Meeting Date: February 19, 2004 Budgeted: Yes

Program/Line Item No.: 2.6

Staff Contact: Joe Oliver/ Hydrologic Monitoring/2-6-1 H. and 2-6-2 D.

Tom Lindberg Cost Estimate: NA

General Counsel Approval: NA

Committee Recommendation: NA

CEQA Compliance: NA

SUMMARY: Water quality results from the Fall 2003 sampling of the Monterey Peninsula Water Management District’s (District) monitor well networks in the Carmel Valley aquifer and Seaside Coastal Ground Water Subareas are presented and briefly summarized below.

RECOMMENDATION: This report is for information purposes only. The Board should review the report and provide staff with any comments or questions. Staff will make any needed revisions and finalize the report, if this item is approved with the Consent Calendar.

BACKGROUND: Since the inception of the District’s ground water quality monitoring program in 1981, the District has worked cooperatively with the Monterey County Water Resources Agency (MCWRA), which provided data collection and analysis services to the District. In 1995, however, District staff assumed all field data collection responsibilities and now works directly with the Monterey County Consolidated Chemistry Lab to conduct the water quality analyses, as a cost saving measure.

As part of the District’s Strategic Plan, District 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 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 2003 sampling are provided in Exhibit 5-A. Fourteen monitor wells in the lower Carmel Valley were sampled during Fall 2003, as per the sampling modification described above. The locations of these sampling points are shown on the maps in Exhibit 5-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 2002 (data reported in the February 27, 2003 Board packet and provided here in Exhibit 5-B). In 2003, it was noted that the analysis for several constituents (i.e., sodium and potassium) at one well, 16S/1W-14Jf, were measured at expected concentrations, given that the ground water at this coastal location was approximately 45 percent of the concentration of typical seawater. This well is located at the Carmel River State Beach parking lot, approximately 375 feet from the shoreline. In 2002, the data for this well showed anomalously low sodium and anomalously high potassium levels. It is possible that chemical interference influenced the 2002 analysis; this has occurred previously in the coastal samples that are within the mixing zone between fresh water and seawater in this area of the aquifer. This well is one of an array of three wells (16S/1W-14Jh, f and g) completed at different depths within the aquifer at this location. From the graphs provided herein as Exhibit 5-D and Exhibit 5-E, it can be seen that specific conductance and chloride concentrations were slightly lower in both the shallow and intermediate wells in Fall 2003 relative to Fall 2002, and these constituents were significantly lower in all three wells in Fall 2003 relative to the seven-year high in Fall 1997. 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 - Since 1990, the District has been collecting water quality samples from coastal monitor wells in the Seaside Ground Water Basin, for the purposes of water quality characterization and sea-water intrusion monitoring. In Fall 2003, 12 monitor wells were sampled. Two wells that are usually sampled in the Fall, 15S/1E-15K4 and 15S/1E-15K5, were not sampled in 2002 due to access constraints and the expense of renting a large compressor necessary to conduct the sampling in Seaside wells, which are considerably deeper than the Carmel Valley monitor wells. Staff resumed sampling of these wells, along with the other wells in the Seaside Ground Water Basin monitor network in Fall 2003. Results of water quality sampling from Fall 2003 and Fall 2002 for the Seaside wells are provided in Exhibit 5-A and Exhibit 5-B, respectively. The locations of the Seaside wells are shown on the map in Exhibit 5-F. 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 Ground Water Basin at the present time. One well, 15S/1E-23Ca, did show an 23 percent increase in specific conductance from 2002 to 2003, but this one reading is not considered significant. This well is the shallower of a pair of monitor wells completed at Ord Terrace School. Other wells in the basin did not show a similar increase in specific conductance, and no remarkable changes were detected in other constituent concentrations from this or other wells. Staff will continue to track results for trends that might indicate significant changes in this or other 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, which is available at the District office.

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