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Home My WebLink AboutMS 2020-0004; ADAMS STREET HOMES; GEOTECHNICAL INVESTIGATION FOR INFILTRATION BMP'S FOR PROPOSED ADAMS STREET HOMES; 2020-09-144r.-4&ii Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 14 September 2020 Rincon Homes P.O. Box 1949 Bonita, CA 91908 Attn: Mr. Thomas St. Clair Job No. 20-12852 Subject: Report of Limited Geotechnical Investigation for Proposed Storm Water Infiltration BMPs Adams Street Homes 3745 Adams Street Carlsbad, California Dear Mr. St. Clair: In accordance with your request and our work agreement dated July 10, 2020, Geotechnical Exploration, Inc. herein provides this report of limited geotechnical investigation for evaluation of the feasibility of utilizing storm water infiltration BMPs at the location of the proposed residential development. The field work was conducted on August 3, 2020. I. PROJECT SUMMARY AND SCOPE OF SERVICES It is our understanding that the lot is to be developed to receive four two-story single- family homes with detached garages, detached accessory dwelling units (ADUs) and associated improvements, with a new proposed entry driveway to access the residences at the center of the subject property from Adams Street to the north. 7420 TRADE STREET• SAN DIEGO, CA. 92121 • (858) 549-7222 • FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com Adams Street Homes Carlsbad, California Job No. 20-12852 Page 2 We have reviewed a preliminary grading plan provided to us in preparation of this report. We are also providing our "Report of Preliminary Geotechnical Investigation," dated September 14, 2020, conducted on the same date for the subject site. The scope of work performed for this investigation included a site reconnaissance and subsurface exploration program, laboratory testing, simple open pit falling head testing, preliminary plan review, document and report review, and the preparation of this report. The data obtained and the analyses performed were for the purpose of evaluation of the feasibility of utilizing storm water infiltration BMPs. Although preliminary infiltration rates have been provided in this report, the final infiltration rates are subject to change after grading operations have been performed and elevations have been raised for the proposed development and proposed bio-filtration BMP basin. Infiltration retesting is recommended after site grading has been performed for the proposed BMP basin and for final design. II. SITE DESCRIPTION The lot is known as Assessor's Parcel No. 205-270-13-00, per Map No. 1681, in the City of Carlsbad, County of San Diego, State of California. For the purposes of this report, the existing residence is assumed to face eastward to Adams Street but, in fact, faces east-northeastward. Refer to Figure No. I, the Vicinity Map, for the site location. The rectangular shaped lot, consisting of 42,688 square feet, is bordered on the north by two single-family residential developments at roughly the same elevations; on the south by a single-family residential development and parking lot at roughly the same elevations; on the west by a school playground at a slightly lower elevation; and on the east by Adams Street at a slightly higher elevation. Refer to Figure No. II, the Plot Plan. Adams Street Homes Carlsbad, California Job No. 20-12852 Page 3 The existing property is currently developed with a two-story single-family residential structure and associated improvements. Vegetation on the site primarily consists of an ornamental garden, shrubbery, weeds, grasses and many mature trees. The property slopes from the eastern property line to the western property line. Approximate elevations across the property range from approximately 81 feet above Mean Sea Level (MSL) along the western property line of the site to 92 feet above MSL at the eastern property line. Survey information concerning elevations across the site was