CEE 577 Spring 2009

Notes on QUAL2E and QUAL2K

QUAL2E/QUAL2K are a computer codes long supported and distributed by the US E.P.A. (Environmental Research Laboratory, Athens, GA) for the purpose of modeling conventional pollutants and nutrients in rivers. Their mechanistic forumlations are echoed in other widely used models (e.g., WASP). Version 3.3 represents the most recent Fortran code in a long line of programs dating back to the late 1960's. This latest version is equipped to simulate up to 15 constituents:

Conventional Pollutants:

1. Dissolved Oxygen (DO)

2. Biochemical Oxygen Demand (BOD)

3. Coliforms

Nutrients & Algae:

4. Chlorophyll a

Nitrogen Species

5. Organic Nitrogen

6. Ammonia

7. Nitrite

8. Nitrate

Phosphorus Species

9. Organic Phosphorus

10. Dissolved Phosphorus

Others:

11. Temperature

12. One Arbitrary Non-conservative constituent

13. Three Arbitrary Conservative constituents

This model can be used with branched rivers. It is a one-dimensional model (river is segmented along the longitudinal axis), and therefore presumes complete mixing in cross-section. QUAL2E can accommodate a very large number of point and non-point sources and withdrawals. These sources or withdrawals must be treated as constant in time, however.

QUAL2E may be used as either a steady-state or a limited dynamic model. Most applications to conventional pollutant modeling will use the steady-state mode of operation. Dynamic modeling is primarily used when information on diurnal variations in algal metabolism is desired. Impacts from single events (e.g., pollutant spill) cannot be simulated with QUAL2E, because the only time-varying inputs allowed are the meterological ones (i.e., temperature, sunlight).

The basic kinetic formulations are centered around dissolved oxygen. Figure 1 shows how the DO, BOD, nutrients, and algae interact in this modeling framework. The symbols shown in Figure 1 are further defined in Table 1 which follows. They all describe, in some way, the rate of transformation of the various constituents. Temperature may be provided by the user, or it may be modeled from meterological data. It is then used to adapt the various rate constants. Coliforms and the arbitrary conservative and non-conservative substances are treated separately, and do not interact with each other or with any other constituents.

QUAL2K is an updated version of QUAL2E, programmed in the Windows macro-language; Visual Basic for Applications (VBA). Microsoft Excel is the graphical user interface

Figure 1

Major Constituent Interactions in QUAL2E

(After Brown & Barnwell, 19871)

1. Brown & Barnwell, "The Enhanced Stream Water Quality Models: QUAL2E and QUAL2E-UNCAS: Documentation and User Model", EPA/600/3-87/007, 1987.)

TABLE I

DO/BOD REACTION COEFFICIENTS

Variablea Range of Variable Typical

QUAL2E(T&M) Description Units Values by Reach. Value .

AE Evaporation coefficient ft/hr-in-Hg No 0.00068

AFACT Light averging factor none No 0.92

BE Evaporation coefficient ft/hr-in-Hg No 0.00027

K Dispersion constant 5.9-6000 Yes 5.9

K1 (Kd) Carbonaceous deoxygenera- day-1 0.02-3.4 Yes

tion rate constant (in-stream)

K2 (Ka) Reaeration rate constant day-1 0.0-100 Yes

K3(Ks) Rate of loss of BOD due day-1 -0.36-0.36 Yes 0

to settling

K4(SB) Benthic O₂ uptake (SOD) mg-O2/ft³-day 0-100 Yes

K5 Coliform die-off rate day-1 0.05-4.0 Yes

K6 Arbitrary non-conservative day-1 Variable Yes

decay coefficient

Kb (K1) Bottle constant for rate day-1 0.05-0.4 0.2

of CBOD deoxygenation

KL Michaelis-Menton half- Btu/ft2- 0.02-0.10 No

saturation constant min

for light (Option 1)

KL Light saturation Btu/ft2- 0.25-0.90 0.75

Coefficient (Option 3) min

TABLE I (cont.)

DO/BOD REACTION COEFFICIENTS

Variablea Range of Variable Typical

QUAL2E(T&M) Description Units Values by Reach. Value .

(KN) NBOD deoxygenation rate day-1

KN Michaelis-Menton half- mg-N/L 0.01-0.40 No 0.20

saturation constant

for nitrogen

Kp Michaelis-Menton half- mg-P/L 0.01-0.05 No 0.04

saturation constant

for phosphorus

KNITRF Nitrification inhibition L/mg 0.3-5 No 0.65

coefficient

PN Algal preference factor - 0.0-1.0 No

for ammonia

TFACT Fraction of photo- none No 0.45

synthetically active

radiation

0 Ratio of chlorophyll-a ug Chl a/mg A 10-100 No 20

to algal biomass

1 Fraction of algal biomass mg-N/mg A 0.07-0.09 No 0.085

that is Nitrogen

2 Fraction of algal biomass mg-P/mg A 0.01-0.02 No 0.014

that is Phosphorus

3 O2 production per unit of mg-O/mg A 1.4-1.8 No 1.6

algal growth

4 O2 uptake per unit of mg-O/mg A 1.6-2.3 No 2.0

algae respired

TABLE I (cont.)

