Using thermocline manipulation to remediate mercury-contaminated reservoirs in southwestern Utah

Using thermocline manipulation to remediate mercury-contaminated reservoirs in southwestern Utah

USGS, Utah/Wisconsin/Arkansas Water Science CentersUtah DNR/DWRUtah DEQ/DWQ

Finnish Environment Institute

USGS, Utah/Wisconsin/Arkansas Water Science CentersUtah DNR/DWRUtah DEQ/DWQ

Finnish Environment Institute

PROBLEM

TOPICSTOPICS

♦Thermocline manipulation in Finland

♦Application to reservoirs in Utah

♦Remediation objectives

♦Thermocline manipulation in Finland

♦Application to reservoirs in Utah

♦Remediation objectives

METHYL Hg PROFILEMETHYL Hg PROFILEFr

om F

orsi

usan

d ot

hers

, 200

6

THERMOCLINE DEPRESSIONTHERMOCLINE DEPRESSIONFr

om F

orsi

usan

d ot

hers

, 200

6

Pretreatment epilimnion

Post-treatment epilimnion

Post-treatment hypolimnion

EQUIPMENTEQUIPMENT

♦Experiment originally designed for climate change

♦Artificially decrease thermocline volume

♦ Increase depth of oxygen penetration during summer stratification

♦More amenable to wind erosion

Thermocline mixing equipment (MIXOX).

From

For

sius

and

othe

rs, 2

006

MIXOX DEPLOYMENTMIXOX DEPLOYMENT

♦Cost is about 2,000 EU

♦Powered via lake bottom cable from on-shore power source

♦Platform provides for easy deployment of additional instruments

♦Powered via wind/solar/hydroelectric at remote reservoir sites

Deployment of mixing equipment and surface platform

From

For

sius

and

othe

rs, 2

006

DEPRESSION = 2.0 METERSDEPRESSION = 2.0 METERSD

EP

TH B

ELO

W L

AK

E S

UR

FAC

E, I

N M

T, oC

DECREASE IN METHYL Hg (Rask and others, in review)

DECREASE IN METHYL Hg (Rask and others, in review)

Fish tissue Water

(small perch, 70-80 mm) (epilimnion)0.6

0.4

0.2

0.0M

eHg,

ng/

L

Before During/after pumping pumping

Thermocline pumping

X = 0.54

X = 0.16

DECREASE IN METHYL HgDECREASE IN METHYL Hg♦Decreased volume

of anoxic hypolimnion

♦Increased volume of oxic epilimnion

♦Decreased surface area of anoxic sediment

♦Longer ice-free season

Pre-pumping

Post-pumping

POTENTIAL APPLICATION TO SMALL RESERVOIRS IN UTAH

POTENTIAL APPLICATION TO SMALL RESERVOIRS IN UTAH

NEWCASTLE RESERVOIRNEWCASTLE RESERVOIR

Water/sediment sampling site

♦Reservoir dam completed in 1956

♦Small reservoir (66 hectares)

♦Mean depth = 7.2 meters

♦Water and sediment sampled during July 2007

♦ Trout/wipers accumulating high Hg levels in 3 months

NEWCASTLE BIOTANEWCASTLE BIOTA

10

8

6

4

2

0

14 16 18 20 22

WATER TEMPERATURE, oC

DE

PTH

BE

LOW

WA

TER

SU

RFA

CE

, IN

ME

TER

STHERMOCLINETHERMOCLINE

Hg(inorg)

CH3 Hg

[HgTot ]whole water

[1.45 ng/L]

[2.91 ng/L]

Explanation

2.5 ng/L

0.2 ng/L

HISTORIC MERCURY DEPOSITION RATES HISTORIC MERCURY DEPOSITION RATES

1930

1940

1950

1960

1970

1980

1990

2000

2010

0.00 0.01 0.02 0.03 0.04

Hg DEPOSITION (UG/CM2/YR)

YE

AR

OF

SE

DIM

EN

T D

EP

OS

ITIO

N

Dam completion

Sediment core, Newcastle Reservoir, Utah

Dry mass (g/cm2) * Hg conc. (μg/g)

deposition period (yrs)

Spillway raised

NEWCASTLE REMEDIATION OBJECTIVES

NEWCASTLE REMEDIATION OBJECTIVES

1. Calibrate a hydrodynamic model to simulate the naturally induced thermal stratification in Newcastle Reservoir over an annual cycle

2. Utilize the calibrated hydrodynamic model to determine the optimal location(s) and pumping rates needed to depress the thermocline elevation by 1 to 2 meters

3. Utilize results from objective 2 to design a field experiment to depress the thermocline in the experimental reservoir

4. Utilize pre-pumping and pumping data to determine if the thermocline manipulation has resulted in a measurable decrease in mercury concentration in water, sediment, and biota

NEWCASTLE REMEDIATION YR 1 TASKS/SCHEDULE

NEWCASTLE REMEDIATION YR 1 TASKS/SCHEDULE

National Park Service QW sampling boat, Lake Powell, Utah

♦Baseline Hg data

♦Determine if pumping will work

NEWCASTLE REMEDIATION YR 2 TASKS/SCHEDULE

NEWCASTLE REMEDIATION YR 2 TASKS/SCHEDULE

Limnology profiling, Lake Powell, Utah

♦Conduct pumping experiment

♦Model observed pumping results

NEWCASTLE REMEDIATION YR 3 TASKS/SCHEDULE

NEWCASTLE REMEDIATION YR 3 TASKS/SCHEDULE

Sediment coring platform, Newcastle Reservoir, Utah

♦Continue field experiment/modeling

♦Decide if results warrant implementation

Hg IN UTAH RESERVOIRSHg IN UTAH RESERVOIRS

♦Many small reservoirs with fish advisories for Hg

♦Cost effective ($4,000/pump to remediate a fishery)

♦Baseline (pre-treatment) fish data already collected

♦Alternative remediation options??