ARCHIVED REPORTS XR0005572 - Laserfiche WebLink

Home Browse Search

. 23 Monitoring Well Installation, Development, Sampling and Analysis In the three 8-inch diameter soil borings, 2-inch diameter groundwater monitoring wells were installed One of the monitoring wells, MW-1 was located approximately 40 feet east of the former UST excavation The second monitoring well, MW-2 was positioned approximately 80 feet west of the former UST excavation The third monitoring well (MW-3) was located approximately 180 feet south of the former UST excavation to evaluate the potential migration of the plume of impacted groundwater toward the nearest municipal water well, approximately 600 feet southeast of the site 2 3 1 Monitoring Well Construction Each of the three wells was constructed of 15 feet of two-inch diameter, Schedule 40, flush- threaded and machine-slotted (0 020-inch) polyvinyl chloride (PVC) well screen In MW-1 and MW- 3, the well screen interval ranged from 10 to 25 feet bgs In MW-2, the well screen extends from 8 5 to 23 5 feet bgs Blank PVC casing was threaded into the top of each of the well screens and extends to ground surface A filter pack of Monterey#3, graded and washed sand was placed through the hollow stem augers as they were slowly retrieved and until the sand pack reached approximately 2 feet above the top of • the screened interval Overlying the sand pack, 2 feet of hydrated bentonite pellets were placed within the annular space, between the borehole and the well casing Over the hydrated bentonite, a surface seal of neat cement was installed The tops of each of the wells were secured with water- tight locking caps and traffic-rated, flush-mount street boxes 2 3 2 Monitoring Well Development and Elevation Survey Each of the wells was surged by the driller, following the placement of the sand packs and prior to the installation of the well seals On June 2, 1998, after the monitoring wells were completed and the seals had sufficient time to set (at least 72 hours), the wells were fully developed and sampled Prior to developing the wells, the well volumes were calculated and documented To complete the well development, the wells were pumped with a downhole electric pump until at least 5 well volumes were purged and groundwater temperature, pH and electrical conductivity had stabilized The well development, monitoring and sampling field data are noted on Groundwater Monitoring and Sampling Forms (Appendix B) The elevation of each of the newly-installed wellheads was surveyed by Morrow Surveyors, a state of California licensed land surveyor (#5161) The surveyor measured the top of the well casings to i