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Lake Mead
Participants in the InteragencyPartnership
City of Henderson
City of Las Vegas
Clark County Water Reclamation District
Clark County Regional Flood Control District
Lake Mead National Recreation Area (NPS)
Nevada Department of Environmental Protection
Nevada Department of Wildlife
Southern Nevada Water Authority
United States Bureau of Reclamation
United States Geological Survey
Participants in Field Sampling City of Henderson
City of Las Vegas
Lake Mead National Recreation Area (NPS)
Southern Nevada Water Authority
United States Bureau of Reclamation
United States Geological Survey
Manufacturers
Hydrolab, Eureka Environmental, YSI, In-Situ*
In-Situ instruments were provided by the manufacturer andare not regularly used by any of the participating agencies
Measurements Variable, depending on the sampling event
Temperature
pH
Specific Conductance
Dissolved Oxygen
Clark cell and Optical (technology varied by manufacturerprobes and date of sampling)
Surface to bottom (5 m intervals frequently)
Coordinated equilibration time
Calibration Variable, depending on sampling event
All parameters except temperature every time
Generally followed the manufacturer's instructions Completely independent calibration; independent
standards and locations
Some coordination; common lot of standards,independent locations
Complete coordination, common container of standard,common location
“Forced” calibration, setting previously calibratedinstruments to an average reading for all instruments
Calibration Results Calibration practices matter
The greatest benefit to the group has arisen from thefocus on careful adherence to protocol and toinstrument servicing
Improvements can be made by sharing calibrationsolutions
Improvements can be made by completely coordinatedcalibration
“Forced” calibration procedures are extremely useful intrying to assess issues Reduces the impact of independent calibration
Limits the ability to address the “right” value
Lake Test Over time ~20 coordinated sampling events have been
held at Lake Mead (bi-annual)
Iterative process
Sampling event
Data review
“Problem” identification
Suggested solution implemented at the next samplingevent
February 2008
0
20
40
60
80
100
120
7 7.5 8 8.5 9 9.5 10 10.5 11
De
pth
m
Dissolved Oxygen mg/L
August 2011 Sampling0
20
40
60
80
100
120
10 15 20 25 30
De
pth
(m)
Degrees C
0
20
40
60
80
100
120
800 900 1000 1100
De
pth
(m)
Specific Conductance µS/cm
August 2011 Sampling
0
20
40
60
80
100
120
60 80 100 120
De
pth
(m)
Dissolved Oxygen % Saturation0
20
40
60
80
100
120
7 7.5 8 8.5 9
De
pth
(m)
pH
Tank Test Basics
Instruments put into thetank Thursday afternoon
Instruments set to collectdata every 15 minutes Temp, Sp Cond, pH, DO
Some instruments poweredand on constantly (ACpower), others came on tocollect data (DC power)
This test should identifyunderlying instability, ifit exists
28.4
28.5
28.6
28.7
28.8
28.9
29.01
8:0
0
19:0
0
20:0
0
21:0
0
22:0
0
23:0
0
0:0
0
De
gre
es
C
Tank Test Results
Pressure Test Set-Up
So
nd
e
• Sonde put into test chamber• Chamber sealed• Pressure gradually increased to<180 psi ~125 m simulateddepth with an air compressor
• Parameters recorded aspressure was increased anddecreased in most cases
Pressure Test Results
Data Presentation
0
20
40
60
80
100
120
-1.00 -0.50 0.00 0.50 1.00
DO Difference mg/L
5.50
6.00
6.50
7.00
7.50
8.00
8.50
9.00
9.50
10.00
5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 10.00
Winkler Value (DO mg L-1)
Instrum
entValu
e(D
Om
gL-1
)
EODO
ECDO
YODO
HCDO
HODO
Winkler
Comparing instrument DO to Winkler DO
Mean pH
8.20 8.25 8.30 8.35
Measure
dpH
7.9
8.0
8.1
8.2
8.3
8.4
8.5
SNWACOLV
SNWS 143SNWS 144COH Eureka
COH hydrolabNPSUSGSUSBR Hydrolab 5
USBR hydrolab4ABOR LCRL-1BOR LCRL- 2
Comparing variability to tech specs
Conclusions We have made significant strides in data consistency
through this process Calibration and maintenance enhancements
Collaborative evaluation of shared results
Greater understanding of the sampling procedures andtechniques of other agencies
Increased communication on sampling issues and datasharing
Some issues have been resolved by improvementswithin and among the group
Some issues have required the assistance ofmanufacturers
Still to Come Continued Interagency Sampling Events
Continue the exchange of data and ideas
Continue assurance that data from all agencies isequivalent
Assess changes that occur as new instrumentation isadopted
We need to develop “confidence intervals” for thegroups data based on the published specifications forthe instruments
