Installation of well screen and riser
Step 1. Assembly. The joints between the screen sections and between the screen and riser pipe shall be welded with stainless steel rod. Particular care should be exercised to avoid damaging the screen and riser. It shall be centered in the well hole or casing and held securely in place during placement of the filter by means of spiders and approved centering guide, tremie holder, or other approved method. Prior to installation of any screen and riser the Contractor shall submit to the Contracting Officer for approval full details of the method, equipment, and devices he proposes to use for centering and holding the screen and riser pipe in the well hole.
Step 2. Install&ion. The assembled screen and riser pipe shall be placed in the well hole in such a manner as to avoid jarring impacts and to insure that the assembly is not damaged or misaligned.
Step 3. Alignment. Each completed well shall be sufficiently straight and plumb that a cylinder 10 feet in length and 2 inches smaller in diameter than the inside diameter of the well may be lowered for the full depth of the well and withdrawn without binding against the sides of the screen or riser pipe. A variation of 6 to 12 inches will be permitted in the alignment of the screen and riser pipe from a plumb line at the top of the well; however, this will not relieve the Contractor of the responsibility of maintaining adequate clearance for bailing, surging, and pumping required for pumping the wells.
(d) Placement of sand filter (A). After the screen and riser pipe have been placed, the filter sand shall be trended into the annular space between the well screen or riser pipe and the drilled hole using a 4- or 5-inch-diameter tremie pipe with flush screw joints and at least two slots Vie inch wide and about 6 inches long per linear foot of tremie. The tremie pipe shall be lowered to the bottom of the hole and then filled with filter sand. (If the filter sand has a tendency to segregate, the filter sand shall be kept moist following delivery to the work site in order to minimize segregation.) After the tremie has been filled with filter sand, it shall be slowly raised, keeping the tremie full of filter sand at all times until the filter sand has filled the hole up to within 15± feet of the ground surface. The bottom of the tremie pipe shall be kept slightly below the surface of the filter sand in the hole as the tremie is raised.
(e) Development of well. After installation of the well, it shall be developed by surging with a surge block and pumping, as described below, for not less than 30 minutes. (If Revert or equivalent approved organic drilling additive has been used in drilling the hole, a breakdown agent such as Johnson’s Fast-Break or equivalent shall be added to the well in accordance
with the manufacturer’s recommendations prior to surging.) Development of the well shall be started within 4 to 12 hours after the well has been installed. Surging of the well shall be accomplished with a surge block raised and lowered through the well screen at a speed of 2 to 3 feet per second. The gaskets on the surge block shall be slightly flexible and have a diameter about 1 inch smaller than the inside diameter of the well screen. The amount of material deposited in the bottom of the well shall be determined after each cycle (about 10 to 20 trips per cycle). Surging shall continue until the accumulation of material pulled through the well screen in any one cycle becomes less than 0.2 foot. The well screen shall be bailed clean with a piston-type bailer when the accumulation of material in the bottom of the screen becomes more than 2 to 3 feet at any time during surging; the well shall also be cleaned after surging is completed. After completion of surging, the well shall be pumped with the pump section about 1 foot off the bottom of the well until the discharge is clear and is reasonably free of sand (less than 10 to 20 parts per million sand). Such pumping shall begin within 2 hours after surging and shall continue for not less than 30 minutes. The well shall be pumped so as to achieve a drawdown of not less than 20 feet, or a flow of approximately 1000 gallons per minute, whichever is first. If, at the completion of pumping, the well is producing sand at a rate in excess of 10 to 20 parts per million, it shall be resurged and pumped again, Alternate surging and pumping shall be continued until material entering the well during either surging or pumping is less than the amount specified above, but not for a period longer than 6 hours. Wells which continue to produce an excessive amount of sand or filter material during development shall be abandoned as requested by the C. O.R. except that, if he or she so elects, he or she may request the Contractor to continue to develop the well by an approved method. If, after such further development, a well meets the above stated requirements, it shall be completed, and after successful completion of the required pumping test, the well will be accepted. If, after completion of all surging and pumping, there is more than 0.5 foot of material in the bottom of the well, such material shall be carefully removed with either a piston-type bailer or by pumping. The water resulting from pumping the well shall be discharged outside the work area at locations approved by the C. O.R. Pertinent data regarding installation of the wells will be recorded by the C. O.R. After completion of satisfactory development of a well, the grout seal shall be placed.
(g) Disinfection of drill hole and filter sand. During the drilling operation, a minimum of 1 pound of calcium hypochlorite shall be added to the drilling fluid every 2 hours. As the filter sand is placed in the
well, calcium hypochlorite shall be added to evenly distribute a minimum of 2 pounds per ton of filter. Upon completion of development of the well and prior to installing the well cover, a minimum of 5 pounds of granular 70 percent calcium hypochlorite shall be dropped in the well and allowed to settle to the bottom.
(h) Covers. The top of a well shall be sealed immediately after completion of installation with a watertight seal which shall be kept in place at all times, except during cleaning and pumping operations, until the pump and gear drive are installed.
