According to SFPUC studies SF discharges approximately 1.5 billion gallons of combined sewage (mostly rain water) in an average year of which over 468 million gallons comes out of the Division St. outfall (see Modeling Results below), at the western end of Mission Creek. Currently there are about 12 discharges here in an average year. This water is approximately 5% household sewage and 95% rainwater. That means there's about 23 million gallons of raw sewage coming out of 1 outfall into Mission Creek every year. The combined sewage is held back by the large gates at the outfalls along Mission Creek, which open to prevent flooding when the sewer storage boxes are full. Unfortunately, when these gates open, the water rushes out so fast it brings all the pollution from the sewers with it.

Division St. outfall discharging into Mission Creek. This is estimated to happen 12 times a year.

Transport Storage: The Key to SF’s Combined Sewage/Stormwater Treatment

The central concept of the SF combined sewer systems design and permitting was to build large sewage boxes called the “Transport/Storage System” (T/S)  that can store large amounts of storm water, holding the water for treatment at the sewer treatment plants around the City. In dry weather, these boxes also intercept the normal sewage flows and transport it to the pumps to send to the treatment plants. In smaller storms, as the pumps to the treatment plants reach their maximum flow and the combined sewage starts to back up, the storage is enough to prevent any sewage spilling out. In slightly larger storms, once the boxes are full, they would provide some "treatment" before allowing the water to enter the bay. 

This is called “equivalent to primary” in San Francisco’s permit and also called “decanting”. The idea was to allow much of the pollution to settle out inside the boxes before discharge. This is done by slowing the water and letting some of the pollutants settle out and have floatable debris held back in the sewer system by baffles, large walls hanging from the top of the boxes to keep lighter items inside the sewer boxes. The water is held in by weirs, essentially walls that the water can spill over the top of once the boxes are full. In theory, the pollutants held back should be carried back to the sewer treatment plant after the storm as the boxes drain. In some parts of the system this is very effective and given the right design, can remove more pollutants from the water than the sewer treatment plants.

Mission Creek Outfalls - Graphic from Calif.High Speed Rail report

The Transport Storage box that helps protect Mission Creek is the Channel Outfalls Consolidation Sewer. This is a large box that starts at Howard St. on The Embarcadero and goes down The Embarcadero and King St., turning on 4th St. then going down Berry St. to the Channel Pump Station at the dead-end of Mission Creek, next to the Division St. outfall.

This system has 2 outfalls (Brannan and Howard) that go directly into the bay, where the tides and currents help reduce the concentration of the sewage pollution, as well as 7 outfalls into Mission Creek itself, the 3 largest  ones (5th St, 6th St and Division) are controlled by gates. 

The largest of these is the Division St. outfall, with the 12 gates that account for 463 million gallons of raw sewage discharged in an average year, or nearly 31% of all combined sewage discharged by San Francisco citywide. The water that is discharged from this outfall does not go through the Transport Storage boxes, instead it is discharged directly from the large sewer into the dead-end of the Mission Creek Slough.

Problem: Most of the System Fails to Provide Meaningful Treatment:

 Unfortunately, many of the outfalls around San Francisco do not allow the water to slow down enough and do not hold the water long enough to effectively remove the pollutants before the water is dumped into the Bay and ocean. 

Velocity through the opened gates is much higher then over a fixed weir.

In some cases, sewage passes right through the outfall structures themselves without ever even reaching the boxes. Once the system is full and water is passing out through these structures, the speed of the water is high enough to wash out what pollutants may have settled, potentially causing the pollution that reaches the bay and ocean to actually be worse than in the sewers themselves. In much of the City, where the sewage discharges 8-10-12 times a year, the speed of the sewage through the transport/storage chambers in common storms seen many times each year is enough to prevent any meaningful settling of the pollutants. Storms seen 4-6 times a year are not “major storms”, they are routine. The system should be designed to provide adequate treatment throughout these routine storms. 


In Mission Creek, because of the low elevation of the areas surrounding the Creek such as SOMA, the discharges are released by opening gates to help reduce flooding in the lower areas. When these gates open a large amount of water comes out of the Division St. and other outfall gates very quickly, the sewer boxes are not able to provide any settling and the baffles are ineffective, meaning massive amounts of pollution and debris come out with the massive flush of water when the gates open. The gates essentially drain the top 4’ of the T/S box, when they are open there is no weir to slow the water down. Opening the gates is like flushing a toilet, where the velocity of the water passing through the outfall structures is enough to wash out any pollutants that had settled in the structures before discharge. The largest outfall in Mission Creek is the Division St. outfall which has 12 large gates that all open at the same time. 

