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Home My WebLink About20190866 Ver 1_Notice of Initial Credit Release - NCDMS Huntsman Mitigation Site_20221007% &V WILDLANDS ENGINEERING October 6, 2022 ATTN: Ms. Kim Isenhour Mitigation Project Manager, Regulatory Division U.S. Army Corps of Engineers 69 Darlington Avenue Wilmington, NC 28403-1343 RE: Huntsman Mitigation Site - MYO Report Comments Yadkin River Basin — CU# 03040102, Wilkes County USACE Action ID No. SAW-2019-00836 NCDWR Project No. 20190866 DMS Project ID No. 100123, Contract # 7891 Dear Ms. Kim Isenhour, Thank you for your comments in the email dated September 14, 2022 referencing the Huntsman Mitigation Site Monitoring Year 0 (MYO) Report. Wildlands Engineering, Inc. (Wildlands) has reviewed these comments and our responses are noted below. A georeferenced CCPV map has been included with our responses as requested. A photolog has also been included to aid your review. Kim Isenhour, USACE: 1. In addition to DWR's concerns, please confirm what size rock was used in the constructed riffles on UT1. As I recall, there was degradation on a steep section near STA 210+50 (?). DWR expressed concerns about the size of the material used; and questioned whether using larger rock in these riffles and embedding some Class I and only top dressing with any remaining on -site smaller material may have been more appropriate. Please provide more detail on this repair. Wildlands Response: Displaced riffle material was removed from pools and larger stone was embedded into the affected riffles. Furthermore, Wildlands plans on installing larger sized stone as a coarse base with smaller stone used to cap and fill in the voids of the larger stone. Erin Davis, NCDWR: 1. The PP14 photo shows the Ingle Hollow Road culvert. In response to WRC's draft mit plan review comment regarding the perched culvert being an aquatic passage barrier, a sill was to be added downstream setting the elevation to submerge the pipe outlet six inches. Based on the photo it's difficult to see if water is being backed up into the culvert. Please confirm that the structure was installed as noted and the barrier has been abated. Wildlands Response: The downstream sill was installed at the correct elevation; however, the stream flow is piping around the sill and lowering the water surface elevation at the culvert's outlet. Wildlands will repair this issue but since construction equipment will be needed, the repair may be delayed until late 2022 or early 2023. Photos are included in the attached photolog. 2. The photo of veg plot 2 appears to show exposed soil with no signs of germination or straw cover, unlike the other veg plot photos. Has cover/stabilization of this area been addressed? Additionally, please watch for rill formation and sediment migration along graded slopes that were not matted (e.g., PP8 and PP9). Between working with pond bottom sediments, areas of priority 2 and very steep side slopes, DWR is concerned about sediment movement within and adjacent to the site becoming a stream pollutant risk beyond initial construction. Wildlands Response: As shown in the photo for VP2 on the attached photo log, herbaceous cover has become established. Wildlands acknowledges the IRT's concern about rill formation and potential sediment loading and will make sure to inspect these areas during site visits. Currently, rill formation in P2 areas is of little concern and photos of the well vegetated hillslopes in the vicinity of PP8 & PP9 are included in the attached photolog. 3. The step pool conveyance BMP photos for Old Bus Branch (PP27) and Rifle Trib. (PP23) appear very different, with Rifle Trib. having significantly more riprap. What facilitated the Rifle Trib. BMP design change from a vegetated BMP to a riprap step pool conveyance channel? It seems the vegetated BMP would offer more water quality benefits. Wildlands Response: The approved Mitigation Plan showed the BMP on Rifle Tributary as a BMP with a rock weir and a rip rap outlined channel rather than a "vegetated BMP" The BMP was changed to a Step Pool conveyance channel in the final design stage. A copy of the BMP detail from the Mitigation Plan is included for your review. 