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HomeMy WebLinkAboutPD 2020-0049; HOPE ELEMENTARY SCHOOL; ASSESSMENT OF DESIGN PHASE INFILTRATION FEASIBILITY; 2020-10-01DVBE  SBE  SDVOSB  SLBE GEOTECHNICAL MATERIALS SPECIAL INSPECTION www.usa-nova.com 944 Calle Amanecer, Suite F San Clemente, CA 92673 P: 949.388.7710 4373 Viewridge Avenue, Suite B San Diego, CA 92123 P: 858.292.7575 Carlsbad Unified School District October 1, 2020 6225 El Camino Real NOVA Project No. 2019157 Carlsbad, CA 92009 Attention: Derrick Anderson Subject: Report Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization 3010 Tamarack Avenue, Carlsbad, California Dear Mr. Anderson, The intent of this report is to address the design phase infiltration conditions and related feasibility for permanent stormwater Best Management Practices (‘stormwater BMPs’) for drainage management areas (DMAs) at the above-referenced site. The report is provided in response to permit requirements of the City of Carlsbad Land Development Engineering Department requesting results of a design-phase infiltration analysis. Additional work was completed by NOVA to adequately address these requirements. This design-phase infiltration evaluation has been in accordance with guidance contained in the City of Carlsbad BMP Design Manual, February 2016 edition (hereinafter, ‘the BMP Manual’). This report has been prepared by NOVA Services, Inc. (NOVA) for Carlsbad Unified School District. NOVA is retained by Carlsbad Unified School District as Geotechnical Engineer-of- Record (GEOR) for this project. OVERVIEW General The Hope Elementary School Modernization project is currently in the construction/design phase of development. Geotechnical analysis for this project is reported in NOVA 2019. This report presents NOVA’s design-phase infiltration feasibility assessment, which includes additional testing to address the proposed BMP locations as they are currently planned. Feasibility of Stormwater BMPs As is well-established by the BMP Manual, the feasibility of stormwater infiltration is principally dependent on structural, geotechnical, and hydrogeologic conditions at the project site. Development of permanent stormwater infiltration BMPs is feasible at this site, assuming a “partial” infiltration condition, as determined by field testing of infiltration rates. Infiltration rates presented herein may be used in the BMP sizing calculations, so long as care is taken in the 2 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 placement of future BMPs, such that factors listed in Section C.2 of Appendix C of the BMP Manual will not adversely impact the future structures. BACKGROUND Location Hope Elementary School is located at 3010 Tamarack Avenue in Carlsbad, California. The approximately 12.5-acre campus is bounded to the north, west, and south by descending natural slopes. A residential development is located across Tamarack Avenue to the east. Figure 1 (following page) depicts the site location and limits. Current Site Use The site is currently occupied by Hope Elementary School, consisting of a number of school buildings, asphalt playgrounds, a parking area, and a grass playfield. The site is currently undergoing modernization improvements as presented in RP 2019 (see Attachment 1, References). Historical Grading and As-Graded Condition Insight into existing cut and fill conditions may be obtained by review of older civil drawings associated with development of the groundform that is now occupied by Hope Elementary School (DDA 1986). Existing cut and fill depths will not be affected appreciably by the modernization operations. DDA 1986 indicates that the campus is located atop a large cut-and-fill pad with a finished elevation of +224.5 feet mean sea level (msl). Pre-grading topography consisted of a ridge with descending slopes and drainages on the north, south, and west of the site, with elevations that ranged from +255 feet msl at the top of the hill, near the eastern boundary of the campus, descending to about +120 feet msl to the bottom of the western drainage. Development required fills and cuts that ranged to about 30 feet, with the deepest fill being on the northernmost edge of the playfield. 