SL-2
P-4
TD: 7.5’
GEOTECHNICAL MAP
LEGEND
Meritage Homes
Proposed Residential Development
La Sierra Avenue/Alhambra Avenue
Riverside, California
Project Number: 23145-01
Date: December 22, 2023
Plate 1
H-6
TD: 30.5’
Qalo @ 0-21.5’
Kgr @ 21.5’+
Approximate Location of Hollow Stem
Auger Boring, Showing Total Depth,
Depth to Earth Units, and Depth to
Groundwater (if encountered) in Feet.
Approximate Location of Hollow Stem
Auger Boring and Percolation Test,
Showing Total Depth in Feet.
Afu
Earth Units - Circled Where Buried
Undocumented Artificial Fill
Basemap Source: Google Earth
TP-8
TD: 13.5
Afu @ 0-1.5’
Qalo @ 1.5-11’
Kgr @ 11’+
Approximate Test Pit Location,
Showing Total Depth, and Depth
to Earth Units in Feet.
Qalo Older Alluvium
Kgr Granitic Bedrock
Geologic Contact, Dotted Where Buried
Seismic Refraction Line
TP-1
TD: 11.5’ (Refusal)
Qalo @ 0-2.5’
Kgr @ 2.5’+
Afu
Kgr
TP-2
TD: 8.5’ (Refusal)
Qalo @ 0-8’
Kgr @ 8’+
TP-3
TD: 11.5’ (Refusal)
Qalo @ 0-6.5’
Kgr @ 6.5’+
TP-4
TD: 15’
Afu @ 0-5.5’
Qalo @ 5.5’-12.5
Kgr @ 12.5’+
TP-5
TD: 9.5’ (Refusal)
Afu @ 0-2.5’
Qalo @ 2.5-7’
Kgr @ 7’+
Afu/Qalo
Kgr
TP-6
TD: 9.5’ (Refusal)
Afu @ 0-1.5’
Qalo @ 1.5-7’
Kgr @ 7’+
TP-7
TD: 14’
Afu @ 0-2.5’
Qalo @ 2.5’-14’
TP-8
TD: 13.5’
Afu @ 0-1.5’
Qalo @ 1.5-11’
Kgr @ 11’+
H-1
TD: 8’
(R
efusal)
H-2
TD: 30’
Qalo @ 0-5’
Kgr @ 5’+
H-3
TD: 30.5’
Qalo @ 0-11’
Kgr @
11’+
H-4
TD: 30.5’
Qalo @ 0-4’
Kgr@ 4’+
H-5
TD: 30’
Qalo @ 0-11.5’
Kgr @ 11.5’+
GW @ 26.5’
H-6
TD: 30.5’
Qalo @ 0-21.5’
Kgr @ 21.5’+
P-1
TD: 5’
P-2
TD: 5’
P-4
TD: 7.5’
P-3
TD: 10’
Afu/Qalo
Kgr
Afu/Qalo
Kgr
Afu/Qalo
Kgr
Kgr
THIS PAGE INTENTIONALLY LEFT BLANK
La Sierra Alhambra Residential Project
CEQA Guidelines Section 15183 Consistency Checklist
FCS
F.2 - Water Quality Management Plan
THIS PAGE INTENTIONALLY LEFT BLANK
- 1 -
Project Specific Water Quality Management Plan
Project Title: La Sierra Hills
Development No : GP-2024-13856
Design Review/Case No: PR 2024-001711
Original Date Prepared
: November 2024
Revision Date(s) : April 2025
Prepared for Compliance with
Regional Board Order No . R8-2010-0033
Contact Information:
Prepared for:
Louisa Feletto
Meritage Homes of California, Inc.
5 Peters Canyon Road, Suite #310
Irvine, CA 92606
Telephone: (949) 299-3833
Email: [email protected]
Prepared by:
Kirk Myers, PE
Kimley-Horn and Associates, Inc.
3801 University Avenue, Suite 300
Riverside, CA 92501
Telephone: (951) 543-9868
Email: [email protected]
Preliminary
Final
- 2 -
A Brief Introduction
This Project-Specific WQMP Template for the Santa Ana Region has been prepared to help guide you in documenting compliance for your project. Because th is document has been designed to specifically document compliance, you will need to utilize the WQMP Guidance Document as your “how-to” manual to help guide you through this process. Both the Te mplate and Guidance Document go hand-in-hand, and will help facilitate a well prepared Project-Specific WQMP. Below is a flowchart for the layout of this Template that will provide the steps required to document compliance.
Section A
Project and Site
Information
Section B
Optimize Site
Utilization
Section C
Delineate Drainage
Management Areas
(DMAs)
Section G
Source Control
BMPs
Section I
Operation,
Maintenance, and
Funding
Section F
Hydromodification
Section E
Alternative
Compliance
Section D
Implement LID
BMPs
Section H
Construction Plan
Checklist
- 3 -
OWNER’S CERTIFICATION
This Project-Specific Water Quality Management Plan (WQMP) has been prepared for Meritage Homes of California, Inc. by Kimley-Horn and Associates for the MLC La Sierra project.
This WQMP is intended to comply with the requiremen ts of City of Riverside for PR 2024-001711 which includes the requirement for the preparation and implementat ion of a Project-Specific WQMP.
The undersigned, while owning the property/project described in the preceding paragraph, shall be resp onsible for the implementation and funding of this WQMP and wil l ensure that this WQMP is amended as appropriate t o reflect up-to-date conditions on the site. In addi tion, the property owner accepts responsibility for interim operation and maintenance of Stormwater BMPs until such time as this responsibility is formally transf erred to a subsequent owner. This WQMP will be reviewed with t he facility operator, facility supervisors, employe es, tenants, maintenance and service contractors, or any other p arty (or parties) having responsibility for impleme nting portions of this WQMP. At least one copy of this W QMP will be maintained at the project site or proje ct office in perpetuity. The undersigned is authorized to certif y and to approve implementation of this WQMP. The undersigned is aware that implementation of this WQ MP is enforceable under the City of Riverside Water Quality Ordinance (Municipal Code Section 14.12.315).
"I, the undersigned, certify under penalty of law t hat the provisions of this WQMP have been reviewed and accepted and that the WQMP will be transferred to f uture successors in interest."
Owner’s Signature Date
Louisa Feletto Developer
Owner’s Printed Name Owner’s Title/Position
PREPARER’S CERTIFICATION
“The selection, sizing and design of stormwater tre atment and other stormwater quality and quantity co ntrol measures in this plan meet the requirements of Regi onal Water Quality Control Board Order No. R8-2010-0033 and any subsequent amendments thereto.”
Preparer’s Signature Date
Kirk Myers Project Manager
Preparer’s Printed Name Preparer’s Title/Posi tion
Preparer’s Licensure: C71470
2/21/25
Docusign Envelope ID: EA983C18-6C48-4DAE-A8D8-5D6851989B20 4/23/2025
- 4 -
Table of Contents
Section A: Project and Site Information........................................................................................................ 6 A.1 Maps and Site Plans ............................................................................................................................ 6 A.2 Identify Receiving Waters ................................................................................................................... 7 A.3 Additional Permits/Approvals required for the Project: .................................................................... 7 Section B: Optimize Site Utilization (LID Principles) ..................................................................................... 8 Section C: Delineate Drainage Management Areas (DMAs) ......................................................................... 9 Section D: Implement LID BMPs ................................................................................................................. 11 D.1 Infiltration Applicability .................................................................................................................... 11 D.2 Harvest and Use Assessment ............................................................................................................ 12 D.3 Bioretention and Biotreatment Assessment .................................................................................... 14 D.4 Feasibility Assessment Summaries ................................................................................................... 15 D.5 LID BMP Sizing .................................................................................................................................. 16 Section E: Alternative Compliance (LID Waiver Program) .......................................................................... 18 E.1 Identify Pollutants of Concern .......................................................................................................... 19 E.2 Stormwater Credits ........................................................................................................................... 20 E.3 Sizing Criteria ..................................................................................................................................... 20 E.4 Treatment Control BMP Selection .................................................................................................... 21 Section F: Hydromodification ..................................................................................................................... 22 F.1 Hydrologic Conditions of Concern (HCOC) Analysis .......................................................................... 22 F.2 HCOC Mitigation ................................................................................................................................ 23 Section G: Source Control BMPs ................................................................................................................. 24 Section H: Construction Plan Checklist ....................................................................................................... 26 Section I: Operation, Maintenance and Funding ........................................................................................ 27
- 5 -
List of Tables
Table A.1 Identification of Receiving Waters ................................................................................................ 7 Table A.2 Other Applicable Permits .............................................................................................................. 7 Table C.1 DMA Classifications ....................................................................................................................... 9 Table C.2 Type ‘A’, Self-Treating Areas ......................................................................................................... 9 Table C.3 Type ‘B’, Self-Retaining Areas ....................................................................................................... 9 Table C.4 Type ‘C’, Areas that Drain to Self-Retaining Areas ...................................................................... 10 Table C.5 Type ‘D’, Areas Draining to BMPs ............................................................................................... 10 Table D.1 Infiltration Feasibility .................................................................................................................. 11 Table D.2 LID Prioritization Summary Matrix ............................................................................................. 15 Table D.3 DCV Calculations for LID BMPs ................................................................................................... 16 Table E.1 Potential Pollutants by Land Use Type ........................................................................................ 19 Table E.2 Water Quality Credits .................................................................................................................. 20 Table E.3 Treatment Control BMP Sizing .................................................................................................... 20 Table E.4 Treatment Control BMP Selection .............................................................................................. 21 Table F.1 Hydrologic Conditions of Concern Summary .............................................................................. 22 Table G.1 Permanent and Operational Source Control Measures ............................................................. 24 Table H.1 Construction Plan Cross-reference ............................................................................................. 26
List of Appendices
Appendix 1: Maps and Site Plans ................................................................................................................ 28 Appendix 2: Construction Plans .................................................................................................................. 29 Appendix 3: Soils Information ..................................................................................................................... 30 Appendix 4: Historical Site Conditions ........................................................................................................ 31 Appendix 5: LID Infeasibility ........................................................................................................................ 32 Appendix 6: BMP Design Details ................................................................................................................. 33 Appendix 7: Hydromodification .................................................................................................................. 34 Appendix 8: Source Control ........................................................................................................................ 35 Appendix 9: O&M ....................................................................................................................................... 36 Appendix 10: Educational Materials ......................................................................................................... - 6 -
- 6 -
Section A: Project and Site Information
The proposed MLC La Sierra Tract 39008 will include the construction of residential development with associated residential landscaping, concrete hardscape, and asphalt paving streets. The proposed development is approximately 9.87 acres and is located at the southeast corner of La Sierra Avenue and Alhambra Avenue in the City of Riverside. BMPs are proposed for storm water quality treatment.
PROJECT INFORMATION
Type of Project: Residential
Ward Area: Ward 7
Community Name: La Sierra Hills
Development Name: Tract 39008
PROJECT LOCATION
Latitude & Longitude (DMS): 33.9419°, -117.5013°
Project Watershed and Sub-Watershed: Santa Ana Region Watershed, Santa Ana River Subwate rshed Gross Acres: 9.88 acres
APN(s): 149-052-004,-009,-011,-012-014
Map Book and Page No.: Book 11 Maps, Page 82
PROJECT CHARACTERISTICS
Proposed or Potential Land Use(s) SFR-Residential
Proposed or Potential SIC Code(s) 1521, General Builder Contractor, Single-
Family Residential
Area of Impervious Project Footprint (SF) 429,940
Total Area of proposed Impervious Surfaces within t he Project Limits (SF)/or Replacement 223,570 Does the project consist of offsite road improvemen ts? Y N Does the project propose to construct unpaved roads ? Y N Is the project part of a larger common plan of deve lopment (phased project)? Y N
EXISTING SITE CHARACTERISTICS
Total area of existing Impervious Surfaces within t he project limits (SF) 9162 Is the project located within any MSHCP Criteria Ce ll? Y N If so, identify the Cell number: N/A
Are there any natural hydrologic features on the pr oject site? Y N Is a Geotechnical Report attached? Y N
If no Geotech. Report, list the NRCS soils type(s) present on the site (A, B, C and/or D) B What is the Water Quality Design Storm Depth for th e project? 0.69 A.1 Maps and Site Plans
Appendix 1 includes a map of the local vicinity and existing site. In addition, WQMP Site Plan, locate d in Appendix 1, includes the following:
• Drainage Management Areas
• Proposed Structural BMPs
• Drainage Path
• Drainage Infrastructure, Inlets, Overflows
• Source Control BMPs
• Buildings, Roof Lines, Downspouts
• Impervious Surfaces
• Standard Labeling
- 7 -
A.2 Identify Receiving Waters
In order of upstream to downstream, the receiving w aters that the project site is tributary to are as follows. A map of the receiving waters is included in Appendix 1.
