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Mckinley water vault FAQs

We will continue to update the FAQs as the project continues. 


What is the McKinley Water Vault?
The Vault is basically a large underground cistern. It’s a temporary storage facility that will reduce wastewater outflows and storm water flooding during a large storm event, then it will slowly feed the wastewater into the combined sewer system at a rate that is sustainable as the storm subsides. The Vault will be designed for a 6-hour, 10-year storm event.

The project will likely consist of excavating one large area and building a below ground concrete tank. It will be covered with a soil cap and, when complete, be invisible to park goers.

How big will the Vault be?
The size of the Vault has not been finalized yet, but it will likely be in the range of 5-7.5 million gallons.

Where in the park will it be?
The Vault will be located beneath the baseball field along 33rd Street between the picnic and rose garden areas. We will have more specific information on the Vault size and dimensions at the end of the design phase.  

Why is the Vault necessary in East Sacramento?
East Sacramento is at the top end of the combined sewer system that flows to the Sacramento Regional Wastewater Treatment Plant. When the combined sewer system is at maximum capacity, flooding and outflows occur in East Sacramento from local runoff and sewage. The McKinley Water Vault will reduce flooding and outflows by temporarily storing the wastewater. 

What will the McKinley Water Vault store?
The Vault will reduce the amount of wastewater (storm water runoff and sewage) that floods the streets in the combined sewer system by temporarily storing it during large storm events. The Vault will be kept empty except during large storm events and will be drained within one to three days after the storm.

What does the odor control facility do?
The odor control facility will filter the air that comes out of the Vault. The facility will be located below ground. The City is successfully operating three similar underground storage facilities without creating order issues. 



What is the combined sewer system?
The combined sewer system collects and carries wastewater (sewage) and storm water runoff through a single pipe network for treatment at the Sacramento Regional Wastewater Treatment Plant and the City’s wet weather treatment facilities during significant storm events. 

The system serves over 200,000 City residents including people in the downtown, East Sacramento, Land Park, Curtis Park and Oak Park neighborhoods. Combined sewer systems are rare on the west coast. San Francisco and Sacramento are the only large cities in California that have one. Many parts of the system are aging and do not have the capacity to protect the community from street flooding.

What is the benefit of a combined sewer system? 
The combined sewer system provides water quality benefits by conveying 97% of storm water in the combined sewer system to the regional wastewater plant for tertiary (high quality) treatment prior to being released into the river. This means that rather than the storm water going back into the river untreated, it is highly treated before it’s released back into the river. Drainage outside of the of the combined sewer system is discharged directly to area streams and rivers.



What is an outflow?
Wastewater flowing out of the combined sewer pipes and onto surface streets. Outflows occur when the combined sewer flows exceed its capacity.

What is a 6-hour, 10-year storm event?
It is one of the standard “design storms” Utilities considers in assessing the effectiveness of modifications to the combined sewer system. This represents the amount of rainfall from a storm event that lasts six hours and returns once every 10 years. It is based on the statistics of nearly 100 years of Sacramento rainfall data from the National Weather Service. It is terminology used to categorize a “design storm” for engineering analyses.

What are the benefits of the McKinley Water Vault?
The Vault will increase public safety by significantly reducing combined sewer outflows onto low-lying streets and adjacent properties that occurs during major storm events. It will also significantly reduce street and park flooding which benefits neighbors, walkers, park goers and business patrons visiting the area.  

Has Utilities evaluated separating the sewer and drainage system before?
Yes, we have. We evaluated separating it in 1992.

What was the cost of separating the sewer and drainage system when Utilities evaluated the option in 1992?
It was estimated to cost $1.416 billion (over $2 billion today) to construct a separated sewer and separated drainage system to replace the existing combined sewer system. 

Why don’t we separate the combined sewer system?
There are significant problems with separating the combined sewer system including:

  • It is prohibitively expensive. It would cost over $2 billion today based on the 1992 study.
  • It would result in a substantial rate increase to the ratepayers that live in areas with separated sewers in addition to those in the combined area.
  • The 1992 study estimated that it would take 22 years to design and construct a separated sewer system. 
  • Construction impacts would be devastating to businesses, residents, the community and employees that work in the combined sewer area.  Almost every street in downtown, midtown, East Sacramento, Land Park, Curtis Park and Oak Park neighborhoods would experience construction impacts.
  • Construction impacts would affect services provided by all utilities that are located underground in City streets like fiber optic lines, gas pipes, water pipes and underground electric lines to name a few.
  • Relocation of underground utilities that conflict with the construction of a new sewer and new drainage system would add many years to the construction timeline. Financial impacts to those utility owners would be excessive.
  • Storm drainage would no longer be treated and would result in an adverse water quality impact to receiving waters.

