ATTACHMENT #1
2025
Triennial Public Health Goal Report:
Report on the City’s Water Quality Relative to Public Health Goals Prepared by Paul Jorgensen, Water Quality Supervisor
June 25, 2025
Background
In 1996, the California Legislature passed SB 1307 (Sher/Calderone). This legislation became codified in the California Health and Safety Code Section 11647(b). These provisions require water utilities with greater than 10,000 service connections to prepare a report every three years if any constituent in their water supply exceeds any applicable Public Health Goal (PHG). A public hearing must be held to accept comments on the report. The initial City of Thousand Oaks (City) report was presented to the City Council on July 28, 1998, at a noticed public hearing. Successive triennial reports were presented to the City Council on May 21, 2001, July 13, 2004, July 1, 2007, September 28, 2010, September 24, 2013, October 25, 2016, October 8, 2019, and September 28, 2022.
PHGs are non-enforceable goals established by the California Office of Environmental Health Hazard Assessment (OEHHA) to identify thresholds for health effects associated with contaminants in Drinking Water. The law also requires that if OEHHA has not adopted a PHG, water suppliers are to use the Maximum Contaminant Limit Goals (MCLGs) established by the United States Environmental Protection Agency (EPA) as a basis of comparison. Only constituents that have a California primary drinking water standard, known as a Maximum Contaminant Level (MCL) for which there is an adopted PHG or MCLG, are addressed in this report. There are a few constituents that are routinely detected in drinking water for which OEHHA or the EPA has yet to adopt a PHG or MCLG. These will be addressed in a future report after the adoption of a new PHG by OEHHA.
If a constituent was detected in the City’s water supply during the reporting years of 2023, 2024, and 2025 at a level exceeding an applicable PHG or MCLG, the law defines the information that needs to be included in this report.
Requirements:
1. Compare the numerical goals on the list of PHGs or applicable MCLGs to the analytical results contained in the City’s Annual Water Quality Reports for the reporting years of 2023, 2024, and 2025.
2. Identify any constituents detected at levels above the PHG or MCLG threshold.
DPW:1025-40\ev\Council\2025\09232025\Triennial PHG Water Quality Att 1.pdf
DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
3. Obtain health risk assessment information from existing governmental regulatory source documents, including the type of health risk related to each contaminant above the PHG and the numerical public health risk of both the MCL and the PHG.
4. For those constituents identified in number two above, determine the Best Available Technology (BAT) for removal or treatment of each of those contaminant(s). Estimate the total cost to the system and the cost to the customer for the purveyor to install, operate, and maintain the identified BATs to lower the subject contaminant(s) to below the PHG.
5. Combine the results from the above-noted steps into a written report. This report will include a brief description of what action (if any) the City intends to take to reduce the concentration of the noted contaminant(s) and the basis for that decision.
6. Conduct a public hearing to accept public comment on the report.
7. Repeat the process in three years to address any new PHGs and/or MCLGs in effect at that time.
Public Health Goals (PHG) and Maximum Contaminant Levels (MCL)
PHGs are set by the OEHHA, which is part of Cal-EPA. PHGs are based entirely on public health risk considerations. Contrastingly, when MCLs are set (which are the enforceable standards), other factors are taken into consideration. These factors include health risks, analytical detection capability, treatment technology availability, costs, and/or benefits.
MCLs are set by the EPA and/or the State. Unlike MCLs, PHGs are not enforceable and are not required standards to be met by any public water system. MCLGs are the Federal equivalent of PHGs.
In addition to each contaminant having an MCL and either a PHG or MCLG standard, they also have a Detection Level for Reporting Purposes (DLR). When a contaminant is tested and the results are below the DLR, the results are to be reported as non-detect (ND) because once the analytical results are below the DLR, the accuracy of the results cannot be verified with current analytical techniques. Many of the PHGs are set below the DLR.
Water Quality Data Considered and Water Sources
All water quality data collected for the City water system in 2022, 2023, and 2024 for purposes of compliance with drinking water standards were considered. These analytical results are summarized in the 2023, 2024, and 2025 Annual Water Quality Reports (AWQR), which were made available to City water customers by July 1st of each year on the City’s website at www.toaks.co/waterqualityreport.
DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
The City purchases its water from Calleguas Municipal Water District (CMWD) in Thousand Oaks, which purchases its water from the Metropolitan Water District (MWD).
Most of the data used for this PHG report, as well as the AWQR, is from the analytical testing results from MWD, since they are the agency responsible for supplying and treating most of the water the City purchases. The remainder of the data comes from analytical testing results generated by CMWD and the City. For the 2024 and 2025 reporting years, as with most years, about 98 percent of the water the City received from MWD was from the State Water Project, coming from Northern California through the State Water Project, and was treated at MWD’s Jensen Treatment Plant located in Granada Hills. In 2023, due to the drought, 24 percent of the water the City received from MWD was from the Colorado River Aqueduct system and treated at MWD’s Weymouth Treatment Plant in La Verne, and 6 percent of the water was delivered from the CMWD’s Las Posas Wellfield. CMWD treats and delivers water to the City from their Lake Bard Water Filtration Plant (LBWFP) for about one to two weeks per year when MWD has a shutdown of their system for maintenance and repairs. Water the City received from the LBWFP accounted for about 1 to 2 percent of the water supply for the reporting years.
The City does not treat the water that it delivers to its customers.
Guidelines Followed
There are currently no formal guidelines established by regulatory agencies for the preparation of PHG reports. To assist water utilities, the Association of California Water Agencies (ACWA) convened a workgroup that developed voluntary guidelines for use in preparing these reports. The ACWA guidelines were followed in the preparation of this report, along with the requirements outlined in California Health and Safety Code Section 116470(b).
Best Available Technology and Cost Estimates
The EPA and SWRCB adopt lists of BAT techniques, which are understood to be the best-known methods for reducing contaminant levels in water to meet specific MCLs.
Costs can be estimated for applications of such technologies. However, since many of the PHGs and MCLGs are much lower than the MCLs, it is not always feasible to determine the type of treatment needed to further reduce or eliminate a constituent to meet a PHG or MCLG, many of which are set at zero. Estimating costs to reduce a constituent to zero is difficult, if not impossible, because it is not possible to verify by analytical means that a constituent is not present at any concentration. In some cases, treatment to reduce the existing concentrations of a constituent may have adverse effects on other constituents or water quality parameters.
The City purchases and distributes treated water but does not own or operate any water treatment facilities, nor does it have the capacity or certified personnel required to implement additional treatment processes. Any further treatment to reduce levels to the PHGs would need to be conducted by the City’s wholesale suppliers, the MWD and/or CMWD. Given these factors, it is not practical or feasible for the City to estimate the costs associated with reducing contaminant levels in purchased water to meet the PHGs.
DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
Understanding the Units
To illustrate some of the terms used to define the units of measure used in this report, it may be helpful to visualize the scale:
One “part per million” (ppm) is equivalent to one drop of water in an aquarium (13.2 gallons).
One “part per billion” (ppb) is equivalent to one drop of water in a standard swimming pool (13,208 gallons)
Constituents Detected that exceed a PHG (or MCLG)
Table 1: 2022, 2023, and 2024 Water Quality Data Results The quality of the City’s water supply met all State and Federal MCLs. The quality of the City’s water supply also met all State PHGs except for arsenic, bromate, and uranium.
Where a PHG has not yet been developed, all the MCLGs have also been met, except for two radiological constituents, Gross Alpha Particle Activity (Gross Alpha), and Gross Beta Particle Activity (Gross Beta). These detections above the PHG and MCLG did not occur regularly but were mostly on an infrequent basis due to the different water sources the City received.
Supply Sources
MWD
Jensen
Plant
MWD
Weymouth
Plant
Calleguas
Las Posas
Wellfield
Calleguas
LBWFP
MWD
Jensen
Plant
Calleguas
LBWFP
MWD
Jensen
Plant
Calleguas
LBWFP
68% 24% 6% 2% 99% 1% 98% 2%
Arsenic ppb 10 0.004 Range 2.4 ND 2.0 - 5.0 3.0 ND 3.0 ND 2.0 - 4.0 Bromate** ppb 10 0.1 Range ND - 15 ND - 7.6 ND ND ND - 14 ND ND - 5.4 ND Gross Alpha pCi/L 15 (0) Range ND ND ND - 3.1 ND ND 3.2 ND ND Gross Beta pCi/L 50 (0) Range ND - 5.0 4.0 - 7.0 ND 4.2 ND 4.4 ND 5.4 - 5.6 Uranium pCi/L 20 0.43 Range ND - 3.0 1.0 - 3.0 1.8 - 2.8 1.4 2.0 - 3.0 1.5 2.0 - 3.0 1.4 - 1.5 **The Bromate compliance standard is based on a Running Annual Average, which were below the 10 ppb MCL during the reporting years.
