M E M O R A N D U M. 1. PSOMAS position on vertical datum differences between NGVD29 and NAVD88 for the NLIP project (submitted by Brian Bullock:

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1 M E M O R A N D U M Date: August 5, 2009 Prepared by: SAFCA NLIP Consultants Purpose: Response to the request by the Board of Senior Consultants (BOSC) in Board Report No. 1; Initial Recommendations Following First Meeting of the Board of Senior Consultants on March 4-5, 2008, dated May 9, 2008, Section 3, Subsection A entitled Vertical Datum. 1. PSOMAS position on vertical datum differences between NGVD29 and NAVD88 for the NLIP project (submitted by Brian Bullock: In late 2006, the SAFCA team decided to transition the vertical datum for the NLIP project from the National Geodetic Vertical Datum of 1929 (NGVD29) to the North American Vertical Datum of 1988 (NAVD88). For the SAFCA NLIP project area, Psomas has determined a conversion factor from the NGVD29 datum to the NAVD88 datum of feet for topographic mapping, ground surfaces, and fluid surfaces. The maximum deviation between this conversion factor and the actual elevation values of the SAFCA NLIP project control is 0.07± feet. We determined this conversion factor for this project by the following processes: For the initial establishment of elevations for the NLIP project control on NGVD29 datum: Researching existing published bench marks (from various sources such as DWR, NGS, Sacramento County, Sutter County) along the perimeter of the project. Performing a level circuit around the project through a number of these bench marks using second-order procedures and Leica digital levels. Performed an additional level circuit along Del Paso Road to further strengthen and check the original level circuit. Performed a minimally-constrained evaluation of the digital leveling data to confirm the results of our survey and initially evaluate the various published bench marks to determine those that do not seem to be in agreement with the majority of the published bench marks. (within accepted surveying tolerances) A fully-constrained least squares adjustment of the data was performed holding those bench marks that agreed within accepted surveying tolerances with the results being excellent. (Full detail is available in the Psomas SAFCA NLIP Project Control Report) Digital level circuits were performed and adjusted off the project vertical control loop to establish the elevations of NLIP project survey control points. Page 1 of 9

2 For establishment of elevations for the NLIP project control on NAVD88 datum: Researched published bench marks with NAVD88 values near the project perimeter. Three were found. One benchmark was found within several miles of the northeast extremity of the project. Another bench mark was found within several miles of the southeast area of the project, and the third bench mark was within several miles of the southwest extremity of the project. A level circuit following similar procedures described above were performed to tie the original project level circuit to each of these three bench marks. A minimally-constrained analysis of the data was performed to confirm the integrity of the data. This data together with the raw data from the original level circuit was adjusted by constraining the adjustment to the three new bench marks. This adjustment met the same statistical criteria as the previous adjustment, and provided NAVD88 elevations for each of the SAFCA NLIP project control points as well as the bench marks utilized in the NGVD29 level circuit. To establish a conversion factor for the NLIP mapping that had already been accomplished prior to the decision for the project datum change, Psomas did the following: We determined the mean difference between the NGVD29 elevations and NAVD88 elevations for each control point and bench mark. This value was found to be 2.28 feet with NAVD88 elevations being higher than NGVD29. When applying this conversion factor to the NGVD29 control points, we found the maximum difference between the actual NAVD88 elevation and the NAVD88 elevation determined by applying this conversion factor to be 0.07± feet. Since it is accepted practice to measure ground elevations to within 0.1± feet, we have utilized this conversion factor for this project. The existing mapping for Natomas Cross Canal, the first portion of the Sacramento River, and the GGS mapping was converted to NAVD88 by translating break lines and spot elevations from NGDVD29 to NAVD88 by adding 2.28 to all elevations. These adjusted break lines and spot elevations were used to generate the digital terrain model (DTM) and contours on the NAVD88 datum. Because the aerial photogrammetric models were already set for the mapping of the Sacramento River, we have continued to apply the conversion factor to the aerial compilation data for the balance of the Sacramento River mapping, Riverside Canal mapping, and GGS mapping that utilizes the original aerial photography for the project. For the new aerial photography on borrow sites, Pleasant Grove Creek Canal (PGCC), and Natomas East Main Drainage Canal (NEMDC), the surveys and aerial compilation have been prepared on NAVD88 datum. NOTE: Any surveying being performed for this project must utilize the project control and/or bench marks included in Psomas control survey for the NLIP project because 1) other published agency bench marks not utilized in Psomas survey may differ Page 2 of 9

3 significantly from the published agency bench marks utilized for this project and 2) the horizontal datum we utilized was NAD83 ( epoch) so the NLIP data would be on the same coordinate system as previous work performed by Psomas for SAFCA on the North Area Improvements program. (Psomas SAFCA NLIP Project Control report is available on SAFCA NLIP Project Solve for all SAFCA NLIP consultants or upon request by others as approved by SAFCA. The shorter version of this report provides the control information needed for use of the Psomas control with a brief explanation as to our approach. For those who wish to review Psomas approach, data, and adjustments in detail, a second binder containing this data is available) 2. Kleinfelder s response to the change in vertical datum for the SAFCA NLIP (submitted by Lynn O Leary): Near the end of 2007 the Natomas Levee Improvement Program (NLIP) project team transitioned to referencing all vertical elevations to the North American Vertical Datum of 1988 (NAVD88), specifically the American River north levee, Natomas Cross Canal south levee, and Sacramento River east levee. Kleinfelder s analyses (seepage and stability), drawings, boring logs, and reports published prior to 2008 referenced elevations to the National Geodetic Vertical Datum of 1929 (NGVD29). Kleinfelder received a conversion factor for the entire basin from PSOMAS in an from Tim Busch with Mead & Hunt dated November 28, 2007 to allow a conversion of NGVD29 to NAVD88 datum. This conversion factor adds 2.3 to the NGVD29 elevations to obtain NAVD88 elevations. In order to globally change the vertical datum referenced for the NLIP project the following steps were taken: 1) All new boring logs (2008) were drafted using NAVD88 elevations. 2) All old boring logs ( ) were adjusted using the conversion factor to reflect NAVD88 elevations. 3) Levee profiles were adjusted using the conversion factor to reflect NAVD88 elevations. 4) Old analyses files for the Sacramento River and Natomas Cross Canal being carried forward in current design were adjusted using the conversion factor to reflect NAVD88 elevations. (It should be noted that the American River analyses have not yet been updated to reflect the new elevation datum.) 5) All new analyses were setup using NAVD88 elevations. 6) Old reports will not be revised or reissued using the new datum. New reports, addendums, letters, technical memorandums will reference NAVD88 elevations. 3. Wood Rodgers response to the change in vertical datum for the SAFCA NLIP (submitted by Jonathan Kors): Civil design work within Wood Rodgers scope of work has been performed using the Page 3 of 9

