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..e 11ae September 10, 2004 NOA Project Number: E040104A _ 2.0 GROUND WATER ANALYSIS 2.1 Regional Ground Water A discussion of regional ground water, including depth to ground water and directional ground water gradient, is included in Section 4.1 of the SSS. No significant seasonal trends were evident from the maps consulted. 2.2 Potential Ground Water Contamination Issues _ A discussion of issues related to potential ground water contamination is included in Section _ 4.2 of the SSS. 2.3 Current and Future On-Site Ground Water Uses A description of the existing wells on the Site is included in Section 4.3 of the SSS. Ground water is used for domestic purposes and for agricultural irrigation. Ground water will be developed and used on all the proposed parcels in the future. 3.0 SOURCES AND IMPACT OF NITRATE TO GROUND WATER 3.1 Current Off-Site Sources of Nitrate We recognize that septic systems, agriculture, and dairies in the area may be the most significant sources of nitrate. Septic tank use in the vicinity is discussed in Section 3.4 of the _ SSS. The ground water sample, discussed in Sections 4.3 through 4.6 of the SSS, was found to have a nitrate concentration of 32.5 mg/L-NO3. This concentration indicates that the ground water aquifer may be experiencing nitrate leaching from various sources in the area over the long term. 3.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall and evapotranspiration for Stockton, California. The estimate first determines whether the average monthly precipitation exceeds average monthly potential _ evapotranspiration. If so, then the difference is potential deep percolation. This method does not consider runoff. See Plate 9 for the data and calculation. 3 _ _