State Water Resources Control Board
Division of Drinking Water
May 22, 2025
System No. CA5010017
Mike Willet, Director of Public Works
City of Patterson
1 Plaza
Patterson, CA 95363
[email protected]
HEXAVALENT CHROMIUM MAXIMUM CONTAMINANT LEVEL EXCEEDANCE The State Water Resources Control Board, Division of Drinking Water (Division) has received the results of the hexavalent chromium samples collected between December 10, 2024 and March 4, 2025, from City of Patterson’s Well No. 07. The table below summarizes the sample results received and their running annual average.
Table 1: Hexavalent Chromium Sample Results by Source
Source Name Quarterly Sample
Date
Hexavalent
Chromium Result
(mg/L)
Quarterly
Average (mg/L)
Well No. 07
12/10/2024 0.0208 0.0208
2/25/2025 0.0223 0.0310 3/4/2025 0.0397
Running Annual Average 0.013 mg/L
The average of the initial samples is over the hexavalent chromium maximum contaminant level (MCL) of 0.010 milligrams per liter (mg/L). (Cal. Code Regs., tit. 22, § 64432.) Therefore, quarterly sampling must continue and the public must be notified of the MCL exceedance. (Cal. Code Regs., tit. 22, §§ 64432, subd. (g), 64463.4, subd. (a).) The water system is also required to take specific actions described in the hexavalent chromium regulation, the first step of which is to develop a compliance plan that includes the following items:
City of Patterson - 2 - May 22, 2025
x The proposed method the water system will use to achieve compliance with the hexavalent chromium MCL. The method could be providing treatment or using an alternative source. If treatment is proposed a pilot study must be included. x The date by which the system plans to submit the final plans and specifications for any construction related to the proposed methods of achieving compliance. x The dates by which the system plans to start and complete any construction of treatment or alternative source facilities.
x The dates by which the system plans to complete a treatment operations plan associated with the proposed facilities, if applicable. (Cal. Code Regs., tit. 22, § 64432, subd. (q).)
The compliance plan should attempt to meet the deadline(s) below, listed by system size, although we recognize that it may not be feasible in all situations.
Table 2: Hexavalent Chromium MCL Compliance Dates
System Size
(service connections served on October 1, 2024) Compliance Date 10,000 or more October 1, 2026
1,000 to 9,999 October 1, 2027
Fewer than 1,000 October 1, 2028
A hexavalent chromium compliance plan template is available at bit.ly/Cr6-Rulemaking.
A compliance plan must be submitted to the Division by June 30, 2025.
If you have any questions regarding this matter, please contact Gena Farley of my staff at (209) 948 – 7488 or at [email protected]. You may also contact us via email at [email protected].
Sincerely,
Bhupinder S. Sahota, P.E.
District Engineer, Stockton District
Division of Drinking Water
State Water Resources Control Board
Appendix: Instructions for Tier 2 Hexavalent Chromium Exceedance Notice cc: Maria Encinas, [email protected]
Mike Heard, [email protected]
R:\DDW\Stockton\Dist10\Stockton System Files\50 Stanislaus County\5010017 - City of Patterson\Miscellaneous\Hex Chrom
Bhupinder Sahota Digitally signed by Bhupinder
Sahota
Date: 2025.05.22 14:13:32 -07'00'
State Water Resources Control Board 2024
Instructions for Tier 2 Hexavalent Chromium Exceedance Notice Template Attached
An exceedance of the hexavalent chromium maximum contaminant level (MCL) requires Tier 2 notification, and you must provide public notice to persons served as soon as practical but within 30 days after learning of the exceedance. (Cal. Code Regs, tit. 22, § 64463.4, subds. (a)(4) and (b).) Such an exceedance is not considered a violation until after the applicable compliance date (see table below). Each water system required to give public notice must submit the notice to the State Water Resources Control Board, Division of Drinking Water (Division) for approval prior to distribution or posting, unless otherwise directed by the Division. (Cal. Code Regs, tit. 22, § 64463, subd. (b).)
System Size
(service connections served on October 1, 2024) Compliance Date 10,000 or more October 1, 2026
1,000 to 9,999 October 1, 2027
Fewer than 1,000 October 1, 2028
Notification Methods
You must use the methods summarized in the table below to deliver the notice to consumers. If you mail, post, or hand deliver the notice, print your notice on letterhead, if available.
The notice attached is appropriate for the notification methods described below, however, you may wish to modify it before using it for posting. If modified, the notice must still include all the required elements, including the health effects and mandatory language, which must be in italics. (Cal. Code Regs, tit. 22, § 64465, subd. (a)(3).) Community Water Systems must use the primary method below and one or more secondary methods to reach persons not likely to be reached by the primary method.
Primary Method
1. Mail or direct delivery. The notice must be distributed to each customer receiving a bill including those that provide their drinking water to others (for example schools or school systems, apartment building owners, or large private employers), and other service connections to which water is delivered by the water system.
Secondary Methods (use one or more of the following methods to reach persons not likely to be reached by the primary method)
1. Publication in a local newspaper.
2. Posting in conspicuous public places served by the water system or on the internet. The notice must be posted in place for as long as the exceedance or occurrence continues, but in no case less than seven days.
3. Delivery to community organizations. (Cal. Code Regs, tit. 22, § 64434.4, subd. (c)(1).)
State Water Resources Control Board 2024
Non-Community Water Systems must use the primary method below and one or more secondary methods to reach persons not likely to be reached by the primary method.
Primary Method
1. Posting in conspicuous locations throughout the area served by the water system. The notice must be posted in place for as long as the exceedance or occurrence continues, but in no case less than seven days.