Table A.1 Identification of Receiving Waters
Receiving Waters EPA Approved 303(d)
List Impairments
Designated
Beneficial Uses
Proximity to RARE
Beneficial Use
La Sierra 36” Storm Drain
(Existing Storm Drain
System)
NOT LISTED NOT LISTED N/A
Arlington Valley Channel NOT LISTED NOT LISTED N/A
Unnamed Lined Channel
Downstream of
Arlington Valley Channel
NOT LISTED NOT LISTED N/A
Santa Ana River Reach 3 COPPER, LEAD,
INDICATOR BACTERIA AGR, GWR, RARE, REC1, REC2, WARM, WILD 7.2 MILES Santa Ana River Reach 2 CADMIUM AGR, GWR, RARE, REC1, REC2, WARM, WILD 9.28 MILES Tidal Prism of Santa Ana
River (Reach 1) NOT LISTED BIOL, REC1, WARM, REC2, WILD 21.79 MILES Pacific Ocean Nearshore
Zone NOT LISTED IND, NAV, REC1, REC2, COMM, WILD, RARE, SPWN, MAR, SHEL, MUN 33.9 MILES
Pacific Ocean Offshore
Zone NOT LISTED IND, NAV, REC1, REC2, COMM, WILD, RARE, SPWN, MAR, MUN 34.3 MILES
A.3 Additional Permits/Approvals required for the Project:
Table A.2 Other Applicable Permits
Agency Permit
Required
State Department of Fish and Game, 1602 Streambed Alter ation Agreement Y N State Water Resources Control Board, Clean Water Ac t (CWA) Section 401 Water Quality Cert. Y N US Army Corps of Engineers, CWA Section 404 Permit Y N US Fish and Wildlife, Endangered Species Act Sectio n 7 Biological Opinion Y N Statewide Construction General Permit Coverage: Y N
Statewide Industrial General Permit Coverage Y N
Western Riverside MSHCP Consistency Approval (e.g., JPR, DBESP) Y N Other (please list in the space below as required)
City of Riverside Conditional Use Permit
City of Riverside Design Review
City of Riverside Building Permit
City of Riverside Grading Permit
City of Riverside Construction Permit
Y
Y
Y
Y
Y
N
N
N
N
N
- 8 -
Section B: Optimize Site Utilization (LID Principles)
Site Optimization
Did you identify and preserve existing drainage patterns? If so, how? If not, why? Yes. The proposed site grading intends to maintain the existing flow pattern by predominantly draining in the southeast direction.
Did you identify and protect existing vegetation? If so, how? If not, why? Within the vacant portion of the site that will be developed, the existing vegetation will not be prot ected. The vacant portion of the project site does not have an y existing vegetation, other than annual grass. The proposed development will add landscape throughout the site, making the proposed development approximately 48% pervious.
Did you identify and preserve natural infiltration capacity? If so, how? If not, why? Yes, natural infiltration capacity will be maintain ed to the maximum extent possible. Compaction of soils within proposed landscaped area will be kept to a minimum to preserve natural infiltration capacity.
Did you identify and minimize impervious area? If so, how? If not, why? Yes. The site plan was done with the intent of maxi mizing the pervious area on the site to the maximum extent possible. This was accomplished by using landscape planters throughout the site and perimeter landsca ped areas.
Did you identify and disperse runoff to adjacent pervious areas? If so, how? If not, why? Yes. Roof drains and site drainage will be routed t o adjacent landscaping to the maximum extent possib le.
- 9 -
Section C: Delineate Drainage Management Areas
(DMAs)
Table C.1 DMA Classifications
DMA Name or ID Surface Type(s) 12 Area (Sq. Ft.) DMA Type DMA A Concrete/Asphalt/Landscape Areas 339,768 Type “D” – Area that drains to BMP
DMA C-1 Concrete/Asphalt/Landscape Areas 23,526 Type “D” – Area that drains to BMP
DMA C-2 Concrete/Asphalt/Landscape Areas 21,918
Type “D” – Area that
drains to BMP
DMA C-3 Concrete/Asphalt/Landscape Areas 21,919
Type “D” – Area that
drains to BMP
DMA C-4 Concrete/Asphalt/Landscape Areas 22,806
Type “D” – Area that
drains to BMP
1Reference Table 2-1 in the WQMP Guidance Document to populate this column 2If multi-surface provide back-up
Table C.2 Type ‘A’, Self-Treating Areas
DMA Name or ID Area (Sq. Ft.) Stabilization Type Irrigation Type (if any)
Table C.3 Type ‘B’, Self-Retaining Areas
Self-Retaining Area
Type ‘C’ DMAs that are draining to the Self- Retaining
Area
DMA
Name/ ID
Post-project
surface type
Area
(square
feet)
Storm
Depth
(inches) DMA Name / ID
[C] from Table C.4 = Required Retention
Depth (inches)
[A] [B] [C] [D]
= +
∙
- 10 -
Table C.4 Type ‘C’, Areas that Drain to Self-Retaining Areas DMA Receiving Self-Retaining DMA
DMA Name/ ID
Area
(square feet)
Post -project
surface type
Impervious
fraction
Product
DMA name /ID
Area (square
feet) Ratio
[A] [B] [C] = [A] x [B] [D] [C]/[D]
Table C.5 Type ‘D’, Areas Draining to BMPs
DMA Name or ID BMP Name or ID
DMA A Bioretention Basin A
DMA C-1 Bioretention Basin (C-1)
DMA C-2 Bioretention Basin (C-2)
DMA C-3 Bioretention Basin (C-3)
DMA C-4 Bioretention Basin (C-4)
Note: More than one drainage management area can drain to a single LID BMP, however, one drainage management area may not drain to more than one BMP.
- 11 -
Section D: Implement LID BMPs
D.1 Infiltration Applicability
Is there an approved downstream ‘Highest and Best U se’ for stormwater runoff (ref: Chapter 2.4.4 of the WQMP Guidance Document)? Y N
Geotechnical Report
A Geotechnical Report is required by the City of Ri verside to confirm present and past site characteristics that may affect the use of Infiltration BMPs, see Appendix 3.
Is this project classified as a small project consi stent with the requirements of Chapter 2 of the WQM P Guidance Document? Y N
Infiltration Feasibility
Table D.1 Infiltration Feasibility
Does the project site… YES NO
…have any DMAs with a seasonal high groundwater mark shallower than 10 feet? X If Yes, list affected DMAs:
…have any DMAs located within 100 feet of a water supply well? X If Yes, list affected DMAs:
…have any areas identified by the geotechnical repo rt as posing a public safety risk where infiltratio n of stormwater could have a negative impact? X
If Yes, list affected DMAs:
…have measured in-situ infiltration rates of less than 1.6 inches / hour? x If Yes, list affected DMAs: All
…have significant cut and/or fill conditions that w ould preclude in-situ testing of infiltration rates at the final infiltration surface? X
If Yes, list affected DMAs:
…geotechnical report identify other site-specific factors that would preclude effective and safe infiltration? X Describe here:
- 12 -
D.2 Harvest and Use Assessment
Please check what applies :
☐ Reclaimed water will be used for the non-potable water demands for the project. ☐Downstream water rights may be impacted by Harvest and Use as approved by the Regional Board (verify with the Copermittee).
☒The Design Capture Volume will be addressed using I nfiltration Only BMPs. In such a case, Harvest and Use BMPs are still encouraged, but it w ould not be required if the Design Capture Volume will be infiltrated or evapotranspired.
Harvest and Use BMPs need not be assessed for the site.
Irrigation Use Feasibility
Step 1:
Total Area of Irrigated Landscape : 4.74 acres
Type of Landscaping (Conservation Design or Active Turf) : Conservative Design Step 2:
Total Area of Impervious Surfaces: 5.13 acres
Step 3:
Enter your EIATIA factor : 1.32
Step 4:
Minimum required irrigated area : 5.13 acres x 1.32 = 6.77 acres Step 5:
Minimum required irrigated area (Step 4) Available Irrigated Landscape (Step 1)
6.77 acres 4.74 acres
The project proposes to use infiltration BMPs to retain the water quality volume. - 13 -
Toilet Use Feasibility
Step 1:
Projected Number of Daily Toilet Users: 58 (58 lots)
Project Type: Residential
Step 2:
Total Area of Impervious Surfaces: 5.13 acres
Step 3:
Enter your TUTIA factor: 116
Step 4:
Minimum number of toilet users: 116 x 5.13 = 595 toilet users Step 5:
Minimum required Toilet Users (Step 4) Projected nu mber of toilet users (Step 1) 595 toilet users 58 toilet users
The project proposes to use infiltration BMPs to retain the water quality volume.
Other Non-Potable Use Feasibility
Step 1:
Average Daily Demand: N/A
Step 2:
Total Area of Impervious Surfaces: N/A
Step 3:
Enter the factor from Table 2-4: N/A
Step 4:
Minimum required use: N/A
Step 5:
Minimum required non-potable use (Step 4) Projected average daily use (Step 1) N/A (Residential Only) N/A (Residential Only)
- 14 -
D.3 Bioretention and Biotreatment Assessment
Other LID Bioretention and Biotreatment BMPs as des cribed in Chapter 2.4.7 of the WQMP Guidance Document are feasible on nearly all development sites with sufficient advance planning.
Select one of the following:
☒ LID Bioretention/Biotreatment BMPs will be used fo r some or all DMAs of the project as noted below in Section D.4.
☐ A site-specific analysis demonstrating the technic al infeasibility of all LID BMPs has been performed and is included in Appendix 5.
☐ N/A – Infiltration BMPs are proposed.
- 15 -
D.4 Feasibility Assessment Summaries
Table D.2 LID Prioritization Summary Matrix
DMA
Name/ID
LID BMP Hierarchy No LID
(Alternative
Compliance) 1. Infiltration 2. Harvest and use 3. Bioretention 4. Biotreatment DMA -A
DMA -C1
DMA -C2
DMA -C3
DMA -C4
- 16 -
D.5 LID BMP Sizing
Table D.3 DCV Calculations for LID BMPs
DMA
Type/ID
DMA
Area
(square
feet)
Post-Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA
Areas x
Runoff
Factor
DMA A/Basin South
Underground Infiltration Basin
[A] [B] [C] [A] x [C]
DMA A 176,679 Concrete or
Asphalt
1 0.89 157598
Design
Storm
Depth
(in)
Design
Capture
Volume,
VBMP (cubic
feet)
Proposed
Retention
Volume
on Plans
(cubic
feet)
DMA A 163,088 Ornamental
Landscaping
0.1 0.11 18014
339,767 175,612 0.69 10,098 10,248
DMA
Type/ID
DMA Area
(square
feet)
Post-Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA Areas
x Runoff
Factor
DMA C/Basin East
Bioretention Basin
[A] [B] [C] [A] x [C]
DMA C-1 15630 Concrete or
Asphalt
1 0.89 13942
Design
Storm
Depth
(in)
Design
Capture
Volume,
VBMP
(cubic feet)
Proposed
Volume
on Plans
(cubic
feet)
DMA C-1 7896 Ornamental
Landscaping
0.1 0.11 872
23526 14814 0.69 852 867
DMA
Type/ID
DMA
Area
(square
feet)
Post -
Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA
Areas x
Runoff
Factor DMA C/Basin East
Bioretention Basin [A] [B] [C] [A] x [C]
DMA C-2 15630 Concrete or
Asphalt
1 0.89 13942
Design
Storm
Depth
(in)
Design
Capture
Volume,
VBMP
(cubic feet)
Proposed
Volume
on Plans
(cubic
feet)
DMA C-2 6288 Ornamental
Landscaping
0.1 0.11 695
21918 14637 0.69 842 867
- 17 -
DMA
Type/ID
DMA
Area
(square
feet)
Post -
Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA
Areas x
Runoff
Factor DMA C/Basin East
Bioretention Basin [A] [B] [C] [A] x [C]
DMA C-3 15630 Concrete or
Asphalt
1 0.89 13942
Design
Storm
Depth
(in)
Design
Capture
Volume,
VBMP
(cubic feet)
Proposed
Volume
on Plans
(cubic
feet)
DMA C-3 6289 Ornamental
Landscaping
0.1 0.11 695
21919 14637 0.69 842 867
DMA
Type/ID
DMA
Area
(square
feet)
Post -
Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA
Areas x
Runoff
Factor DMA C/Basin East
Bioretention Basin [A] [B] [C] [A] x [C]
DMA C-4 15630 Concrete or
Asphalt
1 0.89 13942
Design
Storm
Depth
(in)
Design
Capture
Volume,
VBMP
(cubic feet)
Proposed
Volume
on Plans
(cubic
feet)
DMA C-4 7176 Ornamental
Landscaping
0.1 0.11 793
22806 14735 0.69 847 867
[B], [C] is obtained as described in Section 2.3.1 of the WQMP Guidance Document [E] is obtained from Exhibit A in the WQMP Guidance Document [G] is obtained from a design procedure sheet, such as in LID BMP Design Handbook and placed in Appendix 6
- 18 -
Section E: Alternative Compliance (LID Waiver Program)
LID BMPs are expected to be feasible on virtually a ll projects. Where LID BMPs have been demonstrated to be infeasible as documented in Section D, other Treatment Control BMPs must be used (subject to LID waiver approval by the Copermittee). Check one of the following Boxes:
☒ LID Principles and LID BMPs have been incorporated into the site design to fully address all Drainage Management Areas. No alternative complianc e measures are required for this project and thus this Section is not required to be completed.
- Or -
☐ The following Drainage Management Areas are unable to be addressed using LID BMPs. A site-specific analysis demonstrating technical infeasibility of LID BMPs has been approved by the Co-Permittee and included in Appendix 5. Additional ly, no downstream regional and/or sub- regional LID BMPs exist or are available for use by the project. The following alternative compliance measures on the following pages are bein g implemented to ensure that any pollutant loads expected to be discharged by not incorporating LID BMPs, are fully mitigated.
