WATER SUPPLY PLANNING COMMITTEE
ITEM:		DISCUSSION ITEM
3.	UPDATE ON SEASIDE WELL FO-09 AND SEAWATER INTRUSION
Meeting Date:			April 5, 2021	Budgeted:	N/A
From:			David J. Stoldt	Program/	N/A
			General Manager	Line Item:
Prepared By:			David Stoldt	Cost Estimate:	N/A
General Counsel Review: N/A
Committee Recommendation: N/A
CEQA Compliance: This action does not constitute a project as defined by the California Environmental Quality Act Guidelines section 15378.

SUMMARY: 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 consultants concluded that 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-09 Shallow). However, none of the Watermaster’s Sentinel Wells, located closer to the coastline than monitoring wells FO-09 and FO-10, detected seawater intrusion in the shallow aquifer in their induction logs. This was reported to the Water Supply Planning Committee at its February meeting.

The consultants concluded that the sampling frequency for monitoring wells FO-09 Shallow and FO-10 Shallow should be increased to quarterly to establish if their chloride concentrations are true trends, or anomalous. Following the December 2, 2020 report to the Watermaster board, FO-09 shallow was sampled on January 5^th 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.

On March 23^rd, District staff pulled the pump at FO-09 Shallow and consultant Martin Feeney ran an induction and fluid conductivity log of the well. At 185' below grade, the conductivity greatly spiked and was high all the way down the well. The likely cause of this is a crack in the casing or a separated joint. This is problematic because it means the shallow seawater intrusion in the dune sands has found a pathway to the Paso Robles. However, this is a good discovery because it is the source of the rising chlorides in the well. The sample pump was deployed at 130 feet with a drop tube down to the screens. A seal in the pump had failed and instead of pulling water from the screens, which would have detected the high conductivity water, the pump was pulling from its base at 130 feet above the crack in the casing leaving it undetected. Good news: no seawater intrusion. Bad news: as the owner of the well, the District will need to destroy the well.

The consultant (Feeney) wants to video the well to see the problem, which District staff thinks is a good idea to get an idea of the damage and inform us how to move forward. However, even if the damage is slight and it appears as if a slip seal could be slid and placed in the well, Monterey County Health Department only allows casing down to 2 inches, and in this case when installed would be on the order of 1 inch, which would not likely be approved by the County. Instead, we would be instructed to destroy the well. It is staff’s recommendation that we should not make a repair to this well outside of spec. We would use the video to write the specifications for destruction. After the video, we should let the Health Department know what we have found and that we plan to take care of the issue.

The District needs to destroy this well because it is allowing seawater intrusion to short circuit the Paso Robles strata. However, the District does not use data from this well for any of its programs. FO-09 Deep is in the ASR permits, but not the shallow completion. We can destroy the shallow completion and retain the deep (we will also video the deep so we can prove it is not damaged), so this borehole will still provide the data we need. These FO wells were drilled by Joe Oliver in the early 1990s as exploratory bores to help define the hydrogeology of the Northern Coastal Sub Area and prior to the formation of the Watermaster these wells were infrequently sampled. Upon formation of the Watermaster, quarterly sampling of FO-09S was incorporated into the Court adopted Monitoring and Maintenance plan. Many of the completions from the early 1990 FO effort are not monitored and are nearing the end of life expectancy. If they were found damaged they would be destroyed and not replaced. FO-09S is one of those completions.

The Watermaster and Marina Coast will likely want this well replaced, as it is in their official monitoring plans for the MMP and GSP respectively. The District does not need this well replaced. A replacement well is on the order of $100K. The District will have to decide what, if any, financial contribution it would make to a replacement, since a replacement is not needed for District purposes. The District has not informed either of those entities that the outcome of the cracked casing we be to destroy the well.

Here are some approximate costs for the proposed options for FO-9S:

Video Survey - Pacific Surveys and Supervision - $3K

Well repair – Will depends on survey, use as estimate - $15K

Well destruction - including permits, contractor time, concrete, concrete pumper, supervision, - $15K cheaper if done at time of new construction.

Well replacement – Est. $140/foot ($84K) and $30K supervision - $114K

EXHIBITS

None

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