ITEM:

INFORMATIONAL ITEMS/STAFF REPORTS

 

26.

SEMI-ANNUAL GROUNDWATER QUALITY MONITORING REPORT

 

Meeting Date:
July 20, 2015

Budgeted: 

Yes

 

From:

David Stoldt,

Program/

2.6 Hydrologic Monitoring

 

General Manager

Line Item No.:

2-6-1

 

Prepared By:

Thomas Lindberg

Cost Estimate:

N/A

 

General Counsel Review:  N/A

Committee Recommendation:  N/A

CEQA Compliance:  N/A

 

SUMMARY:  Water-quality results from the Spring 2015 sampling of the Monterey Peninsula Water Management District’s (District’s) well network in the Carmel Valley aquifer are presented in Exhibit 26-A and briefly summarized below.  Results from Summer 2014 are also provided for comparison.

 

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, the sampling schedule for Carmel Valley is staggered, with upper valley wells (i.e., upgradient of the Narrows) normally sampled in Spring, and lower Carmel Valley wells sampled in Fall, to coincide with the historically higher nitrate concentrations in these respective areas.  Collection of samples from the Seaside Basin coastal water-quality monitor wells is conducted once per year in Summer, coinciding with the seasonally low water levels in the basin at that time of the year. 

 

DISCUSSION/ANALYSIS:  Carmel Valley Aquifer Monitor Wells - Results from the Spring 2015 and Summer 2014 samplings are provided in Exhibit 26-A.  Three shallow monitor wells in the upper Carmel Valley are normally sampled each Spring, per the sampling schedule described above.  The locations of these sampling points are shown on the map in Exhibit 26-B.  Review of these water-quality results indicates little significant changes in overall water quality in Spring 2015 compared to samples collected in Summer 2014.  Samples were analyzed by Monterey Bay Analytical Services.  All constituents that have established Drinking Water Standards are within acceptable limits in Spring 2015 with the exception of a borderline high Iron concentration in one well, although the amount of Iron detected was far lower in 2015 than in 2014, as discussed in the following paragraph.  A brief discussion of results for each well is provided below.

 

16S/2E-33Q1: This well is located along Boronda Road, approximately 12.5 miles upstream from the Carmel River mouth.  All of the constituents reported were slightly higher in 2015 relative to 2014, with the exceptions of Iron, Manganese and Potassium.  Anomalous spikes in total Iron and Manganese concentrations were observed in 2011 and 2014, but concentrations had dropped back to expected levels by Spring 2015.  Dissolved Iron or Manganese were not detected from any of the wells in 2015. 

 

17S/2E-03La:  This well is located 13.65 miles from the river mouth near the parking lot of De Dampierre Park.  All of the constituents reported were slightly lower or unchanged in 2015 relative to 2014.

 

17S/R2E-10B1:  This well is located 14.28 miles from the river mouth on a dirt easement beside Via Helechos Road.  Originally it was located in a manhole in the road, but the road was slightly realigned after the river flooded it in 1995.  2015 water quality results indicate moderate increases in general mineral constituents as well as nitrate and Total Organic Carbon, relative to the 2014 data.  Currently the property adjacent to the easement is in foreclosure, and there have been episodes of the wellhead being buried, covered by a cut-down tree, or otherwise obstructed with vehicles.  Although the well is protected by a tight sealing cap and manhole, this activity may be linked to the increased concentrations of most of the reported constituents here between 2014 and 2015.  As stated earlier, all constituents that have established Drinking Water Standards were within acceptable limits in Spring 2015, but staff will continue to monitor results of sampling in this well in particular to see if the decline in its water quality progresses.  

 

It should be noted that historical sampling revealed relatively high nitrate concentrations (up to 22 milligrams per liter [mg/L]) in two upper Carmel Valley monitor wells in Spring 1998, although those observed nitrate concentrations were well below the drinking water standard of 45 mg/L.  The Carmel Valley Master Plan established an “action level” of 25 mg/l of nitrate due to concern about the limitations of septic systems in this unsewered portion of Carmel Valley. Those relatively high readings were attributed to the flushing effect of severe storm events in the winter of 1998.  Results of more recent samplings from all three shallow wells indicate that nitrate concentrations have returned to more normal levels.  In 2015, the nitrate levels in two wells (17S/2E-10B1 and 16S/2E-33Q1) remained below the action level.  The nitrate concentration in the third well (17S/2E-03La) remained below the practical quantitation limit (i.e., detection limit).

 

EXHIBITS

26-A    Groundwater Quality Monitoring Results for Spring 2015 and Summer 2014

26-B    Map of Monitor Well Locations in Upper Carmel Valley

 

 

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