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HomeMy WebLinkAboutSDP 2021-0029; IONIS LOTS 21 AND 22; RESPONSE TO CITY OF CARLSBAD REVIEW COMMENTS; 2023-01-23Project No. 06442-32-31A January 23, 2023 Ionis Pharmaceuticals, Inc. 2855 Gazelle Court Carlsbad, California 92010 Attention: Mr. Wayne Sanders Subject: RESPONSE TO CITY OF CARLSBAD REVIEW COMMENTS IONIS PHARMACEUTICALS LOTS 21 AND 22 (CARLSBAD OAKS NORTH BUSINESS PARK) CARLSBAD, CALIFORNIA References: 1. City of Carlsbad Review Comments, Ionis Lots 21 & 22, Carlsbad Oaks North Business Park (1st review), Project ID: SDP2021-0029, Memorandum dated December 7, 2022. 2. Update Geotechnical Report, Ionis Lots 21 and 22 (Carlsbad Oaks North Business Park), Carlsbad, California, prepared by Geocon Incorporated, dated October 19, 2021 (Project No. 06442-32-31A). Dear Mr. Sanders: In accordance with the request of Mr. Jon Olhson with DGA Planning/Architecture/Interiors, we have prepared this letter to respond to a City of Carlsbad Review comment (Reference 1) for the project. The City review comment pertaining to geotechnical issues followed by our response is provided below. Issue No. 1:The submitted “Update Geotechnical Report…” consist essentially geotechnical conclusions and recommendations for the proposed development that are based on previous work at the site back in 2007 and 2004, and does not include recent subsurface exploration, laboratory testing, etc., to address the currently proposed project. While the reviewer understands that Geocon Inc., performed the geotechnical observation and testing during the mass grading of the site in 2007, a stand-alone geotechnical report for the proposed development is required by the City. The following comments are provided with the intent of forming a stand-alone geotechnical report for the proposed project. Response:As stated in Reference No. 2 and by reviewer above, we provided testing and observation services during mass grading of the property. As part of our services, we collected soil samples during grading operations and performed laboratory testing. Pertinent laboratory information collected during mass grading is presented in Reference No. 2, Appendix A. The existing “subsurface” information is comprehensive and adequate to provide recommendations for the continued development of the property. In this regard, no additional subsurface exploration is required. Issue No. 2:Please provide a copy of the “Final Repot of Testing and Observation Services during Site Grading, Carlsbad Oaks North…”by Geocon, Inc., dated December 11, 2007, that reports the previous mass grading activities that established the subject GEOCON INCORPORATED G E OT E CHN I CAL ■E NV I RONMENTA L ■ MA T ER I A L S 6960 Flanders Drive ■ Son Diego, California 92121-297 4 ■ Telephone 858.558.6900 ■ Fax 858.558.6159 Project No. 06442-32-31A - 2 - January 23, 2023 lots and has reportedly been used as the basis for the conclusions/recommendations provided in the “Update Geotechnical Report…”. Response:We will provide an electronic copy to DGA for submittal. Issue No. 3:Please provide a copy of the rippability study report (addressing the required local excavation of the underlying granitic rock) that is discussed in the “Update Geotechnical Report...” Response:We will provide an electronic copy to DGA for submittal. Issue No. 4:As the “Update Geotechnical Report…” is almost a year old, please review the most current revision the grading plans for the proposed project prepared by Pasco Laret Suiter & Associates and provided any update conclusions/recommendations as necessary. Response:We understand that the grading plans are undergoing revisions to address City comments. Per Section 8.16 of Referenced No. 2, we will review grading plans prior to final design City submittal and check weather additional analyses and/or recommendations are required. Issue No. 5:Please provide an updated “Geologic Map” (providing all the geotechnical information currently shown) using the most current version of the project grading plan as the base map. Response:We performed cursory review of the grading plans prepared by Pasco Laret Suiter & Associates (PLSA). The planned improvements presented on the project grading plans are generally the same as presented on the geologic map included in Reference No. 2. We opine that revising our geologic map is not warranted. Issue No. 6:Please revise Geologic Cross-Sections A-A’, B-B’, and C-C’ as necessary based on the updated “Geologic Map” requested in comment #5 above. Please also add the following to the cross-sections a) the temporary slopes (per comment #19 below) associated with the excavations for the basement levels of the proposed office building and parking structure, b) graphically show the approximate locations/elevations of the over-size rock fragments (approximate 2 to 4’ plus size boulders) that were reportedly placed during the mass grading of the lots as they relate to the basement levels of the proposed office building and parking structure, and c) show/label the depths of the recommended over-excavations/re- recompaction to prepare the building pads for both the basement level and at-grade portions of the proposed office building/parking