ML21035A218
| ML21035A218 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 01/21/2021 |
| From: | NRC/OCIO |
| To: | |
| Shared Package | |
| ML21035A187 | List:
|
| References | |
| NRC-2020-000123 | |
| Download: ML21035A218 (16) | |
Text
1009496.0001.06.02 Turkey Point Plant Annual Monitoring Report August 2016 Prepared by:
Prepared for:
Prepared for Global Environmental Specialists ecology and environment, inc.
An Au
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-4 Figures 5.1-5 and 5.1-6 depict chloride concentration cross-sections for March 2016. The approximate location of the 19,000 mg/L chloride line is shown. MDC has defined hypersaline water as chloride concentrations above 19,000 mg/L (MDC 2015a). This isopleth represents an estimated extent of hypersaline water west of the CCS and is based on interpolation methods and best professional judgment. Further refinement of this line will be made based on additional monitoring data collected.
5.2 Water and Salt Balance Model Tetra Tech developed a model of the water and salt balance for the CCS. The purpose of this model is to quantify the volume of water and mass of salt entering and exiting the CCS over a 12-month period. Details of this Excel-based model, the underlying conceptualization of the relationship between the CCS and the surrounding environmental systems, key calculations, and results were provided in the Comprehensive Pre-Uprate Monitoring Report (FPL 2012a). That version of the model simulated water and salt flow to and from the CCS for the period between September 2010 and June 2012. The conceptual model and associated calculations are predominantly unchanged since last presented in the Comprehensive Pre-Uprate Monitoring Report (FPL 2012a). In the Comprehensive Post-Uprate Monitoring Report, refinements to the model were made and water and salt flow to and from the CCS was simulated for the period between September 2010 and May 2015. In this report, the modeled period encompasses the reporting period (12-month period) from June 2015 through May 2016. This period includes the effects of the CCS salinity reduction efforts. A brief summary of the model is provided below.
Model results and corresponding conclusions regarding the operation of the CCS are based on the current calibrated water and salt balance model and are provided herein. The Excel spreadsheet that comprises the model is provided in a separate data file.
5.2.1 Model Summary As Figure 5.2-1 depicts, the water balance for the proposed control volume for this monitoring period is comprised of seepage (lateral through the sides and vertical through the bottom),
blowdown (additional water pumped from other units to the CCS), added water (pumped from L-31E canal and/or groundwater), precipitation (including runoff from earthen berms between canals), and evaporation. Aside from evaporation and precipitation, these are the same mechanisms by which salt flows into and out of the CCS. The means by which water and/or salt is transferred (e.g., seepage, evaporation) are calculated using various equations provided in the Comprehensive Pre-Uprate Monitoring Report (FPL 2012a). Calculations were performed for a 12-month period from June 2015 through May 2016. Average flows of water and salt into and out of the control volume were calculated for each day of this period using hydrologic, water quality, and meteorological data measured within, beneath, and adjacent to the CCS. The average daily flows were summed to estimate the amount of water and salt that enters or exits the control volume (i.e., the CCS) during each month and the entire 12-month period. These calculations demonstrate and validate the conceptual model of the CCS and, in so doing, illustrate the hydrologic mechanisms by which the CCS functions.
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-5 Calculated water flows are reported in 106 gallons per day (millions of gallons per day [MGD]).
The mass flux into or out of the control volume is calculated by multiplying the volumetric flow by the salinity of the body of water from which the water is flowing. Salinity was monitored at all groundwater and surface water stations employed in the ensuing calculations and was reported in the practical salinity scale (PSS-78), which is equivalent to grams per liter (g/L).
Calculated mass fluxes are reported in thousands of pounds per day (lb x 1,000/day).
