No-Rise Certification for Georgia-Pacific Toledo Llc 15- and 30-Acre Ponds on the Yaquina River Toledo, Oregon

ENGINEERING CERTIFICATION NO-RISE CERTIFICATION FOR GEORGIA-PACIFIC TOLEDO LLC 15- AND 30-ACRE PONDS ON THE YAQUINA RIVER TOLEDO, OREGON March 25, 2020 This is to certify that I am a duly qualified registered professional engineer licensed to practice in the State of Oregon. This is further to certify that the attached report supports the finding that the grading inside the 15-acre and 30-acre ponds of the Georgia-Pacific Toledo LLC facility on the south side of the Yaquina River in Toledo, Oregon as shown on plans titled “Stockpile Plan and Profile” (dwg no. 6166-18-0843-C-FIG-21 Revision C dated April 16, 2019), if constructed in substantial accordance with the horizontal and vertical alignments shown on the drawings, copies of which were provided to Wood Environment & Infrastructure Solutions, Inc. (Wood), will not change the 1-percent-annual-chance (100-year) regulatory (base) flood elevations or flood conveyance on the Yaquina River at published or unpublished cross-sections in the vicinity of the proposed ponds. There are no mapped floodway or cross-sections in this reach of the Yaquina River, so no floodway would be affected by this project. The attached report dated March 20, 2020 supports this finding. This certification was prepared exclusively for Georgia-Pacific Toledo LLC (GP) by Wood Environment & Infrastructure Solutions, Inc. (Wood). The quality of information, conclusions, and estimates contained herein is consistent with the level of effort involved in Wood services and based on: i) information available at the time of preparation, ii) data supplied by outside sources, and iii) the assumptions, conditions, and qualifications set forth in this report. This No-Rise Certification is intended to be used by GP for the proposed ground surface grading within the 15-acre and 30-acre ponds and behind the berms for those ponds only, subject to the terms and conditions of Wood’s contract with GP. Any other use of, or reliance on, this report by any third party is at that party’s sole risk. While this report was prepared in accordance with standard engineering practice by qualified engineering professionals, GP should understand that this report evaluated a specific storm recurrence interval and assumes free-flowing hydraulic conditions on the river-side of the berms. It is reasonable to assume that a storm event of greater magnitude or that changes in water-way conveyance capacity might cause higher stages than estimated for this assignment. March 25, 2020 Seth Jelen, PE, CFM, CWRE Wood Environment & Infrastructure Solutions, Inc. 15862 SW 72nd Ave Suite 150 Portland, Oregon 97224 Phone: (503) 639-3400 Page 1 of 1 Wood Environment & Infrastructure Solutions, Inc. 15862 SW 72nd Ave., Suite 150 Portland, Oregon 97224 USA T: 503-639-3400 Memo www.woodplc.com To: Georgia-Pacific Project: 6166180843.4.3 From: Seth Jelen, PE, CFM c: Project File Tel: 503-636-1908 Date: March 25, 2020 Subject: Base Flood Elevation Study for the Yaquina River Toledo, OR Wood performed a Base Flood Elevation (BFE) Study for the Yaquina River near Toledo, Oregon (Figure 1). This study found that the proposed project would have no effect on BFEs or flood storage volumes in the Yaquina River outside the berms. This study was performed to meet requirements of Lincoln County. Attached to this Memo is a No-Rise Certification. The river reach studied was from about river mile (RM) 12.9 (downstream of Butler Bridge) to about RM 14.6 which is the upstream extent of the detailed flood insurance study by the Federal Emergency Management Agency (FEMA, 2019). This study compared BFEs for existing ground topography to BFEs expected under grading changes proposed by Georgia-Pacific (GP) in the 15-acre and 30-acre ponds, including BFEs if a berm around the ponds were removed (breached). Figure 1 shows the study area vicinity. Figure 2 shows the location of the two ponds and their berms that are the subject of this study. The 15-acre pond is just northwest of the 30-acre pond. The BFE is the flood elevation for the 1-percent- annual-exceedence (100-year) flood. The results of this Base Flood Elevation Study for the Yaquina River concluded that no rise in water surface elevation, and no loss of effective floodplain storage, would result in the special flood hazard area (SFHA, or 100-year floodplain) of the Yaquina River from proposed changes of grading of materials stored behind the berms surrounding the 15-acre 30-acre ponds on the south bank of the Yaquina River near Toledo, Oregon. The proposed changes are as shown on the existing and proposed site plans attached as Appendix A. The following sections describe the background, study