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- u U City of Ripon Welt*12 - Nitrate Study Report May 31,20D6 7.0 CONCLUSIONS Based on the review of the data and observations presented in the previous sections, we conclude that: • The Ripon Farm Services site is a source of nitrate contamination to local groundwater. Water quality data collected from monitoring wells recently installed near the RFS liquid bulk fertilizer storage facility clearly show the effect if this source. • The impact of this source is very likely superimposed upon regional, or background, nitrate concentrations in groundwater that are on the order of tens of mg/I. • The circumstances of the nitrate source to groundwater and the full extent of the resulting impact cannot be known at this time as RFS has apparently began to investigate the problem only recently. However, more that eight years of nitrate data collected from the RFS water supply well indicate that deeper groundwater is impacted by the source on an annual basis. This impact occurs during late summer and the fall when the groundwater system is at its maximum stress as a result of agricultural and other pumping and elevates deeper nitrate concentrations to almost 1000 mg/I. The only known nitrate concentrations of such magnitude are observed in shallow groundwater immediately adjacent to the RFS water supply well at the RFS liquid fertilizer storage facility. • Shallow groundwater nitrate concentrations have migrated from the RFS site in the prevailing westerly to northwesterly direction of groundwater flow. The direction of shallow groundwater flow appears to be the result of naturally occurring regional hydrologic conditions. • Nitrate concentrations in deeper groundwater near the RFS site have resulted from the downward migration of the shallow nitrate plume emanating from the RFS site. This impact, which is driven by a regionally pervasive and pronounced downward hydraulic gradient that results from well pumping, is obvious at the RFS supply well and is likely a significant contributor to the nitrate contamination present in the city and private supply wells sampled in this work. Specific factors that may affect differences in concentrations among the supply wells include well construction and operation, and local sediment stratigraphy. • The nitrate concentration history for City Well 12 does not appear to have resulted from the operation of that well. If concentrations had increased as a result of operations (between 2001 and 2004), they would have decreased as a result of inactivity(in 2005) as has been the case for other City wells. • Additional investigation that could clarify technical assessment of the RFS nitrate source and migration include: 1) nitrogen/oxygen isotope analysis conducted on samples from the RFS and other wells to further evaluate the contribution of the RFS source on nitrate concentrations in nearby water supply wells and 2) deep monitoring well installation and water level data logging to evaluate temporal variations in deeper groundwater flow direction in the immediate site vicinity. Ripen WM,2Reppt tloc 7-1 The Source Group,Inc.