4 North American Vertical Datum of 1988 (NAVD 88). Topographic surveying and mapping, which serves as the base map for this work, has been provided by Psomas, Inc. using NAVD 88, and therefore conversion has not been required. There are a few instances, however, where it has been necessary convert data from others to NAVD 88. These instances include the following: Hydraulics Information Geotechnical Boring Stick Logs Existing Facilities As-Builts Hydraulics Information Hydraulic modeling for the NLIP is being prepared by MBK Engineers, Inc. Of particular interest is the design water surface elevation, which establishes the water surface for freeboard evaluation, seepage modeling, and levee raising design. The hydraulic models provide information based upon the National Geodetic Vertical Datum of 1929 (NGVD 29). To convert design water surface information to NAVD 88, Wood Rodgers has applied a conversion factor of 2.28 (NGVD 29 Elevation = NAVD 88 elevation). Geotechnical Borings Geotechnical information for the program is being prepared by Kleinfelder, Inc. Kleinfelder has determined the appropriate elevations for extension of cutoff walls to cut off levee underseepage. Kleinfelder generally includes a graphical exhibit in each Problem Identification Report which plots stick logs on a profile of the levee. The vertical scale on the left hand side of the profile is typically based upon NGVD 29. To determine the appropriate depth of the cutoff wall, the same conversion applied to the water surface elevation described above is performed on the wall bottom elevations as provided by Kleinfelder update: According to Mark Stanley with Kleinfelder, Kleinfelder has since updated the NCC Phase 2 report to reference NAVD88; pg 4 of 8 under geotechnical borings indicates they are converting from NGVD29. Existing Facilities As-Builts SAFCA, Reclamation District 1000, and the Natomas Mutual Water Company maintain historical as-built plan sets for previous levee and infrastructure improvement projects which are of use in conveying the scope of construction work to be completed on the levee improvement projects. The as-builts are also based on NGVD 29 and must be converted to NAVD 88 as described above. Each individual civil design plan set prepared by Wood Rodgers identifies the vertical datum as NAVD 88. This information is contained in a general note on a survey data drawing provided within the plan set. Page 4 of 9

5 4. MBK s response to the change in vertical datum for the SAFCA NLIP (submitted by Mike Archer): As part of the Sacramento and San Joaquin River Basins Comprehensive Study (Comp Study), the U.S. Army Corps of Engineers (USACE) developed a UNET model of the Sacramento River basin. UNET is a one-dimensional unsteady open-channel flow model with the ability to simulate exchange of flow between river channels and floodplains, which was originally developed for the USACE Hydrologic Engineering Center (HEC). UNET is the predecessor of the unsteady flow routine in the current HEC-RAS program. The elevation data of the geometric features and boundary conditions in the UNET model are in NGVD 1929 vertical datum. UNET was used for this model because at the time of the model development the unsteady flow routine had not yet been incorporated into the HEC-RAS program which will use NAVD 1988 as the primary vertical datum. Converting the Sacramento River UNET model to HEC-RAS is a significant task and is currently being undertaken by the USACE. In the meantime, the UNET model is being used for hydraulic analyses in the Sacramento River basin using NGVD 1929 vertical datum until the HEC-RAS model is finalized and released by the USACE. MBK Engineers converted the water surface elevations calculated from the UNET model from NGVD 1929 to NAVD 1988 using the standard conversion factor of feet (i.e. 0 NGVD = NAVD). The conversion factor was provided by Psomas and was applied to all water surface elevations around the Natomas Basin at the following segments of Rivers and Canals: Sacramento River: River Mile (RM) 60.4 to RM 79.3 Natomas Cross Canal: RM 0 to RM 5.3 Pleasant Grove Creek Canal: RM 0 to RM 3.2* Natomas East Main Drainage Canal: RM 2.2 to RM 14.9* American River: RM 0 to RM 2 River Miles based on Comprehensive Study * - extrapolated RM along Canal 5. HDR s response to the change in vertical datum for the SAFCA NLIP (submitted by Blake Johnson): All design work for the NLIP Sacramento River East Levee is based upon NAVD 88. The following information has been provided to HDR by SAFCA team members: Base mapping (topography and planimetrics have been provided by Psomas in NAVD 88. Water surface elevations have been provided by MBK Engineers. MBK Engineers has converted the NGVD 29 water surface datum to NAVD 88 datum and provided this information to HDR via spreadsheets. Page 5 of 9

