### TECHNICAL MEMORANDUM

EPA-REGION 

### 10 CAPTAINS BAVWASP MODEL: RESULTS FOR INCREASED BOD LOADING Prepared For: Prepared 

### By: Date: Distribution: 

### Summary Westward Seafoods, Inc. Steve Costa, 

### gde David Wilson, CH2M HILL 11 May 2000 Dave Boisseau, Westward Seafoods Burney 

### Hill, EPA-Region 

### 10 

## CH2MHILL 

# gde

This Technical Memorandum presents the approach and results of the Captains Bay WASP model simulation using the 

### 1992 data for minimum dissolved oxygen and the effluent BOD loading as defined in EPA's April 28, 2000 letter to Westward Seafoods (Attachment I). The WASP model parameters specified by EPA as acceptable to the agency are very conservative values, and they represent a rather unexpected decision by EPA reversing prior agreements. The objective of the modeling was to determine the loading capacity and effluent limitations based on EPA's model parameters and consistentwith the dissolved oxygen (DO) water quality standard of 5.0 mg/1. The Captains Bay WASP model was recalibrated and executed using the same input file and procedures used by EPA in the original 

### 1993 formulation. The only change in the modeling was that a different loading, as directed by EPA, was used to calibrate the model. Therefore, the results obtained are completely consistent with the original EPA modeling. The results indicate that a wasteload biological oxygen demand (BOD) discharge loading increase of 35% is justified, based on the BOD loading and ambient dissolved oxygen levels specified by EPA to calibrate the model. This result isEPA-REG ION 10 ';APTAINS BAVWASP M OD EL: RESULTS FOR INCREASED BOD L OADING predicated on a DO water quality standard of 5 mg/l as defined for estuarine waters by the State of Alaska. 

### Background In 1993, EPA Region 10 developed a WASP model to investigate and develop the allowable BOD loading capacity and effluent limitations for Westward Seafoods discharge to Captains Bay. This model has recently been re-examined both in terms of formulation and available data for calibration. The final result of this model reexamination effort included the following points: • Although the WASP model is intended to deal with average values of DO for defined model segments, EPA has directed that the model be calibrated using the lowest observed DO in the water column in the discharge segment, over a specified seasonal period, as was done for the 1993 modeling report This essentially results in the model being used as a correlation tool (or model) rather than as an actual simulation (or model) of physical processes. When the model is calibrated in this fashion it cannot be used to represent the physical behavior of the Captains Bay as a physical hydrodynamic system . • EPA Region 10 has directed that the data to be used for calibration be restricted to data collected during the summer of 1992 and that the model be executed in a steady-state mode. This precludes any ability to verify or validate the model or data set used for calibration using the extensive additional water column data available for the 1993-1999 time period. • EPA Region 10 has concluded that the appropriate loading to be used for calibration is not the loading used by EPA in 1993 but rather the average loading over the time period that DO was depressed below the water quality standard level of 5.0 mg/] during the summer of 1992. This loading was higher than that used in the previous 1993 modeling and results in a higher loading capacity and higher effluent limitations than were calculated and applied by EPA in 1993. The model was run and correlated using the original EPA model formulation as described in the 1993 FactSheet (Attachment II) for the increased loading sceanario. The 1993 Fact Sheet provides the basic description of management objectives, technical basis of the model, and uncertainties in the modeling. These factors will not be repeated here, and the reader is referred to the fact sheet for those specific technical details.

20F 10EPA-REGION 10 ";APTAINS BAVWASP MODEL: RESULTS FOR INCREASED BOD LOADING 

### ModeJ Formulation The model was run using the original EPA model formulation as described in the 1993 Fact Sheet (Attachment II). EPA (Attachment I) indicated that "minor corrections" should be made to errors in geometry, boundary exchanges, and typos found in the original models. However, exactly what changes to make and what changes would be unacceptable was not specified. Since the model, as formulated by EPA, is basically used as an elaborate correlation scheme, the changes indicated do not cause any meaningful changes to the results. Therefore, the model was run in its original 1993 EPA formulation. Using that approach there is full consistency with the previous modeling done by EPA and there can be no argument about whether something was changed that should nothave been changed. With two minor exceptions, the only changes to the EPA input file other than title entries to identify specific model cases, were the loading and the calibration coefficients. The exceptions were the elimination of the advective flow in Data Group D of the WASP input and the time step for one of the calibration cases considered. Thejustifications for these exceptions are as follows: • Itwas previously demonstrated that the exclusion of the advective flow data makes no difference whatsoever in the model DO predictions, within the accuracy of the model output 

