HomeMy WebLinkAbout05-05-2015 SS1 Wastewater Collection System Infrastructure Renewal StrategyCity of San Luis Obispo, Council Agenda Report, Meeting Date, Item Number
FROM: Carrie Mattingly, Director of Utilities
Prepared By: Dave Hix, Deputy Director, Wastewater
Jennifer Metz, Utilities Projects Manager
SUBJECT: REVIEW OF WASTEWATER COLLECTION SYSTEM INFRASTRUCTURE
RENEWAL STRATEGY
RECOMMENDATION
Review the Wastewater Collection System Infrastructure Renewal Strategy and provide feedback.
BACKGROUND
The City of San Luis Obispo provides wastewater collection and treatment services to the residents,
businesses, and visitors of the City as well as Cal Poly and the County of San Luis Obispo Airport. The
City’s wastewater collection system includes approximately 136 miles of gravity sewer mains and 2,900
manholes, as well as nine lift stations with three miles of force main. There are more than 14,000 private
sewer laterals in the City which is estimated to be approximately 172 miles of piping.
The collection system has nearly 18 miles of pipe that are more than 75 years old. The oldest pipes
exceed 100 years of age. Based on a nominal design life of 75 years, pipes installed before 1940 are
likely approaching the end of their useful life.
Prior studies confirm the collection system suffers from inflow and infiltration (I/I), with flow increasing
from an average of 3.72 million gallons per day (mgd) to 36.3 mgd during a ten‐year 24‐hour storm. I/I
is caused by pipe that has become permeable allowing stormwater or groundwater to leak into the sewer
system. The City has identified private sewer laterals as a primary source of I/I. The City’s Sewer
System Management Plan requires the City to assure that the collection system has adequate capacity to
convey peak wet weather sewage flows. The City has been making that assurance through aggressive
operations, inspection and maintenance programs.
On March 19, 2013 the City Council approved the issuance of the Request for Proposals for the
preparation of an Infrastructure Renewal Strategy including development of a hydraulic model of the
collection system to evaluate and identify capacity constrained pipelines, recommend I/I reduction
programs, and a data-driven, long-range rehabilitation/replacement strategy. Specifically, the City had
the following objectives:
1. Incorporate the 2014 updates to the General Plan Land Use and Circulation Element into the
flow projections and hydraulic model.
2. Plan for infill development and densification growth expected in the City.
3. Plan for expansion of service to new areas in the City to support economic development.
4. Develop an accurate hydraulic model of the collection system.
5. Identify existing and future system deficiencies.
6. Develop a prioritized replacement program, including anticipated costs, to address the
deficiencies and assure capacity of the collection system.
May 5, 2015
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Infrastructure Renewal Strategy Study Session Page 2
7. Create an Infrastructure Renewal Strategy the City can update regularly using the ongoing
CCTV inspections, sewer main cleaning and infrastructure rehabilitation.
8. Recommend several potential options for reducing I/I in the system contributed by private sewer
laterals.
9. Establish benchmarks to measure performance of recommended Renewal Strategy and I/I
reduction.
On June 7, 2013 the City Manager awarded a contract to Water Systems Consulting, Inc. (“WSC”).
DISCUSSION
City staff and WSC have worked collaboratively to prepare the Wastewater Collection System
Infrastructure Renewal Strategy (Renewal Strategy). It incorporates existing and future land use data
from the 2014 Land Use Element provided by Community Development Department staff. The Renewal
Strategy presents a strategy to guide policy, operations, and asset management planning decisions in an
efficient and cost effective manner. The Renewal Strategy features an adaptable framework that will be
updated on a regular basis to keep the guidance relevant to the evolving needs of the City. The key
issues addressed by the Renewal Strategy are the aging collection system, storm flows, and capacity
assurance. The Renewal Strategy:
1. Develops a method the City can use to identify and prioritize pipelines for rehabilitation.
2. Determines the length of pipeline the City should rehabilitate/upgrade each year to keep the
collection system functional, assure capacity and minimize Sanitary Sewer Overflows (SSOs).
3. Identifies programs the City can implement to reduce I/I, especially I/I from private sewer
laterals.
4. Recommends monitoring to assess the performance of the Renewal Strategy to assure the money
being spent is achieving the desired goals.
Prioritizing Pipeline Rehabilitation
The Renewal Strategy has key elements that build on existing programs to further assist the City in
planning for pipeline rehabilitation:
1. Predictive Maintenance/Preventative Maintenance Program
2. Data management systems with ongoing CCTV inspections, updated asset information as new
pipelines are installed and cleaning frequency
3. Pipeline condition ranking database used to determine which pipelines require rehabilitation
Replacement/Rehabilitation Rate
Based on an assumed useful life of 75‐years, an age-based Replacement/Rehabilitation model was
developed. With no pipeline rehabilitation, the City’s collection system would eventually cease to
function. WSC evaluated three alternatives for pipeline rehabilitation rates: one, two or three miles per
year. In order to maintain the collection system in its current state, a minimum of two miles per year
should be rehabilitated. The City currently has about 17 miles of pipe that are past due for rehabilitation.
Reducing Inflow/Infiltration
For consideration, nine programs are proposed to encourage and assist property owners to replace
private sewer laterals when needed. These programs include strategies such as requiring inspection of
laterals upon sale of a property, low interest loan assistance for lateral replacement, and inspection prior
to obtaining a building permit.
