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4 Florida Groundwater is particularly important to F3 or Ida . The state depends almost totally on groundwater for more than 90 percent of its drinking water and uses aquifers for more than 50 percent of all other water uses. Furtner- more, the state's groundwater and surface water supplies are closely linked, with groundwater discharges contrib- uting significantly to Florida's stream flows. The demand for water will grow rapidly, since Florida is experiencing rapid increases in population and development. Four major aquifers supply the groundwater used for drinking water. The largest in areal extent, underlying most of the state, is the Floridan aquifer; it provides drinking water in the north and central areas of the state and supplies 43 percent of the groundwater used for public supply. In general, it is protected from surface pollution by clay beds, by shallow overlying aquifers, and by its considerable depth. In some areas in central Florida, however, this aquifer comes close to the surface and is highly susceptible to pollution. Along On August 16 and 20, 1984, Holden visited various individuals in Florida familiar with groundwater problems associated with agricultura1 chemicals. The institutions represented by the persons interviewed included the Florida Department of Environmental Regulation (DER), Ground Water Section; the Florida Department of Bealth and Rehabilitative Services (DHRS); the Florida Depart- ment of Agriculture and Consumer Services (DACS); and the Pesticide Research Laboratory, Institute of Food and Agricultural Sciences (IFAS), and the Department of Soil Science, University of Florida. 81
82 the east and southeast coast and in southern Florida, the Floridan aquifer is not potable. In heavily populated southeast Florida, the Biscayne aquifer is the sole source of drinking water for Dade, Broward, and part of Palm Beach counties, and thus receives special protection under the Federal Safe Drinking Water Act. . This aquifer, which supplies 44 percent of the groundwater used for public supply in the state, is highly permeable and productive of good-quality water, except where saltwater has intruded. It has no confining layer to protect it from surface pollution. Shallow aquifers supply 10 percent of the state's groundwater used for public supply. Areas along the east and southeast coasts and in southern Florida rely on these aquifers for groundwater. ~ ~ They overlie nonpotable portions of the Florida aquifer and are under either water table or artesian conditions. Their water quality is variable, and they may be susceptible to saltwater intrusion. m e remaining 3 percent of the groundwater used for Florida's public supply comes from a sand-and-gravel aquifer located in the extreme western portion of the Florida panhandle. Consisting of sand, gravel, and interbedded clay layers, the aquifer varies between unconfined and artesian conditions . The unconfined and coastal areas are vulnerable to contamination. Florida's unique hydrogeology allows fast movement of surface contaminants into aquifers. Pollution sources in the state include 6,000 mostly unlined surface impoundments; 9,000 drainage wells that inject wastewater or low-quality water into receiving aquifers; 40,000 underground storage tanks, many of which are periodically submerged in groundwater; saltwater intrusion; several hundred hazardous waste sites; and Florida's active agricultural industry, with its associated fertilizers, pesticides, and other agricultural chemicals. Agriculture is important to Florida's economy, con- tributing S4.4 billion in cash receipts for 1982. Citrus accounted for more than $1 billion in sales, and _ vegetable, melon, and strawberry crops accounted for just under 81 billion. ~ . . .. Pesticides are Vapor ten t to the pro- aucezon or these commodities, and possible contamination of groundwater by two of them--aldicarb and EDs has led to monitoring and regulatory responses Programs to detect other pesticides in groundwater are just getting under way.
