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Mr. Joe Intermill May 6, 2005 ` Page 3 CIVIL RES'~URCES,LLC ENGINEEg9 & PLANNEg9 Summary of Chronoloov We onginally proposed that the mine dewatering volume-be conveyed through the box culverts and/or. ciroular pipes direcfly. CDOT responded that they did-not believe the structures had sufficient capacity to. convey this flow along with the storm flows that would be tributary to each stmcture. We demonstrated that these stnuctures do have morothan adequate capacity and CDOT subsequerifly rosponded. that they would not allow any of the dewatering volume to be conveyed through the box because of erosional concems. We . offered to discharge the water in an encased pipe through the' box culvert or inside the existing circular pipes (pressurized discharge pipe inside.an encasement pipe that would be inside a concrete box culvert orpipe) and to add riprap erosion protection as necessary to address their concems with regard to erosion. CDOT responded that they just weren't going to allow any discharge of water under the highway through the ezis$hg structures because if this project was allowed to discharge through these §trirctures then they would have to let everybody else. We stated that we do not believe anybody else has a legal right or desire to access the subject property (that is Private) owned Y ) through ihese:culverts. Further, the Porter Seepage Ditch and the Ogilvie Seepage Ditch have the legal right to return water to the South Platte River.- Historic Use Historically; these culverts have Civil Resources' staff stood atfb Schriever) during oursite iiiSiCar Seepage ditch an~(lirough the 6 groundwater front agricultural~iitL' the surrounding land owne~s;`ob: functronmg discharge aonveyanci response toCDOT's ctei~that t,t do you meanthose rigfifsr~ve every Ume I itngat y fie ~ before CDOI'"acgt~dits H~ subject to prior ngh'~sof (jjese• ttcl R~~ 'en used for flow from fait water return ditches from the agricultural lands; op~ofthe erosion.escarpment with DMG staff (Erica Crosby and Tom watched agricultural return water being discharged to the Porter ',culvert. The sources of retum:ivater have.historically included anc{surface rights'th'at were used to rmgate't~e~eieps• Tesfimony from v~d use 6f the ditches foragncultural re'tum ffoivs aruf~flte preserice of rs phhysical proof that this rs an histoncuse of these stme~h`res. In e seet3age drtches`may have beer abandon d; ~eba~ndoned, );watch my tarlwater floxrthrou -Mr ~~mksaid °What rer~`iot``e~f`iat the seepage ditches (late 1806gs'~ero o ~dotn9es SS°~nght-et wayr(1950's);and therefore the higfiway n~tttof way is .. ~ - ~ ~ ~, a; . Other mitigating factors with regard to use of the existing structures to convey drscharge'water include• 'The miner is rosporisible for repair of any damage resulting from discharge from the site.. The DMG would require corrective actions if any erosional damage is observed. • ~ Based ogexperience on other.sites (with larger saturated thickness, coarser a 99re9ates and .larger acfjve mining area) we believe that 10 cfs is a more realistic estimate. We intendto. use: (1) 2 to 4 cfs of this flow to recharge the aquifer upstream of the project to as a hydrologic mitigafloh measure; (2)1to 2 cfs in the gravel operation (washing, dust suppression, concrete production); and (3) evaporation and natural silt pond infiltration will further reduce the discharge volume from the site. ~... Bu1TE ZC9 ~ P.O. Bpx 6B^ ~ FaEOEgIaK,~ CO 80530 ~ (303) 833-141 ~6 ~ (3C3) 833.285p • Fnx