The gain/loss of water and salt mass within the control volume during some period of time results in a change in the control volumes water and salt mass storage. Increased water storage, for instance, occurs when more water enters the control volume than exits. Storage, then, can be estimated by summing all of the components of the water (and salt) balance. When the net flow is positive (into the control volume) during a specified period of time, the storage of control volume increases. Conversely, a net negative (out of the control volume) flow implies a decrease in storage during a specified time period.
Another manner in which a change in storage can be estimated relies on direct measurements of water elevations and salinities within the control volume. A change in water elevation within the control volume can be calculated as a difference between water elevations at the beginning and end of a specified time period. The product of this change in water elevations and the surface area of the control volume provide an estimate of the change in the volume of water contained in the control volume during that period of time. Estimates of daily storage changes derived from this method are used to further calibrate the water and salt balance model to ensure an accurate simulation of temporal trends for CCS water elevation and salinity.
5.2.2 Model Calibration, Results, and Discussion The individual components of the water and salt balance were simulated daily and summed for each month from June 2015 through May 2016, as well as for the collective 12-month period.
The individual components of flow are summed in order to calculate a simulated change in volume for each month and for the 12-month period. These simulated changes in storage were compared to observed changes in CCS water and salt storage for each month and the entire calibration period (June 2015 through May 2016). Errors between the simulated and observed storage changes were minimized by adjusting key variables associated with the flow balance model; this process is called calibration. The calibration process ensures that the model can accurately reflect the average changes in CCS storage over the 12-month time frame, while also effectively capturing day-to-day changes in CCS water and mass storage. Calibration of the water and salt balance model was achieved by adjusting hydraulic conductivities of the aquifer materials adjacent to and beneath the CCS that factor into the calculation of seepage to/from groundwater and Biscayne Bay. Additional adjustable parameters include the coefficients in the wind function (FPL 2012a), the amount of runoff that enters the control volume as percentage of precipitation, the amount of Unit 5 cooling tower water that is lost to evaporation before entering the CCS, and the salinity of the Unit 5 blowdown as a percentage of seawater. The calibrated model parameter values are provided in Table 5.2-1.
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-6 5.2.2.1 Parameter Adjustments The horizontal hydraulic conductivities laterally adjacent to the control volume were calibrated to range between 100 ft/day and 500 ft/day. The calibrated vertical conductivities beneath the control volume ranged from 0.1 ft/day to 2 ft/day. In order to achieve a better match to observed hydrologic and salt concentration conditions, the northern portion of the internal discharge canals into the CCS and return canals were calibrated to have higher vertical hydraulic conductivities (1.9 ft/day and 0.9 ft/day, respectively) than the middle/southern portions of the internal CCS discharge canals and southern portion of the return canals (0.1 ft/day). The variability in these vertical hydraulic conductivities is attributable to the non-uniform depth of a shallow high flow zone that is variably intersected by deeper CCS canals. The magnitudes of and variability in horizontal and vertical hydraulic conductivities are on the same order of magnitude as those in the prior model, where vertical hydraulic conductivity ranged from 0.1 to 3 ft/day and horizontal hydraulic conductivities ranged from 400 to 850 ft/day.
In addition to changes in hydraulic conductivities, revisions were made to both evaporation and precipitation. The equation for evaporation (FPL 2012a) includes an empirical factor. This factor was reduced from 0.66 to 0.60 during the calibration of the 12-month balance model. As the modeled balance is very sensitive to evaporative losses, this was a significant change. The percentage of additional precipitation-based inflow due to runoff from canal berms is an adjustable model parameter. This parameter is time-invariant and increases precipitation-based inflow for all precipitation events; as the precipitation increases, so too does the additional runoff inflow. Since the precipitation is a key inflow to the CCS for moderating salinity, the balance model is sensitive to this parameter. The balance is also sensitive to precipitation-based inflow.
As such, the reduction of runoff-based inflow from 35% to 10% of precipitation was also a notable change. This adjustment was necessary in order to match both the balance of water and salt flows, as well as the magnitude of CCS water levels and salinity, particularly in months with notable rainfall events.
