ITEM:

INFORMATIONAL ITEM/STAFF REPORTS

 

26.

RECEIVE AND FILE SEMI-ANNUAL GROUND-WATER QUALITY MONITORING REPORT

 

Meeting Date:

February 24, 2005

Budgeted:

Yes

 

From:

David A. Berger,

Program/

2.6

 

General Manager

Line Item No.:

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

 

Prepared By:

 

Tom Lindberg

Joe Oliver

Cost Estimate:

N/A

 

General Counsel Approval:N/A

Committee Recommendation: N/A

CEQA Compliance:N/A

 

SUMMARY:Water quality results from the Fall 2004 sampling of the Monterey Peninsula Water Management Districtís (Districtís) monitor well networks in the Carmel Valley Alluvial Aquifer and coastal subareas of the Seaside Ground-Water Basin are presented and briefly summarized below.This report is presented to the Board for information purposes and to provide an opportunity for staff to respond to any questions regarding the water quality data or this District program.

 

BACKGROUND:The District has maintained a ground-water quality monitoring program in the Carmel Valley Aquifer since 1981, and in the Seaside Ground-Water Basin since 1990.As part of the Districtís former Strategic Plan, staff conducted an assessment of the ground-water quality monitoring program in 1996.Based on review of the long-term data trends, it was determined that some modifications could be made to the sampling schedules in both the Carmel Valley and Seaside Basins, without compromising the effectiveness of the program.Accordingly, collection of samples from the Carmel Valley monitor wells has been reduced from semi-annual to annual.The sampling schedule for Carmel Valley is now staggered, with upper valley wells (i.e., upgradient of the Scarlett Narrows) being sampled in Spring and lower Carmel Valley wells in Fall, to coincide with the historically higher nitrate concentrations in these respective areas.Collection of samples from the Seaside Basin monitor wells has also been reduced to once per year in Fall, coinciding with the historically low water levels in the basin at this time of the year.

 

DISCUSSION/ANALYSIS:Carmel Valley Aquifer Monitor Wells - Results from the Fall 2004 sampling are provided in Exhibit 26-A.Fourteen monitor wells in the lower Carmel Valley were sampled during Fall 2004, as per the sampling modification described above.The locations of these sampling points are shown on the maps in Exhibit 26-C.Review of these water quality results indicates that, in general, there are only minor changes in overall water quality compared to samples collected in Fall 2003 (data reported in the February 19, 2004 Board packet and provided here in Exhibit 26-B).Staff is particularly interested in tracking indicators of potential sea-water intrusion in the coastal portion of the Carmel Valley Aquifer.To that end, an array of three wells (16S/1W-14Jh, f and g) completed at different depths is located at the Carmel River State Beach parking lot, approximately 375 feet from the shoreline.Exhibit 26-D shows that specific conductance was lower in the shallow well in Fall 2004 relative to Fall 2003, higher in the intermediate depth well, and slightly higher in the deepest well.However, specific conductance is significantly lower in all three wells in Fall 2004 relative to the 14-year highs during the last extended drought. The higher values observed early in the sampling program are at least partially attributable to the fact that there was no fresh water inflow to the lagoon for approximately four years (April 1987 until March 1991).This situation is further discussed in Technical Memorandum 90-04, Summary of Carmel Valley Ground Water 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.

Seaside Coastal Subareas Monitor Wells -In Fall 2004, 12 monitor wells were sampled from the coastal subareas of the Seaside Basin.Results of water quality sampling from Fall 2004 and Fall 2003 for the Seaside Basin wells are provided in Exhibit 26-A and Exhibit 26-B, respectively.The locations of these wells are shown on the map in Exhibit 26-E.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 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 Basin at the present time.One well, 15S/1E-23Ca, that showed a 23 percent increase in specific conductance from 2002 to 2003, increased an additional eight percent from 2003 to 2004.Results from this single well are not considered significant.This well is the shallower of a pair of monitor wells completed at Ord Terrace School.The other wells in the basin did not show a similar increase in specific conductance, although results for specific conductance were slightly higher in every well relative to Fall 2003.No remarkable changes were detected in other constituent concentrations any wells in the area.Staff will continue to track results for trends that might indicate significant changes in any wells in the basin.†† A more complete historical summary of the Seaside Basin coastal ground water 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††† Fall 2004 Ground Water Quality Monitoring Results

26-B††† Fall 2003 Ground Water Quality Monitoring Results

26-C††† Maps showing locations of MPWMD Carmel Valley water quality monitoring wells

26-D††† Specific Conductance in three coastal wells in Carmel Valley

26-E††† Map showing Seaside Basin coastal water quality monitor well locations

 

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