3 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Figure 1. Site Location and Limits (source: adapted from Google Earth 2017) Subsurface Exploration by NOVA in 2019 Select data from NOVA’s field exploration conducted in 2019 was used in this infiltration assessment. The previous investigation included subsurface exploration methods with separate geologic and geotechnical objectives. • Three (3) large diameter (30-inch) geologic borings (LD-1, LD-2 and LD-3) were drilled to depths of 40 to 78 feet and down-hole logged on July 26 through July 30, 2019. • A single geologic core boring (C-1) was drilled on August 8-9, 2019 to a depth of 120 feet. The core boring was drilled through large-diameter boring LD-1 which was initially advanced to 40 feet bgs and was abandoned without downhole logging due to unstable and unsafe conditions, i.e. perched irrigation water resulting in the overlying fill caving into the boring. • Eleven (11) geotechnical borings ( B-1 through B-11) were drilled on July 23-24, 2019. Subsurface Geology and Groundwater Conditions Geologic units encountered by the subsurface investigation included engineered fill (Qaf) and the underlying sandstones of the Eocene-Age Santiago Formation (Tsa). For the purposes of this report, the subsurface may be considered to occur as the sequence of soil units described below. 4 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 1. Unit 1, Fill. A layer of fill of varying thickness mantles the site. The fill ranges from approximately 1 to 30 feet in thickness, where encountered in the geotechnical borings. The upper 5 feet of fill is comprised of predominantly ‘cleaner’ fine to medium grained sands (i.e., sands with limited amounts of silt and clay -sized particles) of medium dense to dense consistency. In areas of fills thicker than 5 feet, the lower portions of the fill encountered was found to be clayey, ranging from clayey sands to low plasticity clays. Though the fill is known to be engineered, NOVA has not been able to locate the grading reports that document grading of the site. Most of the fill appears to have been derived by processing sandstones from the Santiago Formation. 2. Unit 2, Santiago Formation. Beneath the fill, the borings encountered sandstones of the Tertiary-aged Santiago Formation (Tsa). These formational sedimentary rocks were observed to consist of white to light gray silty sandstone of dense to very dense consistency. The sandstone extends to below the depths explored in the borings. The dense consistency of the sandstones is characterized by SPT blow counts (‘N’, after ASTM D 1586), commonly in excess of practical refusal of the sampling device at N > 100. Unconfined compression testing of this unit showed strengths ranging from 50 pounds per square inch (psi) to 490 psi. The hollow stem auger drilling tools were refused on two (2) borings. Groundwater seepage was encountered in the geologic borings at depths of 60 to 78 feet below existing ground surface. No seepage was observed at the surface of the underlying natural slopes at or below this elevation during the site reconnaissance. Groundwater will not affect the planned construction. PROPOSED BMPS Locations of prospective BMPs were determined by coordination with the project civil engineer (FPL and Associates, Inc.). Locations for testing were analyzed across the entirety of the site with specific consideration of avoiding areas adjacent to steep slopes, existing structures and foundations, existing utilities, and areas with variable fill conditions. As may be seen on Figure 2 (following page), three areas were selected for design phase testing. The northernmost area is in the playfield, and underlain by approximately 25 feet of fill. The southern areas were chosen because the infiltration surface will be within the Santiago Formation, and the areas are sufficiently set back from existing structures and steep slopes. 