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CHARLOTTE COUNTY v. SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
C. Effects of Groundwater Withdrawals in the District and the District's Efforts to Address Them.
182. The coastal areas of Hillsborough, Manatee and Sarasota Counties have been a source of concern since the mid-to-late 1980s because of deteriorating water quality in wells drilled into the UFAS. As discussed in more detail below, the District's concerns in this region led to the initiation of the Eastern Tampa Bay Water Resources Assessment Project ("ETB WRAP") and the establishment of the Eastern Tampa Bay Water Use Caution Area ("ETB WUCA"). 183. To the east of Hillsborough County, potentiometric pressures of the UFAS in southwest Polk County showed dramatic decreases throughout the 1960s,47 reaching a low point in 1975 in the area around Bartow.48 184. Along the central and southern portions of the eastern boundary of the District is an area commonly referred to as the Highlands Ridge (the "Ridge" or "HR"), which encompasses portions of Polk and Highlands Counties.49 The Highlands Ridge consists primarily of high sandy areas and a large number of lakes. There tends to be a great deal of interconnection between the groundwater system and surface waters in this area. Lake levels in this area have been in a general state of decline since the late 1950s. 185. Some Petitioners have suggested that many of the problems are the result of accrued deficits in annual rainfall. The more persuasive evidence established that declines in water levels cannot be attributed solely to rainfall. Analysis of water levels, rainfall and pumping indicate that water level declines (including seasonal fluctuations) are, to a large extent, related to increased groundwater pumping. 2. Saltwater Intrusion and Upconing 186. In a marine coastal environment, freshwater aquifers are recharged landward of the coastline. The terrestrial groundwater then moves from the inland region of higher potentiometric pressure to the coast's lower potentiometric pressure and is discharged. The denser seawater remains below the freshwater as it discharges along the sea floor, creating a wedge of seawater beneath the fresh, terrestrial groundwater. Where the freshwater and saltwater meet and mix, a transitional zone or "interface" is formed. 187. The coastal area where fresh groundwater discharges is called the "discharge zone," and is located on the sea floor for an unconfined aquifer or at the base of the unit(s) immediately above a confined aquifer. At the discharge zone, dilute seawater is forced upward by the denser, undiluted seawater, producing a flow of seawater that circulates within the interface where it becomes further diluted and discharged above with freshwater. 188. As groundwater at the base of the aquifer flows towards the coast, it skims along the evaporite layer dissolving minerals and producing a sulfate-rich water. Thus, higher sulfate concentrations are often found near the coast due to the regional freshwater flow pattern. Saltwater intrusion can occur as a result of the landward movement of saline water from the marine environment or from upconing (upward movement) of sulfate water from the base of the aquifer. The two sources of saline water can be distinguished by monitoring the ratio of sulfates to chlorides. In seawater, the ratio is constant, but water from the aquifer's base has a much higher ratio of sulfates to chlorides. Protecting the quality of the resource requires consideration of the movement of both types of water. The District monitors sulfate-to-chloride ratios through monitor wells to understand better the nature, extent, and movement of saltwater intrusion. 189. Pressure differentials determine the rate and direction of the saltwater transition zone's movement. Saltwater intrusion will occur when groundwater heads are lowered, even if they remain above sea level. 190. In the Southern Basin, saline water intrusion into the freshwater of the UFAS is caused by a decline in hydraulic potentionals resulting from groundwater withdrawals from the UFAS. Due to geologic and transmissivity differences, the saltwater intrusion zone does not move as a straight or uniform front.50 Within six to ten miles of the coast, the chloride-rich portion of the transition zone has approximately one degree of slope and almost always appears within the Avon Park Formation of the UFAS. Because of the high transmissivity of the fractured dolomite, this formation is particularly susceptible to saltwater intrusion and most of the interface movement is in this formation. 191. The upward and landward movement of this interface ("saltwater intrusion") causes the lens of freshwater in the aquifer in areas to be replaced by nonpotable water. The movement of the interface (which lies closer to the surface near the coast) has been reflected by deteriorating water quality in wells located in southern Hillsborough and central Manatee Counties. Since it leads to water quality deterioration, some parties contend saltwater intrusion should be treated as a pollution source. 