6 All reports submitted to HDR by Kleinfelder are in NGVD 29 (2007 and early documents). No new documents from Kleinfelder have been submitted to HDR that have been converted to NAVD 88. It is assumed all 2008 and later documents from Kleinfelder will be in NAVD Update: According to Mark Stanley today, HDR's section on pg 5 of 8 states that no new documents from Kleinfelder have been submitted by HDR" which was true at the time the comment was written but is not the case today. Pre-design documents (2007 documents) were completed in NGVD 29, including the Alternatives Analysis and Plan Formulation Report (these documents were planning documents, vertical elevation was not a critical factor). These reports will not be resubmitted in NAVD 88. However, all new (2008 and later) design and pre-design documents will be completed in NAVD 88 incorporating the appropriate information from Kleinfelder, MBK, Psomas, and the remaining consultants. This will include the revised Alternatives Analyses for each Phase of work and all plans, specifications, and cost estimates. All conversions to NAVD 88 have been completed by Psomas and MBK as needed and HDR has incorporated this new information as appropriate. HDR has not directly converted datum from NGVD 29 to NAVD 88. HDR design has incorporated the new NAVD 88 survey in all design documentation, thus no conversion is necessary. 6. NHC s response to the change in vertical datum for the SAFCA NLIP (submitted by Ken Rood): Design work within Northwest Hydraulic Consultant s scope of work was converted to the North American Vertical Datum of 1988 (NAVD 88) in late Topography and bathymetry at our design sites was provided by Psomas, Inc. in NAVD 88, and conversion was not required. Northwest had previously surveyed bathymetry at the erosion sites along the Sacramento River in NGVD 1929, based on control provided by Psomas. We provided our point files in the earlier datum to Psomas, who then converted the vertical datum and returned combined topography and bathymetry in NAVD 88 at our design sites. Design water surface elevations provided by MBK Engineers, Inc and previously calculated seasonal water surface elevations and scour elevations along the Sacramento River were converted from the National Geodetic Vertical Datum of 1929 (NGVD 29) to NAVD 88 with the factor of 2.28 feet provided by Psomas, Inc. The conversion was applied as follows: NGVD 29 Elevation = NAVD 88 elevation. 7. Mead and Hunt s response to the change in vertical datum for the SAFCA NLIP (submitted by Stephen Sullivan/Tim Busch): Civil design work within Mead & Hunt s scope of work has been performed using the NAVD88 datum per the base mapping provided by PSOMAS. Topographic surveying and mapping, which serves as the base map for this work, has been provided by Page 6 of 9

7 PSOMAS, Inc. using NAVD88, and therefore conversion has not been required. There are a few instances, however, where it has been necessary convert data from others to NAVD88. These instances include the following: Hydraulics Information Existing Facilities As-builts In general, the conversions required are between the NGVD29 datum and NAVD88 datum. To convert elevation information from NGVD29 to NAVD88, Mead & Hunt has applied a conversion factor of 2.28 feet as follows: NGVD29 Elevation feet = NAVD88 elevation. The NLIP is an average conversion for the project area provided by PSOMAS. Specific benchmark data is provided in the March 12, 2007 NLIP Project Control Report which was distributed to the NLIP consultants and used for reference as required during design. Hydraulics Information Hydraulic modeling for the NLIP is being prepared by MBK Engineers, Inc to establish the design water surface elevation, which establishes the water surface for freeboard evaluation in the Wind and Wave analysis performed by Mead & Hunt. Results for this modeling are presented in NGVD29. Other data utilized were reports and mapping from FEMA which are also presented in NGVD29. The data being utilized for frequency analysis during waterside facility design originated from the USGS Verona Gage. This facility provides historical data based upon a USED datum. The published elevation conversion for the Verona Gage to NGVD29 is minus 3 feet, therefore to utilize this data for NLIP values are converted to NAVD88 with an average conversion factor of minus 0.72 feet (Verona Gage Height minus 3.0 feet plus 2.28 feet = NAVD88 elevation). Existing Facilities As-Builts Historical as-built plan sets for previous levee and infrastructure improvement projects available for projects by SAFCA, Reclamation District 1000, U.S. Army Corps of Engineers, Natomas Mutual Water Company and others contain data utilizing various datums. Generally the work is tied to NGVD29 datum; the bases of other datums are normally described on as-built plan sets. Only data with verifiable datums are being utilized directly for final design. Where the vertical datum cannot be verified, a survey request is provided to PSOMAS to obtain as-built data in the NLIP vertical datum NAVD88. Where data cannot be accurately verified, the information is presented as approximate with a note to contractor to verify prior to construction. Each individual civil design plan set prepared by Mead & Hunt identifies the vertical datum as NAVD88. This information is contained in a general note on a survey data drawing provided within the plan set. Only elevation data provided by PSOMAS is presented on topographic mapping. As-built elevations presented elsewhere on plan sets, not verified by PSOMAS, are noted as approximate with a notation that data should be field-verified. Page 7 of 9

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10 TECHNICAL MEMORANDUM TO: FROM: Mr. John Bassett, SAFCA Mr. Ric Reinhardt, MBK Jonathan L. Kors, P.E. DATE: August 30, 2008 SUBJECT: SAFCA NLIP, Response to Comment 3B of the Recommendations of the Board of Senior Consultants Dated May 9, 2008 INTRODUCTION The following is provided by Wood Rodgers, Inc. in response to Comment 3B of the recommendations of the Board of Senior Consultant (BOSC) as presented in the report titled: Initial Recommendations Following First Meeting of the Board of Senior Consultants on March 4-5, 2008, dated May 9, Comment 3B, Intersections/Connections of Different Levee Improvements- The Board understands that different levee improvements are being designed for different reaches of levees (e.g., slurry cut-off walls vs. seepage berms vs. pressure relief wells). The Board recommends that the design team produce a technical memorandum detailing the assumptions and procedures that will be used for connecting/overlapping different levee improvements and for connecting/overlapping different levee improvements to areas where no improvement is provided. This should be achieved in order to prevent one type of improvement from adversely impacting an adjacent reach, and that the connection between elements should represent the strongest area of flood protection rather than its weakest. This technical memorandum should also identify procedures for assuring that, when a levee improvement is left only partially completed before the flood season, no adverse impacts are created (i.e., the levee is not left with a reduced flood protection that is lower than what it was prior to construction see recommendation on Interim Emergency Action Plans). This technical memorandum should also be concurred with by the Sacramento District of the Corps. RESPONSE TO COMMENT As suggested by the BOSC, Wood Rodgers is preparing a technical memorandum to address this issue. This memorandum is significant effort involving the collaboration of HDR, Wood Rodgers, and Kleinfelder and is currently in process. At this time, an outline of the memorandum has been prepared and is included below. The technical memorandum will be forwarded to the BOSC when complete.

