2015-05-26_PWETC_AgendaPacket - Laserfiche WebLink

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Page 22 of 38 Permit No: MNR040000 F. Alum or Ferric Chloride Phosphorus Treatment Systems If the permittee uses an alum or ferric chloride phosphorus treatment system, the permittee shall comply with the following: 1. Minimum Requirements of an Alum or Ferric Chloride Phosphorus Treatment System a. Limitations (1) The permittee shall use the treatment system for the treatment of phosphorus in stormwater. Non-stormwater discharges shall not be treated by this system. (2) The treatment system must be contained within the conveyances and structural stormwater BMPs of a small MS4. The utilized conveyances and structural stormwater BMPs shall not include any receiving waters. (3) Phosphorus treatment systems utilizing chemicals other than alum or ferric chloride must receive written approval from the Agency. (4) In -lake phosphorus treatment activities are not authorized under this permit. b. Treatment System Design (1) The treatment system shall be constructed in a manner that diverts the stormwater flow to be treated from the main conveyance system. (2) A High Flow Bypass shall be part of the inlet design. (3) A flocculent storage/settling area shall be incorporated into the design, and adequate maintenance access must be provided (minimum of 8 feet wide) for the removal of accumulated sediment. 2. Monitoring During Operation a. A designated person shall perform visual monitoring of the treatment system for proper performance at least once every seven (7) days, and within 24 hours after a rainfall event greater than 2.5 inches in 24 hours. Following visual monitoring which occurs within 24 hours after a rainfall event, the next visual monitoring must be conducted within seven (7) days after that rainfall event. b. Three benchmark monitoring stations shall be established. Table B-1 shall be used for the parameters, units of measure, and frequency of measurement for each station. c. Samples shall be collected as grab samples or flow -weighted 24-hour composite samples. d. Each sample, excluding pH samples, must be analyzed by a laboratory certified by the MDH and/or the MPCA, and: (1) Sample preservation and test procedures for the analysis of pollutants shall conform to 40 CFR Part 136 and Minn. R. 7041.3200. (2) Detection limits for dissolved phosphorus, dissolved aluminum, and dissolved iron shall be a minimum of 6 micrograms per liter (µg/L), 10 µg/L, and 20 µg/L, respectively. (3) pH must be measured within 15 minutes of sample collection using calibrated and maintained equipment.