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HomeMy WebLinkAboutAMEND 2023-0001; SMAC; STORM WATER MANAGEMENT INVESTIGATION; 2025-02-10STORM WATER MANAGEMENT INVESTIGATION 5801 AND 5807 VAN ALLEN WAY PARKING EXPANSIONCARLSBAD, CALIFORNIA FEBRUARY 10, 2025 PROJECT NO. G2123-52-04 PREPARED FOR:BEST BUILDERS, INC. GEOCON • HARBOR ASSOC I ATES Project No. G2123-52-04 February 10, 2025 5801-5807 Van Allen Owner, LLC c/o Rich McEvoy | Principal Harbor Associates 12501 Seal Beach Boulevard, Suite 225 Seal Beach, CA 90740 Subject: STORM WATER MANAGEMENT INVESTIGATION 5801 AND 5807 VAN ALLEN WAY PARKING EXPANSION CARLSBAD, CALIFORNIA Reference: Limited Geotechnical Investigation, 5801 and 5807 Van Allen Way Parking Expansion, 5801 and 5807 Van Allen Way, Carlsbad, California, prepared by Geocon Incorporated, dated February 29, 2024 (Project No. G2123-52-04). Dear Mr. McEvoy: In accordance with your request, we herein submit the results of our storm water management investigation for the proposed improvements to the subject site in Carlsbad, California (see Vicinity Map). Vicinity Map GEOCON INCORPORATED GEOTECHNICAL ■ ENVIRONMENTAL ■ MATERIALS ~ 6960 Flanders Drive ■ San Diego, California 92121-297 4 ■ Telephone 858.558.6900 ■ Fax 858.558.6159 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 2 - February 10, 2024 SITE AND PROJECT DESCRIPTION The subject property is currently developed with two, two-story commercial buildings with accommodating auxiliary structures, concrete flatwork, concrete/asphalt pavements, utilities and landscape. The site is located on the southwest corner of Faraday Avenue and Van Allen Way in Carlsbad, California. Existing grades surrounding the existing structures are relatively flat with elevations of approximately 235 to 245 feet above Mean Sea Level (MSL). The Existing Site Plan shows the current site conditions. Existing Site Plan The locations, site descriptions, and proposed development are based on our site reconnaissance, review of published geologic literature, field investigations, and discussions with project personnel. If development plans differ from those described herein, Geocon Incorporated should be contacted for review of the plans and possible revisions to this report. STORM WATER MANAGEMENT INVESTIGATION We understand storm water management devices including permeable pavers are being proposed in accordance with the 2016 City of Carlsbad BMP Design Manual (Third Update Effective January 2, 2024). If not properly constructed, there is a potential for distress to improvements and properties located hydrologically down gradient or adjacent to these devices. Factors such as the ~GEOCON 5801 Van Allen Way 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 3 - February 10, 2024 amount of water to be detained, its residence time, and soil permeability have an important effect on seepage transmission and the potential adverse impacts that may occur if the storm water management features are not properly designed and constructed. We have not performed a hydrogeological study at the site. If infiltration of storm water runoff occurs, downstream properties may be subjected to seeps, springs, slope instability, raised groundwater, movement of foundations and slabs, or other undesirable impacts because of water infiltration. Hydrologic Soil Group The United States Department of Agriculture (USDA), Natural Resources Conservation Services, possesses general information regarding the existing soil conditions for areas within the United States. The USDA website also provides the Hydrologic Soil Group. The following table presents the descriptions of the hydrologic soil groups. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. In addition, the USDA website also provides an estimated saturated hydraulic conductivity for the existing soil. HYDROLOGIC SOIL GROUP DEFINITIONS Soil Group Soil Group Definition A Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. B Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. C Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. D Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high-water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. The following table presents the information from the USDA website for the subject property. The Hydrologic Soil Group Map presents output from the USDA website showing the limits of the soil units. The property is underlain by previously placed fill and should be classified as Soil Group D with a kSAT of 0.00 to 0.06 inches/hour. ~GEOCON 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 4 - February 10, 2024 USDA WEB SOIL SURVEY – HYDROLOGIC SOIL GROUP* Map Unit Name Map Unit Symbol Approximate Percentage of Property Hydrologic Soil Group kSAT of Most Limiting Layer (Inches/Hour) Altamont Clay, 5 to 9 Percent Slopes AtC 86% D 0.06 to 0.20 Huerhuero Loam, 2 to 9 Percent Slopes HrC 13% D 0.00 to 0.06 Las Flores Loamy Fine Sand, 15 to 30 Percent Slopes, Eroded LeE2 1% D 0.00 to 0.06 *The areas of the property that possess fill materials should be considered to possess a Hydrologic Soil Group D. Hydrologic Soil Group Map ~GEOCON 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 5 - February 10, 2024 GEOLOGIC HAZARDS AND CONSIDERATIONS Groundwater Elevations We did not encounter static groundwater during our field investigations to the maximum depth explored of approximately 11 feet. We expect static groundwater exists at depths greater than 50 feet below existing grades. New or Existing Utilities Existing utilities are located in the roadways adjacent to the site and within the current site limits. Full or partial infiltration should not be allowed in the areas of the existing or proposed utilities to help prevent potential damage/distress to improvements. Mitigation measures to prevent water from infiltrating the utilities consist of setbacks, installing cutoff walls around the utilities and installing subdrains and/or installing liners. The horizontal and vertical setbacks for infiltration devices should be a minimum of 10 feet and a 1:1 plane of 1 foot below the closest edge of the deepest adjacent utility, respectively, if they were allowed. Existing Fill Materials We encountered previously placed fill in all of our borings. In Boring B-1, the fill extended to a depth of approximately 10 feet; in Borings B-2, B-3, and B-4, the fill extended to the maximum depth explored of approximately 8.5, 6, and 2 feet, respectively. Thicker fills may be present in unexplored areas of the site. Existing fill materials should be considered Hydrologic Soil Group D soils and assumed to possess relatively slow infiltration rates (0.01 inches/hour). In addition, fill soils have the potential for lateral water migration. We understand permeable pavement is proposed for the project. Partial (incidental) infiltration within the soils underlying the proposed permeable pavers may be considered feasible provided the design includes the use of side liners and subdrains. We should be contacted to evaluate potential infiltration characteristics if other storm water BMPs are proposed. Existing and Planned Structures Existing buildings and parking lots are situated throughout the site and roadway structures exist adjacent to the site. Water should not be allowed to infiltrate in areas where it could affect the neighboring properties and existing structures, improvements and roadways. Mitigation for existing structures consists of not allowing water infiltration within a lateral distance of at least 10 feet from the new or existing foundations and property lines. ~GEOCON 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 6 - February 10, 2024 Slope Hazards A descending slope having a maximum height of approximately 30 feet exists to the