11 TECHNICAL MEMORANDUM SAFCA NLIP August 30, 2008 Page 2 of 3 1. Introduction 1.1 NLIP Background 1.2 Board of Senior Consultants Comment No. 3B 1.3 Definitions for Levee Improvement Transitions, Terminations, and Interim Gaps 2. Technical Basis for Improvement Transitions and Terminations 3. Technical Basis for Improvement Interim Gaps 4. Application of Improvement Transition and Termination Recommendations External (Stream to Stream) Improvement Transitions and Terminations Natomas Cross Canal at Sacramento River Natomas Cross Canal at Pleasant Grove Creek Canal Natomas East Main Drainage Canal at American River American River at Sacramento River Internal (Reach to Reach) Improvement Transitions and Terminations NCC Phase 1 to Phase 1B NCC Phase 1B to Phase SREL Reach 1 to SREL Reach 3 to 4A SREL Reach 4B to 5A SREL Reach 5A to 5B SREL Reach 9B to SREL Reach 10 to 11A SREL Reach 12 to 12B SREL Reach 13 to SREL Reach 14 to SREL Reach 16 to SREL Reach 19A to 19B 5. Application of Improvement Interim Gap Recommendations 5.1 NCC at Bennett Pump Station 5.2 NCC at Northern Main Pump Station 6. Anticipated PGCC, NEMDC, and ARNL Improvement Transitions and Terminations

12 TECHNICAL MEMORANDUM SAFCA NLIP August 30, 2008 Page 3 of 3 FIGURES 1 Basin Map Showing Location of Improvement Transitions, Terminations, and Interim Gaps 2 External Improvement Transition Natomas Cross Canal at Sacramento River East Levee 3 External Improvement Transition Natomas Cross Canal at Pleasant Grove Creek Canal 4 Internal Improvement Transition Cutoff Wall to Seepage Berm 5 Internal Improvement Transition Cutoff Wall to Adjacent Levee 6 Internal Improvement Transition Adjacent Levee to Seepage Berm 7 Internal Improvement Transition Relief Well to Seepage Berm 8 Internal Improvement Transition Relief Well to Cutoff Wall 9 Improvement Interim Gap And Future Closure NCC at Bennett Pump Station 10 Improvement Interim Gap And Future Closure NCC at Northern Main Pump Station

13 Technical Memorandum RESPONSE TO COMMENT NO. 4. SEISMIC STABILITY BOSC REPORT NO. 1, MAY 9, 2008 Sacramento River East Levee August 22, 2008 Reviewed by: Prepared by: Chris Krivanec, PE, GE Barry Meyer, PE Introduction This memorandum is intended to respond to comment number 4 presented in the NLIP Board of Senior Consultants Report No. 1 (dated May 9, 2008), which is as follows: (end of paragraph 1) The Board recommends that the design team develop a seismic mitigation design approach, and that such measures be implemented as part of the Natomas improvements. Seismic Stability Evaluation A seismic stability evaluation was performed by Kleinfelder for SREL Stations 0+00 to for Reaches 1 through 11. The results are presented in their draft Appendix I to their Draft Geotechnical Alternatives Analysis for SREL-2 (Reach 5A to 9B) and is attached. The results of their analyses show that liquefaction with post-earthquake static slope stability factors of safety less than 1.0 could occur for an earthquake with a 200 year return period in segments of Reaches 4 through 7 in SREL-2. As discussed at the March 2008 BOSC meeting, it is not practical to develop measures to mitigate liquefaction potential; however, a strategy to deal with potential post liquefaction damage is necessary. Although it is not intended to mitigate liquefaction potential, consideration will be given to the selection of seepage mitigation measures for the proposed adjacent levee. The primary seepage mitigation alternatives being considered with the adjacent levee are seepage berms and SB cut-off walls. Post-Earthquake Operational Strategy As part of the SREL design, an operational strategy will be developed This strategy will consider the following: Identification of levee segments where the post-earthquake static slope stability factor of safety is less than 1.0 Sacramento Are Flood Control Agency 1 Natomas Levee Improvement Program September 11, 2008 U:\mitra\NLIP\meetings\BOSC\Session 1\Response to Comments\final\BOSC Response - Comment _HDR.doc

14 Technical Memorandum Estimation of the quantity of earthfill required to restore the adjacent levee prism to a stable cross-section with a crest elevation that is at least 2 feet above the 25 year water surface elevation. An Emergency Action Plan to allow the levee restoration (25 year WSE plus 2 feet) to occur within three (3) weeks after the liquefaction event. This plan would include: o o o o Estimation of the earthfill quantities Location of the earthfill stockpiles Plan to have contractors available to begin the repairs within three (3) days after the event Weather permitting and site access A plan to have the levee embankment fully restored to pre-earthquake conditions within 3 to 6 months of the event. A draft of the SREL operations and maintenance plan that includes the liquefaction operational strategy will be completed as part of the NLIP. Sacramento Are Flood Control Agency 2 Natomas Levee Improvement Program September 11, 2008 U:\mitra\NLIP\meetings\BOSC\Session 1\Response to Comments\final\BOSC Response - Comment _HDR.doc