5 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Figure 2. Location of BMP Test Areas (source: adapted from RP 2020- North to Right of Figure) PERCOLATION TESTING BY NOVA General NOVA conducted six (6) borehole percolation tests (‘P-1’ through ‘P-6’) in the design stages of planning for the site’s development on September 22 to September 23, 2020. The percolation testing was conducted within 50 feet of the planned BMP structures in accordance with the BMP manual. All testing was completed in accordance with procedures detailed in the referenced City of Carlsbad BMP Design Manual (Carlsbad 2016). The design phase percolation test borings (‘P- 1’ through ‘P-6’) were drilled to the elevation of the bottom of the proposed BMP structures. The geologist directed sampling and maintained a log of the subsurface materials that were encountered. A record of these logs is provided in Attachment 2. For the exploratory borings required in east BMP location, NOVA utilized explorations from the 2019 investigation (‘LD-1/C-1’, ‘B-9’ and ‘LD 2’) as these were excavated near the planned BMP structures, and were advanced to at least 10 feet below the bottom of BMP elevation. The purpose of the exploratory borings in a BMP investigation is to evaluate the stratigraphy of the soils underlying the proposed BMP that may affect infiltration. Figure 3 (following page) depicts the tested locations. Plate 1, provided following the text of this report, reproduces this graphic in larger scale. 6 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Figure 3. Percolation and Subsurface Excavation Locations (source: adapted from RP 2020) Drilling The percolation test borings were drilled with an 8-inch solid stem auger to depths of 7.5 feet bgs (below ground surface). Field measurements were taken to confirm that the borings were excavated to approximately 8 inches in diameter. The borings were logged by a NOVA geologist, who observed and recorded exposed soil cuttings and the boring conditions. Logs of these borings are attached to this report. Exploratory borings excavated by NOVA in 2019 were used in conjunction with NOVA’s field evaluation to determine subsurface conditions at the site and near the proposed BMP. Figure 4 (following page) depicts the drilling operations directed by NOVA on September 22, 2020. 7 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Figure 4. Drilling Operations September 2020 Conversion to Percolation Wells Once the percolation test borings were drilled to the desired depths, the borings were converted to percolation test wells by placing an approximately 2-inch layer of ¾-inch gravel on the bottoms, then extending 3-inch diameter Schedule 40 perforated PVC pipe to the ground surface. The ¾-inch gravel was used to partially fill the annular space around the perforated pipe below the existing finish grade to minimize the potential of soil caving. Percolation Testing The percolation test wells were pre-soaked by filling the holes with water to at least 5 times the well radius. The pre-soak water did not percolate at least 6 inches into the soil unit within 25 minutes; therefore, the holes were filled with water to the ground surface elevation and testing commenced the following day, within a 26-hour window. The day of the test, water levels were then recorded every 30 minutes for 6 hours (minimum of 12 readings), or until the water percolation stabilized after each reading. At the beginning of each test interval, the water level was raised to approximately the same level as previous tests 8 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 in order to maintain a near-constant head during all test periods. Figure 5 depicts the percolation well construction directed by NOVA on September 22, 2020. Figure 5. Percolation Well Construction September 2020 Closure At the conclusion of the percolation testing, the PVC pipe was removed and the resulting hole was backfilled with soil cuttings and patched to match the existing surfacing. Infiltration Rates The percolation rate of a soil profile is not the same as its infiltration rate (‘I’). Therefore, the field percolation rate was converted to an estimated infiltration rate utilizing the Porchet Method in accordance with guidance contained in the BMP Manual. Table 1 (following page) provides a summary of the infiltration rates determined by the percolation testing. 