Temperature Modeling for the Steam Condensate Discharge at Naval WeaponsStation Earle, NJ

Draft Technical Memorandum

27 March, 2008

SPAWAR Systems Center San DiegoEnvironmental Sciences Branch

53560 Hull St.San Diego, CA 92152

1

Introduction

Discharge modeling for the steam condensate discharge at Earle, NJ was conducted andevaluated by SPAWAR Systems Center San Diego, Environmental Sciences Branch. Weused a simple, but well-accepted two-dimensional mixing model to predict temperaturechanges in ambient waters resulting from the steam condensate discharge. Thepredictions are based on diffusive mixing equations developed in Fischer et al. (1979),the classic treatise on mixing in coastal and inland waters. The model predicts the two­dimensional, steady-state dispersion of concentration (or heat) assuming that (1) thedischarge is mixed vertically to a prescribed mixing depth after the discharge plungesinto the ocean from above, (2) dispersion is dominated by lateral mixing followingdischarge, (3) there is no further vertical mixing after discharge (consistent with strongstratification associated with a warm, fresh discharge), (4) stream-wise mixing isnegligible relative to lateral mixing, and (5) there is no heat exchange with theatmosphere. These generally conservative assumptions greatly simplify thehydrodynamic equations and are quite reasonable given the scenario.

Model

The two-dimensional mixing equation used to predict the heat distribution was:

where:H(x,y) =heat content associated with the discharge as a function of x and yM =effluent heat flux/.l =ambient current speed

d =mixing depth~t =transverse mixing coefficientx =distance downstreamy =lateral distance

and the effluent heat flux was calculated as

M = pQCpflT

where:p =water densityQ =discharge rateCp =heat capacity of waterflT =temperature difference between discharge and ambient

Following mixing, the temperature distribution (T(x,y) was then calculated as:

~e

2

Ta =ambient temperature

Inputs to the Model

The discharge parameters in the model included a mixing depth of 0.05 m (- 2"), and afixed effluent discharge rate of 0.00038 LIs (8.64 gpd) at a temperature of 100 DC. Themixing depth chosen reflects a realistic minimum depth at which a temperaturemeasurement would be made and is thus a conservative value. The temperature onhitting the water is also a conservative assumption given that the droplets would lose heatduring their fall to the water surface.

We ran two scenarios to evaluate temperature changes observable at 100 m given that theNew Jersey Department of Environmental Protection (NJDEP) identified two regulatoryseasonal requirements:

Winter: September through May (Delta Temperature limit of 2.2 DC) and

Summer: June through August (Delta Temperature limit of 0.8 DC).

The NJDEP futher requested that the temperature values be based on 95th percentile valuefor summer and winter conditions over a three-year data set. We collected historicalambient temperaure data from NOAA's Ports historical data retrieval system(http://tide andcurrenL .noaa.go ) for its Sandy Hook, NJ site (Station ill: 8531680), asite that is only a few miles from the discharge area. The roughly 230,000 data recordsfrom 2005 through 2007 are shown in Figure 1. The 5th and 95th percentile ambient watertemperatures from the dataset were respectively 1.08 DC and 25.74 DC (Figure 2).

The NJDEP requested using the 95th percentile value for salinity as well. However, themodel conservatively assumes that the plume remains at the surface (vertically stratified)and salinity is therefore not a parameter used in the model calculations.

The NJDEP requested that 20-min average current speeds be used for the modeling. Wedo not have access to measured current data. However, we were able to evaluatemodeled current speed data from the New York Harbor Observing and Prediction System(NYHOPS) system and the Center for Maritime Systems, Stevens Institute of Technology(http://hud on.d!. tevens-tech.edulmaritimeforecastlmaincontro!.shtrnl). We steppedthrough the model graphical results (roughly IS-min interval data) for two recentlycompleted spring-neap tide (max-min tide) cycles for the area off of the Sandy Hook, NJsite. Current speeds were all below 0.5 rnIs (l kt) over the time period. Because we didnot have actual current data, and particularly, the 10th percentile values as requested bythe NJDEP, we ran the model incrementally for current speeds between 0.01 and 0.5 m/s(0.02 to 1 kt). Given that current speeds less than 0.01 rnIs are not measurable, the rangecovers all expected conditions for the site, including the 10th percentile value.

The last input to the model is the lateral mixing coefficient. Typical observed values canrange over an order of magnitude or more under a variety of natural conditions (Fischeret aI., 1979). We therefore ran the model incrementally for a range in mixing coefficient

3

values between 0.01 and 0.5 m2/s that bracket the values identified in Fischer et a!., 1979.The ranges in these values bound all realistic conditions expected at the site.

Results

Results for representative Winter conditions are shown in Figures 3 through 5. Figure 3shows the maximum temperature observed at 100 m downstream of the discharge pointfor an ambient water condition of 1.08 °C, an ambient current velocity of 0.1 rn/s and alateral mixing coefficient of 0.12 m2/s. Figure 4 shows the spatial temperaturedistribution from the effluent discharge location to a distance of 100 m downstream underthe same conditions used for Figure 3. Results for this representative case show amaximum temperature difference of -0.002 °C at 100 m downstream. Figure 5 shows themaximum temperature predicted at 100 m downstream after varying the ambient velocityand lateral mixing coefficient over the full range of expected conditions at this location.The plot shows a maximum temperature differential of -0.0022 °C for the entire range ofconditions. The regulatory delta temperature limit of 2.2 °C during the Septemberthrough May timeframe is met under all tested conditions.