obtained from the topographic survey template of the preliminary site plan by Kirk Moeller Architects, Inc., dated June 05, 2020. II. FIELD INVESTIGATION On August 3, 2020, we performed a geotechnical investigation for the proposed development. The field investigation consisted of a surface reconnaissance and a subsurface exploration program using a backhoe and hand tools to investigate the subsurface soils. During the investigation, two hand pits were excavated to a depth of 2 feet and 2½ feet in the area of the proposed bio-filtration basin location on the western portion of the property and the most feasible location for evaluating storm water infiltration BMPs, per the requirements of the City of Carlsbad Storm Water Standards, BMP Design Manual, in accordance with the Geotechnical and Groundwater Investigation Requirements (Appendix C), and Approved Infiltration Rate Assessment Methods for Selection and Design of Storm Water BMPs (Appendix D). The approximate locations of the simple open pit testing are shown on the Plot Plan (Figure No. II). The soils encountered in the exploratory excavations were continuously logged in the field by our field geologist and described in accordance with the Unified Soil Classification System, refer to Appendix A. Representative samples were obtained ;el Adams Street Homes Carlsbad, California Job No. 20-12852 Page 4 from the exploratory excavations at selected depths appropriate to the investigation. All samples were returned to our laboratory for evaluation and testing. III. SOIL DESCRIPTION Our recent subsurface exploration program revealed that the western proposed bio- filtration basin location, and the most feasible location for storm water infiltration BMPs, is underlain by approximately 1 to 1 ½ feet of silty sand fill soils and a limited thickness of topsoil, as encountered in our infiltration test locations (INF-1 and INF- 2). Our review of the geologic map by Kennedy and Tan, 2008, "Geologic Map of San Diego, 30'x60' Quadrangle, CA," indicate that the site is underlain by late to middle Pleistocene-Aged Old Paralic Deposits, Units 2-4 (Qop2-4) formational materials. The mapped old paralic deposits were not encountered within our simple open test pit testing locations. Both of the simple open test pit excavations were bottomed in the natural silty sand topsoil. Refer to the Excavation Logs, Figure Nos. IIIa and IIIb. Based on the preliminary site plan available for the preparation of this report, approximately 4 to 5 feet of fill soils will be placed in the area of the proposed bio- filtration basin. Infiltration rates have been provided for preliminary design only. Infiltration retesting is recommended after site grading and raising of grades been performed for the proposed BMP basin. The exploratory excavations and related information depict subsurface conditions only at the specific locations shown on the Plot Plan and on the particular date designated on the logs. Subsurface conditions at other locations may differ from conditions occurring at these handpit locations. Also, the passage of time may result in changes in the subsurface conditions due to environmental changes. Adams Street Homes Carlsbad, California Job No. 20-12852 Page 5 IV. LABORATORY TESTS AND SOIL INFORMATION The following laboratory test was conducted on the sampled soils: 1. Determination of Percentage of Particles Passing #200 Sieve (ASTM 01140-17) The particle size smaller than a No. 200 sieve analysis aids in classifying the tested soils in accordance with the Unified Soil Classification System and provides qualitative information related to engineering characteristics such as expansion potential, permeability, and shear strength. Based on our laboratory test results at infiltration test location INF-1, 31 % of the soils passed the #200 sieve; and at test location INF- 2, 29% of the soils passed the #200 sieve. V. GROUNDWATER Free groundwater was not