To the members of the:
CITY COUNCIL ✓ Date~ CA~ CC _
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January 16, 2025
Council Memorandum
To:
From:
Honorable Mayor Blackburn and Members of the City Council Paz Gomez, Deputy City Manager, Public Works
Via: Sheila Cobian, Assistant City Manager );)~
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Carlsbad
Memo ID# 2025008
Re: Water Contact Advisories Issued for Carlsbad Beaches via the Beach & Bay Water Quality Program, County of San Diego, Department of Environmental Health and Quality (District 1)
This memorandum provides information related to recent water contact advisories issued at two Carlsbad beaches: one at the Buena Vista Lagoon outlet and the other at the terminus of Tamarack Avenue.
Background
As described in previous memoranda dated February 9, 2023 (Attachment A), June 30, 2022 (Attachment B), June 22, 2023 (Attachment C), and August 1, 2024 (Attachment D), beach water quality in Carlsbad is among the cleanest in the state. As discussed in Attachment A, the County of San Diego Department of Environmental Health and Quality (County DEHQ) conduct water quality monitoring at coastal sites as part of their Beach and Bay Water Quality Program, with the intent of protecting public health.
Discussion
On December 31, 2024, water quality samples taken by the County DEHQ from the Carlsbad beaches at the Buena Vista Lagoon outlet and Tamarack Avenue were analyzed using the ddPCR1 method and were determined to be in exceedance of the state's health standard for bacteria in recreational waterbodies. The regulatory standard for bacteria using the ddPCR method is 1,413 copies/100 milliliter (ml).
The results for the Buena Vista Lagoon outlet and Tamarack Avenue beaches were determined to be 2,113 copies/100 ml and 2,488 copies/100 ml, respectively. As a result, water contact advisories were issued for both beaches on the evening of December 31, 2024. 1 ddPCR refers to droplet digital polymerase chain reaction -a rapid method that looks for bacterial deoxyribonucleic acid (DNA). More detail can be found in Attachment A.
Public Works Branch
Environmental Sustainability Department
1635 Faraday Avenue I Carlsbad, CA 92008 I 442-339-2799
Council Memo -Water Contact Advisories Issued for Carlsbad Beaches (District 1) January 16, 2025
When beach advisories are issued, the County DEHQ typically performs follow-up sampling the next day to reevaluate the conditions. However, due to the New Year's holiday and a staffing shortage on January 2, 2025, the Buena Vista Lagoon outlet and Tamarack Avenue beaches were not resampled until January 3, 2025. Results from the follow-up samples were determined to be in exceedance of the recreational standard as well. The results for the Buena Vista Lagoon outlet and Tamarack Avenue beaches for samples taken on January 3, 2025, were 5,391 copies/100 ml and 10,652 copies/100 ml, respectively.
The County DEHQ protocol for beaches that exceed the recreational standard for two consecutive samples is to shift their assessment method to analyze the most recent five samples taken within a 30-day period as opposed to assessing only the most recent single sample. This statistical analysis used to calculate longer-term exceedances is referred to as a geometric mean calculation.
The advisory threshold for the geometric mean is significantly lower than the single sample threshold. Due to this change in assessment method, both beaches remain under advisory despite sample results from January 7, 2025, falling well below the single sample recreational standard. Analytical results of samples taken on January 7, 2025, at the Buena Vista Lagoon outlet and Tamarack Avenue beaches were 97 copies/100 ml and 291 copies/100 ml, respectively.
On January 2, 6, and 7, 2025, Watershed Protection Division staff investigated both beach locations in the sampling areas, broader surrounding areas and nearby storm drain outfalls and found no evidence of potential bacteria sources that may have contributed to the bacterial exceedances. The Buena Vista Lagoon outlet was not flowing into the ocean during any of the investigations. Additionally, there was no flow from any of the storm drain outfalls in the vicinity of either beach.
According to County DEHQ staff, the most likely cause of the exceedances is the king tides in combination with the larger-than-normal surf washing bacteria from areas that are not typically in contact with seawater back into the surf zone. The king tides occurring during the sampling timeframe were the highest tides observed during this winter season thus far. County DEHQ staff also confirmed that no other potential sources of bacteria were observed at either beach and that the Buena Vista Lagoon outlet was disconnected from the ocean during all of their sampling efforts.
Next Steps
The County DEHQ will continue to conduct weekly water quality sampling at all eight of its regular Carlsbad beach sites to monitor bacteria levels. Results from the Buena Vista Lagoon outlet and Tamarack Avenue beaches will be incorporated into the geometric mean calculation and updated accordingly.
Council Memo -Water Contact Advisories Issued for Carlsbad Beaches (District 1) January 16, 2025
The current advisory status of Carlsbad beaches can be found on the website for the Beach & Bay Water Quality Program at https://www.sdbeachinfo.com/ . With the regular weekly sampling, it is likely that one or both of the beaches will remain under advisory for approximately one month, depending on the exact results.
Staff are evaluating the feasibility of performing additional in-house beach water quality sampling to supplement the regular monitoring performed by the County DEHQ with the intent of potentially minimizing the duration of the beach advisories. Using the previously described geometric mean statistical analysis, recording additional sample results below the recreational standard would reduce the total number of days those beaches are under advisory if the results are favorable. Based on historical data, staff expect that to be the case.
Staff will continue to closely monitor this situation and provide updates to the City Council as needed.
Attachments: A. Council Memorandum dated February 9, 2023 B. Council Memorandum dated June 30, 2022
C. Council Memorandum dated June 22, 2023
D. Council Memorandum dated August 1, 2024
cc: Geoff Patnoe, City Manager
Cindie McMahon, City Attorney
Gary Barberio, Deputy City Manager, Community Services
Laura Rocha, Deputy City Manager, Administrative Services Christie Calderwood, Police Chief
Michael Calderwood, Fire Chief
Gina Herrera, Assistant City Attorney
Tom Frank, Transportation Director/City Engineer
Kyle Lancaster, Parks & Recreation Director
Amanda Flesse, Utilities Director
Kristina Ray, Communication & Engagement Director
James Wood, Environmental Sustainability Director
Tim Murphy, Senior Program Manager