192. Saltwater intrusion is a long term problem that has resulted from long-term pumpage and while it is a matter of great importance that demands attention, the District has calculated that an immediate "fix" is not necessary or even possible without drastic reductions in changes reductions in pumping. The District considers saltwater intrusion a long-term management issue. The District is concerned not only with saltwater intrusion that is currently occurring, but also with the existence of conditions in the potentiometric surface that encourage further and potentially more serious intrusion. 193. The evidence established that changes in potentiometric surface levels affect saltwater intrusion, but the actual inland movement of the saltwater interface occurs over decades. In other words, while potentiometric levels will equilibrate quickly throughout a basin, the saltwater transition zone moves at the rate of groundwater velocity. Thus, if all pumping within a basin were halted, the potentiometric surfaces throughout the basin would recover relatively quickly, but the saltwater transition zone would take longer to return to predevelopment conditions. Consequently, the implementation of any strategy to slow saltwater intrusion should extend over a sufficient period of time to ensure effectiveness of the program. 194. With the first withdrawal of water from the Floridan Aquifer in the SWUCA, saltwater intrusion theoretically began. Man's decision to utilize water from the Floridan Aquifer System unavoidably altered the system from its "predevelopment" condition. Management of saltwater intrusion is critical to protection of the District's water resources, particularly in the southern portion. The difficult task is balancing the use of the resource with the need to protect its long-term health -- a test of man's scientific knowledge combined with critical policy choices. The District's ability to implement an appropriate regulatory scheme is complicated by the heterogeneity of the areas involved and the practical and financial constraints of essential scientific analysis. 195. In a confined region such as the Southern Basin, managing saltwater intrusion can be accomplished only by reducing and/or regulating groundwater withdrawals. 3. Development of Water Resource Assessment Projects and Water Use Caution Areas (Highlands Ridge, Eastern Tampa Bay, Northern Tampa Bay, and Southern) 196. As noted above, during the 1980s, the District initiated and completed "Groundwater Resource Availability Inventories" for most of its jurisdictional area. The purpose of these inventories was to identify areas where pumping was excessive or projected to become excessive and try to quantify the amount of water available for allocation. The inventories were helpful in identifying certain critical areas. 197. The District Governing Board directed staff to conduct comprehensive hydrogeologic evaluations, referred to as Water Resource Assessment Projects ("WRAPs"), in the areas of greatest concern. The District identified the WRAP areas based on a "number of factors including hydrogeologic regime, types of impacts observed, and profile of water use and future growth". The WRAPs sought, among other things, to provide the Board with scientific and technical information necessary to assess the amount of water that could be safely withdrawn in the particular areas. Four WRAP areas were initially identified: Eastern Tampa Bay, Northern Tampa Bay, Highlands Ridge, and the Peace River Valley. 198. The District's assessment of water resource conditions in Eastern Tampa Bay, including Manatee and southern Hillsborough Counties, began in approximately 1987 and was completed in approximately 1992. The results of the project were presented to the Governing Board over a five-month period. A written report was completed in March, 1993, and is known as the ETB WRAP. 199. In the Northern Tampa Bay ("NTB") area, where surface waters are more directly affected by groundwater withdrawals, a lowering of water levels prompted the initiation of a WRAP in approximately 1988. 200. A WRAP for the Peace River basin (which flows through Polk, Hardee and DeSoto Counties and discharges through Charlotte Harbor) was also begun in the late 1980s. The status of the Peace River WRAP is not clear from the record and is beyond the scope of this proceeding. Apparently, the data and information developed as part of some of the other studies, including the ETB WRAP, prompted the District to focus its efforts on development of a strategy for the entire Southern Basin. 201. Before the District began the ETB and NTB WRAPs, it had begun studying problems along the Highlands Ridge. An initial study of lake level declines along the Ridge was conducted in 1978-80 (the "Ridge I report"). A subsequent study, the "Ridge II Report" was initiated around 1985-86, after the District observed a continued drop in lake levels in the years following the completion of the first report. The Ridge II Report was completed in 1989. Those reports documented a continuing decline in lake levels along the Ridge. 