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Draft North & East Metro Groundwater Management Area Plan 3-2 Objective I. Groundwater use in the GWMA does not harm aquifers and ecosystems, and does not negatively impact surface waters. Groundwater and surface waters together make up a connected hydrologic system that is affected by climate, geology and soils, land use and land cover, water use, and water quality changes.Therefore, impacts to aquifers, ecosystems, and surface waters resulting from water appropriations are related under this objective. Aquifer Sustainability The first part of this objective deals with preventing harm to aquifers.The purpose is to ensure that groundwater continues to be available for use in the future while protecting ecosystems and surface waters (described below). Groundwater use always reduces storage unless there is an equivalent increase in recharge through surface-water infiltration. Limits on appropriations can help ensure aquifer sustainability. In Minnesota Rules, parts 6115.0630 and 6115.0670,the concept of safe yield is used as the measure of limits on allowable groundwater use. The concept looks at the impact that water withdrawals from an aquifer have on aquifer water quality, levels, and pressure (sometimes referred to as 'heads'). It does not address potential impacts to other resources such as surface waters. Safe yield is defined separately for water-table aquifers and for artesian (confined) aquifers (see Section 7 for glossary of terms). For artesian aquifers, a water elevation level in an observation well (obwell) may be set as a threshold for aquifer protection that ensures compliance with safe yield (Figure 3-1).To protect the aquifer from being drawn down too far, 25 percent of the 'available' head (water height above the top of the aquifer, before pumping) must remain in an observation well. A warning threshold of 50 percent of the available head may be established to allow time for contingency plans to be put in effect if water levels decline. For water-table aquifers, safe yield is a total-use rate that does not exceed the long-term average recharge rate (Minn. Rules, part 6115.0630). In short,output (pumping) for the aquifer does not exceed input (recharge) over the long term. Again,this does not account for impacts surface waters, which are addressed in the next section. Pumping from artesian aquifers (such as the Prairie du Chien and Jordan aquifers) typically causes water from the water-table aquifer to flow down into the artesian aquifers. Therefore, safe yield should be determined based on both direct and indirect withdrawals from water- table aquifers. Water levels that have stabilized to a pattern of variations above the threshold indicate compliance with safe yield. Understanding pumping history and measured water levels is important when evaluating compliance with safe yield. Declining water levels that remain above the threshold are expected in some situations, even while use remains within the safe yield.This occurs if pumping rates gradually increase overtime, the system has not come into equilibrium with recent pumping rates, or natural fluctuations create a temporary downward trend. P51