Home Archived October 29, 2018
(i)

South Florida Information Access (SOFIA)


publications > water resources investigations > report 90-4108 > estimates of transmissivity and hydraulic conductivity > tests conducted during this study


Estimates of Transmissivity and Hydraulic Conductivity

Tests Conducted During this Study

Abstract
Introduction
Study Area
Aq. Framework and Definitions
Estimates of Transmissivity and Hydraulic Conductivity
- Production Wells
- Earlier Aq. Tests
> Tests this Study
Hydrogeology
Ground-Water Flow System
Summary and Conclusions
References Cited
Plates
The field tests may be divided into two types: single-well aquifer tests in which only the pumped wells were used for observations of response in the production zone; and multiple-well aquifer tests, in which one or more separate observation wells in the pumped zone were also monitored. The single-well aquifer tests included step drawdown, drawdown recovery, and specific capacity. Discharge as much as 1,000 gal/min was obtained by use of a 6-in, suction pump, and discharge as much as 500 gal/min was obtained by a 4-in. pump. Well construction data, transmissivities, and hydraulic conductivities obtained from the aquifer tests are listed in table 5. The test sites are shown in figure 9. The wells were installed using an air-circulation method (no drilling mud). As a result, clogging of pore spaces or cavities and the effects of clogging on the test results were minimized.

Step-drawdown tests were conducted at sites with moderate to high transmissivities. For zones that had high transmissivity, pumping rates typically were about 350, 530, 730, and 950 gal/min, but for zones that had low transmissivity, the pumping rates were reduced as needed. For the lowest transmissivity zones, only specific-capacity tests were conducted at low pumping rates to minimize well losses. The step-drawdown tests were usually run as independent cycles (30 minutes of pumping followed by a recovery period for each cycle). The Biscayne aquifer recovered within 1 or 2 minutes, which was much too quickly to provide satisfactory measurements during the recovery. However, because recovery was slow in the gray limestone aquifer drawdown-recovery tests, step-drawdown tests were performed at most sites.

Jacob (1947) expressed drawdown in a pumped well by the relation:

SW = BQ + CQ2   (6)

where

SW is drawdown in pumped well,
BQ is aquifer loss term,
CQ2 is well-loss term,
B, C are constants, and
Q is discharge.

The step-drawdown test is a method of evaluating the aquifer loss (B) and well loss (C) constants and assigning proportional amounts of drawdown (head loss) to the aquifer and to the well. Bierschenk (1963) used the relation between SW /Q and Q to determine B (the Y-intercept) and C (the slope of the line). Once B is determined, the specific capacity of an ideal well (one that measures only aquifer losses) can be calculated from Q/s = 1/B, and a transmissivity can be estimated from this specific capacity. The average constant 270 was used, as before, for the Biscayne aquifer.

Aquifer tests were performed at five sites with one or more observation wells in the production zone. The observation wells were placed near the pumped wells to minimize the effects of leakage and to obtain measurable drawdowns. The observation well data were analyzed by a nonleaky semilog drawdown method described by Cooper and Jacob (1946) and by the recovery method (Theis, 1935; Todd, 1980, p. 131-135).

An estimate of average horizontal hydraulic conductivity can be calculated from the transmissivities obtained from the tests (table 5) using equation 3. For the single-well tests (specific capacity or step drawdown), the length of open hole or screen is a reasonable estimate of the thickness of the aquifer that contributes most of the flow to the well, if the aquifer has significantly greater horizontal hydraulic conductivity than vertical hydraulic conductivity (as shown by layering), and if the open interval is relatively long (McClymonds and Franke, 1972, p. E11). In the aquifer tests, the hydraulic conductivity is calculated for the main permeable zone in the aquifer and excludes adjacent sand beds or slightly cemented calcareous beds.


Table 5. Aquifer hydraulic properties determined in aquifer tests during this investigation

[See figure 9 for well locations and table 1 for site names. OH, open hole; S, screen; Hydrogeologic units: B, Biscayne aquifer; BS, basal sand unit; GL, gray limestone aquifer; S, semiconfining unit. Geologic formation: Qa, Anastasia formation; Qf, Fort Thompson Formation; Qk, Key Largo Limestone; Qm, Miami Oolite; Tt, Tamiami Formation. Type of test: 1, Step drawdown (Jacob, 1947; Bierschenk, 1963); 2, Multiple-well aquifer (Theis, 1935; Cooper and Jacob, 1946; Hantush and Jacob, 1955; Cooper, 1963); 3 Specific capacity (Theis and others, 1963; McClymonds and Franke, 1972)]