encountered in the exploratory excavations at the time of excavation. It must be noted, however, that fluctuations in the level of groundwater may occur due to variations in ground surface topography, subsurface stratification, rainfall, and other possible factors that may not have been evident at the time of our field investigation. VI. INFILTRATION TESTING RATES AND SUMMARY We performed simple open pit falling head testing at two locations considered feasible for potential storm water infiltration BMPs at a depth of 24 and 30 inches at locations INF-1 and INF-2, per the requirements of the City of Carlsbad Storm Water Standards, BMP Design Manual, in accordance with Appendix D. Our infiltration testing was conducted in the of the proposed bio-filtration basin. This is considered ;Ji Adams Street Homes Carlsbad, California Job No. 20-12852 Page 6 the most feasible location on the property (i.e., relatively gentle gradient, away from structures, away from fill slopes, and away from utilities and retaining walls). Testing at the two locations (INF-1 and INF-2) revealed falling head rates of 20 and 11.7 minutes/inch. The simple open pit falling head test rate results for INF-1 and INF-2 have been converted to infiltration rates, using the Porchet Method, and indicate infiltration rates of 1.694-inch/hour and 3.258-inch/hour, respectively, or 0.847-inch/hour and 1.629-inch/hour, respectively, with a minimum factor of safety of 2 applied. Refer to Appendix B for simple open pit test rate results and simple open pit to infiltration rate calculations. Based on our review of USDA Web Soil Survey, the site has been assigned to hydrologic soil group (HSG) B. Hydrologic soil group B indicates " ... soils having a 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 ... " it is our opinion that that USDA's assigned hydrologic soil group of B is representative of the encountered sandy surface soils on the site. Refer to Appendix C for USDA Web Soil Survey. VII. CONCLUSIONS AND RECOMMENDATIONS The following conclusions and recommendations are based on the field investigation conducted by our firm, our laboratory test results, infiltration test results, document and preliminary plan review, and our experience with similar soils and formational materials in this area of San Diego County. IP Adams Street Homes Carlsbad, California Job No. 20-12852 Page 7 Based on the results of our simple open pit falling head testing and evaluation of the infiltration rates, and the results of the percent soil passing No. 200 sieve, it is our professional opinion that the proposed bio-filtration basin location has relatively favorable geologic and soil conditions, along with the measured soil infiltration rates, for the design of full infiltration BMPs at this time and is therefore suitable at current ground elevations for full to partial infiltration of stormwater discharge on the subject site. Again, due to infiltration rate testing being performed prior to grading for the proposed BMP basin, the rates are subject to change after grading has been performed and elevations have been raised. If the on-site fill and formational materials are used for the grading of the proposed BMP basin, we anticipate full to partial infiltration of storm water discharge on the subject site. Infiltration retesting is recommended after site grading has been performed for the proposed BMP basin and for final design. No infiltration of water in any amounts should be allowed within the currently proposed building pads, structures or near and/or atop proposed permanent fill slopes needed for the building pads. VIII. LIMITATIONS The findings, opinions, and conclusions presented herein have been made in accordance with generally accepted principles and practice in the field of geotechnical engineering within the City of Carlsbad. No warranty, either expressed or implied, is made. Our findings, opinions and conclusions are