The impact of the parameters changes, particularly the adjustments made to evaporation and precipitation parameters, is a relatively accurate simulation of the monthly flow balance and simulated daily CCS conditions during the 12-month period between June 2015 and May 2016.
5.2.2.2 Flow Balance Comparisons Results of the calibrated 12-month water and salt balance model are provided in Tables 5.2-2 and 5.2-3, respectively. The modeled net flow of water, as calculated by summing the components of the water balance for the 12-month calibration period, is denoted as the Modeled Change in CCS Storage and was calculated to be an average outflow of 0.63 MGD over the 12-month calibration period. The observed change in storage, which is the difference in the volume of water in the CCS between the final and first days of the calibration period, divided by the number of days in the period, was observed to be an increase in storage at a rate of 1.17 MGD.
Though the model underestimated the change in storage, the residual error between the simulated and observed flow is only 1.8 MGD. This error is small (2.3%) relative to the variability in monthly net observed flows, which range from a net outflow of 34.4 MGD (February 2016) and a net inflow of 42.7 MGD (September 2015).
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-7 The model simulated a net loss of salt over the 12-month period at rate of 3,723 (lb x 1,000)/day.
The corresponding observed rate of salt outflow was calculated by multiplying the average observed salinity in the CCS on the final day and first day of the calibration period by the corresponding CCS volumes on those days. The difference between these two products, divided by the number of days in the calibration period, provides the observed net outflow of salt, 2,958 (lb x 1,000)/day. The error associated with the mass flux is an overestimation by approximately 765 (lb x 1,000)/day. As in the case of water balance simulation, the magnitude of this overestimation is small (2.4%) relative to the range in monthly average flows: the observed monthly net mass fluxes range from an outflow of 20,838 (lb x 1,000)/day (November 2015) to an inflow of 10,965 (lb x 1,000)/day (July 2016).
Figures 5.2-2 and 5.2-3 illustrate the models ability to match the magnitude and direction of net monthly flows of water and salt, respectively. Figure 5.2-2 compares observed and modeled net monthly flows of water into and out of the CCS. There is a general seasonal trend in observed flows to/from the CCS, where inflows are generally associated with the wet season and outflows are generally associated with the dry season. The key exception to the dry season outflows occurs in December 2015, during which a total of approximately 15 inches of precipitation fell on the CCS. The model is able to replicate the general trends in flow, as well as the unusual inflow of water in December, with reasonable accuracy. However, there are two isolated months where the model does not accurately simulate the net flow (i.e., April 2016 and May 2016).
During these two months, the model simulates a loss of storage (net outflow), whereas an increase in storage was observed.
Figure 5.2-3 compares observed and modeled net monthly flows of salt into and out of the CCS.
A seasonal trend in salt mass flows is apparent (storage decrease during dry season, storage increase during wet season). Like the modeled water flows, estimated salt mass fluxes generally match observed fluxes well. Note that a significant reduction in salt storage (salt outflow) was observed in November and December 2015. The reductions in salt storage observed during these two months are largely attributable to seepage to groundwater. Previously, the greatest observed rate of salt loss (12,726 lb x 1,000/day) from the CCS occurred in October 2014 (FPL 2014); the October through December 2015 salt outflows exceed the October 2014 outflow by 4%, 64%,
and 31%, respectively. Conversely, the calculated volumetric water seepage in these three months exceeds that of October 2014 (25.65 MGD) by 4%, 21%, and 110%, respectively. As such, the greater salt mass outflow in late-2015 is attributable to greater water seepage at a relatively lower concentration of salt. This is consistent with the observed range of CCS salinity in late-2015 (34 to 58 g/L) being lower than the range of CCS salinity in October 2014 (65 to 85 g/L). It is important to note that the increased seepage of water from the CCS is a hydrologic response to the addition of L-31E canal water at an average rate of 21 MGD during October and November 2015 and the significant precipitation-based (14.7 inches of rainfall) inflow to the CCS in December 2015.
