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November 8,2004 �NOA Project Number: E040110A LV 2.3 Current and Future On-Site Ground Water Uses L A description of the existing wells on the Site is included in Section 4.3 of the SSS. Ground water is currently used for agricultural irrigation. Ground water will be developed and used on all the proposed parcels in the future. r L /3.0 SOURCES AND IMPACT OF NITRATE TO GROUND WATER !/ 3.1 Current Off-Site Sources of Nitrate L We recognize that septic systems, agriculture,and dairies in the area may be the most significant L 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& +,�/T N 3. This concentration indicates that the ground water aquifer is likely not experiencing nitrate leaching from 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 Lodi,California. The estimate fust detem-iines 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. Average potential evapotranspiration was obtained from the California Irrigation Management Information System (CIMIS). Stockton is located within evapotranspiration zone number 12. The ` average rain fall for the Stockton area was obtained from the Western Regional Climate Center (www.wrcc.dri.edu), and was found to be 1.16 inches per month for the years 1965 through 1977. i Based on this method, the average deep percolation of rain for the Lodi area is estimated to be 6.84 inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 3.3 Current On-Site Sources of Nitrate LCurrent on-site sources of nitrate include any fertilizers applied to agriculture. { As indicated in the Surface Subsurface Contamination Report, completed by our office on June 16, i2004,Ms. Griffith has recently purchased the land. The report indicates an unsuccessful attempt to contact the previous owner,Miguel Estrada. Since Ms. Griffith became the owner no fertilizers or L water have been applied to the property (personal communication, October 28, 2004). There is no reason not to assume that an appropriate quantity of fertilizer was being applied while the land was 4