structure and parking areas. Response:Based on our response to Issue No. 5, revised geologic cross-sections are not necessary. Part A: the base map used to prepare the geologic map included in Reference No. 2 and the grading plan prepared by PLSA do not show temporary slopes; therefore, temporary slopes are not shown on our geologic map. In this regard, it is the contractors responsibility to select the appropriate temporary slope excavation geometry in accordance with OSHA. Part B: It is assumed this comment was made in jest. Individual rock fragments are not mapped during mass grading operations; however the rock restriction zones are. Refer to update geotechnical report regarding discussion of previous grading operations. Part C: Not necessary. Refer to Section 8.3.8 of Reference No. 2 for undercut recommendations. Issue No. 7:Please provide a statement addressing the potential impact of the project on adjacent properties. Please include a discussion on the potential impacts to Project No. 06442-32-31A - 3 - January 23, 2023 adjacent properties from the apparent need to locally excavate (blast?) the granitic rock underlying the site to establish proposed pad grades and/or over-excavate to address cut/fill transition conditions. Response:We opine that potential impact of the subject project grading to adjacent properties is low provided geotechnical recommendations presented in Reference No. 2 are followed. If blasting is required, the grading/blasting contractor is required to address any impacts to adjacent improvements. Issue No. 8:Please describe the approximate range of fill thickness beneath the existing site grades and the approximate thickness of fill that will exist beneath the proposed office building and parking structure subsequent to the recommended site grading for the project. Response:As shown on geologic map included in Reference No. 2, Lot 21 existing fill thicknesses range between approximately 5 feet and 40 feet. On Lot 22, the existing fill thickness ranges between approximately 5 feet and 20 feet. After proposed fine grading the fill beneath planned office building will range between approximately 5 feet and 30 feet. For the parking garage, the fill will range between approximately 5 feet and 14 feet. Issue No. 9:Please provide a discussion addressing the local and regional faulting associated with the subject site. Please include names, distances, and potential magnitudes of faults potentially impacting the subject property. Response:See Section 7.1 of Reference No. 2. The information requested is not relevant in design of the planned improvements. Issue No. 10:Provide subsurface exploration as necessary to determine and assess the current subsurface soil and groundwater conditions at the subject site with respect to the proposed development (both as-grade and basement levels of the proposed office building and parking structure). (also see comment #11 through 14 below). Response:See Section 6 of Reference No. 2. Issue No. 11:As there is no recent subsurface exploration to address the current project and current soil conditions provided in the “Update Geotechnical Report…,” please justify the geotechnical parameters (strength, expansion potential, sulfate exposure, etc.) that are provided in the report for the soils that will be exposed at both the as-grade parking/driveway areas and basement levels of the office building and parking structure. Response:Please see response to Issue No. 1. In addition, and as discussed in Sections 8.2.2 and 8.2.3 of Reference No. 2, we will perform additional expansion potential and water-soluble sulfate testing after completion of grading operations to evaluate the soils present within the upper approximately 3 feet of ultimate design finish elevation. As is standard for ultimate development of a property, we will collect soil samples and perform necessary laboratory testing during grading to check our geotechnical design parameters presented in Reference No. 2. If necessary, we will provide revised recommendations based on information collected during grading. Issue No. 12:As there is no current subsurface exploration and associated laboratory testing provided in the “Update Geotechnical Report…,” please provide the basis for the values of total and differential settlement for the proposed development that are provided in the report. Project No. 06442-32-31A - 4 - January 23, 2023 Response:Please see response to Issue No. 1. Pertinent laboratory information collected during mass grading is presented in Reference No. 2, Appendix A. Issue No. 13:As there is no current subsurface exploration and associated laboratory testing provided in the “Update Geotechnical Report…,” please provide the basis for the R-values recommended for pavement design that are provided in the report. Response:Please see Section 8.11.1 of Reference No. 2. The pavement sections are PRELIMINARY and not for construction. The final pavement sections will be provided after the grading operations are completed, subgrade soils are sampled, and laboratory resistance value (R-Value) testing is performed on the soil samples collected. Issue No. 14:As the absence of current subsurface exploration to evaluate the site, please