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The overarching goal of the RMP is to collect data and communicate information about water quality in San Francisco Bay in support of management decisions. The RMP was created in 1993 through Regional Board Resolution No. 92-043 that directed the Executive Officer to implement a Regional Monitoring Plan in collaboration with permitted dischargers pursuant to California Water Code, Sections 13267, 13383, 13268, and 13385. The goal was to replace individual receiving water monitoring requirements for dischargers with a comprehensive Regional Monitoring Program.

The Program is guided by a Memorandum of Understanding (MOU) between the Regional Board and SFEI, first approved in 1996 and amended at various times since (see Appendix C of this Charter). Section VIII of the MOU states the roles and responsibilities of the Regional Board and SFEI in the implementation of the Program. Participating dischargers pay fees to the Program to comply with discharge permit requirements. The cost allocation schedule for Participants is described in Appendix B. The RMP provides an open forum for a wide range of Participant Groups and other Interested Parties to discuss contaminant issues, prioritize science needs, and monitor potential impacts of discharges on the Bay.

In support of the overarching goal described above, the following guiding principles define the intentions and expectations of RMP Participants. Implementation of the RMP will:

• Develop sound scientific information on water quality in the Bay;
• Prioritize funding decisions through collaborative discussions;
• Conduct decision-making in a transparent manner that consistently represents the diversity of RMP Participant interests;
• Utilize external science advisors for guidance and peer review;
• Maintain and make publicly available the data collected by the Program;
• Enhance public awareness and support by regularly communicating the status and trends of water quality in the Bay; and
• Coordinate with other monitoring and scientific studies in the Bay-Delta region to ensure efficiency.

Urban runoff has been identified in water quality policy documents for San Francisco Bay as a large and potentially controllable source of pollutants. In response, concentrations of suspended sediments and a range of trace organic pollutants were intensively measured in dry weather and storm flow runoff from a 100% urban watershed. Flow in this highly urban watershed responded very quickly to rainfall and varied widely resulting in rapid changes of turbidity, suspended sediments and pollutant concentrations. Concentrations of each organic pollutant class were within similar ranges reported in other studies of urban runoff, however comparison was limited for several of the pollutants given information scarcity. Consistently among PCBs, PBDEs, and PAHs, the more hydrophobic congeners were transported in larger proportions during storm flows relative to low flows. Loads for Water Years 2007-2010 were estimated using regression with turbidity during the monitored months and a flow weighted mean concentration for unmonitored dry season months. More than 91% of the loads for every pollutant measured were transported during storm events, along with 87% of the total discharge. While this dataset fills an important local data gap for highly urban watersheds of San Francisco Bay, the methods, the uniqueness of the analyte list, and the resulting interpretations have applicability for managing pollutant loads in urban watersheds in other parts of the world.