southwest of the site. Water should not be allowed to infiltrate within a horizontal distance of 1.5 times the height of the slope. CONCLUSIONS AND RECOMMENDATIONS Storm Water Evaluation Narrative and Conclusion Due to the presence of existing fill soils greater than 5 feet thick, we did not perform in-place infiltration testing at the site. Existing fill materials should be as considered Hydrologic Soil Group D soils and assumed to possess relatively slow infiltration rates on the order of 0.00 to 0.06 inches/hour, as mapped by USDA. Partial or incidental infiltration within the soils underlying the proposed permeable pavers may be considered feasible provided the design includes the use of side liners and subdrains. The civil engineer should evaluate potential infiltration at the site using kSAT rates on the order of 0.00 to 0.06 inches/hour. We should be contacted to evaluate potential infiltration characteristics if other storm water BMPs are proposed. Storm Water Infiltration Recommendations Side liners and subdrains should be incorporated into the design and construction of the planned storm water devices. The side liners should be impermeable (e.g. High-density polyethylene, HDPE, with a thickness of about 30 mil or equivalent Polyvinyl Chloride, PVC) to help prevent lateral water migration. The bottom of the storm water devices would remain unlined and allow for incidental infiltration. The subdrains should be perforated within the liner area, be at least 3 inches in diameter and consist of Schedule 40 PVC pipe. The subdrains outside of the liner should consist of solid pipe. The penetration of the liners at the subdrains should be properly waterproofed. The subdrains should be connected to a proper outlet. The devices should also be installed in accordance with the manufacturer’s recommendations. Storm Water Standard Worksheets The locations of the potential storm water management devices have not yet been determined. Assuming that the recommendations provided herein are incorporated into the design, we have evaluated the potential basins/BMPs with respect to the infiltration restrictions contained in Table D.1- 1 in Appendix D of the City of Carlsbad BMP Design Manual. The following table provides the information. ~GEOCON 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 7 - February 10, 2024 Restriction Element Is Element Applicable? (Yes/No) Mandatory Considerations BMP is within 100’ of Contaminated Soils No BMP is within 100’ of Industrial Activities Lacking Source Control No BMP is within 100’ of Well/Groundwater Basin No BMP is within 50’ of Septic Tanks/Leach Fields No BMP is within 10’ of Structures/Tanks/Walls No BMP is within 10’ of Sewer Utilities No BMP is within 10’ of Groundwater Table No BMP is within Hydric Soils No BMP is within Highly Liquefiable Soils and has Connectivity to Structures No BMP is within 1.5 Times the Height of Adjacent Steep Slopes (≥25%)No County Staff has Assigned “Restricted” Infiltration Category No Optional Considerations BMP is within Predominantly Type D Soil Yes BMP is within 10’ of Property Line No BMP is within Fill Depths of ≥5’ (Existing or Proposed)Yes BMP is within 10’ of Underground Utilities No BMP is within 250’ of Ephemeral Stream No Other (Provide detailed geotechnical support)No Result Based on examination of the best available information, I have not identified any restrictions above. ☐ Unrestricted Based on examination of the best available information, I have identified one or more restrictions above. ☒ Restricted Form D.2-4 of the BMP Design Manual provides guidance to the project civil engineer to estimate the factor of safety based on several factors. The following table describes the suitability assessment input parameters related to the geotechnical engineering aspects for the factor of safety determination. GUIDANCE FOR DETERMINING INDIVIDUAL FACTOR