Sediment Monitoring Background Sediment Quality Guidelines   Sediment Bioassays References

Background

Sediments are monitored because they are an important component of the Bay and Estuary ecosystem and information about sediments addresses aspects of all RMP Objectives (RMP Objectives are listed in Chapter 1: Introduction). In this Chapter, patterns and trends in sediment contamination are described (Objective 1) and compared to several sets of sediment quality guidelines (Objective 4). The results are used to make some inferences about the sources and loadings of sediment-associated contaminants (Objective 2). Sediment bioassays and the Benthic Pilot Study address contaminant effects (Objective 3). Several RMP Pilot and Special Studies and summaries of Regional Board studies on sediments are included addressing Objective 5.

Information about sediment contamination is used in making decisions related to many important management issues: the identification of sediment "toxic hot spots" is currently a priority for the State and Regional Boards, the clean-up of numerous military bases in the region requires information about background contaminant levels, and the continuous dredging of the Estuary requires testing and comparisons to some reference, or background concentrations. The RMP provides information that may be used by others to assess the condition of Estuary sediments.

Most contaminants accumulate in sediments to concentrations that are orders of magnitude above those in water. The geochemistry of sediments is complex, and in order to interpret contaminant concentrations measured in sediments it is necessary to understand how hydrology (flows) and other non-contaminant sediment properties may affect contaminant concentrations. An overview of Estuary hydrology and water quality was presented in Chapter 1: Introduction. CTD (conductivity, temperature, depth) profiles of the water column were collected at all RMP sediment stations. Those data are not presented in this report, but are available from SFEI upon request. Several sediment quality parameters that may affect sediment contaminant concentrations (grain-size, organic carbon, ammonia, and sulides) are also monitored, and are listed in Appendix C: Data Tables.

Sediment contaminant monitoring includes trace elements and trace organic contaminants at 22 RMP Base Program stations. Sediments were also monitored at two stations at the southern end of the Estuary in cooperation with the Regional Board and the cities of San Jose (station C-3-0) and Sunnyvale (station C-1-3). In addition, sediments were monitored at two stations in the southern end of the Estuary, Standish Dam on Coyote Creek (station BW10), and Alviso Slough on the Guadalupe River (station BW15), as part of the Estuary Interface Pilot Study (see Chapter 6: Pilot and Special Studies).

Station locations are shown on the inside of the front cover. Sediment samples were collected during the wet season (January­February) and dry season (August). Sampling dates are shown on Table 1.2 in Chapter 1: Introduction. Appendix A contains detailed methods of collection and analysis. Table 1.1 in Chapter 1: Introduction lists parameters measured in sediment. Sediment quality parameters including station depths, and all contaminant concentrations are tabulated in Appendix C.

In order to compare sediment monitoring results among the major sub-regions of the Estuary, the RMP stations are separated into six groups of stations in five Estuary reaches based subjectively on geography, similarities in sediment types, and patterns of trace contaminant concentrations. The Estuary reaches are: the Southern Sloughs (C-1-3 and C-3-0), South Bay (seven stations, BA10 through BB70), Central Bay (five stations, BC11 through BC60), northern Estuary (eight stations, BD15, through BF40), and Rivers (BG20 and BG30). Stations with coarse sediments (>60% sand: six stations in the wet season and five in the dry season) generally have considerably lower contaminant concentrations and were identified on Figures 4.1- 4.15.

Concentrations of copper and silver are not reported for some sites because the method blanks were contaminated to a degree above acceptable levels. Those samples are identified on Figures 4.4 and 4.9.

Sediment Quality Guidelines

There are currently no Basin Plan objectives or other regulatory criteria for sediment contaminant concentrations in the Estuary. However, there are several sets of sediment quality guidelines (Table 4.8) that may be used as informal screening tools for sediment contaminant concentrations, but hold no regulatory status.

The U.S. EPA has produced draft criteria for five trace contaminants: three PAHsacenapthene, fluoranthene, and phenanthreneand two pesticidesdieldrin and endrin (EPA, 1991). Those draft criteria have recently been redesignated as "guidelines".

