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W . • <br />W <br />process. A number of provisions are utilized in the rules for. <br />protecting surface water supplies. Specifically, restrictions <br />include limits on the number and types of wastewater discharges, <br />limits on development densities and guidelines governing allowable <br />land use practices. Limitations within the critical areas <br />defined as 1 mile and draining to the normal pool elevation of <br />reservoirs or 1 mile and draining to a river intake are more <br />stringent than requirements outside the critical area. The normal <br />pool elevation for impoundments is the water level at which the <br />impoundment is usually maintained. In "backwater" areas, this <br />level can be difficult to determine. Staff has made its best <br />interpretation based on existing maps and data.' <br />Limits on wastewater discharges are controlled on the state <br />level by DEM through the National Pollution Discharge Elimination <br />System (NPDES) permitting program. Based on the classification of <br />a potential receiving stream, DEM determines whether a discharger <br />is appropriate in a certain area and if so, establishes appropriate <br />effluent limits on the discharge to assure that the use of the <br />waters is not negatively impacted. Wastewater discharges of <br />certain types are prohibited in some water supply critical and <br />watershed areas. WS -I watersheds, the highest classification, are <br />protected as natural and undeveloped with no wastewater discharges <br />allowed except for groundwater remediation projects where no other <br />alternative is feasible. Restrictions on the allowance for treated <br />wastewater discharges become progressively less stringent as you <br />move to subsequent classifications. <br />In developing watersheds the effects of urban growth on water <br />quality have been documented by a number of sources. The addition <br />of built -upon surface area - such as roof tops, roads, <br />parking lots, etc., which prevent the natural infiltration of <br />rainfall into the soil surface - increases the amount of rainfall <br />that becomes surface runoff. The nature of the land uses - <br />associated with the built -upon areas also increases the types and <br />amounts of pollutants that are available to be carried by the <br />surface runoff. As rainfall runoff flows across these surfaces it <br />picks up soil particles and other pollutants. The runoff then <br />flows to surface waters where these pollutants can have significant <br />impacts on water quality. The water supply protection rules, in an <br />attempt to minimize the impacts of stormwater runoff from highly <br />developed areas, place limits on development densities. These <br />limitations are to be administered by local governments through the <br />implementation of land use management plans, zoning and ordinances. <br />In developing management strategies to minimize the effects of <br />stormwater runoff, the DEM feels that the most effective practice <br />is maintaining low density development through lot size or <br />built -upon area restrictions. Maintaining low density development <br />prevents the need for the engineered stormwater control structures <br />which are required for high density development. These structures <br />capture and hold stormwater runoff for time periods that will allow <br />for removal of some pollutants through settling and biological <br />processes. Where local governments choose to utilize these <br />structures it is essential that appropriate design, operation and <br />2 <br />