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InterotFfice Memo ~ ~~~ ~~- • •~ <br />To: Roger E. Moore ~ ~ <br />From: Cilen A. Miller <br />Date: February 21, 2006 ~ ~ ~ ~ <br />RE: 20 Road Gravel Pit -Monitoring Program ®~~~ Jun, [;,,. , <br />Laivf :i~„ .. . <br />Regulatory requirements and possible impacts from groundwater changes due to the mining <br />operetions require ground water monitoring. Mr. Steve Shucy of Department ol'Natural Resources <br />has identified the large wttonw•ood trees on the Fawcett propeny as potentially being impacted (a <br />two foot decline in water level can kill a cottonwood tree). There is also a pond south of the <br />cottonwoods and a lake south of the site; both may be affected by pit dewatering. <br />Monitoring groundwater is done via shallow wells, and must be designed to: <br />1. Provide a "baseline" of conditions prior to mining <br />2. To track and evaluate changes as mining progresses <br />3. To assess changes toward and define a "post-mining" baseline <br />4. To provide adequate information to design, if needed, any remediation to the <br />groundwater system. <br />Monitoring Test Vlrells (2" PVC, about 20' depth, perforated from 10'-20') <br />L Initial wells - 15 total, 7 around perimeter, 5 in mining azea (see attached map for <br />tentative location) and three additional wells on the perime[er completed as dual <br />cased,(onc pipe to 30 feet depth perforated from 28 to 30 feet in the Mancos shale <br />and scaled with hcntonite to 20 feet. and then a normal 20 !-oot pipe perforated from <br />IO-20' perforated in Alluvium). this will provide pre-mining "baseline" on the <br />~tancos. Note that there may be significant seasonal changes in the water table. <br />2. Prior to mining, install 12 additional w•clis in 6 rows of 3 (1 initial well and 2 <br />additional) perpendicular to the pit to determine and track groundwater gradient into <br />the dew•atering area (see attached map for tentative location). <br />3. Complete 3-5 ofl=site wells to the NVl', on D.O.T. right of w•ay as part of the permit <br />system. These wells would be between the pit and the cottonwoods and pond. <br />~. For each well, survey in location and top of casing elevation. <br />Monitoring -Testing <br />1. Water levels are of primary interest -most can be done by owner. Frequency of <br />measurement will be tied to rate of water level change (e.g., most frequent during <br />initial dewstering; probably monthly during operations in non-affected wells. <br />Concenuzttc on wells between pit and Cottonwood trees and Lakc. <br />2. Water Quality -much can be done by owrott if test instruments arc purchased, or <br />done by consultant. Need field data (ec-t-pH) initially, select perhaps 2-5 wells for <br />laboratory analyses (major ions, Se). Future data frequency will be tied to changes <br />in water levels and water quality data results. <br />3. Permeabiliq• testing in several wells would allo+v predictions of water level <br />draw•down and pumping rates <br />