N/A
- 19 -
E.1 Identify Pollutants of Concern
Table E.1 Potential Pollutants by Land Use Type
Priority Development
Project Categories and/or
Project Features (check those
that apply)
General Pollutant Categories
Bacterial
Indicators Metals Nutrients Pesticides
Toxic
Organic
Compounds
Sediments Trash &
Debris
Oil &
Grease
Detached Residential
Development P N P P N P P P
Attached Residential
Development P N P P N P P P (2)
Commercial/Industrial
Development P
(3) P P(1) P (1) P (5) P (1) P P
Automotive Repair
Shops N P N N P (4, 5) N P P
Restaurants
(>5,000 ft
2) P N N N N N P P
Hillside Development
(>5,000 ft
2) P N P P N P P P
Parking Lots
(>5,000 ft
2) P(6) P P(1) P (1) P (4) P (1) P P
Retail Gasoline Outlets N P N N P N P P
Project Priority Pollutant(s)
of Concern
P = Potential
N = Not Potential
(1) A potential Pollutant if non-native landscaping exists or is proposed onsite; otherwise not expected (2) A potential Pollutant if the project includes uncovered parking areas; otherwise not expected (3) A potential Pollutant is land use involving animal waste (4) Specifically petroleum hydrocarbons
(5) Specifically solvents
(6) Bacterial indicators are routinely detected in pavement runoff
- 20 -
E.2 Stormwater Credits
Table E.2 Water Quality Credits
Qualifying Project Categories Credit Percentage 2
N/A N/A
Total Credit Percentage 1
1Cannot Exceed 50%
2Obtain corresponding data from Table 3-8 in the WQMP Guidance Document
E.3 Sizing Criteria
Table E.3 Treatment Control BMP Sizing
DMA
Type/ID
DMA
Area
(square
feet)
Post-
Project
Surface
Type
Effective
Impervious
Fraction, I f
DMA
Runoff
Factor
DMA
Area x
Runoff
Factor
Enter BMP Name / Identifier Here
[A] [B] [C] [A] x [C]
N/A
Design
Storm
Depth
(in)
Minimum
Design
Capture
Volume or
Design Flow
Rate (cubic
feet or cfs)
Total Storm
Water
Credit %
Reduction
Proposed
Volume
or Flow
on Plans
(cubic
feet or
cfs)
AT =
Σ[A]
Σ= [D] [E] F = DxE
G [F] X (1-[H]) [I]
[B], [C] is obtained as described in Section 2.3.1 from the WQMP Guidance Document [E] is for Flow-Based Treatment Control BMPs [E] = .2, for Volume-Based Control Treatment BMPs, [E] obtained from Exhibit A in the WQMP Guidance Document
[G] is for Flow-Based Treatment Control BMPs [G] = 43,560, for Volume-Based Control Treatment BMPs, [G] = 12 [H] is from the Total Credit Percentage as Calculated from Table E.2 above [I] as obtained from a design procedure sheet from the BMP manufacturer and should be included in Appendix 6
- 21 -
E.4 Treatment Control BMP Selection
Treatment Control BMPs typically provide proprietar y treatment mechanisms to treat potential pollutants in runoff, but do not sustain significan t biological processes. Treatment Control BMPs must have a removal efficiency of a medium or high effectiveness as quantified below:
• High : equal to or greater than 80% removal efficiency • Medium : between 40% and 80% removal efficiency
Table E.4 Treatment Control BMP Selection
Selected Treatment Control BMP
Name or ID 1
Priority Pollutant (s) of
Concern to Mitigate 2
Removal Efficiency
Percentage 3
1 Treatment Control BMPs must not be constructed with in Receiving Waters. In addition, a proposed Treatm ent Control BMP may be listed more than once if they possess more than one qualifying pollutant removal efficiency. 2 Cross Reference Table E.1 above to populate this column. 3 As documented in a Co-Permittee Approved Study and provided in Appendix 6.
- 22 -
Section F: Hydromodification
F.1 Hydrologic Conditions of Concern (HCOC) Analysis
The project does not create a Hydrologic Condition of Concern, meeting the criteria for HCOC Exemption as shown below:
HCOC EXEMPTION 1: The Priority Development Project disturbs less than one acre. The Copermittee has the discretion to require a Project-Specific WQ MP to address HCOCs on projects less than one acre on a case by case basis. The disturbed area ca lculation should include all disturbances associated with larger common plans of development.
Does the project qualify for this HCOC Exemption? Y N
HCOC EXEMPTION 2 : The volume and time of concentration 1 of storm water runoff for the post-
development condition is not significantly different from the pre-development condition for a 2-year return frequency storm (a difference of 5% or less is considered insignificant) using one of the following methods to calculate:
• Riverside County Hydrology Manual
• Technical Release 55 (TR-55): Urban Hydrology for S mall Watersheds (NRCS 1986), or derivatives thereof, such as the Santa Barbara Urban Hydrograph Method • Other methods acceptable to the City of Riverside
Does the project qualify for this HCOC Exemption?
Y N
If Yes, report results in Table F.1 below and provi de your substantiated hydrologic analysis in Appendix 7.
Table F.1 Hydrologic Conditions of Concern Summary
2 year – 24 hour
Pre-condition Post-condition % Difference
Time of
Concentration
Volume (Cubic Feet)
1 Time of concentration is defined as the time after the beginning of the rainfall when all portions of the drainage basin are contributing to flow at the outlet.
- 23 -
HCOC EXEMPTION 3 : All downstream conveyance channels to an adequate sump (for example, Prado Dam, Lake Elsinore, Canyon Lake, San ta Ana River, or other lake, reservoir or naturally erosion resistant feature) that will rece ive runoff from the project are engineered and regularly maintained to ensure design flow capacity; no sensitive stream habitat areas will be adversely affected; or are not identified on the Co-Permittees Hydromodification Susceptibility Maps.
Does the project qualify for this HCOC Exemption? Y N Based upon the HCOC Applicability Map, the project site is located within a HCOC non applicable area in which all downstream waterbodies are considered ‘not susceptible stream channels”.
F.2 HCOC Mitigation
As an alternative to the HCOC Exemption Criteria ab ove, HCOC criteria is considered mitigated if the project meets one of the following conditions, as indicated:
a. Additional LID BMPS are implemented onsite or offsite to mitigate potential erosion or habitat impacts as a result of HCOCs. This can be conducted by an evaluation of site-specific conditions utili zing accepted professional methodologies published by en tities such as the California Stormwater Quality Association (CASQA), the Southern California Coasta l Water Research Project (SCCRWP), or other Co- Permittee approved methodologies for site-specific HCOC analysis. b. The project is developed consistent with an app roved Watershed Action Plan that addresses HCOC in Receiving Waters.
c. Mimicking the pre-development hydrograph with t he post-development hydrograph, for a 2- year return frequency storm. Generally, the hydrolo gic conditions of concern are not significant, if t he post-development hydrograph is no more than 10% gre ater than pre-development hydrograph. In cases where excess volume cannot be infiltrated or captur ed and reused, discharge from the site must be limited to a flow rate no greater than 110% of the pre-development 2-year peak flow. d. None of the above.
- 24 -
Section G: Source Control BMPs
Table G.1 Permanent and Operational Source Control Measures Potential Sources of Runoff
pollutants Permanent Structural Source Control BMPs
Operational Source Control BMPs
On-site storm drain inlets Mark all inlets with the word “Only Rain Down the Storm Drain” or similar. Catch
Basin Markers may be available from the
Riverside County Flood Control and Water
Conservation District.
Maintain and periodically repaint
or replace inlet markings. Provide
stormwater pollution prevention
information to new site owners,
lessees, or operators. See
applicable operational BMPs in
Fact Sheet SC-44, “Drainage
System Maintenance” provided in
Appendix 10: Educational
Materials. Include the following in
lease agreements: “Tenant shall
not allow anyone to discharge
anything to storm drains or to
store or deposit materials so as to
Need for future indoor &
structural pest control
Incorporate building design features that
discourage entry of pests:
For Foundations and Slabs: use corrosion
resistant, pest-resistant mesh on crawl
space vents: foundation vents should be at
least 6 inches above finish ground level;
pour concrete patios as part of the main
slabs to minimize entry of pests via joints; if
slab joints are necessary, consider termite
barriers; use epoxy sealants, or mesh
barriers, or sand barriers for utility breaks.
For Siding: use non-wood siding options; use
high quality caulks and sealants; siding and
stucco should begin at least six inches above
soil level. For Lighting: use bird-resistant
light fixtures. Use gutters with downspouts;
use flap valves or mesh on downspouts to
prevent rodents from entering downspouts.
Use metal mesh to prevent animal access
under sheds, decks, and porches.
Provide Integrated Pest
Management information to
owners, lessees, and operators.
Provided “Pest Prevention by
Design” Guidelines in Appendix 10.
Landscape/Outdoor
Pesticide Use
Final landscape plans will accomplish all of
the following.
Design landscaping to minimize irrigation
and runoff, to promote surface infiltration
where appropriate, and to minimize the use
of fertilizers and pesticides that can
contribute to stormwater pollution.
Where landscaped areas are used to retain
or detain stormwater, specify plants that are
tolerant of saturated soil conditions.
Consider using pest-resistant plants,
Maintain landscaping using
minimum or no pesticides. See
applicable operational BMPs in
“What you should know
for...Landscape and Gardening”
provided in Appendix 10:
Educational Materials.
Provide IPM information to new
owners, leases, and operators.
- 25 -
especially adjacent to hardscape.
To ensure successful establishment, select
plants appropriate to site soils, slopes,
climate, sun, wind, rain, land use, air
movement, ecological consistency, and plant
interactions.
Note: No outdoor material storage or outdoor vehicl e/equipment maintenance shall take place for proposed project.
- 26 -
Section H: Construction Plan Checklist
Table H.1 Construction Plan Cross-reference
BMP No. or ID BMP Identifier and Description Plan Sheet Number(s) Latitude / Longitude DMA A Bioretention Basin 5; WQMP EXHIBIT 33.94175, -117.50002 DMA C-1 Bioretention Basin 5; WQMP EXHIBIT 33.94311, -117.50101 DMA C-2 Bioretention Basin 5; WQMP EXHIBIT 33.94311, -117.50101 DMA C-3 Bioretention Basin 5; WQMP EXHIBIT 33.94311, -117.50101 DMA C-4 Bioretention Basin 5; WQMP EXHIBIT 33.94311, -117.50101
- 27 -
Section I: Operation, Maintenance and Funding
The Copermittee will periodically verify that Stormwater BMPs on your site are maintained and continue to operate as designed. To make this possible, your Copermittee will require that you include in Appendix 9 of this Project-Specific WQMP:
1. A means to finance and implement facility maintenan ce in perpetuity, including replacement cost.
2. Acceptance of responsibility for maintenance from t he time the BMPs are constructed until responsibility for operation and maintenance is leg ally transferred. A warranty covering a period following construction may also be required.
3. An outline of general maintenance requirements for the Stormwater BMPs you have selected.
4. Figures delineating and designating pervious and im pervious areas, location, and type of Stormwater BMP, and tables of pervious and impervio us areas served by each facility. Geo- locating the BMPs using a coordinate system of lati tude and longitude is recommended to help facilitate a future statewide database system.
5. A separate list and location of self-retaining area s or areas addressed by LID Principles that do not require specialized O&M or inspections but will require typical landscape maintenance as noted in Chapter 5, pages 85-86, in the WQMP Guidan ce. Include a brief description of typical landscape maintenance for these areas.
Your local Co-Permittee will also require that you prepare and submit a detailed Stormwater BMP Operation and Maintenance Plan that sets forth a ma intenance schedule for each of the Stormwater BMPs built on your site. An agreement assigning res ponsibility for maintenance and providing for inspections and certification may also be required.
Maintenance Mechanism: Meritage Homes of California , Inc. during construction and sales period.
Once construction is completed and all homes have b een sold, responsibility for O&M will be transferred to the H ome Owner’s Association.
Will the proposed BMPs be maintained by a Home Owne rs’ Association (HOA) or Property Owners Association (POA)?
Y N
Include your Operation and Maintenance Plan and Maintenance Mechanism in Appendix 9. Additionally, include all pertinent forms of educational material s for those personnel that will be maintaining the proposed BMPs within this Project-Specific WQMP in Appendix 10. - 28 -
Appendix 1: Maps and Site Plans
Location Map, WQMP Site Plan and Receiving Waters M ap
LOCATION MAP
NOT TO SCALE
MLC LA SIERRA
PROJECT LOCATION
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
PRELIMINARY
6 STRUCTURAL SOURCE CONTROL BMP NOTES
ARLINGTON AVE
LA SIERRA AVE
MAGNOLIA AVE
VAN BUREN BLVD
RIVERSIDE FWY W
ONTARIO FWY S
PROMENADE AVE
TYLER ST
CITY OF RIVERSIDE
WQMP EXHIBIT
LA SIERRA
LEGEND
VICINITY MAP
WQMP EXHIBIT1
TYPICAL BIO-RETENTION DETAIL
N.T.S.
LA SIERRA AVE.
ALHAMBRA AVE.
STREET A
STREET A
STREET A
STREET A
ALHAMBRA AVE.