(i) Abandoned wells. Holes for wells abandoned prior to placement of well screen and riser pipe shall be filled with sand and cement grout. Wells abandoned after placement of well screen and riser pipe may be pulled and the remaining hole filled with sand to within 25 feet of the surface. The remaining 25 feet should then be backfilled with an approved cement grout. Bentonite may be added to the grout to improve its pumpability. If the Contractor elects to leave an abandoned well screen and riser in place, it shall be plugged as described above. Wells which are abandoned as a result of alignment or plumbness being outside of these specifications, or wells which produce sand in excess of 5 parts per million after development and pump testing, shall be replaced by the Contractor at no cost to the Government.
(j) Well records. The following information regarding the installation of each well will be recorded by the C. O.R. The Contractor shall cooperate and assist the C. O.R. in obtaining the following information: well number, location, top of riser (mean sea level), date and time test started and stopped, depth to water in well before and at end of pumping, elevation of water in well immediately before and at end of pumping, flow in gallons per minute, depth of sand in well before and after completion of pumping, rate of sanding at end of pumping period, depth of sand in well after cleaning, screen length, depth of hole, inside depth of well, depth to sand in well after cleaning, top of well screen (mean sea level), top of filter (mean sea level), bottom of well (mean sea level), top of well, method of surging, material surged into well (last cycle) in feet, total material surged into well in feet, rate of pumping and drawdown, total pumping time, and rage of sand infiltration at end of pumping in parts per million.
(3) Pumping test on each well.
(a) Upon completion of installation, surging, and developing pumping, each well shall be subjected to a pumping test. Prior to commencement of the pumping test, and again after completion of the pumping test, the depth of the well shall be measured when the C. O.R. is present by means of an approved flat-bottom sounding device.
(b) The pump shall be capable of pumping at the rate of 1500 gallons per minute, over a period of time sufficient to satisfactorily perform the pumping test specified. An approved means for accurately determining the water level in the well and a calibrated flow meter or orifice of standard design for the purpose of measuring the discharge from the well during the pumping test shall be provided. The Contractor shall furnish and install the necessary discharge line so that the flow from the well can be pumped into an adjacent area approved by the C. O.R. The pumping and sand infiltration test shall be conducted in the presence of the C. O.R., who will record the following test data: well number, location, top of riser (mean sea level), date and time test started and stopped, depth to water in well before and at end of pumping, elevation of water in well immediately before and at the end of pumping, rate of sanding at end of pumping period, and depth of sand in well after cleaning.
(c) The Contractor shall test each well by pumping continuously for a minimum of 2 hours. Pumping shall be at a constant rate sufficient to produce either a drawdown of 20 feet, or a constant rate of flow of 1500 gallons per minute, whichever occurs first. The computed rate of sanding shall take into consideration the pumping rate, the rate of sand emerging from the pump, and the amount of emptying or buildup of sand in the bottom of the well during the (sand) testing period as determined accurately with a flat-bottom sanding device. No test pumping of a well will be permitted concurrently with drilling, surging, or pumping of any other well within 300 feet thereof.
(d) In the event that sand or other materials infiltrate into the well during the pumping test, the following procedure will be followed: If the rate of sand infiltration dumg the last 15 minutes of the pumping test is more than 5 parts per million, the well shall be resurged by manipulation of the test pump for 15 minutes after which the test pumping shall be resumed and continued at the rate specified above until the sand infiltration rate is reduced to less than 5 parts per million. If at the end of 6 hours of pumping the rate of infiltration of sand is more than 5 parts per million, the well shall be abandoned unless the C. O.R. requests the Contractor to continue to test pump and perform such other approved remedial work as he considers desirable. If, after such additional test pumping and other remedial measures, the sand infiltration rate of the well is reduced to less than 5 parts per million, the well will be accepted. Upon completion of the pumping test, any sand or filter material in the bottom of the well shall be removed by pumping or with a piston-type bailer.
(4) Installation of pump and chlorination. Each dewatering well shall be chemically treated with calcium hypochlorite (chlorine) within 24 hours after the test pump is removed, A solution of calcium hypochlo – rate (HTH) shall be mixed with water in a tank (minimum capacity of 3000 gallons to obtain a 1000-parts – per-million chlorine solution). (Fifteen pounds of (dry) 70 percent calcium hypochlorite will make 1000 gallons of 1000-parts-per-million chlorine solution.) A minimum of 30 gallons per foot of screen shall be pumped into the well through a hose extended to the bottom of the well. As the chlorine solution is pumped into the well, the hose shall be withdrawn at a rate which will insure that the chlorine solution is added uniformly from the bottom of the well to a point 10 feet above the top of the well screen. The chlorine solution in the well shall then be surged with a loose fitting surge block for 1 hour. The permanent dewatering pump shall then be immediately installed, and the well pumped until the chlorine is essentially removed. (If it is not possible to promptly install, the permanent pump, the chlorine should be allowed to set 3 or 4 hours, and the well pumped by some means to remove the chlorine.) If the permanent pump is subsequently installed, the well and pump shall be rechlorinated as described above except the surging shall be omitted.