15 TECHNICAL MEMORANDUM Date: August 4, 2008 To: Mr. Christopher Krivenac, PE, GE HDR, Inc. Geotechnical Engineering Materials Testing & Inspection Environmental Science & Engineering Water Resources Earthquake Engineering Air Quality From: Lynn O Leary, PE Mark H. Stanley, PE, GE Kleinfelder Project: Natomas Levee Improvement Program II Subject: Response to Comment No. 5 NLIP BOSC Report No. 1 dated May 9, 2008 Natomas Levee Improvement Project Sacramento and Sutter Counties, CA Below is Kleinfelder, Inc. s response to Comment 5 of NLIP Board of Senior Consultants Board Report No. 1: BOSC Comment No. 5: 5. Hydrology and Hydraulic Design Approach As presented during the briefings, the hydraulic design stage for the 200-year flood event is being determined using traditional deterministic approaches. In these approaches, an expected, or median, water surface for the 200-year flood event is calculated and employed as the design water surface. Freeboard, typically three feet, is then added to this water surface to establish the crown elevation of the levee and tapered up another one foot at structures. The Federal Emergency Management Agency (FEMA) has traditionally employed and/or accepted this approach for a 100-year level of flood protection. For the Natomas Basin, the 200-year water surface is based on 2002 hydrology developed by the Sacramento-San Joaquin River Basins Comprehensive Study, with recent modifications in the hydraulic model made by MBK Engineers. However, there were significant conservative assumptions employed in the hydraulic model, including the assumption that all of the rural levees upstream of Natomas have had their design freeboard deficiencies remedied, that rural levees can be overtopped and act like weirs without failing, and that no urban levees upstream of Natomas can either overtop or fail. The assumption of overtopping without failure is a significant conservatism, partly because many rural levees could not sustain any significant overtopping, but also because there are structural deficiencies in many of these levees. The Board believes that these are appropriate assumptions for design purposes, considering the consequences of failure of the Natomas levees, and that the flood protection of different basins should not rely upon the failure of other levees and the flooding of other basins to achieve a minimum level of flood protection. However, the Board wishes to note that there is a significant amount of conservatism in these assumptions and that additional conservative assumptions should not be cumulative. Page Fite Circle Sacramento, California fax

16 The Board also understands that the Corps has abandoned this type of deterministic approach and now requires that risk and uncertainty be explicitly incorporated in determining the design water surface profile for the establishment of the top of levee profile, and for analyzing slope stability and seepage issues. In fact, the Corps and FEMA have been urged to sign a memorandum of agreement to phase in risk and uncertainty analyses over a 10 year period. The Corps has been unclear on how it performs geotechnical analyses with different water surfaces but seems to be using conventional deterministic geotechnical analysis techniques based upon a risk-based water surface (90% or 95% probability of non-exceedance) and/or by setting the design water surface at the top of the levee, whichever is the higher water surface. One of the issues that must be addressed when using a risk-based hydrology/hydraulic approach is what assumptions should be made with regard to upstream levee failures many are concerned that going to high probabilities of nonexceedance without allowing for levee failures at high levels of overtopping will be unrealistic and lead to excessively conservative designs. Preliminary analysis results using the risk and uncertainty approach and incorporating levee failures when overtopping conditions developed were presented to the Board for the Natomas Basin levees and are as follows: 90% probability of non-exceedance for 100-year flood ~ 1.4 feet above 200-year deterministic stage 95% probability of non-exceedance for 100-year flood ~ 1.8 feet above 200-year deterministic stage 90% probability of non-exceedance for 200-year flood ~ 1.7 feet above 200-year deterministic stage 95% probability of non-exceedance for 200-year flood ~ 2.2 feet above 200-year deterministic stage The implications of the above preliminary results suggest that the Corps risk and uncertainty approach may give about 1½ to 2 feet higher stages for 90 and 95% probability of non-exceedance over the 200-year deterministic approach, assuming that upstream levee failures are incorporated into the risk analyses. With the addition of 3 feet of freeboard to the deterministic design water surface, it may turn out that a 90-95% probability of non-exceedance water stage would thus not necessarily require additional levee height over the 3 feet of freeboard that is currently being incorporated into the designs. However, both the 100-year and the 200-year R&U design water surface might end up being a couple of feet higher than the 200-year deterministic stage, and the risk and uncertainty approach could possibly lead to requiring more extensive levee improvements. The Board believes that the proposed deterministic approach using conservative assumptions about upstream levee failures is an adequate design approach for a 200-year design flood given the current point in time with respect to changing criteria by different agencies. However, the Board also recommends the following: Current Corps levee design criteria require that an underseepage exit gradient at the toe of the levee be less than 0.5 for the design water surface elevation. It is our understanding that this 0.5 exit gradient criterion is being used in the Natomas designs with the 200-year deterministic water surface (i.e. not the top of the levee which is set 3 feet higher). The Board concurs that this is an adequate approach, but also recommends that the underseepage exit gradient at the toe of the levee be less than 0.6 for a water surface set at the top of the levee. This latter recommendation is intended to ensure that the levee is structurally adequate for water surfaces rising all the way up to the top of the levee. It is our understanding that the State may require this additional underseepage criterion as well. While not clear at the current time, the Corps risk and uncertainty approach will undoubtedly lead to higher design water surfaces (perhaps a foot or two above the current 200-year deterministic water surface). Further, some interpretations of Corps policy indicate that the design water surface should be at the top of the levee based upon a specific probability level. The implications of this is that the Corps will probably not recognize a 200-year level of protection based on designs employing the 200-year deterministic water surface only, nor might they recognize or certify a 100-year level of protection since seepage/stability evaluations were not performed to the higher probabilistic water levels. While other Page Fite Circle Sacramento, California fax