83 Although Florida receives an average of 53 inches of rainfall per year, irrigation is practiced during early spring. Irrigation--at nearly 9,200 acre-feet/day in 1980--is the single largest use of water in Florida, accounting for more than 40 percent of tota} use. Slightly more than half of the water used for irrigation is drawn from groundwater sources. The acreage irrigated tripled from 414,000 to 1,217,000 acres in the first half of the 1960s, and rose to nearly 2,000,000 acres in 1978. In the north-Florida Suwannee River Water Management District, agricultural irrigation grew at a rate of 15 to 20 percent per year from 1975 to 1982, and growth is expected to continue. In the central St. John's River Water Management District, however, irrigation is not expected to increase beyond present use levels, which already cause some problems due to large withdrawals. AS one way of addressing their problems, the districts are cooperating with the University of Florida on an exper imental program to improve irr igation Of f iciencies . The unique hydrogeology of Florida, the recognition of groundwater contamination problems, and the increasing demands for quality water have prompted several state initiatives. In 1982 the speakers of the Florida House of Representatives appointed a task force to examine water issues in the state. The resultant Report of the Speaker's Task Force on Water Issues. was published in March 1983. Pesticide contamination was one of the issues explicitly addressed. Later in 1983 the Florida legislature passed the Water Quality Assurance Act. A number of its provisions concern pesticide contamination of water and are discussed in context. To: STATUS OF EFFORTS TO MONITOR GP~UNOWATER FOR RESIDUES OF AGRICUL~L PESTICIDES Past Monitor ing Ef for ts Historically, there has been no systematic monitoring for pesticide residues in Florida's groundwater. How- ever, the aldicarb incident in Long Island, New York, aroused concern about contamination that led to the discovery in Florida of two significant problems and the establishment of a future monitoring program.
84 AIdicarb Aldicarb--trade name Temik--is most commonly used in Florida to control citrus nematodes and mister. Approxi- mately 10 percent of the 848,000 acres in citrus produc- tion acreage in 1982 were treated regularly with aldicarb. Before 1983 typical annual rates of aldicarb application totaled about 10 lbs ai/acre, often split into two applications. Approximately two-thirds of the aldicarb has been applied in Polk and Lake counties in the so-called sandy ridge or central ridge area of central Florida. Ald~carb is also used on potatoes in the Hastings area of northeastern Flor ida . In mid-1982 the Florida Department of Environmental Regulation (DER) initiated a water sampling program to assess possible aldicarb contamination of Florida's groundwaters. Aldicarb was first discovered in ground- water at an experimental agricultural area in August 1982. Subsequent monitoring detected aldicarb in ground- water near application sites at levels approaching 600 ppb. The f inditing of aldicarb residues in groundwater led the state to adopt a 10-ppb health advisory quality level, a 1-year ban on many uses of the pesticide, and two monitoring programs. These programs include a continuing study of residues at seven sites in the state and a survey of drinking-water wells. Union Carbide Corporation participated in both monitoring efforts. While the 1983 ban on aldicarb was in effect, monitoring continued and new use restrictions were developed. These restrictions state that · No more than 5 lbs ai/acre of Temik 15G can be applied per year; · Only one application of Temik 15G is allowed per year, which for citrus growers (the major users) must occur between January 1 and April 30; o No use of Temik 15G is permitted within 300 feet lateral distance of any drinking-water well; ~ Use is to be suspended in areas where aldicarb is found in drinking water at concentrations greater than 10 ppb; ~ A notice of intended use must be posted prominently on property where aldicarb is being applied, and wells in treatment areas shall be posted with warnings, snot for human consumption. "
85 m e DER also proposed that ridge citrus users conduct annual monitoring of shallow groundwater downgradient of all application sites and that aldicarb not be applied 600 feet (instead of 300 feet) upgradient from any drinking-water well . These additional rests lotions were not adopted by DACS. An observation program at seven Florida sites is collecting field data on the behavior and fate of aldicarb. The data provide a check for Union Carbide mathematical models that describe degradation and movement of aldicarb residues and for pesticide use restrictions intended to protect groundwater. The seven sites include two citrus ridge groves, two bedded orange groves, a west coast orange grove, a fernery, and a potato field. Sampling conducted at cluster wells permits temporal and special assessment of residues. Results indicate that aldicarb residues from applica- tions in potato fields and bedded citrus groves in coastal areas may reach surficial aquifers, but generally degrade relatively rapidly. Factors reducing the impacts on groundwater in these areas (compared to sandy ridge areas ) are lower groundwater hydraulic gradients, f iner sands with high shell matter and more organic content, and waters with higher pE values. In fact, most believe the data base is adequate to conclude that aldicarb applied to potato and bedded citrus sites is not contaminating groundwater and that no further sampling of these areas is required. But in the sandy ridge area of central Florida, residues may be found