DetentionPondConstructionProjectFrequentlyAskedQuestions(FAQ)

Whatisadetentionpond,andwhydoweneedit?• Adetentionpondtemporarilyholdsstormwaterrunoffanddelaysitbeforeflowing

downstreamintoalargerbodyofwaterforstorage.• Adetentionpondpreventserosionandfloodingbycontrollingwaterflow,andisrequiredof

builderswhendevelopingland.• OxfordMillhasadetentionpond,whichconsistsofasmallearthendamwithadrainagepipe,

whichflowsintoaplungepoolandeventuallydownacreekintotheFallsofAutryMill.

Whereisit?Whobuiltit?• Thedetentionpondislocatedonornearseveralhomeowner’spropertiesbetweenthe

cul-de-sacsofDartingtonWayandBishopswoodPlace(seeAppendix).• ItwasbuiltbythedeveloperofOxfordMillcommunityapproximately25+yearsago.

Wheredoesthewatercomefrom?

• Thewaterisfromstormwaterrunoffthatflowsfromourstreetsandpropertiesintonaturalcreeksandstreams.

• ThisdetentionpondistheprimarybasinforthelandsouthofJonesBridgeRoad,whichisapproximately260squareacres.

What’swrongwithit?

• Thereareseveralissueswiththedetentionpondthatrequireattention(seepicturesbelow).• Thedrainagepipeis54”indiameterismadeofcorrugatedmetal,whichhasalifespanof20-30

years.Becauseofyearsoferosionandcorrosiontothemetalpipe,itispronetocollapseatanytimeinthenearfuture.Ifitcollapsesbeforewetakeremedialaction,wewillbeforcedtofollowallnewbuildingcodes.Thiswilladdadditionalcoststoanyrequiredrepair.

• Thedownstreamconcreteheadwallhasbeendislodgedfromhighwaterflow,anddroppedintotheplungepool,exposingthepipeandunderlyingsoiltofurthererosion.

• Theplungepoolwasbuiltwithinadequaterock(knownas“riprap”)whichhassincedisintegratedandwasheddownstream.Thus,asignificantamountoferosionhasoccurredtotheplungepoolanddownstreamchannelwhichnowhasexposedtreerootsandsewerpipe.

• Therearenumeroustreesgrowingonandnearthedam,whichcreatearisktoitsintegrity.Wetsoilwithstormwindswillcausetreestofall.Italsouprootsthesoilandweakensthedam.

Whatisneededtofixit?

• The54”corrugatedmetalpipeneedstobereplacedwithanon-erodingconcretepipe,whichinvolvesdiggingouttheexistingpipe.

• Theplungepoolneedstobereconstructed,whichwillrequireinstallationofasignificantamountoflargeripraprock(approximately25dumptruckloads).

• Anytreesonthedamwillbecutdown,theirstumpsandrootsgrubbed,andthegroundseededwithgrassorotherformofapprovedgroundcover.

• Theworkwillrequireaccessbyheavyconstructionequipment,includingabackhoeanddumptrucks.Accesstotheworksitewillbeasignificantchallenge,andwillrequireaccessthroughadjacenthomeowners’properties.

• Thiswillbeapermanentfixthatwillonlyrequireonlysomeperiodiclandscapingmaintenance.

Whydoesitneedtobefixed?Whathappensifwedonothing?• Shouldthedrainagepipefail,stormwaterwillnolongerbeabletodrainproperly.Thiswill

createalargepoolofstandingwaterinthedetentionpond,whichwillfloodandencroachonadjacenthomeowner’sproperties.

• Waterwillcontinuetoerodethesoilonthedam.SedimentwillflowdownstreamtoimpacthomesandthelakewithintheFallsofAutryMill.Rebuildingthedamifitfailswillhaveasignificantlyhighercost.

• SedimentflowingdownstreamwillcausesilttobuildupinthelakeattheFallsofAutryMill.ThiscreatesasubstantialfinancialliabilityfortheOxfordMillHOA.ShouldtheHOAbesuedfornotproperlymaintainingthedetentionpond,wewouldincurlegalexpensesinadditiontothecoststodredgepartofthelake,whichcouldresultinfutureassessmentstoOxfordMillhomeowners.

