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[nn,r.r n,~t. V, w.,re u. <br />May 9, 2006 RECEt .~ Ep <br />Ms Erica Crosby MAY ~ ~ <br />Dwisron of Minerals and Geobgy <br />1313 Sherman Street. Room 215 rr''10101 "r hr'nn+I+ and nieotopy <br />Denver, Cobrado 80203 <br />RE: Hall-Irwin Corporation. Application No. M-2006.003 <br />ParkeriDersham Sand and Gravel Resource; May 8, 2006 Groundwater Model Review <br />Dear h!s Crosby <br />Following is our response to your Adequacy Review dated May 8.2006. Groundwater Modol Review. 'Parker- <br />Dersham Gravel rdme' Hall-rrwm Co~,~orahon Frle Af-?006 003 Claes Pr:nn!t <br />1. The applicant must commit to a groundwater level monitoring program with monthly water level <br />measurements at the six (6) existing piezometers throughout the life of the operation, or until such <br />time that the Division determines that the monitoring schedule of groundwater levels at the Parker <br />Dersham Gravel Mine maybe revised or is no longer needed. <br />Hall-Invn commas ro rror•~rtor groundwater levels montnly a; the six ex~stno a!ezometers throughout the hfe <br />of tf>e mme. or unld such time that the D!vrsion detertmnes !hat the monitoring suiedule of groundwater <br />levels at the Parker-Dersham ;,ravel Mine may be revised or s no longer seeded Half-irwm will submit this <br />!n!ormat,on to the Division with their annual report or upon request If groun:fwater levels drop below the <br />trigger level ;he Drv!sion well be notiF?d <br />2. The applicant must commd to an action level or' trigger" that will prompt the need for mitigation <br />measures to be implemented. (The Division suggests that the applicant consider a trigger of 3' <br />beyond the observed baseline groundwater elevation, as the natural seasonal fluctuation at most <br />piezometers appears to be 2'1 <br />The appticant wdl commd to a trigger response in the event :he mmrng phase of the opprahon causes a <br />drawdown of three feet or greater The miner w,ll first ~nstau a temporary piezometer near the neighbonng <br />well and water level readings will be taken everyday for one week to determine if the water level reading is <br />accurate (unless !t !s observed mat immediate action rs necessary) Surrounding grourdwater stresses <br />(other mines dewatenng farmers runn!ng pumpst wdl betaken mto account during this week observat!on <br />perwd The average observed water level and the surrounding stresses wilt than be used to determine the <br />correct m~bgaGon measures per ;he Section 4 2 t m Ine Groundwa!er Study <br />3. The applicant must specify provisions for reporting of action levels encountered during mining as <br />well as the reporting of annual water monitoring data and summary results to the Division. The <br />applicant may also want to specify measuring criteria to be used to verity that a true exceedance of <br />an action level has occurred. <br />As discussed above m comment 2 the applicant wdl measure groundwater levels for one ~,wek and generate <br />a report descnbmg what was observed and if mitigation measures will be implemented The Drv~swn NnA be <br />notified if groundwater levels drop below the tugger level as discussed m comment i <br />iS! ^, x Siue[~. Swr[ 209 ~ O.D. Bax 6B0 • Fwc oER~c x. CO 8.--- _: • r 433-1 •i 16 ~ (303: 83 x-2850 - res <br />