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ITEM: |
INFORMATIONAL
ITEMS/STAFF REPORTS |
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20. |
SEMI-ANNUAL GROUNDWATER QUALITY
MONITORING REPORT |
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Meeting
Date: |
August 15, 2005 |
Budgeted: |
Yes |
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From: |
David A.
Berger, General
Manager |
Program/ Line Item No.: |
2.6 Hydrologic Monitoring 2-6-1 |
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Prepared
By: |
Thomas
Lindberg |
Cost Estimate: |
N/A |
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General Counsel Approval: 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 Spring 2005 sampling of the Monterey Peninsula Water Management District’s (District’s) well network in the Carmel Valley aquifer are presented in Exhibit 20-A and briefly summarized below. Results from Spring 2004 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. As part of the District’s former Strategic Plan, the District conducted an assessment of the ground water quality monitoring program in 1996. Based on review of 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 staggered, with upper valley wells (i.e., upgradient of the Narrows), to be 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 was also 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 Spring 2005 and Spring 2004 samplings are provided in Exhibit 20-A. Three shallow monitor wells in the upper Carmel Valley are sampled each Spring, as per the sampling modification described above. The locations of these sampling points are shown on the map in Exhibit 20-B. Review of these water quality results indicates no significant change in overall water quality in Spring 2005 compared to samples collected in Spring 2004. As noted in last year’s report, Potassium concentrations in two of the wells (16S/2E-33Q1 and 17S/2E-10B1), were slightly higher in Spring 2004, and that trend continued in Spring 2005 for well 16S/2E-33Q1, but the concentration of Potassium in well 17S/2E10B1 remained essentially the same. There is no California Title 22 Drinking Water Standard for Potassium, and historically, Potassium levels were higher in 2002 and 2001, so there is no cause for alarm. All constituents for which Drinking Water Standards exist are within acceptable limits.
It should be noted that relatively high nitrate concentrations (up to 22 milligrams per liter [mg/L]) were measured in two upper Carmel Valley monitor wells in Spring 1998, although the 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. The relatively high readings were attributed to the flushing effect of severe storm events in the Winter of 1998. All results of more recent samplings from all three shallow wells indicate that nitrate concentrations have returned to more normal levels.
20-A Ground Water Quality Monitoring Results for Spring 2005 and Spring 2004
20-B Map of Monitor Well Locations in Upper Carmel Valley
Revised
8/10/05
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