Several lines of evidence from the Regional Monitoring Program and other studies have suggested that sediment grain size characteristics influence amphipod (Eohaustorius estuarius) survival in 10 day toxicity tests.  Two workshops were convened to address the influence of non-contaminant factors on amphipod toxicity tests, and the current project was prioritized based on the recommendations of experts participating in these workshops.  The study was designed to investigate the effects of kaolin clay on amphipod survival since this is the dominant clay type in Francisco Estuary sediments.  In these experiments reference sand was spiked with increasing concentrations of kaolin to determine whether there was a dose-based relationship between amphipod mortality and increasing concentrations of this type of clay. Wild-caught E. estuarius were collected from Beaver Creek Beach (Oregon) and supplied by Northwest Aquatic Sciences. The initial experiment did not demonstrate a dose-response relationship: E. estuarius survival in all concentrations from 10% to 100% kaolin was lower than in the sand control, and survival in the clay spiked sand was also highly variable.  This experiment exposed a mixture of amphipod size classes representative of those typically provided by the amphipod supplier.  Reasoning that variable response to clay was related to variable tolerances by the different amphipod size classes, a follow-up experiment was conducted to investigate this relationship.  Amphipods were separated into small, medium and large size classes and these were exposed to 100% kaolin.  These results showed survival in 100% clay was 86%, 82% and 66% by small, medium and large amphipods, respectively.  To further investigate size-related responses to clay, small, medium and large amphipods were exposed to concentrations of sand spiked with clay from 0 to 100%.  The results of this experiment showed that smaller amphipods tolerated high clay concentrations better than larger animals, but there was not a strict monotonic dose-response relationship.  Conclusions based on this experiment were constrained by an inability to sort amphipods into three distinct size classes, because there were not enough of the largest animals present at the Oregon collection site.  In addition, grain size analysis of the sand spiked clay suggested that the clay tended to flocculate in the treatments above 70% kaolin.  This experiment was repeated when three distinct size classes were present in December 2014.  The results of this experiment also showed that smaller amphipods tolerated high kaolin better than larger amphipods.  As in the previous experiment, there was not a monotonic response to clay, especially at the higher kaolin concentrations, and the grain size analysis also showed flocculation occurred in the highest clay treatments.  Despite these inconsistencies, the results of this experiment suggest that tolerance of E. estuarius to clay varies with amphipod size.  Average survival was 81%, 79%, and 65% for small, medium and large amphipods, respectively in concentrations > 50% clay.  Possible mechanisms for size specific clay effects on this amphipod species include lower survival related to reduced energy reserves in larger animals, inhibition of gill function, and inhibition of feeding and locomotion through clogging of amphipod setae.  The results suggest that use of smaller amphipods in routine monitoring of high clay sediments will reduce the influence of this factor on test results.  Additional experiments with high clay reference site sediments from San Francisco Bay are recommended to confirm the size related response with field sediments.

The Environmental Data Summit, convened under the auspices of the Delta Stewardship Council’s Delta Science Program in June 2014, witnessed remarkable participation from experts across California, the nation, and even the world. Summit attendees from the public, private, federal, and non-profit sectors shared their views regarding the urgent needs and proposed solutions for California’s data-sharing and data-integration challenges, especially pertaining to the subject of environmental resource management in the era of “big data.” After all, this is a time when our data sources are growing in number, size, and complexity. Yet our ability to manage and analyze such data in service of effective decision-making lags far behind our demonstrated needs.

In its review of the sustainability of water and environmental management in the California Bay-Delta, the National Research Council (NRC) found that “only a synthetic, integrated, analytical approach to understanding the effects of suites of environmental factors (stressors) on the ecosystem and its components is likely to provide important insights that can lead to enhancement of the Delta and its species” (National Research Council 2012). The present “silos of data” have resulted in separate and compartmentalized science, impeding our ability to make informed decisions. While resolving data integration challenges will not, by itself, produce better science or better natural resource outcomes, progress in this area will provide a strong foundation for decision-making. Various mandates ranging from the California Water Action Plan to the President’s executive order demanding federal open data policies demonstrate the consensus on the merits of modern data sharing at the scale and function needed to meet today’s challenges.

This white paper emerges from the Summit as an instrument to help identify such opportunities to enhance California’s cross-jurisdictional data management. As a resource to policymakers, agency leadership, data managers, and others, this paper articulates some key challenges as well as proven solutions that, with careful and thoughtful coordination, can be implemented to overcome those obstacles. Primarily featured are tools that complement the State’s current investments in technology, recognizing that success depends upon broad and motivated participation from all levels of the public agency domain. Executive Summary

This document describes examples, practices, and recommendations that focus on California’s Delta as an opportune example likely to yield meaningful initial results in the face of pressing challenges. Once proven in the Delta, however, this paper’s recommended innovations would conceivably be applied statewide in subsequent phases.