5.2.2.3 Simulated CCS Water Levels and Salt Implicit in the models ability to simulate monthly net water and salt mass flows is the accurate simulation of daily flows to and from the CCS. Because the model is able to characterize the
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-8 daily flows of water and salt, the model estimates the daily changes in CCS water and salt storage. As previously mentioned, these changes in storage are associated with daily changes in CCS water levels and salinity. Figure 5.2-4 shows the model-calculated water level in the CCS, which varies over the period of record. These modeled water levels range between approximately -1.1 ft North American Vertical Datum of 1988 (NAVD 88) and 2.1 ft NAVD 88, and reflect an average water level throughout the entire CCS. Also shown in this figure are the observed CCS water levels over time; the observed values reflect the mean of daily-averaged water elevations across the seven sensors in the CCS. Note, the maximum average observed CCS water level (1.7 ft NAVD 88) exceeds the previous maximum (since fall 2010) average observed CCS water level (0.87 ft NAVD 88) by 0.83 ft.
As mentioned above, nearly 15 inches of rain fell on the CCS in December 2015; this amount of rainfall far exceeds the average December rainfall at Turkey Point over the previous 5 years (0.86 inches). Simulated water elevations are calculated by dividing the simulated daily change in CCS storage by the average daily CCS surface area and adding the resulting value (which reflects a change in water level) to the previous days simulated water elevation. It is evident from this figure that the model effectively captures the general trend in CCS water elevations over the 12-month period, and accurately simulates average CCS water elevations throughout much of the calibration period.
Similarly, changes in salt mass storage within the CCS can be used to calculate average CCS salinity changes over time. The simulated daily net flow of salt is divided by the simulated volume of water in the CCS, which results in a change in salinity. This change in salinity is added to the simulated salinity calculated for the previous day to produce a simulated salinity for the current day. Like the simulated CCS water level, the modeled salinity reflects a representative daily salinity throughout the CCS. Figure 5.2-5 compares the simulated salinities to those observed in the CCS over the period of record. Observed salinities are the mean of daily averaged salinities measured in the CCS monitoring stations. The modeled CCS salinity changes over time match changes in the average observed CCS salinity throughout the 12-month period of record. This timeframe includes a reduction in average observed CCS salinity from approximately 95 g/L (PSS-78 scale) in June 2015 to approximately 34 g/L (PSS-78 scale) in December 2015; subsequent to the reduction in CCS salinity between June and December 2015, CCS salinity generally increased to approximately 55 g/L (PSS-78 scale). The ability of the model to match both increasing and decreasing trends in salinity reinforces the underlying conceptual model, which suggests that changes in CCS salinity are predicated solely on changes in the flow of water (which includes evaporation) into and out of the CCS.
5.2.2.4 Conclusions The accurate simulation of changing CCS inflows, outflows, water elevations, and salinities is complex due to the different components of the balance model and their varying impacts upon CCS water and salt storage. For instance, vertical flows into and out of the control volume are generally larger than horizontal flows, and have a greater impact on CCS water elevation. The salinity of inflowing water, however, can vary depending upon the source of the water. For example, horizontal flow from the west (L-31E) is non-saline and has a pronounced mitigating impact on CCS salinities; vertical flow from groundwater beneath portions of the internal CCS
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-9 discharge canals is saline to hyper-saline and generally increases the salinity of the CCS. The correct balance of both water and salt mass flow is difficult to estimate in the model. In addition, observed CCS return canal intake (i.e., at TPSWCCS-6) water temperatures varied over 17°C (from approximately 18°C to 35°C) during the simulated timeframe. The model addresses associated impacts to the CCS by explicitly simulating the effects of water/air temperature gradients on evaporation. Whereas myriad sources and sinks of water, varying salinities, and changes in water temperature do increase model complexity, the need to accurately simulate these different components of CCS operation constrains the number of possible solutions.
