HomeMy WebLinkAboutCT 80-46; HIGHLAND DRIVE 5 LOT SF RESIDENCES; STORM WATER MANAGEMENT INVESTIGATION HIGHLAND 5; 2023-01-27STORM WATER
MANAGEMENT INVESTIGATION
HIGHLAND 5
2908 – 2924 HIGHLAND DRIVE
CARLSBAD, CALIFORNIA
PREPARED FOR
JANUARY 27, 2023
PROJECT NO. G2861-11-01
California West
Project No. G2861-11-01 January 27, 2023
California West Communities 5927 Preistly Drive, Suite 110 Carlsbad, California 92008
Attention: Mr. Matt Howe
Subject: STORM WATER MANAGEMENT INVESTIGATION HIGHLAND 5 2908 – 2924 HIGHLAND DRIVE CARLSBAD, CALIFORNIA
Reference: 1. Update Geotechnical Investigation, Highland 5, 2908 – 2924 Highland Drive, Carlsbad, California, prepared by Geocon Incorporated, dated December 29, 2021 (Project No. G2861-11-01).
2. Preliminary Geotechnical Evaluation, Proposed 5-Lot Subdivision, Tract No. 80-46 Carlsbad, San Diego County, California, Assessor’s Parcel Number (APN’s) 156-200-28, -29, -30, -31, -32, prepared by GeoSoils, Inc., dated February 1, 2021 (W.O. 8037-A-SC).
Dear Mr. Howe:
In accordance with the request of the City of Carlsbad, we prepared this storm water management
investigation to supplement the previously submitted storm water study performed by GeoSoils, Inc.
and to address Table D1.1 from the January 2023 BMP Design Manual Update for the Highland 5 project
located in the City of Carlsbad, California (see Vicinity Map).
Vicinity Map
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
Geocon Project No. G2861-11-01 -2 - January 27, 2023
SITE AND PROJECT DESCRIPTION
The approximately 1.4-acre property consists of two residential houses with a long driveway providing
access from Highland Drive. The site is located south of an existing park, east of Highland Drive, north
of an existing single-family residence and Newland Court, and west of existing houses. Existing grades
are gently to moderately sloping to the west towards Highland Drive. Elevations at the site range
between approximately 163 to 184 feet Mean Sea Level (MSL) from west to east. The high point at the
site is roughly 100 feet from the eastern property line. The Existing Site Map shows the current site
conditions.
Existing Site Map
We understand the project will consist of demolishing the existing structures and improvements to
construct a 5-lot residential subdivision with accompanying accessory dwelling units (ADUs),
driveways, utilities and landscaping. We anticipate the residential structures will be one to two stories.
Two storm water basins on the west and south side and two buried storm trap structures within the
driveway are planned at the property.
We prepared the referenced update geotechnical investigation report for the site and proposed
development. The previous field investigation performed by GeoSoils, Inc. consisted of performing 8
borings, including 2 infiltration borings. They encountered one formational unit (Old Paralic Deposits)
in their study but undocumented fill associated with the existing structures at the site is most likely
Geocon Project No. G2861-11-01 -3 - January 27, 2023
present. The occurrence, distribution, and description of each unit encountered are shown on the
Geologic Map, Figure 1, and on the boring logs in Appendix A of the referenced report.
STORM WATER MANAGEMENT INVESTIGATION
We understand storm water management devices are being proposed in accordance with the Carlsbad
BMP Design Manual. 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 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
as a result 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. Table 1 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.
TABLE 1
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.
Geocon Project No. G2861-11-01 -4 - January 27, 2023
The property is underlain by undocumented fill, topsoil, and the Old Paralic Deposits. Table 2 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.
TABLE 2
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)
Marina loamy coarse sand, 2
to 9 percent slopes M/C 52 B 0.57 – 1.98
Maria loamy coarse sand, 9 to
30 percent slopes M/E 48 B 0.57 – 19.8
Hydrologic Soil Group Map
STORM WATER MANAGEMENT CONCLUSIONS
The Geologic Map, Figure 1, included in the referenced update investigation, depicts the existing
property, the approximate lateral limits of the geologic units and the locations of the field excavations.
The following presents a discussion of the soil types on site regarding storm water infiltration feasibility.
Geocon Project No. G2861-11-01 -5 - January 27, 2023
Soil Types
Undocumented Fill (Qudf) – Undocumented fill is most likely present beneath the existing structures
at the site to a depth of up to 3 feet. The undocumented fill was not tested or observed during placement
and should be considered highly variable. Water that is allowed to migrate within the undocumented fill
soil cannot be controlled, would destabilize support for the existing improvements, and would shrink
and swell. Therefore, full and partial infiltration should not be allowed within the undocumented fill.
Topsoil (Unmapped)– Topsoil is present as a relatively thin veneer locally overlying the Old Paralic
Deposits across the site. The topsoil has a thickness up to about 1 foot thick and can be characterized as
loose, moist, silty sand with numerous roots..
Old Paralic Deposits (Qop)– The Old Paralic Deposits are present near existing grade across the site.
