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Coverage issued: October 28, 2021 Permit expires: November 15, 2025 MS400047 Page 18 of 28 - Duluth, and Lake Superior College), the permittee must maintain a written plan that identifies specific activities the permittee will implement to reduce thermal loading during the permit term. The written plan may include, but is not limited to: a. implementation of infiltration BMPs such as bioinfiltration practices; b. disconnection and/or reduction of impervious surfaces; c. retrofitting existing structural stormwater BMPs; or d. improvement of riparian vegetation. [Minn. R. 7090] 23.1 Alum or Ferric Chloride Phosphorus Treatment Systems. [Minn. R. 7090] 23.2 If the permittee uses an alum or ferric chloride phosphorus treatment system, the permittee must comply with Section 23 requirements. [Minn. R. 7090] 23.3 The permittee's alum or ferric chloride phosphorus treatment system must comply with the following: a. the permittee must use the treatment system for the treatment of phosphorus in stormwater. Non-stormwater discharges must not be treated by this system; b. the treatment system must be contained within the conveyances and structural stormwater BMPs of the MS4. The utilized conveyances and structural stormwater BMPs must not include any receiving waters; c. phosphorus treatment systems utilizing chemicals other than alum or ferric chloride must receive written approval from the Agency; and d. in -lake phosphorus treatment activities are not authorized under the General Permit. [Minn. R. 7090] 23.4 The permittee's alum or ferric chloride phosphorus treatment system must meet the following design parameters: a. the treatment system must be constructed in a manner that diverts the stormwater flow to be treated from the main conveyance system; b. a high flow bypass must be part of the inlet design; and c. a flocculant storage/settling area must be incorporated into the design, and adequate maintenance access must be provided (minimum of 8 feet wide) for the removal of accumulated sediment. [Minn. R. 7090] 23.5 A designated person must 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. [Minn. R. 7090] 23.6 Three (3) benchmark monitoring stations must be established. Table 1 in Appendix A must be used for the parameters, units of measure, and frequency of measurement for each station. [Minn. R. 7090] 23.7 Samples must be collected as grab samples or flow -weighted 24-hour composite samples. [Minn. R. 7090] 23.8 Each sample, excluding pH samples, must be analyzed by a laboratory certified by the Minnesota Department of Health and/or the Agency, and: a. sample preservation and test procedures for the analysis of pollutants must conform to 40 CFR Part 136 and Minn. R.7041.3200; b. detection limits for dissolved phosphorus, dissolved aluminum, and dissolved iron must be a minimum of 6 micrograms per liter, 10 micrograms per liter, and 20 micrograms per liter, respectively; and c. pH must be measured within 15 minutes of sample collection using calibrated and maintained equipment. [Minn. R. 7090] 23.9 In the following situations, the permittee must perform corrective action(s) and immediately notify the Minnesota Department of Public Safety Duty Officer at 800-422-0798 (toll free) or 651-649-5451 (Metro area): a. the pH of the discharged water is not within the range of 6.0 and 9.0; b. any indications of toxicity or measurements exceeding water quality standards which could endanger human health, public drinking water supplies, or the environment; or c. a spill or discharge or alteration resulting in water pollution as defined in Minn. Stat. 115.01, subd. 13, of alum or ferric chloride.