Meeting Date:

February 22, 2018





David Stoldt,


Hydrologic Monitoring 2.6


General Manager

Line Item No.:

2-6-1 G, and 2-6-2 D


Prepared By:

Jonathan Lear/

Cost Estimate:



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 2017 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 2016 and Fall 2017 sampling of the Seaside Basin coastal monitor wells are included in this report.



Carmel Valley Aquifer Monitor Wells - Results from the Fall 2017 sampling are provided in Exhibit 20-A.  Six monitor wells in the lower Carmel Valley were sampled during Fall 2017, 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 2016 (provided here as a reference in Exhibit 20-B).  A seventh well that is normally sampled in the Fall (16S/1E-13Md), was not sampled in Fall 2017 or Fall 2016 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 20-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 2017 (Exhibit 20-D) with some notable fluctuations.  Both SEC and Chloride declined from 2006 to 2008, but have trended generally upward since then.  However, current Chloride and SEC levels are below peak levels observed at this location in Water Year 2013.  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, likely attributable to flooding along the roadside where this well is located.  Results indicate no significant changes to water quality here in 2017 relative to 2016.  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 2017 relative to 2016, but a graph of SEC and Chloride is included to track long-term trends as was described in previous Board packet reports (Exhibit 20-E).  This graph indicates a downward trend in both SEC and Chloride at this site; most other constituents were not significantly different in 2017 relative to 2016.


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 2017, 11 dedicated monitor wells at six different sites were sampled.  Results of water-quality sampling from 2017 and 2016 for the Seaside wells are provided in Exhibit 20-A and Exhibit 20-B, respectively.  Because laboratory results for the Fall 2017 samples needed to be received and processed earlier than in years prior to 2008 in order to complete an Annual Report to the Seaside Groundwater Basin Watermaster, some of the Seaside wells were actually sampled in July and August of 2017.  The locations of the Seaside monitor wells are shown on the map in Exhibit 20-F.  Results for most constituents in most of the wells were not significantly different in 2017 relative to 2016, with few exceptions.  Concentrations of Iron were notably higher in three wells (15S/1E-N2, -15F2, and -11Pb) in 2017 relative to 2016.  Concentrations of Iron in well 15S/1E-F1, while still elevated, were considerably lower in 2017 compared to 2016.  Although the concentration of Iron in well 15S/1E-11Pb was elevated relative to the 2016 report, it is significantly lower than the level reported in 2015 (5.772 mg/l). The level of Iron in well 15S/1E-11Pa recovered to a concentration lower the Drinking Water Standard, but staff will continue to watch it as it was elevated in 2016.  The concentration of Iron in well 15S/1E-11Fc was high, but lower than in 2016, and the concentration in well -11Fa was about the same as reported in 2016.  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.



20-A    Groundwater-quality Monitoring Results - Fall 2017

20-B    Groundwater-quality Monitoring Results - Fall 2016

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

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

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

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