in the surficial groundwater several hundred lateral feet from the site of application. Shallow water tables, high recharge rates, and sandy acid soils with low organic matter all contribute to the persistence of aldicarb and its contamination of groundwater. This finding has called into question the usefulness of mathematical models in describing environmental fate and transport behavior and the adequacy of the current restriction prohibiting aldicarb applications only within 300 feet of drinking-water wells. As a result, in 1984 Union Carbide agreed to drill additional test wells to clarify the movement of aldicarb in the groundwater at two sites. The wide variations in Florida of hydrogeologic and soil conditions cause the differences in the environ- mental fate of aldicarb. In the northeast Florida potato growing area, despite shallow groundwater and a long history of aldicarb use, no aldicarb residues have been detected in drinking-water wells and only trace levels
86 have been detected in monitoring wells. AS noted, the specific conditions of that area appear to cause rapid degradation of aldicarb. In the sandy, acid soil of the central ridge area, however, aldicarb residues are regularly detected in monitoring wells. Clearly, the half-life of aldicarb in soil and groundwater is site- specific in Florida. In another major aldicarb monitoring program, the DER contracted the Department of Engineering Sciences, University of Florida, to study aldicarb residues in dr inking-water supplies . The study is being conducted in three phases. In the first phase, completed in the first half of 1984, the 10 largest water supplies were sampled in each of 34 counties where aldicarb was used in 1982 or 1984. No residues were found above the 2-5-ppb concentration that represents the lowest quanti- fiable detection limit for the method of analysis used. In the second phase, a large portion of all public com- munity drinking-water systems in Polk, Lake, Orange, Jackson, St. Lucre, Dade, Sundry, and Highlands counties were sampled. me counties were selected on the bases of their potential for groundwater contamination and their known use of aldicarb. No residues over the guideline were detected. In the third phase, samples will be collected from cluster wells in sensitive locations, and aldicarb migration through the soil and groundwater will be monitored. Three sets of samples will be taken during the study. In June 1984 Union Carbide Corporation presented information on groundwater contamination by aldicarb to the EPA's Science Advisory Panel. At that time, accord- ing to Union Carbide, more than 1,100 samples from 900 drinking-water wells in 27 Florida counties had been analyzed, and no aldicarb residues were found above the 10-ppb level. Detectable levels of less than 10 ppb were found in three wells, but in each instance the well casing was either damaged or poorly constructed. Ethylene Dibromide The nematocide ethylene dibromide (SDB), or 1,2-Dibromoethane, is the second pesticide to cause known groundwater problems in Florida. EDB was primarily used as a soil fumigant to control burrowing nematodes on citrus. It was applied for more than 15 years by private individuals and by the state to establish barrier zones
87 to control the nematodes' spread and was also used extensively on golf courses and to some extent on such crops as peanuts and soybeans. Its use had increased in recent years as a replacement for the pesticide DBCP. Because EDB is highly volatile, its potential to contaminate groundwater was originally unsuspected. Studies of its environmental behavior are under way, and preliminary data indicate that EDB in groundwater has a half-life measured in years. After the discovery of EDB in the groundwater of other states, a testing program for EDB in Florida wells was begun in August 1983. When EDB was indeed detected, the state banned its use (September 1983); set a 0.1-ppb tolerance in drinking water; and formed an EDB Task Force consisting of representatives of five state agencies. The state installed a toll-free hotline and established an EDB newsletter. Information on EDB application sites was mapped, and the task force proposed sampling all wells located within 300 feet of such sites, with priority given to public drinking-water wells located within 1,000 feet of EDB applications. m e volume and sophistication of tests to detect EDB required contracts with major state university laboratories. m e sampling program that began in August 1983 had, by February 13, 1985, tested 7,609 wells; 828 (11 percent) showed the presence of EDB. The three counties with the largest number of contaminated wells--Polk, Highlands, and Lake--form the heart of the central ridge citrus area. Analysis of the data from wells in which EDB was detected statewide shows that while the average contam- ination is about 6.5 ppb, high averages and extreme values are found in Polk and Highlands counties. This is attributed to the high application rates in these counties, the large number of application sites, the lack of organic matter in the soil, and the high susceptibility of the surface aquifers to contamination. Most of the EDB contamination appears to be confined to surficial aquifers. In Highlands County, most of the 103 contaminated wells (643 tested) are less than 200 feet deep. In Polk County (331 contaminated wells of 2,796 tested), however, a 700-foot-deep well at Lake Wales is contaminated, which could indicate contamination of the Floridan aquifer. Golf course applications have been related to contamination at a number of specific sites; all the contaminated wells in Duvall County tl4 of 203 tested), for example, are accounted for by this use.