These deposits are characterized as dense to very dense, reddish brown, silty, sandstone. The infiltration
rates estimated within the Old Paralic Deposits are moderate to high based on the USDA Web Soil
Survey map. We expect the proposed bio-retention basins will be constructed within the Old Paralic
Deposits.
Infiltration Rates
GeoSoils, Inc. performed 2 infiltration tests within the general areas of potential storm water
management devices. The tests were performed using the open pit, falling head test method. The results
of the tests provide parameters regarding the saturated hydraulic conductivity and infiltration
characteristics of the geologic units. Table 3 presents the results of the estimated field saturated hydraulic
conductivity and estimated infiltration rates obtained from the infiltration tests. The field data sheets for
GeoSoils, Inc.’s testing are included following the text of this report.
TABLE 3
FIELD PERMEAMETER INFILTRATION TEST RESULTS
Test No. Geologic
Unit
Test
Depth/Elevation
(feet, MSL)
Field-Saturated Hydraulic
Conductivity/Infiltration
Rate, ksat (inch/hour)
Worksheet Infiltration
Rate1 (inch/hour)
IB-1 Qop 5.0 / 158 1.74 0.87
IB-2 Qop 5.0 / 158 2.82 1.41
1 Using a Factor of Safety of 2.
Infiltration categories include full infiltration, partial infiltration and no infiltration. Table 4 presents the
commonly accepted definitions of the potential infiltration categories based on the infiltration rates.
Geocon Project No. G2861-11-01 -6 - January 27, 2023
TABLE 4
INFILTRATION CATEGORIES
Infiltration Category Field Infiltration Rate, I
(inches/hour)
Factored Infiltration Rate1, I
(inches/hour)
Full Infiltration I > 1.0 I > 0.5
Partial Infiltration 0.10 < I < 1.0 0.05 < I < 0.5
No Infiltration (Infeasible) I < 0.10 I < 0.05
1 Using a Factor of Safety of 2.
Groundwater Elevations/Well or Groundwater Basin
The BMP Design Manual indicates that the depth to the groundwater table beneath an infiltration BMP
must be greater than 10 feet for infiltration to be allowed. We did not encounter groundwater during our
investigation and we expect groundwater is greater than 50 feet below grade. We did not observe a well
or groundwater basin within 100 feet of the proposed basins. Therefore, infiltration due to groundwater
elevations, wells or groundwater basins would be considered feasible at the site to within each drainage
management areas.
New or Existing Utilities
New utilities are proposed within the planned project area. Existing utilities are located adjacent to the
property boundaries within existing streets. Therefore, full infiltration near these utilities should be
considered infeasible within these areas. Setbacks for infiltration should be incorporated. The setback
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.
Soil/Groundwater Contamination or Industrial Activities
We did not observe soil or groundwater contamination during our investigation and GeoSoils, Inc. did
not indicate any soil or groundwater contamination in their report. Additionally, we did not observe any
industrial activities adjacent to the site. The environmental consultant should evaluate if infiltration
would be possible from an environmental standpoint, if allowed. We expect infiltration associated with
this risk would be considered feasible.
Slopes and Other Geologic Hazards
The City of Carlsbad BMP Design Manual recommends a minimum setback of 1½ times the height of
adjacent steep slopes greater than 4:1 or 25 percent.
Fill slopes of less than 10 feet high will be constructed at the site. Infiltration would be feasible outside
of the slope setback areas.
Geocon Project No. G2861-11-01 -7 - January 27, 2023
Due to the dense nature of the underlying formational material, allowing infiltration could create a
“perched” and mounded water table while increasing the risk of distress to existing and proposed
improvements. Therefore, full and partial infiltration at the site should be considered infeasible due to
geologic hazards.
Septic Tanks/Leach Fields
We understand the site does not have any existing septic tanks or leach fields. Full or partial infiltration
is feasible at the site as long as a 50-foot setback from existing or proposed septic tanks or leach fields
is incorporated into the design.
Existing or Planned Structures
The site is gently sloping with from east to west with elevations ranging between 163 and 184 feet MSL.
Existing homes and ancillary structures are present in the eastern portion of the site but will be
demolished to construct five single family residences. Full or partial infiltration should be considered
feasible in the western portion of the site due to the vicinity of the existing homes. Mitigation for existing
structures consists of not allowing water infiltration within a lateral distance of at least 10 feet from the
existing structures.
Storm Water Narrative
The Highland 5 site is underlain by undocumented fill, topsoil, the Old Paralic Deposits. Based on our
evaluation of the property, the west side of the site is considered acceptable for potential infiltration due
to the sloping conditions/topography of the site.
Based on the infiltration test results, full infiltration would be feasible at the site within the Old Paralic
Deposits. However, due to geologic hazards identified by GeoSoils, Inc. of “perched” and mounded
water table, we consider infiltration to be infeasible at the site.
Storm Water Management Devices
Liners and subdrains should be incorporated into the design and construction of the planned storm water
devices. We recommend that the basins be fully lined to prevent lateral migration of water. Additionally,
and overflow protection device should be incorporated into the design of the basins. The liners should
be impermeable (e.g. High-density polyethylene, HDPE, with a thickness of about 30 mil or equivalent
Polyvinyl Chloride, PVC) to prevent water migration.
