USGS_GeophysicalLoggingInSLV_Report

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The inflections in both the free-flowing and The water level measured in well ALA.8 is a shut-in flowmeter measurements occur at similar composite measurement of the heads in the lower depths, so under free-flowing and shut-in conditions, (760?1,250 ft) and the upper (650?760 ft) flow zones. significant head differences are not present between the flow zones open to this well. The water level Well ALA.9 measured in ALA.6 represents a composite of head Well ALA.9 is an intermittently flowing well. conditions in several permeable layers over an interval The 6.2-inch-diameter casing extends from land of 271 ft in the confined-aquifer system. surface to a depth of 26 ft and the well is uncased from 26 to 130 ft. A lithologic log was not available for this Well ALA.8 well (fig. 9). The free-flowing trolling flowmeter log indi- Well ALA.8 has 17.0-inch-diameter casing from cates that most inflow to this well occurs at depths land surface to a depth of 91 ft, 14.0-inch-diameter from about 114 to 130 ft. Discharge from the well casing from 91 to 513 ft, and 10.0-inch-diameter during the time the flowmeter log was being recorded casing from 513 to 1,301 ft. Three intervals contain was about 5 gal/min. A decrease in specific conduc- torch-cut slots: (1) 578 to 663 ft, (2) 683 to 1,080 ft, tance indicates that inflow may occur at a depth of and (3) 1,100 to 1,301 ft (fig. 8). A lithologic log was about 74 ft, although the flowmeter did not detect not available for this well. inflow at that depth. A spinner flowmeter was used to measure flow Inflow to well ALA.9 occurs in a fairly narrow in this well because the EM flowmeter was not avail- depth interval from 114 to 130 ft, even though the well able. The free-flowing trolling flowmeter did not is uncased over the entire interval from 26 to 130 ft. detect flow below 1,280 ft as indicated by the trace of The water level measured in ALA.9 is a composite the flow log matching the tool-velocity line below head measurement derived from the relatively long 1,280 ft. The decreases in flow indicated by the free- uncased interval in this well. flowing trolling flowmeter log at 91 ft and 513 ft are caused by changes in casing diameter at those depths. Well ALA.10 Specific-conductance, temperature, and free- Well ALA.10 was constructed in 1964 for irriga- flowing trolling flowmeter logs show several fairly tion use and is a flowing well. The casing is 12.0-inch narrow zones of inflow at depths of about 1,000, diameter from land surface to a depth of 824 ft and 1,070, 1,125, 1,200, and 1,250 ft. The free-flowing 9.0-inch diameter from 824 to 2,067 ft. The intervals trolling flowmeter log also shows inflow zones at a containing torch-cut slots (907 to 1,189 ft; 1,228 to depth of 650 ft and from 720 to 760 ft that are not indi- 2,015 ft) are open to lithologic layers containing cated on the specific-conductance and temperature (1) sand or gravel with some clay or (2) sand, gravel, logs. or cobbles (fig. 10). These lithologic layers contrib- uting water to the well occur below a 603-ft-thick Shut-in stationary flowmeter measurements layer of clay with some sand or gravel that is present show upflow in the well originating below a depth of from 93 to 696 ft. 1,100 ft. Much of the inflow measured below a depth of 760 ft exits the well at depths from 650 ft to 760 ft, The temperature and free-flowing trolling flow- but there was still measurable flow at a depth of 525 ft. meter logs indicate four inflow zones in this well at These stationary flow measurements indicate that depths from 900 to 940 ft, 1,440 to 1,600 ft, 1,700 to during the time the measurements were being 1,860 ft, and 1,880 to 1,980 ft. Under shut-in condi- recorded, the head in the lower zone (below 760 ft) tions, the stationary flowmeter measurements indicate was higher than the head in the upper zone (above 760 inflow from 1,400 to 2,067 ft and outflow from 907 to ft). This head difference could occur if the flow zone 1,200 ft. The decrease in flow recorded in both flow- from 650 ft to 760 ft was more transmissive than the meter logs at a depth of 824 ft is caused by the change flow zone from 1,000 ft to 1,250 ft and the head in the in casing diameter at that depth. Outflow into the zone upper zone decreased due to loss of pressure during from 907 to 1,200 ft may occur to equalize the differ- free-flowing conditions. ence in heads among the flow zones below 1,400 ft ANALYSIS OF GEOPHYSICAL LOGS 15