Water Quality

Modeling

October 23, 2012 TWG

meeting

Study Purpose: How to

characterize and conduct

operational assessments of

water quality of the Susitna-

River

Water Quality

Modeling

Overview

• Goals and Objectives

• Issues

• Resolutions

• Additional Work

• Interdependency Chart

Water Quality

Modeling

Goals and Objectives

• Identify an appropriate reservoir and riverine

water temperature model;

• Model water quality conditions in the

proposed reservoir including: field

parameters, general chemistry, and metals

(including mercury); and

• Model water quality conditions in the

proposed river downstream including: field

parameters, general chemistry, and metals

(including mercury).

RSP’s Goals and Objectives are consistent with PSP

Water Quality

Modeling

Toxics Modeling

● Mercury Inputs to the Reservoir

● Toxicity Effects to Aquatic Organisms

RSP Provides Additional Detail

● Reservoir Water Quality Model

a. Surface water predictions

b. Mechanisms for transfer

● Riverine Water Quality Model

a. Surface water predictions

b. Influence of Operational scenarios

c. Hourly time-step (able to model shorter intervals)

● Potential for Bioaccumulation: Pathways Analysis

a. Predict water quality conditions that mobilize toxics

b. Determine if metals present are bioavailable

Comment: Study should

predict potential toxic

impacts.

Water Quality

Modeling

Mercury Modeling

Surface Water Issues ● Mercury Inputs, Methylation, Uptake, and

Biomagnification

RSP includes additional modeling

● Mercury toxicity model within the EFDC Model for

the reservoir

a. Predict Total Hg and Methylated Hg in the reservoir

b. Hourly time-step predictions to accommodate for

operational scenarios

● Metals toxicity model for the reservoir and

riverine portions of the Project area

Comment: Study should

address Mercury

Ecosystem Response

Baseline Water

Quality Modeling

Determining Toxicities

RSP include Modeling and Provides

Additional Detail regarding Standards

and Thresholds

● Alaska State Water Quality Standards

- Surface Water (acute/chronic criteria)

● NOAA SQuiRT Tables

- sediment, surface water, tissues

- acute/chronic toxicity benchmarks

Comment:

Study should address

other potential toxic

metals

Water Quality

Modeling

Model Selection

● Environmental Fluid Dynamics Code

(EFDC) selected (consensus from August 17,

2012 TWG)

● Model Resolution

- Main Channel (250m – 1km)

- Focus Areas (100m – 250m)

● Multiple Scales – One Model

- Mercury model within Main Model

- Focus Area model within Main Model

RSP includes TWG

Consensus on Model

Selection

Water Quality

Modeling

Influence of Groundwater on Transfer of Metals

Approach

● Intense Sample Areas

a. Identify specific “Focus Areas”

b. Samples across each transect (100 to 500

meters depending upon location morphology)

c. Sampled periodically

d. Continuous sampling for field parameters

e. Piezometers on each transect

f. Seepage meters as part of Instream Flow

Study

Additional Work in

Response to Agencies’

Comments on PSP

Water Quality

Modeling

Interpretation of Toxicity

Model Results

● Combining Model Results

Additional Work in

Response to Agencies’

Comments on PSP

Models (Surface Water) 1. Reservoir

2. Riverine

3. Focus Area

4. Mercury Model

Models (Fish Tissue) 1. Reservoir/Riverine Boundary

Pathway Analysis:

Potential for Bioaccumulation

Surface Water Toxics Modeling

Fish Tissue Toxics Modeling

Water Quality

Modeling

Pathways Analysis Example:

Step 1

Actions

1. Examine Reservoir

conditions (factors) that

promote methylation and

transfer of mercury between

media.

Fate Processes Affecting

Methylation of Mercury *

Transport/ Ecological

CompartmentsEffects

Water Column

Presence of aquatic vegetation

Reducing and low oxygen conditions

Factors thought to generally

increase methylation:

Increased nutrients,

temperature, microbial

respiration, dissolved organic

carbon

Neutral to low pH

Factors thought to generally

decrease methylation:

Higher oxygen conditions

Presence of sulfides, acid-volatile sulfides

Presence of selenium in sediments

Atmospheric Deposition

Sediments

Bioconcentration

&

Bioaccumulation

Trophic transfer and

biomagnification through the

food web – May result in

toxic effects

Methylmercury

* Mercury is typically most bioavailable and toxic as methylmercury

Mercury

Water Quality

Modeling

Pathways Analysis Example:

Step 2

Actions

2. Determine if a potential

for mercury mobilization

and bioaccumulation in

the reservoir

3. Are fish likely receptors

of mercury mobilization?

(Combine fish tissue results with

modeling results to determine if a

toxicity pathway is likely)

Note:

Highlighting will indicate likely

transfer pathways in the reservoir

(based on existing information)

Potential Mercury Processes in Project Area

Water Column

Surficial Sediment

Anoxic layer

Deeper Sediment

Aquatic

VegetationAnoxic Zone

Methylation of Hg

Methylation of Hg

Sink / Source of Hg

Methylmercury

Atmospheric Deposition

Tributaries &

lentic erosion

Hg bound to

organic matter

& sediments

Settling &

Resuspension

Hg bound to

organic matter

& sedimentsphytoplankton

zooplankton

forage fish

predator fishother consumers

bioconcentration

Bioaccumulation

Unassociated Hg

Bacterial

uptake/transport

Ice Processes in the Susitna

River

Fish and Aquatics Instream Flow

Ice Dynamics •Formation •Breakup •(4Q-2013?)

Water Quality Data

(1975-2003)

ADEC Mercury in Fish Tissue

(2006)

Hydraulic Routing Model

(4Q-2013?)

INTERDEPENDENCIES FOR WATER RESOURCES STUDIES

Water Quality

Monitoring

Mercury Toxics Data

Baseline Water Quality

Monitoring Study

Water Quality Modeling Study

Mercury Assessment and Potential for

Bioaccumulation Study

River Productivity Study (nutrient availability)

Fish Tissue Analysis Sediment Toxics Analysis Surface Water Analysis Health Impact Assess.

(1Q-2014)

Water Quality Model (EFDC) • Ice Dynamics • WQ Calibration Data • Mercury (metals) Data • Hydraulic Routing Model • Reservoir Trap Efficiency a) Focus Study Areas b) Mainstem Conditions • Riverine Model • Reservoir Model

(2Q-2014)

Water Quality Characterization

(Monthly Monitoring) a) Surface Water b) Groundwater • In Situ parameters • General parameters • Metals (one-time)

(1Q-2014)

Water Quality Model

Development

Groundwater-Related Aquatic Habitat Study

Geomorphology Study