ITEM:		INFORMATIONAL ITEM/STAFF REPORT
26.	SEMI-ANNUAL GROUNDWATER-QUALITY MONITORING REPORT
Meeting Date:			January 27, 2022	Budgeted:	Yes
From:			David Stoldt,	Program/	Hydrologic Monitoring 2.6
			General Manager	Line Item No.:	2-6-1 G, and 2-6-2 D
Prepared By:			Jonathan Lear/	Cost Estimate:	N/A
			Tom Lindberg
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: Water-quality results from the Fall 2021 sampling of the Monterey Peninsula Water Management District’s (District’s) monitor well networks in the Carmel Valley aquifer and the coastal areas of the Seaside Groundwater Basin are presented and briefly summarized below.

BACKGROUND: The District has maintained a groundwater-quality monitoring program in the Carmel Valley Aquifer since 1981, and in the Seaside Groundwater Basin since 1990. Currently, collection of samples from the Carmel Valley monitor wells is conducted on an annual basis. The sampling schedule for Carmel Valley is staggered, with upper valley wells (i.e., upgradient of the Narrows), sampled in Spring and lower Carmel Valley wells in Fall, to coincide with the historically higher nitrate concentrations in these respective areas. Beginning in 2007, the District was retained by the Seaside Basin Watermaster to collect water-quality samples from the District’s Seaside Basin coastal monitor wells on a quarterly basis. The results of that sampling are reported to the Seaside Basin Watermaster Board on an annual basis. Results of the Fall 2021 and Fall 2020 sampling of the Camel Valley and Seaside Basin coastal monitor wells are included in this report.

DISCUSSION/ANALYSIS:

Carmel Valley Aquifer Monitor Wells - Results from the Fall 2021 sampling are provided in Exhibit 26-A. Six monitor wells in the lower Carmel Valley were sampled during Fall 2021, per the sampling schedule described above. Review of these water-quality results indicates that, in general, there are minor changes in overall water quality compared to samples collected in 2020 (provided here as a reference in Exhibit 26-B). A seventh well that was formally sampled in the Fall (16S/1E-13Md), was not sampled in Fall 2021 or Fall 2020 because it was submerged under high water in the Carmel River Lagoon wetlands during the sampling period. Another well that had been sampled during this period was destroyed by flooding in March of 2011 when the river scoured away the south end of the Carmel River State Beach parking lot. The locations of the sampling points are shown on the map in Exhibit 26-C. Changes in water quality for specific wells are discussed below.

Staff is particularly interested in tracking indicators of potential seawater intrusion in the coastal portion of Carmel Valley. Accordingly, three clustered sets of wells were established west of Highway 1, with each set being made up of three wells completed at different depths. Review of historical data indicated that the shallower and intermediate depth wells in the coastal area are subject to the mixing of fresh water and saline water as high tides and surf overtop the sand berm between the lagoon and the ocean. This contributes to episodic mixing within the shallower and intermediate zones of the aquifer, but is not indicative of larger-scale seawater intrusion into the aquifer. All three wells in the cluster closest to the ocean were destroyed by river erosion in 2011, and all three of the wells in the next closest cluster to the ocean were inaccessible due to high water during the sampling period, so currently, only the deeper well at one of the three coastal locations is sampled.

Well 16S/1W-13Lc is the deepest in the array of three wells located State Parks property near the Carmel Area Wastewater District treatment plant at River Mile (RM) 0.65, currently the most proximate well to the ocean in Carmel Valley that is available for sampling. There is an overall increasing trend in Specific Electrical Conductance (SEC) and Chloride from 1989 to 2021 (Exhibit 26-D) with some notable fluctuations. Both SEC and Chloride declined from 2006 to 2008, but have resumed a generally upward trend since then. Current Chloride concentrations are below peak levels observed at this location in Water Year 2013, but SEC has risen above the 2013 value. Additional background on historical water-quality at the coastal monitor well sites can be found in District Technical Memorandum 90-04, Summary of Carmel Valley Groundwater-quality from Coastal Monitor Wells, which is available at the District office. Staff will continue to track future results for trends that might indicate significant changes in concentrations of these or other constituents in the coastal area of the aquifer.

Well 16S/1E-23E4, located 6.53 miles upstream from the mouth of the Carmel River, has had fluctuating water quality in the past - primarily as variably elevated iron and manganese, possibly attributable to flooding along the roadside where this well is located. Elevated iron and manganese concentrations are not unusual in Carmel Valley; four of the six wells sampled in Fall 2021 showed levels above the State Drinking Water Standards for these constituents. Results indicate no significant changes to water quality here in 2021 relative to 2020. Staff will continue to monitor the site to ensure the wellhead is secure from surface-water sources.

Well 16S/1E-23La, located 6.72 miles upstream from the river mouth, does not show a significant change in 2021 relative to 2020, but a graph of SEC and Chloride is included to track long-term trends as was described in previous Board packet reports (Exhibit 26-E). This graph indicates an overall downward trend in both SEC and Chloride at this site, although both constituents were higher in 2021than in the previous two years. Most other constituents were not significantly different in 2021 relative to 2020.

Seaside Groundwater Basin Coastal Monitor Wells - Since 1990, the District has been collecting water-quality samples from coastal monitor wells in the Seaside Groundwater Basin, for the purposes of water-quality characterization and sea-water intrusion monitoring. In 2009 District staff switched from air-lifting samples from wells in Seaside to “micro-purging”, which generally extends the well life. In Fall 2021, 9 dedicated monitor wells at six different sites were sampled. Results of water-quality sampling from 2021 and 2020 for the Seaside wells are provided in Exhibit 26-A and Exhibit 26-B, respectively. The locations of the Seaside monitor wells are shown on the map in Exhibit 26-F. Results for most constituents in most of the wells were not significantly different in 2021 relative to 2020, with few exceptions. Four of the wells in the Seaside Groundwater Basin showed levels of Iron above the Drinking Water Standard (0.3 milligrams per liter) in Fall 2021. A graph of SEC and Chloride trends in one pair of wells (15S/1E-15N3 and -15N2) is provided (Exhibit 26-G). A more complete historical summary of the Seaside Basin coastal groundwater-quality data is contained in District Technical Memorandum 97-02 Seaside Basin Coastal Monitor Wells: Ground Water-quality Monitoring Results, 1990-1996, which is available at the District office.

EXHIBITS

26-A Groundwater-quality Monitoring Results - Fall 2021

26-B Groundwater-quality Monitoring Results - Fall 2020

26-C Location of MPWMD Lower Carmel Valley Water-quality Monitoring Wells

26-D Water-quality Results in Well 16S/1W-13Lc in Carmel Valley

26-E Water-quality Results in Well 16S/1E-23La in Carmel Valley

26-F Location of MPWMD Seaside Basin Water-quality Monitoring Wells

26-G Water-quality Results in Wells 15S/1E-15N3 and -15N2 in Seaside

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