Occurrence of Iron in Surface Waters of the Upper St. Johns River Basin

Transcription

1 Occurrence of Iron in Surface Waters of the Upper St. Johns River Basin Prepared by Florida Department of Environmental Protection Bureau of Watershed Management Ground Water Protection Section December 16, 2004 Authors: Richard Hicks, PG, Ground Water Protection Section; Xueqing Gao, Ph. D, Watershed Assessment Section; Ann Stansel, Watershed Assessment Section

2 DRAFT Occurrence of Iron in Surface Waters of the Upper St. Johns River Basin Introduction This evaluation was conducted to assist in determining the cause and significance of iron in surface waterbodies of the Upper St. Johns River Basin (USJRB). Several waterbodies in the basin are listed as potentially impaired due to elevated iron concentrations. Like other areas of the state, however, iron concentrations is surface water can be related to naturally elevated levels in shallow ground water. The following sections of this document describe the conditions within the USJRB that may influence the concentration of iron in surface waterbodies. Overview of the Hydrologic System The St. Johns River begins as a series of marshes underlain by peat deposits that extend along the length of the USJRB. This basin includes the river s headwaters which form in this elongate marsh system; several inter-connected lakes that occur as a chain separated by river segments; numerous smaller less-connected streams to the west of the river that occur in primarily undeveloped areas; and networks of canals and ditches in farmland and urban areas to the east of the main marsh system. Three distinct surface water regions were evaluated separately due to their unique hydrologic characteristics and water quality influences. These include the main river drainage, the smaller tributaries west of the river, and the hydrologically modified canal-dominated sub-basins to the east and southeast of the river. Figure 1 shows the general layout and hydrology of the basin and waterbodies included in the evaluation. The characteristics of the surface waters in the three regions as well as other information are summarized in Table 1. Table 1 Median values for Iron-related Constituents Median Values Iron (ug/l) ph (std units) Color (Pt-Co) Area of Watershed (sq mi) St. Johns River Drainage total area Lakes SJR Segments Marsh Streams West of SJR average area Drained Farmland in Drainage Districts, SE Basin Statewide Medians for Surface Water Ground Water in USJRB average area Streams Lakes Blackwater Surficial Aquifer Floridan Aquifer Notes: Surface water data for Upper St. Johns River Basin (USJRB) obtained from IWR 17_0.; period of record Statewide surface water medians from Typical Water Quality Values for Florida s Lakes, Streams and Estuaries (FDEP WAS, May 2004 in draft) Ground water data obtained from FDEP OGWIS database via Hydroport retrieval system; no specified period of record. USJ Iron Evaluation 1

3 All iron measured as total Fe. Figure 1. Upper St. Johns River Basin USJ Iron Evaluation 2

4 The main drainage feature in the USJRB is the St. Johns River and its headwaters, which together occur as a single hydrologic sub-basin of more than 964 square miles in area. The river originates in the marshes in the southern part of the basin and extends northward. Blue Cypress Lake, Lake Helen Blazes, Sawgrass Lake, Lake Washington, Lake Winder, Lake Poinsett, and Puzzle Lake are enlargements of the river connected by areas of open marsh and river segments, some of which are hydrologically modified. This hydrologic unit receives surface inflows from many tributary streams and canals along its reach. Six of the lakes, five segments of the St. Johns River, and three natural marsh areas and one hydrologically modified marsh within this hydrologic unit had sufficient iron data to be included in this analysis. To the west of the main river drainage are numerous but order-of-magnitude smaller stream basins, most of which are unaltered. These included streams such as Blue Cypress Creek, Jane Green Creek, Crabgrass Creek, Wolf Creek plus several others that are all relatively similar in watershed area (average area 38 square miles). Ten of these streams have sufficient iron data to be evaluated. In the eastern and southeastern parts of the basin, which include urban and agricultural areas, drainage canals are the main surface water features. They provide flood protection and drainage of farmland in the southeastern part of the USJRB that was converted from marsh to intensively-managed citrus production areas. Canal networks drain and transport irrigation water between blocks and convey stormwater eastward to the Indian River Lagoon. Two of the drained farmland sub-basins have sufficient iron water quality data to be evaluated. Their average area is approximately 18 square miles, but their watersheds are artificially extended by the canal networks. Surface Water Quality - Iron The review of surface water data in the Department s IWR Database included historic and current data reflective of the 2004 verified list period of record ( ) for iron (total), color, ph, and other pertinent parameters. The data were compiled and reviewed for all waterbodies within the basin that had iron data for the verified period, with data comparisons made by waterbody type and by sub-basin (Table 1). Sub-basin comparisons were for (1) the river segments, lakes and marsh that comprise the main St. Johns River drainage sub-basin; (2) the smaller streams and tributaries west of the main river drainage; and (3) canals that drain farmland in the southeastern part of the basin. Average iron concentrations for these three hydrologic regions are illustrated in Figure 2. Individual waterbodies with iron data and median concentrations are shown in Figure 3. According to the recent summary of typical values for streams, lakes and blackwaters in Florida (FDEP, 2004), all waterbodies in the Upper St. Johns drainage sub-basin and the western streams have higher than typical iron concentrations and color. Color is associated with humic and fulvic acids that come from the peat and organic muck within which these surface waters occur. As can be seen for blackwaters in Table 1, high color combined with low ph is typically associated with high iron concentrations in the water. While not so extreme as the typical blackwater condition in color, ph and iron, it appears that this model hold true for streams west of the SJR, where median ph is lowest, median color is highest, and the associated median iron concentration is also highest of these three regions of the basin. Conditions within the drained farmland area also follow the model. Medians in these areas reflect the highest ph, lowest color, and much lower iron concentration. USJ Iron Evaluation 3

