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4.6 WATER RESOURCES The potential effect on groundwater quality can be estimated by constructing a chemical-water mass balance. This accounts for all major sources of nitrogen and water input to the soil and groundwater system to compute the estimated average,long-term concentration of nitrate-nitrogenin percolating waters reaching the groundwater. The mass balance analysis constructed for the Buckeye Ranch project, along with a statement of the key assumptions and the resulting calculations, is presented below (Table 4.6-5). The long-term nitrate concentration in the local groundwater,as influenced by the project, is estimated to be approximately 5.7 mg/l as N, or about 25 mg/l as NO,. This compares to a nitrate drinking water standard of 10 mg/l as N, and 45 mg/l as NO,. According to this analysis, a rise in the nitrate concentration in groundwater can be expected from the project; but it will not adversely affect the suitability of groundwater for domestic uses or other water supply purposes. Miti ag tion 4.6-6 No mitigation measure is required or recommended. Erosion Impacts Impact 4.6-7 Large amounts of grading and excavation for the project could have a potentially significant erosion impact. Erosion can cause numerous types of impacts. Eroded soil contains nitrogen, phosphorus, and other nutrients. When these are carried into water bodies,these nutrients can trigger algal blooms that reduce water clarity, deplete oxygen, and create odors. Excessive deposition of sediments in streams may blanket fauna and clog streams. The increased turbidity from the erosion may also reduce photosynthesis that produces food supply and natural aquatic habitats. This impact is considered a potentially significant short-term impact. Following construction,the completed project should cause minimal erosion and sediment related impacts to downstream water bodies, due to landscaping and paving of possible sediment source areas. Because the project is located on relatively flat slopes and the soils are moderately susceptible to erosion, impacts from erosion would be limited. However, unprotected alterations in drainage patterns could compound and increase erosion on the site. 4.6-21