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HomeMy WebLinkAbout20230684 Ver 1_ltr_ncdeq_add_info_clt10_20230803_20230803Stantec Consulting Services Inc. 521 East Morehead Street, Suite 425 Stantec Charlotte NC 28202-2695 August 3, 2023 Ms. Sue Homewood 401 & Buffer Permitting Branch Division of Water Resources North Carolina Department of Environmental Quality 512 North Salisbury Street Raleigh, North Carolina 27699 Sue. Homewood@deq.nc.gov Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action ID# SAW-2023-00665; Catawba County Dear Ms. Homewood, On behalf of the applicant, Microsoft Corporation (Microsoft), Stantec Consulting Services Inc. (Stantec) is pleased to submit this response to the North Carolina Department of Environmental Quality (DEQ) Division of Water Resources' (DWR) request for additional information dated June 23, 2023. A request for a two - week extension to the due date for submittal of a response was made to DWR and approved on July 7, 2023. The approved due date was changed to August 4, 2023. As design has progressed on the buildings and utility layouts, the final grading plans have required changes at two impacts as described below. The overall permanent stream impacts onsite have decreased from 686 linear feet (LF) to 674 LF, an overall decrease of 12 LF. The Preferred Alternative will now result in permanent impacts to 674 LF (0.07 AC) stream channel and temporary impacts to 258 LF (0.02 AC) of stream channel. An updated set of Jurisdictional Impact Maps is provided in Attachment 1. SUMMARY OF DESIGN CHANGES Impact SC1 As shown on Figure 1 below, with final grading and utility layouts the access road between the substation and Buildings 13 and 14 must be widened, resulting in an increase in permanent impacts at Impact SC1 from 5 LF to 25 LF. This increase is necessary because the width of the perimeter road has been increased due to: • The requirement to place three electrical conduits, a waterline, sanitary sewer and one fiber conduits within and along the roadbed. • Each utility has a required depth and separation from other utilities as required by the federal, state and local regulations that apply, and the utility services' requirements. • The locations of the substation pond and the Building CLT14 pond limit changes to the alignment of the perimeter access road and utilities. Design with community in mind August 4, 2023 Ms. Sue Homewood Page 2 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action IN SAW-2023-00665; Catawba County 'y d TEMPORARY IMPACT SC2 7$ Vt (0.004 Act; PERMANENT IMPACT $C1 25 LF! (O.ODY AG! Y I J f Figure 1. Updated Impact SC1 Impact SC4 In an effort to further minimize stream impacts, the length of the proposed culvert pipes at Impact SC4 has been minimized by pulling back the headwalls at the inlet and outlet. The permanent impact proposed with the installation of the culvert pipes has decreased from 358 LF to 326 LF. PERMANENT WPACT !!! F ! 6! 11 11 � IYWi s . _ , li��l�[�111llllllllllll Figure 2. Updated Impact SC4 An updated impacts table is provided in Table 1 below with the modified impacts bolded. Design with community in mind August 4, 2023 Ms. Sue Homewood Page 3 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action ID# SAW-2023-00665; Catawba County Table 1. Updated Impacts Table Impact Type of Impact Permanent Stream Impacts Temporary Stream Impacts AC LF AC LF SA1 Fill for access road 0.001 16 - - SA2 Temporary construction access - - 0.001 11 SA3 Temporary construction access - - 0.003 44 SA4 Road Crossing - Culvert 0.013 225 - - SA5 Riprap Outfall 0.002 33 - - SA6 Temporary construction access - - 0.001 48 SC1 Fill for access road/utlities 0.001 25 - - SC2 Temporary construction access - - 0.004 78 SC3 Temporary construction access - - 0.004 27 SC4 Road Crossing - Culvert 0.045 326 - - SC5 Riprap Outfall 0.007 49 - - SC6 Temporary construction access - - 0.007 50 TOTAL 0.07 AC 674 LF 0.02 AC 258 LF UPDATE TO MITIGATION The required compensatory mitigation has decreased slightly, and 1,184 credits are now proposed to be provided through a credit purchase from the NCDEQ Division of Mitigation Services (DMS) In -Lieu Fee Program. Table 2. Stream Compensatory Mitigation Impact Length of Impact (L) Mitigation Ratio (MR) Compensation ent Requirement LF (L x MR) SA1 16 2:1 32 SA4 225 2:1 450 SA5 33 N/A (PNNL)" 0 SC1 25 2:1 50 SC4 326 2:1 652 SC5 49 N/A (PNNL)" 0 TOTAL 674 Total CR 1,184 "Permanent No Net Loss Impacts (Riprap) Design with community in mind August 4, 2023 Ms. Sue Homewood Page 4 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action IN SAW-2023-00665; Catawba County REQUEST FOR ADDITIONAL INFORMATION Your questions are presented first, followed by our answers in italics. 