The basins should incorporate a subdrain into their design. The subdrains should be perforated within
the liner area, installed at the base and above the liner, 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
Geocon Project No. G2861-11-01 -8 - January 27, 2023
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.
Considerations of Infiltration Restrictions
The regional storm water standards include Table D.1.1:Considerations for Geotechnical Analysis of
Infiltration Restrictions that determines the infiltration restrictions at the site. Table 5 presents the
mandatory and optional considerations for the site.
TABLE 5
CONSIDERATIONS FOR GEOTECHNICAL ANALYSIS OF INFILTRATION RESTRICTIONS
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 No
BMP is within 10’ of Property Line No
BMP is within Fill Depths of >5’ (Existing or Proposed) No
BMP is within 10’ of Underground Utilities No
BMP is within 250’ of Ephemeral Stream No
Other (Provide detailed geotechnical support) – Geologic Hazards Yes
Result
Based on examination of the best available information, I have not identified any restrictions above O Unrestricted
Based on examination of the best available information, I have identified one or more restrictions above X Restricted
Storm Water Standard Worksheets
The regional storm water standards also have a worksheet (Worksheet D.5-1 or Form I-9) that helps the
project civil engineer estimate the factor of safety based on several factors. Table 6 describes the
Geocon Project No. G2861-11-01 -9 - January 27, 2023
suitability assessment input parameters related to the geotechnical engineering aspects for the factor of
safety determination.
TABLE 6
SUITABILITY ASSESSMENT RELATED CONSIDERATIONS FOR INFILTRATION FACILITY
SAFETY FACTORS
Consideration High Concern – 3 Points Medium Concern – 2 Points Low Concern – 1 Point
Assessment Methods
Use of soil survey maps or
simple texture analysis to estimate short-term infiltration rates. Use of well permeameter or borehole methods without accompanying continuous boring log. Relatively sparse testing with direct infiltration methods
Use of well permeameter
or borehole methods with accompanying continuous boring log. Direct measurement of infiltration area with localized infiltration measurement methods (e.g., Infiltrometer). Moderate spatial resolution
Direct measurement with
localized (i.e. small-scale) infiltration testing methods at relatively high resolution or use of extensive test pit infiltration measurement methods.
Predominant Soil Texture Silty and clayey soils with significant fines Loamy soils Granular to slightly loamy soils
Site Soil Variability
Highly variable soils
indicated from site assessment or unknown variability
Soil boring/test pits
indicate moderately homogenous soils
Soil boring/test pits
indicate relatively homogenous soils
Depth to Groundwater/ Impervious Layer <5 feet below facility bottom 5-15 feet below facility bottom >15 feet below facility bottom
Based on our geotechnical investigation and the previous table, Table 7 presents the estimated factor
values for the evaluation of the factor of safety. 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
(Part B) and use the combined safety factor for the design infiltration rate.
TABLE 7
FACTOR OF SAFETY WORKSHEET DESIGN VALUES – PART A
Suitability Assessment Factor Category Assigned Weight (w) Factor Value (v) Product (p = w x v)
Assessment Methods 0.25 1 0.25
Predominant Soil Texture 0.25 2 0.50
Site Soil Variability 0.25 1 0.25
Depth to Groundwater/ Impervious Layer 0.25 1 0.25
Suitability Assessment Safety Factor, SA = p 1.25
1. The project civil engineer should complete Worksheet D.5-1 or Form I-9 using the data on this table. Additional
information is required to evaluate the design factor of safety.
Geocon Project No. G2861-11-01 -10 - January 27, 2023
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
Kenneth W. Haase
CEG 2775
Shawn Foy Weedon
GE 2714
KH:SFW:arm
Attachments: Form I-8: Categorization of Infiltration Condition
Storm Water Management & Percolation Data Sheets - GeoSoils, Inc.
(e-mail) Addressee
Storm Water Standards February 2016 Edition
Appendices: BMP Design Manual
I-3
Appendix I: Forms and Checklists
Categorization of Infiltration 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?
Note that it is not necessary to investigate each and every criterion in the worksheet if infiltration is precluded.
Instead a letter of justification from a geotechnical professional familiar with the local conditions substantiating
any geotechnical issues will be required.
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.
X
Provide basis:
Yes. Testing demonstrates that the estimated reliable infiltration rate is 0.87 in/hr, which is greater than 0.5
in/hr
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.
No
Provide basis:
No. This is a 5-lot project. Given the nature of the bedrock, there is a high potential for mounding, and
lateral migration of groundwater, onsite and offsite, to adversely affect existing and proposed
improvements, causing distress.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
Shawn Foy Weedon, GE 2714
)lOL
Storm Water Standards February 2016 Edition
Appendices: BMP Design Manual
I-4
Page 2 of 4
Criteria 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 comprehensible evaluation of the factors
presented in Appendix C.3.
Provide basis:
No response required. See Criteria No. 2.
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 a 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:
No response required. See Criteria No. 2.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion
of study/data source applicability.
Part 1
Result*
In the 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
Proceed
to Part 2
* To be completed using gathered site information and best professional judgement considering the definition of MEP in the MS4
Permit. Additional testing and/or studies may be required by [City Engineer] to substantiate findings.