All these outfalls also have side weirs, which can release water more slowly in smaller storms if the gates were not opened. Currently most of the outfalls are directly across from the sewers sending the water into the boxes. Ideally this input or "loading" should be offset, allowing the water should travel through the boxes, giving the pollutants time to settle, instead of travelling straight across the boxes and out.

Channel Drainage Basin - 5,665 acres,

San Francisco has had many opportunities to do minor improvements to its operations to help reduce this pollution. Most of these would cost nearly nothing, or relatively small amounts of money simply by changing the way the gates operate. All of the gates have side weirs,walls that hold back the water until it gets to the top of the wall, which allows water to slowly discharge. If SF only opens the gates in larger storms when flooding is a threat, most of the water can be kept in the boxes and the water can be discharged more slowly. SF engineers worked on optimizing the gates like this 12 years ago, but SF has chosen to do nothing. 


Worse yet, they have failed to maintain the Brannan Street Outfall that discharges directly into the bay on The Embarcadero at Brannan St. It hasn't operated in over 10 years. When this outfall was open, flows could travel down the large transport storage boxes, settling solids as they go and being discharged away from the confined Mission Creek. They would go directly into the bay where it would disperse faster and be more diluted, as well as slowing down and getting more "treatment" in the boxes. Instead, they are flushed out from the large sewer directly into the dead end of the creek.


Instead of fixing the system and improving it over the last 40 years, SF has neglected the system and allowed it to become more of a problem. The discharge permit that allows SF to dispose sewage into the bay requires SF to improve and optimize the system. SF has vigorously fought  attempts to get it to do anything and even avoided making changes that would cost nearly nothing. Because of this intransigence, SF is now backed into a corner and will have to deal with multiple lawsuits trying to get them to improve. 


What WE can do about it:

We can all work with SF to convince them it will be much less expensive to address these problems now, with reasonable and relatively simple improvements to its system, instead of fighting for the right to dump sewage directly into the bay, as well as into people’s homes. SF can be making improvements to its system now that can be useful for future sea level rise as well as improve its current performance. There are opportunities to improve the treatment provided by its system now, in places where future pumping will be needed to reduce the impact of rising sea level.

San Francisco is currently pushing back against the US EPA, the State Regional Water Quality Control Board and Baykeeper, who are trying to get SFPUC to improve it's system. It is likely that relatively minor improvements to SF's system can provide major improvements in it's environmental performance. SFPUC, instead of attempting to implement any improvements, is claiming that the only solution to the current problems is to spend 10s of billions of dollars and therefore SF should not be required to improve. All of us need to work with the Mayor and the Board of Supervisors to convience SFPUC management to negotiate reasonable improvements and settle these cases.  More information about these cases are below in the section SF’s fight against the EPA, and the Clean Water Act

We can request that SF PUC do incremental improvements to it's system, every year. Most importantly, maintaining the system in good repair is a minimum. Currently, because of lack of maintenance, the Brannan St. outfall has not been working, forcing water that would travel through the boxes before being discharged into the bay, being discharged through the Division St. outfall instead. Brannan St. outfall discharges directly into the bay, where tides and currents would help dilute the sewage. Instead, by forcing the water out through the Division St. (and other Mission Creek outfalls) the sewage has less time in the boxes to settle out pollutants and the sewage is being discharged at a higher velocity, causing increased pollution to be swept out into the creek.

We can request that SF PUC do things that are relatively low cost but that can have substantial improvements. First thing to do would be to improve the management of the sewage discharge gates into Mission Creek. If these gates are opened more slowly during smaller storms, water can discharge more slowly, getting improved pollutant removal before entering the creek.

We can request that SF PUC do relatively simple projects as a part of other ongoing projects to improve it's current combined sewage discharge performance. 

In the upcoming “Folsom Stormwater Improvement Project”, required by the State Regional Water Board to reduce sewage discharges into homes in the Mission District, will add 2.5mil gals of storage in the proposed 12’ tunnel. Within a total amount of storage in the transport/storage system serving this area there is a total of 28 million gallons of storage, so this less then a 10% increase in storage. 