88 In 1984 the Florida legislature authorized $3.1 million to remedy well water contamination problems resulting from the state application or use of EDB. The EDB task force stipulated that activated carbon filters be installed on contaminated wells, except where connections to nearby uncontaminated public water supplies are feasible. As of May 3, 1984, 36 municipal and 601 private wells in the state had been found to be contaminated; 492 of these were contaminated by EDB applied by the state, and the remainder were contaminated by privately applied EDB. Another 200 private wells are expected to be found contaminated. The total cost to clean up wells contaminated by state actions is estimated to be $4.7 million plus $331,000 for annual operation and maintenance. The total cost to clean up wells contamin- ated by other applicators is estimated to be S2.25 million. As of January 30, 1985, 247 well owners signed releases, and their wells were slated for corrective action. Remedial actions were also authorized for two community drinking-water wells--Lake Alfred and Lake Wales, both in the central ridge area of the state. Other Pesticides As the first step in establishing an ambient ground- water quality monitoring program, the Florida DER con- tracted the U.S. Geological Survey (USGS) to sample 96 public water supply systems. All 96 systems tapped the Floridan aquifer and together supplied water for some 3 million people. me samples were tested for 16 major chemical constituents and physical properties, 10 selected trace metals, 4 herbicides,a 17 insecticides,b and 28 volatile organics.C In March 1984 the USGS reported to the DER that of the 96 systems sampled, only 8 had detectable levels of organics. These were aSilvex; 2~4-DP; 2~4-D total*; 2r4r5-T total. bAldrin; methoxychlor; per thane; toxaphene; DDE total; dieldrin total; endrin; gross polychlorinated naphtha- lenes (PCN) total; heptachlor total; lindane total; mirex total; chlordane total; ODD total; DOT total; endosulfan I; gross PCBs total; heptachlor epoxide total. CIncludes EDB. *.Total. refers to the substance and all its metabolizes.
