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CITY OF LATHROP 5. Individual well casings shall have a minimum two(2)separation between other casings and borehole wall (Figure 3). 6.The casing shall be suspended in tension from the surface by means of an appropriate hanger or clamp. The bottom of the casing shall be at a sufficient distance above the bottom of the reamed hole to ensure that none of the casing will be supported from the bottom of the hole. 7. Circulation through the tremie pipe shall continue during the casing installation. 8. If, for any reason, the casing cannot be landed in the correct position or at a depth acceptable to the City, the Contractor shall remove the casing, recondition the borehole and reinstall the casing to the specified depth. If the casing cannot be removed from the borehole the contractor shall construct another well immediately adjacent to the original location and complete the well in accordance with these Technical Provisions at no additional cost to the City. The abandoned hole shall be sealed in accordance with these Technical Provisions and in accordance with any laws pertaining to proper well abandonment at no additional cost to the City. 9. If any of the casing assembles collapse prior to well completion, the remaining hole shall be abandoned in accordance with these Technical Provisions at no cost to the City. A replacement borehole and well shall be drilled and constructed at an adjacent location as directed by the City. 2.3.6 GRAVEL ENVELOPE AND INTERMEDIATE BENTONITE SEALS A. Scope -- This item shall consist of providing and installing gravel or coarse-grained sand opposite the screen intervals and intermediate bentonite or sand/cement seals between the screen intervals, as specified by the Engineer, in the annulus between the casing and screens and the well bore of each well. Intermediate bentonite seals may be used in saturated zones. Sand/cement grout shall be used for intermediate seals in unsaturated zones. B. Methods 1. Prior to placement of the gravel pack and intermediate seals in the well, the drilling fluid shall be thinned with clean water. Thinning shall be accomplished by reducing the viscosity of the drilling fluid in the sump to a maximum marsh funnel viscosity of 30 seconds and a maximum weight of 8.9 pounds per gallon by the addition of clean water to the sump. The Contractor shall avoid the direct injection of water into the well bore through the tremie pipe in order to prevent unbalancing the fluid consistency in the borehole. 2. Gravel packing and sealing material shall be pumped or gravity fed through the tremie pipe. The gravel pumping system shall consist of a hopper, which will allow for the LUHDORFF&SCALMANINI CONSULTING ENGINEERS 14