VALUES (TABLE D.2-4) Consideration High Concern – 3 Points Medium Concern – 2 Points Low Concern – 1 Point Infiltration Testing Method Any At least 2 tests of any kind within 50’ of BMP At least 4 tests within BMP footprint, OR Large/Small Scale Pilot Infiltration Testing over at least 5% of BMP footprint Soil Texture Class Unknown, Silty, or Clayey Loamy Granular/Slightly Loamy Soil Variability Unknown or High Moderately Homogenous Significantly Homogenous Depth to Groundwater/ Obstruction <5’below BMP 5-15’ below BMP >15’ below BMP Based on our geotechnical investigations and the previous table, the following table (Table D.2-3 from the BMP Design Manual) presents the estimated factor values for the evaluation of the factor of safety. ~GEOCON 5801 and 5807 Van Allen Way Parking Expansion Storm Water Management Investigation Project No. G2123-52-04 - 8 - February 10, 2024 This table only presents the suitability assessment safety factor (Part A) of the worksheet. The project civil engineer should evaluate the safety factor for design and use the combined safety factor for the design infiltration rate. FACTOR OF SAFETY WORKSHEET DESIGN VALUES (TABLE D.2-3, PART A) Consideration Assigned Weight (w) Factor Value (v) Product (p = w x v) Suitability Assessment (A) Infiltration Testing Method 0.25 3 0.75 Soil Texture Class 0.25 2 0.50 Soil Variability 0.25 2 0.50 Depth to Groundwater/ Obstruction 0.25 1 0.25 Suitability Safety Factor, SA = Σp 2.00 The project civil engineer should complete Part B of Worksheet D.2-3 using the data on this table. Additional information is required to evaluate the design factor of safety. If you have any questions regarding this correspondence, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED Bradley R. Kuna RCE 89846 Matt Love GE 3238 BRK:ML:kv Attachments: Infiltration Setback Map, Figure 1 Boring Logs B-1 through B-4 (e-mail) Addressee ~GEOCON B-1 B-2 B-3 B-4 APPROXIMATE PROJECT LIMITS 233 227 217 239 234 220 Qpf1/ Qpf 2/ 5801 FF=244.3' 5801 5807 (8.5'+) (10') GEOLOGIC MAP THE GEOGRAPHICAL INFORMATION MADE AVAILABLE FOR DISPLAY WAS PROVIDED BY GOOGLE EARTH, SUBJECT TO A LICENSING AGREEMENT. THE INFORMATION IS FOR ILLUSTRATIVE PURPOSES ONLY; IT IS NOT INTENDED FOR CLIENT'S USE OR RELIANCE AND SHALL NOT BE REPRODUCED BY CLIENT. CLIENT SHALL INDEMNIFY, DEFEND AND HOLD HARMLESS GEOCON FROM ANY LIABILITY INCURRED AS A RESULT OF SUCH USE OR RELIANCE BY CLIENT. 1 HARBOR ASSOCIATES SAN DIEGO, CALIFORNIA 6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121 - 2974 PHONE 858 558-6900 - FAX 858 558-6159PROJECT NO. G2123 - 52 - 04 DATE 02 - 29 - 2024FIGURE GEOTECHNICAL ENVIRONMENTAL MATERIALS Plotted:02/29/2024 10:45AM | By:JONATHAN WILKINS | File Location:Y:\PROJECTS\G2123-52-04 Harbor Associates\SHEETS\G2123-52-04-GeologicMAP.dwg B-4 GEOCON LEGEND ........PREVIOUSLY PLACED FILL (Placed in 2020 Under Observation and Testing of Geocon) ........APPROX. LOCATION OF GEOTECHNICAL BORING ........APPROX. LOCATION OF GEOLOGIC CONTACT ........APPROX. ELEVATION OF SANTIAGO FORMATION BASED ON PREVIOUS STUDY AND SITE GRADING (In Feet) 239 Qpf1 ........PREVIOUSLY PLACED FILL (Placed in 1990's, Observation and Testing by Others) Qpf 2 ........SANTIAGO FORMATION (Dotted Where Buried) Tsa (10')........APPROX. DEPTH TO SANTIAGO FORMATION (In Feet) INFILTRATION SETBACK LEGEND .......SITE AREA WITH GREATER THAN 5 FEET OF EXISTING FILL AND UNDERLAIN BY TYPE D SOILS. PARTIAL/ INCIDENTAL INFILTRATION FEASIBLE WITH THE USE OF SIDE LINERS AND SUBDRAINS INFILTRATION SETBACK MAP , t, ,, r ,.. t, o· 100' 200' r I - - -- - -r ,. I. SCALE 1"= 100' {On 11x17) t, ,, , ,. f ,.. ,. , GEOCON INCORPORATED ■ ■ PREVIOUSLY PLACED FILL (Qpf) Very stiff to hard, moist, light grayish brown, Sandy CLAY Very stiff to hard, moist, dark gray CLAY SANTIAGO FORMATION (Tsa) Very stiff to hard, moist, gray, FAT CLAY; well-consolidated mudstone