Storm Water Standards February 2016 Edition
Appendices: BMP Design Manual
I-5
Page 3 of 4
Part 2 - Partial Infiltration vs. No Infiltration Feasibility Screening Criteria
Would infiltration of water in an 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.
X
Provide basis:
Testing and analyses show the near-surface earth materials have an estimated reliable infiltration rate of
roughly 0.87 in/hr in the general vicinity of the proposed BMP.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
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.
X
Provide basis:
If storm water infiltration into the onsite soils were to occur, there would be an increased potential for
shallow perched groundwater conditions (i.e., groundwater mounding) to develop, owing to the collection
of water upon the indurated and less permeable unweathered old paralic deposits, which occur at depths
ranging between approximately 2 feet and 3 feet below the existing grades, within the project area. Perched
groundwater conditions which would adversely affect the performance of the existing and proposed
improvements, onsite and offsite, as well as the public right-of-way, and cuase distress, has a high potential
to occur.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
Storm Water Standards February 2016 Edition
Appendices: BMP Design Manual
I-6
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:
See criteria No. 6
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
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:
Downstream water rights are a legal matter that do not fall under the purview of geotechnical engineering.
However, there are no water courses traversing the subject site. See criteria No. 6
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
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.
No
Infiltration
* To be completed using gathered site information and best professional judgement considering the definition of MEP in the MS4
Permit. Additional testing and/or studies may be required by Agency/Jurisdictions to substantiate findings.
Appendix I: Factor of Safety and Design Infiltration Rate Worksheet
D-19 February 26, 2016
Factor of Safety Infiltration Rate Worksheet Form I-9
Factor Criteria Factor Description Assigned
Weight (w)
Factor
Value (v)
Product (p)
p = w x v
A Suitability
Assessment
Soil assessment methods 0.25 1 0.25
Predominant soil texture 0.25 1 0.25
Site soil variability 0.25 1 0.25
Depth to groundwater/impervious layer 0.25 1 0.25
ASuitability Assessment Safety Factor, S = Ep Min = 2.0
B Design
Level of pretreatment/expected sediment loads 0.5
Redundancy/resiliency 0.25
Compaction during construction 0.25
BDesign Safety Factor, S = Ep
total A BCombined Safety Factor, S = S x S 2.0 min
observedObserved Infiltration Rate, inch/hr, K
(corrected for test-specific bias)1.74 in/hr
design observed totalDesign Infiltration Rate, in/hr, K = K / S 0.87 in/hr
Supporting Data
Briefly describe infiltration test and provide reference to test forms: See Appendix E of Geotechnical Report
by GeoSoils, Inc. (2021).
GeoSoils, Inc.
Cross Real Estate Investors, LLC W.O. 8037-A-SC
Tract 80-46, Carlsbad January 27, 2021
File:e:\wp12\8000\8037.pge Page 37
STORM WATER TREATMENT AND HYDROMODIFICATION MANAGEMENT
USDA Study
A review of the United States Department of Agriculture database ([USDA]; 1973, 2020)
indicates that site soils located within the upper and lower elevations of the western two-
thirds of the site are classified as Marina loamy coarse sand (2-30 percent slopes). The
USDA study further indicates that the Marina series is classified as belonging to Hydrologic
Soil Group “B.” A review of USDA (1973 and 2019) indicates that the capacity of the most
limiting layer to transmit water (Ksat) within the Marina loamy coarse sand is moderately high
to high (0.57 to 01.98 inches per hour [in/hr]). Some soils identified as Marina loamy coarse
sand may be removed and recompacted as engineered fill during grading operations.
Infiltration Feasibility
Per our onsite infiltration test results, an infiltration rate at the location tested onsite ranged
between 1.74 inches per hour to 2.82 inches per hour (See Table below). Test holes IB-1
and IB-2 are generally above the recommended feasibility threshold of 0.52 inches per hour
per the EPA (Clar, et al., 2004), and 0.50 inches per hour per the County (2019) for full
infiltration. With a factor of safety of 2, and utilizing the most conservative design infiltration
rate for IB-1, the design rate is 0.87 inches/hour. The permeability of the underlying
soil/bedrock can be expected to decrease with depth, as the soil/bedrock becomes less
weathered, thereby promoting the lateral migration of water in soil. Test data sheets are
presented in Appendix E. Boring locations (IB-1, IB-2 and IB-3), are shown on Plate 1.
INFILTRATION
TEST HOLE
OBSERVED FIELD INFILTRATION
RATE (INCHES PER HOUR)SOIL UNIT PER USDA (1973)
IB-1 1.74 Marina Loamy Coarse Sand
IB-2 2.82 Marina Loamy Coarse Sand
Proposed or existing fill, and/or moisture-sensitive improvements, such as pavements, and
utility trench backfill, foundations, retaining walls, and below grade building walls, would
likely be adversely affected by excessive soil moisture, including existing offsite
improvements, causing settlement and distress. Bio-basins can adversely affect the
performance of the onsite and offsite structures, foundation systems by: 1) increasing soil
moisture transmission rates through concrete flooring, 2) reducing the stability of slopes,
and 3) increasing the potential for a loss in bearing strength of soil. Onsite mitigative grading
of compressible near-surface soils for the support of structures generally involves removal
and recompaction. This is anticipated to create the potential for permeability contrast, and
the potential for the development of a shallow “perched” and mounded water table, which
can reasonably be anticipated to migrate laterally, beneath the structure(s), or offsite onto
adjacent property, causing settlement and associated distress. Based on City (2016), the
I I
I I I I
GeoSoils, Inc.