5 Average Fe Concentration (ug/l) USJR Drainage Western Streams Drained Farmland Figure 2 Comparison of Iron in Surface Water Regions According to the 2004 evaluation of impaired surface waters in the USJRB, there are four surface waterbodies that meet Chapter , FAC criteria as impaired by iron (Figure 3).. Three of these are Class 1 waters designated for potable use that have an iron standard of 300 micrograms per liter (ug/l), which is much lower than the Class 3 standard of 1,000 ug/l that applies to most of the basin. Average iron concentrations in the USJR drainage and the western streams approach or exceed the 300 mg/l standard for Class 1 waterbodies. Ground Water and Iron In the USJRB there are two aquifer systems of significance, the Floridan aquifer and the surficial aquifer. The Floridan aquifer is less connected to the surface water regime in this area but has an influence on water quality under certain circumstances. The surficial aquifer, on the other hand, is closely related to surface water and is the source of base flow to streams. Deep below land surface and confined by hundreds of feet of clay and other impermeable material is the Floridan aquifer, which consists of porous and permeable limestone and dolomite. Ground water in the Floridan aquifer beneath much of this area is highly mineralized and non-potable due to its dissolved solids (TDS) content. It is however a significant source of irrigation water in the drainage USJ Iron Evaluation 4

6 Figure 3 Iron Concentrations in Surface Water and the Surficial Aquifer and Base Flow Estimates USJ Iron Evaluation 5

7 districts of the southeastern part of the basin. Iron concentrations in the Floridan aquifer are low (the median iron concentration for the basin is 76 ug/l), ph is high and color is low when compared to the surficial aquifer. (Table 1). These characteristics may to some extent be reflected by surface water quality in the drained farmland sub-basins where irrigation water from the Floridan aquifer may actually be a significant source of water in canals. The Floridan aquifer occurs under artesian pressure in the USJRB and may also discharge to surface water from damaged or uncapped flowing wells or potentially by way of seepage into the St. Johns River through faults and fractures in the geologic material. Ground water data show that it is not a source of iron found in surface waters. Throughout most of the USJRB, the surficial aquifer is highly colored, moderately acidic, and high in iron content (Table 1). Low ph and high color (reflective of dissolved organic carbon content) are also common to surface waters having high iron content. The median iron concentration in wells monitoring the surficial aquifer in this basin is 1,023 ug/l, which is higher than both the Class 1 and Class 3 surface water standards as well as Florida s secondary maximum contaminant level (MCL) for ground water (300 ug/l, the same as the Class 1 surface water standard). The basin-wide distribution of iron (measured as total Fe) in the surficial aquifer is shown in Figure 3. Base flow estimates show that the surficial aquifer is a significant source of water to some surface waters in the basin. Base flow was estimated for the St. Johns River and streams west of the river that have United States Geological Survey (USGS) gauging stations using a base flow separation analysis technique. No hydrograph data were available for the drained farmland east of the river. The USGS HYSEP computer program (USGS WRI Report ) was used to break stream-flow hydrographs into base-flow and surface-runoff components. Base flow is less significant to larger basins where precipitation, runoff, and surface water inflows predominate, but can be more significant in smaller basins that collect less runoff. At the only St. Johns River gauging station not influenced by water control structures, the base-flow contribution was 29 percent, which is probably typical for a river with a large basin. Base-flow estimates for the eight smaller streams ranged between 38 and 65 percent of total flow, with the average being 47 percent. Base flow percentages are shown in Figure 3. Anthropogentic Sources of Iron Point sources of contamination were reviewed in this evaluation. Wastewater discharges, solid waste facilities and waste cleanup sites were reviewed. There are more than 60 permitted wastewater treatment facilities in the basin; about 40 are domestic wastewater facilities and most are located east of the river near the population centers. Most facilities are located in the more heavily populated area along the eastern boundary of the basin. Department databases show that in the USJRB there are 9 facilities that discharge directly to surface water and 59 that do not have direct surface water discharges. Of this total, about half are domestic wastewater facilities (not typically high in iron content) and the remaining ones are industrial. Industrial discharges include such things as car washes, concrete batch plants, alligator and fish farms, and parking lots. There is also one peat mining operation. There are 10 permitted landfills in the basin, most located east of the river. Half of the landfills receive general solid waste and the remaining ones receive construction/demolition wastes. There is only one state-funded waste cleanup site in the basin, an electroplating facility located in Cocoa Beach (east of the river). Figure 4 shows these point sources along with surface waterbodies that have iron data. While several of these point sources (such as landfills) generate iron and could USJ Iron Evaluation 6