Results for representative Summer conditions are shown in Figures 6 through 8. Figure 6shows the maximum temperature observed at 100 m downstream of the discharge pointfor an ambient water condition of 25.74 °C, an ambient current velocity of 0.1 rn/s and alateral mixing coefficient of 0.12 m2/s as an example. Figure 7 shows the spatialtemperature distribution from the effluent discharge location to a distance of 100 mdownstream under the same initial conditions used for Figure 6. Results for thisrepresentative case show a maximum temperature difference of -0.0015 °C at 100 mdownstream. Figure 8 shows the maximum temperature predicted at 100 m downstreamafter varying the ambient velocity and lateral mixing coefficient over the range ofexpected conditions at this location. The plot shows a maximum temperature differentialof -0.0015 °C for the entire range of conditions. The regulatory delta temperature limitof 0.8 °C and absolute limit of 29.4 °C during the June through August timeframe is metunder all tested conditions.

Iterative model runs indicate that the discharge flow rate could be increased by over afactor of 600 before there would be a potential to exceed delta temperature limits.

References

Fischer, H.B., List, EJ., Koh, R.c.Y., Imberger, J., and Brooks, N.H., 1979, Mixing inInland and Coastal Waters: Academic Press, Inc., Orlando, Florida, 483, p.

4

70.0

60.0

50.0

~ 40.0

'" 30.0"-OJ+'

'" 20.0"-'""-E 10.0"f-

0.0

-10.0

-20.01l1/Ill/ll5 B7/01/ll5

water temp. -----

NOAA/NOS/CO-OPSAir/~~ter Temperature Plot

6531680 Sandy Hook, NJfro~ 2005/01/01 - 2007/12/31

Date/Time (Local)

air temp ----

Figure 1. Three-year record of water temperature measurements derived from NOAA'sCO-Ops Sandy Hook, NJ site (Station ill: 8531680).

o:~08

1

07

~ 0.6

C0-Q) 0.5u::E:::J OAr0

0310.2f-

01 f0 1-5 0 5 10

Temp (C)

15 20 25

j

30

Figure 2. Cumulative frequency distribution for temperature at Sandy Hook, NJ site forthe three year period 2005-2007. Dotted lines indicate the 5th and 95th percentiletemperatures of 1.08 C and 25.74 C, respectively.

5

1.0825 .-------,---,------r---,----.----~--__,__-__,

201510-10-151.08 L.-_--'__---'-__---<:__---'--__--"'-__.........__-l-_-'

-20

1.082

uOJ(])

U(])"-

10815::::l+-'(\J"-(])

0-E(])

l-E 1.081::::l

E·x(\J

L

10805

-5 0 5Lateral Distance (m)

Figure 3. Winter Condition Example. Downstream water temperature distribution at adistance of 100 m for discharge of 100°C effluent into ambient water at 1.08 °C(J.l=0.1 m/s, ~t =0.12 IU

2/s). Maximum temperature differential at 100 m is-0.002°C.

6

20

15

10

~

E 5<Dvcm...... 0(f)

ism'-<D -5tu

-10

-15

-20

1.096

1094

1.092

1.09

1.088

1.086

10 20 30 40 50 60 70 80 90 100downstream distance (m)

Figure 4. Winter Condition Example. Plan view (x,y) of ambient water temperaturedistribution after discharge of 100°C effluent into ambient water of 1.08 °C ().l=0.1mis, ~t =0.12 m2/s). The maximum temperature differential at 100 m is -0.002 °C.

7

Max Temp Delta @ 100 m downstream; Ambient Temp = 1.08 C

-3x10

2.5~, .

u 2~:- .' '

(\J......(]) . .o 1.5"':""" :0.. , ,

E(])

~ 1~'"::::J

E

~ 0.5-.;""

oo o

ambient velocity (m/s)05

lateral mixing (m2/s)

Figure 5. Winter Condition. Maximum temperature difference (above ambient of1.08 DC) predicted at lOO m downstream location as a function of changes in bothambient current velocity (0,01 to 0.5 m/s) and lateral mixing coefficients (O.Olto 0.5m2/s). Maximum temperature difference was less than 0.0022 °C under all testedconditions.

8

25.7416

257414

25.7412u0)Q)

25.741uQ)'-::J+-'m 257408'-Q)0-EQ)

25.7406l-E::J

E 25.7404·xmL

25.7402

25.74

25.7398-20 -15 -10 -5 0 5

Lateral Distance (m)10 15 20

Figure 6. Summer Condition Example. Downstream water temperature distribution at adistance of 100 m for discharge of 100°C effluent into ambient water at 25.74 °C(11=0.1 mis, ~t =0.12 m

2/s). Maximum temperature differential at 100 m is

-0.0015°C.

9

20

15

10

E 5~

Q)uc('U

t) 0D('U'-Q)

-5m

-10

-15

-20

25752

2575

25.748

10 20 30 40 50 60 70 80 90 100downstream distance (m)

Figure 7. Summer Condition Example. Plan view (x,y) of ambient water temperaturedistribution after discharge of 100°C effluent into ambient water of 25.74 °C (~=O.l

rn/s , ~t =0.12 rn2/s). The maximum temperature differential at 100 m is -0.0015 0c.

10

Max Temp Delta @ 100 m downstream; Ambient Temp = 25.74 C,', '

-3x10

2~

u~ 1.5Q)

oa.E 1Q)

f-E:::JE 0.5x(lJ

zoo

ambient velocity (m/s)05 0.5lateral mixing (m2/s)

Figure 8. Summer Condition. Maximum temperature difference above ambient value of25.74 °C predicted at 100 m downstream location as a function of changes in bothambient current velocity (0.01 to 0.5 m/s) and lateral mixing coefficients (0.01 to 0.5m2/s). Maximum temperature difference was:S 0.0015 °C under all testedconditions.

11