2003-10-14_REVISION - M1992069 (2)

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Ms.Kaie Pickford Division Of Minerals and Geology October 8, 2003 Page 3 oj4 Wells identified as domestic use are located east and southwest of the' existing permit boundary. However, wells listed as domestic use in this particular area are not typically used for drinking water purposes since other domestic water supplier taps are available. Additionally, it is believed that the local groundwater gradient is towards the north and the Cache la Poudre River. Domestic wells near the future groundwater lake are, therefore, up-gradient or cross-gradient from the lake. 4. Since the stormwater drain is not yet constructed, no surface water runoff is available for analysis. The potential surface water runoff quality collected by the drainage system was evaluated in the text of TR-005. Based on City of Greeley programs and practices For stormwater quality protection, the watershed characteristics, and the design of the stormwater channel itself, it is anticipated that stonnwater delivered to the future groundwater lake will not significantly impact surface water or groundwater quality. The City of Greeley recently applied for coverage under the Colorado Phase II Municipal Stormwater Discharge Permit. The measures under this permit include public education and outreach, public participation/involvement, illicit discharge detection and elimination, construction site stormwater runoff control, post-construction stormwater management, and pollution prevention/good housekeeping for municipal operations. Once applied, these measures have been shown to significantly reduce most pollutant concentrations in urban runoff. It should also be noted that the City of Greeley operates separate stormwater and domestic sewer systems. Therefore, during major storm events, there is no possibility of domestic sewer overflow into the stonnwater channel entering the site. Additionally, the groundwater lake will only receive stormwater flows that exceed the 5-year stormwater runoff event (please reference the North Eagleview Regional Detention Pond Concept Phase Report). Base flows from the stormwater drain system and flows from more frequent minor stonnwater events would not flow irito the future groundwater lake. These base flows and frequent minor stormwater flows typically contain the highest concentrations of potential contaminants. During major stormwater events, such as those that would be expected to reach the future groundwater lake, the concentration of potential contaminants in stormwater runoff is significantly reduced by the large volume of stormwater produced. During major stonnwater events, stonnwater flows entering the future groundwater lake will be passed through the lake. The lake is not intended to provide a major source of groundwater recharge: It is predicted that during the 100-year stormwater event, the lake surface will only rise 2.5 feet and will return to the normal surface elevation within days (please reference the North Eagleview Regional Detention Pond Concept Phase Report and North Eagleview Regional Detention Pond Design Report). The limited amount of time that the lake surface elevation is above the surrounding groundwater table will significantly limit the amount of surface water recharging the local groundwater from the lake. 5. Adjacent landowners are provided on the attached Figure l .