Bulletin No. 64


 As in the three primary wells, the confining zone in this area contains alternating layers of mudstone, wackestone, packstone and dolostone, with widely varying porosity values and permeabilities, and moderate to good induration (Appendix A4 and Plates 1, 2, & 3). Fractures were observed in core from 1,904 to 1,912 feet BLS.

 The background water-quality report (Geraghty & Miller, Inc., 1984) shows that the ambient conditions at the level of the deep monitor zone, before injection began in August 1986, were as follows: TDS = 31,000 mg/L, chloride = 17,000 mg/L, and TKN = <0.04 mg/L. The 10,000 mg/L boundary occurs at approximately 1,200 feet BLS.

 Deep monitor zone water-quality data show trends similar to those seen in the three primary wells, though the patterns are more erratic. TDS values declined from over 31,000 mg/L in 1986 to under 25,000 mg/L in 1991, and chloride concentrations declined from over 18,000 mg/L to under 13,000 mg/L in the same period. The more erratic patterns of decline may be due to the variable rates of injection at the site. Injection volumes commonly vary by tens-of-millions of gallons from month-to-month. TKN values did increase to over 2 mg/L by mid-1991, but the trend is not very dramatic. No trends were discernible in the upper monitor zone data.

 Grant Street

 The Grant Street well has a total depth of 2,700 feet BLS in the Oldsmar Formation. The main confining zone, as defined by Hydro Designs (1989), is from 1,815 to 2,050 feet BLS in the lower Avon Park and upper Oldsmar Formations. The major injection interval extends from 2,035 to 2,700 feet BLS in the Oldsmar Formation (Appendix A5). There are two separate monitor wells at the site. The upper well monitors from 1,100 to 1,150 feet BLS in the upper Avon Park Formation, and the lower well monitors from 1,594 to 1,644 feet BLS in the lower Avon Park Formation.


 The confining zone can be divided into two broad categories. The upper section, from 1,815 to 1,880 feet BLS, is predominantly dolostone, with interbedded wackestones and packstones (Appendix A5). Permeabilities are generally low, and porosity ranges from five to ten percent. Induration is generally good. The lower section, from 1,880 to 2,050 feet BLS, is composed mainly of packstone, with a few interbedded wackestone and thin dolostone beds. Permeabilities are generally high, porosity ranges from 15 to 35 percent, and induration is poor to moderate.

 The background water-quality report for the lower monitor zone shows a TDS value of 23,600 mg/L, a chloride concentration of 850 mg/L, and a TKN value of 0.5 mg/L (Hydro Designs, 1989). These values appear to be slightly low, because Florida DER monitoring data (unpublished data, 1991) show initial values that start higher than those quoted in the Hydro Designs report. Further examination of the water-quality report indicated that the samples for the background readings were taken soon after the well was developed, and ambient conditions were probably not reestablished at that time. TDS values exceed 10,000 mg/L at approximately 1,250 feet BLS.

 Injection began in April 1989. The water-quality data show trends at this site, but the magnitudes of changes are not as great as at other wells. TDS values decline in a somewhat irregular manner from just over 27,000 mg/L in mid1989 to around 17,000 mg/L in 1991. Chloride concentrations show a small but fairly steady decline from over 16,000 mg/L in 1989 to below 13,000 mg/L in 1991. TKN values increased from 2.0 mg/L in 1989 to a high of about 10.0 mg/L in 1990, and then declined to about 5.0 mg/L by mid-1 991.

 Data from the upper monitor well show increases consistent with rising formation waters. Background analyses showed a chloride concentration of 215 mg/L, a TDS value of 2.5