Agenda - Environmental Policy Board - 01/18/2017

Home

Item-by-item guidance Chapter Additional Resources: • MPCA Construction Stormwater web page: http://www.pca.state.mn.us/wfh. An estimate of the stormwater impact on the quality of receiving waters should be made. The level of sophistication of this analysis must be guided by the likely magnitude of the impact and the sensitivity of the water body(les) affected. Where it is clear that only a minor degradation of water quality and negligible impairment of water use would result,only a general qualitative discussion is needed. Where noticeable impairment may occur,however,more quantitative assessment methods should be employed, and predictions should be made about whether any water quality standards will be violated. Factors to consider when making this decision include: amount of impervious surface proposed,degree and location of excavation activities,proposed activities that could result in exposure of contaminants to stormwater, water quality impairments—especially impairments for turbidity,nutrients, and aquatic life, and trout streams (including the potential for thermal impacts). A stormwater discharge that may affect a lake is an example of a situation in which the RGU must exercise judgment about the extent of analysis needed. Generally regarded as sensitive and valued resources,the lake may require a numerical nutrient budget analysis to adequately characterize the extent of the potential impact.Any nutrient budget analysis performed should be based on a generally accepted model of a lake's response to an increase in phosphorus loading or other critical nutrients if phosphorus is not the limiting factor. The choice of a model should be based on available data, and its expected accuracy based on the likely magnitude of the impact,in addition to the time and costs of using the model. In other words,the greater likelihood of the impact,the greater the need is for a more sophisticated model. If insufficient data is available to allow the use of any numerical model,it is necessary to gather the minimally needed data unless the EAW can establish through other analysis that there is no reason to expect noticeable degradation. If the matter is left in doubt in the EAW,it may result in requests for an EIS for the project and, associated with that,a more in-depth analysis. The amount of detail provided about management or treatment methods should befit the significance of the quantities and quality of the runoff.Where it is clear or suspected that the stormwater runoff associated with the project would pose water quality problems if not adequately managed or treated, sufficient detail is needed so that reviewers can judge the adequacy of the proposed system. Locations, dimensions and design capacities of detention or retention basins should be given if they will be used to manage runoff. The EAW should discuss the conformance of the proposed system with any applicable requirements of the local unit of government and any watershed district with jurisdiction over the area, such as ensuring stormwater pipes are designed for larger storm events, and ensuring that projects that impact municipal storm and sewer pipes do not create or exacerbate potential overflow and contamination concerns due to connected storm and sewer pipes. If the project is subject to a Stormwater Pollution Prevention Plan(SWPPP),it should be discussed in the EAW. iii. Water Appropriation. The EAW should describe any water use such as water supply,dust control,dewatering or pond testing, and give the source and the permit number if there is an existing appropriation. Distinguish between temporary construction water use and ongoing operational water use. Appropriation of water in excess of 10,000 gallons per day or one million gallons per year requires permits from the DNR Division of Waters.If a project requires an appropriation permit it is suggested that the proposer or RGU contact the applicable DNR regional or area hydrologist's offices to determine what information should be provided. In cases of major appropriations(permitted water appropriations in excess of 100 million gallons/year),or where cumulative appropriations are great,it may be necessary to include a quantitative analysis of the impacts on ground water levels. Environmental Quality Board EAW Guidelines—October 2013 27