Sediment quality guidelines developed by Long et al. (1995) are based on data compiled from numerous studies in the United States that included sediment contaminant and biological effects information. The guidelines were developed to identify concentrations of contaminants that were associated with biological effects in laboratory, field, or modeling studies. The Effects Range-Low (ERL) value is the concentration equivalent to the lower 10th percentile of the compiled study data, and the Effects Range-Median (ERM) is the concentration equivalent to the 50th percentile of the compiled study data. Sediment concentrations below the ERL are interpreted as being "rarely" associated with adverse effects. Concentrations between the ERL and ERM are "occasionally" associated with adverse effects, and concentrations above the ERM are "frequently" associated with adverse effects. Effects range values for mercury, nickel, total PCBs, and total DDTs have low levels of confidence associated with them. The Effects-Range values used for chlordanes and dieldrin are from Long and Morgan (1990). There are no Effects-Range guidelines for selenium, but the Regional Board has suggested a guidelines of 1.4 ppm (Wolfenden and Carlin, 1992), and 1.5 ppm (Taylor et al. 1992).

A new set of sediment quality guidelines developed by the Regional Board is introduced in this report. Ambient Sediment Concentration (ASC) values are based on ambient or "background" concentrations (see article by Gandesbery et al. in this Chapter).

Sediment Bioassays

Sediment bioassays are conducted to determine the potential for biological effects from exposure to sediment contamination. Two sediment bioassays were conducted at 14 of the RMP stations (Figure 4.16) in January­February and again in August of 1997. Sampling dates are listed in Table 1.2 of Chapter 1: Introduction. Amphipods (Eohaustorius estuarius) were exposed to whole sediment for ten days with percent survival as the endpoint. Larval mussels (Mytilus sp.) were exposed to sediment elutriates (water-soluble fraction) for 48 hours with percent normal development as the endpoint. The control sediment used in the Eohaustorius test was "home" sediment from Yaquina Bay, Oregon where the amphipods were collected. The control used for the Mytilus (mussel) test was clean seawater from Granite Canyon, California. Appendix A contains detailed methods of collection and testing and Appendix B contains quality assurance information. There were no significant quality assurance exceptions in the 1997 sediment bioassays.

When a sample is found to be toxic, it is interpreted as an indication of the potential for biological effects. However, since sediments are mixtures of numerous contaminants, it is difficult to determine which contaminant(s) may have caused any toxicity observed (see Sediment Discussion).

A sample was considered toxic if:

• there was a significant difference between the laboratory control and test replicates using a t-test, and
• the difference between the mean endpoint value in the control and the mean endpoint value in the test sample was greater than the 90^th percentile minimum significant difference (MSD).

The MSD is a statistic that indicates the difference between the two means that will be considered statistically significant given the observed level of between-replicate variation and the alpha level chosen for the comparison. The 90^th percentile MSD value is the difference that 90% of the t-tests will be able to detect as statistically signifi

cant. Use of the 90^th percentile MSD is similar to establishing statistical power at a level of 0.90, and is a way to insure that statistical significance is determined based on large differences between means, rather than small variation among replicates. MSDs were established by analysis of numerous bioassay results for San Francisco Bay (Anderson and Hunt, unpubl.; Hunt et al. 1996). Based on those analyses, the 90^th percentile MSD for Eohaustorius was 18.8% and for the bivalve larvae test 21%. For the 1997 sediment bioassays, an amphipod bioassay was toxic if it had below 79.2% survival in February or 80.2% survival in August. A larval bivalve bioassay was toxic it if had below 73% or 69% normal development in January­February or August, respectively.

References

EPA. 1991. Proposed sediment quality criteria for the protection of benthic organisms: 5 draft reports: Acenaphthene; Dieldrin; Endrin; Fluoranthene; Phenanthrene.

Hunt, J.W., B.S. Anderson, S. Tudor, M.D. Stephenson, H.M. Puckett, F.H. Palmer, and M. Reeve. 1996. Marine Bioassay Project, Eighth Report: Refinement and implementation of four effluent toxicity testing methods using indigenous marine species. Report #94-4. State Water Resources Control Board, Sacramento, CA. pp. 85­104.

Long, E.R. and L.G. Morgan. 1990. The potential for biological effects of sediment-sorbed contaminants tested in the National Status and Trends Program. NOAA Tech. Memo NOS OMA 52. National Oceanic and Atmospheric Administration, Seattle, WA. 175p.

Long, E.R., D.D. MacDonald, S.L. Smith and F.D. Calder. 1995. Incidence of adverse biological effects within ranges of chemical concentrations in marine and estuarine sediments. Env. Mgmt. 19:18­97.

Wolfenden, J.D. and M.P. Carlin. 1992. Sediment screening criteria and testing requirements for wetland creation and upland beneficial reuse. California Environmental Protection Agency and California Regional Water Quality Control Board.

Taylor, L., W. Pease, J. Lacy, and M. Carlin. 1992. Mass Emissions Reduction Strategy for Selenium. San Francisco Regional Water Quality Control Board, Oakland, CA. 61p.