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ITEM:
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INFORMATIONAL
ITEMS/STAFF REPORTS
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27.
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SEMI-ANNUAL GROUNDWATER-QUALITY
MONITORING REPORT
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Meeting
Date:
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February 25, 2010
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Budgeted:
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Yes
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From:
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Darby Fuerst,
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Program/
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Hydrologic Monitoring 2.6
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General
Manager
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Line Item No.:
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2-6-1 G, and 2-6-2 D
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Prepared
By:
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Joe
Oliver/
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Cost Estimate:
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N/A
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Tom Lindberg
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General Counsel Review: N/A
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Committee Recommendation: N/A
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CEQA Compliance: N/A
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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.
DISCUSSION/ANALYSIS:
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.
EXHIBITS
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