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Toxlclty <br />We suspect that toxicity is due to the organisms being in a solution that is reacting as the pH with <br />in the sample raises from 7.2 to 8.0 during the 24 hours between renewals of test solutions. This <br />raise in pH facilitates the formation of calcium carbonate making the solution unstable, <br />potentially allowing other chemical reactions to occur. The rise in pH is due to the reaction of <br />oxygen with the sample. Groundwater is frequently low in oxygen (relative to surface water)and <br />upon reaching the surface the water absorbs oxygen which can react to oxidize ions in solution. <br />It is stressful on organisms, especially the Ceriodaphnia, to be in a solution which is going <br />through these changes, the wide swing in pH and the calcium carbonate formation. It is this <br />stress that is causing the toxicity seen in the acute Ceriodaphnia test. <br />The TDS at 4,000 mg/L is near the toxicity threshold for the Ccriodaphnia but the 007 site has <br />similar TDS and does not demonstrate toxicity, so is not likely to be the cause of mortality. <br />Aliquots of both sites were sent to ACZ lab in Steamboat Springs for metals analysis to ensure <br />that these are trot the cause. ICP Mass Spec methods were requested to provide detection limits <br />in the 5 ppb range. Metals analysis requested were arsenic, cadmium, chromium, lead, nickel, <br />silver, zinc, sodium and potassium. We should get the report back about the 20's of this month. <br />Treatment <br />Aeration/I-Iolding Time <br />This treatment involves aerating the sample to speed up the calcium/carbonate reaction and then <br />holding the water for some time allowing the water to stabilize before it is discharged. This is <br />basically what is happening in pond 007, but aeration should decrease the amount of time needed <br />to stabilize the water. Bench top tests performed in the lab on the January 2, 2002 sample show <br />that aeration of four hours will reduce toxicity to no mortality in I00% after 48 hours. If shorter <br />time frames are needed shortened aeration tests can be performed to estimated the minimum time <br />required for treatment. <br />CO2 Enriched Atmosphere Tests <br />While preparing this report the potential for testing using CO2 enriched atmosphere presented <br />itself as a modification that could be used to test the sample without onsite treatment. This <br />method uses CO2 in a sealed test chamber to stop the pH drift and hold the pH at or near the pH <br />of the sample when it was received at the lab. This will bold the pH below the level which <br />calcium carbonate begins to form. This modification would need to be approved by your <br />regulating authority before It can be used and used for your NPDES reports. The basic theory <br />behind this modified testis that the CO2 reacts with the water forming carbonic acid in solution <br />lowering the pH. The trick is to get the right concentration of CO2 which holds the pH but does <br />not depress it to much. This is a fairly common procedure and is frequently approved for use in <br />masking ammonia toxicity. If you are interested in this seeing the results of a CO2 atmosphere <br />