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<br />DRAFT <br /> <br />Water RescOUrc8S <br />CIty of CentelV/lle <br />2030 Comprehensive Plan <br /> <br />Table 30 - MPCA Impalnnent designation thresholds for detennlnlng use support <br />for lakes <br /> <br /> Ecorealons <br /> North Central Hardwood Forest Western Com Belt Plains <br />Impairment Not Listed Review Listed Not Listed Review Listed <br />Designation ranoe ranoe <br />TP ( gill <40 40 - 45 >45 < 70 70-90 > 90 <br />Chlorophyll - <15 N/A >18 <24 N/A >32 <br />( oILI <br />Secchl disk > 1.2 N/A < 1.1 > 1.0 N/A <0.7 <br />transparencY (m) <br /> <br />To be listed on the 303(d) Impaired waters list, by the MPCA, In-lake monitoring data <br />must show that TP and either Chlorophyll - a or Secchi depth were violated. If data <br />show a lake is not meeting the support criteria for anyone of the variables, It may be <br />placed on a review list. The MPCA uses a weight of evidence approach to determine If a <br />lake will be listed as Impaired (MPCA 2005). <br /> <br />To be de-listed, the lakes must achieve these criteria. However, there Is provision for <br />goal-setting flexibility. The listing criteria may not be realistically achievable for some <br />lakes, and therefore an altemative goal may be proposed on a site specifiC basis. <br /> <br />Additionally, the MPCA has acknowledged that shallow lakes should not be assessed <br />with the same criteria as deep lakes. Shallow lakes are different then deep lakes due to <br />differences in ecological characteristics and Intemel nutrient cycling. The MPCA has <br />deflned shallow lakes es having a maximum depth less than 15 feet, or having greater <br />than BO% surface area as littoral (less than 15 feet deep) surface area. Table 31 shows <br />MPCA's proposed numerical standards for shallow lakes. As of spring 2007, these <br />criteria were scheduled to be reviewed and Included in Minnesota Rule by January 200B. <br /> <br />Table 31 - Proposed MPCA Impalnnent designation thresholds for detennlnlng <br />t I k <br /> <br /> use SUDDort or a es <br />Parameters Ecorealons <br /> North Central Hardwood Forest Western Com Belt Plains <br /> Shallow DeeD Shallow DeeD <br />TP( oILI 60 40 90 65 <br />Chlorophyll - 20 14 30 22 <br />( oILI <br />Secchl disk <br />transparency 1.0 1.4 0.7 0.9 <br />1m) <br /> <br />Status: <br />Only a handful of TMDls have been completed or are in process. The flrst TMDl <br />Implementation plan for Cenlerville lake Is In process by RCWD. <br /> <br />96 <br />