Contaminant concentrations from the Sacramento-San Joaquin River watershed were determined in water samples mainly during flood flows in an ongoing effort to describe contaminant loads entering San Francisco Bay, CA, USA. Calculated PCB and total mercury loads during the 6-year observation period ranged between 3.9 and 19 kg/yr and 61 and 410 kg/yr, respectively. Long-term average PCB loads were estimated at 7.7 kg/yr and total mercury loads were estimated at 200 kg/yr. Also monitored were PAHs, PBDEs (two years of data), and dioxins/furans (one year of data) with average loads of 392, 11, and 0.15/0.014 (OCDD/OCDF) kg/yr, respectively. Organochlorine pesticide loads were estimated at 9.9 kg/yr (DDT), 1.6 kg/yr (chlordane), and 2.2 kg/yr (dieldrin). Selenium loads were estimated at 16 300 kg/yr. With the exception of selenium, all average contaminant loads described in the present study were close to or below regulatory load allocations established for North San Francisco Bay.

Building on previous environmental flow discussions and a growing recognition that hydrogeomorphic processes are inherent in the ecological functionality and biodiversity of riverscapes, we propose a functional-flows approach to managing heavily modified rivers. The approach focuses on retaining specific process-based components of the hydrograph, or functional flows, rather than attempting to mimic the full natural flow regime. Key functional components include wet-season initiation flows, peak magnitude flows, recession flows, dry-season low flows, and interannual variability. We illustrate the importance of each key functional flow using examples from western US rivers with seasonably predictable flow regimes. To maximize the functionality of these flows, connectivity to morphologically diverse overbank areas must be enhanced in both space and time, and consideration must be given to the sediment-transport regime. Finally, we provide guiding principles for developing functional flows or incorporating functional flows into existing environmental flow frameworks.

GreenPlan-IT is a planning level tool that was developed by SFEP and SFEI with support and oversight from BASMAA to provide Bay Area municipalities with the ability to evaluate multiple management alternatives using green infrastructure for addressing stormwater issues in urban watersheds. GreenPlan-IT combines sound science and engineering principles with GIS analysis and optimization techniques to support the cost-effective selection and placement of Green Infrastructure (GI) at a watershed scale.  Tool outputs can be used to develop quantitatively-derived watershed master plans to guide future GI implementation for improving water quality in the San Francisco Bay and its tributary watersheds.

This report provides an overview of the GreenPlan-IT Tool and demonstrates its utility and power through two pilot studies which is summarized in this report as a case study. The pilot studies with the City of San Mateo and the City of San Jose explored the use of GreenPlan-IT for identifying feasible and optimal GI locations for mitigation of stormwater runoff. They are provided here to give the reader an overview of the user application process from start to finish, including problem formulation, data collection, GIS analysis, establishing a baseline condition, GI representation, and the optimization process. Through the pilot study application process the general steps and recommendations for how GreenPlan-IT can be applied and interpreted are presented.

Structurally, the GreenPlan-IT is comprised of three components: (a) a GIS-based Site Locator Tool to identify potential GI sites; (b) a Modeling Tool that quantifies anticipated watershed-scale runoff and pollutant load reduction from GI sites; and (c) an Optimization Tool that uses a cost-benefit analysis to identify the best combinations of GI types and number of sites within a watershed for achieving flow and/or load reduction goals. The three tool components were designed as standalone modules to provide flexibility and their interaction is either through data exchange, or serving as a subroutine to another tool. This user manual addresses each of the tools separately, though they are designed to complement each other.