9 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Table 1. Infiltration Rates Determined by Percolation Testing BMP Structure Boring Approximate Ground Elevation (ft, msl) Depth of Test (ft) Approximate Test Elevation (ft, msl) Infiltration Rate (in/hr) Infiltration Rate (in/hr, FS=2*) Northern Area 1 P-1 +219 7.5 +211.5 0.44 0.22 P-2 +219 7.5 +211.5 0.32 0.16 Southern Area 2 P-3 +223.5 7.5 +216 0.45 0.22 P-4 +223.5 7.5 +216 0.19 0.10 Southern Area 3 P-5 +223 7.5 +215.5 0.74 0.37 P-6 +223 7.5 +215.5 0.58 0.29 Notes: (*) ‘FS’ indicates ‘Factor of Safety’ As may be seen by review of Table 1, a factor of safety (FS) is applied to the infiltration rate (I) determined by the percolation testing. This factor of safety considers the nature and variability of subsurface materials, as well as the natural tendency of infiltration structures to become less efficient with time. In coordination with the design engineer, Form I-9 was completed after guidance contained in the BMP Manual, and resulted in FS = 2. According to Carlsbad 2016, infiltration rates less than 0.5 inches per hour, in which there are no geotechnical constraints to infiltration, imply that the soil and geologic conditions may allow for ‘partial’ infiltration. REVIEW OF GEOTECHNICAL FEASIBILITY CRITERIA Overview General Section C.2 of Appendix C of the BMP Manual provides seven factors that should be considered by the project geotechnical professional while assessing the feasibility of infiltration related to geotechnical conditions. These factors are listed below. • C.2.1.1 Soil and Geologic Conditions • C.2.1.2 Settlement and Volume Change • C.2.1.3 Slope Stability • C.2.1.4 Utility Considerations • C.2.1.5 Groundwater Mounding • C.2.1.6 Retaining Walls and Foundations • C.2.1.7 Other Factors 10 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 The above geotechnical feasibility criteria are reviewed in the following subsections. Soil and Geologic Conditions The soil borings and percolation test borings completed for this assessment disclose the sequence of soil units below. 1. Unit 1, Fill. Tests P-1 and P-2 were conducted in an area with approximately 25 feet of fill, thus the infiltration surface for the BMP would be in fill. The upper 15 feet of fill is comprised of lifts of light gray silty sand, sandy silt and clayey sand derived of the Santiago Formation, of medium dense to dense consistency. Below 15 feet the fill encountered was found to be clayey, ranging from clayey sands to low plasticity clays. 2. Unit 2, Santiago Formation. Tests P-3 through P-6 tested areas where the infiltration surface will be within the Santiago Formation. These formational sedimentary rocks were observed to consist of white to light gray silty sandstone of medium dense to very dense consistency. The sandstone extends to below the depths explored in the borings. During the geological and geotechnical investigation, the dense consistency of the sandstones was characterized by SPT blow counts (‘N’, after ASTM D 1586), commonly in excess of practical refusal of the sampling device at N > 100. Settlement and Volume Change Settlement and volume change due to stormwater infiltration is not a concern with: (i) BMPs sited well-away from any structures, (ii) no potential for liquefaction, and (iii) no potential for hydro collapse. Slope Stability BMPs located near slopes should be lined with impermeable