In 1992, separation of the combined sewer system was proposed to City Council. Council denied the proposal.  They wanted to assess the condition of the utility infrastructure throughout the City. Council requested that the Department of Utilities prepare an infrastructure report on the condition of the water, separated sewer and drainage infrastructure in the rest of the City. In addition to the $1.416 billion for the combined sewer area, it was estimated that an additional $375 million was needed to maintain the infrastructure in the City. Separation of the combined sewer system proved to be prohibitively expensive and overly impactful to the City. 

The City then developed the Combined Sewer System Improvement Plan to rehabilitate the combined sewer system as an alternative to separation. In 1995, the Regional Water Quality Control Board approved the Combined Sewer System Improvement Plan and shortly after they rescinded the cease and desist order that they issued in 1990. In resolution number 95-687, City Council directed City staff to proceed with the Combined Sewer System Improvement Plan to rehabilitate the combined sewer system instead of separating the entire system. 

Review a map of the streets in Sacramento that would be affected by the separation of the combined sewer system.

Download the City Council resolution about the Combined Sewer System Improvement Plan. 

How does the combined sewer system provide a water quality benefit?
In a typical year, approximately 97 percent of the drainage, by volume, from the combined sewer system is treated before it’s released into the river which provides a water quality benefit to the Sacramento River. This storm drainage water would go directly, untreated, to the river is the system was separated. Water in the the storm drainage system has chemicals, pollutants, pet waste, cigarette butts and other items that flow into storm drains and are not been treated at a water or wastewater treatment plant. 

How does groundwater affect the project cost?
Higher groundwater tables require a more extensive design and construction process which drives up costs. The groundwater table rises as it nears the river. We are trying to avoid digging in water saturated soils as much as possible to reduce the project cost. 

Will Utilities cut down trees to create space for the Vault?
The pre-design surveys and layout analyses underway as part of the pre-design phase will help answer this question. Utilities will make every reasonable effort to avoid the need for tree removal.

What above ground structures do you anticipate as part of this project? 
We anticipate a bathroom facility that will blend in with the look of the park. This structure will also house the electrical controls for the Vault. We will work with the community on this aspect as it progresses. 

What park areas will construction affect? What will the Vault look like when you’re done?
Although design is only conceptual at this time, we anticipate constructing the Vault beneath the baseball field along 33rd Street between the picnic and rose garden areas. Construction will cause disruptions in the park, to neighbors, rose garden events and the community. We are committed to mitigate these impacts as much as possible. After construction has been completed, we will plant new sod and install a new irrigation system. 

How will construction affect parking and neighborhood traffic?
Utilities will examine and determine potential impacts during pre-design analyses which is underway. We will have a public outreach program to alert neighbors and businesses of impacts to parking and traffic before and during construction.

Will construction create dust?
Yes. Construction will occur in accordance with the City’s standard specifications for public works projects with inspectors assigned to monitor it. The specifications require the contractor to control dust at all times. There are enforceable penalties of up to $15,000 per day (City and State fines combined) if the contractor fails to properly implement appropriate erosion, sediment and pollution control measures. 

How will you update us about construction?
Construction updates will be provided through a variety of channels. We are continually updating this website with information about the project. Information will also be shared through the media, signage, social media, electronic communications, Nextdoor and direct mail. 

Why is the project paid for by rate payer dollars, not by developers or industry?
Flooding in East Sacramento is an existing problem that was identified long ago. Developers are required to mitigate their impacts to the system. The McKinley Village development was required to build separated sewer and drainage systems. The drainage is pumped to the American River.

Why is McKinley Park the preferred project location? Why not McKinley Village?
Utilities identified the need for underground storage to reduce street flooding and outflows in the McKinley Park and East Sacramento neighborhoods. The initial concept included a deep tunnel under Alhambra Blvd. with a large diameter pipe and additional underground storage in the McKinley Village development. This concept was further evaluated in the 2015 Combined Sewer System Improvement Plan (CSSIP) Update. Because of the high cost for the deep tunnels, Utilities studied four other possible locations in East Sacramento as part of the 2015 CSSIP, and McKinley Park was identified as the best location. 

How can I get involved or stay updated?
You can sign up for email updates at, visit the project website at or call 916-808-5545 for information. You can also follow us on Facebook and Twitter.