1. If the USACE requests a response to any comments received as a result of the Public Notice, please provide the Division with a copy of your response to the USACE to ensure we have all relevant information to complete our review in accordance with ISA NCAC 02H .0506(b). Response: A copy of our response to Public Notice comments received from the USACE will be provided to DEQ DWR when they are submitted to the USACE. 2. The Division appreciates the applicant's efforts to provide evaluations of multiple on -site alternatives to document avoidance and minimization of impacts. In order to complete the Division's avoidance and minimization evaluation, please indicate the proposed width of the roads at the stream crossing locations (i.e. how many lanes, how wide per lane, etc). In addition, please specify the proposed roadside slopes and provide a discussion regarding the feasibility of reducing slopes and/or using retaining walls to further minimize stream impacts at both crossing locations. Response: Updated Jurisdictional Impact Mapping is provided in Attachment 1. The width of the roads at the creek crossings are constrained by the need for multiple utilies to be located within the roadbeds. As illustrated on the cross-section provided on Exhibit 2-1 in Attachment 1 the road crossing at Impact SA4 will contain: • A 30-foot-wide roadway in the center. • Two fiber duct banks on the road shoulders that require 65 feet of horizontal separation from each other. • A 12-inch fire line; and • An 8-inch domestic waterline. As illustrated on the cross-section provided on Exhibit 4-1 in Attachment 1 the road crossing at Impact SC4 will contain: • A 30-foot-wide roadway in the center. • Two fiber duct banks that require 65 feet of horizontal separation from each other. • Six electrical duct banks to bridge power between the two building pads. • A 12-inch fire line. • An 8-inch domestic waterline. • A 24-inch reinforced concrete pipe (RCP) for stormwater. As previously discussed, Impact SC4 has been further minimized through the use of taller headwalls at the inlet and outlet, decreasing the permanent culvert stream impact by 32 LF. With regards to the roadside slopes, project site grades impacts to stream features are reduced where possible using retaining walls and/or slopes steeper than 3:1. However, this approach was not feasible at the stream crossings as noted below. Design with community in mind August 4, 2023 Ms. Sue Homewood Page 5 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action IN SAW-2023-00665; Catawba County • Placing 2:1 slopes immediately adjacent to the streams present a safety hazard for landscape maintenance and security personnel required to access to the security fence which will be installed around the facilities. Safety is a primary focus of project design. Use of 2:1 slopes would require periodic flat benches (-10 feet wide) along the slope to ensure long-term stability. Per Section 6.02 of the NCDEQ Erosion and Sediment Control Planning and Design Manual requires the "use of slope breaks, such as diversions or benches to reduce the length of cut -and -fill slope to limit sheet and rill erosion and prevent gullying." Slope breaks for 2:1 slopes are required at least every 20 ft. At the narrow creek crossing sections, the height of the slopes will be in excess of 20 ft and this benching would result in minimal overall reduction of stream impacts. • The use of retaining walls at the road crossings was investigated but was found to be impractical while providing minimal to no reduction of stream impacts. This is because: o Placing a retaining wall at the base of the fill slope would not provide adequate stability for the required road and utilities to be installed in the fill. In this case, the most practical/best engineering solution would be to construct a retaining wall further upslope. o The presence of significant critical utility infrastructure required in the roadbed at the stream crossings does not allow this arrangement due to the need for geogrid reinforcement behind the retaining walls. In order to accommodate retaining wall construction, the sides along the roadbed would need to be widened past the utility infrastructure to allow for the geogrid reinforcement installation behind the walls. o Tall retaining walls require foundation stabilization measures, the construction of which has the potential to increase impacts to the stream. The walls would need to sit on a 10 ft wide bench with a 3:1 slope below it. Based on these considerations, the 3:1 side slopes as indicated in the exhibits reduce stream impacts as much as practical while ensuring proper safety and maintenance can be sustained throughout the life of the project. 