SANTA BARBARA, CURACAO LANDSIDE KARST AQUIFER PIT - A SUSTAINABLE SEAWATER INTAKE SOURCE

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1 SANTA BARBARA, CURACAO LANDSIDE KARST AQUIFER PIT - A SUSTAINABLE SEAWATER INTAKE SOURCE George A. Schlutermann, P.G., PB Americas, Inc., Orlando, FL William Conlon, P.E., DEE, F.ASCE,Doosan Hydro Technology, Inc., Tampa, FL Brian Megic, P.E., PB Americas, Inc., Orlando, FL Ing. Henry L. Demei, Aqualectra Production, Curaçao, N.A. Abstract The project was part of the newly constructed Seawater Reverse Osmosis Plant in Santa Barbara, Curacao, N.A. Initially, the plan was to construct a pump house near the sea edge, which involved excavating a pit to a depth of about 8 meters. The geological setting of the project site is a formation which is a complex coral limestone (calcilutite) with a young karst surface. For dewatering purposes, sheet piles were installed in a rectangular arrangement. Due to the large inflow of groundwater into the sheet pile area, the contractor believed that dewatering the pit would not be possible. Rather than construct a pumping station within the pit, it was decided to investigate the use of the pit as a sustainable seawater intake source. By the end of September 2004, several pump tests were carried out which showed that high pumping capacities would likely be feasible from the coral limestone pit. The remaining question was the sustainability of the supply which resulted in continued testing in October and November. A three-dimensional numerical groundwater flow model was developed to represent conditions in the vicinity of the test pit. This model was used due to the non-homogeneous lithology of the site. Each pumping rate was operated until steady-state conditions had been reached. A calibrated flow model was used to perform various simulations to test the effects of the different flow conditions on the drawdown inside the pit. Two of the simulations included lining the pit floor with concrete, a possible final design of the proposed seawater intake pit. The analyses results indicated that the intake pit would be sufficient to provide seawater for all proposed operational ranges for the projected 20-year life of the project, and would be sufficient to provide seawater up to 4.5 times the maximum pumping rate.

2 SANTA BARBARA, CURAÇAO LANDSIDE KARST AQUIFER PIT A SUSTAINABLE SEAWATER INTAKE SOURCE Background The production of all power and potable water for the Island of Curaçao, Netherlands Antilles is carried out by Aqualectra Production at its facility at Mundo Nobo, situated about 2 kilometers to the west of the capital, Willemstad. Aqualectra Production management made the decision to reduce their dependence on thermal desalination processes and to decentralize their thermal and reverse Figure 1. Location Map osmosis water treatment capacity from the existing location at Mundo Nobo. It has been determined that ultimately all Aqualectra water and power production capacity at Mundo Nobo would be relocated elsewhere on the island to make way for new tourist infrastructure on the present site. In addition, Aqualectra Production has been concerned over the rising cost of fuel for its thermal processes and the effects on its water tariff. The first such move towards decentralization was to commission the construction by Suez Degrémont of the 18,000 m3/day Santa Barbara Seawater Reverse Osmosis (SWRO) Plant adjacent to Fuikbaai in Santa Barbara approximately 13 km to the east of the capital, as shown in Figure 1. Initially, the plan was to construct a seawater pump house and use a seawater intake as the source of supply. This would have required the installation of an HDPE conduit pipe across Fuikbaai, through an inlet channel, across an environmentally sensitive reef, and down the sea slope with the intake about 600 meters off shore. In order to construct the original planned seawater pump house, a pit was excavated in the young karst limestone to a depth of approximately 8 meters. For dewatering Figure 2. A rectangular pit was excavated with sheet piles driven into the coral limestone.