Project Background

Over the past century and a half, lower Novato Creek and the surrounding tidal wetlands have been heavily modified for flood control and land reclamation purposes. Levees were built in the tidal portion of the mainstem channel beginning in the late 1800s to convey flood flows out to San Pablo Bay more rapidly and to remove surrounding areas from inundation. Following levee construction, the wetlands surrounding the channel were drained and converted to agricultural, residential, and industrial areas. These changes have resulted in a considerable loss of wetland habitat, reduced sediment transport to marshes and the Bay, and an overall decreased resilience of the system to sea level rise.
In addition to tidal wetland modification, land use changes upstream in the Novato Creek watershed have resulted in several challenges for flood control management. Dam construction and increased runoff in the upper watershed have resulted in elevated rates of channel incision, which have increased transport of fine sediment from the upper watershed to lower Novato Creek. Channelization of tributaries and construction of irrigation ditches have likely increased drainage density in the upper watershed, also potentially contributing to increased rates of channel incision and fine sediment production (Collins 1998). Downstream, sediment transport capacity has been reduced by construction of a railroad crossing and loss of tidal prism and channel capacity associated with the diking of the surrounding marsh. As a result of the increased fine sediment supply from the watershed and the loss of sediment transport capacity in lower Novato Creek, sediment aggradation occurs within the channel, which in turn reduces the flood capacity of the channel, necessitating periodic dredging.

Currently, the Marin County Department of Public Works (MCDPW) is coordinating the Novato Watershed Program, which includes Marin County Flood Control and Water Conservation District, Novato Sanitary District, and North Marin Water District. Within lower Novato Creek, the Program is seeking to implement a new approach to flood control that includes redirecting sediment for beneficial use, reducing flood channel maintenance costs, restoring wetland habitat, and enhancing resilience to sea level rise. Included as part of this goal is the re-establishment of historical physical processes that existed before major channel modification, which in turn will re-establish historical ecological functions and help to create a tidal landscape that is resilient to increasing sea level.

This report explores the potential for integrating ecological functions into flood risk management on lower Novato Creek. It presents an initial vision of how ecological elements could contribute to flood protection, based on a broad scale analysis and a one day workshop of local and regional experts. The Vision is not intended to be implemented as is, but rather adapted and applied through future projects and analysis. Other actions (e.g., floodwater detention basins) may also need to be implemented in the interim to meet flood risk objectives.

Hydroxylated polybrominated diphenyl ethers (OH-BDEs) are a new class of contaminants of emerging concern, but the relative roles of natural and anthropogenic sources remain uncertain. Polybrominated diphenyl ethers (PBDEs) are used as brominated flame retardants, and they are a potential source of OH-BDEs via oxidative transformations. OH-BDEs are also natural products in marine systems. In this study, OH-BDEs were measured in water and sediment of freshwater and coastal systems along with the anthropogenic wastewater-marker compound triclosan and its photoproduct dioxin, 2,8-dichlorodibenzo-p-dioxin. The 6-OH-BDE 47 congener and its brominated dioxin (1,3,7-tribromodibenzo-p-dioxin) photoproduct were the only OH-BDE and brominated dioxin detected in surface sediments from San Francisco Bay, the anthropogenically impacted coastal site, where levels increased along a north-south gradient. Triclosan, 6-OH-BDE 47, 6-OH-BDE 90, 6-OH-BDE 99, and (only once) 6’-OH-BDE 100 were detected in two sediment cores from San Francisco Bay. The occurrence of 6-OH-BDE 47 and 1,3,7-tribromodibenzo-p-dioxin sediments in Point Reyes National Seashore, a marine system with limited anthropogenic impact, was generally lower than in San Francisco Bay surface sediments. OH-BDEs were not detected in freshwater lakes. The spatial and temporal trends of triclosan, 2,8-dichlorodibenzo-p-dioxin, OH-BDEs, and brominated dioxins observed in this study suggest that the dominant source of OH-BDEs in these systems is likely natural production, but their occurrence may be enhanced in San Francisco Bay by anthropogenic activities.

EXECUTIVE SUMMARY
As sea level rise accelerates, our shores will be increasingly vulnerable to erosion. Particular concern centers around the potential loss of San Francisco Bay’s much-valued tidal marshes, which provide natural flood protection to our shorelines, habitat for native wildlife, and many other ecosystem services. Addressing this concern, this study is the first systematic analysis of the rates of marsh retreat and expansion over time for San Pablo Bay, located in the northern part of San Francisco Bay.