### (±O.Ol mg/I). Eliminating this data block eliminates approximately 13 error messages at runtime, making the model more convenient to use, and the results are identical to those obtained if the Data Group D are included. • For vertical diffusion coefficients, Kv, of greater than about 0.004 m2/sec, the EPA coded time step of 0.05 days is too large and the model will not run. Therefore a time step of 0.01 was used for some model runs. This will have no significant effectexcept to make the model runtime about five times longer. The original time step of 0.05 was used in all simulations except 1 set of runs with a Kv 

### = 0.01. The model source code, the model executable file, and the input file, originally used by EPA Region 10 could not be located by EPA. A listing of the input file was included as Appendix D in the 1993 Fact Sheet, and this input file was reproduced (Attachment III). The Fact Sheet indicates that a WASP4 model Guly 1991 version) was used. However, as mentioned above the model was not available from EPA and the inputfile was incompatible with the WASP4 code in our possession.

3 OF 10EPA-REGION 10 ";APTAINS BAY WASP MODEL: RESULTS FOR INCREASED BOD LOADING 

### However, the input file was compatible with the WASPS (September 1993 version). It 

### is likely thatEPA Region 10 used a version of the analysis engine that was intermediate between the two versions available to us. The WASPS formulation was used throughout the study reported in this memorandum. 

### ModeJ Calibration Approach The calibration process for an analysis engine such as WASP requires the internal adjustment of various parameters until the input forcing function(s) resultin a target output response(s). The model, as formulated by EPA Region 10, was recalibrated to match the DO response in model Segment76 to BOD loading as requested by the 28 April 2000 EPA letter (Attachment I). 

### Model Segment 76 is the defined discharge segment where the BOD load is placed. The segment is 200 by 220 meters in horizontal extent and extends vertically from 5 meters below the surface to 15 meters below the surface. The effluent BOD loading used for calibration was the average of all Westward**Seafood~s** 

### BOD load values for the time period 21 July through 10 September 1992, as directed by EPA. The BOD loading included the stickwater component, which was not included in the original 1993 model analysis butEPA has indicated it should have been included. The letter from EPA indicates that the ultimate BOD should be used. The WASP model requires ultimate BOD as input, but EPA previously approximated this parameter with the BODzo (20-day BOD) value. Therefore, we used BOD20 as the loading, calculated based on the conversion factor EPA provided in the 1993 Fact Sheet. The effect of not using BODzo should not be substantial, given that the model, in its original EPA formulation, is basically being used as a correlation tool and it is not simulating realistic physical processes. It

### appears that the results from using the BODzo value, as derived by EPA, would provide a conservative estimate ofeffects on DO (that is, the model overstates the DO depression caused by a given loading). The difference between EPA BODzo conversion and the generally accepted ultimate BOD conversion is 1.31 xBODs compared to 1.46xBODs, respectively. The EPA procedure appears to understate the actual ultimate BOD loading by approXimately 10 percent. Therefore, this approach provides an additional "safety factor" of about 10 percent to an already very conservative model. The model loading was calculated as shown in Table 1. As directed by EPA Region 10, the model was calibrated assuming that the average BOD loading from Table 1 results in 

### an arbitrary average DO of 3.1 mg/I in 

### model Segment76 (D076 

### = 3.1). Based on a review of the DO monitoring data requested

4 OF 10EPA-REGION 10 <;APTAINS BAY WASP MODEL: RESULTS FOR INCREASED BOD LOADING earlier by EPA-Region 10, the actual average DO in this model segment for the time period in question was found to be 7.63 mg/1. This value was based on the monitoring stations representative of the discharge segment for the time period 25 July to 7 September 1992. EPA's assumption of the low DO is based on the lowest two or three point values of over three hundred measurements observed in the vertical profiles. The process of forcing the model to simulate the low DO point measurements rather than the average value, as the WASP model is designed to do, is what makes the modeling a correlation exercise rather than a simulation of physical processes. This is considered an extremely conservative approach. Table 1 1992 Critical Period BOD Loading Date BOD. (mg/I) Flow (mgd) BOD. (Ibs/day) 21 July 5775 3.62 174,351 3D July 5082 4.24 179,707 3 August 5070 3 .67 155,181 10 August 3542 4.16 122,887 20 August 4854 3.57 144,522 2 September 3788 3.59 113,414 10 September 4296 4.03 144,389 Average BOD5 147,779 Average BOD20 (BOD20 : BOD5 x 1 .31) 193,590 The calibration of WASP, as for any model of this type, is performed by adjusting a variety of selected parameters until the required output for given input is achieved. Typically the parameters used include horizontal and vertical diffusion, reaeration, and other model input parameters. As described in the 1993 Fact Sheet , EPA set all parameters to constants and varied two parameters to calibrate the modeL The calibration for this study was done in the same fashion as indicated in the 1993 Fact Sheet, by adjusting the vertical diffusion coefficient, Kv, and the deoxygenating coefficient, KDc. The use of two calibration parameters to match a single response value does not have a unique solution. Because of the way the model is formulated and calibrated, there is no strictly correctway to select the appropriate calibration pair or resultant loading values to use. Such a situation is often considered a fatal flaw in modeling exercises, but is acceptable to EPA in this case. Typically, one would match the DO over a number of model segments throughout the Bay to provide a model that is simulating physical processes and to at least partially account for uncertainties in