89 resa~pled and analyzed, and 4 systems were confirmed to be contaminated, of which 2 involved pesticides: Orlando, 0.02-ppb silvex; and Clearwater, 0.01-ppb 1 indane . Subsequently, the DER contracted with the USGS to collect and analyze water samples from systems tapping the Biscayne aquifer plus several southwest Florida systems withdrawing from the Floridan aquifer. Seventeen systems were sampled in this phase. Preliminary results indicated that two systems were contaminated with an organic chemical that was not a pesticide. During 1983-1984, the EPA, in cooperation with the Florida DER, sampled and analyzed 218 public water supplies in Broward, Dade, and Palm Beach counties. The samples were analyzed for volatile organic compounds BLOCS) and trihalomethanes ( ~ s). Four water supplies were found to exceed Florida's pending maximum contam- inant levels for VOCs (discussed in the next section), and 18 others had detectable levels. TEMs in excess of the 0.1-ppb maximum contaminant level (MCL) were found in 40 water supplies. In addition, 83 noncommunity water supplies were sampled; 23 had detectable levels, of which S exceeded applicable MCLs. Testing of groundwater itself indicated hot spots of elevated VOCs: an exten- sive area of the Biscayne aquifer in the Miami Springs- Bialiah-Miami International Airport-Medley vicinity is contaminated with VOCs up to 100 times drinking-water MCKEE. As a result, millions of dollars for new well- fields, system modifications, and increased water treat- ment have been required. Another area of the Biscayne aquifer near the Fort Lauderdale Executive Airport and extending to the Fort Lauderdale Executive welifield is contaminated by VOCs up to 2,000 times MCLs. This testing did not include screening for pesticides. Although the DER suggested that other organic compounds be looked for during the TOM analytic work, this apparently was not done. Current Monitoring Efforts The contamination of groundwater by EDB has focused attention on the need for close monitoring of groundwater in areas where pesticides and other chemicals are used. The problem is extremely difficult because of the large areas involved, the dispersion of pollutants, and the scarcity of accurate records of application areas and
so rates. Furthermore, the dispersed responsibilities concerning this problem make it essential that the departments of Environmental Regulation, Health and Rehabilitative Services, Agriculture and Consumer Services, and Community Affairs cooperate in order to locate pesticide application areas and to design monitoring wells to identify potential groundwater contamination problems. Under the 1983 Florida Water Quality Assurance Act, the state is establishing an extensive groundwater monitoring network. The act requires the DER, in cooperation with other state and federal agencies, water management districts, and local governments, to establish Ha groundwater quality monitoring network designed to detect or predict contamination of the state's ground- water resources." To do this, a three-phase program has been established. The DER has entered into agreements with the state's five water management districts to carry out the program tasks. In Phase 1, a wide range of basic data pertinent to groundwater contamination will be collected. m ese data will encompass the location of point and nonpoint sources of pollution, including specifically the location of agricultural and other areas where pesticides and fertilizers are heavily used; the characteristics of aquifers, including the location of impermeable zones, well drawdown, outcrop areas of the Floridan aquifer, and recharge areas; saltwater intrusion boundaries; and the location and plugging of artesian wells. In Phase 2, the number and location of existing wells suitable for monitoring will be determined. A DER search has located 1,800 wells that may be suitable for the monitoring network. New wells will be drilled as necessary where none exist or where existing ones are not suitably located. The existing wells and new monitoring wells will be located in relation to pollution sources so that ambient groundwater quality can be evaluated. In Phase 3, water samples will be collected and analyzed. The sampling will be designed to provide baseline water quality data for subsequent monitoring of water quality trends. The Water Quality Assurance Act also provides for groundwater data storage and retrieval so that informa- tion will be readily available for decision making regarding land and water use. The DER is establishing a central repository of data and will issue an annual bibliography of published data. When complete, the data system will be publicly accessible.