202. A WRAP was subsequently initiated for the Highlands Ridge. At the time of the hearing, the HR WRAP had not been completed. 203. Several parties have suggested that the SWUCA Rules are premature, since the HR WRAP and other studies are still ongoing. The District believes that it has developed sufficient information to proceed with the proposed regulatory strategies which are embodied in the SWUCA Rules. 204. The District anticipates continued study of the entire Southern Basin throughout the foreseeable future. However, based upon the information being gathered, the District concluded it could not wait until the completion of all the studies before taking action to protect the water resources. The more persuasive evidence supports the District's conclusion that there is adequate information available to proceed with the implementation of a regulatory strategy for the Southern Basin. However, as discussed in Sections IV and V below, there are some problems with the proposals set forth in the SWUCA Rules. 205. When the District determines that an area has critical water supply problems or that such problems will occur within the next twenty years, it designates the area a water use caution area, commonly called a WUCA. On June 28, 1989, the District established the Northern Tampa Bay Water Use Caution Area ("NTB WUCA"), the Eastern Tampa Bay Water Use Caution Area ("ETB WUCA"), and the Highlands Ridge Water Use Caution Area ("HR WUCA") because of its growing concerns regarding wetlands impacts, saltwater intrusion and lowered lake levels. 206. The NTB WUCA includes portions of Hillsborough, all of Pinellas and part of Pasco Counties. The ETB WUCA includes portions of Hillsborough, Manatee and Sarasota Counties. The HR WUCA includes portions of Polk and Highlands Counties. Several work groups were formed by the District in connection with the declarations of these WUCAs. In addition, various advisory committees established by the District for various user groups including public supply and agriculture, gave the District feedback during the process leading up to the declaration of the WUCAs. 207. The WUCA declarations were part of the Board's three-stage strategy to develop short mid- and long-term solutions to water resource problems in each of the study areas. Short-term protection measures were prescribed within the WUCA declarations. Mid-term measures -- including demand management, metering requirements and designation of a "most impacted area" for ETB (described in BOR Section 7), were subsequently completed.51 According to the District, final, long-term remediation and resource protection measures for ETB and Highlands Ridge are embodied in the proposed SWUCA Rules. 208. As noted above, a WRAP was initiated for the NTB area in the late 1980s and the area was designated a WUCA in 1989. The status of the WRAP report and the nature and extent of the problems in the NTB area are beyond the scope of this proceeding. 209. Certain developments in the regulation of that area are, however, relevant to note. First, because of perceived impacts to wetlands and record low water levels in lakes near wellfields in the NTB area, the District has taken some steps to reduce groundwater pumping in an effort to prevent further adverse impacts to the natural systems. On March 1, 1994, the District issued two Declarations of Water Shortage, which sought to limit public demand and reduce pumping at certain wellfields in the northern Tampa Bay region. In June of 1994, the District issued an Emergency Water Shortage Order requiring West Coast to reduce groundwater pumping at certain wellfields in NTB. In addition, the District sought to reduce the permitted quantities at some of the wellfields. The Emergency Water Shortage Order and permit renewals are subjects of separate ongoing litigation. 210. The Highlands Ridge was not originally included in the District, but was added in the late 1970s upon recognition of a persistent flow-line which ran southward from the Green Swamp parallel with and along the length of the center of the Ridge itself. The HR contains land both east and west of the persistent flow-line. 211. The Highlands Ridge is an area of approximately 750 square miles and is characterized by discontinuous ridges separated by broad valleys. On the eastern side of the Highlands Ridge, surface water drains to the Kissimmee River and on the western side it drains to the Peace River. 212. The Highlands Ridge is characterized by numerous sinkhole lakes that resulted from dissolution of the underlying limestone and dolomite and ultimate collapse of the Karst terrain. Sinkhole features can provide paths for water to flow from the lake/surficial aquifer system to the underlying Floridan Aquifer. 