Memo. Background. South Rochford Road Type recipient(s) here HDR, Inc. Roadway Options for Protection of Iron Fen Wetlands. Rochford Cemetery Fen

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1 Mem Date: Mnday, January 05, 2015 Prject: T: Frm: Subject: Suth Rchfrd Rad Type recipient(s) here HDR, Inc. Radway Optins fr Prtectin f Irn Fen Wetlands Backgrund Sphagnum angustiflium a U.S. Frest Service (Frest Service) Regin 2 sensitive species is likely present within the Prject Areas, specifically within the Rchfrd Cemetery Fen lcatin. The habitat fr this species f mss wuld include any fen within the Prject Areas, but the Rchfrd Cemetery Fen has a significant value due t its classificatin as an acidic irn fen. When Suth Rchfrd Rad was riginally cnstructed, it crssed thrugh the Rchfrd Cemetery Fen which resulted in fill and likely damaged prtins f the fen and altered grundwater mvement. There are als lng term effects resulting frm grund water leaching thrugh fill materials and ersin frm the gravel surface. These lng term effects caused alteratins in the verall fen chemistry, changing the habitat fr fen species. Rchfrd Cemetery Fen S. Rchfrd Rad Prject Areas A natinal fen expert, Dr. David Cper, visited the prject area t evaluate the status f the fens and prvide ptential recmmendatins fr prtecting the existing fen and imprving the

2 hydrlgic and gechemical cnditins. Dr. Cper s site visit mem is attached as Appendix A. In the mem, Dr. Cper identified three factrs that shuld be cnsidered fr prmting healthy fens f this nature: Perennial flw f grundwater Lw mineral sediment input Highly acidic water inflw He stated that when the existing radway was cnstructed; it changed the hydrlgy and chemistry f the existing fens. The changes had immediate impacts, but the radway is als gradually degrading the nature f the fens ver time. Carbnate rich limestne and dlmite materials were used fr fill which has added mineral sediment. The grundwater flw was cut ff by the rad embankment and the water supply was channelized thrugh a culvert. Dr. Cper indicated that a new radway prject shuld attempt t replace the existing fill with material that is mre cmpatible with the fens such as crushed granite. Anther recmmendatin was the use f a permeable base layer in the radway. The permeable base wuld imprve shallw grundwater mvement acrss the embankment. This memrandum evaluates radway ptins that culd be cnstructed in the build alternatives t help minimize the impacts f the radway thrugh fen areas and imprve the hydrlgy and gechemical cnditins f the fen systems. These ptins include the permeable base layer fr the radway as per Dr. Cper s recmmendatin, a bridge ver the fen crssing, and additinal cnveyance t spread the flw as it crsses frm west t east. Permeable Base / Subbase Layer In Dr. Cper s mem, he described a permeable base layer that included a carse material verlaid with a getextile separatr fabric, tpped with a finer material, which wuld be tpped with pavement. Althugh this type f pavement sectin has been used n several prjects, it is nt well dcumented at this time. Rads cnstructed with permeable base layers have been used in the upper Midwest primarily as Best Management Practices (BMPs) fr temprary access rads thrugh sensitive wetland areas. Other regins have used permeable base layers as mre f a standard practice when cnfrnted with grade limitatins that make underdrain systems infeasible. The Federal Highway Administratin (FHWA) has issued a Technical Brief thrugh the Cncrete Pavement Technlgy Prgram (CPTP) titled Daylighted Permeable Bases (2009) (the Brief). The Brief prvides infrmatin n design, cnstructin, maintenance, cst, etc. f permeable base layers that daylight t adjacent grade. The permeable layer is partially r fully expsed n bth sides f the radway, allwing free crss drainage. Belw are a few ntes and practices that were described in the Brief: Several states were listed which have develped specificatins fr permeable bases. A base layer thickness f 18 t 24 is typically cnstructed when there are cncerns with frst / freezing. The base layer can be cnstructed entirely with carser materials, but it is cmmn t use a layer f carse material tpped with finer material (maximum particle size f 2 ).

3 A getextile separatr fabric shuld be used if there is fine material present that culd penetrate and plug the permeable layer. The expsed edges f a daylighted permeable layer shuld be visually inspected nce per year with maintenance cnducted as necessary. Maintenance includes remving debris, weeding, and flushing the edges with water. The cst t cnstruct a radway with the permeable base layer ranges frm 100% t 120% f traditinal cnstructin csts. Figures 1 and 2 shw examples f the daylighted permeable base layers. The permeable layer used fr the Suth Rchfrd Rad crssing wuld be designed t cnvey bth surface water and shallw grundwater. A culvert culd als be incrprated t handle sme f the baseflw and t prvide a secndary rute fr snwmelt runff if the base layer were t freeze. The permeable base wuld still serve its purpse in cnnecting the grundwater flw acrss the radway and prviding a media fr spreading ut sme f the flw at the crssing. Figure 1. Daylighted permeable base n US 50 in Kansas (Gisi, Brennan, and Luedders 2004). Permeable Layer Figure 2. Partially Daylighted Permeable Layer

