las tablas creek watershed assessment · lft_fcs_presentation.potx author: cdm created date:...
TRANSCRIPT
24-Sep-15
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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
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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
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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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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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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
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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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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
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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
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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
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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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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