3 purposes, sheet piles were installed in an 8 meter by 17 meter rectangular arrangement, as shown in Figure 2. Due to the large inflow of groundwater into the sheet pile area, it was determined by the contractor that dewatering the pit would not be possible with conventional means (a 700 m3/hr pump was attempted). General Geology Neogene and Quaternary calcareous sediments cover large parts of the surface of Curaçao, which were deposited dome-like over a series of much thicker Upper Cretaceous and Lower-Tertiary volcanics and sediments. The Neogene and Quaternary carcareous rocks were formed mainly as a result of reef growth in relatively restricted shallow areas of the seas. The geological setting of the project site, as shown in Figure 3, is in the Lower Terrace Formation, which is described as faintly dipping (2 degrees), approx 600 m (NE side) to 200 m (SW side) wide coastal zone of limestone rocks. The basal plane of the Lower Terrace limestones rapidly dips below sea level and the basal plane near the cliff fronts may be situated at a depth of 20 m (or even more) below the surface of the sea. The Lower terrace complex is maximum 35 m thick, the upper part of which are m above sea level. The Lower Terrace limestone of the island has almost everywhere a young karst surface. The Lower Terrace limestone is as a rule sufficiently permeable to drain the rain water in a vertical direction. Figure 3. Map of Sta. Barbara, Curaçao Local Project Site Geology The site is located near the Fuikbaai were the Lower Terrace Formation is present (Figure 4). From the borehole drilled at the location of the proposed pit, the geology is described as follows: One borehole has been sunk at the pump station site to a depth of m below ground surface. Here also moderately strong porous coral limestone is present with solution Figure 4. Geological Section of Sta. Barbara Region2

4 cavities up to 110 cm. The top 1.2 m is strong coral limestone (calcilutite). At several depths thin layers of much stronger coral limestone (calcilutite) are present too... 1 The Initial Challenges The initial challenges were two-fold: first, the inability to pump down the site for the seawater pump station; and second, there was difficulty in obtaining vital permits necessary for the source of supply and residuals disposal. Normally, permits are in place before a project is released for bidding. If the permits are not obtained, serious project delays and cost overruns can occur. It was initially assumed by the contractor and client that permitting for the designed intake and outfall lines would be routine and easy. After bidding and contractor selection, the construction began concurrently with the permitting efforts. Two adjacent property owners and five government agencies objected to the permitting associated with the intake line. Rather than constructing a pumping station within the pit and the planned intake line, it was decided to investigate the use of a karst aquifer pit as a sustainable seawater intake source. If feasible, this would resolve two problems; the inability to pump the pit down for the pump station construction and the issues related to obtaining an intake line permit. Pumping Test To investigate this alternative, a large scale pumping test was required. This pumping test was originally planned to start on September 21, 2004, but was abandoned a week later as the pumping capacity of 3,500 m 3 /hr (the future maximum capacity of the facility) could not be reached with the pumps available at the time of the test. Other pumps had to be located which was a time consuming operation, as only a few large capacity pumps are available on Curaçao. It was decided that all pump test efforts would be halted until the design capacity of 3,500 m 3 /hr was available, installed, and working properly. A testing program was prepared in the meantime by PB and GeoCom. Figure 5. George Schlutermann and a Suez Degremont employee estimate flow from the discharge pipes during the long term pumping test of the pit. Prior to October 18, 2004, a total of 10 pumps were installed, tested, and calibrated for their actual discharge capacity. The water flow from all pumps was measured using the Carpenter Square method 3 as shown in Figure 5. This empirical method was used daily to calculate flow. A magnetic flowmeter was provided and

5 installed by Aqualectra for several days on one of the discharge pipes. The flow recorded by the installed flowmeter was compared with the flow using the Carpenter Square method. The calibrated capacities of the pumps are given in Table 1. As a result of this comparison, measured flows from other pumps were calibrated. Figure 6. Location of Pumps and Suction Hoses during Pit Test The location plan of the ten pumps and the suction hoses are displayed in Figure 6. Prior to the pump test, the sheet pile construction was opened by cutting several holes into the sheet pile wall to allow free draining of water in and out of the sheet pile pit area. A total of five water level observation points were established: 1 inside the pit, 1 outside the pit, 2 monitoring wells located between the sea and the pit site, and 1 at the observed sea front. These points were marked with red paint, their heights surveyed, and distances relative to the seafront were tape measured. The pumping test started on October 18, Water level measurements and water quality sampling were taken 24 hours per day. Pumping was performed in four steps of 1200 (step 1), 2500 (step 2), 3100 (step 3), and 3500 m 3 /hr (step 4) until November 2, Each pumping rate was operated for a long enough period for steady-state conditions to have been reached, as shown in Figure 7. At the end of the pump test, a full scale recovery test was carried out until November 7, Afterward, a long-term pumping test was conducted at the initial design rate of 2,500 m 3 /hr (the current capacity of the facility) to monitor water quality on a long-term basis. It was observed that the difference in drawdown between each pumping rate was about 0.2 m in all four land side observation points. A maximum drawdown of 0.69 m was observed inside the pit at a pumping rate of 3,500 m 3 /h. The water elevation in the sea was not impacted by the pumping test. Following the pumping test, a recovery test was carried out. The objective of the recovery test was to record the time required for the groundwater at vicinity of the pit site to reach its initial head. Full recovery of the water level inside the pit was achieved approximately 8 hours after initiation of the test. After completion of the recovery test, it was noticed that the average water level inside the pit was similar to the average water level observed in the sea. Average water level elevations at both locations were approximately 0.2 m. This similarity appeared to be due to the proximity of both locations, which was approximately 90 m.

