Presented by: Bob Gensemer September 25 th , 2012 Colorado Mining Association Pre-filtration: Study Results and Proposal for 303(d) Listing Methodology 1
Background Water quality criteria typically based on dissolved or total recoverable fraction • Dissolved measures the ecologically relevant form that is bioavailable and potentially toxic to aquatic life • Total recoverable also measures small colloidal or hydroxide phase metals (removed by the 0.45 µm filtration used for dissolved), which for Fe and Al can be toxic − But also measures metals associated with non-toxic particulates (i.e., “chunks”) − Problematic at sites with lots of suspended particles − Likely overestimates the concentration of metal that would actually be toxic to aquatic life 2
Background GEI, ARCADIS, and New Mexico Environment Department studies • Pre-filtration before total recoverable analysis • Do toxic colloidal forms of metals get through? • Provide a better representation of the metals that are toxic to aquatic life Is coarse pre-filtration appropriate and protective? 3
Study Goals 1. Determine if total recoverable iron and aluminum are reduced in proportion to the total suspended solids (TSS) in the sample. 2. Determine if particle size distribution analysis confirms removal of only non-toxic forms. 3. Confirm removal of non-toxic metal forms via toxicity testing on the species most sensitive to iron and aluminum. 4
Goal #1: TSS vs. Fe and Al Correlation between iron and TSS concentrations in raw water samples (i.e., unfiltered). 35 30 25 Iron (mg/L) 20 R 2 = 0.392 15 10 5 0 0 500 1000 1500 2000 2500 3000 3500 5 TSS (mg/L)
Goal #1: TSS vs. Fe and Al Stronger correlation between aluminum and TSS concentrations in raw water samples (i.e., unfiltered). 30 25 Aluminum (mg/L) 20 R 2 = 0.934 15 10 5 0 0 500 1000 1500 2000 2500 3000 3500 6 TSS (mg/L)
Goal #1: Filter Effectiveness Confirmed decrease in iron using 5.0 µm filtration, without complete removal. 100 Raw 20.0 µm 10.0 µm 10 5.0 µm 1.0 µm 0.45 µm Iron (mg/L) 1 0.1 * * * * * * * 0.01 * 0.001 GEI-1 GEI-2 GEI-3 GEI-4 GEI-5 ARCADIS-1 ARCADIS-2 ARCADIS-3 ARCADIS-4 ARCADIS-5 NMED-1 NMED-2 7 Sites
Goal #1: Filter Effectiveness Confirmed decrease in aluminum using 5.0 µm filtration, without complete removal. 100 10.0 µm 1.0 µm Raw 5.0 µm 0.45 µm 20.0 µm 10 Aluminum (mg/L) 1 0.1 * * 0.01 0.001 GEI-1 GEI-2 GEI-3 GEI-4 GEI-5 ARCADIS-1 ARCADIS-2 ARCADIS-3 ARCADIS-4 ARCADIS-5 NMED-1 NMED-2 8 Sites
Goal #1: Filter Effectiveness Confirmed decrease in iron to levels below criteria using 5.0 µm filtration. Table 1. Iron data and chronic criteria from the relevant state (mg/L). Bold red font indicates values exceeding the chronic standard. New Mexico does not have an iron standard, so the standard of 1.0 mg/L is only used for comparative purposes. Standard Filter Size (µm) and Measured Iron (mg/L) TSS Sample Acute Chronic Raw Raw 20 µm 10 µm 5.0 µm 1.0 µm 0.45 µm GEI 1 NA 1.0 166 6.69 -- -- 0.05 <0.02 <0.02 GEI 2 NA 1.0 42.4 2.97 -- -- 0.04 <0.02 <0.02 GEI 3 NA 1.0 1102 30.6 -- -- 0.02 -- <0.02 13.6 -- -- GEI 4 NA 1.0 1110 0.09 -- <0.02 -- -- GEI 5 NA 1.0 81.6 3.55 1.35 <0.02 <0.02 ARCADIS 1 NA 1.0 NA 0.36 -- -- 0.07 0.012 0.018 ARCADIS 2 NA 1.0 2 0.22 -- -- 0.032 0.013 0.025 ARCADIS 3 NA 1.0 5 0.13 -- -- 0.056 0.023 <0.010 ARCADIS 4 NA 1.0 330 13.0 -- -- 0.62 0.075 0.059 ARCADIS 5 NA 1.0 510 43.0 -- -- 0.5 0.49 0.61 NMED 1 NA 1.0 600 5.50 0.08 <0.05 <0.05 <0.05 -- 9 17.5 NMED 2 NA 1.0 3020 0.12 0.055 0.055 0.065