specifically limited to the scope of services described herein, for the evaluation and feasibility of storm water infiltration BMPs. When final project plans are completed, they should be made available for our review. Additional or modified recommendations may be provided as warranted. gt Adams Street Homes Carlsbad, California Job No. 20-12852 Page 8 This opportunity to be of continued service is sincerely appreciated. Should you have any questions, please do not hesitate to contact us. Reference to our Job No. 20- 12852 will expedite a response to your inquires. Respectfully submitted, Jai rr , .E. .C.E. 34422/G.E. 2007 Senior Geotechnical Engineer ~ Steve Osetek Staff Geologist ~ ' C.E.G. 999/P.G. 3391 VICINITY MAP Adams Street Homes 37 45 Adams Street Carlsbad, CA. Figure No. I Job No. 20-12852 20-12852-p.ai 11Y1fl f'-1 .. ~-/~•-;::;:ij<! r ----~-----, • ' flURil .m__ .,, ..... ~ T-2 .. 1"¥.AOO I Ffi,1182 PAD#fl/.5 .£1. -, '.f..'~z~.€~ ""'<::·' : I -~1 t:::.. -=--=-- , '/;-F' '2:f FILJ. SI.OPE_c.,c:,, .1 ¢=''···¢=>" ¢= ¢= ¢= . ¢= . r ., ~WJ.I.""-'----, .,; I • si '-1. • ' I -~ ·I. ~- · .. t -~ '11 APN;\ 20Sp0-1Ul, \ ,.,.,., •·c~j%'.,;~;\~~: •••NBfmz-£;.;r : c,, • .,,L,,c. ''"'':1:7' '' .GEOLOGY LEGEND Qaf Qop 2-4 Artificial Fill Old Paralic Deposits ( units 2~4) I LEGE ND INF-2 Approximate Location of Exploratory Trench Approximate Location of Infiltration Test 0 '·!(--~9121 f'L.:jf.i1 7<, l • • --~~;.:., f"l::.9~...,1 I I f1 Scale: l" = 30' (approximate) I GIIU'fCIC.4le f"•ff ---• 0 PRELJM/NARY Sll'E PLAN 3145 ADAMS Sl1IEEr CITYOFCAALS&IO PASCO LARET SUITER !..,•-!!"1111!,ll!!-.■..!11!1..J ~= AmaR.259.82l2lwww.~ NOTE: This Plot Plan is not to be used for legal purposes. Locations and dimensions are approximate. Actual property dimensions and locations of utilities may be obtained from the Approved Building Plans or the "As-Built" Grading Plans. REFERENCE: This Plot Plan was prepared from an existing undated PRELIMINARY SITE PLAN by PASCO LARET SUITER & ASSOCIATES and from on-site field reconnaissance performed by GEi. PLOT PLAN Approximate Location of Proposed Biofiltration Basin Adams Street Homes 37 45 Adams Street Carlsbad, CA. Figure No. II Job No. 20-12852 Geotechnical Exploration, Inc. ( September 2020) ~ Geotechnical Exploration, Inc. EQUIPMENT: Hand Tools ~ DIMENSION & TYPE OF EXCAVATION: DATE LOGGED: August 03, 2020 2 ft. x 2 ft. x 2 ft. Handpit LOGGED BY: SO SURFACE ELEVATION: ± 81.5' Above Mean Sea Level REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND Q X l:i: Q w CLASSIFICATION :E Q Cl) l >,;::-l ~ 's 'o ~ I-a: (.) ~ ~1 z z w Q a. w Q a. ::::, w-:E -~ 0 ..I w w a: :E a: ;!:....1 0 :c 0 ..I DESCRIPTION AND REMARKS 0::::, 0~ ::::, ::::, ::::,~ ~ iii 0 Cl) zO I-:;.-m II.. (.) s I-s iii :E I-:E -iii z 3: :!: -Cl) _Cl) < rn <( II.. QI :!: (Grain Size, Density, Moisture, Color) en a.~ a..z I--xz z a. z a. 0 w QI > c( •O 'W a..O <( w w xO ~ ..I 0~ rn rn :::i ~:e Zc 0 :e :e Q Q WO Ill SIL TY SAND, fine-to medium-grained. Loose. Dry. Dark SM -brown. With roots and trash debris. -FILL (Qaf) - 1 SILTY SAND, fine-to medium-grained. Loose to medium SM dense. Dry. Brown. With roots. TOPSOIL 1 --31 % passing No. 200 sieve. 4.7 2 Bottom of excavation at 2 feet. - - - 3- - - - 4- - - - 5- - - - 6- JOB NUMBER: 20-12852 PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE JOB NAME: LOG NO. INF-1 MODIFIED CALIFORNIA SAMPLE IN-PLACE HAND-DRIVE SAMPLE STANDARD PENETRATION TEST Adams Street Homes SITE LOCATION: 37 45 Adams Street, Carlsbad, CA FIGURE NO. Illa g c:i 0 w ..I a. :E <( rn ~ Geotechnical Exploration, Inc. EQUIPMENT: Hand Tools DIMENSION & TYPE OF EXCAVATION: ~ DATE LOGGED: August 03, 2020 2 ft. x 2 ft. x 2 ft. Handpit LOGGED BY: SO SURFACE ELEVATION: ± 81' Above Mean Sea Level REVIEWED BY: LDR/JAC GROUNDWATER/SEEPAGE DEPTH: Not Encountered FIELD DESCRIPTION AND 0 i:;j t: 0 :E 0 -CLASSIFICATION >c;:::->c;:::-0 ~ "' ~ ~ I-!a., a: 0 !a., a: 0 e ~~ z z w 0 a. w 0 a. ::, ...I w w a: w-:E a: :i;-~..J 0 0 J: 0 ...I DESCRIPTION AND REMARKS 0::, 0~ ::, ::, ::,~ ~ iii 0 "' zO I--m a. 0 5 I-Siii :E I-:E-iii z 3: -"' <"' c( fu QI :!E :!E (Grain Size, Density, Moisture, Color) a. !:!? -rn Cl) a. z I--xz z a. z a. 0 > < •O 'W a. 0 c( w w i:;j8 i:;j ..J c~ en en :::i ~ :E Zo 0 :E :E 0 0 ID SIL TY SAND, fine-to medium-grained. loose. Dry. Gray-SM -brown. Some roots and trash debris. -FILL (Qaf) - 1 - - SIL TY SAND, fine-to medium-grained. loose to medium SM dense. Dry. Brown. With roots. 