! #"#$ "#%&$
'#
()
#
#*#+#+#,#-/.& #101 $ 2"#3
4 5# %6 7#18
'#%&(#"9:;;
(#$ 2"#($ #1
<
<
= <
2"
<
"#(#$ (#$#"#3>$ #17#
$ 1%? #"#9("#($ # %&8@
!-A.& # %
8
B%6 #
#(#"#$ C!>
#"#7#=#<
7:" D7# %6$ C!=#$ 7#-
EF01"
!2 G# #$#*#+#+#,#HI01 $ 2"#3
4 5# %6 7#
HI01
3;" (#
J
(#$
7)C!2#KLMN
41O
.&P&P
Temescal Creek, Reach 1
Santa Ana River, Reach 3
Anza Park Drain
Lake Evans
Arlington Channel
La Sierra Channel
Mockingbird Reservoir
Lake Matthews
Sycamore Creek
Lake Evans to Santa Ana River, Reach 3
Tequesquite Arroyo (Sycamore Creek) to Santa Ana River, Reach 3 Anza Park Drain to Santa Ana River, Reach 3
Santa Ana River, Reach 3
Mockingbird Reservoir to Temescal Creek, Reach 1 to Santa Ana River, Reach 3 - via Arlington Channel
Temescal Creek, Reach 1 to Santa Ana River, Reach 3 - via Arlington Channel
Temescal Creek, Reach 1 to Santa Ana River, Reach 3 - via La Sierra Channel to Arlington Channel
Outside City Limits
San Jacinto Watershed
RECEIVING WATERS MAP
LEGEND
© 2009. All Rights Reserved. City of Riverside, California.
PROJECT
LOCATION
RIVERSIDE COUNTY FLOOD
CONTROL AND WATER
CONSERVATION DISTRICT
Isohyetal Map
for the 85th Percentile
24 hour Storm Event
July 2011
Rain Gage Locations
PROJECT LOCATION
- 28 -
Appendix 2: Construction Plans
Grading and Drainage Plans
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
6 LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
6 ARLINGTON AVE
LA SIERRA AVE
MAGNOLIA AVE
VAN BUREN BLVD
RIVERSIDE FWY W
ONTARIO FWY S
PROMENADE AVE
TYLER ST
DEVELOPER
CITY OF RIVERSIDE
TENTATIVE TRACT MAP 39008
LA SIERRA
ENGINEER
BENCHMARK
OWNER
SOILS ENGINEER
LEGAL DESCRIPTION
’”
’’”
’”
EXISTING EASEMENTS
ZONING
LAND USE
AREA SUMMARY
UTILITY PROVIDERS
LEGEND
PROJECT SITE
VICINITY MAP
COVER SHEET
NOTES
PERIMETER SETBACKS
1 LOT SETBACKS
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
6 LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
62 COVER SHEET
FOR REFERENCE ONLY
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
63 ASSESSOR'S PARCEL NO
SITE PLAN
LEGENDABBREVIATIONS
CITY OF RIVERSIDE
SITE PLAN
TENTATIVE TRACT MAP 39008 - LA SIERRA
SOMERVALE DR.
LA SIERRA AVE.
ALHAMBRA AVE.
STREET A
(PRIVATE)
STREET A
(PRIVATE)
STREET A
(PRIVATE)
STREET A
(PRIVATE)
ALHAMBRA AVE.
STREET B
(PRIVATE)
FRANCISCO DRIVE
O.S. 59
0.3 AC
O.S. 60
0.02 AC
O.S. 58
0.2 AC
O.S. 57
0.3 AC
LINDY ST.
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
6 LEGEND
TENTATIVE TRACT MAP
CITY OF RIVERSIDE
TENTATIVE TRACT MAP
TENTATIVE TRACT MAP 39008 - LA SIERRA
4 LA SIERRA AVE.
ALHAMBRA AVE.
STREET A
STREET A
STREET A
STREET A
ALHAMBRA AVE.
O.S. 59
0.3 AC
O.S. 60
0.02 AC
O.S. 58
0.2 AC
O.S. 57
0.3 AC
(PRIVATE)
(PRIVATE)
(PRIVATE)
(PRIVATE)
LINDY ST.
SOMERVALE DR.
PARCEL AREA TABLE PARCEL AREA TABLE PARCEL AREA TABLE
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
PRELIMINARY
6 CONCEPTUAL GRADING
CITY OF RIVERSIDE
PRELIMINARY GRADING
LA SIERRA
& DRAINAGE PLAN
& DRAINAGE PLAN
LEGEND
SECTION A-A
N.T.S.
SECTION B-B
N.T.S.
SECTION C-C
N.T.S.
SECTION D-D
N.T.S.
SECTION E-E
N.T.S.
SECTION F-F
N.T.S.
SECTION G-G
N.T.S.
SECTION H-H
N.T.S.
NOTE
5 TYPICAL BIO-RETENTION DETAIL
N.T.S.
LA SIERRA AVE.
ALHAMBRA AVE.
STREET A
(PRIVATE)
STREET A
(PRIVATE)
STREET A
(PRIVATE)
STREET A
(PRIVATE)
ALHAMBRA AVE.
STREET B
(PRIVATE)
D4
E4
C
4 A
4 G
4 F
4 LINDY ST.
H
4 B4
0+001+00
E-E PROFILE
F-F PROFILEG-G PROFILE
LA SIERRA AVE.
ALHAMBRA AVE.
STREET A (PRIVATE)
STREET A (PRIVATE)
STREET A (PRIVATE)
STREET A (PRIVATE)
ALHAMBRA AVE.
STREET B (PRIVATE)
FRANCISCO DRIVE
O.S. 59
0.3 AC
O.S. 60
0.02 AC
O.S. 58
0.2 AC
O.S. 57
0.3 AC
LINDY ST.
LA SIERRA AVE. & ALHAMBRA AVE.
TENTATIVE TRACT MAP 39008
FOR REVIEW
66 ASSESSOR'S PARCEL NO
PRELIMINARY PARKING AND CIRCULATION PLAN
LEGEND
ABBREVIATIONS
CITY OF RIVERSIDE
PRELIMINARY PARKING CIRCULATION PLAN
TENTATIVE TRACT MAP 39008 - LA SIERRA
SOMERVALE DR.
FIRE TRUCK TURNING CLEARANCE DETAIL
N.T.S.
- 29 -
Appendix 3: Soils Information
Geotechnical Study and Other Infiltration Testing Data
1000 North Coast Highway Suite 10 Laguna Beach, California 92651 (949) 403-7229 SAgeotechnical.com
December 22, 2023
Project No. 23145-01
To: Meritage Homes
5 Peters Canyon Road, Suite 310
Irvine, California 92606
Attention: Ms. Louisa Feletto
Subject: Geotechnical Due Diligence E xploration and Preliminary Design Recommendations, Proposed Residential De velopment, Southwest Corner of La Sierra Avenue and Alhambra Avenue, City of Riverside, California
At your request, SA Geotechnical , Inc. (SA GEO) has conducted a geotechnical due diligence exploration and review for the pr oposed residential development lo cated at the southwest corner of La Sierra Avenue and Alhambra Avenue in the City of Rivers ide, California (Figure 1). The purpose of this study was to evaluate the geotec hnical site conditions in light of the proposed grading and improvements in order to provi de a geotechnical summary and preliminary recommendations for project design, grading and construction. Our evaluation included review of collected geologic maps and data pertinent to the subject site; subsurface exploration; laboratory testing and analysis; and preparation of this report.
The subject site consists of a mixture of v acant/undeveloped property and rural single-family residential development. The s ite is composed of several c onjoined parcels/lots, totaling approximately 9.8 acres. Based on our study, the primary geotechnical cons traints at the site include: the presence of granitic bedrock at existing grade and/ or shallow depth underlying the alluvium, the presence of undocumented artificial fills and weathered/unsu itable alluvium near- surface, and seismic shaking during a strong seismic event. The site geology generally consists of approximately 2.5 to 21.5 feet of older alluvium capping grani tic bedrock. Along the central portion of the westerly boundary, granitic rock is mapped at existing grad es. The older alluvium generally consists of reddish-brown silty sa nd and sandy silt with "Very Low" to "Medium" expansion potential. The underlying bedrock consis ts of fine to coarse-grained granitic bedrock (monzogranite, granodiorite, and diorite) that is generally weathered ("decomposed") in the uppermost 18 to 35 feet and cons idered rippable with heavy duty earthmovi ng equipment (i.e.:
Caterpillar D9 bulldozer or equi valent). Groundwater was encount ered in one bo ring (H-5) at a depth of 26.5 feet below ground surface. Percolation testing was also performed during this study and indicates that shallow stormwater infiltration is generally feasible at the site.
23145-01
December 22, 2023
ii
231222 Meritage La Sierra (23145-01) DD Report.docx
This report presents our findi ngs, conclusions, and preliminary design reco mmendations for the subject residential deve lopment. Based on our review, the pr oposed development is considered geotechnically feasible provided the recommenda tions in this report are implemented during design, grading, and construction. Additional geot echnical exploration and analysis may need to be performed once the project pl ans for grading, foundations, a nd stormwater infiltration are developed.
References pertinent to the site are included in Appendix A. Boring and test pit logs are included in Appendix B. Laboratory test data is included in Appendix C. The geophysical survey/rippability report is included in Appendix D. Percolation test data is presented in Appendix E. Seismic design parameters are presented in A ppendix F. General earthwork and grading specifications are presented in Appendix G.
If you have any questions regardi ng this report, please contact our office. We appreciate the opportunity to provide our services.
Respectfully submitted,
SA GEOTECHNICAL, INC.
Anthony Zepeda, CEG 2681 Reza Saberi, GE 3071
Project Geologist Principal Engineer
Peter Anderson, CEG 2596
Principal Engineering Geologist
23145-01
December 22, 2023
iii
231222 Meritage La Sierra (23145-01) DD Report.docx
TABLE OF CONTENTS
EXECUTIVE SUMMARY ........................................................................................................ 1
1.0 INTRODUCTION .............................................................................................................. 3
1.1 Introduction and Scope of Services ................................................................................ 3
1.2 Site Location, Existing Conditions, and History ............................................................ 4
1.3 Proposed Grading and Improvements ............................................................................. 4
1.4 Subsurface Exploration ................................................................................................... 5
1.5 Laboratory Testing ........................................................................................................ .. 5
2.1 Geologic Setting and Earth Units ................................................................................... 7
2.2 Geotechnical Conditions ................................................................................................. 7
2.3 Groundwater ............................................................................................................... .... 9
2.4 Regional Faulting and Seismicity ................................................................................... 9
2.5 Settlement ................................................................................................................ ....... 9
2.6 Shrinkage and Bulking .................................................................................................. 10
2.7 Rippability and Generation of Oversize Material ......................................................... 10
2.8 Percolation Testing ....................................................................................................... 10
2.3 Existing Utilities ........................................................................................................ ... 11
3.0 CONCLUSION AND PRELIMI NARY RECOMMENDATIONS ................................. 12
3.1 General Conclusion and Recommendation ................................................................... 12
3.2 Site Preparation and Earthwork .................................................................................... 12
3.2.1 Site Demolition and Clearing ..................................................................................... 12
3.2.2 Protection of Existing Impr ovements and Utilities .................................................... 13
3.2.3 Remedial Grading Measures ...................................................................................... 13
3.2.4 Lot Capping/Overexcavation ...................................................................................... 13
3.2.5 Rippability and Placement of Oversize Material ........................................................ 14
3.2.6 Fill Placement .......................................................................................................... ... 15
3.2.7 Import .................................................................................................................. ....... 15
3.3 Settlement Potential ...................................................................................................... 15
3.4 Foundation Design ........................................................................................................ 16
3.5 Retaining Wall Design and Lateral Earth Pressures ..................................................... 18
3.6 Seismic Design Parameters ........................................................................................... 18
3.7 Slope Setback ............................................................................................................. ... 19
3.8 Corrosivity ............................................................................................................... ..... 20
3.9 Expansion Potential ...................................................................................................... 20
3.10 Interior Slab Mois ture Mitigation ................................................................................. 20
3.11 Exterior Concrete ........................................................................................................ .. 21
3.12 Preliminary Asphalt Concre te Pavement Design .......................................................... 22
3.13 Trench Excavation and Backfill .................................................................................... 22
3.14 Groundwater .............................................................................................................. ... 23
3.15 Stormwater Infiltration .................................................................................................. 23
3.16 Surface Drainage and Irrigation .................................................................................... 24
3.17 Maintenance of Graded Slopes ..................................................................................... 25
3.18 Additional Subsurface Exploration and Laboratory Testing ........................................ 25
3.19 Review of Future Plans ................................................................................................. 2 5
3.20 Observation and Testing during Grading and Construction ......................................... 25
4.0 LIMITATIONS ............................................................................................................. 2 6 23145-01
December 22, 2023
iv
231222 Meritage La Sierra (23145-01) DD Report.docx
TABLE OF CONTENTS (Continued)
List of Illustrations
Figure 1 – Site Location Map – Rear of Text
Figure 2 – Regional Geologic Map – Rear of Text
Figure 3 – Regional Fault Map – Rear of Text
Figure 4 – Retaining Wall Drainage Detail – Rear of Text
Appendices
Appendix A – References
Appendix B – Boring and Test Pit Logs
Appendix C – Laboratory Test Data
Appendix D – Geophysical Survey Report
Appendix E – Percolation Data
Appendix F – Seismicity Data
Appendix G – General Earthwork and Grading Specifications
Plates
Plate 1 – Geotechnical Map – Rear of Appendices
23145-01
December 22, 2023
1 231222 Meritage La Sierra (23145-01) DD Report.docx
EXECUTIVE SUMMARY
The subject site is generally underl ain at or near-surface by granitic bedrock that is successively overlain by variable thicknesses of older alluvium, generally th ickening to the east. Granitic bedrock is exposed at the surface within the western portion of th e site. Undocumented artificial fill associated with prior land use/grading was encountered in se veral test pits across the site, ranging from 1.5 to 5.5 feet thick. The older all uvium generally consisted of yellowish-brown, reddish-brown, and brown silty fine to coarse sa nd, sandy silt and sandy clay that was damp to moist and medium dense/stiff where encounter ed, ranging in thickness from 2.5 to 21.5 feet.
