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Standards for Protection of Lakes /;) Subject: Standards for Protection of Lakes Date: Wed, 1 Dee 2004 10:41 :29 -0600 From: "Maschwitz, David" <David.Maschwitz(~)state.mn.us> To: <megehee@lstate.net> CC: "Lkiskm-y, Steven" <Stcven.Heiskary(@state.rnn.us>, "Gross, Greg" Dear Ms. McGehee: As we discussed on the phone on November 29,2004 I am writing to clarify recent to Minnesota Rules Chapter 7050 regarding narrative standards that protect lakes from excess nutrient loading (eutrophication). Minnesota R. ch. 7050 contains a beneficial use classification system applicable to all waters of the state, numeric and narrative water quality standards that protect those uses from pollution, and many other provisions that protect Minnesota's water resources. I have included Web sites that contain rule language and other pertinent information. Currently the standard that protects lakes from the adverse effects of nutrient loading, such as algae blooms and reductions in water clarity, is a narrative standard. This narrative eutrophication the authority for the Minnesota Pollution Control Agency (MPCA) to assess the water and to identify lakes that are impaired due to excess nutrient loading. The implementation of a narrative involves the interpretation of the language of the standard; and, in the case of the eutrophication standard, use of numeric guideline values to assess the degree of eutrophication that has occurred in a given lake. The eutrophication guideline values are for total phosphorus (the nutrient most often responsible for negative impacts), chlorophyll-a (a green pigment used to measure the abundance of algae) and Secchi disk (a measure of water clarity). The guideline values, their origin, and how they are used in lake assessments are described in the MPCA 2004 assessment guidance (first document under "Publications": I1ttpji.W.Y1.YYJ1.ca .st~le .Inil .us/water/tmd l/ind(~x.html#Qu blicationm. In 2002 the MPCA proposed amendments to Minn. R. 7050.0150 that added substantial detail to the eutrophication narrative standard. These amendments were adopted as final on February 3, 2003; see specifically Minn. R. 7050.0150, Subpart 5 (b!1P-://www.revisoLlea.state.mn.us/arule17050/0150.html). The added language specifies that data for phosphorous, and either chlorophyll-a or Secchi disk transparency are needed to assess the trophic status of a lake, and it also provides information about how assessments should be carried out. These amendments do not alter the MPCA's authority to assess and protect lakes based on the narrative eutrophication standard. Prior to February 2003 the narrative eutrophication standard was limited to the language now in Minn. R. 7050.0150, subpart 3. The narrative standard was used to assess lakes throughout Minnesota for the MPCA 2002 and 2004 lists of impaired waters (303(d) list), as required by the federal Clean Water Act M1Q://vfjyw .pea .state.m n .us/w.?lterltmdl/index.html). If you have questions or need further information please contact me or Steven Heiskary (651-296-7217). A letter to you will follow this email. Sincerely, David Maschwitz Research Scientist 12i5i2004 3:21 PIvf lof2