During this project SF can also build a large storage/decant facility on Berry St. between De Haro and 7th St. This could add an additional 7-9 mil gallons of storage. These 2 projects together would increase the storage in the Channel system by 25% to 39 mil gallons. The additional decant box can provide some flow-through treatment before discharge as well as be used to provide for pumping in the future to help SF address rising sea levels.

 More importantly however, adding it in a way that helps slow the water and decant before it gets to Mission Creek could greatly improve the quality of the water that does get discharged. If the additional boxes are designed to slow the water down and allow it to “decant” slowly out of the system, it can also get UV disinfection at 2-3 of the outfalls before being discharged into the creek reducing the impact on the Creek and the beneficial uses such as kayaking, and jumping into the bay after home run balls!


We can request that SF PUC add UV disinfection on most flows into areas that the discharges impact the public's use of recreational beaches. This does not have to be all overflows. SFPUC could provide treatment to 70-80% of the volume of discharges with relatively simple, local units at key outfalls, directing discharges to these locations first.


These ideas can be applied around SF’s system, where with minor improvements to the decant facilities, UV can be added to reduce the impact of the combined sewage discharges in smaller storms. 

According to documents SFPUC provided to the State's water quality regulators at the regional board in 2015, SF had studied changing the way the gates operate to improve both flooding in bigger storms and water quality in smaller storms by openning the gates more slowly during small storms and allowing the water to flow over the existing weirs, slowing the water down and improving the effectiveness of the decanting within the sewage boxes.  Even though these changes would cost nearly nothing, SFPUC decided to ignore these recommendations and instead have allowed the Brannan St. discharge gate, which discharges the sewage away from the creek, to break down and hasn't operated since around 2012.

Sea Level Rise: 

In the future, as sea levels rise, during large rainstorms SF will have to start pumping to prevent low lying areas around the City from getting inundated by the water draining off the hills. System changes today can make these future efforts easier, or harder. Adding decant and treatment in key locations today, before the impacts of sea level rise, can reduce the level of work future San Francisco generations will have to do to stay dry as well as help improve our beaches, creeks and the bay.

Recommendation: 

We recommend that SFPUC take a more positive approach to addressing pollutant discharge into the Bay and Ocean. Many steps can be taken for relatively small investment that can incrementally improve the quality of the sewage discharges currently being dumped into the Bay and ocean. Further, we’d proposa a 15 year, $350mil program (about $20mil per year) to modify the existing system, building structures or modifying the existing system to improve decant and start providing UV disinfection around the City. Overall this is less than 4% of what SFPUC is currently spending on its capital improvement program. A well established, ongoing program of improvement and optimization of existing facilities with distributed treatment can be considerably less expensive and more beneficial to future needs, then a single large mega engineering project at a single sewer treatment plant. These systems can be better monitored and improved upon over time. This will only work if SF adopts the approach of constantly improving upon the system, not neglecting it and letting it degrade.  We're hoping that through some gentle persuasion, SFPUC can work with us to provide ongoing, common sense, inexpensive improvements to its system.

Decanting: The Basis of SF’s  Discharge Permit

Primary sedimentation is the process of reducing the velocity of sewage below the point at which it can transport suspended matter, causing much of it to settle and can be removed as sludge. In wastewater treatment, decant water is water that has separated from sludge and is removed from the layer of water above the sludge. Decantation is performed through the sedimentation process of suspended material in the wastewater.


San Francisco’s Transport Storage system was originally proposed to provide “equivalent to primary” treatment within the large boxes. In the 1970s,  San Francisco was the first city in the US to be required to address combined sewage overflows under the US Clean Water Act. The US EPA and the state Regional Board through civil action and judicial orders forced SF to take action to reduce the massive pollution being put into the bay every time it rained. Initially, the requirement was to develop a plan to treat all combined sewage discharges in an “average” year, with larger, less frequent storms allowed to flow out. ½ of the cost of the plan was to be paid by the federal government and an additional 40% was paid with loans from the state and federal government. 


As the cost of treating nearly all sewage discharges was so high, the EPA and regional board negotiated a smaller system, allowing from 1 to 10 sewage overflows a year. The ocean side system would be allowed 8, the north shore system would be allowed 4, along the central bayside 10 and south of Islais Creek, 1 per year. 