approach, and resulting finding of no-rise. Existing Conditions Site Description Figure 2 shows the existing conditions in the study area of interest. Two settling ponds are operated on the southwest (left) side of the Yaquina River – the 15-acre pond and the 30-acre pond. The ponds extend from RM 13.2 to 14.0. They are separated from each other and from the river by high berms. West of the 15-acre Pond is the mill’s onsite landfill. ‘Wood’ is a trading name for John Wood Group PLC and its subsidiaries Memo Base Flood Elevation Study for the Yaquina River The proposed re-grading would excavate sludge material to provide additional storage capacity in the 30- acre pond and move that material to the 15-acre pond and onto the slope of the onsite landfill. All grading would be confined to areas “behind” the berms; no ground changes occur in areas connected to the Yaquina River. Appendix A shows the existing and proposed grading. The 30-acre pond has a berm on the riverside that separates the pond from the “active” or effective river channel plus a land-side berm that separates the pond from a dead-end flow path. The land-side berm wraps around and connects with high ground to the west so water on the land side of that berm is backwater with elevation the same as water at the upstream end of the 30-acre pond. Figure 3 is a photo of the riverside berm looking downstream and showing the vegetation on the riverbank and the water that is higher in the pond than in the river. Figure 4 is a photo looking southwest across the Yaquina River toward the 15-acre pond berm. Both photos and other similar photos were used to characterize how the bank ground cover and vegetation might affect river flow. Flood Insurance Study The study area includes areas mapped by the Federal Emergency Management Agency (FEMA) as within the SFHA, commonly called the 100-year floodplain. The present study was done to confirm that proposed grading behind the pond berms would not affect the SFHA area or volume of water outside the pond berms. Excerpts from the flood insurance study are included in Appendix B. Figure 5 shows the effective flood insurance rate map (FIRM) developed by FEMA with the floodplain boundary. It is annotated to show study area features. The prior FIRM had ignored the berm contours; this recent mapping does include topography in the 15-acre and 30-acre ponds. The berms are mapped as high ground above (outside of) the floodplain. Areas behind the berms appear to be mapped at the same elevation as the adjacent river outside the berms. It appears that the new FIRM mapped the same flood elevations, but used current LiDAR data. Wood did not seek to use or investigate the old base model because it is outdated. Instead, the entire study area of interest to the ponds and berms was surveyed new for this study and was tied to the existing profile. The flood insurance study (FIS) report for Lincoln County (FEMA, 2019) states that the lower Yaquina River was studied by detailed hydraulic modeling in October 1977. However, expected study information is missing – no cross-sections are shown or labeled on the FIRM or the flood profile, no floodway was modeled so there is no table listing BFEs, and the flood profiles appear as straight lines with no visible inflections from varying channel geometry. Existing Flows The FIS, in Table 10, lists existing flows for the Yaquina River. Figure 6 maps flow locations relevant to this study area. One flow is at the confluence with Mill Creek. This is the upstream end of this study area and is also the upstream end of FEMA’s mapped detailed study. Another flow point is at Coquille Point several miles downstream of the study area. Olalla Creek / Slough enter the study area from the north. Its flow was calculated by Wood as the net increase from the upstream to downstream boundary of this study area. The downstream flow was interpolated by Wood using drainage area following the equation shown in the prior FIS Report (FEMA, 2009) Section 3.1 Hydrologic Analyses. Project # 6166180843.4.3 | 3/25/2020 Page 2 of 14 Memo Base Flood Elevation Study for the Yaquina River The equation is as follows: n Qa / Qb = ( Aa / Ab ) Q is flow and A is watershed area at points “a” and “b”, and “n” is an exponent that is site-specific. Wood calculated the exponent by matching FIS flows and areas at Coquille Point and Mill Creek; the values used for “n” were 0.94, 0.958, 0.945, and 0.95 for the 10-, 50-, 100-, and 500-year flows, respectively. The flows downstream of Butler Bridge were interpolated using its area. Appendix L provides additional information where the existing FIS flows are compared to flows calculated from current regression equations published by the US Geological Survey (USGS, 2020).

Load more