213. Lake levels in the Highlands Ridge have been declining since the late 1950s. Long-term well hydrographs from this area show a downward trend in annual peak water levels and an increase in seasonal water level fluctuations since the 1960s. The period of decline coincided with a period of low annual rainfall and increasing groundwater withdrawals for agricultural irrigation, mining, and public supply. A multitude of factors can affect the level of a lake. Groundwater withdrawals are only one of the influencing factors, and its significance can vary greatly from lake to lake. Changes in surface water drainage can play an important role. 214. Contrary to the suggestion of some Petitioners, the long-term declines in lake levels cannot be attributed solely to a reduction in local rainfall or to an increase in sinkhole activity that breaches the underlying semi-confining layer. The District's Ridge II Report concluded that water use outside the Ridge area contributed to declines in aquifer potentiometric levels along the Ridge, which in turn contributed to lower lakes levels. The more persuasive evidence supports the District's conclusion that some lakes on the Highlands Ridge have been significantly harmed by groundwater withdrawals from the UFAS. 215. Over the last five years, lake levels along the Highlands Ridge have improved somewhat as groundwater pumping has decreased in the area. In addition, higher-than-normal rainfall in recent years has contributed to higher lake levels. 216. Although September wet-season levels have been generally maintained since the 1980s, they have not recovered to historical levels recorded prior to 1964. Accordingly, the potential for induced recharge from the surficial aquifer to the UFAS remains higher than under predevelopment conditions with the net effect being decreased water levels in lakes and the surficial aquifer.52 It should be noted that, during the period of recovery, the potentiometric surface of the UFAS has been close to the proposed minimum aquifer level in the SWUCA Rules, thus indicating that the minimum level will help prevent further declines in the lake levels. 217. The primary concern addressed in the ETB WRAP was a deterioration in water quality, especially in the area along the coast. There was also concern that declining water levels could lead to well failures or increased pumping costs for existing wells. 218. Aided by the District's utilization of the expertise of hydrogeologic consultants, the ETB WRAP included a review of existing data and information, analysis of data, expansion of the existing data network, groundwater flow and transport model development and calibration, analysis of cause and effect relationships, and simulations of historic and potential withdrawal scenarios. Peer review for the ETB WRAP report was provided by District staff, U.S. Geological Survey professionals, and professors of geology and hydrogeology from the University of South Florida. 219. The District undertook expensive and extensive efforts to collect and analyze water quality data from the field, including data from existing monitor and production wells, supplemented by surface exploration and the construction of new monitor wells. Some Petitioners have claimed that the quality and reliability of the data collected vary greatly because of the different sources and that not all of the data supports the District's conclusions. The heterogeneous nature of the aquifer naturally results in great variation of water quality in wells with similar construction characteristics, pumping rates, and location. Nonetheless, by analyzing numerous wells over time, trends in water quantity can be observed. The more persuasive evidence established that the District's efforts to assimilate and analyze field data were well planned, scientifically and statistically sound, and reasonably framed. The District's efforts are ongoing as reflected by the Supplemental Investigations Report discussed below. It is expected that the continuing accumulation of data will provide further understanding of the condition, changes and functioning of the groundwater system. 220. The ETB WRAP determined that there had been significant lowerings of the potentiometric surface levels in the Southern Basin since predevelopment, and these changes were directly related to groundwater pumping. Some of the specific findings are discussed in Section IV below. 221. The ETB WRAP concluded that reduced groundwater levels resulting from pumpage within the entire Southern Basin contribute to several problems: 1) the saltwater intrusion problem in the coastal region of the Basin; 2) reduced well efficiencies as a result of pumps being required to lift groundwater from lower depths; 3) reductions in spring-flow and stream-flow; 4) wetlands impacts; and 5) lowered lake levels in Highlands and Polk Counties. In addition, the ETB WRAP concluded that the UFAS in the Southern Basin was a highly transmissive, well confined aquifer. Because it is such an interconnected system, groundwater levels at any location in the Southern Basin were found to be a function of the cumulative groundwater withdrawals occurring throughout the Basin. Accordingly, the ETB WRAP concluded that the "safe yield" for ETB was partly a function of the amount of water withdrawn from other areas within the groundwater basin. 