USGS well number USGS site identification number Well finish Diameter of open interval
(inches)
Open interval
(feet below land surface)
Hydro-
geologic unit
Geologic formation Type of test Transmissivity
(feet squared per day)
Estimated hydraulic conductivity
(feet per day)
G-3294D 255707080254805 OH 7.5 21 - 86 B Qf, Qk 1 1,000,000+ 15,000+
G-3294E 255707080254806 OH 6.0 90 - 110 B Tt 3 39,000 2,000
G-3296D 255224080380501 OH 7.5 20 - 45 B Qf 1 1,000,000+ 40,000+
G-3297D 255058080290301 OH 7.5 20 - 55 B Qf, Qk 1 1,000,000 29,000
G-3297E 255058050290301 OH 6.0 60.0 - 78.4 B Tt 3 8,600 470
G-3301D 254537080493605 OH 7.5 11.0 - 16.8 SCU Qf 3 3,100 530
G-3301E 254537080493606 OH 6.0 101 - 149 GL1 Tt 2 39,000 780
G-3302D 254542080421705 OH 7.5 11 - 17 SCU Qf 3 2,700 450
G-3302E 254542080421706 OH 6.0 81 - 138 GL1 Tt 2 25,000 420
G-3303D 254545080361705 OH 7.5 20 - 34.8 B Qf 1 600,000 40,000
G-3303E 254545080361706 OH 6.0 121 - 150 GL1 Tt 2 13,000 430
G-3303I 254545080361710 S 2.0 59 - 72 SCU1 Tt 3 1,200 94
G-3304E 254539080300606 OH 7.5 30 - 55 B Qf 1 1,000,000+ 40,000+
G-3304G 254539080300608 OH 6.0 80.0 - 95.9 B Tt 3 3,800 240
G-3305D 254536080230305 OH 7.5 21 - 87 B Qf, Qk 1 1,000,000 15,000
G-3305F 254536080230307 S 2.0 164.2 - 171.2 B Tt 3 430 61
G-3305H 254536080230309 S 2.0 131.7 - 141.7 B Tt 3 49 4.9
G-3310D 253714080345905 OH 7.5 10 - 45 B Qm, Tt 1 1,000,000+ 29,000+
G-3311F 253746080295007 OH 7.5 32 - 56 B Qf 1 1,000,000+ 42,000+
G-3311H 253746080295009 OH 6.0 145 - 173 GL Tt 3 5,800 210
G-3312D 253842080225805 OH 7.5 26 - 94 B Qf, Qa, Tt 1 220,000 3,300
G-3313D 253831080180205 OH 7.5 32 - 114 B Qf, Qk, Qa, Tt 1 710,000 8,700
G-33l4E 253018080333505 OH 7.5 21 - 48 B Qf 1 1,000,000+ 37,000+
G-3315E 253119080274806 OH 7.5 32 - 69 B Qf 1 1,000,000+ 27,000+
G-33l5F 253119080274806 OH 6.0 94.0 - 111.5 SCU Tt 3 65 3.7
G-3317D 252326080475705 OH 6.0 8 - 28 B Qm, Qf 1 730,000 36,000
G-3319E 252507080342706 OH 7.5 21.0 - 39.3 B Qf 1 1,000,000+ 55,000+
G-3320C 252555080281004 OH 7.5 32 - 80 B Qf 1 1,000,000+ 21,000+
G-3324E 251948080271806 OH 7.5 16 - 58 B Qm, Qf, Qk 1 1,000,000+ 24,000+
G-3394A 252944080395102 OH 7.5 10 - 34 B Qm, Qf 1 1,000,000+ 42,000
G-3394B 252944080395103 S 6.0 110 - 145 GL Tt 2,3 14,000 400
G-2316D 255732080325605 OH 7.5 15 - 54 B Qf 1 1,000,000+ 26,000+
1At well G-3301E, the interval from 100 to 150 feet below land surface is the more permeable part of the aquifer. At well G-3302E, the gray limestone aquifer extends from 77 to 136 feet below land surface. At well G-3303E, the gray limestone from 120 to 150 feet is the main part of the aquifer, but slightly cemented, calcareous sandstone from 150 to 165 feet may exceed a hydraulic conductivity of 100 feet per day. At well G-3303I, shell layer in semiconfining unit.


< Previous: Earlier Aquifer Tests | Next: Hydrogeology >




| Disclaimer | Privacy Statement | Accessibility |

U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/publications/wri/90-4108/testsconducted.html
Comments and suggestions? Contact: Heather Henkel - Webmaster
Last updated: 04 September, 2013 @ 02:04 PM (KP)