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L L April 14, 2006 NOA Project Number. E06038A L ✓2.2 Potential Ground Water Contamination Issues A discussion of issues related to potential ground water contamination is included in Section V of Lthe original study. )2.3 Current and Future On-Site Ground Water Uses LCurrently, there are three operating wells located on the property. The wells are located on the northwest portion of the property. The wells are located about 40 to 50 feet apart in a north-south orientation. The northern and southern wells are used for fire safety and industrial water;these wells are tied together into a common service pipe. The center well is independent of the other two and is used for domestic purposes. IL 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 Lsources of nitrate. Septic tank use in the vicinity is discussed in Section IV of the original study. Two on-site water samples were analyzed for nitrate as part of the original study. The sample M collected from the combined-flow-of-them nd south wells (fire safety/industrial/ag wells) was i. found to have nitrate at a level 3.7 mg L-"6.6 mg/L-NO3,,and the sam c ed-6em the domestic water supply well (center well) was found to have nitrate at a level of 2.5APg�T.-(1'1.3 \ mg/L-NO3). Both of these samples are well below the maximum contaminant level (MCL) set by L the US EPA of 10 mg/L-N (45 mg/L-NO�. DBCP was not detected in the sample from the domestic water supply well;the other well was not tested for DBCP. (/3.2 Contribution of Rainfall L An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The L estimate of deep percolation of rain is based on the average monthly precipitation of rain fall and evapotranspiration for the Lodi area of California (the closest data set available). An estimate of potential deep percolation of rain determines whether the average monthly precipitation exceeds 6. average monthly potential evapotranspiration. If so, then the difference is potential deep percolation. This method does not consider runoff. See Plate 2 for the data and calculation. 6 ✓ Average potential evapotranspiration data were obtained from the California Irrigation Management Information System (CIMIS). Lodi is located within evapotranspiration zone number 12. Rainfall data was obtain frofn-tlie 5 1 Survey of San Joaguix Couuoy. The average rainfall for the Lodi area was found to e17.16fche per year for the years 1948 through 1987. 3 "44L