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Of Cp DEPARTMENT OF NATURAL RESOURCES <br /> DIVISION OF WATERRESOJRCES <br /> jobn ffcRft%WW <br /> e <br /> 18Mike T <br /> January 31, 2011 �em�biret6m <br /> Dick Wolfe,P.E. <br /> Directar/5tam Engineer <br /> David L Nettles,P.H. <br /> Divi6m Engineer <br /> COLBY J. HAYDEN <br /> DEERE&AULT CONSULTANTS, INC. <br /> 600 S. AIRPORT ROAD, BLDG A, STE 205 <br /> LONGMONT, CO 80503 <br /> RE: LA POUDRE AGGREGATE MINE(WDID 0303010)—DRMS M1983090 <br /> SLURRY WALL LEAK TEST 5OR LA POUDRE RES NO 3 (WDID 0303376)& <br /> ir <br /> LA POUDRE RES NO 4(WDI10 <br /> '0303377) <br /> WATER DIVISION 1,WATER DISTRICT 5 <br /> Dear Colby: <br /> Our_letter dated .January' 3, 2011.-expressed condefris regarding the use of 100% <br /> predpitation in:the mass,balanoe equations, and the lack of discussion regarding any- <br /> 0m ge in.storage volume, Your email doled Januxt 20, 2011 responded to those- <br /> c*mh*nts: The purpose of this letter is to respond to your email. <br /> Ste Volume <br /> The supplemental information and discussion within your email is sufficient to accept the <br /> claim of negligible change in 'storage volume. Therefore we approve not including this <br /> volume in'throe mass balance equation for this leak test. <br /> Precipitation <br /> Our position, as stated in the January 3, 2011 letter, is that 100% of the rainfall does not <br /> make it to the pump and therefore 100% should not be used as a credit against pumping. <br /> This is important as the more rainfall that can be shown,to flow through the pump, the less <br /> ground water infilo k would be documented during the leak test. Thus an overestimation of <br /> rainfall leads to an underestimation of ground water Wows. In an effort to show accepted <br /> common practice,your email provided a list of eighteen other approved leak test that Deere <br /> &Auk was involved with and all of which used 16A precipitation.- I reviewed nine of those <br /> tests whose data I had readily available. <br /> Of those nine sites, one reoorded no rainfall data during the test and therefore did not <br /> include.precipitation in b mass balance equation, four elected not to use rainfall data as it <br /> would have produced a negative leak value, and the other four would have passed <br /> regardless of the rainfall percentage Used. In the "Shores Ponds A Leak Test Report° in <br /> discussing why precipitation was riot included you state "Including the prec#*ation values, <br /> results in a negative leakage value. This is likely due to a significant portion of the rainfaft <br /> infiltrating into the so# and being taken up to replace soil moisture in the dry soils rather <br /> than resuking in effective runoff at the dewatering sump.' Indeed, our standard for effective <br /> precipitation (that portion of rainfall that infiltrates into the soil and is taken up to replace soil <br /> moisture)when looking at historical consumptive use Is 70% bf total precipitation; a value in <br /> line with the statement of!a significant portion." <br /> Water Division 1 • Greeley <br /> 810 911,Street,Suite 200•Greeley,CO 80631 •Phone.970 352-8712•Pax 970-392-1816 <br /> http://water.state.co.us <br />