provide the basis that only the upper 12 inches of the existing subgrade of the subject lots requires remedial grading prior to fill placement or other construction. Response:Our recommendations are based on field observations during the ultimate development of Carlsbad Oaks North Business Park Lots 4, 5, 13, 14, 20, 23 and 25 that consisted of same soil conditions as Lots 21 and 22. In rare instances remedial grading may need to be extended deeper than 12-inches. This is why the statement in Section 8.3.5 of Reference No. 2 states “Near-surface soils may need to be processed to greater depths depending on the amount of drying or wetting that has occurred within the soils since the initial sheet grading of the pad. The actual extent of remedial grading should be determined in the field by the geotechnical engineer or engineering geologist”. Issue No. 15:With respect to the laboratory testing that was reported previously performed as part of the mass grading of the site 2007 (Appendix A of the “Update Geotechnical Report…”), please indicate the specific locations and depth/elevations within the subject lots that the samples for direct shear, expansion index, and soluble sulfate tests were taken. Response:Please see response to Issue No. 11 and Issue No. 14. Issue No. 16:The “Updated Geotechnical Report…” indicates that the expansion index testing previously performed as part of the mass grading of the site in 2007 (Appendix A of the “Update Geotechnical Report…” was relative to the soil cap mantling the upper 3’ of the subject lots. Please address and justify the expansion potential of the soils that will be exposed at the grade of the proposed basement levels of the office building and parking structure and provide geotechnical design parameters accordingly (see comments #10 and 11 above and #17 below). Response:Please see response to Issue No. 11 and Issue No. 14. Issue No. 17:The text of the “Update Geotechnical Report…” indicates that the foundation recommendations are based on soils with an Expansion Index less than 50. As soils with expansion index (EI) over 20 are considered expansive and require mitigation in accordance with Sections 1803.5.3 and 1808.6 of the 2019 CBC, please provide recommendations as necessary and a statement that the proposed foundation system/slabs on-grade will meet the requirement of Section 1808.6 (1808.6.1 through 1808.6.4) that is being recommended to satisfy the code requirement, and provide the Effective Plasiticity Index and any other parameters for foundation design in accordance with WRI/CRSI Design of Slab-on-Ground floors or a post- Project No. 06442-32-31A - 5 - January 23, 2023 tensioned design in accordance with PTI DC 10.5 as necessary to address section 1808.6.2 for slabs on-ground. Response:We have not been provided with the project foundation plans for our review. We will address this issue when that occurs. Issue No. 18:As the “Update Geotechnical Report…” indicates that the mass grading for the site included placing boulder-size granitic rocks (approximately 2 to 4’ plus size) at depth in the fill beneath the subject lots, please provide remedial grading recommendations as necessary for the basement level building pads for the office building and parking structure relative to the potential occurrence of the boulders at the elevation of the basement pads. Response:The comment does not apply to the parking garage and the west portion of the building pad as planned grading consists of placing fill to achieve design grade. For the remainder of the pad where grading consists of excavating into existing fill to achieve design grade, the recommendations presented in Section 8.3.8 of Reference No. 2 are applicable if oversize rock is encountered at ultimate grade. Also, see response to Issue No. 14. Issue No. 19:Please provide the OSHA Type Soil (A, B, or C) and associated temporary slope inclination (H:V) that the construction plans and contractors should adhere to during the design and construction of the development. Response:Please see Section 8.3.12 of Reference No. 2. The contractors are responsible for ensuring that all excavations and trenches are properly shored, maintained and excavated to appropriate configuration in accordance with the applicable OSHA rules and regulations. In this regard, the contractors “competent person” is responsible for determining the soil class for use in temporary excavations. Issue No. 20:Please provide a complete summery list of the geotechnical observations/testing services that should be performed as part of the construction of this proposed development. Response:As indicated is Sections 8.3.3 and 8.8.7 of Reference No. 2., we will provide testing and observation services on a full-time basis during grading operations and planned soil nail wall. We will check foundation excavations prior to placement of rebar and concrete. As for balance of improvements, we will provide our services on a requested basis during trench backfill, wall backfill and construction of surface improvements. Should you have any questions regarding this letter, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED Emilio AlvaradoRCE 66915 David B. EvansCEG 1860 EA:DBE: (e-mail) Addressee