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Snow and rain infiltrate rocks upgradient ofthe NW Panels sealed sump. As these waters travel through the rock mass, soluble constituents enter the water. As these meteoric waters containing dissolved solids mix with the fault waters in the sump, the sump water changes in composition. The addition of Ca and Mg might be explained by the dissolution of dolomite -- (CaMg)CO;. If dolomite was dissolved, the incoming fluid containing it should also contain an equivalent (more-or-less) amount of bicarbonate. The seep water contains a lower amount of bicarbonate than the fault, but more than enough to balance the Ca and Mg from dolomite dissolution. Therefore, it is feasible that the incoming meteoric water contained Ca, Mg and bicazbonate, but the bicarbonate was lower in that fluid than the fault waters, so the net effect was to lower bicarbonate in the mixture. The fault waters are chazacterized as sodium bicarbonate waters whereas the seep waters are sodium potassium calcium bicarbonate sulfate waters. The same meteoric water [hat contained dissolved dolomite could also contain dissolved potassium and sodium, both of which aze probably readily available in local Cretaceous rocks. The relative increase in K (from about 3 mg/L in the fault water to 8 in the seep water) would indicate that the meteoric water contained the higher K content. The minor, if any, decrease in Na likewise can be attributed to the relative concentrations of Na in the fault waters and the meteoric water, the meteoric water having the lower concentration. The introduction of meteoric water could also explain the drop in pH. Meteoric water has a typical pH in the range of ~.5 - 6.5 (see for instance, A.W. Hounslow, 199, Water Quality Data, Analysis and Interpretation, CRC/Lewis Publishers, New York, p. 169). The Edwards Portal seep has a pH of 6.79 compared with pH values in excess of 8 for the fault waters. Easily, dilution of [he fault waters by rain or snow could explain this shift, and as noted above, meteoric water mixing is consistent with several findings. Isotope geochemistry. At first glance, an increase in sulfate in the water Wright indicate gypsum (or anhydrite) dissolution. However two points argue against gypsum as a source. First, there is not enough Ca to balance the sulfate, so that eliminates a gypsum source unless a parallel mechanism is developed to remove Ca from solution. However, that approach may be unnecessarily complex. The second point lies in the sulfur isotope composition of the dissolved sulfate. The SJ4S values, which range up to +44.4 per mil, are up [0 15 permit enriched over even the heaviest seawater sulfate. (Seawater is the source from which most gypsum/anhydrite derives, especially in the Paleozoic and pre-Tertiary rocks of this area which are dominantly marine in origin). Furthermore, the S'4S values are about 25 permit enriched over late Cretaceous seawater, which arguably is the most likely ultimate source of gypsum locally (see Holler and Kaplan, 1966, Chemical Geology, vol. 1, No. 2, p. 93-135). Thus, gypsum or anhydrite in the sedimentary column are not the likely source of the sulfate in the Lone Pine seal and Edwards Portal seal waters. As mentioned above, the enriched (isotopically heavy) S"S values of the sulfate azgue for a source area where sulfate, possibly in [he presence of methane oxidation, has undergone enrictunent due to the preferential reduction of sulfate containing the lighter