> I'm trying to model the mixing of two streams (Rio Grande and the Pecos) in Lake Amistad. I've obtained the values below for Aug/1984 (I'd like to compare to 8/1998 later). I'm using the measured inflow rates for the mixing ratios. 1- Rio Grande, 2-Pecos & 3- is a Bouy in the lake. > Is there something I can do to decrease uncertainty and reduce the # of models (I get > 100). The simplest way to reduce models is to use the -minimal option. That should make many fewer models by eliminating phases that are not needed within the given uncertainty. I would also remove some phases. I don't know the system that well, but I'm guessing clay and biotite reactions probably are not the dominant reactions. So I'd limit reactions to CO2, calcite, and silica; reactions that could be biologically driven. Calcite is near saturation and could probably dissolve or precipitate. Gypsum is well undersaturated, as is halite. Maybe these are reasonable aeolean phases, but I don't know if they could really affect the water chemistry. Your mixing calculation is not saved, so it is not used in the inverse modeling, but the inverse model calculates the mixing fraction anyway. In the file below, it is about 60/25 percent for the two waters. It also requires a dilution with pure water (~10%). From here you need to add your own knowledge of the variability in the input waters, alternative phase selections, the importance of direct precip and runoff. The dilution seems a bit too much, but I would probably attribute the problem to uncertainties in the two source waters. Good luck, David TITLE Rio Grande & Pecos Mixing at Buoy1 SOLUTION_SPREAD -units mmol/l Number pH Ca Mg Na Cl S(6) Si K temp Alkalinity 1 7.6 1.85 0.3745 3.6 0.96 2.5 0.267 0.138 27.5 1.0 2 7.6 2.25 2.016 13.04 13.8 2.91 0.217 0.15 28.5 1.10 3 8 1.80 0.864 5.65 3.95 2.18 0.30 0.13 21.0 1.20 MIX 1 1 0.85 2 0.15 3 1.0 INVERSE_MODELING 1 -solutions 1 2 3 -uncertainty 0.1 -phases # Ca-montmorillonite CO2(g) H2O(g) Calcite Chalcedony # Gypsum -balances Cl 0.1 0.1 0.1 Ca 0.1 0.1 0.1 Mg 0.1 0.1 0.1 K 0.1 0.1 0.1 S(6) 0.1 0.1 0.1 Si 0.1 0.1 0.1 Na 0.1 0.1 0.1 -range 1000 -tolerance 1e-010 -mineral_water true PHASES Biotite KMg3AlSi3O10(OH)2 + 6H+ + 4H2O = Al(OH)4- + 3H4SiO4 + K+ + 3Mg+2 log_k 0 CH2O CH2O = 0.5 CH4 + 0.5 CO2 log_k 0 END David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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