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DISCUSSION <br />In August of 1996 a Toxicity Identification Evaluation (TIE) was performed on effluent waters <br />from the Bear Coal Company mine site. The results of that TIE indicated that Total Dissolved <br />Solids possibly in solution with bicarbonate were causing toxicity towards Ceriodaphnia dubia. <br />Records indicate that no further characterization tests were run to verify exactly what element(s) <br />of TDS was causing toxicity. <br />Upon reviewing effluent chemical data from that TIE and comparing it with current effluent <br />chemical data, CT&E decided to run a more simplified series of tests (PTI) geared specifically <br />towards reconfirming TDS toxicity. A full TIE seemed unnecessary. <br />None of the tests performed in this Preliminary Toxicity Identification removed toxicity. Most <br />of the tests performed did not significantly decrease toxicity in the Bear Coa] Co. effluent, with <br />the possible exception of the Filtration/pH Adjustment (pH 3) and Filtration/pH Unadjustment <br />(pHi) tests. <br />However, the following observations were made that indicate Total Dissolved Solids may be the <br />source of toxicity: <br />• The pH adjustment test did not remove or significantly reduce toxicity. This is an indication <br />of TDS toxicity (USEPA 1999). <br />• A precipitate was not visible in the pH adjustment test, filtration/pH adjustment test, and <br />aerationipH adjustment test. This is an indication of TDS toxicity (USEPA 1999). <br />• TDS may be indicated because there was greater sensitivity by C. dubia compared to D. <br />magma (API 1998). <br />• TDS may be indicated because there was greater sensitivity by C. dubia compared to fathead <br />minnows (API 1998). Please note that this observation was made from prior bioassays. <br />• Conductivity exceeded 3,000 µmhos/cm at the LCso for C. dubia (USEPA 1991). <br />Many other tests are available to further confirm TDS toxicity towards Ceriodaphnia dubia. <br />These tests include preparing a mock effluent mimicking the constituent cations and anions in <br />the actual effluent. If the toxicity in the mock effluent testis similar to effluent toxicity, TDS <br />toxicity is further supported. Also, an ion balance program should be able to identify ions or <br />combinations of ions that may contribute to TDS toxicity. These ions can be evaluated by <br />spiking dilution water with the suspect ions and observing the resulting toxicity. <br />