Bedrock was found to consist of yellowish-brown, olive brown, pale reddish-brown, and gray fine to coarse-grained granitic rock (mixtures of monzogranitic, granodiorite, and diorite) that is damp to saturated, and dense to very dense. In general, the bedrock is weathered ("decomposed") in the uppermost 18 to 35 feet and moderately weathe red to unweathered below. Bedrock will be encountered during onsite grading and within excavations for utility lines throughout the site. The granitic bedrock is generally considered exca vatable (rippable) with heavy duty earthmoving equipment (i.e. Caterpillar D9 bulldozer) to a minimum depth of 18 feet. However, oversize rocks will be generated during grading and excavation for utilities.
The primary geotechnical constraints for site development include the following:
Presence of shallow granitic bedrock throughout the site; Presence of undocumented fill and weathered/unsuitable alluvium near surface; and, Potential for strong seismic shaking during an earthquake event.
The undocumented fill and near su rface/highly weathered older alluvium and granitic rock are considered unsuitable for support of compacted fill material and the proposed improvements.
Remedial grading for the site should consist of the removal and recompaction of all undocumented fill materials, and highly weathered or disturbed alluvium and/or bedrock. Remedial removals are anticipated to range from 2.5 to 6 feet below existing grades. Overexcavation (within cut areas) is recommended to depths of 3 to 4 feet belo w design grades. Remedial removals and/or overexcavation within streets or utility alignments/connections should be performed to 1 foot below the deepest utility to facilitate future utility pipeline constructi on. The recommended remedial removal and overexcavation will also help reduce the potential for future differential settlement at the site. Based on verbal communication with the current landowner, the existing onsite residences rely on septic tanks and leach fields for sewage management. These features should be anticipated during demolition and grading. Wells , septic tanks, seepage pits, and related appurtenances will need to be properly removed and/or abando ned in accordance with County of Riverside Department of Environmental H ealth requirements (or other gove rning agency) and the project environmental consultant’s recommendations.
Groundwater was encountered in one boring (H-5) during our exploration at a depth of 26.5 feet below ground surface. In ge neral, groundwater is anticipated to remain more than 10 feet below design grades upon the completion of grading. Howe ver, perched groundwater may be present at shallow depths locally and along the bedrock contact. Groundwater will fluctuate on an annual and seasonal basis.
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Building foundations and slabs should be designed to tolerate a total sett lement of 1 inch and differential settlement of ½-inch over a span of 40 feet. The site is categor ized as Site Class "C" for seismic design. Onsite soils are anticipated to have "Very Low" to "Low" expansion potential at the completion of grading. Onsite soils are not anticipated to be corrosive to concrete but are corrosive to metals.
Based on our findings, we conclude that the proposed residential development is feasible from a geotechnical viewpoint, provided it is design ed and constructed in accordance with the recommendations presented in this report and any future design/plan review re ports. The site is considered locally suitable for infiltration of stormwater at shallow depths.
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1.0 INTRODUCTION
1.1 Introduction and Scope of Services
At your request, SA Geotechnical , Inc. (SA GEO) has conducted a geotechnical due diligence exploration and review for the proposed residential development at the subject property in the City of Riverside, California (Figure 1). The purpose of our study was to assess the onsite geologic and geotechnical conditions and provide prelimin ary recommendations for design, grading, and construction of the proposed improvements. We ha ve reviewed the Conceptual Site Plan, dated November 8, 2023, which shows the generalized lot layout; however, contains no existing or proposed grades. A Google Earth satellite image was utilized as the base for our Geotechnical Map (Plate 1).
Our scope of services for this study included the following tasks:
Review of available geologic and geotechnical maps, reports, and data for the subject site and surrounding area. A list of references is included in Appendix A. Review of available historic aerial photographs and topographic maps dating back to 1948. Notification and coordination with DigAlert to identify and clear boring and test pit locations of underground utilities.
Subsurface exploration consisting of ten hollow-stem auger borings (H-1 through H-6 and P- 1 through P-4) to depths ranging from 5 to 30.5 feet below ground surface (bgs). Eight backhoe test pits (TP-1 through TP-8) we re also excavated, ranging in depth from 8.5 to 15 feet bgs.
Boring and test pit logs are included in Appendix B.
Percolation testing in four borings (P-1 through P-4) in general conformance with the 2011 Riverside County Design Handbook for Low Im pact Development Best Management Practices.
A geophysical refraction survey, which include d two survey lines (SL-1 and SL-2), was performed to collect compression wave (p-wave) velocity data to assist in evaluation of hardness and rippability of the mapped granitic bedrock. Laboratory testing of selected samples to de termine engineering properties of onsite soils, including in-situ moisture and density, grain size distribu tion, plasticity, consolidation, shear strength, maximum density and optimum moisture content, R-value, expansion potential, and soluble sulfate content. Laboratory test results are included in Appendix C. Geotechnical evaluation and analysis of the compiled data with respect to the proposed grading and development.
Preliminary evaluation of faulting, seismicity, and seismic and static settlement in accordance with the 2022 California Building Code (CBC).
Preparation of this report incl uding our findings, conclusions, preliminary recommendations, and accompanying illustrations.
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1.2 Site Location, Existi ng Conditions, and History
The subject site is located at the southwest corner of the La Sierra Avenue and Alhambra Avenue intersection, in the city of Riverside, Calif ornia. The approximately 9.8-acre site is bound by La Sierra Avenue to the east, Alhambra Avenue to the north and west, and existing single family residential developments to the south and west. We understand that the subj ect site is composed of six conjoined lots/parcels, three of which are developed with rural single-family residences. The other parcels remain largely undeveloped and/or used for equestrian activity. The site is moderately sloping to the sout heast with several mature trees throug hout. Based on verbal communication with the current property owner, the existing onsite reside nces rely on septic systems and leach fields for sewage waste management.
Based on our review of available historic aer ial photographs dating back to 1948, the following summarizes our understanding of the site history:
1948: The aerial photograph depicts the northerly portion of the site used for agriculture (citrus orchard). Three residences appear to occupy the subject site, two of which are still present on site (at the east and southeast portions of the site). Various outbuildings are also located onsite. La Sierra Avenue and Al hambra Avenue are present. Neighboring properties to the south and northwest are un developed. Scattered rural residences are located to the north and west.
1959: The subject property remained largely unchanged. A chicken farming operation was constructed to the northwest of the site, whil e scattered rural residences were constructed to the west.
1966/1967: No significant changes were observed onsite. 1985: The site appears to have been partiall y cleared of the orchard. The residence and swimming pool along the western boundary were present by this time. Additional outbuildings and equestrian-rel ated features were also noted. The chicken farming operation to the northwest had been removed/demolished. 1994: By 1994, the remaining portion of the orchard was removed. Additional equestrian- related features were noted in the northerly portion of the site. Otherwise, the site appears mostly unchanged. The single-family residences (offsite) adjacent to the southerly property line were constructed.
1998/1999: No discernable changes to the site were observed. 2002-2023: The site remained relatively unchanged during this time. Various outbuildings and equestrian features were added/removed. By 2018 the single-family residences to the northwest (Lindy Street) were under construction.
1.3 Proposed Grading and Improvements
Prior to site development and grading, the exis ting structures/foundations, and utilities to be abandoned will be demolished and removed from the site. Based on review of the Conceptual Site Plan, the development is proposed to include gradi ng of 93 single-family residential lots, interior streets, a park/amenity area, stormwater infiltr ation features, and utility improvements to support the development. We anticipate that the proposed single-family units will be one to two-story wood-framed structures. Slopes and/or retain ing walls will most likely be required to 23145-01
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accommodate grade changes, especially along the western property boundary. Grading cuts/fills and utility depths are not known at this time.
1.4 Subsurface Exploration
Our subsurface exploration was performed on December 6 through 13, 2023, and included drilling of 10 hollow-stem auger borings, ex cavation of eight backhoe test p its, field percolation testing, and a geophysical refraction survey consisting of two survey lines. The approximate boring, test pit, and seismic survey line locations are s hown on the Geotechnical Map (Plate 1). Boring and test pit logs are provided in Appendix B.
Hollow-stem auger borings (H-1 through H-6 and P-1 through P-4) were drilled to depths of 5 to
30.5 feet below ground surface (bgs). All borings were geotechnically logged, and samples were taken at selected intervals. Relatively undisturbed ring samples were obtained from the exploratory borings with a 2.5-inch inside-diame ter, split-barrel sampler. The samplers were driven into the soil with a 140-pound automatic sa fety hammer, free-falling 30-inches. The drive samples were also used to obtain a measure of resistance of th e soil to penetration (reco rded as blows-per-foot on our geotechnical boring logs). Bulk samples we re collected for additi onal laboratory testing.
After completion of drilling the excavations were backfilled with soil cuttings and tamped.
Following drilling, percolation testing was performed in four borings (P-1 through P-4) in general conformance with the 2011 County of Riverside Design Handbook for Low Impact Development Best Management Practices.
The test pit exploration included eight locations (TP-1 through TP-8) that were excavated with a rubber-tired backhoe (Deere 310SL) to depths ranging from 8.5 to 15 feet bgs. The excavations were geotechnically logged by an engineering ge ologist. Representative bulk samples of onsite soils were collected from trenching spoils and used for additional soil identification purposes.
A geophysical refraction survey was performed by GeoVision on December 13, 2023, and included two survey lines (SL-1 and SL-2), focu sed within the westerly portion of the site underlain by granitic bedrock at existing gr ades. The approximate geophysical survey line locations are shown on the Geotechnical Map (Plate 1). The refraction survey was used to measure compressional (P) wave velocities of the granitic bedrock as part of our rippability assessment.
The geophysical report is provided in Appendix D.
1.5 Laboratory Testing
Laboratory testing was performed on representati ve samples of onsite soils collected during our field exploration to characterize their engineer ing properties. Laborator y tests performed on selected samples included:
Moisture content and dry density;
Grain-size distribution;
Atterberg limits;
Direct shear;
Expansion Index;
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R-value;
Soluble sulfate; and
Maximum dry density and optimum moisture content.
Laboratory tests were conducted in general conformance with applicable ASTM International test methods. Laboratory test results are provided in Appendix C. In-s itu moisture content and dry density data are included on the geotechnical boring logs (Appendix B).
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2.0 GEOTECHNICAL FINDINGS
2.1 Geologic Setting and Earth Units
The site is located in the Peninsular Range s geomorphic province of Southern California, characterized by series of ranges and northwest trending valleys, subparallel to regional faults. The subject site is mapped by the United States Geological Survey (USGS, 2001 & 2002) as underlain by older alluvial fan deposits ove rlying granitic bedrock. Granit ic bedrock is also mapped at existing grade within the western-most portion of the site. Also, undocumented artificial fill material, associated with prior land use, was enco untered in various test pits across the site. The Geotechnical Map (Plate 1) depicts the site earth unit distribution and estimated depth to bedrock.
The earth units, as encountered during our explora tion are described below from oldest to youngest.
Granitic Bedrock (Map Symbol - Kgr): The site is underlain by Cretaceous-age intrusive igneous bedrock that is generally described as yellowish-brown, olive brown, pale reddish-brown, and gray fine to coarse-grained granitic rock (monzogranite, granodiorite, and diorite) that is damp to saturated, and dense to very dense. In general, the bedrock is weathered ("decomposed") in the uppermost 18 to 35 feet. Boring H-1 was terminat ed due to hard rock and difficult drilling conditions at a depth of 8 feet bgs; the remainder of borings were drilled 10 to 27 feet into bedrock without encountering refusal. The backhoe test p its were generally excavated 2.5 to 9 feet into bedrock before encountering diff iculty digging and/or refusal. Test pit location TP-2 was terminated less than 1 foot into bedrock due to hard rock conditions. Th e depth to bedrock, as encountered during our subsurface exploration, is provided on the Geotechnical Map (Plate 1).
Older Alluvium (Map Symbol – Qalo): Older alluvium is mapped covering most of the site and generally varies in thickness from 2.5 to 11.5 feet. Locally, along the easterly property line, older alluvium was encountered to a depth of 21.5 f eet bgs. The alluvium ge nerally consisted of yellowish-brown, reddish-brown, and brown silty fine to coarse sand, sa ndy silt, and sandy clay that was damp to moist and medium dense/stiff.
Undocumented Artificial Fill (Map Symbol – Afu): Undocumented artificial fill material was encountered in several test pi ts across the site, varying in thickness from 1.5 to 5.5 feet. The undocumented artificial fill materi al generally consists of brown to reddish brown silty fine-to- coarse sand that was damp to mo ist and loose to medium dense. Undocumented artificial fill is also mapped overlying bedrock in the western portion of the site (beneath the existing home/pool) as a result of grading and terracing for home construction.