222. The ETB WRAP sought to develop the technical information necessary to formulate a management strategy to halt saltwater intrusion along the coast. One of the principal objectives was to develop tools or mechanisms for the Board to utilize in regulating water use. As part of that effort, the District sought to develop a "safe yield" for the region. 223. "Safe yield" is not defined in Chapter 373 or the District's rules. It is commonly understood as being the level of use which can be sustained without causing unacceptable effects. In this regard, safe yield is comprised of both hydrologic and socioeconomic components. The hydrologic element involves the determination of the adverse impacts associated with the withdrawal of specific quantities of water. The socioeconomic element involves the determination of what is an unacceptable adverse impact. 224. During the ETB WRAP process, unacceptable impact was considered to be any further landward movement of the saltwater - freshwater interface. In other words, "safe yield" in this context was viewed as the quantification of the amount of water that could be withdrawn from existing wells in the ETB WUCA without producing significant additional movement of the saltwater-freshwater transition zone. 225. As part of the ETB WRAP, two "safe yield" scenarios were analyzed for the region. The first was to reduce groundwater withdrawals to 100 MGD in the Eastern Tampa Bay WUCA; the second was to reduce groundwater withdrawals in the Eastern Tampa Bay WUCA to 150 MGD and limit groundwater withdrawals in the remainder of the Basin to about 500 MGD.53 To arrive at these safe yield quantities, the District utilized a groundflow model for the region. Using an assumed pumping distribution based on existing withdrawals, the flow model predicted future potentiometric surfaces for the UFAS in the area. Model scenarios were run for 50 year periods with pumping quantities reduced until the models did not project any additional movement of the saltwater interface. 226. The modeling results confirmed that if pumping continued to increase as projected by the Needs and Sources Study, movement of the saltwater interface would affect water quality in wells further inland. In fact, the studies indicated that saltwater would continue to replace fresh water in the aquifer if 1989 water use levels continued in the future. 227. When presented with the results, the District decided that the potentiometric levels and projections of continued movement of the saltwater interface associated with 1989 pumping levels would result in significant harm to the resource and were unacceptable. As discussed in more detail in Section IV below, the District ultimately selected the potentiometric surfaces that occurred in 1991 as the proposed minimum level for the SWUCA. The 1991 levels reflect a reduction in groundwater pumpage from 1989 of approximately 30 percent within the ETB WRAP area and approximately 15 percent throughout the SWUCA. The 30 percent/15 percent reductions are roughly comparable to the safe yield proposal in the ETB WRAP. 228. The approach, results, and conclusions of the ETB WRAP have been evaluated by several independent experts. In addition, the ETB Computer Model Report has had extensive high level peer review. Comment and input from reviewers regarding the groundwater quality and trend analysis in the ETB WRAP led to further analysis of existing data utilizing two different statistical methods. These further analyses confirmed that there was a deterioration in water quality as measured by chlorides, sulfates and total dissolved solids in the UFAS. 229. The information developed as part of the ongoing ETB and HR WRAPs led the District to conclude that the Floridan Aquifer within the Southern Basin was an highly transmissive and well-confined aquifer, with groundwater withdrawals anywhere in the Basin contributing to overall resource conditions in the Basin. The District analyzed the information and determined a need to develop a regulatory strategy for the Southern Basin as a whole.54 In October 1992, it created the Southern Water Use Caution Area or SWUCA. The declaration of the SWUCA was meant to be an interim step while more information was obtained. 230. The boundaries of the SWUCA were developed by the District based upon a rough approximation of persistent flow lines within the UFAS. Encompassing nearly all of the Southern Basin and including most of the District south of the Hillsborough River, the SWUCA consists of about 5,100 square miles, and includes all of DeSoto, Hardee, Manatee, and Sarasota Counties, and portions of Charlotte, Highlands, Hillsborough, and Polk Counties. 231. The SWUCA includes those portions of the District previously designated as the ETB WUCA and the HR WUCA, as well as land areas that lie between those two WUCAs (the "non-WUCA SWUCA"). 