Secondary Methods (use one or more of the following methods to reach persons not likely to be reached by the primary method)
1. Publication in a local newspaper or newsletter distributed to customers.
2. Email message to employees or students.
3. Posting on the internet or an intranet. The notice must be posted in place for as long as the exceedance or occurrence continues, but in no case less than seven days.
4. Direct delivery to each customer. (Cal. Code Regs, tit. 22, § 64434.4, subd. (c)(2).)
Multilingual Requirement
The notice must contain information in Spanish regarding the importance of the notice or contain a telephone number or address where Spanish-speaking residents may contact the public water system to obtain a translated copy of the notice or assistance in Spanish.
If any non-English-speaking group, other than Spanish-speaking, exceeds 1,000 residents, or 10 percent of the residents served by the public water system, the notice must include (1) information in the appropriate language(s) regarding the importance of the notice or (2) the telephone number or address where such individuals may contact the water system to obtain a translated copy of the notice from the water system or assistance in the appropriate language. (Cal. Code Regs, tit. 22, § 64465, subd. (c)(2).) Population Served
Make sure it is clear who is served by your water system -- you may need to list the areas you serve.
Corrective Action
In your notice, describe corrective actions you are taking. Do not use overly technical terminology when describing treatment methods. Listed below are some steps commonly taken by water systems with chemical or radiological violations/exceedances.
Use one or more of the following actions, if appropriate, or develop your own:
x “We are working with [local/state agency] to evaluate the water supply and researching options to correct the problem. These options may include treating the water to remove hexavalent chromium or connecting to [system]’s water supply.”
State Water Resources Control Board 2024
x “We have stopped using the contaminated well. We have increased pumping from other wells, and we are investigating drilling a new well.” x “We will increase the frequency at which we test the water for hexavalent chromium.”
x “We have since taken samples at this location and had them tested. They show that we meet the standards.”
After Issuing the Notice
Send a copy of each type of notice and a certification that you have met all the public notice requirements to the Division within ten days after you issue the notice. (Cal. Code Regs, tit. 22, § 64469, subd. (d).) Public water systems must also issue a certification that they have met all the public notice requirements for any repeat notices in addition to meeting any repeat notice requirements the Division sets.
It is recommended that you notify health professionals in the area of the exceedance.
People may call their doctors with questions about how the exceedance may affect their health, and the doctors should have the information they need to respond appropriately.
It is a good idea to issue a “problem corrected” notice when the MCL is no longer being exceeded.
State Water Resources Control Board 2024
IMPORTANT INFORMATION ABOUT YOUR DRINKING WATER
Este informe contiene información muy importante sobre su agua potable.
Tradúzcalo o hable con alguien que lo entienda bien.
[System] Has Levels of Hexavalent Chromium
Above the Drinking Water Standard
This is not an emergency. As our customers, you have a right to know what you should do, what happened, and what we are doing to correct this situation. We routinely monitor for the presence of drinking water contaminants. Water sample results received on [date] showed hexavalent chromium levels of [level and units]. This is above the standard, or maximum contaminant level (MCL), of 0.010 milligrams per liter (10 ppb).
We are working with the State Water Resources Control Board to address this exceedance and comply with the MCL within a compliance timeline.
What should I do?
x You do not need to use an alternative water supply (e.g., bottled water). x This is not an emergency. If it had been, you would have been notified immediately. However, some people who drink water containing hexavalent chromium in excess of the MCL over many years may have an increased risk of getting cancer.
x If you have other health issues concerning the consumption of this water, you may wish to consult your doctor.
What happened? What is being done?
x A new Hexavalent Chromium MCL of 10 ppb became effective October 1, 2024. x Hexavalent chromium was detected at levels that exceed the MCL. However, a water system of our size is not considered in violation of the Hexavalent Chromium MCL until after [INSERT APPLICABLE TABLE 64432-B COMPLIANCE DATE].
x We [are working to complete / have completed] a Hexavalent Chromium Compliance Plan that [will be reviewed / is being reviewed / has been approved] by the State Water Resources Control Board.
x We are working with the State Water Resources Control Board to address this exceedance and comply with the MCL. Specifically, we are [Describe actions taken (may include pilot studies, environmental review, funding applications, etc.) and planned actions (may include treatment, source changes, etc.)] [Optional:
discuss approved compliance plan if already approved by the Division]. x We anticipate resolving the problem by [estimated time frame (Compliance plan finalization date, if applicable)].
For more information, please contact [name of contact] at [phone number] or [mailing address].
Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in State Water Resources Control Board 2024
apartments, nursing homes, schools, and businesses). You can do this by posting this public notice in a public place or distributing copies by hand or mail.
If you are a school or school system, the owner or operator of residential rental property, or the owner or operator of a business property, then you are legally required to notify the following people of the information in this notice within ten days of your receipt of this notice:
x SCHOOLS: You must notify school employees, students, and parents (if the students are minors).
x RESIDENTIAL RENTAL PROPERTY OWNERS OR MANAGERS (including nursing homes and care facilities): You must notify tenants. x BUSINESS PROPERTY OWNERS, MANAGERS, OR OPERATORS: You must notify employees of businesses located on the property. x If you fail to notify the above people, you may be civilly liable up to $1,000 per day for each day that you fail to notify them. (Health & Saf. Code, §§ 116450, subd. (g); 116650, subd. (e).)
This notice is being sent to you by [system].
State Water System Number: [Insert water system number].
Date distributed: [Insert date the notice is distributed].