6 Groundwater Flow Model and Analysis PB developed a three-dimensional numerical groundwater flow model to represent conditions in the vicinity of the test pit. The finite-difference MODFLOW code of the U.S. Geological Survey (USGS) 4 was used to develop the flow model. A numerical model was used in lieu of an analytical model due to the nature of the layout of the pit site. Both the shape and size of the pit would not be accurately represented using an analytical solution as these solutions were typically developed to analyze borehole (cylindrical) wells and are not effective at representing large irregular open water bodies. Another limitation of using analytical procedures is that they are typically for homogeneous aquifers. It was felt that the young karst limerock aquifer at the test pit had a higher horizontal hydraulic conductivity than vertical hydraulic conductivity which can not be adequately represented by an analytical solution. MODFLOW allows the user to easily modify any parameter and evaluate its impact on the area of study. A dense horizontal and vertical grid was used in the model to simulate the horizontal and vertical water flows in the vicinity of the pit site. The total thickness of the unconfined aquifer was estimated to be approximately 30 m. Based on water level observations recorded at the seafront monitoring location during the pumping test, the average sea level was estimated to be 0.2 m above sea level. Water levels recorded at the seafront, in the test pit, and at monitoring wells 1 and 2 during periods of no pumping indicate that minimal to no hydraulic gradient exists between the pit and the sea front. Due to this, the starting heads of all cells in the model were set at 0.2 m. The vertical dimension of the groundwater flow model was represented by four layers, with a thickness of 5.8 m, 5 m, 5 m and 11.4 m for layers 1, 2, 3, and 4, respectively. The thickness of layer 1 was set at the approximate depth of the pit below the model starting head. The remaining 21.4 m of aquifer below the starting heads in the model was divided into three layers. The thickness of layers 2 and 3 were set at a thickness similar to layer 1 but smaller than layer 4 as to better simulate potential vertical flow that may be occurring near the test pit due to pumping. This was considered reasonable as layer 4 is likely deep enough below the pit as to not be a significantly active portion of the flow field. The horizontal model domain covered 10,200 m x 20,000 m, and cell sizes ranged from 100 m x 100 m at distance to 0.5 m x 0.5 m in the vicinity of the pit site. The model represents groundwater flow between the sea and the pit site, and the inland area surrounding the pit site. A constant head boundary of 0.2 m was used along the seawater front in layer 1 of the model. This layer was calculated as the average sea level observed at the ocean monitoring location during the pumping test. No-flow boundaries were used along the lateral sides of the grid as well as the inland area of model layer 1, except for one cell in each of the inland model corners, which were set as constant head. No-flow boundaries were chosen for the non-seawater front sides of the model as to not allow artificial flow from outside the model boundaries into the model domain. No-flow boundaries are a conservative boundary condition. The constant head boundaries set at the two inland corners of the model were chosen for model stability. No-flow boundaries were set for all model sides of layers 2, 3, and 4 for conservatism.

