{"data":{"id":"us/40-cfr-421.252","jurisdiction":"us","citation":"40 CFR 421.252","heading":"Effluent limitations guidelines representing the degree of effluent reduction attainable by the application of the best practicable control technology currently available.","body":"Except as provided in 40 CFR 125.30 through 125.32, any existing point source subject to this subpart shall achieve the following effluent limitations representing the degree of effluent reduction attainable by the application of the best practicable technology currently available:\n(a) Smelter wet air pollution control.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/troy ounce of gold and silver smelted\nLead 0.546 0.260\nMercury 0.325 0.130\nSilver 0.533 0.221\nZinc 1.898 0.793\nGold 0.130\nOil and grease 26.000 15.600\nTotal suspended solids 53.300 25.350\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(b) Silver chloride reduction spent solution.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant of pollutant property Maximum for any 1 day Maximum for monthly average\nmg/troy ounce of silver reduced in solution\nLead 0.168 0.080\nMercury 0.100 0.040\nSilver 0.164 0.068\nZinc 0.584 0.244\nGold 0.040\nOil and grease 8.000 4.800\nTotal suspended solids 16.400 7.800\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(c) Electrolytic cells wet air pollution control.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/troy ounce of gold refined electrolytically\nLead 83.160 39.600\nMercury 49.500 19.800\nSilver 81.180 33.660\nZinc 289.100 120.800\nGold 19.800\nOil and grease 3,960.000 2,376.000\nTotal suspended solids 8,118.000 3,861.000\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(d) Electrolyte preparation wet air pollution control.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/troy ounce of silver in electrolyte produced\nLead 0.021 0.010\nMercury 0.013 0.005\nSilver 0.021 0.009\nZinc 0.073 0.031\nGold 0.005\nOil and Grease 1.000 0.600\nTotal suspended solids 2.050 0.975\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(e) Calciner wet air pollution control.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/kg (pounds per million pounds) of mercury condensed\nLead 78.200 37.240\nMercury 46.550 18.620\nSilver 76.340 31.650\nZinc 271.900 113.600\nGold 18.600\nOil and Grease 3,724.000 2,234.000\nTotal suspended solids 7,634.000 3,631.000\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(f) Calcine quench water.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/kg (pounds per million pounds) of mercury condensed\nLead 7.392 3.520\nMercury 4.400 1.760\nSilver 7.216 2.992\nZinc 25.700 10.740\nGold 1.760\nOil and Grease 352.000 211.200\nTotal suspended solids 721.600 343.200\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(g) Calciner stack gas contact cooling water.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/kg (pounds per million pounds) of mercury condensed\nLead 1.743 0.830\nMercury 1.038 0.415\nSilver 1.702 0.706\nZinc 6.059 2.532\nGold 0.415\nOil and Grease 83.000 49.800\nTotal suspended solids 170.200 80.930\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(h) Condenser blowdown.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/kg (pounds per million pounds) of mercury condensed\nLead 5.796 2.760\nMercury 3.450 1.380\nSilver 5.658 2.346\nZinc 20.150 8.418\nGold 1.380\nOil and Grease 276.000 165.600\nTotal suspended solids 565.800 269.100\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.\n(i) Mercury cleaning bath water.\nBPT Limitations for the Primary Precious Metals and Mercury Subcategory\nPollutant or pollutant property Maximum for any 1 day Maximum for monthly average\nmg/kg (pounds per million pounds) of mercury condensed\nLead 0.588 0.280\nMercury 0.350 0.140\nSilver 0.574 0.238\nZinc 2.044 0.854\nGold 0.140\nOil and Grease 28.000 16.800\nTotal suspended solids 57.400 27.300\npH (1) (1)\n1 Within the range of 7.5 to 10.0 at all times.","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER N—EFFLUENT GUIDELINES AND STANDARDS","PART 421—NONFERROUS METALS MANUFACTURING POINT SOURCE CATEGORY","Subpart W—Primary Precious Metals and Mercury Subcategory"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"0d3bab2f4ddece04a85d1a4ee8d608407488b9bd3c11d5c9458c3786195621ec","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-421.251","next":"us/40-cfr-421.253"},"notice":"GroundRules: Original legal text. Not legal advice."}