In negotiating the design criteria for managing the sewer discharges, SF officials proposed that the transport storage boxes would provide flow-through treatment of the combined sewage during larger storms to reduce the pollutants being discharged into the Bay and ocean, as well as to help protect “beneficial uses” of the beaches and bay. 


In theory, this seems reasonable as the boxes are long and could provide a good place to slow the water down to allow much of the pollutants to settle out before being discharged. A 2009 study appears to show that in some conditions, some of the better designed boxes and overflow structures can remove as much pollution as the sewer treatment plants. 


Unfortunately, except for a few exceptions, the boxes were not designed to allow the water to slow down and rest. In most cases the water from the uphill sewers go into the box then directly out the other side of the box, traveling less then 15-20’ at fairly high speeds before going out the discharge pipe. In many of the sewage outfalls, the combined sewage doesn’t even flow into a box, the sewage just goes into the outfall structure and out into the bay with no settling what-so-ever.


This is considerably worse in Mission Creek, where instead of storing the water, when the gates open it rushes out so quickly it actually picks up pollutants that might have been deposited, flushing out into the creek. The speed of the water going through the boxes, under the baffles and out, is so high the baffles do not stop the large floating objects and there is little to no settling.



Division St. outfall - 468.8 million gallons of combined sewage estimated annual discharge 12 times a year.  Water coming out of the sewer quickly passes under the baffle and out the 12 tide gates

This was known in 2012 when SF engineers did a study to change the way the gates operate. According to this study:

The analysis focused on four primary objectives in the Channel Basin:

• Improve the water quality of discharges entering the Channel Basin. This improvement in water

quality can be achieved by increased flows over weirs as opposed to through gates.

• Reduce the total volume of discharges in Channel Basin.

• Give preference to discharges exiting the system directly into the bay as compared to those

entering Mission Creek. The Brannan and Howard outfalls provide routes directly into bay.

• Improve or do not worsen flooding.


Sadly, this study was never implemented, although it appears the cost would have been very low.

Permits 

(future section)

SF’s fight against the EPA, and the Clean Water Act:

The US EPA and the state Regional Board have been trying to get SF to improve it’s performance for many years, In 2019, together they issued a new discharge permit to SF for the Westside system including the Oceanside Treatment plant and the combined sewage outfalls, which required SF to do more to protect the public and the environment. SF has been appealing this for the last 5 years and has now taken this to the US Supreme court: https://www.supremecourt.gov/search.aspx?filename=/docket/DocketFiles/html/Public/23-753.html. Also, see Politco's: Strange bedfellows align in latest Supreme Court water case.


In March 2024, SF Baykeeper started a Clean Water Act Citizen lawsuit with a Notice of Intent, listing many violations of the discharge permits.


 Baykeeper:San Francisco Caught Dumping Millions of Gallons of Sewage Into SF Bay Every Year

and Notice of Intent (first step in legal action): https://baykeeper.org/sites/default/files/image_upload/images/2024.03.06%20Baykeeper%20SFPUC%20Notice%20Letter%20w%20Exhs.pdf 


In May 2024 the EPA and Regional Board took further action to start the civil enforcement process:

...San Francisco’s combined sewer systems are in a state of disrepair, and the City’s failure to properly operate and maintain them has led to additional combined sewage discharges that has put members of the public at risk for unknowingly coming into contact with untreated sewage. San Francisco has also consistently failed to properly notify the public about the presence of untreated sewage at popular water recreation locations, overflows from manholes onto sidewalks and streets and the risks of coming into contact with untreated sewage.

United States and California Take Enforcement Action Against San Francisco for Violations of the Clean Water Act | US EPA

US EPA/Regional Board federal complaint: https://www.epa.gov/system/files/documents/2024-05/3-24-cv-02594-city-county-san-francisco-complaint-2024-05-01.pdf

Modeling results:

These tables show the results of San Francisco's hydraulic model after updates in 2016 and 2019. These results are provided to the state and federal regulators as examples of the current discharges and effectiveness of SF's combined sewer system. See the links below for the full documents.


Notes:


Opening the Gates at Division defeats the goals of decanting and needs to be limited.

When the gates open, the water rushes out so fast that it drags the pollution from the sewers out with it. When the water is going so fast, the baffles which are supposed to stop floating debris don't function as well so trash and floating sewage is dragged out also.


Combined sewer graphic from Oakland Museum Creeks page (full image)