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:

where

S_W 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 S_W /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.