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III IIIIIIIIIIIII III <br />EX t~ti B+~ D 1 <br />Environmental Services, Inc. <br />Water Resource/Environnrental/Civll Engineering <br />July 4, 2001 <br />Loretta Van Norstrand <br />P.O. Box 773688 <br />Streamboat Springs, CO 80477 <br />Re: Letter Response To Colorado Division of Minerals and Geology <br />Camilletti Gravel Pit #2 <br />Dear Loretta: <br />[ have reviewed the letter response you faxed to me from Camilleti to the Colorado Division of <br />Minerals and Geology. There are number of concerns DMG raised about the proposed mining <br />project. Two of the issues I gleamed from purview of the document (it was not the complete letter) <br />are (1) what are the potential effects on well pumping and (2) location of the pits relative to the <br />floodplain. <br />In regazds to Milner wells and the potential effects that dewatering will have on groundwater levels, <br />I have never been involved with this aspect of the project. My focus has been on review of the flood <br />study and delineation of the floodplain. However, I will provide you c.+ith a brief opinion of <br />Camilletti's response to DMG on the effects ofdewatering. First, to answer your question "What are <br />boundary conditions?" <br />In order to simulate groundwater flow, mathematical models have been developed that <br />provide an interpretation of the physical processes that govern subsurface flow. Boundary <br />conditions are mathematical statements specifying head (water level) or the mathematical <br />derivative of head called flux (flow rate per unit area). To solve the mathematical equations <br />for groundwater flow, a boundary condition must be selected. Generally, the selection of an <br />appropriate boundary condition is the step most subject to error. <br />Physical boundaries that influence groundwater flow systems include impermeable barriers <br />(rock, clay), groundwater divides (a high point where water flows in two different directions), <br />rivers, and lakes. In order to model the effects that these physical boundaries can have on <br />groundwater flow, prescribed mathematical conditions (boundary conditions) have been <br />developed. They are (1) Specified head, (2) specified flow (flux), and (3) head dependent flow <br />350 South 39th Street .Boulder Colorado 80305. (303) 444-7977 <br />