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Alluvium/Colluvium The colluvial deposits on the south side of the main ridge are • receiving the majority of their recharge directly from precipita- tion, particularly in the form of snowmelt. The OW-4 hydrograph (Figure 3.3-11) indicates seasonal water levels vary up to 10 feet. Discharge of this water is most likely to the alluvium of Alkali Creek in the form of underfloor, since there are no indications of springs or seeps at the alluvium-colluvium contact. Evapotranspir- ation of a portion of this water during the growing season is likely. Water in the Alkali Creek alluvium is a part of the overall surface-ground water flow system in this Colorado River tributary. Water levels and water quality of this ground water are sensitive to both seasonal fluctuations and man-induced changes. It is not known why the water quality of the downgradient site is slightly better than that at the upgradient site. It may be due to ac- tivities on the Porter Ranch or contribution by tributaries of better quality water between the two sites. Irrigation activity on the Porter Ranch has changed over the years. Barton Porter has changed his system from flood irrigation to sprinklers, which may have an impact on water quantity and qua7A~i.ty in both the surface and ground water. Water level data from colluvial wells on the north side of the main ridge (OW-4L, OW-8, and OW-14) indicate there is a seasonal variation in water levels of up to 0.5 feet (Figures 3.3-13, 3.3-19 and 3.3-15) during the period of measurement. The timing of the variation suggests that responses at OW-8 are due to irrigation in mid to late summer, whereas responses at OW-14 and OW-4L are due to recharge by precipitation in early spring to early summer. However, since correlations with precipitation and/or irrigation schedules have not been made, the timing of the variations could be explained by delayed responses. NCBC - Coal Ridge #1 3-32 ASC/1145/900301 •