17 engineers are likely to be able to certify that the designs provide the 100-year level of flood protection for the purposes of FEMA accreditation using current FEMA criteria, the Corps may not fully credit the Natomas improvements for use in funding future phases of work unless a full risk and uncertainty analysis (Corps of Engineers style) is performed and design water surface elevations determined accordingly. The Board recommends that the design team evaluate the additional costs and consider using the top of the levee as the design water surface (i.e., the 200-year deterministic stage plus 3 feet would be used with a maximum exit gradient of 0.5 at the toe of the levee). This is not as much a recommendation for additional safety as much as it represents a business decision that would weigh additional current costs versus potential future credits. In addition, the design team should consider lowering the current design elevation for the top of levee by approximately 1 foot to be consistent with the 200-year 95 percent non-exceedance value (Corps R&U approach), and then using this as the design water surface with no extra freeboard. This analysis would take into consideration the conservative assumptions of upstream levee scenarios (non-overtopping urban levees and non-failures when overtopping occurs) previously pointed out. The addition of the 3- foot freeboard on top of the 200 year deterministic water surface elevations could be considered adding conservatism on top of already conservative assumptions. Any extra cost for seepage mitigation would possibly be offset by a decreased quantity of material for raising and widening the existing levees. This latter approach should still meet the traditional FEMA requirements for 100-year protection (100-year deterministic water surface plus three feet) as well as satisfy Corps of Engineers requirements. Kleinfelder, Inc. Response to Comment No. 5: In general, the following geotechnical design criteria were adopted for use in the Natomas Levee Improvement Project. The U.S. Army Corps of Engineers (USACE) criteria for stability, where a factor of safety of 1.4 is used for steady state seepage conditions, 1.3 for end of construction conditions, and greater than 1.2 for rapid drawdown conditions. Our current guidance on allowable seepage gradients indicates the maximum seepage gradient allowable at the toe of the existing and/or adjacent levee is 0.5, corresponding to a factor of safety (FoS) of approximately 1.6 The maximum seepage gradient allowable at the toe of a seepage berm is 0.8, corresponding to a FoS of approximately 1.0, for the 200 yr plus (+) 1 foot or less water surface elevation (WSE), discussed below. This assumes a minimum saturated soil unit weight of 112 pounds per cubic foot (pcf). These criteria are adjusted to a have a maximum allowable seepage gradient of 0.6 at the toe of the existing and/or adjacent levee for the top of levee (TOL) water surface (200 year +3 feet WSE), corresponding to a FoS of greater than 1.3, in accordance with draft Department of Water Resource (DWR) criteria. Currently, the toe of seepage berm criteria is unchanged for the TOL water surface analysis. For design purposes the adjacent levee is assumed to be constructed of a relatively homogeneous fill, no intended zoning. The embankment fill soils will consist of what has been previously denoted as Types 1 and 2 soils with the following criteria, liquid limit of less than or equal to 55, plasticity index (PI) of between 8 and 35 (inclusive), and a fines content (material passing the No. 200 sieve size) of at least 30 percent. Based upon discussions with the USACE the homogeneous levee will have a maximum liquid limit of 55 or less and plasticity indices between 8 and 40. This criterion is based upon extensive investigation and laboratory testing of the North Airport Borrow Site materials. Appropriate seepage berm materials criteria were discussed with the USACE, and it was determined that any material can be used to construct the berm, including fat clay and sand. Seepage berms are assumed to be a minimum of 4 times the height of the levee but in no case less than 80 feet in width. If calculated seepage gradients at the toe of the seepage berm are in excess of 0.8 (FoS 1.0) then relief wells may be required to reduce the seepage gradient to a maximum value of 0.8 between the relief wells. Page Fite Circle Sacramento, California fax

18 Unless specified otherwise, seepage cutoff walls are assumed to be constructed of soil-bentonite (SB) slurry with an average permeability (hydraulic conductivity) less than k h = 1 x 10-6 cm/s. For stability analyses the SB cutoff wall will be assigned a strength (cohesion) of 20 pounds per square foot (psf) and a fluid weight of not less than 80 pcf. A soil-cement-bentonite (SCB) cutoff wall was constructed on the western portion of the Natomas Cross Canal in The SCB wall was modeled as a SB cutoff wall. Seepage analyses will consider the following mean water levels: 100-year, 200-year, 200-year +1 foot, and 200- year + 3 feet (TOL). The water levels may be determined based on deterministic or probabilistic (USACE Risk and Uncertainty) methods, depending on the guidance given to the hydraulics and hydrology consulting engineer (MBK) by SAFCA and/or USACE. Our current understanding is that the design plans are being generated based on the deterministic mean 200-year WSE. Although other water levels will be analyzed during the alternatives analysis portion of design sequence, the basis of design report (BODR) will be developed using the deterministic mean 200-year WSE. Engineering analysis is being conducted in accordance with USACE Levee Design Manual (EM ), Design Guidance for Levee Underseepage (ETL ), and Sacramento District Geotechnical Levee Practice (Revision 1). Steady state seepage analysis is being conducted to calculate seepage gradients for all levees. The soil pore pressures are then imported into the slope stability models for all levees except the Sacramento River East Levee, where there will be an engineered adjacent levee. A modified analysis to model high underseepage pressures has been tentatively agreed upon with the USACE for the Adjacent Levees. Page Fite Circle Sacramento, California fax

19 Water Resources Flood Control Water Rights M E M O R A N D U M DATE: August 28, 2008 TO: FROM: Natomas Levee Improvement Program, Board of Senior Consultants MBK Engineers SUBJECT: Response to Comment 7, BOSC Report 1, May 9, 2008 Introduction: This memorandum is in response to Comment 7 from the NLIP BOSC Report No. 1, stated as follows: The Board understands that an Emergency Action Plan is being developed for the Natomas Basin. The Board recommends that interim plans be developed that define the actions necessary to respond to flood emergencies while the levee improvements are underway. This is particularly important since the system as a whole will have different levels of protection until the project is finalized. This, in turn, means that under similar catastrophic flooding conditions, overtopping locations and possible failure modes could change, depending on what phase the project is in. The interim plans would consider the potential modes for distress and failure, and account for changes in conditions and locations as the improvements progress. We expect that these would differ considerably between the present time and after the 200-year level of protection is in place. Response: There is an ongoing effort among SAFCA staff in collaboration with the City of Sacramento, Sacramento County, Reclamation District 1000 and Operation of Emergency Services to develop emergency action plans for the entire Sacramento area including the Natomas Basin. The overall plan will leverage the existing roles and responsibilities of the agencies when monitoring highwater events and responding to flood emergencies. The existing emergency action plans will be reviewed to determine if they need to be updated. Recommendations for altering patrols will be made annually prior to each flood season and will be based on the implementaiton of new levee improvements and the best available engineering and geotechnical information. Part of the interim action plan may include assigning key on-call staff from each NLIP consultant organization for specific duties during a high-water event.