2 TOPSOIL 1 -29% passing No. 200 sieve. 3.3 Bottom of excavation at 2.5 feet. - 3- - - - 4 - - - - 5 - - - - 6 - JOB NUMBER: 20-12852 PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE JOB NAME: LOG NO. INF-2 MODIFIED CALIFORNIA SAMPLE IN-PLACE HAND-DRIVE SAMPLE STANDARD PENETRATION TEST Adams Street Homes SITE LOCATION: 37 45 Adams Street, Carlsbad, CA FIGURE NO. lllb I ci ci w ..J a. :E < "' APPENDIX A UNIFIED SOIL CLASSIFICATION CHART SOIL DESCRIPTION Coarse-grained (More than half of material is larger than a No. 200 sieve) GRAVELS, CLEAN GRAVELS (More than half of coarse fraction is larger than No. 4 sieve size, but smaller than 3") GRAVELS WITH FINES (Appreciable amount) SANDS, CLEAN SANDS (More than half of coarse fraction is smaller than a No. 4 sieve) SANDS WITH FINES (Appreciable amount) GW GP GC SW SP SM Well-graded gravels, gravel and sand mixtures, little or no fines. Poorly graded gravels, gravel and sand mixtures, little or no fines. Clay gravels, poorly graded gravel-sand-silt mixtures Well-graded sand, gravelly sands, little or no fines Poorly graded sands, gravelly sands, little or no fines. Silty sands, poorly graded sand and silty mixtures. SC Clayey sands, poorly graded sand and clay mixtures. Fine-grained (More than half of material is smaller than a No. 200 sieve) SIL TS AND CLAYS Liquid Limit Less than 50 Liquid Limit Greater than 50 HIGHLY ORGANIC SOILS (rev. 6/05) ML Inorganic silts and very fine sands, rock flour, sandy silt and clayey-silt sand mixtures with a slight plasticity CL Inorganic clays of low to medium plasticity, gravelly clays, silty clays, clean clays. OL Organic silts and organic silty clays of low plasticity. MH Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts. CH Inorganic clays of high plasticity, fat clays. OH Organic clays of medium to high plasticity. PT Peat and other highly organic soils APPENDIX B INFILTRATION TEST DATA AND RATE CALCULATIONS Simple Open Pit Falling Head Test Sheet Project Name: Adams Street Homes Project No. 20-12852 Date Excavated: 8/3/20 Test Hole No: INF-1 Initial Time (Minutes) Final Time (Minutes) 1145 1245 1250 1350 1355 1455 Time interval (minutes) 60 60 60 Initial Water Level (inches) 17.500 18.000 17.875 Tested By: SO Soil Classification: SM Depth of Test Hole: 24" Test Hole Dia: 24" Final Water Level (inches) 23.500 23.125 20.875 Change in water (inches) 6.000 5.125 3.000 Falling Head Rate (min/inches) 10.000 11.707 20.000 Simple Open Pit Falling Head Test Sheet Project Name: Adams Street Homes Project No. 20-12852 Date Excavated: 8/3/20 Test Hole No: INF-2 Initial Time (Minutes) Final Time (Minutes) 1150 1235 1240 1340 1345 1445 Time interval (minutes) 45 60 60 Initial Water Level (inches) 23.875 23.500 24.000 Tested By: SO Soil Classification: SM Depth of Test Hole: 30" Test Hole Dia: 24" Final Water Level (inches) 30.000 30.000 29.125 Change in water (inches) 6.125 6.500 5.125 Falling Head Rate (min/inches) 7.347 9.231 11.707 Simple Open Pit Rate to Infiltration Rate Conversion (Porchet Method) Project Name: Adams Street Homes Project No. 20-12852 Test Hole No: INF-1 Test EB Depth Delta T Water Depth No. (inches) (min) 1 (inches) 1 24 60 17.500 2 24 60 18.000 3 24 60 17.875 4 5 6 7 8 9 Calculated By: SO Checked By: Test Hole Dia: 24" Date: 8/3/2019 Date: Depth of Test Hole: 24" Porchet Corrections Infiltration rate=((delta h*60r)/(delta t*(r+2 h avg)) Water Depth hl