7 Initial horizontal conductivity values were assigned based on an estimated transmissivity calculated using the method of images (wells near boundaries) 5 and from the specific capacities (pumped flow/drawdown) calculated during the pump test. Transmissivity was converted to horizontal hydraulic conductivity using the assumed thickness of each layer. Transmissivity was assumed to be the same for each of the flow model layers. The excavated area of the test pit is effectively an open water body; therefore, a transmissivity value of 300,000 m 2 /d was assigned within the limits of the test pit in layer 1 to simulate a smooth water surface. Initial horizontal and vertical anisotropy ratios of 1 were assumed. The horizontal anisotropy factor represents the ratio of horizontal hydraulic conductivity in the two principle directions of the model, which in a homogenous or isotropic aquifer is equal to one. The vertical anisotropy factor represents the ratio of horizontal hydraulic conductivity to vertical hydraulic conductivity, which in a homogenous or isotropic aquifer is equal to one. The anisotropy factors were later adjusted to 10 as part of a sensitivity analysis of the hydraulic parameters. Horizontal and vertical conductivity values were adjusted during the model calibration to obtain a reasonable fit to head values observed at the four observation points. The leakance (or leakage coefficient ) is defined as the ratio of the vertical hydraulic conductivity of a semi-confining unit to its thickness. Leakance arrays were required in the model to represent the three semi-confining units between the four aquifer layers. It is important to note that there is not true confinement between the four modeled aquifer layers. However, MODFLOW requires a layer between the active horizontal layers for model stability. To simulate this system as accurately as possible a semi-confining unit of zero thickness was assigned between the aquifer layers. Leakance values for these units were calculated based on the vertical hydraulic conductivity and thickness of the active layers above and beneath the unit. This equation can be expressed as follows: L Z 2K 1 1 Z 2 2 v1 K v 2 where: L is the effective leakance, [T -1 ]; Z 1 is the thickness of Layer 1, [L]; Z 2 is the thickness of Layer 2, [L]; K v1 is the vertical hydraulic conductivity of Layer 1, [LT -1 ]; K v2 is the vertical hydraulic conductivity of Layer 2 [LT -1 ]. Leakance was then adjusted during model calibration based on calibration adjustments made to hydraulic conductivity. Rainfall at the site was collected during the pumping test; however, no estimates of evaporation or evapotranspiration (ET) at the test pit were available. Due to this, a net recharge (rainfall minus ET) to the aquifer could not be estimated. As previously discussed, there appears to be little to no hydraulic gradient between the pit site and the seafront. This

8 is an indication that rainfall is not contributing a significant amount of recharge to the groundwater system to cause a significant ambient hydraulic gradient. In addition, the test pit is close to and greatly influenced by the sea and (based on water quality testing) is significantly seaward of any saltwater/freshwater interface that exists in the aquifer landward of the test pit. For each of the above reasons, a recharge rate of zero was initially assigned to the model. The MODFLOW ET package was not used due to the lack of data. As part of model calibration, the test pit was simulated using the MODFLOW hydraulic flow barrier package to represent the sheet pile wall. Small openings in the hydraulic flow barrier were assigned to simulate the sheet piles that were removed prior to the pump test. During calibration, vertical water level variations within each model cell were computed and compared to the observed drawdown recorded at the test pit during the pumping test performed in October This was done by creating observation points in MODFLOW at the locations of the four land side monitoring locations in the test pit area. A steady state calibration was performed in the vicinity of the pit site using a pumping rate of 3,500 m 3 /h. The calibration was a reasonable representation of the observed head field between the seafront and the pit site. No observed data was available to perform a calibration of the model at the inland areas away from the pit site. Transmissivity values of 22,000 m 2 /d and 7,300 m 2 /d were estimated initially using horizontal anisotropy factors of 1 and 10, respectively. Transmissivity values of 39,600 m 2 /d and 22,000 m 2 /d were estimated using vertical anisotropy factors of 1 and 10, respectively. The anisotropy factors were varied as part of a sensitivity analysis because little information on the variation between horizontal and vertical hydraulic conductivities of the aquifer near the test pit was available. Anisotropy factors of 10 were chosen as an estimate that would provide a reasonable range of transmissivity values. It was assumed that horizontal hydraulic conductivity toward (perpendicular to) the sea was greater than horizontal hydraulic conductivity parallel to the sea and that horizontal hydraulic conductivity was greater than vertical hydraulic conductivity for the following reasons: The limestone aquifer is known to have been deposited in relatively horizontal layers, which is evident in the excavated area of the test pit. Fissures and areas of dissolution in the aquifer observed in the excavated test pit are predominantly horizontal. Though minimal, the groundwater gradient is toward the sea. A short pump test was performed before several of the individual sheet piles were removed from the sheet pile wall. During this pump test, drawdown in the test pit was approximately 2.3 m at a flow rate of 1,200 m 3 /h. This is significantly greater than the approximately 0.7 m of drawdown observed at a flow rate of 3,500 m 3 /h during the pumping test performed after several sheet piles were removed. This is a strong indication that the horizontal conductivity is greater than the vertical hydraulic conductivity (anisotropy factor > 1). For each of the reasons noted above, an anisotropy factor less than 1 was not simulated.

