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Subsurface Storage in the Floridan Aquifer System in Southern Florida: Municipal and Industrial Liquid Wastes

Injection of municipal and industrial liquid wastes through wells into the Floridan aquifer system is prevalent in the southeastern part of the Florida peninsula (fig. 28). The start of this practice was mentioned previously in the report. Liquid wastes from both sources were injected into brackish water-bearing zones of the Upper Floridan aquifer because the criteria at that time required only that the receiving rocks contain water having a chloride concentration of at least 1,500 mg/L. Problems ultimately developed with the operation of both systems. In the municipal wastewater injection system (site 14), the low transmissivity of the aquifer and the high suspended solids in the injectant caused frequent plugging of the wellbore and excessive injection pressure (McKenzie and Irwin, 1984). In the furfural plant system (site 15), the hot acid waste migrated upward from the lower part of the Floridan aquifer to appear in a monitored zone near the top (Kaufman and McKenzie, 1975; McKenzie, 1976; Vecchioli and others, 1979).

The practice of deep-well injection of liquid wastes became increasingly attractive in 1969 when a test injection well drilled at a wastewater-treatment plant (fig. 28, site 16) tapped the highly transmissive saltwater-filled Boulder Zone of the Lower Floridan aquifer. An evaluation of the natural water-level fluctuations in the well by Meyer (1974) suggested that the transmissivity of the Boulder Zone was about 3.2 x 10⁶ ft²/d; however, a later pumping test at a wastewater treatment plant (fig. 28, site 22) suggested that the transmissivity was about 2.5 x 10⁷ ft²/d (Singh and others, 1983). The success of the injection well at site 16 soon led to rapid exploitation of the Boulder Zone as a receptacle for nonhazardous municipal and industrial liquid wastes.

Figure 31. Annual and cumulative volumes of municipal and industrial liquid wastes injected, 1959-83. [larger version]

The characteristics of the Boulder Zone meet the current criteria for Class I injection wells as required by the Florida Department of Environmental Regulation (that is, the receiving zone is deep, confined, thick, porous, and highly transmissive and contains ground water whose dissolved solids concentration exceeds 10,000 mg/L).

During 1959-70, the volume of liquid wastes injected into the Floridan aquifer system increased gradually from 98 to 465.6 Mgal/yr (fig. 31, table 13). In 1971, the volume of liquid wastes injected began to increase exponentially, and in 1983 it reached 26.8 billion gallons per year (Ggal/yr). The total amount injected for the 25-yr period (1959-83) was 112 Ggal. Of that, 4 Ggal were industrial liquid wastes (sites 15 and 20) and 108 Ggal were treated municipal wastewater.

The injected industrial liquid waste at site 15 is chiefly acetic acid, a byproduct of the production of furfural. Neutralization of the acid waste takes place in the receiving zone by dissolution of the carbonate rocks and release of carbon dioxide. High concentrations of biogenic hydrogen sulfide and methane also result from reaction in the receiving zone. Characteristics of the injected industrial liquid wastes (site 15) are compared with those of the local water supply and the native ground water in the Boulder Zone in table 14.

Table 13. Summary of municipal and industrial injection of liquid wastes in southern Florida, 1959-83 [In million gallons. Site locations shown in fig. 28]
Year	Site 141	Site 15	Site 16	Site 17	Site 18	Site 19	Site 20	Site 21	Site 22	Site 23	Yearly total	Cumulative
1959	98										98	98
1960	182										182	280
1961	182										182	462
1962	182										182	644
1963	182										182	826
1964	219										219	1,045
1965	219										219	1,264
1966	219	2.0									221	1,485
1967	182	45.4									227.4	1,712.4
1968	219	104.6									323.6	2,036.0
1969	219	121.8									340.8	2,376.8
1970	265	200.6									465.6	2,842.4
1971	223	213.4	577.0								1,013.4	3,855.8
1972	248	246.5	1,046.0								1,540.5	5,396.3
1973	293	307.5	1,275.0	179.5							2,055.0	7,451.3
1974	259	284.3	1,341.0	483.9	570.6						2,938.8	10,390.1
1975	10	311.1	1,537.0	582.3	1,299.4						3,739.8	14,129.9
1976		317.6	1,732.0	531.4	1,284.0						3,865.0	17,994.9
1977		157.6	1,715.5	646.8	1,415.1	175.7					4,110.7	22,105.6
1978		187.8	1,734.8	902.1	1,671.3	4,253.3					8,749.3	30,854.9
1979		272.1	1,957.7	1,134.5	1,816.6	5,673.7	0.2				10,854.8	41,709.7
1980		375.6	1,723.5	1,006.5	1,756.7	8,531.5	20.4				13,414.2	55,123.9
1981		358.4	1,754.8	1,277.9	1,850.6	8,910.2	44.2				14,196.1	69,320.0
1982		201.3	1,856.0	1,022.0	1,993.6	10,639.3	66.8	81.2			15,860.2	85,180.2
1983		161.1	139.3	82.3	2,001.3	11,125.1	55.3	742.5	12,376.9	144.6	26,828.4	112,008.6
Total	3,401	3,868.7	18,389.6	7,849.2	15,659.2	49,308.8	186.9	823.7	12,376.9	144.6	112,008.6
1Estimated except for 1969 through 1974.