BORING TERMINATED AT 11 FEET Groundwater not encountered Backfilled on 02-12-2024 101.9 107.6 99.7 102.5 23.0 20.3 24.6 23.9 B1-1 B1-2 B1-3 B1-4 B1-5 32 31 32 39 CL CL CH ... DISTURBED OR BAG SAMPLE GEOCON DEPTH IN FEET Figure A-1, Log of Boring B 1, Page 1 of 1 DR Y D E N S I T Y (P . C . F . ) ... DRIVE SAMPLE (UNDISTURBED) LIMITED ACCESS RIG WITH 6" SFAs PE N E T R A T I O N RE S I S T A N C E (B L O W S / F T . ) BORING B 1 ... CHUNK SAMPLE DATE COMPLETED ... SAMPLING UNSUCCESSFUL SOIL CLASS (USCS) GR O U N D W A T E R A. HESPELER CO N T E N T ( % ) SAMPLE NO.02-12-2024 SAMPLE SYMBOLS MO I S T U R E BY:EQUIPMENT ELEV. (MSL.)240' G2123-52-04.GPJ MATERIAL DESCRIPTION LI T H O L O G Y ... STANDARD PENETRATION TEST ... WATER TABLE OR ... SEEPAGE 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 NOTE: PROJECT NO. THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. G2123-52-04 I] ~ PREVIOUSLY PLACED FILL (Qpf) Very stiff to hard, moist, light grayish brown, Sandy CLAY Very stiff to hard, moist, dark gray CLAY BORING TERMINATED AT 8.5 FEET Groundwater not encountered Backfilled on 02-12-2024 115.4 104.1 101.8 15.7 21.6 23.0 B2-1 B2-2 B2-3 B2-4 24 31 33 CL CL ... DISTURBED OR BAG SAMPLE GEOCON DEPTH IN FEET Figure A-2, Log of Boring B 2, Page 1 of 1 DR Y D E N S I T Y (P . C . F . ) ... DRIVE SAMPLE (UNDISTURBED) LIMITED ACCESS RIG WITH 6" SFAs PE N E T R A T I O N RE S I S T A N C E (B L O W S / F T . ) BORING B 2 ... CHUNK SAMPLE DATE COMPLETED ... SAMPLING UNSUCCESSFUL SOIL CLASS (USCS) GR O U N D W A T E R A. HESPELER CO N T E N T ( % ) SAMPLE NO.02-12-2024 SAMPLE SYMBOLS MO I S T U R E BY:EQUIPMENT ELEV. (MSL.)240' G2123-52-04.GPJ MATERIAL DESCRIPTION LI T H O L O G Y ... STANDARD PENETRATION TEST ... WATER TABLE OR ... SEEPAGE 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 NOTE: PROJECT NO. THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. G2123-52-04 I] ~ PREVIOUSLY PLACED FILL (Qpf) Very stiff to hard, moist, light grayish brown, Sandy CLAY BORING TERMINATED AT 6 FEET Groundwater not encountered Backfilled on 02-12-2024 102.8 100.4 21.4 23.8 B3-1 B3-2 B3-3 31 27 CL ... DISTURBED OR BAG SAMPLE GEOCON DEPTH IN FEET Figure A-3, Log of Boring B 3, Page 1 of 1 DR Y D E N S I T Y (P . C . F . ) ... DRIVE SAMPLE (UNDISTURBED) LIMITED ACCESS RIG WITH 6" SFAs PE N E T R A T I O N RE S I S T A N C E (B L O W S / F T . ) BORING B 3 ... CHUNK SAMPLE DATE COMPLETED ... SAMPLING UNSUCCESSFUL SOIL CLASS (USCS) GR O U N D W A T E R A. HESPELER CO N T E N T ( % ) SAMPLE NO.02-12-2024 SAMPLE SYMBOLS MO I S T U R E BY:EQUIPMENT ELEV. (MSL.)242' G2123-52-04.GPJ MATERIAL DESCRIPTION LI T H O L O G Y ... STANDARD PENETRATION TEST ... WATER TABLE OR ... SEEPAGE 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 NOTE: PROJECT NO. THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. G2123-52-04 I] ~ 3.5 INCH ASPHALT CONCRETE, OVER 8 INCH CLASS II BASE (Base layer was saturated) PREVIOUSLY PLACED FILL (Qpf) Very stiff, moist, light grayish brown, Sandy CLAY BORING TERMINATED AT 2 FEET Groundwater not encountered Backfilled on 02-12-2024 CL ... DISTURBED OR BAG SAMPLE GEOCON DEPTH IN FEET Figure A-4, Log of Boring B 4, Page 1 of 1 DR Y D E N S I T Y (P . C . F . ) ... DRIVE SAMPLE (UNDISTURBED) LIMITED ACCESS RIG WITH 6" SFAs PE N E T R A T I O N RE S I S T A N C E (B L O W S / F T . ) BORING B 4 ... CHUNK SAMPLE DATE COMPLETED ... SAMPLING UNSUCCESSFUL SOIL CLASS (USCS) GR O U N D W A T E R A. HESPELER CO N T E N T ( % ) SAMPLE NO.02-12-2024 SAMPLE SYMBOLS MO I S T U R E BY:EQUIPMENT ELEV. (MSL.)242' G2123-52-04.GPJ MATERIAL DESCRIPTION LI T H O L O G Y ... STANDARD PENETRATION TEST ... WATER TABLE OR ... SEEPAGE 0.0 0.5 1.0 1.5 2.0 NOTE: PROJECT NO. THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC BORING OR TRENCH LOCATION AND AT THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES. G2123-52-04 - - I] ~