Title
Update for City Council Rules Committee on Inflow & Infiltration Impacts on Water Pollution Control Operational Costs Related to a Private Sewer Lateral Ordinance
Staffreport
COUNCIL PRIORITY
• Infrastructure
SUMMARY
This is an update from the September 24, 2025 presentation to the City Council Rules Committee on Private Sewer Laterals. The information presented will give a high-level impact of rain or groundwater entering the City’s sewer system (Inflow & Infiltration or I&I) on the City’s sewer system and treatment plant, which is a primary driver for the City to consider implementing a Private Sewer Lateral Ordinance (PSLO).
RECOMMENDATIONS
Staff request the Committee provide direction about whether to continue researching a PLSO ordinance and whether to commission a study to investigate the sources of the City’s I&I and potential additional cost savings.
BACKGROUND
The City’s Water Pollution Control Division maintains 125 miles of sanitary sewer lines within the City’s service area. There are an estimated 14,000 connections to the City’s sewer main. Private sewer laterals are the responsibility of property owners to maintain up to and including connections to the City’s sewer main. Parts of the City are also serviced by Oro Loma Sanitary District (Oro Loma). Oro Loma has approved the implementation of a Private Sewer Lateral Ordinance and has an estimated program start date of July 1, 2026.
At the September 24, 2025 City Council Rules Committee meeting, staff were asked to provide the scope of the issues that a PSLO could potentially assist to mitigate, in particular potential cost savings to the Water Pollution Control Plant enterprise fund. Staff reviewed operational costs and estimated the quantity of I&I to estimate the total cost of this additional water.
Analysis
Staff first investigated the unit costs of processing water and estimated the quantity of water that is a result of I&I. This was used to estimate the total cost of processing I&I. A PSLO ordinance would incrementally reduce these costs.
Staff used the following assumptions when estimating the costs:
• There is a negligible impact on CIP costs. While processing additional clean water over time has an impact on the equipment due to run time and capacity, this cost does not significantly affect overall CIP costs. There are no costs in the 10-year CIP plan that are directly related to I&I.
• I&I does not increase solids handling costs. Rainwater generally has low solids content and would not be expected to increase the costs to manage or remove biosolids.
• Some operational costs are not volume dependent.
• Data from Fiscal Year 2024-2025 were used to estimate cost by volume.
Methodology
First, operational costs were categorized as either fixed or variable. The fixed costs would not change with the volume of wastewater that is treated and would not be expected to decrease with less water. These include:
• Labor
• Administrative costs such as insurance
• Payments to other government agencies
The variable costs typically vary with the quantity of water. These include:
• Energy consumption
• Chemical use
• Maintenance and repairs
• Biosolids management
Since the addition of storm water will not significantly impact costs for solids processing, this cost was not included.
Using FY 2025 data, costs of electricity, sodium hypochlorite, and maintenance per gallon of wastewater treated were calculated. Staff assumed that variable costs increase linearly with additional water. Electricity and maintenance costs were calculated by using total expenditures in FY 2025. Cost of Sodium Hypochlorite per gallon wastewater treated was calculated using the total usage at the Water Pollution Control Plant for FY 2025. By dividing the total cost for fiscal year 2025 by the total volume of water processed during this time, these unit rates were calculated in Million Gallons (MG):
• Electricity: $382/MG
• Maintenance: $236/MG
• Sodium Hypochlorite: $163/MG
• Total Variable Cost per Gallon of wastewater treated: $781/MG
To estimate the total volume of I&I in a year, Staff assumed that the quantity of water received in the dry season is representative of the baseline water, with little coming from I&I. Subtracting the dry weather flow from the measured water received leaves the estimated quantity from I&I. Staff used the following formula to calculate the total I&I:
Total flow for the year - (Average daily flow during dry months * 365)
Average daily dry weather flow was calculated by averaging daily flow from June through August between 2022-2025. The average daily flow during this period was 4.455 million gallons per day (MGD).
Using this formula, here are the estimated amounts of water from I&I:
• FY 2022: 5.91%
• FY 2023: 18.80% (note increase from a wet year)
• FY 2024: 11.81%
• FY 2025: 6.84%
Given cost per Million Gallons ($781) and estimated percentage I&I, the table below lists cost savings if all I&I was eliminated:
|
Fiscal Year |
Total Flow (MG) |
Percentage of influent from I&I |
Cost savings per year |
|
2022 |
1728 |
5.91% |
$ 79,759 |
|
2023 |
2002 |
18.80% |
$293,950 |
|
2024 |
1844 |
11.81% |
$ 170,083 |
|
2025 |
1745 |
6.84% |
$ 93,219 |
It is not known how much I&I comes from private sewer laterals. When researching their PSLO program, Oro Loma estimated that approximately 47% of I&I is from private laterals and estimated a reduction of 1.2% per year. The City’s quantities are likely similar
I&I Study
Private sewer laterals are only part of the sewer system and their impact on I&I is not known. Methodologies are available to study where water enters the sewer system and locating and eliminating these sources would lower the amount of I&I. These studies review the system as a whole and then use flow meters to check which parts of the system contribute the most water. These sources may be outdoor drains or rain gutters that are connected to the sanitary sewer.
An initial study of the City’s sanitary sewer system would include measurements at various downstream sections to identify areas of concern. More targeted measurements can be taken in areas of concern to get more precise data on the location and sources of I&I.
The cost of initial study is estimated to be $30,000, which would provide a high-level review of the areas that contribute most. More detailed studies would be necessary to more precisely locate the sources. The costs for this are on a per-foot basis of linear sewer and could cost several hundred thousand dollars.
Oro Loma Update
Oro Loma Sanitary District, which provides wastewater services for a portion of the City, is still on target to implement a PSLO starting July 1, 2026. Staff met with Oro Loma leadership to discuss options for working together to manage a PSLO program for the City’s wastewater service area. Further discussions are needed to ensure if this would be a mutually beneficial approach if the City proceeds with implementing a PSLO.
Financial Impacts
If the City Council decides to proceed with performing a study to determine a more precise estimate of I&I impacts there will be a cost associated with this.
ATTACHMENT
A: Presentation
PREPARED BY:
Ramya Sankar, Management Analyst II, Water Pollution Control
Hayes Morehouse, Water Pollution Control Manager