to approximately 3 feet below grade. The neat cement was allowed to set for at least 72 hours before the borehole was filled with a 2-sack sand slurry to within one foot below grade. After an additional 72 hours, the borehole was filled to grade with Type A asphalt. A copy of the boring log for MW-7 is included in Appendix D. 5