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If the depth of well screen placement is not within two feet of the bottom of the boring,bentonite backfill shall be required from the bottom of the boring to within two feet of the base of the screen. Silica sand filter pack(#20-40 mesh)shall be placed in the annulus from two feet below the base of the well screen to three feet above the screen. The well screen shall be surged after initial filter pack placement and before bentonite seal placement to ensure any settlement occurs at that time. A five-foot thick bentonite seal shall be placed above the filter pack and hydrated for one hour before placing cement grout to the top of the well casing. Well surface completion shall consist of a minimum 8-inch protective steel monument flush mount designed for water well usage,and traffic rated,around the PVC well casing/riser to be very slightly above land surface and sloped away from the flush mount to shed rainwater away from the flush mount. The lid opening of the flush mount shall have a bolt-down cover. The protective flush mount shall be seated into the cement grout annular seal. The PVC well casing,completed to be inside the flush mount,shall be equipped with a locking cap. The Government will furnish the padlocks for each well. A metal well identification tag shall be stamped with the site well ID and state identification/permit number,and shall be affixed to the top of the well casing inside the flush mount. Well development shall be considered an integral component of each well installation. The purpose of well development is to remove sediment and turbidity from the well in order for future groundwater samples collected from the well to be representative of the native aquifer formation.Wells shall be sufficiently developed until very fine-grained sediment in the filter pack and nearby formation has been removed so that ground water samples are not highly turbid,and so that silting of the well will not occur. Wells shall be developed by mechanical surging, pumping,and bailing. In addition to development after the well is completed,pre-development shall be conducted by surging inside the well screen after filter pack placement but before bentonite seal and grout placement in order to settle filter pack. Bailers may be used to remove higher volumes of sediment from the well prior to use of the pump,and as a final step in development to ensure the bottom of the well is free of sediment accumulation. The surge block will have a diameter slightly less(approximately 1/8-inch)than the inside diameter of the well casing. Wells shall be developed no sooner than 48 hours after cement grout emplacement and not later than 7 days after cement grout emplacement. Development shall continue for a minimum of four hours or until the USACE field geologist or engineer determines that the well is adequately developed for sampling purposes. Assume maximum volume of development water from each well to be 300 gallons based on previous experience installing and developing similar wells on site. Discharge water during drilling and well development shall be temporarily contained and transported to reside in DOT approved 55-gallon steel drums at a centralized location within the fenced McCormick and Baxter site. 5.9. Task 8(Option)—Decommission Boring up to 300 Feet Depth. Decommissioning of borings in which wells are not to be installed shall be by pressure grouting with cement- bentonite mixture and a tremie pipe from bottom up. This optional task will not be awarded if all four wells are installed as planned. However,should real-time decisions to not complete one or more borings as wells be made, this option may be exercised. Boring decommission information shall be filed with the State of California as per State requirements. The total number of decommissioned borings may be 0, 1,or 2. 5.10. Task 9(Option)—Standby Time. This task may be exercised if there is a period of inactivity on-site by the Contractor caused by the Government. No more than 8 hours of standby time is authorized per work day. No more than 20 hours of total project standby time is anticipated. 5.11. Task 10(Option)—IDW Disposal,Each 55-Gallon Soil Drum Containing Hazardous Waste. This task covers the optional off-site disposal of any and all 55-gallon soil drums which must be disposed as hazardous waste. USACE will be responsible for sampling and analysis of investigation-derived waste(IDW)to determine disposal requirements. If based on Federal waste classification as per RCRA and 40 CFR requirements, and California Health and Safety Code(HSC)and California Code of Regulations(CCR)Title 22,any soil waste is listed as hazardous waste will be transported off site and properly disposed at a facility accepting such waste by the