WORK PLANS - Laserfiche WebLink

Home Browse Search

Section 2 0 Groundwater Monitoring Well Installation Surface Seal—All reasonable attempts will be made to place a neat cement or cement grout sanitary seal from the ground surface to a minimum depth of 20-feet bgs and extending to the top of the bentonite transition seal. However, where shallow groundwater occurs above 24-feet bgs, the well will be constructed to provide the maximum length of sanitary seal and in no case will the sanitary seal be less than 5-feet deep. Figures 2 and 3 depict the typical monitoring well completion details anticipated for the site. Additionally, special attention shall be given to the construction of the monitoring well to minimize the potential for contamination of any materials used in the installation. 2.6 WELL DEVELOPMENT The drilling contractor will develop the wells using a combination of methods. Where practicable and where formations stability permits, well development by gently swabbing the well with a surge block will be initiated before the installation of the bentonite transitional seal or neat cement/cement grout sanitary seal to ensure settling of the filter pack prior to sealing the annulus. Once the seal has been installed and sets up for no less than 12 hours, further development by vigorously swabbing the well with a surge block and manual bailing will ensue and continue until the concentration of suspended solids in the water bailed from the well is sufficiently low to permit pumping with a portable submersible pump. Accumulated fill shall be removed from the bottom of the well screen. Development will continue until the discharge water runs clear and/or field measured turbidity is 5 n.t.u., or less. During the pumping phase of well development, the pump will be moved up and down the entire length of well screen, maximizing the removal of accumulated fines. Water generated from the well during development will be discharged directly to land. 2.7 WELL DISINFECTION It has been ECO:LOGIC's experience that the effectiveness of well disinfection procedures vary. Even when newly installed wells are monitored following initial disinfection it is not uncommon for coliform to initially decline however, then rebound during subsequent monitoring. This is likely attributable to the efficiency of the disinfection procedures, which are limited to the transmission of the disinfectant throughout the borehole, filter pack, and adjacent geologic materials,which may have been contaminated during well drilling/construction. Additionally, the introduction of other sources of water and chemicals may influence sensitive water quality monitoring and generally should be avoided unless absolutely necessary. Furthermore, total coliform organisms are commonly used as an indicator parameter only, due largely to its non- conservative transport in the presence of appreciable fine grained sediment and its abundant presence in the natural environment. As such, the proposed monitoring wells will not be disinfected unless monitoring results indicate persistently elevated densities of coliform organisms present over three consecutive quarters of groundwater monitoring. Recommendations for subsequent disinfection procedures will be presented within the wastewater facility's quarterly or annual groundwater monitoring report(s), should coliform densities fail to decline April 2007 City of Ripon Wastewater Treatment Facility 25 Groundwater Monitoring Well Installation Workplan