• Forexample,somehomeownersintheFallsofAutryMillpreviouslysuedadeveloperbecausetheycausedsilttobedepositedintheirlakewhilebuildinganewsubdivision.Thedeveloperpaidupwardsof$800,000todredgeandremovesoil.Thesehomeownersarekeenlyawareofsiltaccumulationandwillgoafteranysourcethatmaycauseit.

• Notproperlymaintainingitwillresultingovernmentaldirectivesand/orfines.Whoisresponsibleforfixingit?Whydoesn’tthecity,county,orstatefixit?

• ThemasterplatfortheOxfordMillsubdivisionstates“DETENTIONPONDTOBEMAINTAINEDBYHOMEOWNER’SASSOCIATIONINPERPITUITY”(seepicturebelow).

• ThedetentionpondresidesonprivatepropertyandtheexplicitreferenceontheOxfordMillplatmakesithighlyunlikelythattheCity,County,orStatewouldvoluntarilyacceptownership.

• TheCityofJohnsCreekwebsitecontainsanFAQregardingdetentionponds.http://www.johnscreekga.gov/QuickLinks/FAQs/Public-Works-FAQs.aspx

• AlthoughtheCity,County,orStatearenotresponsibleformaintainingit,theystillhaveoversighttoensurethatthedetentionpondisproperlymaintainedbytheHOA.

Whenwoulditbefixed?Whydowehavetodoitnow?

• Thistypeofprojectrequiressignificantleadtime(about9-12months),duetothesurveying,engineering,andgovernmentalpermitting.

• ThebesttimetoperformthisworkisintheSummerorearlyFallastheyarehistoricallythedriestmonths,whichshouldhavetheleastwaterduringconstruction.TheconstructioniscurrentlyplannedtobeginbetweenJuneandSeptember2017,andestimatedtolastapproximately35workdays(or7weeks),weatherpermitting.

• Ifwedelaythefixandthepipecollapses,itwillresultinhighercosts,aswellasputOxfordMillatrisktobeliableforflooding,erosion,andsedimentdisplacementtodownstreamhomes.

• Thistypeofprojectshouldbedoneallatthesametime,asitbecomesmoreexpensiveifchangesaredoneinpiecemeal.

• BecausethisprojectwillrequireheavyequipmentandmaterialstobemovedoverOxfordMillstreets,theengineersandCityofJohnsCreekhaverecommendedthatthedetentionpondconstructionbecompletedbeforetheCityrepavesourroads.TheHOABoardisincommunicationwiththeCity’sprojectmanagerforstreetrepaving.

Whowillhelpusfixit?• TheHOABoardhasengagedSchnabelEngineering,ahighly-experiencedcivil/environmental

engineeringfirm,toanalyzetheconditionsofthedetentionpond,developengineeringdesigns,andoverseeconstruction.

• SchnabelEngineeringwillfacilitateallofthenecessarygovernmentalpermits,includingtheCityofJohnsCreek,GeorgiaEnvironmentalProtectionDivision,andtheArmyCorpsofEngineers.

• Fortheconstructioneffort,SchnabelhasassistedOxfordMilltofacilitatebiddingfromseveralcontractorsandoversightoftheconstruction.

• Wehavereviewedcompetitivebidsfromqualifiedcontractors,andhaveselectedNorthGeorgiaConcrete,Inc.,basedinDahlonega,GA.Theyhavesignificantexperiencewiththistypeofproject.

Howmuchwillthiscost?

• Theconstructionphasecostswillbeapproximately$380,000,includingremediatinghomeowners’propertiesthatwillbedamagedtoaccesstheconstructionsite.

• Inaddition,thereweresomeminorfeesforregulatorypermitsandcontingencycostsifadditionalmaterialsarerequired.

• Unfortunately,costshaveincreasedsignificantlyduetoatightlabormarketinAtlanta.

