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A COMPARISON OF TSS AND SSC DATA. Subtitled What are TSS and SSC data, and who cares?. Sediment Data-Collection Techniques USGS National Training Center Course SW1091 Toutle, Castle Rock, and Vancouver, WA March 24-28, 2014 John R. Gray (jrgray@usgs.gov)
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A COMPARISON OF TSS AND SSC DATA SubtitledWhat are TSS and SSC data, and who cares? • Sediment Data-Collection Techniques • USGS National Training Center Course SW1091 • Toutle, Castle Rock, and Vancouver, WA • March 24-28, 2014 • John R. Gray (jrgray@usgs.gov) • National Sediment Specialist(retired) • USGS Office of Surface Water
TO BE COVERED • Problem Identification. • What are TSS data? SSC data? • Research Results. • Ramifications of TSS data use. • Who cares? Project funded by the USGS Offices of Surface Water, and Water Quality
Background Information • USEPA: Fluvial Sediment andsorbed constituents are the Most Widespread Impairment of the Nation’s Rivers http://iaspub.epa.gov/waters10/attains_nation_cy.control?p_report_type=T#tmdl_by_pollutant • TSS Data are Often the Only Source of Sediment Data Available: 29 of 31 States sediment metric is (was?) TSS (per questionnaire, Gray & Glysson 2003). http://water.usgs.gov/osw/techniques/TSS/pruitt.pdf
I. Societal Relevance of Sediment National Perspective Accessed January 26, 2012 Remove the sediment…“End” 9 of top 10 impairments. ? ?
Societal Relevance of Sediment – Cost $Billions • $25-$65 billion: Annual physical, chemical, and biological damages sediment damages in N. America (SCIENCE, 1995, by Pimental et al., adjusted for inflation); most damages in U.S. • $2.5 billion: Sediment damages and remediation, reservoir-storage facilities (per ARS & USGS). • $0.8-$1.1 billion: Created Louisiana’s coastal wetlands annual costs (per COE estimates). • $1.1 billion: Dredging costs in support of about 490 million tonnes of commerce on the Mississippi and Ohio Rivers in 2007 (per COE estimates). • $1.5-$2.5 billion: Cost for 3-5 overflow diversions to build wetlands in Louisiana; up to 20 could be constructed (per COE estimate). • $0.7 billion: Missouri River Recovery Program, Environmental Management Program, low-flow water-supply infrastructure upgrades (per combined COE estimates). • $Unknown, but Undoubtedly Substantial: Gulf Hypoxia, sediment management from dam removal, sediment-quality impairments, etc. …we ran out of room...
Total Suspended Solids (TSS) versus Suspended-Sediment Concentration (SSC) • The TSS analysis entails withdrawal of an aliquot of the original sample for subsequent analysis. (Standard Methods 2540-D) • The SSC analysis uses the entire water-sediment mixture. (ASTM D-3977)
PROBLEM • TSS data are solid-phase metrics for 29 of 31 States responding to a 2002 questionnaire (Pruitt, in Gray and Glysson, 2003). • The TSS method tends to provide: • Negatively biased, and • More variant data than that for the demonstrably reliable SSC method(when used on samples collected from open-channel flow*). *Important caveat
TSS ANALYTICAL PROCEDURE • Originated for wastewater analyses (Δ in 1976). • In practice, techniques and equipment vary. • Cannot determine particle-size distributions. • Fast turnaround, lower cost? (some say NO) • Uses aliquot of original sample.
SSC ANALYTICAL PROCEDURE • ASTM Standard Procedure based on Federal Interagency Sedimentation Project research, 1940 ++ (along with some home cookin’…I can explain) • Can determine particle-size distributions • Slower turnaround, higher cost? Some say NO. • Measures all sediment and mass of water-sediment mixture using prescribed equipment.
National Sediment Laboratory Quality Assurance Programhttp://sedserv.cr.usgs.gov/ • Training in lab procedures • On-site lab evaluations • Single-blind program • Double-blind program • National quality-control data evaluation • Follow-up evaluations • Documentation of QC plans and procedures
ORGINAL DATA SET • 14,466 pairs of samples from 48 States and Puerto Rico • 53 QC samples from USGS Sediment Lab Quality Assurance Program • Most SSC Samples were Analyzed in USGS-Approved Laboratories using ASTM Standard D-3977 • TSS Analyses were Performed by USGS, State, and Contractor Laboratories
TSS SSC
SSC TSS
Summary of years of record and errors in the estimations of suspended-sediment loads (all errors are in percent)
NATIONAL-SCALE IMPLICATIONS • Difference between TSS and SSC analytical results of paired samples can be substantial; estimates of instantaneous sediment discharges can be orders of magnitude in error. • No simple, straight-forward way to adjust TSS data to estimate SSC without paired data. • TSS-generated load-reliability suspect.
NATIONAL-SCALE IMPLICATIONS (cont) • TSS data are “fundamentally unreliable.” • USGS guidelines ban routine TSS collection • Legal ramifications: Can one prove that TSS results are reliable? • Given the big picture, are production of TSS data in lieu of SSC data justifiable? • Our Conclusion…Quality of Nation’s sediment data would be greatly enhanced all produced by the SSC Method.
INTERNAL USGS GUIDANCEOSW/OWQ Technical Memo 2001.03 • USGS must collect SSC data. • If one must collect TSS sample (compliance, continuity), must also collect duplicate SSC sample. • Collect TSS data alone only if you have proven that they represent the true concentration of solid-phase material. http://water.usgs.gov/admin/memo/SW/sw01.03.html
USGS WRI 00-4191 & OTHER TSS-FOCUSED PAPERSby Gray, Glysson, Conge/Turcios, and Schwarz http://www.usgs.gov/osw/techniques/sediment/ • ADJUSTMENT OF TOTAL SUSPENDED SOLIDS DATA FOR USE IN SEDIMENT STUDIES • COMPARABILITY OF TOTAL SUSPENDED SOLIDS AND SUSPENDED- SEDIMENT DATA • A COMPARISON OF LOAD ESTIMATES USING TSS AND SSC DATA SUSPENDED SOLIDS AND