Dewatering sys tern
(1) Deep-well system. The clay and sand strata below elevation -13.0 feet are continuous over a large area. Removal of soils above elevation -25.0 feet. A deep-well system shall be provided to relieve this pressure. The pressure shall be relieved in the sand strata such as those indicated on boring S-II-SS-1-62(A) from 67.5 to 72.0 feet and from 85.5 to 142.5 feet. These strata will vary in elevation and thickness over the area. The deep-well system shall be of sufficient capacity to lower the hydrostatic head to elevation -40.0 feet as measured in observation wells at nine points in the excavation. One installed spare deep well, complete and ready for immediate operation, shall be provided for each two operating wells. The use of gasoline prime movers will not be permitted in the operation of deep wells. At each of the nine points two observation wells shall be installed. One observation well shall be installed with the screen in the upper sands, and one observation well shall be installed with the screen in the lower sands. The riser pipe for the observation wells will be 2-inch pipe in 5-foot sections. One of the observation points shall be constructed at coordinate N254 460, E260 065. The remainder of the observation points will be located by the Contracting Officer after the dewatering plan is submitted. The exact tip elevation of all observation wells will be established after the dewatering plan is submitted; however, the tip elevation in the lower sand will be at least 100 feet below original ground surface, and the tip elevation of the observation wells in the upper sands will be approximately 70 feet below original ground surface. The Contractor shall maintain the observation wells and keep daily records of readings until otherwise directed by the Contracting Officer.
(2) Wellpoint system. A wellpoint system shall be used above the top of clay shown on the borings at approximate elevation -14.0 feet but to dewater the area from original ground surface to the top of the clay. This system shall have sufficient capacity to lower the head within the excavation to the top of the clay.
c. Available soil test data and pumping test data. The soil test data obtained by the Government are shown on the boring logs. Additional laboratory data and samples of the soils from borings shown in the plans are available in the District office for inspection by bidders. Typical permeability data from laboratory tests at this site are tabulated. Pumping tests have not been made at the site; however, the soil profile at the B-l and B-2 test stand excavation is similar to this site and this excavation is now being dewatered by a deep-well system. Data on this system can be inspected
at the office of the Area Engineer or in the District office.
d. Standby equipment. The Contractor shall furnish standby pumping equipment power as follows:
(1) Diesel, liquid petroleum gas, and gasoline fueled prime movers for pumps shall have 50 percent standby equipment.
(2) Portable electric generators shall have 100 percent standby generating equipment.
(3) Commercial electric power, which is available at the site, shall have 100 percent standby electric generating equipment.
(4) The Contractor shall provide not less than one complete spare pumping unit for every five pumping units other than deep-well pumps in the system. In no case shall less than one standby pumping unit be provided. The sizes of the standby pumping units shall be subject to the approval of the Contracting Officer.
e. Damages. The Contractor shall be responsible for, and shall repair without cost to the Government, any damage to work in place, the other Contractors’ equipment, and the excavation, including damage to the bottom due to heave and including removal of material and pumping out of the excavated area that may result from his or her negligence, inadequate or improper design and operation of the dewatering system, and any mechanical or electrical failure of the dewatering system.
f. Maintaining excavation in dewatered condition.
(1) General. Subsequent to completion and acceptance of all work, including piling and concrete work, in the excavated area, the Contractor shall maintain the excavation in a dewatered condition and the water level in the observation wells at the specified and approved elevation until such time as the succeeding Contractor commences dewatering operations, and a written directive to cease pumping operations has been received from the Contracting Officer. System maintenance shall include but not be limited to 24- hour supervision by personnel skilled in the operation, maintenance, and replacement of system components; standby and spare equipment of the same capacity and quantity as specified in f above; and any other work required by the Contracting Officer to maintain the excavation in a dewatered condition. Dewatering shall be a continuous operation and interruptions due to outages, or any other reason, shall not be permitted.
(2) Responsibility. The Contractor shall be responsible for all damages to accepted work in the excavation area and for damages to any other area caused by his or her failure to maintain and operate the system as specified above or from water overflowing his or her ditch.
g. System removal. Upon receipt of written directive to cease dewatering operations from the Contracting
Officer, the Contractor shall remove all dewatering equipment from the site, including related temporary electrical secondary as approved by the Contracting Officer. All wells shall be plugged and/or filled, Removal work required under this paragraph does not include any of site cleanup work as required elsewhere in these specifications.
h. Method of measurement. Dewatering, as specified in k(2) below, to be paid for will be determined by the number of calendar days (24 hours), counted on a day – to-day basis, the excavation is maintained in a dewatered condition, measured to the nearest hour, from completion and final acceptance of the concrete foundation for the A – 1 test stand area to the date on which a written directive to cease pumping operations is received from the Contracting Officer.