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<br />TRAPPER ~INIp6 I1~C. <br />AUG u 5 1996 <br />July 31, 1996 t M~nora~c ,~ i.,.~ulla;;'. <br />Di~lulOn u <br />Mr. Joseph !. Dudash <br />Environmental Protection Specialist <br />Colorado Division of Minerals & Geology <br />1313 Sherman Street, Room 215 <br />Denver CO 80203 <br />Dear Jce: <br />$ubj.: Ground Water FSeld Sampling at Trapper Mine; Permit No. C-81-010 <br />Trapper Mine recently received wtrespondence from you dated lone 25, 1996 concerning our methods of obtaining <br />ground water samples. Specifically requested was that Trapper review its ground water sampling techniques con- <br />cerning the evacuation of three well bore volumes before obtaining water samples for field and chemical analysis. <br />Attached is a letter from Mr. George Hoffman of Hydro-Engineering, Trapper's consulting hydrologist. Mr. <br />Hoffman explains the ground water sampling techniques used at Trapper. In many cases, obtaining three casing <br />volumes cannot be achieved even with pumping either due to low yields from wells or the large quantities of water <br />in the deep wells. Therefore, stabilisation of field parameters during pumping is also used and has proven to be <br />reliable. The difficulty in effectively bailing three well bore volumes is also presented. Mr. Hoffman agrees that <br />bailing a sample from the perforated interval of the well should theoretically yield a representative sample. Addi- <br />tionally, bailing three bore volumes is extremely difficult under the circumstances encountered al Trapper Mine. <br />Also, it is noted that no consistent differences in water quality analysis have been observed between the bailed and <br />pumped samples.. <br />I would support Mr. Hotfrnan's proposed alternative to sampling Trapper's wells on a quarterly basis. Trapper <br />would propose to revise our ground water sampling scheme to exclusively use pump tests on asemi-annual basis. <br />Semi-annual pumping would produce more water from these wells while assuring sampled ground water in the <br />well casing is fresh. Additionally, quarterly sampling has shown little if any significant changes in Trapper's <br />ground water regime. Semi-annual sampling would still provide the necessary information to morritor any effects <br />of rttining to ground water in the permit area. Sampling would be performed in May/June and September/October <br />each year. <br />Please contact me if you require additional information concerning Trapper's ground water sampling. Tf this pro- <br />posed approach to our sampling program seems acceptable to the Division, a revision package will be submitted. <br />Sincerely, <br />~~~ <br />Forrest V. Luke <br />Environmental Manager <br />LWH/pb <br />tOM4\960'lll~ <br />~~~ II~I~~~I~~~~~'~~ <br />Env! <br />c File 10937 <br />Hyd~o-Enpnmv~g <br />P.O. Box 187 <br />Craig, Colorado 81626 <br />(303) 824-4401 <br />