9 Pumping Test Performed at the Test Pit 1,200 m 3 /h 2,500 m 3 /h 3,100 m 3 /h 3,500 m 3 /h Recovery Test 10/17 10/18 10/19 10/20 10/21 10/22 10/23 10/24 10/25 10/26 10/27 10/28 10/29 10/30 10/31 11/1 11/2 11/3 11/4 11/5 11/6 Step 1 Date Step 2 Step 3 Step 4 Figure 7. Water level elevation verses time. Seafront Well 2 Well1 Outside Pit Inside Pit W a t e r E le v a t io n ( m N M P )

10 Model Simulations to Assess Sustainability A calibrated flow model was used to perform various simulations to test the effects of the different flow conditions on the drawdown inside the karst aquifer pit. Below is a brief summary of the simulations performed: Simulation 1: This simulation was performed at a maximum proposed pumping rate of 3,500 m 3 /h and a horizontal anisotropy factor 1. For this simulation the horizontal flow barrier was removed assuming free flow of water from all four walls and the bottom of the pit. A transmissivity value of 22,000 m 2 /d was assigned, as found in the calibration runs. Simulation 2: This simulation was performed at a pumping rate of 15,772.5 m 3 /h (100 MGD) and a horizontal anisotropy factor 1. For this simulation the horizontal flow barrier was removed assuming free flow of water from all four walls and the bottom of the pit. A transmissivity value of 22,000 m 2 /d was assigned, as found in the calibration runs. Simulation 3: This simulation was performed at a maximum proposed pumping rate of 3,500 m 3 /h and a horizontal anisotropy factor of 10. For this simulation the horizontal flow barrier was removed assuming free flow of the water from all four walls and the bottom of the pit. A transmissivity value of 7,300 m 2 /d was assigned, as found in the calibration runs. Simulation 4: This simulation was performed at a pumping rate of 15,772.5 m 3 /h (100 MGD) and a horizontal anisotropy factor of 10. For this simulation the horizontal flow barrier was removed assuming free flow of the water from all four walls and through the bottom of the pit. A transmissivity value of 7,300 m 2 /d was assigned, as found in the calibration runs. Simulation 5: This simulation was performed at a maximum proposed pumping rate of 3,500 m 3 /h and a horizontal anisotropy factor of 1. For this simulation the horizontal flow barrier was removed assuming free flow of the water from all four walls of the pit. An impermeable barrier was assigned between layers 1 and 2, assuming no flow between the layers. This was done by assigning a leakance of 0 days -1 between model layers 1 and 2 in order to simulate the effect of lining the bottom of the pit with concrete. A transmissivity value of 22,000 m 2 /d was assigned, as found in the calibration runs. Simulation 6: This simulation was performed at a maximum proposed pumping rate of 3,500 m 3 /h and a horizontal anisotropy factor of 10. For this simulation the horizontal flow barrier was removed assuming free flow of the water from all four walls of the pit. An impermeable barrier was assigned between layers 1 and 2, assuming no flow between the layers. This was done by assigning a leakance of 0 d -1 between model layers 1 and 2 in order to simulate the effect of lining the bottom of the pit with concrete. transmissivity value of 7,300 m 2 /d was assigned, as found in the calibration runs. Simulations 5 and 6 include a concrete lined pit floor. This was done as a sensitivity analysis to bracket the solution. At the time this analysis was being performed the final pit could have been potentially designed with no further improvements to the bottom, with an impermeable lined bottom, or something in between. Simulating no lining and an impermeable lining in two different scenarios assists in bracketing the solution for a wide range of potential pit A