232. One of the fundamental conclusions reached by the District (and a major premise behind the SWUCA Rules) is that the entire area should be treated as a linked groundwater basin even though geologic differences exist throughout. For example, there is greater interconnection between the surficial and Floridan Aquifers in the Highlands Ridge area than in Manatee County. In addition, the transmissivity and recharge characteristics vary throughout the SWUCA. Despite these differences, the District has concluded that the impacts of withdrawals from anywhere within the Southern Basin permeate throughout the Basin. While several Petitioners have challenged those conclusions, the more persuasive evidence established that declines in the Upper Floridan's potentiometric surface at a particular location result not only from localized water use, but also from regional water use. Although shifts in the location of pumping can alter the measurable impacts in certain locations, such changes do not refute the existence of regional impacts as well. For example, water use reductions by industry along the Highlands Ridge have been reflected in increased surface levels in some neighboring areas. 233. Upon declaration of the SWUCA, the District Board directed staff to develop a management plan for water use permitting in the area. As part of that effort, the Board authorized the formation of a SWUCA Work Group. The SWUCA Work Group included representation from agricultural, mining, industrial, local government (public water supply), environmental, and citizens' groups. 234. The purpose of the Work Group was both to educate the affected user groups regarding the nature and extent of the problems within the SWUCA, and to furnish the District with input and feedback regarding various options for dealing with those problems. The SWUCA Work Group had no formal decision-making authority. 235. In addition to monthly meetings in various locations throughout the District from January 1993 through September 1993, individual members of the Work Group often met with District Staff to provide input regarding particular issues. 236. The District also utilized a SWUCA Advisory Group of Experts ("SAGE") to assist in the development and review of scientific and technical information related to formulating water management policy for the SWUCA. This technical advisory committee, comprised of experts in various disciplines,55 began its work in 1993, assisted throughout the rule development process, and apparently continued to provide input during the hearing process. The SAGE Group reviewed and critiqued numerous documents prepared by the District with regard to the SWUCA and assisted in the preparation of some studies.56 237. Following the conclusion of the Work Group meetings, the District published a draft SWUCA Management Plan in September 1993. That draft was considered by the Governing Board in a series of public meetings beginning in late 1993. A revised draft Management Plan was prepared and released in April 1994. This version will be referred to as the "SWUCA Management Plan." 238. The primary goal of the SWUCA Management Plan was to develop a long-term strategy to significantly curtail or reduce the advance of saltwater intrusion and stabilize lake levels in Polk and Highlands Counties. Additional goals included preservation of the resource (including environmental features) and protection of existing legal uses. 239. The District says the SWUCA Management Plan is a dynamic process, and it expects to continually revisit the strategies and goals as new information becomes available and conditions change over time. 240. The SWUCA Management Plan included a number of proposed water conservation measures such as basing agricultural use on higher efficiencies, permitting public supply use based on lower per-capita usage rates, and requiring other water users to increase water conservation as appropriate for the particular activity.57 241. The SWUCA Management Plan projects that new alternative water sources can reasonably be pursued to offset existing groundwater demand and/or extend existing surface water sources.58 Potential new water sources include, but are not limited to, reuse of treated waste water, additional use of surface waters, desalination, increased surficial aquifer withdrawals, and storm-water reuse. There are, however, problems associated with several of the potential new sources identified in the Plan.59 242. Even if the conservation and alternative source projections in the Management Plan are met, the Management Plan recognized that to stabilize the saltwater interface and lake level declines within the SWUCA, actual withdrawals from the confined aquifers within the Eastern Tampa Bay area and the remaining SWUCA area had to be limited to 150 MGD and 550 MGD, respectively. 243. Both the ETB WRAP and the SWUCA Management Plan anticipated that achievement of those pumping levels and maintenance of the 1991 potentiometric surface levels throughout the SWUCA would halt saltwater intrusion over the 50-year planning horizon. 