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WATER SUPPLY
PLANNING COMMITTEE |
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ITEM: |
DISCUSSION ITEM |
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4. |
DISCUSSION OF RECENT ACTIVITIES RELATED TO SEASIDE BASIN WELL
WATER QUALITY |
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Meeting Date: |
February 1, 2021 |
Budgeted: |
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From: |
David J. Stoldt |
Program/ |
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General Manager |
Line Item: |
N/A |
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Prepared By: |
David Stoldt |
Cost Estimate: |
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General Counsel Review: N/A |
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Committee
Recommendation: N/A |
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CEQA
Compliance: This action does not constitute a project as
defined by the California Environmental Quality Act Guidelines section 15378. |
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SUMMARY: There have been three recent disclosures of information regarding water quality issues in Seaside Groundwater Basin wells, primarily in the northern region. These are being brought to the Water Supply Planning committee as informational items and do not warrant immediate District action at this time.
1) At the December 2, 2020 Board meeting of the Seaside Groundwater Basin Watermaster, Georgina King of Montgomery & Associates made a presentation on the annual Seawater Intrusion Analysis Report. The consultant’s report states “Seawater intrusion is typically identified through regular chemical analyses of groundwater which can identify geochemical changes in response to seawater intrusion. No single analysis definitively identifies seawater intrusion, however by looking at various analyses we can ascertain when fresh groundwater mixes with seawater. At low chloride concentrations, it is often difficult to identify incipient seawater intrusion. This is due to the natural variation in fresh water chemistry at chloride concentrations below 1,000 milligrams per liter (mg/L). Mixing trends between groundwater and seawater are more easily defined when chloride concentrations exceed 1,000 mg/L. Common geochemical indicators of seawater intrusion are cation and anion ratios, chloride trends, sodium/chloride ratios, and electric induction logging. Based on an evaluation of geochemical indicators in prior years, seawater intrusion has not historically been observed in existing monitoring and production wells in the Seaside Basin.”[1]
Nevertheless, the consultants concluded that “In Water Year 2020 for the first time, what may be a precursor to seawater intrusion was detected in two monitoring wells experiencing increasing chloride concentrations. One of these is north of and outside of the Seaside Basin (monitoring well FO-10 Shallow), and the other is just inside the northern boundary of the Seaside Basin in the Northern Coastal Subarea (monitoring well FO-9 Shallow). However, none of the Watermaster’s Sentinel Wells, located closer to the coastline than monitoring wells FO-9 and FO-10, detected seawater intrusion in the shallow
aquifer in their induction logs.”[2] Well locations are shown in Exhibit 4-A, hereto.
The added, “Since the Sentinel Wells have not detected an increase in salinity, if seawater is starting to impact the FO-9 Shallow and FO10-Shallow monitoring wells, it may be coming from the north out of the Monterey Subbasin where there is already seawater intrusion, rather than directly inland from the coastline of the Seaside Basin.”[3]
The Consultants concluded that the sampling frequency for monitoring wells FO-9 Shallow and FO-10 Shallow should be increased to quarterly to establish if their chloride concentrations are true trends, or anomalous.
2) Following the December 2, 2020 report the Watermaster board report, FO-9 shallow was sampled on January 5th and its chloride concentration was 92.2 mg/L. That was up from 90.4 mg/L from the last Sept 28, 2020 sample, and above the well’s Chloride Threshold Level of 67 mg/L. The last 4 samples have increased above each previous sample.
In the Watermaster Seawater Intrusion Response Plan, four seawater intrusion indicators are combined to form the triggers that prompt contingency actions, including chloride concentration above threshold level. These triggers have been developed using a combination of quantitative and qualitative indicators. Because no one indicator definitively identifies seawater intrusion, a combination of indicators is necessary to identify intrusion. Watermaster staff will be working with consultants to determine whether the combination of indicators is present, and report to the Watermaster board at the February 3, 2021 board meeting.
3) On January 4, 2021 California American Water (Cal-Am) informed the Monterey Peninsula jurisdictions that several samples collected from wells in the Seaside Groundwater Basin on November 19, 2020 had a detection of perfluorooctanoic acid (PFOA) or perfluorooctane sulfonic acid (PFOS) (see Exhibit 4-B, attached. There is no action required by customers. While the concentration of PFOA is above the Notification Level (5.1 ppt), the combined concentration of PFOA and PFOS is significantly below the EPA lifetime health advisory level. Additional monitoring will be performed by Cal-Am.
EXHIBITS
4-A Map of Seaside Basin Well Locations
4-B January 4, 2020 Cal-Am Notification of PFOA and PFOS Detection