20 Technical Memorandum RESPONSE TO BOSC COMMENT 8B - LEVEE EMBANKMENT ZONING AND BORROW AREA ANALYSES Sacramento River East Levee August 22, 2008 Reviewed by: Prepared by: Blake Johnson, PE and Chris Krivanec, PE, GE Tony Quintrall, EIT Introduction This Technical Memorandum summarizes the decision process for the design of the adjacent levee along the Sacramento River East Levee as part of the Natomas Levee Improvement Program. This memorandum is intended to respond to a comment presented in the NLIP Board of Senior Consultants Report No. 1 (dated May 9, 2008), which is as follows: 8b. Levee Embankment Zoning and Borrow Area Analyses The Board was briefed on the plan to zone the embankment to allow incorporation of higher plasticity clays within the center of the levee. The purpose of this was to make use of available plastic clay material within the borrow area and avoid excessive overexcavation and expensive rehandling of the materials in the borrow area. There was significant discussion regarding the difficulty of separating out Type 1 soils with a liquid limit of less than 45 from Type 2 soils with a liquid limit of less than 55 it is very likely that such determinations will be very difficult to do in the field. The Board shares the concerns of the design team that zoning of the embankment will lead to higher costs, and that more work needs to be done in developing a borrow plan. The Board recommends that more attention be given to this issue and that this issue be subject to a constructability review process. The preliminary design approach incorporated a zoned embankment to optimize the available borrow materials while still complying with United States Army Corps of Engineers (USACE) levee design criteria. Following a meeting on July 7, 2008, with the USACE Sacramento District on embankment material requirements, the move to a homogeneous embankment was made to facilitate constructability of the adjacent levee and new material specifications were adopted. Sacramento Are Flood Control Agency 1 Natomas Levee Improvement Program September 11, 2008 U:\mitra\NLIP\meetings\BOSC\Session 1\Response to Comments\final\BOSC Response - Comment 8B _HDR.doc

21 Technical Memorandum Zoned Embankment The original design for the adjacent levee raise included two material types: Soil Type 1 and Soil Type 2. The proposed borrow site is located north of the Sacramento International Airport and was selected due to the proximity with the project and the affordability of the publicly owned land. Generally speaking, the borrow site has a heterogeneous mix of material, some of which does not meet the standard levee select fill specifications found in USACE Sacramento Section Standard Operating Procedure. The material of concern is slightly more plastic than the standard select fill. In order to maximize the use of the Airport North borrow site, it was proposed that the material that would not meet the requirements of select fill be placed in an interior zone of the adjacent levee embankment. The proposed embankment zonation is shown in the attached figure (from a draft 90% plan set). The moisture content of the soils within this zone would not vary as much as the outer zone of the levee, avoiding the desiccation issues associated with highly plastic clays. This zonation also allows more flexibility with the use of the material. However, the design team was concerned that a contractor would have a difficult time visually identifying and separating or blending the two materials. More detailed borrow evaluations have been undertaken to better characterize the borrow sites. Table 1 summarizes the specifications for these two soil types. Soil Type 1 would be used in the outer shell of the adjacent levee and Soil Type 2 would be used for the interior zone. Table 1. Specifications for Zoned Embankment Material Plasticity Index Liquid Limit % Passing #200 Sieve Select Fill Between 8 and 40 Less than or equal to 45 Minimum 20% Soil Type 1 Between 8 and 30 Less than or equal to 45 20% with a moving average of 30% Soil Type 2 Less than 35 Less than or equal to 55 20% with a moving average of 30% Homogeneous Embankment Following discussions with the USACE Sacramento District, the adjacent levee design shifted from the zoned embankment to a homogeneous embankment. It was recognized that the visual classification of material as either Soil Type 1 or Soil Type 2 may be difficult in the field. For proper classification, samples would have to be taken to a lab and tested, resulting in time delays and increased costs. Construction of a zoned embankment could also result in the need to separate the two types of material at the borrow source (double handling material), which could increase the costs significantly. At the meeting with USACE on July 7 th, it was accepted that the adjacent levee could be constructed entirely of Type 2 material, therefore eliminating the need for embankment Sacramento Are Flood Control Agency 2 Natomas Levee Improvement Program September 11, 2008 U:\mitra\NLIP\meetings\BOSC\Session 1\Response to Comments\final\BOSC Response - Comment 8B _HDR.doc

22 Technical Memorandum zonation. The current adjacent levee design consists of a homogeneous embankment. We anticipate that the material found in the borrow site either meets the Type 2 standard or can be blended with additional material to meet it. This will be confirmed in upcoming detailed borrow site evaluations. Table 2 summarizes the specifications for the homogeneous fill. Table 2. Specifications for Homogeneous Embankment Material Plasticity Index Liquid Limit % Passing #200 Sieve Levee Fill Between 8 and 40 Less than or equal to 55 20% with a moving average of 30% Conclusion Preliminary analysis of the available borrow materials for the construction of the adjacent levee suggested a zoned embankment would be the most appropriate method of construction. This was due to the uncertainty associated with the borrow site, as well as USACE criteria regarding levee fill. Recent analysis of the borrow materials coupled with discussions with USACE have caused a change from a zoned embankment to a homogeneous fill with slightly higher plasticity specifications. It is anticipated that this material will be available in the proposed borrow site. Comment: Sacramento Are Flood Control Agency 3 Natomas Levee Improvement Program September 11, 2008 U:\mitra\NLIP\meetings\BOSC\Session 1\Response to Comments\final\BOSC Response - Comment 8B _HDR.doc