244. In the early part of 1994, the Board directed staff to begin development of administrative rules to implement the SWUCA Management Plan. During the rule development process, additional public meetings, hearings and workshops were conducted. c. Supplemental Investigations Report 245. After the ETB WRAP was completed in March 1993, the District, recognizing the complexity of the scientific issues and the implications to numerous parties affected by limiting withdrawals, undertook a series of post-report investigations and analyses to evaluate the conclusions and address certain post-report suggestions and comments received from both internal and external reviewers including the SAGE Group. These supplemental investigations and reports were assembled and published by the District in October 1994. The resulting document is referred to as the "Supplemental Investigations Report". 246. The Supplemental Investigations Report included additional documentation regarding the water-use estimation methods, an assessment of trends in groundwater levels in the SWUCA, an evaluation of the computer modeling utilized in the ETB WRAP, several studies regarding water quality trend analyses in the area including time-domain electromagnetic mapping of the saltwater transition zone and conceptual modeling of saltwater intrusion prepared by HydroGeoLogic, Inc., a nationally recognized consulting firm out of Virginia. 247. The Supplemental Investigations Report included refined and improved modeling techniques. These additional modeling efforts generally confirmed the District's conclusions regarding the interrelationship of withdrawals in the Basin and the ongoing movement of the saltwater interface. The Supplemental Investigations Report concluded that the northern section of the Southern Basin is more susceptible than the southern section to water quality deterioration from saltwater intrusion, and that the ETB WRAP and SWUCA Management Plan's prior estimates of cutbacks necessary to achieving "safe yield" may not halt the landward movement of the saltwater interface from its current location. In other words, the studies revealed that the saltwater interface would continue to move under the "safe yield" scenarios. This modeling, along with the other studies in the Supplemental Investigations Report, confirmed the need to cap withdrawals and redistribute pumping. 248. Some Petitioners have suggested that the different results obtained with the refined modeling indicate that the District has yet to assemble conclusive evidence as to the nature and extent of saltwater intrusion in the SWUCA. The modeling efforts are not the sole or even the primary evidence upon which the District relies to conclude that saltwater intrusion is occurring. As discussed in more detail in Section IV B, the District has relied heavily upon its monitoring well network and actual data regarding the vertical rate of migration of the saltwater interface to reach its conclusions. The District acknowledges that solute transport modeling is very complicated, and the resulting predictions as to future movement are based on assumptions regarding numerous interrelated variables. The modeling efforts confirm the District's analysis of existing data and provide a mechanism to estimate future conditions. The more persuasive evidence supports the District's analysis. d. Conclusions Regarding Scientific Investigations of the SWUCA 249. The evidence established that in assessing the current groundwater conditions in the Southern Basin, evaluating long-term trends in the hydraulic potential of aquifers in the SWUCA, and analyzing the complex and interrelated mechanisms that affect groundwater levels, the District has evaluated the available scientific information and employed a wide variety of highly trained professionals to analyze the information and to assist in developing new techniques and strategies for understanding the functioning of the groundwater systems. The District also sought input from independent scientists and representatives from groups and entities that comprise the primary users of the resource. As part of these efforts, the District developed sophisticated computer programs to project the consequences of future pumping on the groundwater systems. While there are inherent limitations on the accuracy and use of any current computer modeling of groundwater systems, the District has utilized state-of-the-art programs, subjected them to rigorous critique and evaluation from independent, highly qualified experts, and utilized a variety of scenarios to compare and evaluate the impact of different groundwater pumping levels within the Basin. 250. The evidence supports the District's conclusion that saltwater intrusion and lowered lake levels in the SWUCA are regional problems which require a regional solution. The issues cannot adequately be addressed on a permit-by-permit basis with current modeling programs and the District's existing rules. 251. Similarly, the more persuasive evidence supports the District's conclusions that the amount of groundwater withdrawals in the SWUCA in 1989 was detrimental to the water resources of the District, that the current permitted quantity poses a risk that similar or higher withdrawal levels may occur in the future, and that regulatory measures are necessary to address these issues.
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