3. It appears that the culvert design at Impact SC4 may cause over widening and shallowing of the stream flow. The Division's criteria for multiple barrel culverts is stated below. Please provide design plans that will meet this criteria. "Culverts shall be designed and installed in such a manner that the original stream profiles are not altered and allow for aquatic life movement during low flows. The dimension, pattern, and profile of the stream above and below a pipe or culvert shall not be modified by widening the stream channel or by reducing the depth of the stream in connection with the construction activity. The width, height, and gradient of a proposed culvert shall be such as to pass the average historical low flow and spring flow without adversely altering flow velocity. If the width of the culvert is wider than the stream channel, the culvert shall include multiple boxes/pipes, baffles, benches and/or sills to maintain the natural width of the stream channel. If multiple culverts/pipes/barrels are used, low flows shall be accommodated in one culvert/pipe and additional culverts/pipes shall be installed such that they receive only flows above bankfull. Placement of culverts and other structures in streams shall be below the elevation of the stream bed by one foot for all culverts with a diameter greater than 48 inches, and 20% of the culvert diameter for culverts having a diameter less than or equal to 48 inches, to allow low flow passage of water and aquatic life. If the culvert outlet is submerged within a pool or scour hole and designed to provide for aquatic passage, then culvert burial into the streambed is not required. Design with community in mind August 4, 2023 Ms. Sue Homewood Page 6 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action IN SAW-2023-00665; Catawba County For structures less than 72"in diameter/width, and topographic constraints indicate culvert slopes of greater than 2.5% culvert burial is not required, provided that all alternative options for flattening the slope have been investigated and aquatic life movement/connectivity has been provided when possible (e.g. rock ladders, cross -vanes, sills, baffles etc.}. Notification, including supporting documentation to include a location map of the culvert, culvert profile drawings, and slope calculations, shall be provided to DWR 30 calendar days prior to the installation of the culvert. When bedrock is present in culvert locations, culvert burial is not required, provided that there is sufficient documentation of the presence of bedrock. " Response: At Impact SC4, there are two culverts which have been sized to pass the 100-year storm. One 326 ft long 12-ft tall by 7-ft wide reinforced concrete pipe (RCP) will be installed 1-ft below the existing stream elevation to allow a permanent low flow channel to form within the pipe to reconnect the upstream and downstream ends of the creek. The other 12-ft tall by 7-ft wide RCP will be installed at the same depth but will be filled with 30-inches of compacted reinforced bed mix to create a secondary overflow channel 18-inches higher than the low flow channel. The overflow pipe is needed to accommodate higher flows during storms, and thereby reduce erosion downstream of the crossing. A cross-section of the pipes is provided below and in Attachment 1 on Exhibit 4-2. 835 I.......I......I.............I.... 835 830 830 825 PROPOSED GRADE-.--` 825 7' WIDE X 17 HIGH BOX CULVERT (2)_ 820 ,..............,...,.... + 820 r HIGH FLOW CULVERT 815 ........... 815 LOW FLOW CULVERT- 81Q .............. 810 EXISTING GRADE 805.................................... 