Meeting Date:

February 25, 2010





Darby Fuerst,


Hydrologic Monitoring 2.6


General Manager

Line Item No.:

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


Prepared By:

Joe Oliver/

Cost Estimate:



Tom Lindberg


General Counsel Review:  N/A

Committee Recommendation:  N/A

CEQA Compliance:  N/A


SUMMARY:  Water-quality results from the Fall 2009 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 monitor on a quarterly basis.  The results of that sampling are reported to the Seaside Basin Watermaster Board on a quarterly basis.  Results of the Fall 2008 and Fall 2009 sampling of the Seaside Basin coastal monitor wells are included in this report.



Carmel Valley Aquifer Monitor Wells - Results from the Fall 2009 sampling are provided in Exhibit 27-A.  Seven monitor wells in the lower Carmel Valley were sampled during Fall 2009, per the sampling schedule described above.  An eighth well that is normally sampled in the Fall (16S/1E-13Md), was not sampled in Fall 2009 because it was submerged under high water in the Carmel River Lagoon during the sampling period.  The locations of these sampling points are shown on the map in Exhibit 27-C.  Review of these water-quality results indicates that, in general, there are minor changes in overall water quality compared to samples collected in Fall 2008 (data originally reported in the March 21, 2009 Board packet) and provided here as a reference in Exhibit 27-B.  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 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 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.  Currently, only the deeper wells at each of the three coastal locations are sampled.


Well 16S/1W-14Jg is the deepest in the array of three wells located at the Carmel River State Beach parking lot at River Mile (RM) 0.07 (approximately 375 feet from the shoreline).  Water quality results from 2009 show significant improvement at this location relative to 2008, suggesting a seaward movement of the freshwater/seawater interface.  This may be attributable to the later season flows in the lower reaches of the Carmel River in 2009 compared to 2008.  This reverses a trend in increasing Specific Electrical Conductance (SEC) and Chloride over the previous four years (Exhibit 27-E).  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, shows significant improvement in overall water quality in 2009 relative to 2008.  This is likely resulting from wellhead improvements at this site that were make in Summer 2008 to reduce potential flooding along the roadside where this well is located.


Well 16S/1E-23La, located 6.72 miles upstream from the river mouth, does not show a significant change in 2009 relative to 2008, but a graph of SEC and Chloride is included to track long-term trends as was described in the March 21, 2009 Board packet (Exhibit 27-F).


Well 16S/1E-24N5, located 8.02 miles upstream from the river mouth, shows significant increases in major inorganic constituents in 2009 relative to 2008.  This may also be due to surface water getting into the well, as this location is in the middle of a roadway.  Staff will continue to monitor this site to ensure the wellhead is secure from surface-water sources.


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 Fall 2009, 12 dedicated monitor wells at six different sites were sampled.  Results of water-quality sampling from 2009 and 2008 for the Seaside wells are provided in Exhibit 27-A and Exhibit 27-B, respectively.  Because laboratory results for the Fall 2009 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, the Seaside wells were actually sampled in July and August of 2009.  The locations of the Seaside monitor wells are shown on the map in Exhibit 27-D.  These results indicate little change from previous results over the period of record for the existing wells, and that there is no indication of sea-water intrusion in these wells that are completed in the two principal aquifer units -- the Paso Robles Formation (i.e., shallower unit) and Santa Margarita Sandstone (i.e., deeper unit) -- in this area of the Seaside Groundwater Basin at the present time.  Results for most constituents in most of the wells were not significantly different in 2009 relative to 2008, with few exceptions.  In 2009, well 15S/1E-23Cb shows a slight improvement relative to sampling in 2008.  This may be due to a new sample collection method initiated in the Seaside Groundwater Basin sampling network in 2009.  In 2009 District staff switched from air-lifting samples from wells to “micro-purging” wells, which is generally less destructive to the well and gravel pack, is less dangerous for the operator, but is also more time consuming.  The other notable changes occurred in wells 15S/1E-12Fa and 15S/1E-12Fc, where marked increases in Iron and Manganese concentrations were observed in 2009 relative to 2008.  Those changes may also be due to the different sampling technique, and will be tracked for future analysis.   Staff will continue to track results for all wells for trends that might indicate significant changes in the basin.   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.



27-A    Groundwater-quality Monitoring Results - Fall 2009

27-B    Groundwater-quality Monitoring Results - Fall 2008

27-C    Location of MPWMD Carmel Valley Water-quality Monitoring Wells

27-D    Location of MPWMD Seaside Basin Water-quality Monitoring Wells

27-E    Water-quality Results in Well 16S/1W-14Jg in Carmel Valley

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