2.2 Geotechnical Conditions
Based on our review of the geotechnical exploration and laboratory testing data (Appendix C), the geotechnical conditions are generally as follows:
Soil Moisture Content and Dry Density : Laboratory testing performed on samples collected from the borings indicate that the native older alluvium had moisture contents in the range of 1.9 to 14.6 percent and dry densitie s varying from 110.1 to 123.0 pounds per cubic foot (pcf). The blow counts in the alluvium varied from 9 to 61 blows per foot. The granitic bedrock samples had 23145-01
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dry densities in the range of 105.0 to 118.9 pcf and moisture contents in the range of 3.5 to 15.5 percent. Blow counts in bedrock were well over 50 blows per foot.
Soil Properties: Grain-size distribution tests were conducted on two bulk samples collected from the uppermost 5 feet and seven ring samples coll ected at depths of 5, 7.5, 10, and 15 feet. The near-surface bulk samples were classified in accordance with the Unified Soil Classification System (USCS) as sandy clay (CL) and silty sand (SM), with fines contents (passing No. 200 sieve) of 63 and 30 percent, respectively. Soil plasticity testing performed on the bulk samples indicates that the sandy clay soil has a Liquid Limit of 30 percent and Plasticity Index of 13 (USCS classification of CL). The silty sand sample was non-plastic.
The ring samples were found to have fines contents ranging from 44 to 50 percent (at a depth of 5 feet), 12 and 54 percent (at a depth of 7.5 feet), 67 percent (at a depth of 10 feet), and 79 percent (at a depth of 15 feet). The samples were given USCS classifications of SM and SM/ML (5 feet), SP-SM and ML (7.5 feet), CL (10 feet), and ML (15 feet). The Liquid Limit of the ring sample collected at a depth of 10 feet (CL) was 25 percent with Plasticity Index of 9.
Maximum dry density of the near-surface silty/s andy soil indicates a maximum dry density of 132.0 pounds per cubic foot (pcf) at an optimum moisture content of 8.0 percent.
Consolidation: Tests were performed on four samples co llected at depths of 5, 7.5, and 15 feet.
In general, the testing showed that the materials have relatively low compressibility potential. The samples had minor collapse potential (less than 0.75%) upon the addition of water at a load of 3.2 tsf.
Shear Strength: Direst shear testing was performed on one relatively undisturbed ring sample collected at a depth of 5 feet, representative of the native older alluvium. One remolded direct shear (remolded to 90% relative compaction of the maximum density) was also performed, representative of future compacted fill material. The test results for the in-situ sample indicate an ultimate internal friction angle of 32 degrees at zero cohesion with peak internal friction angle of 39 degrees and a cohesion of 100 pounds per square foot (psf). The remolded sample had an ultimate internal friction angle of 27 degrees a nd a cohesion of 150 psf. The peak values for the internal friction angles and th e cohesion of the remolded samp le were 28 degrees and 350 psf, respectively.
R-value: One sample collected from the uppermost 5 feet in Boring H-4 had an R-value of 18.
Expansion Potential: Two near-surface samples collected from the upper five feet were tested to evaluate the expansion potential of onsite alluvi al soils. The testing shows that the silty sand and sandy clays have expansion indices of 0 to 59, respectively, indicating "Very Low" to "Medium" expansion potential.
Chemical Properties: Soluble sulfate content of the soil was measured in two samples representative of the near surface soils. Soluble sulfate content testing indicates the soil may be classified as "S0" per Table 19.3.1.1 of ACI- 318-14. We anticipate that the onsite soils are corrosive to metals.
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2.3 Groundwater
Groundwater was encountered in one boring, H- 5, at a depth of 26.5 feet bgs. Based on the recorded groundwater depth and our understanding of the site geology, perched groundwater can occur within highly weathered portions of graniti c bedrock and/or at th e bedrock/alluvium/fill contact. Historic high groundwater mapping by the State has not been performed for the region.
Groundwater levels may fluc tuate on an annual and seasonal basis, based on variations in future residential irrigation and rainfall amounts. The presence of locally saturated soils and/or perched water cannot be ruled out and may be encounter ed during grading, c onstruction of utility infrastructure and future homeowner improvements.
2.4 Regional Faulting and Seismicity
Regional Faults: The site is not located within a faul t-rupture hazard zone as defined by the Alquist-Priolo Special Studies Zones Act (CGS , 2018). Also, based on mapping by the State (Jennings and Bryant, 2010) and Riverside County (2023), there are no active faults mapped at the site.
Seismicity: Properties in southern Califor nia are subject to seismic hazards of varying degrees depending upon the proximity, degree of activity, and capability of nearby faults. These hazards can be primary (i.e., directly re lated to the energy release of an earthquake) or secondary (i.e., related to the effect of earthquake energy on the physical world). Since there are no active faults at the site, the potential for pr imary ground rupture is considered very low. The primary seismic hazard for this site is ground shaking durin g a future earthquake. The maximum moment magnitude for the controlling fault is 8.1 M
W, which would be generate d from the San Jacinto
Fault.
The site is located within an area of "high" liquefaction susceptibility per the County of Riverside (2023). However, based on the shallow bedrock condition and absence of groundwater within potentially liquefiable soils (older alluvium), th e liquefaction potential is considered very low.
Please also note that the alluvium in Boring H-6, which was enc ountered to a depth of 21.5 feet, generally consisted of fine-grained clayey soils that are typically not considered prone to liquefaction. Other secondary seismic hazards, such as tsunami and seiche are considered nil due to site elevation and distance from the ocean or other confined bodies of water.
2.5 Settlement
In general, the anticipated settlements depend u pon the building loads, type of foundations, and the geotechnical properties of the supporting subgrade. Shallow bedrock is generally present throughout the site. Considering the subsurface so il conditions, laboratory te st data, and lightly loaded residential structures, we estimate total settlement (combined static and seismic) to be on the order of 1 inch with differential settlement of ½-inch over a 40-foot span. This assumes remedial grading measures reco mmended in Section 3.2 of this report are imple mented during grading.
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2.6 Shrinkage and Bulking
The shrinkage and bulking (reduction or incr ease in volume of excavated materials upon recompaction and replacement as fill) varies by soil type, earth unit, and location. The volume changes depend primarily on in-sit u density and the maximum dry density of the soil type. We anticipate that the near surface alluvial materials will have 0 to 5 percent shrinkage. The weathered bedrock is anticipated to bulk less than 5 percent. Ground subsid ence is estimated to be on the order of 0.1 foot. These values exclude losses du e to removal of vegetation and debris and is dependent on the accuracy of the site topographi c survey and type of equipment and compaction method used by the contractor.
2.7 Rippability and Generation of Oversize Material
The rippability characteristics of bedrock depe nd upon the rock type, hardness, the depth and degree of weathering and fracturing, rock structure, equipment size/type used for excavation, and operator experience and skill leve l. Based on our subsurface explor ation, the underlying granitic bedrock is weathered/decomposed to variable depths.
A geophysical refraction survey was performed as part of our study and included two survey lines (SL-1 and SL-2) within the western portion of the site, where grading cuts are anticipated, and the shallowest hard rock was encountered during drilling (see Plate 1). The refraction survey was used to measure compressional (P) wave velocities of the granitic bedrock to assist in rippability assessment. The survey lines we re approximately 205 (S L-1) and 235 (SL-2) feet in length to provide a minimum investigation depth of approximately 40 feet bgs. The published Caterpillar Tractor Company bulldozer ripper performance charts, our experience, and the experience of the geophysics subcontractor indicate th at granitic rocks with velo cities below approximately 5,800 feet/second are "rippable" with some difficulty using a D9R (single shank) bulldozer.
SL-1 and SL-2 encountered weathered rock (p-wave velocity less than 5,800 feet/second) to depths generally ranging from 18 to 35 feet, below whic h mildly weathered to unweathered rock was encountered. Localized "plateaus" of hard rock we re encountered in SL-2, within the vicinity of the existing home and where granitic outcrops were observed in the field. The seismic line velocity profile and accompanying geophysical report are included in Appendix D. Oversize rocks (defined as rock exceeding 12 inches in the maximum di ameter) are anticipated to be generated during grading, especially in deeper excavations.
2.8 Percolation Testing
Percolation testing was performed on Decembe r 12, 2023, in general accordance with the Riverside County Design Handbook for Low Impact Development Best Management Practices (2011). The Percolation Test method was genera lly performed as described in the handbook. In order to prevent caving during testing, a 3-inch-diameter perforated pipe was installed in the boring and the annular space was backfilled with 3/4-inch gravel. The borings were presoaked and tested to determine if onsite soils fell under the "Sandy So il" criteria as define d in the handbook. All percolation borings were considered "Sandy". Test results were tabulated, and final measurements were used to calculate the infiltration rate. The percolation data sheets are provided in Appendix E.
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The County Handbook does not include calculation adjustments to account for the presence of the annular backfill material described above which can result in overe stimation of infiltration rates.
We have used a correction factor to account for the volume loss due to the annular material, based on the porosity, pipe size used, and the boring diameter. The co rrection factor is noted on the percolation test data sheets.
The calculated infiltration rates are provided below, which include the correction factor discussed above; however, the rates do not include a factor of safety reduction. A discussion of the overall feasibility of stormwater infilt ration is provided in Section 3.15. The infiltra tion test results are representative of the location and depths the tests were performed.
TABLE 1 – PERCOLATION TEST RESULTS
Boring No.
Tested Depth
(Below Ground
Surface)
Calculated
Infiltration Rate
(in./hr.)
P-1 3 to 5 1.5
P-2 2.5 to 5 2.6
P-3 7 to 10 0.3
P-4 4 to 7.25 1.0
2.3 Existing Utilities
No onsite utilities were marked during the DigAlert utility clearance process. We understand that active domestic water and numerous irrigation pipelines service the homes and equestrian areas.
Overhead electrical lines are present along Alhambra Avenue, adjacent to the site. Also, based on verbal communication with the current property owner, the existing onsite residences rely on septic systems and leach fields for sewage management. Septic systems and related appurtenances should be anticipated during demolition and grading.
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3.0 CONCLUSION AND PREL IMINARY RECOMMENDATIONS
3.1 General Conclusion and Recommendation
Based on our subsurface exploration and evalua tion, construction of the proposed residential development, as described herein, is considered geotechnically feasible provided the preliminary recommendations in this report are implemented during design, grading, and construction. The geotechnical consultant should review the WQ MP once available. Additional geotechnical exploration and percolation testing may need to be performed during the design phase, depending upon the location/depth of the infiltration device. Also, grading, foundation, utility, structural and wall plans for the project should be reviewed by the geotechnical consultant during the design phase.
Updated recommendations should be provided once the project plans are finalized and reviewed by SA GEO and as needed.
The recommendations in this report should be considered minimum and may be superseded by more restrictive requirements of others. In addition to the following recommendations, General Earthwork and Grading Specifications are provided in Appendix G.
3.2 Site Preparat ion and Earthwork
Site preparation and grading should be performed in accordance with the recommendations included herein and the requirements of the City of Riverside.
3.2.1 Site Demolition and Clearing
Prior to remedial grading, the existing struct ures/foundations, landscape, and utilities to be abandoned should be demolished. Deleterious materials and debris should be cleared and disposed of offsite. Concrete material may be mixed with onsite soils and placed as compacted fill provided that it is broken into pieces that are smaller than 6 inches in the largest diameter and placed in accordance with Section 3.2.5. Excavations for the removal of existing foundations, utilities and vege tation, including onsite trees , should be observed by the geotechnical consultant. Large roots, highly organic soils, and utility/pipeline debris should be removed and not incorporated into new fills.
Soil that is disturbed as part of excavations or during removal of trees or underground utilities should be evaluated by the geotechnical consultant. Excavations that require backfill should be properly documented and compacted under the observation and testing of the geotechnical consultant in accordance with the recommendations provided in Section 3.2.6.
Based on verbal communication wi th the current landowner, the existing onsite residences rely on septic tanks and leach fields for se wage management. These features should be anticipated during demolition a nd grading. Wells (if any), sept ic tanks, seepage pits, and related appurtenances will need to be properly removed and/or abandoned in accordance with County of Riverside Department of Environmental Health requirements (or other governing agency) and the project environmental consu ltant’s recommendations. Any voids created during demolition and removal should be backfilled with suitable onsite or import materials and compacted in accordance with the recommendations provided in Section 3.2.6.
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3.2.2 Protection of Existing Improvements and Utilities Existing buildings, improvements and utilities adjacent to the site that are to be protected in place should be located and visually marked prior to grading operations. Excavations adjacent to improvements to be protected in -place or any utility easement should be performed with care, so as not to undermine existing foundations or destabilize the adjacent ground.
Stockpiling of soils more than 5 feet in height at or near existing structures and over utility lines should not be allowed. If deep excavations are required, shoring or other special measures (i.e., setback or laybacks) to pr ovide safety and mitigate the potential for lateral/vertical movements may be required.
