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3.03.3 Borehole Diameter and Depth A. The borings for monitoring well installation shall have a minimum diameter of 8 inches and shall permit at least 2 inches of annular space between the boring wall and all sides of the centered riser pipe and screen. Approximate depths of individual borings are indicated on the drawings. The actual depth of the monitoring well will be established by the Engineer based on site conditions. 3.03.4 Screen,Well CasingfRiser Pipe Placement A. The monitoring well screen length shall be as shown on the drawings,with specified bottom cap securely attached, set to the appropriate depth. The bottom of the well screen shall be placed no more than 3 feet above the bottom of the drilled borehole. The well screen shall be placed in the borehole as shown in the drawings. The screen and well casing/riser pipe sections shall be joined by flush threaded watertight joints. The well casingtriser pipe shall extend upwards from the screen to an elevation as shown in the drawings. The well screen and riser pipe shall not be dropped or allowed to fall uncontrolled into the borehole. Joints and fastenings shall be watertight and flush threaded;-solvent glue or set screws shall not be used. The well shall be plumb, and centered in the hole by the use of stainless steel centralizers,in accordance with paragraph CENTRALIZERS. The centralizers shall be spaced 120 degrees apart at intervals not exceeding 50 feet along the length of the casing. Centralizers shall not be placed on the screened interval or within the bentonite seal. The alignment of the well shall be verified by passing a 5 foot long section of rigid pipe 1/4 inch smaller in diameter than the inside diameter of the casing through the entire well. If the pipe does not pass freely,the well will not be accepted. The pipe section shall be thoroughly cleaned with high pressure hot water prior to each test. Temporary casing, hollow stem augers or other measures shall be used, as necessary, to prevent collapse of the boring against the well screen and well casing/riser pipe prior to placement of the filter pack and sealing materials. A cap shall be installed on the top of the riser pipe. 3.03.5 Filter Pack Placement A. After the screen and well casing have been concentrically placed in the hole,the approved filter pack shall be constructed around the screen by filling the entire space between the screen and the wail of the hole over the selected screened interval. The lowermost 6 inches of filter pack shall be placed in the boring prior to installation of the well screen and shall serve Foothill Landfill Site Improvement Project 6 GROUNDWATER MONITORING WELLS San Joaquin County Public Works Section 02522