Key findings:
• Over the past two decades, more of the marshes in San Pablo Bay have expanded (35% by length) than retreated (6%).
• Some areas have been expanding for over 150 years.
• Some marsh edges that appear to be retreating are in fact expanding rapidly at rates of up to 8 m/yr.
• Marsh edge change may be a useful indicator of resilience, identifying favorable sites for marsh persistence.
• These data can provide a foundation for understanding drivers of marsh edge expansion and retreat such as wind direction, wave energy, watershed sediment supply, and mudflat shape.
• This understanding of system dynamics will help inform management decisions about marsh restoration and protection.
• This study provides a baseline and method for tracking marsh edge response to current and future conditions, particularly anticipated changes in sea level, wave energy, and sediment supply.

Recommended next steps:
• This pilot study for San Pablo Bay marshes should be extended to other marshes in San Francisco Bay.
• These initial marsh expansion and retreat findings should be further analyzed and interpreted to improve our understanding of system drivers and identify management responses.
• A program for repeated assessment should be developed to identify and track changes in shoreline position, a leading indicator of the likelihood marsh survival.

Hot springs in the Tijuana River? Antelope by the beach? Zip-lines over the international border?
Come find out what the Tijuana River Valley looked like in the not-so-distant past and how the river, estuary, and surrounding areas have changed over the past two centuries. Hear how researchers “recreated” the historical landscape and how this information helps us to better plan for the future.

This report offers guidance for creating and maintaining landscapes in the Sacramento-San Joaquin Delta that support desired ecological functions, while retaining the overall agricultural character and water-supply service of the region. Based on extensive research into how the Delta functioned historically, how it has changed, and how it is likely to evolve, we discuss where and how to re-establish the dynamic natural processes that can sustain native Delta habitats and wildlife into the future. The approach, building on work others have piloted and championed, is to restore or emulate natural processes where possible, establish an appropriate mosaic of habitat types at the landscape scale, use multi-benefit management strategies to increase support for native species in agricultural and urban areas, and allow the Delta to adapt to future uncertainties of climate change, levee failure, and human population growth. With this approach, it will be critical to integrate ecological improvements with the human landscape: a robust agricultural economy, water infrastructure and diversions, and urbanized areas. Strategic restoration that builds on the history and ecology of the region can contribute to the strong sense of place and recreational value of the Delta.

Printed copies of the report are available for purchase.

The physical and ecological environment of the upper San Francisco Estuary has been profoundly altered since the early 1800s. Recent efforts have utilized maps of the upper estuary’s historical habitat types to infer associated changes in desired ecosystem processes and functions. The work presented in this memo builds on these previous efforts, but utilizes a new tool for evaluating change over time: a 3D hydrodynamic model of the pre-development estuary. This model was constructed by Resource Management Associates (RMA) using a new digital elevation model of the pre-development upper estuary generated by SFEI and UC Davis (UCD) and “natural” boundary flows calculated by the California Department of Water Resources (CDWR).

Once completed and calibrated, the pre-development model was paired with a similar model of the contemporary system in order to analyze hydrodynamic changes in the upper estuary. These analyses are presented in a technical memorandum published by RMA (2015). This memorandum takes these analyses and considers the ecological implications of modeled changes (see the “Results” section). Hydrodynamic analyses include analyzing changes in tidal prism, isohaline positions, low-salinity zone habitat, channel velocity, and source water distribution.

 In addition to describing the ecological implications of modeled hydrodynamic changes, this memorandum summarizes major ongoing questions about estuarine hydrodynamics that might be explored using these models, including changes in water residence time, temperature, transport pathways, and the connectivity of aquatic and semi-aquatic habitats. Understanding changes in these and other factors would greatly improve our understanding of the desirable ecosystem functions provided by the historical system and, as a result, improve our ability to recover these functions now and into the future.