Table 14. Selected water-quality characteristics of injectant of industrial liquid wastes, local water supply, and native ground water in the Boulder Zone at site 15, Palm Beach County [Concentrations in milligrams per liter, except where noted; analyses by U.S. Geological Survey. Location of site 15 shown in fig. 28. Dashes indicate no data]
Characteristic	Injectant1	Water supply2	Ground water in the Boulder Zone3
Major inorganics and related physical characteristics
Acidity, as H+	208	0	0
Bicarbonate (HC03)	0	150	200
Calcium (Ca)	140	44	430
Chloride (Cl)	160	99	19,000
Dissolved solids (residue at 180°C).	9,720	>380	36,100
Magnesium (Mg)	63	21	1,300
pH (units)	2.9	8.6	7.9
Potassium (K)	310	5	410
Sodium (Na)	110	60	12,000
Specific conductance (microsiemens per centimeter).	2,400	700	51,500
Sulfate (SO4)	290	66	2,400
Suspended solids (residue at 110°C).	1,500	--	--
Temperature (°C)	475.0	26.5	--
Selected nutrients and related characteristics
Carbon, total organic	7,500	20
Nitrogen, ammonia as N	19	.03
Nitrogen, total as N	138	1.6
Phosphorus, total as P	47	.02
1Sample of plant effluent was collected on July 8, 1974. 2Sample was collected at North New River Canal below hurricane gate and pump station on April 18, 1974. 3Sample was collected from injection well 3 at 3,130 feet on June 29, 1976. 4Temperature of effluent is reduced to about 50.0°C prior to injection.

At site 20, the industrial liquid waste is caustic (chiefly aluminum hydroxide and sodium chloride), a byproduct of the production of pectin. Analyses of the injectant from site 20 were unavailable.

The injected municipal liquid waste is secondary-treated wastewater (that is, wastewater that has had at least 90 percent of the suspended solids and biochemical oxygen demand removed by treatment). The characteristics of the treated wastewater vary from plant to plant, but the wastewaters are distinguished from local water supply by high concentrations of nutrients. The characteristics of the injected wastewater at two wastewater treatment plants (sites 19 and 22) are compared with those of the local water supply and native ground water in the Boulder Zone in tables 15 and 16.

Table 15. Selected water-quality characteristics of injectant of secondary-treated wastewater, local water supply, and native ground water in the Boulder Zone at site 19, Palm Beach County [Concentrations in milligrams per liter, except where noted; analyses by U.S. Geological Survey. Location of site 19 shown in fig. 28. Dashes indicate no data]
Characteristic	Injectant1	Water supply2	Ground water in the Boulder Zone3
Major inorganics and related physical characteristics
Bicarbonate (HC03)	120	150	180
Calcium (Ca)	50	40	390
Chloride (Cl)	240	78	21,000
Dissolved solids (residue at 180°C).	1,060	330	37,400
Magnesium (Mg)	16	8.9	1,300
pH (units)	6.7	8.3	7.6
Potassium (K)	15	3.1	450
Sodium (Na)	160	45	12,000
Specific conductance (microsiemens per centimeter).	1,220	550	>50,000
Sulfate (SO4)	110	33	2,800
Suspended solids (residue at 110°C).	12	--	43
Temperature (°F)	78.8	79.7	<17.5
Selected nutrients and related characteristics
Carbon, total organic	15	--	8.2
Nitrogen, ammonia as N	.03	--	<.01
Nitrogen, total as N	1.6	>.02	.00
Phosphorus, total as P	.08	--	.02
1Sample of effluent from site 19 collected on April 19, 1978. 2Sample of raw surface-water supply (Clear Lake) for site 19 collected on May 9, 1979. 3Sample of native ground water collected from injection well 2 at site 19 on May 30, 1972. Density was 1.022 g/mL (grams per millimeter) at 68°F and hydrogen sulfide was 2.4 mg/L (milligrams per liter).