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24 TECHNICAL MEMORANDUM Date: August 4, 2008 To: Mr. Christopher Krivenac, PE, GE HDR, Inc. Geotechnical Engineering Materials Testing & Inspection Environmental Science & Engineering Water Resources Earthquake Engineering Air Quality From: Lynn O Leary, PE Mark H. Stanley, PE, GE Kleinfelder Project: Natomas Levee Improvement Program II Subject: Response to Comment No. 8c NLIP BOSC Report No. 1 dated May 9, 2008 Natomas Levee Improvement Project Sacramento and Sutter Counties, CA Below is Kleinfelder, Inc. s response to Comment 8c of NLIP Board of Senior Consultants Board Report No. 1: BOSC Comment No. 8c: 8. Recommendations on Specific Design Issues The Board to date has not had the opportunity to review detailed analyses, evaluations, or designs. However, during the initial meeting, the Board discussed several specific issues with the design team. Our recommendations on these selected items are as follows: c. Levee Impervious Zone -The preliminary plans for the levee improvements which incorporate a slurry cutoff wall include the placement of an impervious zone in the upper 10 feet or so of the levee above the cutoff wall. The Board does not understand the need for such an impervious zone as the borrow material is essentially composed of silty and fat clays. Thus, the entire new levee fill that would be placed above the cutoff wall would be essentially impervious and would not need a special impervious zone. The Board believes that this zone is probably unnecessary and that its elimination may reduce costs. Kleinfelder, Inc. Response to Comment No. 8c: Current design details for the Sacramento River East Levee indicate the adjacent levee will be constructed to a height of 10 feet above surrounding grade and then, where required, a soil-bentonite cutoff wall will be constructed through this embankment fill and extend to the specified tip elevation. The Natomas Levee Improvement Project (NLIP) Board of Senior Consultants (BOSC) has asked if varying the location of the wall would impact the seepage exit gradients and adjacent levee slope stability. Kleinfelder has calculated seepage exit gradients at the toe of the adjacent levee assuming the following cutoff wall locations: Page Fite Circle Sacramento, California fax

25 1. Centerline of the adjacent levee penetrating through the partially constructed levee section (current detail) 2. Centerline of the adjacent levee beginning at the existing ground surface (at grade) 3. Below the future adjacent levee landside slope crest at existing grade. Kleinfelder performed this analysis for three cross sections located in SREL PHASE II Reaches 5a (Station ), 6B (Station ), and 8 (Station ) to evaluate the impact of different near surface conditions For these analyses it was assumed the adjacent levee had a permeability of 1x10-5 cm/sec and the cutoff wall had a permeability of 1x10-6 cm/sec. Seepage and stability analyses were conducted for the 200 yr water surface elevation (WSE) and only seepage analysis was conducted for the 200 year plus 3 feet WSE (Top of Levee). These analyses indicate the location of the cutoff wall had minor impacts on the calculated seepage exit gradient at the toe of the adjacent levee and also had minor impacts on the calculated Factor of Safety (FoS) for slope stability. Landslide slope inclinations of 3H:1V were used in the analyses. Calculated FoS were 1.6 (Station lowest FoS) or greater. Calculated seepage exit gradients varied from no seepage gradient (zero) to 0.3 (Station highest seepage exit gradient). This analysis indicates that the through seepage condition is not significantly different if the cut-off wall location is changed to the exiting grade below the proposed adjacent levee. Kleinfelder is currently conducting sensitivity analysis by varying the hydraulic conductivity of the adjacent levee soils and the cut-off wall. We are also evaluating the impact of moving the cutoff wall location to the mid point of the adjacent levee landside slope. Page Fite Circle Sacramento, California fax

26 TECHNICAL MEMORANDUM Date: August 4, 2008 To: Mr. Christopher Krivenac, PE, GE HDR, Inc. Geotechnical Engineering Materials Testing & Inspection Environmental Science & Engineering Water Resources Earthquake Engineering Air Quality From: Lynn O Leary, PE Mark H. Stanley, PE, GE Kleinfelder Project: Natomas Levee Improvement Program II Subject: Response to Comment No. 8d NLIP BOSC Report No. 1 dated May 9, 2008 Natomas Levee Improvement Project Sacramento and Sutter Counties, CA Below is Kleinfelder, Inc. s response to Comment 8d of NLIP Board of Senior Consultants Board Report No. 1: BOSC Comment No. 8d: 8. Recommendations on Specific Design Issues The Board to date has not had the opportunity to review detailed analyses, evaluations, or designs. However, during the initial meeting, the Board discussed several specific issues with the design team. Our recommendations on these selected items are as follows: d. Piezometers Between Pressure Relief Wells In one reach of the proposed levee improvements, a new adjacent setback levee is proposed to be constructed with a 5:1 landside slope. Due to underseepage concerns, a 300-foot-wide seepage berm will also be constructed. To reduce the underseepage exit gradient to a value below 0.8 at the toe of the levee, approximately 60 pressure relief wells are also planned to be installed. It is the Board s understanding that the Sacramento District of the Corps is recommending that a piezometer be placed in the middle of the lengths between each relief well to assure that the exit gradient that develops during flood stages will be less than 0.8. The Board believes that the placement of 60 or so piezometers is excessive and is not required by Corps design procedures. In fact, current published Corps criteria do not even require relief wells at the end of berms more than 300 feet in width (see ETL ). The Board recommends that an appropriate number of piezometers should be between 3 and 5 for this reach. The wells themselves can serve as piezometers during pumping of the wells. A written request should probably be sent to the Sacramento District to receive their approval for reducing the number of required piezometers in this area. Page Fite Circle Sacramento, California fax

27 Kleinfelder, Inc. Response to Comment No. 8d: Kleinfelder is in agreement with the BOSC comment concerning reducing the number of piezometers installed between relief wells along the Reach 4B alignment. (The stated USACE guideline was to install a piezometer midway between every relief well). Piezometers located between relief wells can serve two useful purposes. 1) The piezometric head between relief wells can be used to confirm adequate seepage pressure relief between relief well locations. 2) The piezometric readings can be used to confirm parameters used for modeling underseepage conditions. The installation of the relief wells will require stratigraphic logging as well as pump testing. During pump testing, adjacent relief wells can be monitored for drawdown/well efficiency. It is believed this information can be used for further verification of design adequacy for the relief wells to reduce seepage gradients between relief wells to USACE criteria. Subsurface information along the Reach is generally available at a spacing of about 1,000 ft between explorations. Kleinfelder recommends piezometers be installed between relief wells at this same spacing pattern (consistent with the adjacent boring locations). Future piezometric measurements can then be conveniently compared to the stratigraphy assumed and analytical modeling performed along a particular Reach. Page Fite Circle Sacramento, California fax