Abbreviations:
MCL = Maximum Contaminant Level pCi/L = picoCuries per liter ND = Non-Detect ppb = parts per billion
Parameter Units MCL
PHG
(MCLG)
2022
City of Thousand Oaks Supply
Percent of Supply
Range
2023 2024
DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
Arsenic
The MCL for arsenic is set at 10 ppb (parts per billion), and the PHG is set at 0.004 ppb.
The source of arsenic in California drinking water is from the erosion of natural mineral deposits. Other sources can be from run-off from agriculture and industrial processes.
The concentration in the purchased drinking water supplied to the City during the reporting years ranged from ND - 5.0 ppb. These concentrations are well below the MCL 10 ppb for arsenic.
People who drink water containing arsenic at the MCL throughout their lifetime could experience an increased cancer risk. OEHHA has determined that the numerical health risk associated with drinking two liters of water a day for seventy years with arsenic at the MCL is 2.5 X 10¯3 or two and a half theoretical cancer cases out of 1,000, and the numerical health risk at the PHG is 1 X 10-6 or one theoretical cancer case out of one million.
The two BATs identified for the removal of arsenic from drinking water are Reverse Osmosis (RO) and Ion Exchange. However, it is important to note that BATs are intended to support compliance with MCLs, not PHGs.
The City purchases and distributes treated water but does not own or operate any water treatment facilities, nor does it have the capacity or certified personnel required to implement additional treatment processes. Any further treatment to reduce arsenic levels would need to be conducted by the City’s wholesale suppliers, the MWD and/or CMWD.
Given these factors, it is not practical or feasible for the City to estimate the costs associated with further arsenic reduction. The City’s water supply remains in full compliance with both Federal and State MCLs for arsenic.
Bromate
The State MCL of 10 ppb for bromate went into effect in 2001 for large water systems. In 2009, the State set a PHG for bromate at 0.1 ppb. Bromate is a disinfection byproduct that forms when ozone is used in the presence of naturally occurring bromide in source water. Seawater intrusion on the State Project water in the Sacramento River Delta has resulted in detectable levels of bromide in the imported water supply. Low levels of bromate have subsequently been detected since ozonation was initiated by MWD at the Jensen Filtration Plant in 2005. The concentrations during the reporting years ranged between ND - 15 ppb, but the compliance standard for bromate is based on the Running Annual Average (RAA), which were 7.2 ppb, 7.6 ppb, and 3.1 ppb, respectively, and were all below the MCL of 10 ppb.
People who drink water containing bromate above the MCL throughout their lifetime could experience an increased risk of getting cancer. OEHHA has determined that the numerical health risk associated with drinking two liters of water a day for seventy years with bromate at the MCL is 1 X 10-4 or one theoretical cancer case out of 10,000, and the numerical health risk at the PHG is 1 X 10-6 or one theoretical cancer case out of one million.
DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
The BAT for bromate reduction is the control of the ozone treatment process to minimize bromate formation. As the PHG for Bromate is 0.1 ppb, a level extremely difficult, if not impossible, to achieve in practice due to the presence of bromide in source water and the limitations of current treatment technologies.
Eliminating bromide from source water is not feasible, and discontinuation of ozonation as a treatment method may lead to increased levels of other disinfection byproducts, such as trihalomethanes, which present their own health risks. In fact, ozonation is used specifically to help minimize the formation of trihalomethanes and improve overall water quality.
The City of Thousand Oaks does not operate treatment facilities and relies on the MWD and CMWD to provide treated water. The MWD continues to optimize treatment operations to minimize bromate production while maintaining compliance with all regulatory requirements.