Cross Real Estate Investors, LLC W.O. 8037-A-SC
Tract 80-46, Carlsbad January 27, 2021
File:e:\wp12\8000\8037.pge Page 38
calculated infiltration rate with safety factor added yields a rate of 0.87 inches per hour,
which is above the minimum acceptable rate of 0.025 inches per hour; however, “no
infiltration” is recommended, owing to the potential to cause distress to existing and
proposed improvements, both onsite and offsite. In addition, infiltrating into site soils within
10 feet of any settlement sensitive structure/improvement is considered poor engineering
judgement. In addition, “no infiltration” is recommended within 10 feet of any planned
settlement/expansion sensitive improvement.
Based on our review and engineering analysis, the site belongs to HSG “B” and we
recommend “ no infiltration” BMP design. In addition, due to the potential for associated
settlement, distress, and perched groundwater for any BMP structure within close proximity
(i.e., potentially within 10 feet) of any planned basin to building foundations, retaining walls,
slopes, and other settlement-sensitive improvement, a “no infiltration” BMP design is
warranted. Furthermore, any basin constructed entirely of compacted fill is considered as
belonging to HSG D, and a “no infiltration” BMP design is also warranted (Clar, et al., 2004).
Form I-8 and Form I-9 (City of Carlsbad, 2016) are presented in Appendix E.
Onsite Infiltration-Runoff Retention Systems
General design criteria regarding the use of onsite infiltration-runoff retention systems
(OIRRS) are presented below. Should onsite infiltration-runoff retention systems (OIRRS)
be planned for Best Management Practices (BMPs) or Low Impact Development (LID)
principles for the project, some guidelines should be followed in the planning, design, and
construction of such systems. Such facilities, if improperly designed or implemented without
consideration of the geotechnical aspects of site conditions, can contribute to flooding,
saturation of bearing materials beneath site improvements, slope instability, and possible
concentration and contribution of pollutants into the groundwater or storm drain and/or utility
trench systems.
A key factor in these systems is the infiltration rate (sometimes referred to as the percolation
rate) which can be ascribed to, or determined for, the earth materials within which these
systems are installed. Additionally, the infiltration rate of the designed system (which may
include gravel, sand, mulch/topsoil, or other amendments, etc.) will need to be considered.
The project infiltration testing is very site specific, any changes to the location of the
proposed OIRRS and/or estimated size of the OIRRS, may require additional infiltration
testing. Locally, relatively impermeable residual soils include the underlying bedrock, which
is anticipated to have a very low vertical infiltration rate.
The following geotechnical guidelines should be considered when designing onsite
infiltration-runoff retention systems:
•It is not good engineering practice to allow water to saturate soils, especially near
slopes or improvements; however, the controlling agency/authority may now require
this.
GeoSoils, Inc.
Cross Real Estate Investors, LLC W.O. 8037-A-SC
Tract 80-46, Carlsbad January 27, 2021
File:e:\wp12\8000\8037.pge Page 39
•Areas adjacent to, or within, the OIRRS that are subject to inundation should be
properly protected against scouring, undermining, and erosion, in accordance with
the recommendations of the design engineer.
•Where infiltration systems are located near slopes or improvements, impermeable
liners and subdrains should be used along the bottom of bioretention swales/basins
located within the influence of such slopes and structures. Impermeable liners used
in conjunction with bioretention basins should consist of a 30-mil polyvinyl chloride
(PVC) membrane that is covered by a minimum of 12 inches of clean soil, free from
rocks and debris, with a maximum 4:1 (h:v) slope inclination, or flatter, and meets the
following minimum specifications:
Solid Soils Specific Gravity (ASTM D792): 1.2 (g/cc, min.); Tensile
(ASTM D882): 73 (lb/in-width, min); Elongation at Break (ASTM D882): 380 (%,
min); Modulus (ASTM D882): 32 (lb/in-width, min.); and Tear Strength
(ASTM D1004): 8 (lb/in, min); Seam Shear Strength (ASTM D882) 58.4 (lb/in,
min); Seam Peel Strength (ASTM D882) 15 (lb/in, min).
•Subdrains should consist of at least 4-inch diameter Schedule 40 or SDR 35 drain
pipe with perforations oriented down. The drain pipe should be sleeved with a filter
sock.
•Storm drain, standpipes, and utilities that cross BMPs should be slurried with a 2-sack
mix, to 5 feet outside the structure.
Final project plans (grading, precise grading, foundation, retaining wall, landscaping, etc.),
should be reviewed by this office prior to construction, so that construction is in accordance
with the conclusions and recommendations of this report. Based on our review,
supplemental recommendations and/or further geotechnical studies may be warranted. It
should be noted that structural and landscape plans were not available for review at this
time.