Dissolved copper is one of the more pervasive and toxic constituents of stormwater runoff and is commonly found in stream, estuary, and coastal marine habitats of juvenile salmon. While stormwater runoff does not usually carry copper concentrations high enough to result in acute lethality, they are of concern because sublethal concentrations of copper exposure have been shown to both impair olfactory function and alter behavior in various species in freshwater. To compare these results to other environments that salmon are likely to encounter, experiments were conducted to evaluate the effects of salinity on the impairment of olfactory function and avoidance of copper. Copper concentrations well within the range of those found in urban watersheds, have been shown to diminish or eliminate the olfactory response to the amino acid, l-serine in freshwater using electro-olfactogram (EOG) techniques. The olfactory responses of both freshwater-phase and seawater-phase coho and seawater-phase Chinook salmon, were tested in freshwater or seawater, depending on phase, and freshwater-phase coho at an intermediate salinity of 10‰. Both 10‰ salinity and full strength seawater protected against the effects of 50μg copper/L. In addition to impairing olfactory response, copper has also been shown to alter salmon behavior by causing an avoidance response. To determine whether copper will cause avoidance behavior at different salinities, experiments were conducted using a multi-chambered experimental tank. The circular tank was divided into six segments by water currents so that copper could be contained within one segment yet fish could move freely between them. The presence of individual fish in each of the segments was counted before and after introduction of dissolved copper (<20μg/L) to one of the segments in both freshwater and seawater. To address whether use of preferred habitat is altered by the presence of copper, experiments were also conducted with a submerged structural element. The presence of sub-lethal levels of dissolved copper altered the behavior of juvenile Chinook salmon by inducing an avoidance response in both freshwater and seawater. While increased salinity is protective against loss of olfactory function from dissolved copper, avoidance could potentially affect behaviors beneficial to growth, survival and reproductive success.

The emergence of comparable landscape approaches to wildlife conservation and water quality improvement through federal and California state regulatory and management programs provides an opportunity for their coordination to better protect California’s aquatic resources, especially streams, wetlands, and riparian areas. Such coordination is patently desirable.  A framework has been developed to help coordinate restoration and compensatory mitigation across policies governing wildlife conservation and water quality in the landscape context. The framework is based on the Wetland and Riparian Area Monitoring Plan (WRAMP) of the California Wetland Monitoring Workgroup (CWMW) of the Water Quality Monitoring Council. The framework presented in this memorandum is a version of the standard WRAMP framework. It only differs from the standard framework to better accommodate wildlife conservation planning, assessment and reporting. To distinguish this version from the standard version, it is termed the 'WRAMP for wildlife'.

Context  Effective river restoration requires understanding a system’s potential to support desired functions. This can be challenging to discern in the modern landscape, where natural complexity and heterogeneity are often heavily suppressed or modified. Historical analysis is therefore a valuable tool to provide the long-term perspective on riverine patterns, processes, and ecosystem change needed to set appropriate environmental management goals and strategies.

Objective In this study, we reconstructed historical (early 1800s) riparian conditions, river corridor extent, and dry-season flow on the lower Santa Clara River in southern California, with the goal of using this enhanced understanding to inform restoration and management activities.

Method Hundreds of cartographic, textual, and visual accounts were integrated into a GIS database of historical river characteristics.

Results We found that the river was characterized by an extremely broad river corridor and a diverse mosaic of riparian communities that varied by reach, from extensive ([100 ha) willow-cottonwood forests to xeric scrublands. Reach-scale ecological heterogeneity was linked to local variations in dry-season water availability, which was in turn underpinned by regional geophysical controls on groundwater and surface flow.

Conclusions Although human actions have greatly impacted the river’s extent, baseflow hydrology, and riparian habitats, many ecological attributes persist in more limited form, in large part facilitated by these fundamental hydrogeological controls. By drawing on a heretofore untapped dataset of spatially explicit and long-term environmental data, these findings improve our understanding of the river’s historical and current conditions and allow the derivation of reach-differentiated restoration and management opportunities that take advantage of local potential.