5 OF 10EPA-REGION 10 ';APTAINS BAY WASP MODEL: RESULTS FOR INCREASED BOD LOADING 

### the measured target DO values. However, such a process is not meaningful for WASP unless the average segment DO values are considered. When using the model as a correlation tool for minimum DO values, other approaches to supplement calibration must be used. As described in the 1993 Fact Sheet EPA selected a calibration pair that resulted in a DD76

### = 3.1 mg/l and a DO in model Segment 26, 

### immediately above the Segment 76, 

### of D026 = 5.5 

### mg/1. This value of predicted D026 is 1.3 mg/llower than the "actual" D026listed in EPA's 1993 

### Fact Sheet. No explanation is provided in the Fact Sheet as to why EPA selected the calibration pair that was eventually applied and used. However, for consistency we used the same procedure (D026 value of 5.5 

### mg/l) to select the appropriate calibration pair. 

### Model Calibration As mentioned above, there are an infinite number of solutions to this calibration problem in terms ofpairs of {Kv, Koc }values that will resultin a DD76 = 

### 3.1 mg/I for a given BOD loading. We considered a range of Kv from 0.01 

### to 0.00001 

### and adjusted Koc for each value of Kv considered to obtain DD76 = 3.1 

### mg/1. EPA had previously used a value of Kv 

### = 0.00013. 

### Typically, vertical diffusion is one to two orders of magnitude less than horizontal diffusion. EPA used a horizontal diffusion coefficient of 0.57 

### for spatial scales 20 

### times the vertical scale. This would correspond to expected vertical diffusion coefficients on the order of 0.001. 

### Therefore, the range considered in the current modeling includes the appropriate range based on EPA's previous application of the model, and extends an order of magnitude on either end of that range. A summary ofcalibration runs and results is shown in Table 

### 2, with DO levels indicated for both model Segments 76 

### and 26. 

### At the loading indicated in Table l, 

### for each Kva series of Koc values was considered 

### until the target DD76 of3.1 mg/I was bracketed. A second order polynomial was fit through the curve of Koc versus D076 to determine the value resulting in 3.1 

### mg/1. These graphical results are provided in Attachment IV and summarized in Table 3. The calibration pair that matches the EPA value of both DD76and D02 6is 

### highlighted in Table 3. 

### Model Results - Predicted Effluent BOD Loading Capacity For each pair of calibration parameters that resulted in a D076 of 3.1 mg/I, the model was run for a series of loadings to bracket the BOD20 loading that resulted in a DO of 5.0 

### mg/I in Segment 76 

### (DD76 = 5 

### mg/l). The loading thatresults in a 

### DD7 6of5.0 

### mg/l was then determined by using a second order polynomial curve fit. The loading capacity so determined is obviously a function of the calibration parameter 60F 10EPA-REGION 10 IjAPTAINS BAVWASP MODEL: RESULTS FOR INCREASED BOD LOADING 

### pair used. A summary of the model runs and results is shown in Table 4. Table 5 shows the loading capacity that would result in Do,6 

### of5.0 mg/I and 4.0 mg/1. The loading that will result in a predicted Do,6 = 

### 5.0 mg/I, over the range of calibration pairs considered, ranges from 90,500 Ibs/day to 122,200 Ibs/day of BOD20 

### (Table 5). The lower value is about the same as that predicted by the 1993 EPA modeling (90,000 Ibs/day), which used a much smaller BOD20 

### loading. The higher value is about 35% greater than the 1993 EPA modeling results. These results are summarized in Figure 1. As discussed above, there is no unique calibration for the model as formulated. It 

### is suggested, as mentioned above, that a reasonable procedure is to use the same approach as that provided in the EPA 1993 Fact Sheet. This would maintain full and cornplete consistency with EPA's previous modeling. The calibration pair for the current modeling that results in a DO,6 = 

### 3.1 mg/I and a D026 = 

### 5.5 mg/I is Kv = 

### 0.0001 and Koc 

### = 0.022. The simulations using this pair predict a value ofBOD20 

### loading of 122,200 Ibs/day that results in a DO,6 = 

### 5.0 mg/1. Therefore, an increase of 35% 

### in effluent BOD 

### limitations is justified based on using the more "appropriate" loading values for calibration in the original EPA model. The reasoning for using a smaller BOD 

### loading for calibration value in the 1993 model is unknown. Assuming the same procedure for setting effluent limitations is followed as was previously done, existing permit limitations for maximum daily load and average monthly load should be 

### multiplied by 1.35 to be 

### consistent with the revised loading capacity. The values are calculated are an increase of monthly average BODs 

### load from 58,000 Ibs/day to 78,300 Ibs/day and an increase in daily maximum loading from 90,000 Ibs/day to 121,500 Ibs/day.