The City’s water supply is in full compliance with both Federal and State MCLs for bromate. Because bromate control must occur at the treatment level, and the City neither operates treatment facilities nor has certified treatment personnel, it is not practical or feasible for the City to estimate the cost of reducing bromate concentrations to the PHG level.
Radionuclide Activity: Gross Alpha, Gross Beta, and Uranium
The State MCL for Gross Alpha is 15 picoCuries per liter (pCi/L), 50 pCi/L for Gross Beta, and 20 pCi/L for uranium. The MCLG for Gross Alpha and Gross Beta is zero (0) pCi/L.
The PHG for uranium is 0.43 pCi/L.
Radionuclides are naturally occurring radioactive elements that are present in the Earth’s crust. Uranium and other radionuclides are found in many ground and surface waters due to their natural occurrence in geologic formations.
MWD is required to conduct quarterly monitoring on the finished, treated potable supply for four consecutive quarters every three years, and CMWD conducts this monitoring annually. This monitoring indicated the presence of Gross Alpha, Gross Beta, and Uranium. The concentration range during the reporting years for Gross Alpha was ND –
3.2 pCi/L, but was not detected in the 2025 reporting year. The concentration range during the reporting years for Gross Beta was ND – 7.0 pCi/L. The concentration range during the reporting years for uranium was ND – 3.0 pCi/L.
The health risk associated with radionuclides is an increased cancer risk for those who drink water containing radionuclides above the MCL for many years. OEHHA has determined that the numerical health risk associated with drinking two liters of water a day for seventy years with Gross Alpha at the MCL is 1 X 10-3 or one theoretical cancer case out of 1,000, and the numerical health risk at the MCLG is zero. OEHHA has determined that the numerical health risk associated with drinking two liters of water a day for seventy years with Gross Beta at the MCL is 2 X 10-3 or two theoretical cancer DPW:1025-40\pj\ev\Council\2025\100725\2025 Triennial Public Health Goals Report Att 1.docx
cases out of 1,000, and the numerical health risk at the MCLG is zero. OEHHA has determined that the numerical health risk associated with drinking two liters of water a day for seventy years with uranium at the MCL is 5 X 10-5 or five theoretical cancer cases out of 100,000 and the numerical health risk at the PHG is 1 X 10 -6 or one theoretical cancer case out of one million.
The BAT for reducing Gross Alpha, Gross Beta, and Uranium concentrations in drinking water is RO. While the City’s current uranium levels are already below the MCL, RO would be required to attempt to reduce uranium concentrations to meet the more stringent PHG.
For Gross Alpha and Gross Beta, the MCLG is zero. Estimating the cost to reduce a constituent to zero is extremely challenging, as it is not possible to verify the complete absence of a contaminant through available analytical methods. In practice, reducing naturally occurring radionuclides to non-detectable levels is technically complex and economically infeasible.
The City of Thousand Oaks purchases treated water from the MWD and CMWD and does not operate treatment facilities or employ personnel certified to carry out advanced water treatment processes. Any additional treatment needed to further reduce radionuclide levels would have to be implemented by MWD and/or CMWD.
For these reasons, it is not practical or feasible for the City to estimate the cost of reducing Gross Alpha, Gross Beta, or Uranium to levels at or below their respective PHGs. The City’s water supply remains in full compliance with all applicable Federal and State MCLs for radionuclides.
Recommendations
The quality of the City’s drinking water meets or exceeds all SWRCB and EPA drinking water standards established to protect public health. The constituents addressed in this report are all present at levels well below their respective MCLs, which are health-based regulatory thresholds designed to ensure safe drinking water.
Attempts to further reduce these constituent levels, already significantly below MCLs, would likely yield uncertain or negligible public health benefits. In some cases, additional treatment processes could introduce unintended consequences by affecting other water quality parameters or increasing the presence of other disinfection byproducts. Moreover, the health protection benefits of reducing these contaminants to PHG levels are not clearly quantifiable.
Because the City of Thousand Oaks purchases 100% of its water from wholesale agencies, the MWD and CMWD, all treatment is conducted before delivery. Any additional treatment needed to reduce constituents to PHG levels would need to be implemented by MWD and/or CMWD.
Given these factors, no additional action or treatment is proposed or recommended at this time.