Table 16. Selected water-quality characteristics of injectant of secondary-treated wastewater, local water supply, and native ground water in the Boulder Zone at site 22, Dade County [Concentrations in milligrams per liter, except where noted. Location of site 22 shown in fig. 28. Dashes indicate no data]
Characteristic	Injectant1	Water supply2	Ground water in the Boulder Zone3
Major inorganics and related physical characteristics
Acidity, as H+	--	0	0
Bicarbonate (HC03)	--	260	146
Calcium (Ca)	--	92	430
Chloride (Cl)	65	25	19,000
Dissolved solids (residue at 180°C).	360	322	37,900
Magnesium (Mg)	--	3.2	1,200
pH (units)	6.0	7.5	7.1
Potassium (K)	--	1.7	200
Sodium (Na)	--	16	1,100
Specific conductance (microsiemens per centimeter).	700	540	52,900
Sulfate (SO4)	--	28	2,600
Temperature (°F)	87.8	82.4	<19.0
Selected nutrients and related characteristics
Carbon, total organic	7.65	2.0	3.9
Nitrogen, ammonia as N	17.5	.01	.12
Nitrogen, total as N	18.6	.36	.24
Phosphorus, total as P	1.56	<.01	<.01
1Sample of treated effluent collected on August 14, 1984. Analyses by Miami-Dade Water and Sewer Authority. 2Sample of raw water from the Biscayne aquifer collected on June 6, 1975, at site 22. Analyses by the U.S. Geological Survey. 3Sample of native ground water collected from monitor well BZ-1 between depth of 2,689 and 2,960 feet on October 22, 1981. Sample contained high metal concentrations due to pipe erosion. Analyses by the U.S. Geological Survey.

Injection into the brackish water-bearing zones of the Upper Floridan aquifer occurred only at sites 14 and 15. The combined amount (municipal and industrial) for both sites during 1959-75 was 5 Ggal.

Injection into the middle confining unit and perhaps the upper unit of the Lower Floridan aquifer occurred only at site 15, where about 656.7 Mgal were injected during 1972-75.

Injection into the Boulder Zone of the Lower Floridan aquifer occurred at the eight remaining sites during 1971-83 and at site 15 during 1977-83. The total amount injected into the Boulder Zone during 1971-83 was 106.4 Ggal.

Injection rates have increased exponentially since 1971, when the injection well at site 16 became operational and injection was directed to the Boulder Zone. The rate in 1983 was 73.5 Mgal/d, and the estimated rate in 1984 was 112 Mgal/d (table 17).

In 1983, two injection wells (fig. 28, sites 16 and 17) were removed from service because of small leaks in uncemented (conductor) inner casings, and the effluent from the plant was directed to other treatment facilities of the Miami-Dade Water and Sewer Authority. Also in 1983, a small leak was detected in the uncemented inner casing of a third injection well (fig. 28, site 18), and construction of a replacement well was required by the Florida Department of Environmental Regulation before remedial work could be performed on the leaking well. Despite these minor problems, which have been resolved by enforcement of the UIC regulations, the outlook for deep-well injection in southern Florida is for continued expansion. The outlook, however, should include caution because the injected liquid waste will ultimately conform to the regional ground-water circulation system. The injected waste, thus, will move with the hypothesized inland and upward flow of seawater from the Florida Straits.

Typical construction characteristics of nontoxic municipal and industrial liquid wastes disposal wells are shown in figures 32 and 33 along with the local hydrogeology. The construction of the municipal liquid wastes disposal well (fig. 32) is based on that of well 3 at the city of Fort Lauderdale's Port Everglades wastewater-treatment plant (fig. 28, site 28). The well is constructed with telescoping steel casings to protect drinking water resources in the surficial aquifer and the Upper Floridan aquifer. The casings are cemented in place from top to bottom with special sulfate-resistant cement. The steel inner (conductor) casing is 24 inches in diameter and 1/2 inch thick. The well has a minimum injection capacity of 15 Mgal/d.

The construction of the industrial liquid wastes disposal well is based on that of well 3 at the furfural plant (fig. 28, site 15). The well is also constructed with several steel casings that are cemented in place with special cement to resist heat and corrosion to protect drinking water sources. The inner (conductor) casing is made of a special alloy that is acid and heat resistant. Not shown in figures 32 and 33 are monitor wells, which are located nearby to detect leaks and upward-migrating wastes.