Cost ItemDescription$320,343 PrincipalContractor-NorthGeorgiaConcrete,Inc.$28,000 ConstructionOversight-SchnabelEngineering$1,035 Pre-ConstructionHomeConditionSurvey$6,600 Pre/Post-ConstructionLakeSedimentSurvey$800 ErosionControlMonitoring$25,000 HomeownerRemediation(Estimated)$381,778 Total

Howwillwepayforit?

• EventhoughtheBoardhasbeenfiscallycarefuloverseveralyearstoaccumulatefundsforthisproject,theincreasedconstructioncostcannotbecoveredbyHOAReservefundsalone.TheBoarddoesnotwanttoincreasetheannualHOAduesorrequireaspecialassessment.

• TheBoardisrecommendingfunding50%oftheprojectfromHOAReservefunds,andtheother50%throughaconstructionloan.ThisfinancingwillallowtheHOAtomaintainfundsinReserveaccountsatproperlevelstoaddressmaintenanceneedsandimprovementprojects.

• OxfordMillHOA’sbank,MutualofOmaha,providesfavorableloantermsdesignedespeciallyforhomeowners’associations.A10-yeartermconstructionloancurrentlyhasfixed-rateAPRsfor3.25%(foryear1)and4.70%(foryears2-10)andnopre-paymentpenalty.Withcontinuedfiscalresponsibility,weshouldbeabletoaccelerateloanpaymentstopaydowntheprincipalearly.

• InaccordancewithArticle3,Sections3.19(Borrowing)and3.22(Expenditures)intheOxfordMillHOABylaws,theBoardrequiresatwo-thirds(2/3)approvaloftheTotalAssociationVotetoborroworspendinexcessof10%oftheannualbudget.

Appendix

PreliminaryConstructionSchedule(assumingStartDateof7/24/2017)

Source:FultonCountyGIS

ID ID Task Mode

Task Name Duration Start Finish

1 1 PROJECT - DURATION 35 days Mon 7/24/17 Fri 9/8/172 2 BEGIN PROJECT 0 days Mon 7/24/17 Mon 7/24/173 3 Mobilize 4 days Mon 7/24/17 Thu 7/27/174 4 Erosion Control 35 days Mon 7/24/17 Fri 9/8/175 5 Control of Water 35 days Mon 7/24/17 Fri 9/8/176 6 Clearing & Grubbing 4 days Fri 7/28/17 Wed 8/2/177 7 Strip Topsoil 2 days Thu 8/3/17 Fri 8/4/178 8 Excavate for 54" RCP 4 days Mon 8/7/17 Thu 8/10/179 9 Remove Existing Structures 1 day Fri 8/11/17 Fri 8/11/1710 10 Install 72" Precast Manhole and 54" RCP 3 days Mon 8/14/17 Wed 8/16/1711 11 Pour Cradle, Headwall for 54" RCP 5 days Thu 8/17/17 Wed 8/23/1712 12 Backfill 54" RCP and Rebuild Embankment 4 days Thu 8/24/17 Tue 8/29/1713 13 Install Rip Rap Plunge Pool 4 days Wed 8/30/17 Mon 9/4/1714 14 Re-Spread Topsoil 1 day Tue 9/5/17 Tue 9/5/1715 15 Install Permanent Grassing 1 day Wed 9/6/17 Wed 9/6/1716 16 Clean Up/Demobilize 2 days Thu 9/7/17 Fri 9/8/1717 1718 18 FINAL COMPLETION 0 days Fri 9/8/17 Fri 9/8/17

7/24

9/8

7/16 7/23 7/30 8/6 8/13 8/20 8/27 9/3 9/10 9/17July August September

Task

Split

Milestone

Summary

Project Summary

Inactive Task

Inactive Milestone

Inactive Summary

Manual Task

Duration-only

Manual Summary Rollup

Manual Summary

Start-only

Finish-only

External Tasks

External Milestone

Deadline

Progress

Manual Progress

PRELIMINARY CONSTRUCTION SCHEDULE (6/30/17) OXFORD MILL DETENTION POND REHABILITATION

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NORTH GEORGIA CONCRETE INC.JUNE 30, 2017