91 TABLE 4-1 Florida MCLs for Volatile Organic Compounds Volatile Organic Maximum Containment Estimated Compounds Level ( ug/liter ) Risk Level Tr ichloroethylene 3 1/1, 000, 000 Tetrachloroethylene 3 1/500, 00 0 Carbon Tetrachloride 3 1/400,000 Vinyl Chloride 1 1/1,000,000 1,1,1-Trichloroethane 200 not applicable 1,2-Dichloroethane 3 1/600 ,000 Benzene 1 1/900, 000 1, 2-Dibromoethane 0.02 1/100 ,000 In December 1983 the DER asked owners of public water supply systems serving more than 1,000 people to voluntarily test their drinking water for a wide range of contaminants, including some 25 pesticides. In April 1984 the DER adopted a rule requiring all community water systems to be tested for 8 VOCs for which Florida had set MCLs (Table 4-1) and 118 other synthetic organic compounds . Monitoring for the VOCs only is required at 3-year intervals, with the first sampling and analyses due June 1, 1985, for systems serving more than 1,000 persons and January 1, 1987, for smaller systems. Total estimated triennial cost for statewide monitoring of drinking water for VOCs is 36.58 per average affected consumer. The list of 118 synthetic organic chemicals for which monitoring is required includes a category labeled ~Pesticides, ~ as shown in Table 4-2. (Certain other chemicals with pesticide uses, such as pentachlorophenol are included in other categories.) Analyses for the 118 synthetic organic chemicals were due to be submitted to the DER by January 1, 1985, for all community systems serving more than 1,000 persons (588 systems) and by April 1, 1986, for all smaller com- munity systems (1,789 systems). Samples are to be taken from finished water in the distribution system, not individual wells unless a problem is identified. Analysis is required every 3 years, but it is expected that the number of contaminants for which analyses are required in the future will be reduced substantially, based on known or suspected occurrence in Florida waters Total estimated triennial cost for statewide monitoring of drinking water for the presence of these synthetic
92 TABLE 4-2 Pesticides on Florida List of 118 Synthetic Organic Chemicals Designated for Monitoring Aldrin e-BEC 8-BHC y-BHC 6-BEC Chlordane 4,4'-DDD 4,4'-DDE 4,4'-DDT Dieldr in Endosulfan I Endosulfan II Endosulfan Sulfone Ethion Tr ithion o,p-DDT, DOE, and DDD Tedion Endrin Aldehyde Beptachlor Beptachlor Epoxide Toxaphene PCB1016 PCB-1221 PCB-1232 PCB-124 2 PCB-1248 PCB-12S 4 PCB-1260 Aldicar ~ Diazinon Malathion Parathion Guthion Kelthane (Dicofol) organic contaminants is $2.2 million, or $12.05 per average affected consumer. In 1984 the OERS proposed a groundwater survey of all water systems in which EDB had been detected to check for other pesticide residues. ThiS program has just begun in Bighlands County and will soon be extended to Palm Beach, Polk, and Jackson counties. Palm Beach County leads the state in the quantity of restricted use pesticides applied (Table 4-3). For 1983-1984 the state increased the DER'S budget 127 percent, of which 82 percent was alloted for groundwater and related progr~m~. Included in the increase were 16 new positions and S2.9 million for groundwater moni- toring; 8 new positions and 3250,000 for pesticides/water quality activities; 7 new positions and S350,000 for water quality data collection; and 31.15 million for cleanup of EDB and other pesticides.
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94 CRITICAL PROBLEMS AND NEEDS Data and Information Needs l The unique hydrogeology of Florida and the demands Being placed on groundwater resources have accentuated problems arising from data gaps. Among the most important of these gaps are deficiencies in data on the environmental fate of important pesticides, on pesticides use, and on the significance of residue levels found in groundwaters. Environmental Fate Data The Report of the Speaker's Task Force on Water Issues. observed that the DACS, which registers all pesticides used in Florida, has authority to require, when deemed necessary, evidence concerning the safety of each pesticide and to refuse to register a pesticide. However, the task force noted that the DACS focused its attention on the safety of pesticides in relation to actual use on crops and that no agency had been given the responsibility to evaluate the possible impact of a pesticide's use on Florida Is groundwaters. m e depart- ment passed a rule in late 1984 to require agr~chemical companies to provide additional environmental fate data on specific pesticides beyond that required by EPA if it deemed such data necessary to assess the potential for a pesticide to leach to groundwater. Pesti aide Use Data A lack of pesticide use data is frequently cited as inhibiting both the ability to monitor groundwater quality and the management of pesticide use to minimize contamination. The DACS has compiled limited data on restricted use pesticides; however, reporting of such pesticide usage by certified applicators are not man- datory, and the response to requests for voluntary reporting has been low (in the lo to 30 percent range) Moreover, the use data that are received are not site- specific but are s''=marized by county. Mandatory reporting requirements have been discussed but not adopted. .