DEVELOPMENT CRITERIA
Slope Deformation
Compacted fill slopes designed using customary factors of safety for gross or surficial
stability and constructed in general accordance with the design specifications should be
expected to undergo some differential vertical heave or settlement in combination with
differential lateral movement in the out-of-slope direction, after grading. This
post-construction movement occurs in two forms: slope creep, and lateral fill extension
(LFE). Slope creep is caused by alternate wetting and drying of the fill soils which results
in slow downslope movement. This type of movement is expected to occur throughout the
Project:
Test Hole No.:IB-1
Percolation Rate to Infiltration Rate Conversion
*Infiltration Rate (It) = ∆H Br2 60 =∆H 60 r
∆t(Br2 + 2BrHavg)∆t(r+2Havg)
Where: It = tested infiltration rate, inches/hour
∆H = change in head over the time interval, inches
∆t = time interval, minutes
r = effective radius of test hole
Havg = average head over the time interval, inches
∆t Init Level Fnl Level ∆H Havg It
Infiltration
Test
Numbers
IB-1 @ 5.0 ft.10 13 18 5 32 1/2 1.739
*Conversion per the "Porchet Method" (RCFWCD, 2011)
W.O. Number:
Date Excavated:
8037-A-SC
1/7/2021
Cross Real Estate Investors
I I I I I I I I
I I I
t-d-71
·· ·' . "fest Ho,!e Dimensions {ind,es} lengih ' VJidth
Di,H11ete,(ifrotmd}= i \t ·:s.1d es{ifrectangular):=
'Greater
Time ln!tia! -· ' f-l □a1 diange·in than or
I11ter,rai., Depirhto E)epth to Water Eqtia!to€'?'
TriaJ NO. StartTime Stop Time (rnln.} V\iater (in.} 'Nater (in.} leve1 (in.} {y/n}
l q, ~ 3'\ q ·, 01,\ '2 (, \3.0\J 2.s.S'O 12 r,., " ,, 9~ o5 9~ 1-0 ·2s \'2 .bt> Z.\ .C)O 1.00 ~, ,L
'"if hrv·o cu,ns,ecutive measuren,ents sno'<'J thats.ix inches. of watet see,ps away in less than 25
tninut·es, tr,e test snaii be mo for an additiqnal hour wlth me.asuremerrts taken every :LC: minutes.
otfi~rwi~e,· pre-soak(fil!j ov.ernlgnt. Ootai~ 'at !easttweive me,asm;ements per hole.OVef at !east
six horfrs {approximate!y 3D' mlpute irit~~'a!s} lMith a prec,s,ior:-i of at least o;,25''-' .
. lit . De, ·of. AG·
-nrrie !n~tial Rnal Change iq f''efCGiation
lnterv..al Depth to Depth to \Nater Rate
Trial No. Start:Time Stop Time, (,'mfn.f 'Nater tin.) \,.·later (in.)
9:~~ \ () I z... 00 \~.C)O
C\ • l\-.. ' ID l\.l.t; \7. 2,
'\ ·. <;1 10 \?.Db \1,00 5.00
4. \[,:OC \lhlO \D ',.1c: \b, l ~ i.oo
\(): -Z..\ \ f) l \ .O<:> IL.OD 5.DO i.oo
ll)·. 3'2. I() \3.DO \i .f>0 '2-,00
7
9
10
11
12
14
15
COMMENTS:
Table 5 -Sample Test Data Form for Percolation Test
Rii1erside Cow1fy -low Jmpocf Dere.lopme11f Bf.1P Des,gn Handbook rei•. 9120) J
Page 25
Project:
Test Hole No.:IB-2
Percolation Rate to Infiltration Rate Conversion
*Infiltration Rate (It) = ∆H Br2 60 =∆H 60 r
∆t(Br2 + 2BrHavg)∆t(r+2Havg)
Where: It = tested infiltration rate, inches/hour
∆H = change in head over the time interval, inches
∆t = time interval, minutes
r = effective radius of test hole
Havg = average head over the time interval, inches
∆t Init Level Fnl Level ∆H Havg It
Infiltration
Test
Numbers
IB-2 @ 5.0 ft.10 17 22 1/4 5 1/4 20 3/8 2.816
*Conversion per the "Porchet Method" (RCFWCD, 2011)
W.O. Number:
Date Excavated:
8037-A-SC
1/7/2021
Cross Real Estate Investors
I I I I I I I I
I I I
Test Hole ifo.: .l... B -Z..
IJ-SCSSoH Cia.s.~fication: SM
• Test Ho!e Dimensions finches.), length '
Saridy'soH Crltei:ta rest"
Tr.iaJ No. Start Time S:icp Time
2,5
25
ln!Dat Final
Depth to D,epi:h to
V\iater (in.} '#ater (ln.}
17, DO ~o. DD
V,ticith
'Greater
Change· in tt-ian or
Water
Level (in.}
13, ()()
2L7S
Eqt.ia! to,€'?
