~ DYNEGY DYNEGY MIDWEST GENERATION, LLC East Port Plaza Drive Colli nsville, IL 62234 1500 V ia UPS November 301 2017 Mr. Richard Cobb, P.G. Deputy Division M anager Bureau of Water; Division of Public Water Supplies Illinois Environmental Protection Agency 1021 North Grand Aven ue East Springfield, Illinois 62794-9276 Dear Mr. Cobb: Re: Vermilion Sit e Ash Pond Closures Options Report Enclosed please find the Vermilion site ash pond closure options report requested in your May 30, 2017 letter. Options are identified for the north, old east, and new east ash ponds at our former Vermilion power station site. The report was prepared by Stantec Consulting Services, Inc. (St. Louis, MO). It includes cost estimates for the various identified ash pond closure options and costs for associated river bank stabilization options. This report should be read in conjunct ion with t he river bank stabilization options report submitted to you on November 6, 2017 and the groundwater flow and transport modeling report that will be submitted to you in October 2018. The probable cost estim ates are based on information ava ilable at this time and should not viewed as exact cost determinations. The estimates are based upon numerous assumptions such as the viabi lity of beneficia l reuse, ability to obta in U.S. Army Corp of Engineers permits, availabi lity and costs of materials, etc. At this time, Dynegy Midwest Generation, LLC (DMG) is unable to make a recommendation as to the closure option t hat it would like to implement for each ash pond. DMG bel ieves it must wait until the hydrogeologic studies are completed in October 2018 to make a recommendation . In t he meantime, DMG wi ll proceed with Section 404 permitting w ith Army Corp of Eng ineers (Lou isvi ll e, KY District) for implementi ng river bank stab ilizat ion along the north and old east ash ponds. ECEIVED DEC 0 1 Z017 Div. of Public Water Supplies Illinois EPt We would be happy to meet with you to discuss the enclosed report. You should also feel free to call me at 618/343-7761 if you have questions about the report. Sincerely, Dyne "dwest Generation, LLC by its agent Dynegy Operating Company \ Rick Diericx Managing Director-Environmental Compliance Enclosures ( ) Stantec Stantec Consulting Services Inc. 1859 Bowles Avenue Suite 250, Fenton MO 63026-1944 November 27, 2017 File: let_vermilion_closure_IEPA_20171127 Attention: Mr. Victor Modeer, PE Dynegy Midwest Generation. LLC 1500 Eastport Plaza Drive Collinsville, Illinois 62234 Reference: Closure Options Ash Ponds Closure Vermilion Site Dear Mr. Modeer, Stantec Consulting Services Inc. (Stantec) has completed an evaluation of closure options for the North Ash Pond (NAP), Old East Ash Pond (OEAP). and New East Ash Pond (NEAP) at the Vermilion Site. For your use in responding to the letter from the Illinois Environmental Protection Agency (IEPA) to Dynegy Midwest Generation, LLC (DMG) dated May 30, 2017. please find attached a table that includes an opinion of probable cost. anticipated project duration, and a summary of each closure option evaluated. The attached figures are provided to illustrate each closure option. Details regarding the riverbank stabilization options along the North and Old East Ash Ponds are included in Vermilion Site Riverbank Assessment prepared by Stantec on November 2, 2017 and submitted to the IEPA by DMG on November 6, 2017. The riverbank improvements can be implemented prior to or in conjunction with closure construction. Stantec appreciates the opportunity to support this project. If you have any questions or need additional information, please call. STANTEC CONSULTING SERVICES INC. }4;1~ Matthew Hoy. PE Project Manager/Senior Associate Matthew.Hoy@Stantec.com Matt Vaughan, PE Senior Associate Matt.Vaughan@Stantec.com eel/ Attachments: Table 1 - Closure Options Summary Figure 1 - Close in Place (Option 1) Figure 2 - Closure by Removal (Option 2) \\us1269· ~Gl$El;i~ 17~v6'1!7Sg)Sff51iX'fe chnicoUJsu"e ........ ~Don::.:.:"'°"""·~~~~~~~~~~~~~~~ foc9y ~ .... ~"~171~11D~'~'~~~~~~~~~~~~~ Table 1 - Closure Options Summary Consldo<-.., Oplnlonol l'r-Clobilze rhe branch kJyering ond/or o tx.rSed riprap trench. ContCM.X the ash to promote positive drainage. Consolidate ash in NEAP to o smollet footprint on tho west side prio( to copping . Summary The OEAP ~oPC along the rlvort>onk will bo lotd bock to provide occou for inspoctions. mc:Wltenooce and instolotion ol riverbank stoblization. Construct on enginee 10 yeon. ,Since excovotion for benc~ rovse wit stobiize the riYCtbonk otong tho OEAP ond req...ke 10-20 vcors. stobif~o tho rivorbonlc wll requi'o 3-S yoors. stablize the rivetbont wll roqulro 2~ yoors. stoblize the rworbonk NAP. as neceuory. wUh roct too with tivo olong the OEAP and NAP. os necessorv. with along tho OE.AP and MN". os necessoy. with oiong the OEN' ond N». as necessary. with branch layering ond/Ot o b..ried tiptop trench. rock toe with frvo branch loyering ond/Of o rock toe with rive branch layering ottd/0< o rock roe with five brooch layering ortd/or o bl.Wied riprop h'onch. buried r1:>fop trench. buried riprop trench. IMoisture condition the mh .os needed. prior to loading nto trucks ond hauling ollsite. Excavate tho ash from the lhree ash ponds, if Excovote osh rrom the OEAP and ploce it in lhe,Excavare OSh from the NEAP and ploce it 11"1 lhe neces,say. condition it onsito. and then haul it NAP/NEAP. NAP. Excavate the ash from the th'cc ash ponds ondj to on offsile facl ity lor beneficial reuse. Consolidato osh in NEAP to o smoller footprint toy b<>cli: lho OW slope ~ong tho nvorbont dispose of it ot on offsite lor11::m1. to provide occcss for impections. mointononco Ash that docs nol conform to the requirements Ion tho wost sk:lo priof to copping. of boncriciol rouse wiU bo consdidotod and and lnstollolion of rivofbo nk slobMzolion. !Once 0:1 tho ash has boon removed. soil moteriol from the existing d«es w ill be used to copped with on engineered cop s~tem on-~te The NAP/NEAP ~I be cktsed in ploce with on fill !he bottom of the ll'Yee ponds to promote or disposed of at on ottsite k>ndfil. enginee- PROPOSED DITCH OVERLAND FlOW OiREC110N c::J UMllS OF CLOSURE CAP c::::::::J CLOSURE &Y CONSOLIDATION - soo l . C--.Jys-..: l ,000 Foe I N#IO ltQ~ ..... fatl fll"S1l!ll .... '1. ~DIBOr*ie, Illinois * -· Indiana P'rofKtLocotion ,_.,.,.._ ............. . __........,_ O.V/f'rot(Kt CNent: Dynegy Mtdwest Generotton . LLC ntle: Vermiion Site Project: Ash Ponds Ck>surc f.gure No. .... Option 1: Clo5e in ploco (NAP. OEAPJ: Consoktofeoshond dose in pbco (NEAP) ATTOINEY· CUENT PllVILEGED AND CONllDENTIAL () Stantec LEGEND ASH PONO 90ROER --+-- Pl!Of'OSED OOCH OVERLAND FLOW DIRECTION c:::J ll.V.ITS OF ASH REMOVAL 500 l ,<»J !!!!!!!!!!!!!!!!!!liii=="""""""""""""""""""""' Fool 1 C~~ NAO l lU~._ fld N'S l 301,_. 1~a11er.... lllinola * lndce. ATTOINEY· CUENT ,llVILEGED ANO CONFIDENTIAL () Stantec NORTH ASH POND (CONSOLIDATE 433,000 CV FROM NEAP, ASH LAVBACK, AND STILLING POND) LEGEND __.__ ____. c:::::J c:::::J ASH PONO BORDER PROPOSED OOCH OVULANO now Ol~ECTION UMITS OF CLOSURE CAP CLOSURE &'I' CONSOLIDATION .500 I.COO """""'""''""';;;;;;;;;;-..,,,,.,,,,.,,,,.,,,,.,,,,.~ - Feel l ~~""'° · ~~~fOlffPS l lO l 12.~!S*O..W Illinois * -- -lOOO.. Oonl/- Indiana ....... -. ..._.......M._.,... C5ent: Dynegy Midwest Generation. LLC Tit'8: Vermilion Sito Projocf: Ash Ponds Closure '"~"'°· 5 Title Option 5: Comob:>tc NEAP ond OEAP loybock lo NAP. close OfAP ond NAP In pbce. ATTOINEY-CLIENT , llVllEGED AND CONFIDENTIAL