The simulated timeframe includes a 3-month period where salt mass outflows from the CCS exceed the greatest monthly salt outflow from the previous 4.5 years, which occurred in October 2014. Unlike the salt mass outflow in October 2014, where the outflowing water was of a higher salinity, those mass outflows calculated for October through December 2015 are attributable to a large amount of water at a lower salinity. These outflows occurred due to the higher than normal rainfall that occurred from August through December 2015 coupled with CCS salinity reduction efforts. Consequently, there were greater outflows of water and salt mass from the CCS to the underlying aquifer, primarily from October 2015 through December 2015.
Though the model is able to simulate the complex dynamics associated with the CCS over a 12-month timeframe with reasonable accuracy, there are periods of time where the simulated flows of water and salt do not accurately reflect observed conditions. Consequently, the simulated water level and salinities in the CCS deviate from those that have been observed at various times in the simulation period. However, the overall performance of the model reinforces its utility as a tool for understanding how the CCS has operated, and will operate, under varying meteorological, hydrological, and operational conditions. This is best demonstrated by the fact that the same conceptual model employed to characterize changes in CCS storage of water and salt during the reporting period was used to explain changes in storage during the prior approximately 4.5-year Uprate monitoring period.
The robustness and accuracy in the model underpins FPLs firm understanding of processes that control the CCS and the manner in which the CCS interacts with the adjacent aquifer and water bodies. This accuracy in simulating the historical changes within the CCS bolsters confidence in the models utility as a tool to evaluate the sensitivity of CCS operations to certain factors such as changes in operation, drought conditions, storm events, and other potential environmental stresses. Additionally, the model accuracy validates the fact that the most appropriate data are being collected to effectively capture CCS operations, identify interactions between the CCS and the surrounding environment, and support FPLs comprehension of historical and future operations of the CCS.
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 TABLES
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-10 Table 5.2-1. Calibration Parameters Parameter Name Calibrated Value Units Vertical Hydraulic Conductivity (Zone A) 1.9 ft/day Vertical Hydraulic Conductivity (Zone B) 0.1 ft/day Vertical Hydraulic Conductivity (Zone C) 0.1 ft/day Vertical Hydraulic Conductivity (Zone D) 0.9 ft/day West Face Hydraulic Conductivity 500 ft/day East Face Hydraulic Conductivity 100 ft/day North Face Hydraulic Conductivity 500 ft/day South Face Hydraulic Conductivity 500 ft/day Evaporation Modifier (Factor Multiplier) 0.60 Runoff Modifier (as % of Precipitation) 10%
Blowdown Evaporation Factor 50%
Blowdown Concentration (as % of Seawater) 0.50
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-11 Table 5.2-2. Calculated Fluid Flows from Water Budget Components June 2015 to May 2016 Water Budget Component Flow (MGD)
Volume (gal x 10^6)
Into CCS W. Seepage 0.45 162.92 E. Seepage 0.69 252.32 N. Seepage 0.01 3.35 S. Seepage 1.40 512.04 Bottom Seepage 0.72 260.35 Precipitation and Runoff 24.67 9027.57 Evaporation 0.00 0.00 Unit 3, 4 Added Water 0.55 202.90 Unit 5 Blowdown 0.30 111.01 ID Pumping 6.43 2353.27 Added Water (e.g. L-31E) 20.96 7671.49 Plant Outflow Equal to Intake Plant Intake Equal to Outflow Total In:
56.17 20557.25 Out of CCS W. Seepage 0.00
-0.37 E. Seepage
-1.91
-697.91 N. Seepage
-0.02
-5.93 S. Seepage
-0.76
-278.48 Bottom Seepage
-17.48
-6399.32 Precipitation and Runoff 0.00 0.00 Evaporation
-36.32
-13292.30 Unit 3, 4 Added Water 0.00 0.00 Unit 5 Blowdown 0.00 0.00 ID Pumping 0.00 0.00 Plant Outflow Equal to Intake Plant Intake Equal to Outflow Total Out:
-56.49
-20674.56 Modeled Change in CCS Storage:
-0.63
-302.38 Observed Change 1.17 427.31 Key:
CCS = Cooling Canal System.
gal = Gallon.