7 OF 10EPA-REGION 10 (;APTAINS BAY WASP MODEL: RESULTS FOR INCREASED BOD LOADING Table 2 Summary of Calibration Runs: 800zo Loading 

## =193,600 Ibs/day Case Kv Koc 0076 (mgtl) 0026 (mgtl)

_01 0.0400 1.01 3 .95 _02 0.0350 1.38 4 .29

03 0.0200 3.47 5 .80

- 0.00010 _04 0.0250 2.59 5.21

05 0 .0275 2.22 4.95 - 06 0.0225 3 .01 5.49

11 0 .0400 7 .20 7 .46 - 12 0 .0600 6.69 7.02

- 13 0.1200 5.36 5.88

- 0.00100

14 0.2400 3 .34 4 .20 - 15 0.3000 2.60 3 .57 - 16 0.2700 2.95 3.87

- 21 0.0020 4.64 8 .82 - 22 0.0030 3.64 8.93 - 0.00001

23 0.0035 3 . 18 9 .02

- 24 0.0040 2.76 9 .07

31 0.4000 4. 17 4.71

-

- 32 0.5000 3.49 4 . 12 0 .00200 33 0.6000 2.91 3 .62

- 34 0.7000 2.43 3 .20

42 0.0100 3.89 7 .03 - 43 0.0200 1.25 5.57

- 0 .00005

44 0.0120 3. 16 6.67 - 45 0 . 0140 2.54 6 .35 51 2.0000 4.89 4 .83

- _52 2.4000 4.45 4 .39

53 0.01000 3.4000 3 .55 3 .50 - _54 4.4000 2.87 2 .82 _55 4.0000 3 . 12 3 .07 Table 3 Summary of Calibration Results Kv Koc 0076 (mgtl) 0026 (mgtl) 0.00001 0.0036 3 . 1 8.76 0.00005 0.0122 3 . 1 6 .64 0.00010 0.0220 3.1 5 .55 0.00100 0.2585 3. 1 4.00 0.00200 0.5672 3. 1 3.78 0.01000 4.0320 3 . 1 3 .05

8 OF 10EPA-REGION 10 CAPTAINS BAY WASP MODEL: RESULTS FOR INCREASED BOD LOADING Table 4 Summary of Model Runs with Calibrated Model Case Kv Koc Loading (Ibstday) 0076 (mgtl)

07 170,000 3 .68

-

- 08 130,000 4.77 0.00010 0.0220 09 100,000 5 .65

- 10 80,000 6.25

17 - 170,000 4.47

- 18 130 ,000 5.33 0.00100 0.2585 19 - 100,000 6.01

20 - 80,000 6.47

27 - 170,000 3.49

- 28 130,000 4.22 0.00001 0.0036

- 29 100,000 4.81

30 80,000 5 .21 37 - 170,000 3 .61

- 38 130,000 4.57 0.00200 0.5672 39 - 100,000 5 .35 _40 80,000 5 .89 _47 170,000 3 .67 _48 130,000 4 .72 0.00005 0.0122 49 100,000 5 .58 50 80,000 6 . 17 57 170,000 3 .56

-

- 58 130,000 4.51 0.01000 40320 59 100,000 5 .28

- _60 80,000 5 .81 Table 5 Summary of Model Results Calibration Parameter Pair Loadin' g (lbstday BOD.. ) Resulting in : Kv Koc 0076 

## = 5.0 mgtl 0.00001 0.0036 90,500 0.00005 0.0122 120,233 0.00010 0.0220 122,159 0.00100 0.2585 115 ,949 0.00200 0.5672 113 ,461 0.01000 4.0320 111 ,200 -;: -::'//2.,ZSc

9 OF 106 .5 6 S.S

S 

# - '" 0> §. 4 .S 0 0 co 

### .... 

# - 4 c 

## " E 

### g> IJl 3 .S 3 2 .S

2 SOOOO 7S000 100000 EPA-REGION 10 CAPTAINS BAyWASP MODEL: RESULTS FOR INCREASED BOD LOADING



# · ---r-·------...,...----·

12S000 Loading (Ibs/day) 1S0000 . Kv = 0 .01000 e K v = 0.00200 • K v = 0 .00100 • K v 

## = 0.00010

. K v 

## = O

.OOOOS )f. Kv = 0.00001

17S000 200000 

### Figure 1 Segment 76 DO as a Function of 800 20 

### Loading

10 OF 10