We evaluated both the spatial distribution of gadolinium (Gd) and other rare earth elements (REE) in surface waters collected in a transect of San Francisco Bay (SFB) and their temporal variations within the Bay over two decades. The REE were preconcentrated using the NOBIAS PA-1 resin prior to analysis by high-resolution inductively coupled plasma mass spectrometry. Measurements revealed a temporal increase in the Gd anomaly in SFB from the early 1990s to the present. The highest Gd anomalies were observed in the southern reach of SFB, which is surrounded by several hospitals and research centers that use Gd-based contrast agents for magnetic resonance imaging. Recent increases in that usage presumably contributed to the order of magnitude increase in anthropogenic Gd concentrations in SFB, from 8.27 to 112 pmol kg–1 over the past two decades, and reach the northeast Pacific coastal waters. These measurements (i) show that “exotic” trace elements used in new high-tech applications, such as Gd, are emerging contaminants in San Francisco Bay and that anthropogenic Gd concentrations increased substantially over a 20 year period; (ii) substantiate proposals that REE may be used as tracers of wastewater discharges and hydrological processes; and (iii) suggest that new public policies and the development of more effective treatment technologies may be necessary to control sources and minimize future contamination by REE that are critical for the development of new technologies, which now overwhelm natural REE anomalies.

This memo was developed by SFEI to introduce the EcoAtlas tools, their intended (target) user community, and the short- and long-term intended applications. 

In 2016 The Santa Clara Valley Water District and its consultants conducted a watershed wide survey to characterize the distribution and abundance of the aquatic resources within the Lower Peninsula watershed wtihin Santa Clara County, CA based on available GIS data, and to assess the overall ecological condition of streams within the watershed based on a statistically based, random sample design and the California Rapid Assessment Method for streams (CRAM).

Despite widespread detection of microplastic pollution in marine environments, data describing microplastic abundance in urban estuaries and microplastic discharge via treated municipal wastewater are limited. This study presents information on abundance, distribution, and composition of microplastic at nine sites in San Francisco Bay, California, USA. Also presented are characterizations of microplastic in final effluent from eight wastewater treatment plants, employing varying treatment technologies, that discharge to the Bay. With an average microplastic abundance of 700,000 particles/km2, Bay surface water appears to have higher microplastic levels than other urban waterbodies sampled in North America. Moreover, treated wastewater from facilities that discharge into the Bay contains considerable microplastic contamination. Facilities employing tertiary filtration did not show lower levels of contamination than those using secondary treatment. As textile-derived fibers were more abundant in wastewater, higher levels of fragments in surface water suggest additional pathways of microplastic pollution, such as stormwater runoff.

Municipal wastewater effluent has been proposed as one pathway for microplastics to enter the aquatic environment. Here we present a broad study of municipal wastewater treatment plant effluent as a pathway for microplastic pollution to enter receiving waters. A total of 90 samples were analyzed from 17 different facilities across the United States. Averaging all facilities and sampling dates, 0.05 ± 0.024 microparticles were found per liter of effluent. Though a small value on a per liter basis, even minor municipal wastewater treatment facilities process millions of liters of wastewater each day, yielding daily discharges that ranged from ∼50,000 up to nearly 15 million particles. Averaging across the 17 facilities tested, our results indicate that wastewater treatment facilities are releasing over 4 million microparticles per facility per day. Fibers and fragments were found to be the most common type of particle within the effluent; however, some fibers may be derived from non-plastic sources. Considerable inter- and intra-facility variation in discharge concentrations, as well as the relative proportions of particle types, was observed. Statistical analysis suggested facilities serving larger populations discharged more particles. Results did not suggest tertiary filtration treatments were an effective means of reducing discharge. Assuming that fragments and pellets found in the effluent arise from the 'microbeads' found in many cosmetics and personal care products, it is estimated that between 3 and 23 billion (with an average of 13 billion) of these microplastic particles are being released into US waterways every day via municipal wastewater. This estimate can be used to evaluate the contribution of microbeads to microplastic pollution relative to other sources (e.g., plastic litter and debris) and pathways (e.g., stormwater) of discharge.