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<br />entrainment from water cascading down the open hole. The original pump column was <br />frequently used for the drop pipe. This saved costs and usually delivered the surface water _ <br />to the right level for injection. The sites that used a gooseneck on the delivery line allowed .. <br />the drop pipe to operate without hammering and air locking. This also maintained a full <br />pipe of water in the approach to the injection well so that the flow meter could operate <br />accurately. The first goosenecks used were about 18 inches high; however, testing proved <br />goosenecks from 30 to 36 inches high are more effective. <br /> <br />An air Ivacuum release valve at the top of the gooseneck permits trapped air to be released <br />when starting to inject water into the well. More importantly, it allowed air into the system <br />to prevent developing a vacuum if anything less than the maximum volume than the well is <br />capable of taking is being delivered. At flows of less than full capacity, the siphon effect of <br />the drop pipe can create enough vacuum in the line to collapse it. As a result, the project <br />injection wells were fitted with a simple 3/4-inch ball valve in the top of the gooseneck. <br />This valve was positioned manually as needed. Automatic air Ivacuum release valves are <br />available and could also work in this application, eliminating the need for manual <br />adjustments. <br /> <br />Site 1- Upper Cottonuwod.-Cottcnvlood Creek, the water source for this site; is an inter- <br />mittent stream fed by snowpack and springs in the mountains to the south and west of the <br />groundwater recharge site. <br /> <br />Conveyance facilities consist of a diversion structure on the creek; an open, earthen channel <br />to a sedimentation pond; an intake or control structure which includes a weir to divert . <br />water from the sedimentation pond to the injection well; piping from this structure to the <br />well; the connection to the injection well; and the injection well itself. <br /> <br />An earthen sedimentation pond was constructed to remove silt materials in the injection <br />water. There was no precise formula followed for sizing this and other project sedimenta- <br />tion ponds. Ponds needed to be large enough so that they: <br /> <br />. Were quiescent without obvious currents <br />. Had enough storage for sediment so that frequent cleaning was not needed <br /> <br />The injection well was completed to a depth of 692 feet (sediments from 0-240 feet and <br />limestone from 240-692 feet). The observation well is completed to a depth of 724 feet <br />(sediments from 0-130 feet; rhyolite from 130-434 feet; and limestone from 434-724 feet). <br />Monitoring wells were installed to intersect the same geologic limestone zone as the <br />recharge wells to provide representative monitoring information. None of the wells <br />required cleaning, rehabilitation, or additional construction. The injection well was <br />adequately cased to stabilize the well in the limestone zone. <br /> <br />Site 2 - Lower Cottoflwood.-Cottonwood Creek is also the water supply source for this site <br />further downstream. Spring runoff flows are usually in excess of what can be injected at the <br />Upper Cottonwood site. An open diversion channel from the creek continues on past the <br />Upper Cottonwood site for approximately 1 mile to this site. <br /> <br />. <br /> <br />4 <br />