8 Figure 4 Iron in Surface Waters and Point Sources USJ Iron Evaluation 7

9 contribute iron to surface waters, few point sources are located near sub-basins that contain potentially iron-impaired surface waters and there is no direct evidence of point source influence in these areas. Summary Iron concentrations are naturally elevated in surface waterbodies of much of the USJRB and this natural abundance of iron has resulted in concentrations in some waterbodies that exceed Class 1 and in some cases Class 3 surface water standards. The level of iron in a surface waterbody is related to the amount of water it receives as base flow from the surficial aquifer, which is high in iron content throughout the basin. Surface water quality data show that natural streams west of the St. Johns River are typically highest in iron and the base-flow separation analysis showed that base flow from the surficial aquifer accounts for about half of their flow. Waterbodies that receive irrigation water from deep wells or surface water inflows from the eastern part of the basin and larger lakes that receive more direct precipitation seem to have lower iron concentrations. The iron content in the Floridan aquifer is low and it is not a source of iron in surface water. Point sources in the basin are mainly located in the eastern part of the basin where iron does not seem to be an issue with surface water. Few point sources are located where iron concentrations appear to be highest and no evidence of point source influence is apparent in sub-basins containing waterbodies listed as potentially impaired by iron. USJ Iron Evaluation 8

10 References Boniol, D., Summary of Ground Water Quality in the St. Johns River Water Management District SJRWMD Special Publication SJ96-SP13. Brown, D. W., W. E. Kenner, J. W. Crooks, and J. B. Foster, Water Resources of Brevard County, Florida. Florida Geological Survey Report of Investigations No. 28. Crain, L. J., G. H. Hughes, and L. J. Snell, Water Resources of Indian River County, Florida. Bureau of Geology Report of Investigations No. 80. Davis, J. H., Jr., The Peat Deposits of Florida, Their Occurrence, Development and Uses. Florida Geological Survey Bulletin No. 30. FDEP, Water Quality Status Report for the Upper St. Johns River Basin. FDEP WAS, Typical Water Quality Values for Florida s Lakes, Streams and Estuaries (in Draft). FDEP WAS, Impaired Waters Rule (IWR) Database, Version 17_0. Maddox, G. L, J. M Lloyd, T. M. Scott, T. M, S. B. Upchurch, and R. Copeland, Florida s Ground Water Monitoring Program Background Hydrogeochemistry. Florida Geological Survey Special Publication No. 34. Scott, T. M., J. M. Lloyd and G. L Maddox, Florida s Ground Water Monitoring Program Hydrogeological Framework. Florida Geological Survey Special Publication No. 32. Sloto, R. A., and M. Y. Crouse, HYSEP Computer Program for Streamflow Hydrograph Separation Analysis. USGS WRI Report Toth, D. J. and Huang, C., Investigation of Groundwater Resources in Central Indian River County, Florida. SJRWMD Special Publication SJ98-SP19. USJ Iron Evaluation 9