Goal #1: Filter Effectiveness Similar decrease in aluminum to levels below criteria using 5.0 µm filtration. Table 2. Aluminum data and acute and chronic criteria from the relevant state (mg/L). Bold red font indicates values that exceed the acute and chronic criteria. Bold blue font indicates values that only exceed the chronic standard. Standard Filter Size (µm) and Measured Aluminum (mg/L) TSS Sample Acute Chronic Raw Raw 20 µm 10 µm 5.0 µm 1.0 µm 0.45 µm GEI 1 11.1 1.58 166 3.02 -- -- 0.047 0.014 0.018 0.50 GEI 2 0.75 0.087 42.4 -- -- 0.006 0.004 0.011 GEI 3 22.8 3.26 1102 14.0 -- -- 0.007 -- 0.004 GEI 4 22.8 3.26 1110 6.71 -- -- 0.044 -- 0.006 GEI 5 7.54 1.08 81.6 4.00 -- -- 1.53 0.014 0.077 ARCADIS 1 4.39 1.76 NA 0.64 -- -- 0.31 0.19 0.20 ARCADIS 2 4.90 1.96 2 0.64 -- -- 0.32 0.17 0.18 ARCADIS 3 5.00 2.00 5 0.61 -- -- 0.30 0.16 0.18 ARACDIS 4 4.19 1.68 330 3.10 -- -- 0.22 0.10 0.094 ARCADIS 5 6.74 2.70 510 45.0 -- -- 0.074 0.034 0.04 NMED 1 4.09 1.64 600 8.55 0.055 <0.05 <0.05 <0.05 -- 10 NMED 2 3.95 1.58 3020 26.5 0.095 <0.05 <0.05 <0.05 --
Goal #1: Filter Effectiveness Confirmed decrease in iron and aluminum concentration proportional to TSS consistent with all filter sizes. 20 µm 10 µm 5.0 µm 1.0 µm 0.45 µm TSS Al Fe TSS Al Fe TSS Al Fe TSS Al Fe TSS Al Fe Sample GEI 1 -- -- -- -- -- -- 97.6* 98.4 99.3 97.6* 99.5 99.7 97.6* 99.4 99.7 GEI 2 -- -- -- -- -- -- 90.6* 98.8 98.7 90.6* 99.2 99.3 90.6* 97.8 99.3 GEI 3 -- -- -- -- -- -- 99.1 99.9 99.9 -- -- -- 99.5 99.9 99.9 GEI 4 -- -- -- -- -- -- 99.6* 99.3 99.3 -- -- -- 99.6* 99.9 99.9 GEI 5 -- -- -- -- -- -- 68.0 61.8 62.0 95.1* 99.7 99.4 95.1* 98.1 99.4 ARCADIS 1 -- -- -- -- -- -- -- 51.6 80.6 -- 70.3 96.7 -- 68.8 95.0 ARCADIS 2 -- -- -- -- -- -- -- 50.0 85.5 -- 73.4 94.1 -- 71.9 88.6 ARCADIS 3 -- -- -- -- -- -- -- 50.8 56.9 -- 73.8 82.3 70.5 92.3 ARACDIS 4 -- -- -- -- -- -- -- 92.9 95.2 -- 96.8 99.4 -- 97.0 99.5 ARCADIS 5 -- -- -- -- -- -- -- 99.8 98.8 -- 99.9 98.9 -- 99.9 98.6 NMED 1 -- 99.4 98.5 -- 99.4 99.1 -- 99.4 99.1 -- 99.4 99.1 -- -- -- NMED 2 -- 99.6 99.3 -- 99.8 99.7 -- 99.8 99.7 -- 99.8 99.6 -- -- -- 11
Goal #2: Particle Size Particle size distribution (PSD) analysis was not possible for most of the filtered samples due to insufficient suspended solids remaining after filtration. However, the particle size withheld by the 5.0 µm pre- filtration step is expected to be similar to the size of the particles withheld by the standard TSS filtration step, considering the retention size of the glass fiber filters used for TSS are typically around 1 to 1.5 µm. % Sample of Particle Sample Size 5 µm or greater % TSS Reduction % Al Reduction % Fe Reduction GEI 2 84.3 89.6 98.8 98.7 GEI 3 81.6 99.1 99.9 99.9 GEI 4 91.6 99.6 99.3 99.3 GEI 5 45.2 68.0 61.8 62.0 ARCADIS 4 52.3 -- 92.9 95.2 ARCADIS 5 100 -- 99.8 98.8 12
Goal #3: Toxicity Only 2 of the 10 raw water samples demonstrated minor sublethal toxicity Iron and aluminum concentrations in raw water were up to 43x higher than water quality criteria Supports premise that total recoverable can include measurement of non-toxic forms 13
Conclusions Pre-filtration would adequately remove the majority of the non-toxic, particulate phase metals, which is supported by PSD analysis Toxicity attributable to metals was not observed at iron and aluminum concentrations up to 43 times higher than the water quality standard Total recoverable analysis after coarse pre- filtration provides the most environmentally relevant measurement that is still protective of aquatic life 14
Recommendations Recommend use of a 5 or 10 µm pre-filter • New Mexico is proposing 10 µm • “For aluminum, the criteria are based on analysis of total recoverable aluminum in a sample that is filtered to minimize mineral phases as specified by the department.” In 303(d) Listing Methodology, similar language could be added to Section III.C.1. Chemical Data – General (pages 15-16 of March 10, 2011 version). For example: • g. Attainment of Aluminum and Iron Standards Aluminum and iron standards are based on analysis of total recoverable aluminum and iron in a sample that is pre-filtered through a 5 µm filter to minimize mineral phases. 15
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