11 floor designs. Though these simulations were performed to assist the designers of the test pit, design of the pit is outside the scope of this analysis and no further consideration of the design of the pit was conducted. Results of the model simulations are summarized below. Simulation 1: Assuming horizontal conductivity values of 3,793 m/d, 4,400 m/d, 4,400 m/d and 1,930 m/d for layers 1, 2, 3 and 4 respectively (T=22,000 m 2 /d), a maximum drawdown of 0.65 m was simulated inside the pit for a pumping rate of 3500 m 3 /h. The results for simulation 1 are summarized in Table 1. Table 1. - Computed Results for Simulation 1 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulation 2: Assuming horizontal conductivity values of 3,793 m/d, 4,400 m/d, 4,400 m/d and 1,930 m/d for layers 1, 2, 3 and 4 respectively (T=22,000 m 2 /d), a maximum drawdown of m was simulated inside the pit for a pumping rate of 100 MGD. The results for simulation 2 are summarized in Table 2. Table 2. - Computed Results for Simulation 2 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulation 3: Assuming horizontal conductivity values of 1,259 m/d, 1,460 m/d, 1,460 m/d and 640 m/d for layers 1, 2, 3 and 4 respectively (T=7,300 m 2 /d), a maximum drawdown of m was simulated inside the pit for a pumping rate of 3500 m 3 /h. The results for simulation 3 are summarized in Table 3. Table 3. - Computed Results for Simulation 3 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulation 4: Assuming horizontal conductivity values of 1,259 m/d, 1,460 m/d, 1,460 m/d and 640 m/d for layers 1, 2, 3 and 4 respectively (T=7,300 m 2 /d), a maximum drawdown of m was simulated inside the pit for a pumping rate of 100 MGD. The results for simulation 4 are summarized in Table 4.

12 Table 4. - Computed Results for Simulation 4 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulation 5: Assuming horizontal conductivity values of 3,793 m/d, 4,400 m/d, 4,400 m/d and 1,930 m/d for layers 1, 2, 3 and 4 respectively (T=22,000 m 2 /d) and an impermeable liner at the bottom of the pit, a maximum drawdown of m was simulated inside the pit for a pumping rate of 3500 m3/h. The results for simulation 5 are summarized in Table 5. Table 5. - Computed Results for Simulation 5 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulation 6: Assuming horizontal conductivity values of 1,259 m/d, 1,460 m/d, 1,460 m/d and 640 m/d for layers 1, 2, 3 and 4 respectively (T=7,300 m 2 /d), and an impermeable liner at the bottom of the pit, a maximum drawdown of m was simulated inside the pit for a pumping rate of 3500 m 3 /h. The results for simulation 6 are summarized in Table 6. Table 6. - Computed Results for Simulation 6 Observation Points Initial Water Elevation (m) Final Water Elevation (m) Drawdown (m) Inside Pit Outside Pit Well Well Simulations varying the vertical anisotropy factor were ultimately not performed since the transmissivity calculated from the calibration simulation with a vertical anisotropy factor of 10 was 1.8 times higher than calculated with a vertical anisotropy factor of 1. Therefore, use of a vertical anisotropy factor of 1 is a more conservative assumption. The following conclusions were made from the results of the theoretical modeling: A drawdown of 0.7 m is predicted inside the pit by simulating a pumping rate of 3,500 m 3 /h (well above the proposed pumping rate). This is 5.1 m above the bottom; therefore, the pit is expected to provide sufficient water for all operational pumping rates equal to or lower than the ultimate proposed pumping rate of 3,500 m 3 /h, even considering tidal fluctuations. The predictive groundwater flow modeling scenarios performed as part of this study were steady-state simulations (performed until water levels reached equilibrium at the

13 simulated pumping rate). Due to this, with the exception of any unforeseen or out of historically observed conditions, it is reasonable to assume that the test pit should be sufficient to provide water for the proposed operational range for the projected 20-year life of the project. A maximum drawdown of 4.6 m was simulated by assuming a pumping rate of 20,631 m 3 /hr (100 Million Gallons Per Day). This results in a water level approximately 1.2 m above the pit bottom. This flowrate is 4.5 times the maximum proposed pumping rate. Therefore, the total inflow coming into the pit appears to be sufficiently large to allow the withdrawal of water within and above the proposed operational pumping ranges. The water levels simulated in the groundwater flow model are average water levels. Tidal effects were removed from the modeling analysis for simplicity; however, it can not be neglected. During the pump test, water levels appeared to vary approximately 0.2 m about average sea level due to tidal fluctuations. PB was provided information from Aqualectra that the maximum observed historic fluctuation in sea level due to the tides was 0.4 m. Average sea level during the test also appeared to vary and was typically above 0 m. The average sea level assumed in the groundwater flow modeling was 0.2 m. Considering the above points, water levels could be up to 0.6 m lower than simulated in the modeling due to tidal effects. Considering this offset in the worst-case model simulation, the total drawdown in the pit would be approximately 5.2 m (compared to 4.6 m). The resulting water level is still above the pit bottom, but may be getting too close to the pump intake elevations to be operationally feasible. Assuming an impermeable lining between layer 1 and 2 (i.e., a concrete lined pit bottom) did not result in unacceptable drawdown in the test pit. This indicates that the inflow coming through the bottom of the pit appears to be considerably less than the horizontal flow coming through the walls. Conclusions Based on the water level analyses performed by PB the following general conclusion can be made about the sustainability of the karst aquifer on this project. The karst aquifer pit is predicted to be sufficient to provide seawater for all proposed operational ranges for the projected 20-year life of the project. The karst aquifer pit appears sufficient to provide seawater at up to 4.5 times the maximum pumping rate utilized during the pump test. The construction of the final pit and seawater pump station was completed in July, 2005 with follow-up performance testing in the fall of Figure 8 Figure 8 Completed Pit