{y/n}
*'lf rt1.m cons,ecuthre meas.i:.irements show that ~ix io~esofv.,·atei~ s:eeps away in !ess than 2:5
t1inutes, :trie test snail be run fo, an additional lwur with me.asuremerits taken every lG minutes.
otti~rw:ise, pre-soaik.{fiHj overnigJrt:. Obtain 'at !easttweive meas.uren-,ents: per hole.over at 1east
six hours (approximately 3D: rnlpute inte.rva!s} 1,/tth a pre.cis.iop of at least 0,,25,i_
l!.t D tr: Or· AG.
nrrie Initial Rna! Change in Percofatlon
lrrl:erv..a( Depth to Depth to lN:ater Rate
Trial Mo. StartT1me· Stop Tlrne· tmH1.J! VVater (!n.} \!'-later fin~) Leve~ On.) (inin./ln.}
l 9 ~ 2"1 ci~ 3b \D IR.oo -Zi-t.oo IP .DC I. l,to
1 'I: 3)? q: L\'(! \0 \1.-.7) -zz.so '.5,15 I. 11.i
3 9;49 '1,S'1 \/) \~.1$ 72.JS 5,SD t.i\
4. 10:02 10~1-z, ,o \7,DD ii .is s :'£, s ,~,o
5 \I)'. \3 \O·. 2?. I [) ,~:is 21 .. ~o 5.25 \. \(>
6 \D~ ZL\ \D~ '34 \u 17,DO 7..:l .ic:; S.'l~ \. C\D
7
10
11
12
14
15
COMfvlENTS:
Table 5 -Sample Test Data Form for Percolation Test
RA=erside Co1.mry -Lov., lmpocl Derelopmenl B},1P De.sJgn Handbook
Page 25
UNIFIED SOIL CLASSIFICATION SYSTEM CONSISTENCY OR RELATIVE DENSITY
Major Divisions Group
Symbols Typical Names CRITERIA
Co
a
r
s
e
-
G
r
a
i
n
e
d
S
o
i
l
s
Mo
r
e
t
h
a
n
5
0
%
r
e
t
a
i
n
e
d
o
n
N
o
.
2
0
0
s
i
e
v
e
Gr
a
v
e
l
s
50
%
o
r
m
o
r
e
o
f
co
a
r
s
e
f
r
a
c
t
i
o
n
re
t
a
i
n
e
d
o
n
N
o
.
4
s
i
e
v
e
Cl
e
a
n
Gr
a
v
e
l
s
GW Well-graded gravels and gravel-sand mixtures, little or no fines Standard Penetration Test
Penetration
Resistance N Relative (blows/ft)Density
0 - 4 Very loose
4 - 10 Loose
10 - 30 Medium
30 - 50 Dense
> 50 Very dense
GP Poorly graded gravels andgravel-sand mixtures, little or no
fines
Gr
a
v
e
l
wi
t
h
GM Silty gravels gravel-sand-silt
mixtures
GC Clayey gravels, gravel-sand-clay
mixtures
Sa
n
d
s
mo
r
e
t
h
a
n
5
0
%
o
f
co
a
r
s
e
f
r
a
c
t
i
o
n
pa
s
s
e
s
N
o
.
4
s
i
e
v
e
Cle
a
n
Sa
n
d
s
SW Well-graded sands and gravelly
sands, little or no fines
SP Poorly graded sands andgravelly sands, little or no fines
Sa
n
d
s
wi
t
h
Fi
n
e
s
SM Silty sands, sand-silt mixtures
SC Clayey sands, sand-clay
mixtures
Fi
n
e
-
G
r
a
i
n
e
d
S
o
i
l
s
50
%
o
r
m
o
r
e
p
a
s
s
e
s
N
o
.
2
0
0
s
i
e
v
e
Sil
t
s
a
n
d
C
l
a
y
s
Liq
u
i
d
l
i
m
i
t
50
%
o
r
l
e
s
s
ML Inorganic silts, very fine sands,rock flour, silty or clayey finesands
Standard Penetration Test
Unconfined
Penetration Compressive
Resistance N Strength
(blows/ft)Consistency (tons/ft2)
<2 Very Soft <0.25
2 - 4 Soft 0.25 - .050
4 - 8 Medium 0.50 - 1.00
8 - 15 Stiff 1.00 - 2.00
15 - 30 Very Stiff 2.00 - 4.00
>30 Hard >4.00
CL
Inorganic clays of low to
medium plasticity, gravelly clays,
sandy clays, silty clays, lean
clays
OL Organic silts and organic silty
clays of low plasticity
Si
l
t
s
a
n
d
C
l
a
y
s
Li
q
u
i
d
l
i
m
i
t
gr
e
a
t
e
r
t
h
a
n
5
0
%
MH
Inorganic silts, micaceous or
diatomaceous fine sands or silts,
elastic silts
CH Inorganic clays of high plasticity,
fat clays
OH Organic clays of medium to high
plasticity
Highly Organic Soils PT Peat, mucic, and other highly
organic soils
3"3/4"#4 #10 #40 #200 U.S. Standard Sieve
Unified Soil
Classification Cobbles Gravel Sand Silt or Clay
coarse fine coarse medium fine
MOISTURE CONDITIONS MATERIAL QUANTITY OTHER SYMBOLS
Dry Absence of moisture: dusty, dry to the touch trace 0 - 5 %C Core Sample
Slightly Moist Below optimum moisture content for compaction few 5 - 10 %S SPT Sample
Moist Near optimum moisture content little 10 - 25 %B Bulk Sample
Very Moist Above optimum moisture content some 25 - 45 %–Groundwater
Wet Visible free water; below water table Qp Pocket Penetrometer
BASIC LOG FORMAT:
Group name, Group symbol, (grain size), color, moisture, consistency or relative density. Additional comments: odor, presence of roots, mica, gypsum,
coarse grained particles, etc.
