Installation of jet-eductor wells
(a) Location and depth of wells. The jet-eductor wells shall be installed at the designated locations. Soil conditions where the jet-eductor wells are to be installed are depicted in a general way by the logs of borings made around the excavation. The wells should extend about 2 feet below the bottom of the pervious strata being drained. The required depth of the wells may vary considerably from those indicated on the drawings.
(b) Drilling and jetting. The jet-eductor wells shall be installed in the following manner:
Step 1. Predrill a 10- or 11-inch hole 2 feet below the silt or silty sand stratum to be drained. Hydraulic rotary, or auger, methods of drilling may be used. No drilling muds or additives, other than clear water, shall be used in drilling the hole for the well. The hole shall be kept full of water during the predrilling, and withdrawal of the auger, so as to minimize caving.
Step 2. After predrilling the hole to grade, it shall be washed out by driving and jetting (with clear water) a 12-inch “sanding casing” with a hole puncher to the bottom of the predrilled hole.
Step 3. After the “sanding casing” is driven and jetted to the required depth, it shall be washed clean by jetting with clear water. The jet pump, pipe, and hose shall be of sufficient capacity to produce an upward velocity inside the casing to efficiently remove all material in the casing, so that the well screen and riser can be set to grade. The “sanding casing” shall be kept filled with water until the well screen and filter sand have been placed so as to prevent any “blow in” of the bottom of the hole.
(c) Installation of well screen and filter sand. After the sanding casing has been cleaned by jetting and the clear depth in the casing checked by sounding with an approved device, the well screen shall be lowered to the bottom of the casing. Particular care shall be exercised in handling and placing the screen so as not to damage it. Complete assembly of the screen and riser pipe on the ground’surface will not be permitted. Two or three connections shall be made to the assembly as it is placed in the casing. Approved centralizers shall be furnished and attached to the screen at intervals not greater than 20 feet. The design and attachment of the centralizers to the well screen shall be submitted to the C. O.R. for approval. The top of the riser pipe shall be securely covered or capped to prevent the filter sand from falling into the well. The method of placement shall assure a fairly rapid, continuous, uniform rate of placement of filter sand, which will evenly distribute the filter sand around the screen. The rate of placing the filter sand shall not cause bridging of the sand in the “sanding” casing. As the filter material is placed in the well screen, 70 percent granular calcium hypochlorite shall be added to evenly distribute a minimum of 2 pounds per ton of filter. The method of placement shall be approved by the C. O.R.
(d) Development of jet-eductor wells. Within 12 hours after installation of each well, it shall be developed by means of air-lifting. A 2-inch inner diameter air line shall be lowered in the well to within 1 foot of the bottom of the well and sufficient air be pumped through the air line to cause the well to flow. For low – yielding wells, it may be necessary to add clear water to help develop the well and remove any sand that may have entered the screen. Air-lifting shall continue until all sand or filter material is removed from inside the screen and water from the well flows clear. Each well shall be developed for a minimum of 20 minutes.
(e) Chlorination of well. Upon completion of installation of the well and prior to installing a cap on the top of the riser, a minimum of 3 pounds of 70 percent granular calcium hypochlorite shall be dropped into the well,
(f) Well top. The 4-inch riser shall extend 6 inches above the ground surface and shall be sealed around the riser pipe for the jet-eductor pump. The well number shall be painted on the top of the riser pipe.
(g) Riser pipe. The 4-inch riser pipe for the wells shall be 15 feet in length. The filter sand shall extend to within 8 to 10 feet of the berm surface; the space around the riser pipe from the filter to the berm surface shall be grouted with an approved bentonite-cement grout.
(h) Well records. A report showing depth, elevations, date of installation, approximate rate of flow during development, and any other data concerning installation of each well will be completed by the C. O.R. The water level in the well shall be recorded at the time of installation. The Contractor shall assist in obtaining the installation data. If the jet-eductors or pumps appear to be losing their efficiency with the passage of time, the Contractor may be required to redevelop and/or chemically treat the wells as directed by the Contracting Officer, the cost of which will be paid for under paragraph 3 (Changes) of the General Provisions of the Contract.