14 shows the completed pit. The use of the pit commenced in early October, 2005 with official inauguration of the plant occurring on January 19, References: 1 Geonviro consultancy b.v., 22 November 2003, Geotechnical investigation for Reverse Osmosis Plant Santa Barbara, Curaçao (N.A.) 2 P.H. De Buisonjé, 1974, Neogene & Quaternary Geology of Aruba, Curaçao and Bonaire (Netherlands Antilles) 3 Fletcher G. Driscol, Carpenter Square method is described in Groundwater and Wells, 2 nd Edition, Appendix 16.E. 4 United States Geological Survey (USGS), 1996, Simulation Analysis of the Groundwater Flow System in the Portland Basin, Oregon and Washington. United States Geological Survey Water-Supply Paper 2470-B, Clark County, Washington. 5 Bear, J., Hydraulics of Groundwater. McGraw-Hill Series in Water Resources and Environmental Engineering. Biographical Sketches George Schlutermann, P.G. is a supervising hydrogeologist and project manager with PB Americas, Inc., in Orlando, Florida. George has been working as a consultant for 18 years, 14 with PB. His work experience involves leading hydrogeological studies, reclaimed water facilities design, water supply planning, large production well design, permitting, construction and testing, and groundwater monitoring wells systems design, construction, and permitting. George is a member of the NGWA (AGWSE), AWRA, ASCE, and the AWWA. George is a registered Geologist in the State of Florida and Arizona and a registered Geoscientist in the State of Texas. Address: 100 E. Pine Street, Suite 500, Orlando, FL Bill Conlon, P.E., DEE, F.ASCE is Senior Vice President and Chief Engineer for Doosan Hydro Technology in Tampa, Florida. Bill has been a consulting engineer for over 35 years. He is experienced in all areas of water and wastewater management, operations and design, and he has been a pioneer in the application of reverse osmosis, ultrafiltration, and membrane system components to municipal water treatment. He has initiated innovative plant designs that significantly reduced treatment plant operating costs. Bill is an internationally recognized specialist in the design and operation of membrane process treatment systems. Address: 9001 Brittany Way, Tampa, FL Brian Megic, P.E., is a water resources engineer and project manager with PB Americas, Inc. in Orlando, Florida. Brian has a broad-based background in civil and environmental

15 engineering. In his 7 years with PB he has worked on numerical and analytical groundwater modeling (natural systems analysis and modeling), water resources planning, reclaimed water and water system design, environmental permitting, aquifer performance testing and analysis, hydrogeologic investigations, site development, hydrologic design and analysis including stormwater master planning, cost estimating, pipe network and hydraulic analysis, and pipeline design. Brian is a registered professional engineer in both Florida and Texas. Address: 100 E. Pine Street, Suite 500, Orlando, FL Ing. Henry L. Demei has a mechanical engineering background (energy) in the position of Manager Projects Bureau at Aqualectra Production in Curaçao, Netherlands Antilles. In this position he is in charge of all technical projects ranging from desalination plant, power plants, civil and building projects, retrofitting of existing plants and components, innovative projects such as solar energy and cold water pipe. Furthermore, more he has a vast experience in the maintenance of power and desalination plants. Henry has more than 30 years experience in the aforementioned fields. Address: Rector Zwijssenstraat 1 P.O. Box 2097, Curaçao, N.A.