3.2.3 Remedial Grading Measures
Remedial grading at the site should consist of removal of all undocumented fill materials, unsuitable alluvium, and highly weathered/di sturbed bedrock. In general, we recommend that remedial removals (within design fill areas) consist of removal and recompaction of soils in the upper 2.5 to 6 feet. Where deeper unsuitable material is encountered, the removals should be extended to competent alluvium or bedrock. Bedrock is anticipated to be shallow throughout the site; thus, we reco mmend that removals within the proposed streets and at utility connections be deepened to approximately 1 foot be low the lowest pipeline to facilitate utility construction and limit excava tion difficulty. The geotechnical consultant should review and approve the removal bottoms prior to fill placeme nt and should provide specific recommendations based on actual conditions, if necessary.
Excavations deeper than 4 feet will need to be laid back a minimum inclination of 1H:1V (horizontal to vertical) or provided with shoring. Shallow, unconfined excavations (4 feet or less) may consist of near-vertical excavation, pending field review of the exposed materials.
Excavations should be performed in accordance with Cal/OSHA requirements for Soil Type "B". Locally, Soil Type "C" may be encountered (loose, friable sand) and should be laid back a minimum inclination of 1.5H :1V. The contractor’s qual ified person should verify compliance with Cal/OSHA requirements. Excava tions near existing st ructures (within a 1H:1V projection) should be provided with shoring that is designed to support the surcharge load of the existing structure. Otherwise, excavations may be performed in sections that are 20 feet long or less. The conditions should be reviewed in the field by the project geotechnical consultant. Additional recommendations will be provided based on the actual conditions encountered during excavation and grading, as needed.
3.2.4 Lot Capping/Overexcavation
The proposed grading is anticipated to expose cu t and fill transitions at finish grade within some lots. Lots with design cuts are also anticipated throughout the site but mostly within the western portion of the site. At minimum, we recommend overexcavation of the cut lots in the upper 4 feet and replacement with compacted fill to provide a uniform fill blanket over each lot. Lots with design cuts into bedrock should be overexcavated to depths of 3 to 4 feet.
We recommend shallower overexcavation (3 feet) within the back of the lot and deeper overexcavation (4 feet) within the front of the lots. For lots underlain by bedrock it is recommended that the overexcavation bottoms slope a minimum of 1 percent toward deeper 23145-01
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fill areas or the adjacent st reet to limit ponding of nuisanc e water along the fill/bedrock contact.
In areas where granitic rock is expected w ithin streets or utility trenches/connections, overexcavation is recommended to 1 foot below the deepest ut ility, to facilitate utility construction and limit excavation difficulty.
Additional lot overexcavation may be recomm ended during grading in areas where earth materials are highly variable within an individual lot. The conditions should be evaluated by the geotechnical consultant in the field during grading. The overexcavation bottoms should be mapped and approved by the geotechnical consultant.
A disclosure should be provided to homeowners that hard ro ck may be encountered below compacted fill. A table including a summary of fill thicknesses for each lot may be provided at the completion of grading in order to inform the homeowners of the subsurface soil conditions.
3.2.5 Rippability and Placemen t of Oversize Material
Granitic bedrock with p-wave velocities greater than 5,800 fee t/second are generally regarded as very difficult to rip, marginally rippable, and/or non-rippable (greater than 7,000 to 8,000 feet/second). Velocities below 5,800 feet/second are anticipated to be rippable with some difficulty; however, it should be noted that rock characteristics, fracture spacing and orientation, and skill and experience level of operators play a significant role in determining rippability. These velocity thresholds for rippability should be scaled downward for trenching operations.
Seismic Lines 1 and 2 (SL-1 and SL-2) encounte red weathered rock (p-wave velocity less than 5,800 feet/second) to depths ranging from 18 to 35 feet, below which mildly weathered to unweathered rock was encountered. Locali zed "plateaus" of weathered to mildly weathered rock (velocity of 5,000 to 5,800 feet/second) were encountered in SL-2, within 10 feet of existing grade. Localized hard zones and/or contact irregularities within the weathered rock zone, if encountered, will require a dditional excavation and processing effort. We anticipate bedrock to generally be rippable to the anticipated design/remedial grading and deepest utility lines with heavy duty earthmoving equipment (i.e., Caterpillar D-9 bulldozer, Caterpillar 330 excavator); howev er, this will need to be reviewed by the geotechnical consultant once grading and util ity plans are available. Blasti ng is not anticipated to be required.
Grading cuts within bedrock are anticipated to produce some oversize rock (greater than 12 inches in size). If grading e quipment cannot break down the material into smaller pieces, oversize rock will need to be disposed of in deeper fill areas. Oversize rocks may be placed in fills deeper than 10 feet below design grades. The gr ading contractor should consider performing the remedial grading within design fi ll areas to facilitate placement of oversize rocks. Rocks smaller than 6 inches may be placed in the upper 4 feet of each lot. Rocks larger than 6 inches and smaller than 12 inches in the largest dimension may be placed at depth between 4 and 10 feet below design finish grad es or 1 foot below the deepest utility line, whichever is deeper. Rocks greater than 3 inches in dimension are typically not suitable for 23145-01
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backfill of utility trench excavations (unless accepted by the agency/utility owner). Thus, we recommend that the grading contractor consider placement of rocks larger than 3 inches in dimension outside of proposed utility alignments.
The Grading and Earthwork Specifications in Appendix G include details for placement of oversize rock.
3.2.6 Fill Placement
Upon the completion of remedial grading measures, the approved removal bottoms should be scarified a minimum of 6 inches. The removal bottoms and fill materials should be compacted to at least 90 percent of maximum dry density, as determined by ASTM Test Method D1557. Fill materials should be placed in loose lifts no thicker than 8 inches.
Fill materials should be relatively free of deleterious material. The existing undocumented fill material, native alluvial soils, and bedrock are considered suitable for re-use as compacted fill provided any deleterious material is removed and the recommendations provided in the prior sections are followed. Concrete material ma y be mixed with onsite soils and placed as compacted fill provided it is broken into pieces th at are smaller than 6 inches in the largest diameter and placed in accordance with Section 3.2.5. Placement of concrete as compacted fill should be approved by the project environmental consultant.
We recommend that the moisture content of new compacted fill soils be above the optimum moisture content but should be within the compact able moisture ra nge. Appropriate equipment should be used and other measur es (e.g., mixing, stockpi ling, drying) may be needed to achieve the uniform and correct moistu re content for placement of the fill. If the soils become extremely wet, special measures for mixing and drying may be required that will need to be determined based on the actual field conditions.
3.2.7 Import
The geotechnical consultant should evalua te and accept any import soils prior to transportation to the subject site. We recommend that import soils have similar engineering properties as onsite soils. At minimum, the import materials should have Expansion Index of less than 50, Plasticity Index of less than 15, fines content (passing Sieve 200) of less than 50 percent, and negligible soluble sulfate content.
3.3 Settlement Potential
The amount of settlement will depend upon the type of foundation(s) selected and future loading by additional fill and structures. Based on our subsu rface exploration and analysis, considering the remedial grading recommendations provided in this report are implemented during grading, and the anticipated structural loads typically associated with the proposed residential units, we estimate a total settlement of 1 inch and a differential settlement of ½-inch over a span of 40-foot.
SA GEO should be provided with the foundation pl ans and structural load s, once available, to further evaluate the potential for post-construction settlement of the proposed buildings and associated improvements. Additional laboratory te sting will also be performed at the completion 23145-01
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of grading. The parameters provided herein will then be confirmed/updated based on the planned foundation layout and loads, and additional testing/analysis.
3.4 Foundation Design
The slab and foundations should be designed by the project structural engineer based on the proposed structure type and the anticipated loading conditions. Onsite soils are anticipated to have "Very Low" to "Low" expansion potential (EI> 20) at the completion of grading. Thus, they are subject to climatic and landscape moisture fluctuations an d should be designed in accordance with the requirements of the 2022 California Building C ode. The following foundation recommendations are provided with the assumption that the recommendations included in Section 3.2 of this report are implemented during grading of the site.
The recommended net allowable bearing capacity for continuous and isolated footings may be calculated based on the following equation:
q
all = 600 D + 200 B + 1,000 (but not to exceed 4,000 psf) where:
D = embedment depth of footing, in feet
B = width of footing, in feet
Also, the following parameters may be used for design of foundation and slabs:
Soil unit weight = 120 pcf
Soil internal friction angle = 28 degrees
Coefficient of Friction = 0.35
Subgrade modulus (k) of 100 pci (corrected for large slabs) Soil elastic modulus (Es) of 2,000 psi
The dead load of concrete below adjacent grades (buried concrete foundations) may be neglected.
The allowable bearing pressure and friction coefficient may be increased by one-third for wind and seismic loading.
We recommend that strip and isolated footings for the buildings ha ve a minimum embedment depth of 12 inches below the lowest adjacent gr ade. Continuous footings should be at least 12 inches wide and isolated column footings should be at least 24 inches wide. The footings of freestanding and isolated structures, such as walls and pilasters, should have a minimum embedment depth of 18 inches into approved soils.
The following table provides our general guidelines and preliminary recommendations for design of post-tensioned foundations and slabs on expansive soil in accordance with the 2022 California Building Code (CBC) and Post-Tension Institute (PTI) DC 10.5 Edition provisions.
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GEOTECHNICAL GUIDELINES
FOR DESIGN OF POST-TENSIONED SLABS*
Parameter Recommendation
Center Lift
* Edge Moisture Variation Distance, em
* Center Lift, ym
9.00 feet
0.35 inches
Edge Lift
* Edge Moisture Variation Distance, e
m
* Edge Lift, ym
5.0 feet
0.50 inch
Presaturation, as needed, to obtain the minimum
moisture down to the minimum depth
1.1 x optimum down to
6 inches
*Based on method in CBC 2022
For post-tensioned slabs, we recommend that the slabs have a thickened edge such that the slab is embedded a minimum of 12 inches below the lowest adjacent grade. The thickened edge should be tapered and have a minimum width of 12 inches.
In addition, as indicated in the DC 10.5 Edition of PTI, shape factor calculations should be performed by the project structural engineer in order to determine if strengthening/modification of foundations are necessary. Per PTI guidelines, the modifications to the foundations design should be considered if the shape factor (ratio of s quare of foundation perimeter over foundation area) exceeds 24.
If non-post-tensioned slabs-on-grade and foundations are considered at the site in accordance with Wire Reinforcement Institute (WRI) method (per the 2022 CBC), an effective Plasticity Index of 15 or less is considered appropriate for the upper 15 feet of soil materials. For non-post-tensioned slabs, we recommend a minimum embedment of 12 inches below the lowest adjacent grade for the perimeter footings. Also, the upper 6 inches of subgrade soil should be pre-saturated to 110 percent of optimum moisture content prior to placement of moisture barrier and concrete.
The foundations and slabs should be designed to to lerate the total and di fferential settlements discussed in Section 3.3 of these recommendations.
For the design of pole-type foundations (i.e., light poles, shade structures, etc.), an allowable soil- bearing pressure (
S1) of 340 psf/ft may be used for Equation 18-1 (the "pole" equation) of the 2022 CBC, Section 1807.3.2.1, to determine the depth of embedment for the footings, considering level ground conditions. The equation is applicable for designed embedment depths of less than 12 feet for the purpose of computing lateral pressure. Also, for vertical loads on pole-type foundations, an allowable skin friction of 250 pounds per square f oot may be used. For ca st-in-place pole-type foundations, the vertical end bearing pressure should be neglected.
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3.5 Retaining Wall Design and Lateral Earth Pressures
Recommendations for lateral earth pressures for pe rmanent retaining walls and structures with approved onsite drained soils and above groundwater table are as follows:
Conditions Level (pcf) 2:1 Sloping
Active 43 68
At-Rest 63 90
Passive 340 160 (slopin g down)
The parameters provided above are based on a soil internal friction angle of 28 degrees and soil unit weight of 120 pcf.
To design an unrestrained retaining wall, such as a cantilever wall, the active earth pressure may be used. For a restrained retainin g wall, the at-rest pressure shoul d be used. Passive pressure is used to compute lateral soils resistance developed against lateral structural movement. The passive pressures provided above may be increased by one-third for wi nd and seismic loads. Passive resistance is taken into account only if it is en sured that the soil against embedded structure will remain intact with time. Future landscaping/pl anting and improvements adjacent to the retaining walls should also be taken into account in the design of the retaining walls. Excessive soil disturbance, trenches (excavation and backfill), future landscaping adjacent to footings and over- saturation can adversely impact retaining structures and result in reduced lateral resistance.
For sliding resistance, a friction coefficient of 0.35 may be used at the concrete and soil interface.
The coefficient of friction may be increased by one-third for wind an d seismic loading. The retaining walls may also need to be designed for additional lateral loads if other structures or walls are planned within a 1H:1V projection.
The seismic lateral earth pressure for walls retaining more than 6 feet of soil may be estimated to be an additional 18 pcf for activ e and at-rest conditions. The ear thquake soil pressure has a triangular distribution and is added to the static pressures. For the active and at-rest conditions, the additional earthquake loading is zero at the top and maximum at the base. The seismic lateral earth pressure does not apply to walls retaining less th an, or equal to, 6 feet of soil (2022 CBC Section 1803.5.12).
Drainage behind walls retaining more than 30 inches of soil should also be provided in accordance with the attached Figure 4. Specific drainage connections, outlets and avoiding open joints should be considered for the retaining wall design.