liners along the sides of the facility. Based on the limited height of the slope, combined with the BMP liner, it is NOVA’s judgement that the BMP will not undermine the slope. Utilities Stormwater infiltration BMPs should not be sited within 10 feet of underground utilities. As currently designed, BMPs are not located within 10 feet of underground utilities, that NOVA is aware of. Groundwater Mounding Groundwater seepage was encountered in the geologic borings at depths of 60 to 78 feet below existing ground surface. Due to the depth of groundwater, mounding is not considered to be a hazard of infiltration at this site. 11 Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 Retaining Walls and Foundations Stormwater infiltration BMPs should not be sited within 10 feet from retaining walls and foundations. The proposed stormwater infiltration BMPs investigated herein are not sited within 10 feet from retaining walls or foundations. Other Factors According to NRCS Web Soil Survey, the mapped hydrologic soil group is Group C and Group D. Full infiltration is not required for this hydrologic soil group. Recommendation for ‘Partial Infiltration’ In consideration of the foregoing, and the calculated design infiltration rates, the site is generally suitable for partial infiltration by stormwater BMPs placed within the constraints cited above; however, this judgment should be reviewed when the siting of BMPs with respect to proposed structures, utilities, and other improvements has been finalized by the Civil Engineer. CLOSURE NOVA appreciates the opportunity to be of service to Carlsbad Unified School District on this most interesting project. Should you have any questions regarding this report or other matters, please contact the undersigned at 858.292.7575. Sincerely, NOVA Services, Inc. __________________________ ___________________________ Melissa Stayner, PG, CEG John F. O’Brien, PE, GE Senior Engineering Geologist Principal Geotechnical Engineer Attachments: Plate 1- Subsurface Investigation Map Attachment 1, References Attachment 2, Logs of Borings Attachment 3, Form I-8: Categorization of Infiltration Feasibility Condition Attachment 4, Form I-9: Factor of Safety and Design Infiltration Rate Worksheet Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 PLATE 1 SUBSURFACE INVESTIGATION MAP B-9 LD-2 LD-1C-1 P-1 P-2 P-3 P-4P-5 P-6 00 80'160' N W E N S 4373 Viewridge Avenue, Suite B San Diego, CA 92123 P: 858.292.7575 944 Calle Amanecer, Suite F San Clemente, CA 92673 P: 949.388.7710 NOVA HO P E E L E M E N T A R Y S C H O O L 30 1 0 T A M A R A C K A V E CA R L S B A D , C A 9 2 0 1 0 GEOTECHNICAL MATERIALS SPECIAL INSPECTION SBEDVBE www.usa-nova.com PROJECT NO.: DATE: DRAWN BY: REVIEWED BY: 2019157 SEP 2020 DTJ MS SUBSURFACE INVESTIGATION MAP DRAWING TITLE: SCALE:1"=80' PLATE NO.1 OF 1 SDVOSB SLBE C-1 B-9 LD-2 P-6 GEOTECHNICAL BORING LOCATION OF LARGE DIAMETER BORING PERCOLATION TEST BORING LOCATION OF ROCK CORING KEY TO SYMBOLS Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 ATTACHMENT 1 REFERENCES Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 References Carlsbad 2016. City of Carlsbad BMP Design Manual, City of Carlsbad, February 2016. DDA 1986. Grading and Drainage Plan—Preliminary Phase, Calavera Hills Elementary Site, Carlsbad Unified School District, Davis Duhaime Associates, Architects, Job No. A85-87, March 1986. NOVA 2019. Report, Geotechnical and Geohazard Investigation, Hope Elementary School Modernization, 3010 Tamarack Avenue, Carlsbad, CA, NOVA Services, Inc., Project 2019157, September 05, 2019. RP 2019. Carlsbad Unified School District, Hope Elementary School, New Classroom Buildings and Modernization, Rachlin Partners, DSA Progress Drawings, August 1, 2019. FPL 2020. Postconstruction Hydrology Map for a 25 Year Storm Event, New Classroom Buildings and Modernization, Hope Elementary School, 310 Tamarack Avenue, Carlsbad, CA, Rachlin Partners, civil consultants FPL and Associates, Inc., APPL No. A04-118734, DSA Submittal April 10, 2020. Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 ATTACHMENT 2 LOGS OF BORINGS LIGHT GRAY, SOME CLAY, DAMP DENSE HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-1 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 219 FT MSL NOVA FILL (Qaf): SILTY SAND; BROWN, MOIST, LOOSE TO MEDIUM DENSE, FINE TO MEDIUM GRAINED SM ATTACHMENT 2.1 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. WHITE-GRAY LIGHT GRAY, SOME CLAY, DAMP TO MOIST HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-2 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 219 FT MSL NOVA FILL (Qaf): SILTY SAND; BROWN, MOIST, LOOSE TO MEDIUM DENSE, FINE TO MEDIUM GRAINED SM ATTACHMENT 2.2 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. SANTIAGO FORMATION (Tsa): SILTY SAND; LIGHT GRAY, MOIST, DENSE, FINE TO MEDIUM GRAINED HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-3 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 223.5 FT MSL NOVA FILL (Qaf): SILTY SAND; BROWN TO OLIVE GRAY, MOIST, LOOSE TO MEDIUM DENSE, FINE TO MEDIUM GRAINED SM ATTACHMENT 2.3 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. SC CLAYEY SAND; GRAY, MOIST, VERY DENSE, FINE TO MEDIUM GRAINED SM SANTIAGO FORMATION (Tsa): SILTY SAND; LIGHT GRAY, MOIST, DENSE, FINE TO MEDIUM GRAINED HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-4 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 223.5 FT MSL NOVA FILL (Qaf): SILTY SAND; BROWN TO OLIVE GRAY, MOIST, LOOSE TO MEDIUM DENSE, FINE TO MEDIUM GRAINED SM ATTACHMENT 2.4 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. SC CLAYEY SAND; GRAY, MOIST, VERY DENSE, FINE TO MEDIUM GRAINED SM SANTIAGO FORMATION (Tsa): SILTY SAND; LIGHT GRAY, MOIST, DENSE, FINE TO MEDIUM GRAINED, SCATTEREED ROOTS HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-5 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 223 FT MSL NOVA SM ATTACHMENT 2.5 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. SANTIAGO FORMATION (Tsa): SILTY SAND; LIGHT GRAY, MOIST, DENSE, FINE TO MEDIUM GRAINED HOPE ELEMENTARY SCHOOL 3010 TAMARACK AVENUE CARLSBAD, CALIFORNIA PERCOLATION BORING LOG P-6 DE P T H ( F T ) PROJECT NO.: 2019157 LOGGED BY:GN SO I L C L A S S . (U S C S ) BL O W S PE R 1 2 - I N C H E S REVIEWED BY:MS DATE: SEP 2020 EQUIPMENT:SEPTEMBER 22, 2019 8-INCH DIAMETER AUGER BORING GROUNDWATER NOT ENCOUNTERED 5 10 15 20 25 30 0 GROUNDWATER / STABILIZED BULK SAMPLE SPT SAMPLE ( ASTM D1586) CAL. MOD. SAMPLE (ASTM D3550) ERRONEOUS BLOW COUNT NO SAMPLE RECOVERY GEOLOGIC CONTACT SOIL TYPE CHANGE # * DIRECT SHEAR EXPANSION INDEX ATTERBERG LIMITSSIEVE ANALYSISRESISTANCE VALUE CONSOLIDATIONSAND EQUIVALENT CORROSIVITYMAXIMUM DENSITY KEY TO SYMBOLS GR A P H I C L O G REMARKSBU L K S A M P L E SUMMARY OF SUBSURFACE CONDITIONS (USCS; COLOR, MOISTURE, DENSITY, GRAIN SIZE, OTHER) LA B O R A T O R Y CA L / S P T S A M P L E ELEVATION: DATE EXCAVATED: EXCAVATION DESCRIPTION: GROUNDWATER DEPTH: MDDS EIALSA RVCN SE LAB TEST ABBREVIATIONS CRCATERPILLAR 303.5C EXCAVATOR GPS COORD.: SOIL DESCRIPTION N/A ± 223 FT MSL NOVA SM ATTACHMENT 2.6 BORING TERMINATED AT 7.5 FT AND CONVERTED TO A PERCOLATION WELL. *12''.'/'06#4;5%*11. 6#/#4#%-#8'07' %#4.5$#&%#.+(140+# .#4)'&+#/'6'4$14+0).1).&Ä &' 2 6 *  ( 6 241,'%601 .1))'&$;/5 51 + .  % . # 5 5  7 5 % 5 $. 1 9 5 2' 4    Ä + 0 % * ' 5 4'8+'9'&$;/5 &#6'5'2 '37+2/'06,7.; Ä+0%*&+#/'6'4#7)'4$14+0) )4170&9#6'4016'0%1706'4'&        )4170&9#6'456#$+.+<'& $7.-5#/2.' 5265#/2.' #56/& %#./1&5#/2.' #56/& '4410'175$.19%1706 015#/2.'4'%18'4; )'1.1)+%%106#%6 51+.6;2'%*#0)'  &+4'%65*'#4 ':2#05+10+0&': #66'4$'4).+/+655+'8'#0#.;5+54'5+56#0%'8#.7' %1051.+&#6+105#0&'37+8#.'06 %14415+8+6;/#:+/7/&'05+6; -';615;/$1.5 )4 # 2 * + %  . 1 ) 4'/#4-5$7 . -  5 # / 2 . 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NOVA (+.. 3CH 5+.6;5#0&$4190&4;61&#/2/'&+7/&'05'(+0')4#+0'&5/ #22'0&+:% 5#06+#)1(14/#6+10 6UC 5+.6;5#0&5610'.