95 Significance of Residues The toxicological significance of trace levels of pesticides detected in groundwater is often a critical unknown. In reviewing Trends in Ground Water Protection in Florida," Dr. Rodney Reman of the DER discussed the department's difficulties in setting MCLS for contami- nants. He wrote that The research on the toxicological, public health and environmental Impacts of these hazardous chemicals Is beyond the capabilities of the Department. The U.S. Environmental Protection Agency (EPA) must provide the necessary support for conducting basic research needed to evaluate the hazard stemming from the use and disposal of these agents. . . . In Florida . . . one of the highest environmental priorities is the develop- ment of ~safe. or ~acceptable. levels of toxic chemicals in the water resource. Monitoring Resources and Capabilities Contr ibuting to the lack of data is the resource- intensiveness of monitoring pesticides in groundwater. m e analytic capabilities of the DER and the DACS have been overloaded, and facilities of the University of Florida have been relied on for water quality analyses. For this reason, the DER contracted the U.S. Geological Survey to conduct a Statewide assessment of selected trace metal and organic priority pollutants in ground- water used for public water supplies.. Furthermore, beginning with the 1983-1984 budget, the state substan- tially increased the DER's resources for addressing groundwater contamination. Less expensive, broader analytic techniques would reduce the resources now required to assess groundwater quality. Although the EPA's current Master Analytical Scheme for Organic Compounds in Water will test for a wide range of pesticides, it requires a minimum of 80 hours of laboratory tome plus the use of a gas chromatograph-mass spectrometer. Researchers at the University of Florida's Pesticide Research laboratory are seeking funds for the development of a master analytic (multiresidue) screen for pesticides in water that would be more efficient and less resource-intensive. The
96 proposed screen is a quantitative technique giving accurate concentration levels in the parts-per-billion range for more than 200 pesticides, at an estimated cost Of S500 per sample. It would not require a mass spec- trometer; instead, capillary column gas chromatography with electron-capture detection would follow chemical derivatization of those pesticides considered non- volatile. The technique would require a preparation time of only 15-20 hours per sample, and an additional 2 hours on the gas chromatograph. Point Sources Several potential point sources of pesticide contamin- ation have raised concern in Florida. These sources include formulating facilities where pesticides are mixed and prepared for delivery; sites where EDB was used in fumigation chambers to 'reat citrus; and backflows from chemigation systems, where pesticides or fertilizers are applied via irrigation water. Some sampling is being done at wells near formulation and fumigation sites. To prevent chem~gation problems, Florida adopted an ~anti-backsiphoning. device rule in November 1984. me device prevents pesticides and fertilizers applied in chemigation systems from back- flowing through irrigation lines and down an irrigation well, where the chemicals could contaminate groundwater. It also prevents the flooding of a chemical supply tank, which could cause chemicals to spill onto the ground. [See American Society of Agricultural Engineers (ASAE), Engineering Practice 1409.] AGRICULTURAL ~UDUGE~LNT STRATEGIES AVAILABLE TO MITIGATE PESTICIDE/GROUNDWATER QUALITY PROBLEMS The presence of aldicarb residues in groundwater prompted Florida's DACS to ban the pesticide in 1983 for virtually all field uses except potatoes. When this ban was lifted in 1984, a series of restrictions were Imposed to minimize groundwater contamination. These restric- tions are designed to preserve the benefits of particular aldicarb uses while min Sizing the risks of contaminating groundwater. In 1984 EPA' s Science Advisory Panel reviewed the potential benefits of site and use-specific restrictions and their enforceability and concluded that
97 the restrictions were justified. A major goal of Florida's aldicarb monitoring program is to assess the success of the restrictions. As in California, the complex hydrogeology and many different crop uses of pesticides pose a formidable challenge for the design of site-specific controls. Experts interviewed at the University of Florida believe that management of sensitive hydrologic areas to prevent contamination of groundwater from agricultural chemicals is technically feasible. They suggested that such management would be accomplished more easily with restricted use pesticides and that environmental fate data could be useful to delineate sensitive areas for specific pesticides.