805 80Q -i h` I I i KID 30" OF REINFORCED BED MIX (INVERT 18" HI FILOW LOW CU ER THAN VERT) SECTION A -A SCALE: HOR'I"=60'. VERT 1"=10' Figure 3. Impact SC4 Cross -Section A -A 4. The riprap apron at impact SC5 appears to be significantly wider than the existing stream channel. This impact has been proposed as "no loss of water", however it is unclear how the stream pattern and dimensions are proposed to be maintained within the riprap apron. Please either modify the impact table to account for these impacts as a permanent loss of stream or provide clear plans and details that show how the stream pattern will be provided within the proposed apron. Please note that the response to this item may require submittal of an updated mitigation acceptance letter from the Division of Mitigation Services. Design with community in mind August 4, 2023 Ms. Sue Homewood Page 7 of 7 Reference: Request for Additional Information: Boyd Farm Data Center; DWR# 20230684; Corps Action ID# SAW-2023-00665; Catawba County Response: Current guidelines require a riprap outlet protection pad if the velocity of the water flowing through a pipe during a 10-year storm is greater than 5 cubic feet per second (cfs). For the low flow culvert associated with Impact SC5 a calculated flow of 23.87 cfs is expected during a 10-year storm, thereby necessitating the installation of riprap in the channel. A cross-section of the riprap outfall is provided below and on Exhibit 4-2 in Attachment 1. A large portion of the riprap shown on the plan view is placed in uplands to provide slope stability during a storm event. In order to meet no loss of water, the riprap will be embedded within the stream channel by 3-ft and choked with smaller bedding materials as necessary in order to reform a stream channel between the pipe and the existing downstream channel. 815 I.......I 815 910 81D 3.00' EXISTING GRADE 805 I. 805 r RIP RAP OUTLET PROTECTION PAD B80 + 8fl0 795 795 0+00 0+3.660 SECTION B-B SCALE: HOR V=60': VERT 1"= 10' Figure 4. Impact SC4 Cross -Section B-B Thank you for your assistance with the permit applications. If I can be of further assistance, please contact me at (540) 226-5525 or amber.forestier(a)stantec.com if you have any questions. Sincerely, STANTEC CONSULTING SERVICES INC. Amber Forestier Senior Regulatory Specialist Phone:540-226-5525 Amber.forestier@stantec.com Attachments: Attachment 1: Updated Jurisdictional Impact Maps Cc: Krysta Stygar (USACE), Claire Wolanski (Microsoft), Loretta Cummings (Stantec) Design with community in mind (3 Sta ntec ATTACHMENT 1: Updated Jurisdictional Impact Maps ¢ I / LLLI J r J N00 IE 0 w zN O _ o W LL U � <W < yci LU 2 UcR ' ✓� r� w w N0 0 O� Jj ,1(st V LU LU C AOcn �y aj w ti IL _ 09+p .% < �121HQNflO \ c) uuru, p 8 sndWHC z j i j S ✓ss \ -'rCLT 12��\ � _ _ � O z z z O LLfz U m ¢ m CLT 11 �L / /� a u6 d- wa all � vQ m m CLT 10 Z �N < O z \ www VA w Q/ m OL \ VA �m aVt9 j� O p ¢ o �z J i w W Q CO U HF W > p X X F I- a O O �[if s m U Q Q O Z [V m \ \� LL c 5 MP\DENR 1 H } W Y W ¢ Z L ¢ m m Lo +� LLW m +� LLW m +I W W W OfWO� [if� J Elf ¢ ¢ ¢ N ¢ N V ¢ v v V V U) U N ¢ 2 ¢} F- LU cc z Q = z w o ¢a ow w n m¢ ¢ Q Iw Fr W a w ¢ D m U K Lu o m m �Lo� zz 1 2 2 J J X x x cr 0 0 �F¢ a ¢ a ¢ a J OD Q N N m N a KK � o p d � Q U Q 0 0 0 $� O 0C� N a 0 0 0 00 0 0 0 [Fm F- U LL 'o N CD ti Wd J N N c) 0 ¢ o � g o Q ow a0 m s0 N 0 LO �0 r- CO 0 0 0 0 0 0 F J M a aaaaa�c`�`c3cic�3f°4w Qa m m m m m m m m m m m ai p H g¢ LL¢ ww w LL w x w a a L) ino� w H U- LL m H Co O z Z z Z❑ J W w UW ZO }J} F Df 0 Z K U J O O� O� O w w a �m CD a a a Q Q W 0 a a F x w- w w U a z zLU ¢ W¢7 a� I, a 7 R- m x❑ xw C� LU J I w N 0 �J EL Er L s 1 o l a \ �. �\ / ✓.V// \ 0 Zo z IL _ \ V A I c LL ww ¢+' ¢°� a� A l�\ \V A\ IL LL VA���V A w \ K Z Z V 0 4l \vA VA V oom \ �� lEi\ � � LULu � � > / \ vv VA\ U) ¢ o A oAALL Of \ A E z / aj \ AAA S Q flf W L AAVAAa+i \U)U)W �0 a 1 I I l \ t \ ¢ O o0,c� lww uwE \ \ \ w� o� wLu Y— w \ w w \ m�\b \\ \ VA 07"w L \ VA W Y 't�� \ v >wof \\A Z cC U F w¢ Uni I 0W z U) Uim�U) O) }D�Uw d \U m Z ZQWw W j Zw W P- P n� z Z W maU)Fcno Do 0 ``2o¢ �o a 0z00gQzVwU U U -� �� � �=F- aaXa WwLLJ Q\ N Oa ¢OO oow uwF wit Of F zz¢ Om z d0a U DDw a— �w �\ VAVyAA � \� o \a��� \\ C� �� 1 ` V a N m m o� aO GO GO GO GO m m r /'� I I Q _ LO H +r a Ca > U,CD U a H NU = U + W w C) J 0- < u] o u] o o W u] o u] o U m a]o oNo O m ao w ro G to J G U W Ir Q L� (7 Z H U X W Z m m m ao ao ro ro ro o 0 O Y W ti W m CD+ < 07 Ucn W - U ................... - ..... - - .......�......... ¢ - 9L'£ L8 Ian O—... _ a J 0 I w r+i a m I J U LU Q W 0 _(l-V)L£'l L8 NI ANI l H ¢ 9£'Z LB p o 9£'Z L8 (a7 O Z-V #MH =O co CD o a l a T a L` U) O _ 99'LLS m . 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