ID = Interceptor Ditch.
MGD = Million gallons per day.
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-12 Table 5.2-3. Calculated Mass Flows from Salt Budget Components June 2015 to May 2016 Mass Budget Component lb/day (x1000)
Mass (lb x 1000)
Into CCS W. Seepage 2.57 942.07 E. Seepage 199.17 72897.33 N. Seepage 0.07 24.17 S. Seepage 335.06 122633.52 Bottom Seepage 230.58 84391.66 Precipitation and Runoff 0.00 0.00 Evaporation 0.00 0.00 Unit 3, 4 Added Water 0.00 0.00 Unit 5 Blowdown 44.30 16212.85 ID Pumped Water 563.79 206345.63 Added Water (e.g. L-31E) 3815.95 1396636.59 Plant Outflow Equal to Intake Plant Intake Equal to Outflow Total In:
5191.49 1900083.83 Out of CCS W. Seepage
-80.88
-29603.04 E. Seepage
-694.08
-254032.84 N. Seepage
-6.16
-2254.91 S. Seepage
-279.55
-102315.54 Bottom Seepage
-7853.90
-2874527.56 Precipitation and Runoff 0.00 0.00 Evaporation 0.00 0.00 Unit 3, 4 Added Water 0.00 0.00 Unit 5 Blowdown 0.00 0.00 ID Pumping 0.00 0.00 Plant Outflow Equal to Intake Plant Intake Equal to Outflow Total Out:
-8914.57
-3262733.89 Modeled Change in CCS Storage:
-3723.09
-1362650.06 Observed Change
-2958.37
-1082764.47 Key:
CCS = Cooling Canal System.
ID = Interceptor Ditch.
lb = Pound(s).
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-19 (A)
(B)
Figure 5.2-1. Flow into (A) and out of (B) the CCS, Shown in Cross-Section.
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-20 Figure 5.2-2. Modeled versus Measured Net Monthly Flows of Water for the CCS during the Reporting Period.
-60
-40
-20 0
20 40 60 Jun-15 Jul-15 Aug-15 Sep-15 Oct-15 Nov-15 Dec-15 Jan-16 Feb-16 Mar-16 Apr-16 May-16 Water Flow (MGD)
Modeled Flow Observed Flow
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-21 Figure 5.2-3. Modeled versus Measured Net Monthly Flows of Salt Mass for the CCS during the Reporting Period.
-25000
-20000
-15000
-10000
-5000 0
5000 10000 15000 20000 25000 Jun-15 Jul-15 Aug-15 Sep-15 Oct-15 Nov-15 Dec-15 Jan-16 Feb-16 Mar-16 Apr-16 May-16 Salt Flow (lb x 1000/day)
Modeled Flow Observed Flow
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-22 Figure 5.2-4. Modeled versus Measured Water Elevations (NAVD 88) in the CCS during the Reporting Period; Used to Validate the Conceptual Model and Calibrate the Water Balance Model to Temporal Trends in Water Elevation.
-2
-1.5
-1
-0.5 0
0.5 1
1.5 2
2.5 CCS Water Elevation (ft NAVD 88)
Simulated Water Elevations Measured Water Elevations
FPL Turkey Point Annual Monitoring Report August 2016 Section 5 5-23 Figure 5.2-5. Modeled versus Measured Salinity in the CCS during the Reporting Period; Used to Validate the Conceptual Model and Calibrate the Water Balance Model to Temporal Trends in Salinity.
30 40 50 60 70 80 90 100 CCS Salinity (g/L)
Simulated Concentration (g/L)
Measured Concentration (g/L)