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Infrastructure Renewal Strategy Study Session Page 3
An expanded smoke testing program to identify sources of inflow in the system and a program to
rehabilitate defective structures is suggested.
Monitoring Performance and the Triple Bottom Line
The Renewal Strategy includes performance monitoring metrics to determine if the Renewal Strategy is
effective. These metrics can be used to adapt the strategy to changing conditions and City goals.
The Renewal Strategy meets the City’s goals for projects to meet the triple bottom line to provide
economic, social, and environmental value to the community in that it:
1. Supports economic development and growth in the City.
2. Sets measurable goals to evaluate cost effectiveness of the program.
3. Partners with the community and contractors to explore reasonable and cost effective
replacement of private sewer laterals.
4. Protects the health and welfare of the community by providing safe, reliable conveyance of
sewage.
5. Reduces sanitary sewer overflows to maintain compliance with state regulations.
6. Reliably conveys used water to the Water Resource Recovery Facility for recovery.
ENVIRONMENTAL REVIEW
An Initial Study will be prepared after the City Council’s feedback is incorporated into the Wastewater
Collection System Infrastructure Renewal Strategy. A Negative Declaration, Mitigated Negative
Declaration or Environmental Impact Report, will be included in the Council Agenda Report for final
consideration by the City Council.
FISCAL IMPACT
There is no immediate fiscal impact associated with this report and the recommended action. Funding to
support wastewater collection system improvements and to maintain the hydraulic model developed as
part of the 2015 Infrastructure Renewal Strategy will be identified in future budgets for Council
consideration and approval beginning with the 2015-17 Financial Plan.
AVAILABLE FOR REVIEW IN THE COUNCIL OFFICE
Wastewater Collection System Infrastructure Renewal Strategy, April 2015, prepared by Water Systems
Consulting Inc.
T:\Council Agenda Reports\2015\2015-05-05\WWC System Infrastructure Renewal Strategy (Matting-Hix-Metz)
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Utilities Department
Wastewater Collection System
Infrastructure Renewal Strategy
slowater.org
Wastewater Collection System Infrastructure Renewal Strategy
The City’s wastewater collection system includes 136
miles of gravity sewer mains, 2,900 manholes, nine lift
stations, three miles of force main.
Wastewater Collection System Infrastructure Renewal Strategy
Additionally, there are more than 14,000 private sewer laterals
which is estimated to be approximately 172 miles of piping.
(Property Owner Maintained)
(City Maintained)
Wastewater Collection System Infrastructure Renewal Strategy
The collection system has nearly 18 miles of pipe that
are more than 75 years old. The oldest pipes exceed
100 years of age.
1888
Wastewater Collection System Infrastructure Renewal Strategy
Wastewater Collection System Infrastructure Renewal Strategy
Sanitary sewer overflow.
Deteriorated steel pipe.
Wastewater Collection System Infrastructure Renewal Strategy
Predictive maintenance program.
Wastewater collection database.
Wastewater Collection System Infrastructure Renewal Strategy
Wastewater Collection System Infrastructure Renewal Strategy
Project Goals:
1.Hydraulic model
2.Prioritized replacement
3.Documented strategy for ongoing
renewal
4.I/I reduction options
5.Performance benchmarks
Wastewater Collection System Infrastructure Renewal Strategy
Cityworks Database
Wastewater Collection System Infrastructure Renewal Strategy
Data on sewer main condition from CCTV inspection
Alignment
0.6%
Broken Pipe
13%
Camera
Underwater
13%
Crack
1.6%
Deformed
0.3%
Deposits
1.4%
Fracture
32%
Hole
3.8%
Infiltration
3.2%
Obstacle
1.6%
Repair
Defective
0.4%
Roots
29%
Sag
0.2%
Manhole with root intrusion
at Marsh and Santa Rosa
View of sewer main with root intrusion as seen during CCTV inspection
Wastewater Collection System Infrastructure Renewal Strategy
Wastewater Collection System Infrastructure Renewal Strategy
The City has been using CCTV to inspect sewer mains
since 1991 to assess pipe condition.
Wastewater Collection System Infrastructure Renewal Strategy
Pipelines by Condition Rating
Wastewater Collection System Infrastructure Renewal Strategy
Wastewater Collection System Infrastructure Renewal Strategy
Wastewater Collection System Infrastructure Renewal Strategy
Manhole Surveying
Wastewater Collection System Infrastructure Renewal Strategy
Capacity constrained pipelines.
Wastewater Collection System Infrastructure Renewal Strategy
“Replace two miles of pipe per year for
approximately 50 years to catch up with the
accumulated backlog of aged pipe”
Recommendation #1. Determine the length of pipeline the
City should rehabilitate/upgrade each year.
Wastewater Collection System Infrastructure Renewal Strategy
Recommendation #2 Develop a method the City can use to
identify and prioritize pipelines for rehabilitation.
Wastewater Collection System Infrastructure Renewal Strategy
Recommendation #3.
Identify programs the City
can implement to reduce
I/I, especially I/I from
private sewer laterals.
Wastewater Collection System Infrastructure Renewal Strategy
Recommendation #4.
Monitoring to assess the
performance of the
Renewal Strategy to
assure the money being
spent is achieving the
desired goals.
Wastewater Collection System Infrastructure Renewal Strategy
2015-17 Financial Plan
Wastewater Collection System Infrastructure Renewal Strategy
Questions and Feedback