EXAMPLE:
Sand (SP), fine to medium grained, brown, moist, loose, trace silt, little fine gravel, few cobbles up to 4" in size, some hair roots and rootlets.
File:Mgr: c;\SoilClassif.wpd PLATE B-1
I I I I I I I I I
-
0
5
10
15
20
25
30
SM TOPSOIL:0' SILTY SAND, reddish brown, damp, medium dense; fine to medium
sands.
PARALIC DEPOSITS:@ 0.8' SILTY SAND, reddish light brown, damp, dense; fine sands.
Total Depth = 5'
No Groundwater or Caving Encountered
Backfilled 1-8-21
GeoSoils, Inc.BORING LOG
PROJECT:CROSS REAL ESTATE INVESTORS
2908 Highland Dr., Carlsbad W.O.8037-A-SC BORING IB-1 SHEET 1 OF
DATE EXCAVATED 1-7-21 LOGGED BY:TMP APPROX. ELEV.:163 MSL
SAMPLE METHOD:
Standard Penetration Test Groundwater
Undisturbed, Ring Sample Seepage
GeoSoils, Inc.
PLATE
De
p
t
h
(
f
t
.
)
Bu
l
k
Sample
Un
d
i
s
t
u
r
b
e
d
Bl
o
w
s
/
F
t
.
US
C
S
S
y
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b
o
l
Dr
y
U
n
i
t
W
t
.
(
p
c
f
)
Mo
i
s
t
u
r
e
(
%
)
Sa
t
u
r
a
t
i
o
n
(
%
)
Material Description
1
B-7
H
~
I
I
I
I
I
...
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
--
'(
J
•ii~
I I
0
5
10
15
20
25
30
SM TOPSOIL:@ 0' SILTY SAND, reddish brown, damp, medium dense; fine to medium
sands.
PARALIC DEPOSITS:@ 0.8' SILTY SAND, reddish light brown, damp, dense.
Total Depth = 5'
No Groundwater or Caving Encountered
1-8-21
GeoSoils, Inc.BORING LOG
PROJECT:CROSS REAL ESTATE INVESTORS
2908 Highland Dr., Carlsbad W.O.8037-A-SC BORING IB-2 SHEET 1 OF
DATE EXCAVATED 1-7-21 LOGGED BY:TMP APPROX. ELEV.:163 MSL
SAMPLE METHOD:
Standard Penetration Test Groundwater
Undisturbed, Ring Sample Seepage
GeoSoils, Inc.
PLATE
De
p
t
h
(
f
t
.
)
Bu
l
k
Sample
Un
d
i
s
t
u
r
b
e
d
Bl
o
w
s
/
F
t
.
US
C
S
S
y
m
b
o
l
Dr
y
U
n
i
t
W
t
.
(
p
c
f
)
Mo
i
s
t
u
r
e
(
%
)
Sa
t
u
r
a
t
i
o
n
(
%
)
Material Description
1
B-8
H
~
I
I
I
I
I
...
.
.
.
.
.
.
.
.
.
.
.
.
.
.
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.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
--
'(
J
•ii~
I I
0
5
10
15
20
25
30
SM TOPSOIL:@ 0' SILTY SAND, reddish brown, damp, medium dense.
PARALIC DEPOSITS:@ 0.8 SILTY SAND, reddish light brown, damp, medium dense to very
dense with depth; fine sands.
@ 5' Becomes reddish brown; fine to medium sands.
Total Depth = 15'
No Groundwater or Caving Encountered
Backfilled 1-8-21
GeoSoils, Inc.BORING LOG
PROJECT:CROSS REAL ESTATE INVESTORS
2908 Highland Dr., Carlsbad W.O.8037-A-SC BORING IB-3 SHEET 1 OF
DATE EXCAVATED 1-7-21 LOGGED BY:TMP APPROX. ELEV.:162 MSL
SAMPLE METHOD:
Standard Penetration Test Groundwater
Undisturbed, Ring Sample Seepage
GeoSoils, Inc.
PLATE
De
p
t
h
(
f
t
.
)
Bu
l
k
Sample
Un
d
i
s
t
u
r
b
e
d
Bl
o
w
s
/
F
t
.
US
C
S
S
y
m
b
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l
Dr
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U
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i
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W
t
.
(
p
c
f
)
Mo
i
s
t
u
r
e
(
%
)
Sa
t
u
r
a
t
i
o
n
(
%
)
Material Description
1
B-9
H
~
,,i