+)*6)4#;&#/28'4;&'05' (+0'61/'&+7/)4#+0'&  $14+0)6'4/+0#6'&#6(601)4170&9#6'4'0%1706'4'&01%#8+0) 5/ 64#%'%1#45'5#0&   5%#66'4'&%1#45')4#+0'&5#0&64#%'14#0)'1:+&#6+10  +0%*'51(#52*#.6%10%4'6'18'4+0%*'51(#))4')#6'$#5'   &'05' +06'4$'&&'&/'&+7/)4#;5+.65610'.'05'5 .+)*6)4#;(+0'61/'&+7/)4#+0'&  Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 ATTACHMENT 3 FORM I-8 Appendix I: Forms and Checklists I-3 February 2016 Categorization of Infiltration Feasibility Condition Form I-8 Part 1 - Full Infiltration Feasibility Screening Criteria Would infiltration of the full design volume be feasible from a physical perspective without any undesirable consequences that cannot be reasonably mitigated? Criteria Screening Question Yes No 1 Is the estimated reliable infiltration rate below proposed facility locations greater than 0.5 inches per hour? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. 2 Can infiltration greater than 0.5 inches per hour be allowed without increasing risk of geotechnical hazards (slope stability, groundwater mounding, utilities, or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. The infiltration rate of the existing soils for locations P-1, P-2, P-3, P-4, P-5 and P-6, based on the design phase on-site infiltration study was calculated to be less than 0.5 inches per hour ( P-1= 0.22, P-2 = 0.16, P-3 = 0.22, P-4=0.10, P-5 = 0.37, and P-6=0.29 inches per hour) after applying a calculated factor of safety (FS) of FS=2. No. See Criterion 1. X X Appendix I: Forms and Checklists I-4 February 2016 Form I-8 Page 2 of 4 Criteri a Screening Question Yes No 3 Can infiltration greater than 0.5 inches per hour be allowed without increasing risk of groundwater contamination (shallow water table, storm water pollutants or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. 4 Can infiltration greater than 0.5 inches per hour be allowed without causing potential water balance issues such as change of seasonality of ephemeral streams or increased discharge of contaminated groundwater to surface waters? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. Part 1 Result * If all answers to rows 1 - 4 are “Yes” a full infiltration design is potentially feasible. The feasibility screening category is Full Infiltration If any answer from row 1-4 is “No”, infiltration may be possible to some extent but would not generally be feasible or desirable to achieve a “full infiltration” design. Proceed to Part 2 *To be completed using gathered site information and best professional judgment considering the definition of MEP in the MS4 Permit. Additional testing and/or studies may be required by the City to substantiate findings. Water contamination was not evaluated by NOVA Services. The potential for water balance was not evaluated by NOVA Services. Proceed to Part 2 Appendix I: Forms and Checklists I-5 February 2016 Form I-8 Page 3 of 4 Part 2 – Partial Infiltration vs. No Infiltration Feasibility Screening Criteria Would infiltration of water in any appreciable amount be physically feasible without any negative consequences that cannot be reasonably mitigated? Criteria Screening Question Yes No 5 Do soil and geologic conditions allow for infiltration in any appreciable rate or volume? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D. 6 Can Infiltration in any appreciable quantity be allowed without increasing risk of geotechnical hazards (slope stability, groundwater mounding, utilities, or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2. Provide basis: The infiltration rate of the existing soils for locations P-1, P-2, P-3, P-4, P-5 and P-6, based on the design phase on-site infiltration study was calculated to be P-1= 0.22, P-2 = 0.16, P-3 = 0.22, P-4=0.10, P-5 = 0.37, and P-6=0.29 inches per hour, after applying a calculated factor of safety (FS) of FS=2. Infiltration is considered feasible from a geotechnical perspective. