24-Sep-15

1

Las Tablas Creek Watershed Assessment

Eric Blischke, Stephen Dent, Moosub Eom and Andy Greazel, CDM Smith; Jim Sickles and John Hillenbrand, USEPA

September 23, 2015

Eric Blischke Contaminated Sediments Specialist

CDM Smith/USA

Overview

• Site is located within the Central Coast Range of California

• The watershed is contaminated with mercury due to historical mining activities

• State of California established mercury loading goals due to fish contamination

• Removal activities were completed by EPA between 2002 and 2010

• Watershed based evaluation of contaminant loading, sediment transport and mercury uptake is necessary to develop remedial solutions for the site

September 23, 2015

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2

Conceptual Site Model

September 23, 2015

• Mercury mining and processing activities resulted in mercury contamination throughout the watershed

• Contaminant transport is dominated by particulate transport during winter precipitation events

• Mercury is methylated in reservoir sediments and accumulates in fish tissue at levels that pose a risk to human health

• Las Tablas Creek watershed represents a source of mercury contamination to Lake Nacimiento

Watershed Characterization Approach

• Stream flow and water quality monitoring was conducted to develop contaminant loading estimates

– Precipitation event and base flow monitoring

• Physical characterization to support sediment erosion and deposition analysis

– Mercury Fractionation Study

– Sediment traps and time series bathymetry

– Sediment erodibility study

• Mercury methylation study

– Sediment oxygen demand

– Methylmercury production

– Bioaccumulation potential

• Steam flow and sediment transport modeling

September 23, 2015

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September 23, 2015

Water Quality and Stream Flow Monitoring Locations

Water Quality and Stream Flow Monitoring Approach

• Criteria: ½ inch of precipitation within 24 hours

– Rainfall predictions from CNRFC

• 2013/2014

– 2 wet weather and 1 base flow sampling events

• 2014/2015

– 5 wet weather and 1 base flow sampling events

• Automated samplers allow sampling over the storm hydrograph

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4

Year 1 Sampling Events

February 5, 2014

No flow observed

February 28, 2014

1st Sampling Event

March 31, 2014

2nd Sampling Event

September 23, 2015

17:35

17:37

18:19

February 2014 Spillway Overflow

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5

Year 2 Sampling Events

December 11 and 15, 2014

– 1st and 2nd sampling event

February 6 and 9, 2015 –

3rd and 4th sampling event

April 7, 2015 – 5th

sampling event

Insufficient flow for sampling

October 31, 2014 – Salt

run-off sampling event

September 23, 2015

Year 2 Mineral Salt Sampling

0

2

4

6

8

10

12

14

Mineral Salt 1 Mineral Salt 2 Mineral Salt 3

Tota

l Mer

cury

(ug/

L)

Sample

Total Mercury in Mineral Salt Runoff

September 23, 2015

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6

Cypress Mountain

Road

February 2015 High Flow Conditions

Las Tablas Creek

Ranch Reservoir

Lower Las Tablas

Creek

NPDES Drainage

Ditch

September 23, 2015

Year 1 and Year 2 Total Mercury Results

28-Feb

31-Mar0

50

100

150

200

LLTC

LTCRR

Tota

l Me

rcu

ry (n

g/L)

Year 1 Total Mercury - Lower Stations

28-Feb

31-Mar

0

2000

4000

Tota

l Me

rcu

ry (n

g/L)

Year 1 Total Mercury - Upper Stations

September 23, 2015

11-Dec15-Dec

6-Feb9-Feb7-Apr

0

1000

2000

3000

4000

5000

6000

Tota

l Mer

cury

(ng/

L)

Year 2 Total Mercury - Upper Stations

11-Dec

15-Dec

6-Feb

9-Feb7-Apr

0

100

200

300

400

LLTCLTCRR

Tota

l Mer

cury

(ng/

L)

Year 2 Total Mercury - Lower Stations

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Mercury Fractionation Study

Upper Watershed

Las Tablas Creek Ranch Reservoir

September 23, 2015

Site Bathymetry and Sediment Trap Results

September 23, 2015

Location Date Total Mercury (mg/kg)

SEDTRAP 1 5/13/2014 5.9 SEDTRAP 2 5/13/2014 7.1 SEDTRAP 3 5/13/2014 14 SEDTRAP 1 6/4/2015 5.6 SEDTRAP 2 6/4/2015 6.3 SEDTRAP 4 6/4/2015 6.1 SEDTRAP 3 6/10/2015 6.9

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8

Sediment Erodibility Study

Upper Reservoir Lower Reservoir

September 23, 2015

Mercury Assessment for Receiving Bodies

Tier 1: Oxygen in Bottom Water/SOD

•Does the system foster anaerobic activity?

•How fast does anaerobic activity set in?

Tier 2: MeHg Production

•Are zones of MeHg production at surface sediments

Tier 3: Zooplankton Body Burden vs MeHg in Water Column

•Are zones of MeHg production connected to aquatic food web?