h2 delta h havg 2 (inches) (inches) (inches) {inches) (inches) 23.500 6.500 0.500 6.000 3.500 23.125 6.000 0.875 5.125 3.438 20.875 6.125 3.125 3.000 4.625 r (radius) delta delta t*fr+2 h (inches) h*60r ave:) 12 4320 1140 12 3690 1132.5 12 2160 1275 Infiltration rate (in/hr} 3.789 3.258 1.694 Simple Open Pit Rate to Infiltration Rate Conversion (Porchet Method) Project Name: Adams Street Homes Project No. 20-12852 Test Hole No: INF-2 Test EB Depth Delta T Water Depth No. (inches) (min) 1 (inches) 1 30 45 23.875 2 30 60 24.000 3 30 60 24.000 4 5 6 7 8 9 Calculated By: SO Checked By: Date: 8/3/2020 Date: Test Hole Dia: 24" Depth of Test Hole: 30" Porchet Corrections Infiltration rate=((delta h*60r)/(delta t*(r+2 h avg)) Water Depth hl h2 delta h havg r (radius) 2 (inches) (inches) (inches) (inches) (inches) (inches) 30.000 6.125 0.000 6.125 3.063 12 30.000 6.000 0.000 6.000 3.000 12 29.125 6.000 0.875 5.125 3.438 12 delta h*60r 4410 4320 3690 delta t*{r+2 Infiltration rate h avg) (in/hr) 815.625 5.407 1080 4.000 1132.5 3.258 APPENDIX C USDA Web Soil Survey Map ;: Hydrologic Soil Group-San Diego County Area, California ;: ~ (20-12852 Adams Street Homes) !.> j;j j;j ~ ~ 468tl2ll 468600 468640 468660 468660 468610 468680 468690 468700 468710 468720 <46873) 468740 468700 46878) 466770 33" 9'20"N I I 33" 9'20'N I I I I I-I I--I I I I -I 0 0 I -1 I I I I 33" 9'16"N I 1 33" 9'16'N 468tl2ll 468600 468640 468660 468660 468610 468680 468690 468700 468710 468720 <46873) 468740 468700 46878) 468'770 ;: ;: ~ !.> j;j Map Scale: 1:733 if prinlEd a, A landscape (11" x 8.5") sheet !iii Meters ~ ~ N 0 10 20 40 00 A Feet 0 35 70 140 210 Map projedion: Web MettatDr ComerCXl011:fnatEs: WGS84 Edge tics: U1M Zaie 11N WGS84 USDA Natural Resources Web Soil Survey 8/27/2020 :..Iii Conservation Service National Cooperative Soil Survey Page 1 of4 Hydrologic Soil Group-San Diego County Area, California (20-12852 Adams Street Homes) MAP LEGEND MAP INFORMATION Area of Interest (AOI) D Area of Interest (AOI) Soils Soil Rating Polygons D A D AID D B D BID D C D CID D D D Not rated or not available Soil Rating Lines .,...,,,_ A ,,...,,,. A/0 ,,...,,,. B ,,...,,,. BID ,,...,,,. C ....., CID ,,...,,,. D -,, Not rated or not available Soil Rating Points A ■ AID ■ B ■ BID USDA Natural Resources "' Conservation Service ■ C CID • D C Not rated or not available Water Features .,.._,, Streams and Canals Transportation H-+ Ralls ,,,.,,-Interstate Highways US Routes -Major Roads Local Roads Background Aerial Photography Web Soil Survey National Cooperative Soil Survey The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 15, May 27, 2020 Soil map units are labeled (as space allows) for map scales 1 :50,000 or larger. Date(s) aerial images were photographed: Jan 24, 2020-Feb 12,2020 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 8/27/2020 Page 2 of4 Hydrologic Soil Group-San Diego County Area, California 20-12852 Adams Street Homes Hydrologic Soil Group Map unit symbol Map unit name Rating Acres inAOI Percent of AOI MIC Marina loamy coarse B 1.0 sand, 2 to 9 percent slopes Totals for Area of Interest 1.0 Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (AID, B/D, and C/D). The groups are defined as follows: Group 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. Group 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. Group 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. Group 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. If a soil is assigned to a dual hydrologic group (AID, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition USDA Natural Resources iiiiii Conservation Service Web Soil Survey National Cooperative Soil Survey 100.0% 100.0% 8/27/2020 Page 3 of 4 Hydrologic Soil Group-San Diego County Area, California Component Percent Cutoff: None Specified Tie-break Rule: Higher Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 20-12852 Adams Street Homes 8/27/2020 Page4 of4