4. Since a permanent veg plot was shown in the UT1 lower pond bottom in both draft and final mitigation plan monitoring figures, DWR did not require one in our review comments. However, since that veg plot has been changed to a mobile plot, DWR is now requiring a permanent veg plot within the UT 1 lower pond bottom. Wildlands Response: A permanent vegetation plot (VP13) has been added along UT1 in the lower pond bottom, and vegetation data will be collected with MY1 monitoring. See Figure 3.1 for the location of the added permanent vegetation plot. 5. IRT members expressed concerns about the proposed buffer widths during the mitigation plan review. One reason DWR was concerned about narrower buffers along UT1 was that it meant steeper side slopes, which as the redline shows resulted in multiple riprap lined ditches not planned for in the initial design. Of particular concern is that four of the riprap ditches are in the vicinity of existing chicken houses. Please provide more information on the necessity of adding the riprap ditches. How does this affect the mitigation plan Section 3.4 functional uplift to "diffuse overland non -point source pollutants from adjacent land use"? Additionally, Sheet 1.1.5 shows added riprap covering an existing wetland area. If this was/is a jurisdictional feature, why wasn't a non -hardened stabilization option applied? % &V WILDLANDS ENGINEERING Wildlands Response: Initially the terrace slopes in the left floodplain of UT1 were implemented as designed. (It was the intent that the run-off between the chicken houses would rise and sheet flow down the hillslope from the ridgeline.) Unfortunately, after a few rain events it was evident that the run-off was forming drainage features of concentrated flow and leading to stability issues; therefore, the implementation of the riprapped swales was necessary for terrace slope stability. In order to maintain functional uplift, most of the swales end at the toe of slope to encourage diffuse flow before entering the stream. In addition, based on previous experience, it is anticipated that herbaceous vegetation will become established within the drainage swales over time and provide an additional measure to diffuse run-off. The wetland discharging into North Little Hunting Creek Reach 2 had been permitted for permanent impacts. Based on past experience, it was anticipated that fill measures may need to include some hardening material to stabilize the area of concentrated discharge from the wetland. Riprap was chosen to provide a long-term stabilization measure that would prevent bank erosion along the main channel and subsequent headcut migration across the floodplain. 6. Section 3.3 noted a couple riffle cross sections were larger than designed. Are these areas shown on the redline drawings? If not, can you please identify the locations. Wildlands Response: None of the noted cross -sections (XS) were shown as red lines on the record drawings. The two cross -sections were XS4 on North Little Hunting Creek Reach 2 and XS16 on Barn Branch. 7. Please add stream and reach labels to the CCPV Figures 3.1 and 3.2. Wildlands Response: Stream and reach labels have been added to the CCPV Figures 3.1 & 3.2. Copies of the revised figures are attached. As requested, Wildlands has provided written response to the IRT's comments, as well as georeferenced figures, prior to the site visit on October 13t". We have also included a photolog for additional information. A copy of this comment/response letter and associated documentation will be included in the Appendix of the MY1 Report. If you have any questions, please feel free to contact me. Thank you! Sincerely, 4 -. s, �, Aaron Earley Project Manager aearlev@wildlandseng.com 1 s 1Rea 19 m I �` 1 1 + 1140 I I' Reach 3 1 1 o- IngIJ HoIIow Rd - 1 `+ 1 ,I each Ingle Hello Rd • Reach 1£• I O + -North ff eNunfin9 Creek I + J�ti 1 1 + I *+ J Reach 4 - Reach 3 01 Branch O + + + a + + �-o G Reach 1 a I \q —cam 4 Aerial Photography 1 404 1 1 , 1260 Figure 3.1 Current Condition Plan View WILDLANDS Huntsman Mitigation site ENGINEERING 0 100 200 Feet t Yadkin River Basin(03040102) I I I I I Wilkes County, NC 0 Project Parcels _j Conservation Easement _ Restrictive Covenant Utility Easement 11 Internal Crossing ® Existing Wetlands - Structures Stream Restoration Stream Enhancement II BMP No Credit Non -Project Streams x — Fence -- Top of Bank Topographic Contours (20') Vegetation Plots - MYO QCriteria Met (Permanent) Q Criteria Met (Mobile) Cross -Sections BaroTroll $1 Crest Gage Photo Points Q Reach Breaks Reach PP17 I �PP23 t + ' t ....'ZZo r .... 41 - Figure 3.2 Current Condition Plan View Huntsman Mitigation Site WILD LANDS ENGINEERING 0 100 200 Feet Yadkin River Basin(03040102) I I Wilkes County, NC IRT MYO Comments Photolog NCDWR Comment 1(Erin Davis) — Ingle Hollow Road Culvert — Stream flow is piping around the sill and lowering the water surface elevation at the culvert's outlet (09/27/2022). 6 NCDWR Comment 2 (Erin Davis) — UT1 Reach 1 PP8 & PP9 — Herbaceous cover has become well established on the hillsides of UT1 (09/27/2022). NCDWR Comment 2 (Erin Davis) — VP2, North Little Hunting Creek Reach 2 — Herbaceous cover has become well established in this area (10/03/2022).