DO/BOD REACTION COEFFICIENTS

Variablea Range of Variable Typical

QUAL2E(T&M) Description Units Values by Reach. Value .

5 O2 uptake per unit of mg-O/mg N 3.0-4.0 No 3.43

NH3 oxidation

6 O2 uptake per unit of mg-O/mg N 1.0-1.14 No 1.14

NO2 oxidation

1 Rate constant for the day-1 0.10-1.00 Yes 0.30

biological oxidation

of NH3 to NO2

2 Rate constant for the day-1 0.20-2.0 Yes 0.60

biological oxidation

of NO2 to NO3

3(K12) Rate constant for the day-1 0.01-0.4 Yes 0.03

hydrolysis of organic-

N to ammonia

4 Rate constant for the day-1 0.01-0.70 Yes 0.05

decay of organic-P

to dissolved P

0 Non-algal light extinc- ft-1 Variable No

tion coefficient

1 Linear algal self-shading 1/ft/ug Chl-a/L 0.002-0.02 No 0.00268

coefficient

2 Nonlinear algal self- 1/ft/(ug Chl-a/L)^2/3 0.0165 No 0.0165

shading coefficient (Riley)

max Maximum algal growth rate day-1 1.0-3.0 No 2.5

TABLE I (cont.)

DO/BOD REACTION COEFFICIENTS

Variablea Range of Variable Typical

QUAL2E(T&M) Description Units Values by Reach. Value .

Algal respiration rate day-1 0.05-0.5 No 0.10

1 Algal settling rate ft/day 0.5-6.0 Yes 1.0

2 Benthos source rate for mg-P/ft²-day 0.001-0.01 Yes 0.0015

dissolved phosphorus

3 Benthos source rate for mg-O2/ft²-day 0.004-0.02 Yes 0.002

ammonia nitrogen

4 Organic nitrogen day-1 0.001-0.10 Yes 0.01

settling rate

5 Organic phosphorus day-1 0.001-0.10 Yes 0.010

settling rate

6 Arbitrary non-conservative day-1 Variable Yes

settling rate

7 Benthal source rate for mg-ANC/ft²-day Variable Yes

arbitrary non-conserva-

tive settling rate

aFirst symbol is that used in QUAL2E documentation (Brown & Barnwell, "The Enhanced Stream Water Quality Models: QUAL2E and QUAL2E-UNCAS: Documentation and User Model", EPA/600/3-87/007, 1987.); the second, when present, is that used by Thomann and Mueller, Principles of Surface Water Quality Modeling and Control

New Features in QUAL2K

QUAL2K (Q2K) incorporates the framework estabilished by QUAL2E with the following changes and enhancements:

1. Model segmentation. Q2E segments the system into river reaches comprised of equally spaced elements. In contrast, Q2K uses unequally-spaced reaches. In addition, multiple loadings and abstractions can be input to any reach.
2. Carbonaceous BOD speciation. Q2K uses two forms of carbonaceous BOD to represent organic carbon. These forms are a slowly oxidizing form (slow CBOD) and a rapidly oxidizing form (fast CBOD). In addition, non-living particulate organic matter (detritus) is simulated. This detrital material is composed of particulate carbon, nitrogen and phosphorus in a fixed stoichiometry.
3. Anoxia. Q2K accommodates anoxia by reducing oxidation reactions to zero at low oxygen levels. In addition, denitrification is modeled as a first-order reaction that becomes pronounced at low oxygen concentrations.
4. Sediment-water interactions. Sediment-water fluxes of dissolved oxygen and nutrients are simulated internally rather than being prescribed. That is, oxygen (SOD) and nutrient fluxes are simulated as a function of settling particulate organic matter, reactions within the sediments, and the concentrations of soluble forms in the overlying waters.
5. Bottom algae. The model explicitly simulates attached bottom algae.
6. Light extinction. Light extinction is calculated as a function of algae, detritus and inorganic solids.
7. pH. Both alkalinity and total inorganic carbon are simulated. The river's pH is then simulated based on these two quantities.
8. Pathogens. A generic pathogen is simulated. Pathogen removal is determined as a function of temperature, light, and settling.

Portions of ths are from EPA’s modeling web page. You should consult:

http://www.epa.gov/Athens/wwqtsc/html/qual2k.html

For more on QUAL2K and to download the program