4 Bridge Over Fen Crssing Anther ptin fr aviding impacts and imprving fen hydrlgy wuld be t span the fen crssing with a bridge. Based n the identified fen area fr the envirnmental study, the bridge wuld need t be apprximately 150 feet in length. Depending n the amunt f desired clearance fr the bridge, the radway prfile wuld need t be elevated up t a length f apprximately 500 feet in each directin leading up t the bridge. The resulting earth embankment wuld create additinal cnflicts with the fen n the east side f the radway, s a retaining wall wuld likely need t be cnstructed in rder t avid further impacts. Althugh a bridge wuld pen up the fen crssing area fr pssible restratin, the cnstructin prcess wuld likely include sme negative impacts. The existing crridr is very restrictive with the narrw radway, rck slpe n the west side, and fen areas n bth sides f the rad. Cnstructin f a bridge wuld als require large equipment fr driving piles, cnstructing abutments, setting retaining wall panels, hauling materials, and setting beams in place. The disturbance that is expected with cnstructin culd have a lasting impact n the fen. Installatin f a permeable layer wuld still be necessary with this ptin in rder t imprve shallw grundwater flw acrss the crridr. Alng with the bridge structure and elevated radway cmes a ptential fr ersin. Careful detail wuld be required t prevent any lng term ersin issues. The area under the bridge will nt be able t sustain vegetatin. It wuld likely require a rck lining, which can becme mbile during a large runff event. Hwever, the ptential fr ersin wuld be significantly lwer than the gravel rad which is currently in place. The cst f a bridge structure with retaining walls wuld als be significantly larger than the ther ptins. A frmal cnstructin cst estimate was nt prepared fr this analysis. Additinal Surface Water Cnveyance There is an existing culvert at the fen crssing due t an abandned radway n the west side f Suth Rchfrd Rad that lies nrth f fen. Runff travels frm suth t nrth until it reaches the abandned radbed, where it is then channeled east thrugh a culvert under Suth Rchfrd Rad and int the east fen area. There is als flw frm the west cming ut f the fen which passes thrugh the same culvert. The existing culvert has cnstant baseflw and is linked t sme ersin issues adjacent t the radway. A number f ptins were cnsidered t replace the single pipe culvert crssing that currently exists. Additinal surface water cnveyance culd be prvided thrugh a bx culvert with a wide span r multiple pipe culverts at the crssing lcatin. An underdrain system with multiple utfalls was als cnsidered. The underdrain system wuld cnsist f multiple sltted drain pipes installed transverse t the radway. The pipes wuld daylight n the east, dwnstream side f the rad. Althugh this system culd aid in spreading ut the flw as it discharges n the dwnstream end, it wuld likely result in remving shallw grundwater which is vital t the fen s sustainability. Anther variatin f this wuld be t create a lw pint in the underdrain piping belw the radway. The sltted drain pipes wuld hld water and functin as a siphn. This layut wuld reduce the amunt f water that is extracted frm the grund, but wuld nt

5 prvide enugh capacity fr the surface water runff. The piping may als experience clgging ver time due t the small diameter and the lw pint in the alignment. A mre viable cnveyance ptin wuld be a wide bx culvert r a series f culvert pipes. The additinal capacity wuld likely help with the ersin issues and imprve bank stability. Special grading wuld be required t ensure that the flw enters and discharges frm the culverts in a manner that minimizes impacts t the upstream fen while imprving the dwnstream distributin. Prper installatin f the added culvert(s) and the assciated grading wuld result in additinal disturbance f the fen areas. In rder t reduce ersin frm the radway, the culvert crssing shuld be extended further int the fen area with shaping arund the ends. This ptin wuld nt prvide significant imprvement t the shallw grundwater flw. Evaluatin A number f factrs shuld be cnsidered fr evaluating the prpsed fen crssing. The first fur factrs shwn in Table 1 were ranked as a psitive (+) r negative (-) change ver the existing cnditins (). Fr the last three factrs (prject impact, cst, and maintenance), the three ptins were ranked against each ther. All three f the ptins will prvide an pprtunity t remve the existing carbnate material and replace it with materials that are mre cmpatible with the fens. The surface drainage and hydrlgy shuld als be imprved by all three ptins. The shallw grundwater hydrlgy shuld be imprved with the permeable base layer and the bridge. All three ptins prvide an pprtunity t address the ersin cncerns. The permeable base layer will have the smallest ftprint and shuld have the least verall impact t the adjacent fen areas during cnstructin. The main drawback with the permeable base layer wuld be the maintenance required t keep it functining prperly ver time with regard t surface flw. This culd be addressed with a culvert t add redundancy t the drainage system. The permeable base layer is the recmmended ptin because it has the least cnstructin impacts n the existing fen system while enhancing the hydrlgy dwnstream frm the radway. It als prvides an pprtunity t remve the carbnate fill materials which are degrading the fen. Implementatin f the permeable base layer will result in an imprved verall situatin fr the fen areas relative t the existing cnditins. Table 1. Evaluatin Factrs fr the Fen Crssing. Carbnate Fill Material Surface Hydrlgy Grundwater Hydrlgy Ersin Prject Impact Cst Maintenance Permeable Base Layer Bridge ver Fen Crssing Additinal Cnveyance