• Identify which tier to target for cost effective mitigation

September 23, 2015

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Tier 1: Sediment productivity

• Oxygen/mixing conditions in bottom waters

• Sediment oxygen demand/organic content

• Nutrient budget

• Reducing conditions at sediment water interface

• Iron and manganese enrichment in bottom waters

• Sulfide in sediment

September 23, 2015

Las Tablas Creek Ranch Reservoir Sediment Oxygen Demand

Beutel, 2003

LTCRR is on the high end of

SOD for waterbodies in

California

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

LTCRR Shallow LTCRR Deep

Me

an S

OD

(g/m

2/d

)

Las Tablas Creek Ranch Reservoir Sediment Oxygen Demand

Unmixed

moderately mixed

Highly mixed

September 23, 2015

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10

Tier 2: Methylmercury Production

• Percent MeHg of total Hg is used as a surrogate

for MeHg production (Windham-Myers et al.,

2009)

• Sites with highest surface methylation also have highest fish concentrations (Benoit et al., 2003)

• Growing database in literature to use for comparison

Ho

llwe

g, e

t al.,

20

09

September 23, 2015

Sediment Methylation and Bottom Water Enrichment: Unexpected Results

00% 00% 00% 01% 01% 01%

0,5

2

4

6

Percent Methylmercury of Total Mercury

Sed

imen

t D

epth

, cm

Dry Season

Deep

Shallow

00% 00% 00% 01% 01% 01%

0,5

2

4

6

Percent Methylmercury of Total Mercury

Sed

imen

t D

epth

, cm

Wet Season

Deep

Shallow

0

1

2

3

4

5

WET DRY

Me

Hg,

ng/

L

Axis Title

Near Bottom Methylmercury Wet Vs Dry Season

Shallow

Deep

• Poor alignment with trends in sediment methylation and bottom water enrichment

• Potential for Significant In Water Methylation during Dry Season

September 23, 2015

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Tier 3: Methylmercury Accumulation in the Food Web

Algae

Zooplankton

Prey Fish Predator Fish

100,000x

2-5x

2-5x

2-5x

• Life cycle (zooplankton vs fish) – Daphnia – Females ~ 2 months (E. Bethesda,

2005)

– Bass/Trout– 5 to 20 years (http://dnr.wi.gov/topic/fishing/documents/species/lmbass.pdf)

September 23, 2015

Zooplankton Body Burden: Unexpected Patterns

0

200

400

600

800

1000

1200

1400

1600

WET DRY

Me

rcu

ry, n

g/g

Zooplankton Body Burden

MERCURY

METHYL MERCURY

• Higher levels of mercury in in

zooplankton during the wet

season are likely the result of

storm runoff load

• Poor linkage between base of

the food web and in-water

methylmercury concentration

• Biodilution explains as least

part of the disconnect between

food web and water

concentration

Wet Season Dry Season

Order Shallow Deep Shallow Deep

Ploima (#/m3) 0 0 475 5570

Cyclopoida (#/m3) 728 398 0 6730

Calanoida (#/m3) 0 0 2848 11372

Cladocera (#/m3) 380 995 538 6730

Total Zoop (#/m3) 1108 1392 3861 30401

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Modeling Approach

• Hydrological Modeling System (HEC HMS)

– Developed by U.S. Army Corps of Engineers

– Simulates hydrologic processes of watershed systems

– Simulated hydrographs were developed based on measured precipitation to compensate for limitations in flow data

– Model was calibrated to year 2 stream stage and flow data

– Modeled annual run-off volumes were used in conjunction with water quality data to develop loading estimates

• HEC 6

– One-dimensional model that simulates sediment erosion and deposition within watershed

– Modeling effort focused on long-term estimates of sediment transport is still underway

September 23, 2015

Modeling Results – Annual Run-off Volume

September 23, 2015

0

500

1000

1500

2000

2500

3000

BLM/CMR KB NPDES SF NF LLTC LTCRR

An

nu

al R

un

-off

(ac-

ft)

Las Tablas Creek Watershed Annual Run-off Volume

Year 1 (ac-ft)

Year 2 (ac-ft)

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Long-Term Simulation of Run-Off Volume

September 23, 2015

0

10

20

30

40

50

60

70

80

90

100,0

5000,0

10000,0

15000,0

20000,0

25000,0

30000,0

Tota

l Rai

nfa

ll D

epth

(in

)

Tota

l Ru

no

ff V

olu

me

(ac-

ft)

Total Runoff Volume @ LLTC (ac-ft) Total Rainfall Depth @ FS Gage (in)

Assigning Total Mercury Concentration to Flow

• Mixed results in relationship between flow and total mercury concentration

• Precipitation event mean underestimates contribution from high flow events

• Flow weighted average used to develop loading estimates

y = -0,0003x + 3044,2 R² = 1E-04

0

1000

2000

3000

4000

5000

6000

7000

0 20000 40000 60000 80000 100000 120000 140000 160000

Tota

l Hg

(ng/

L)

Flow (cfs)

NPDES Flow-Total Hg Relationship

y = 7E-06x + 44,657 R² = 0,3192

0

50

100

150

200

250

300

350

400

450

0 10000000 20000000 30000000 40000000

Tota

l Hg

(ng/

L)

Flow (cfs)

Las Tablas Creek Ranch Reservoir Flow-Total Hg Relationship

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14

Long-Term Simulation of Mercury Load within Las Tablas Creek Watershed

000

001

001

002

002

003

003

004

004

Load

(kg

/yr)

Total Mercury Load

Las Tablas Creek Watershed

Total Mercury Load LLTC (kg/year) Total Mercury Load LTCRR (kg/year)

September 23, 2015

Watershed Assessment Summary

• Episodic precipitation events in a remote location were successfully monitored to estimate source area runoff and in-stream contaminant levels

• Difficulties encountered in measuring stream flow were overcome through the use of the HEC-HMS model to estimate stream flow

• Dry season reservoir assessment suggests near bottom water rather than surface sediments are the source of methyl mercury

• Incoming sediment particle concentrations range from 6 to 14 mg/kg with long-term mercury loading estimates to Lake Nacimiento ranging from 0.3 to 3.4 kg/year

• Erodibility measurements and loading estimates indicate that contaminated sediments with Las Tablas Creek Ranch Reservoir are a significant source of mercury contamination to Lake Nacimiento

September 23, 2015