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. Provide basis: C2.1 A geologic investigation was performed at the subject site. C2.2 Settlement and volume change due to stormwater infiltration is not a concern with: (i) low expansive soils,(ii) no potential for liquefaction, and (iii) no potential for hydro collapse.C2.3 Infiltration has the potential to cause slope failures. BMPs are to be sited a minimum of 50 feet away from any slope. C2.4 Infiltration can potentially damage subsurface and underground utilities. As planned, BMPs are not located within 10 feet of underground utilities.C2.5 Stormwater infiltration can result in damaging ground water mounding during wet periods. Mounding is not considerd to be a hazard of infiltration at this site due to the depth of groundwater. C2.6 BMPs are not anticipated to be located near foundations or retaining walls. Infiltration has the potential to increase lateral pressure and reduce soil strength which can impact foundations and retaining walls.C2.7 Other Factors: According to NRCS Web Soil Survey, the mapped hydrologic soil group is Group C and Group D. Full infiltration is not required for this hydrologic soil group. X X Appendix I: Forms and Checklists I-6 February 2016 Form I-8 Page 4 of 4 Criteria Screening Question Yes No 7 Can Infiltration in any appreciable quantity be allowed without posing significant risk for groundwater related concerns (shallow water table, storm water pollutants or other factors)? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. 8 Can infiltration be allowed without violating downstream water rights? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. Part 2 Result* If all answers from row 5-8 are yes then partial infiltration design is potentially feasible. The feasibility screening category is Partial Infiltration. If any answer from row 5-8 is no, then infiltration of any volume is considered to be infeasible within the drainage area. The feasibility screening category is No Infiltration. *To be completed using gathered site information and best professional judgment considering the definition of MEP in the MS4 Permit. Additional testing and/or studies may be required by the City to substantiate findings. Water contamination was not evaluated by NOVA Services. The potential for water balance was not evaluated by NOVA Services. Partial Infiltration Assessment of Design Phase Infiltration Feasibility Hope Elementary School Modernization, Carlsbad, CA NOVA Project No. 2019157 October 1, 2020 ATTACHMENT 4 FORM I-9 Appendix I: Forms and Checklists I-7 February 2016 Factor of Safety and Design Infiltration Rate Worksheet Form I-9 Factor Category Factor Description Assigned Weight (w) Factor Value (v) Product (p) p = w x v A Suitability Assessment Soil assessment methods 0.25 Predominant soil texture 0.25 Site soil variability 0.25 Depth to groundwater / impervious layer 0.25 Suitability Assessment Safety Factor, SA = p B Design Level of pretreatment/ expected sediment loads 0.5 Redundancy/resiliency 0.25 Compaction during construction 0.25 Design Safety Factor, SB = p Combined Safety Factor, Stotal= SA x SB Observed Infiltration Rate, inch/hr, Kobserved (corrected for test-specific bias) Design Infiltration Rate, in/hr, Kdesign = Kobserved / Stotal Supporting Data 1 1 1 1 0.25 0.25 0.25 0.25 1 3 1 1 1.5 0.25 0.25 2 2 P-1=0.44 P-4=0.19P-2=0.32 P-5=0.74P-3=0.45 P-6=0.58 P-1=0.22 P-4=0.10P-2=0.16 P-5=0.37P-3=0.22 P-6=0.29 Briefly describe infiltration test and provide reference to test forms: Design Phase Borehole percolation tests were utilized for all percolation borings (P-1 through P-6) at the bottom of the prospective infiltration BMP structures accompanied by exploratory engineering excavations (LD-1/C-1, LD-2, and B-9) to depths of at least 10 feet below the bottom elevation of the BMP structures. The data is abstracted and detailed in the Assessment of Design Phase Infiltration Feasibility, Hope Elementary School Modernization (NOVA 2020). In coordination with the design engineer, a factor of safety of FS = 2 was determined following the guidance in the BMP Manual.