3.6 Seismic Design Parameters
The following table summarizes the seismic design criteria for the subject site. The seismic design parameters are developed in accordance with ASCE 7-16 and 2022 CBC. Please note that, considering the proposed structures and anticipated structural periods, site-specific ground-motion hazard analysis was not performed for the site. The seismic response coefficient, Cs, should be determined per the parameters provided below and using equation 12.8-2 of ASCE 7-16.
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Selected Seismic Design Parameters
from 2022 CBC/ASCE 7-16
Seismic Design
Values Reference
Latitude 33.6570 North
Longitude -117.1996 West
Controlling Seismic Source Sa n Jacinto USGS, 2023
Site Class per Table 20.3-1 of ASCE 7-16 C
Spectral Acceleration for Short Periods (Ss) 1.5 g SEA/OSHPD, 2023 Spectral Accelerations for 1-Second Periods (S1) 0.57 g SEA/OSHPD, 2023 Site Coefficient Fa, Table 11.4-1 of ASCE 7-16 1.2 SEA/OSHPD, 2023 Site Coefficient Fv, Table 11.4-2 of ASCE 7-16 1.43 SEA/OSHPD, 2023 Design Spectral Response Acceleration at Short
Periods (SDS) from Equation 11.4-4 of ASCE 7-16 1.2 g SEA/OSHPD, 2023 Design Spectral Response Acceleration at 1-Second
Period (SD1) from Equation 11.4-4 of ASCE 7-16 0.543 g SEA/OSHPD, 2023 TS, SD1 /SDS 11.4.6 of ASCE 7-16 0.45 sec
TL, Long-Period Transition Period 8 sec SEA/OSHPD, 2023 Peak Ground Acceleration Corrected for Site Class
Effects (PGAM) from Equation 11.8-1 of ASCE 7-16 0.618 g SEA/OSHPD, 2023 Seismic Design Category, Section 11.6 of ASCE 7-16 D SEA/OSHPD, 2023
3.7 Slope Setback
Footings for structures located above descending slopes should be set back from the slope face in accordance with the minimum requir ements of the City of Riverside and section 1808.7.1 of the 2022 California Building Code, whichever is greater . The setback distance is measured from the outside edge of the footing botto m along a horizontal line to the fa ce of the slope. The tables below summarize the minimum setback criteria for structures above descending slopes:
Structural Setback Requirements
Case A – Building and Retaining Wall Footings
Above Descending Slopes
Slope Height [H] (feet) Minimum Setback
from Slope face (feet)
Less than 10 5
10 to 20 ½ * H
20 to 30 10
Greater than 30 ⅓ * H (maximum of 40')
Case B – Freestanding Wall Footings Above
Descending Slopes
Slope Height [H]
(feet)
Minimum Setback
from Slope face (feet)
Less than 10 5
10 to 20 ½ * H
Greater than 20 Maximum of 10
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For freestanding walls and other st ructures that are sensitive to lateral movement (e.g., smooth stucco finish, glass screens, etc.), SA GEO r ecommends that the structural setback requirements in accordance with Case A above be followed or th at additional design measures be used to help control the potential for cracking and displacemen ts. Otherwise, typical freestanding walls may have a setback in accordance with Case B.
3.8 Corrosivity
Based on prior laboratory testing, soluble sulfate exposure in the onsite soils may be classified as "S0" per Table 19.3.1.1 of ACI-318-14. Structural conc rete elements in contact with soil include footings and building sl abs-on-grade. The flatwork and sidewalk concrete are typically not considered structural elements. Concrete mix for structural elements should be based on the "S0" soluble sulfate exposure class of Table 19.3.2.1 in ACI-318-14. Other American Concrete Institute (ACI) guidelines for structural concrete are recommended. Also, onsite soils are anticipated to be moderately corrosive to metals.
3.9 Expansion Potential
At the completion of grading, we anticipate that onsite soils will have "Very Low" to "Low" expansion potential. The geotechnical recomme ndations provided in this report including the design parameters for foundatio ns, slab-on-grade and flatwo rk improvement should be implemented during design and construction.
Homeowners and their design/construction team should be familiar with the recommendations in this report as well as principles described in a useful reference published by the California Geotechnical Engineers Associa tion (CalGeo), titled, "Coexist ing with Expansive Soil: An Informational Guide for Homeowners." This free booklet can be downloaded at www.calgeo.org.
3.10 Interior Slab Moisture Mitigation
In addition to geotechnical and st ructural considerations, the project owner should also consider interior moisture mitigation when designing and constructing slabs-on-grade.
The intended use of the interior space, type of flooring, and type of goods in contact with the floor may dictate the need for, and design of, measures to mitigate potential effects of moisture emission from and/or moisture vapor transmission thro ugh the slab. Typically , for human occupied structures, a vapor retard er or barrier is recommended under th e slab to help mitigate moisture transmission through slabs. The most recent guide lines by the American Concrete Institute (ACI 302.1R-04) suggest that the vapor retarder be placed directly under the slab (no sand layer).
However, the location of the vapor retarder may also be subject to the builder's past successful practice. Placement of 1 or 2 inches of sand over the moisture retardant has been common practice by builders in southern California. Specifying the strength of the retarder to resist puncture and its permeance rating is important. These qualities ar e not necessarily a function of the retarder thickness. A minimum of 10-mil is typical but so me materials, such as 10-mil polyethylene ("Visqueen"), may not meet the desired standards for toughness and permeance.
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Vapor retarders, when used, should be installed in accordance with standards such as ASTM E 1643 and/or those specified by the manufacturer.
Concrete mix design and curing are also significant factors in mitigating slab moisture problems.
Concrete with lower water/cement ratios results in denser, less permeable slabs that also "dry" faster with regard to when fl ooring can be installed (reduced moisture emission quantities and rates). Rewetting of the slab following curing shoul d be avoided since it can result in additional drying time prior to flooring installation. Proper concrete slab testing prior to flooring installation is also important.
Concrete mix design, the type and location of th e vapor retarder should be determined in coordination with all parties involved in the fi nished product, includ ing the project owner, architect, structural engineer, geotechnical co nsultant, concrete subcontractors, and flooring subcontractors.
3.11 Exterior Concrete
The driveway, patio slabs and other flatwork el ements should be at least 4 inches thick.
Considering that the onsite soils are anticipated to have "Very Low" to "Low" expansion potential at the completion of grading, reinforcement of concrete is not necess ary from a geotechnical standpoint; however, reinforcement will reduce the pot ential for concrete cracking as a result of shrinkage. If reinforcement is used, we recommend that No. 3 bars be placed at 24 inches on center both ways. Equivalent wire mesh reinforcement may also be us ed. Concrete slabs should be provided with construction or weakened plane control joints at a maximum spacing of 10 feet. The control joints should have a thickness that is ¼ of the total concrete thickness. The subgrade soils in the upper 6 inches should be presaturated to 110 percent of optimum moisture content.
For exterior slabs, the use of a granular sublayer is primarily intended to facilitate presaturation and subsequent construction by providing a better working surface over the saturated soil. It also helps retain the added moisture in the native so il in the event that the slab is not placed immediately. Where these factors are not signif icant, the layer may be omitted. If used, we recommend placement of 2 to 4 inches of granular material over subgrade soils.
Exterior concrete elements such as curb and gutter, driveways, sidewalks and patios are susceptible to lifting and cracking when constructed over expansive soils. With expansive soils, the impacts to flatwork/hardscape can be si gnificant, generally re quiring removal and replacement of the affected improvements. Please also note that re ducing concrete problems is often a function of proper slab design, concrete mix design, placement, and curing/finishing practices. Adherence to guidelines of the American Concrete Institute (ACI) is recommended. Also, the amount of post- construction watering, or lack thereof, can have a very significant impact on the adjacent concrete flatwork.
On projects with expansive soils, additional meas ures such as thickened concrete edges/footings, subdrains and/or moisture barrie rs should be considered where planter or natu ral areas with irrigation are located adjacent to the concrete improvements. Design and maintenance of proper surface drainage is also very important.
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For vehicular traffic, at minimum, a pavement section consisting of 6 inches of PCC over subgrade compacted to 95 percent relative compaction should be used. However, the recommended section should be evaluated during the design and grading phase based on the anticipated traffic loads/frequency of use and additional R-value testing.
The above recommendations typically are not applied to curb and gutter but should be considered in areas with highly expansive soils.
3.12 Preliminary Asphalt Concrete Pavement Design
Final structural pavement sections should be based on R-value testing after the completion of grading and in accordance with City of Riverside requirements. The laboratory test results on a sample collected in the upper 5 feet shows an R-value of 18. Using a design R-value of 15 and estimated traffic indices (TIs), we recommend the following preliminary pavement sections:
Street Location Estimated TIs Pavement Section
Parking Stalls TI – 4.0 0.25' AC / 0.35' AB
General Drives TI – 5.5 0.35' AC / 0.65' AB
Driveways with Heavy Truck
Traffic TI – 7.0 0.35' AC / 1.10' AB or
0.45' AC / 0.85'
AC = Asphalt Concrete, AB = Aggregate Base
Please note that for two-stage paving operations, we recommend that the final AC cap be a minimum of 0.10 foot thick and the base AC course have a minimum thickness of 0.25 foot.
Asphalt concrete pavement should be placed in accordance with the requirements of Sections 301 and 302 of the Standard Specifica tions of Public Works Construc tion (the Greenbook). Prior to construction of pavement sections, the subgrade soils should be scarified to a minimum depth of 6 inches, moisture-conditioned as n eeded, and recompacted in-place to a minimum of 90 percent relative compaction (per ASTM D1557). Subgrade should be firm prior to AB placement.
AB materials can be crushed aggregate base or crushed miscellaneous base in accordance with the Greenbook (Section 200-2). The materials should be free of any deleterious materials. Aggregate base materials should be placed in 6- to 8-inch-thick loose lifts, moisture-conditioned as necessary, and compacted to a minimum of 95 percent relative compaction (per ASTM D1557). Asphalt concrete should also be compacted to a minimum relative compaction of 95 percent.
Unpaved median and parkway areas should also be provided with vertical moisture barriers.
3.13 Trench Excavation and Backfill
Excavations should be performed in accordance with the requirements set forth by Cal/OSHA Excavation Safety Regulations (Construction Safety Orde rs, Section 1504, 1539 through 1547, Title 8, California Code of Regulations). In gene ral, onsite soils may be classified as Type "B" soils for excavations into compacted fill, olde r alluvium, or bedrock. Locally, Type "C" soils 23145-01
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(loose, friable sand, bedrock fractures) may also be encountered. Cal/OSHA regulations indicate that, for workmen in confined conditions, the steepest allowable slopes in Type "B" and "C" soils are 1H:1V and 1.5H:1V, respectively, for excavations less than 20 feet deep. Where there is no room for these layback slopes, we anticipate that shoring will be necessary. Adequate shoring/shields should be provided, as deemed necessary. Excavations should be reviewed periodically by the co ntractor's qualified person to confirm compliance with Cal/OSHA requirements.
Utility trench backfill should be in accordance with City of Riverside and/or the governing jurisdiction's specifications. Please note that some agencies require select material for backfilling of trenches and therefore import soils may be required. Native onsite soils are generally considered suitable for use as trench backfill from a geotechnical viewpoint provided that they are approved by the governing agency. Native b ackfill materials shou ld be compacted to a minimum of 90 percent relative compaction (per ASTM D1557). Ro cks greater than 3 inches in largest diameter should generally not be used as trench backfill unless approved by the agency and geotechnical consultant of record. Excavation and backfilling of HDPE pipes (if any) should be in accordance with the manufacturer’s requirement and the Greenbook. Select granular backfill (i.e., clean sand with SE 30 or better) may be used in lieu of native soils but should also be compacted or densified with water jetting and flooding.
Trenches excavated next to structures and foun dations should also be properly backfilled and compacted to provide full lateral support and reduce settlement potential.
3.14 Groundwater
Groundwater was encountered in one boring (H-5) at a depth of 26.5 feet below ground surface.
Groundwater levels may fluc tuate on an annual and seasonal basis, based on variations in future residential irrigation and rainfall amounts. Locally saturated soils and/or perched water may be encountered during grading and co nstruction of utility lines a nd during excavatio ns by future homeowners. In general, groundwater is anticipa ted to remain more than 10 feet below design grades upon the completion of grading; however , perched water should be anticipated within weathered bedrock and/or at the bedrock/alluvium/fill contact.
3.15 Stormwater Infiltration
Based on our onsite percolation testing, storm water infiltration is c onsidered locally feasible at the tested locations, between 3 an d 7 feet bgs. Additional infilt ration testing may need to be conducted onsite once a water quality management plan has been prepared in order to evaluate the infiltration rates at the actual location and depth of the proposed device(s). For preliminary design purposes, a design infiltration rate of 0.4 inches pe r hour may be used for devices that are 3 to 7 feet deep in the vicinity of pe rcolation test borings (P-1 thro ugh P-4). For depths between 7 and 10 feet a rate of 0.1 inches per hour may be used. These rates include a minimum factor-of-safety of 3, in accordance with the 2011 Riverside County Design Handbook for Low Impact Development Best Management Practices.
Infiltration systems should maintain a minimum 5-foot vertical separation from bedrock/confining layers. The depth to granitic bedr ock (Kgr) is noted on Plate 1 (Geo technical Map). Infiltration 23145-01
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systems should also maintain a minimum 10 -foot vertical separation from groundwater.
Considering these constraints and the fine-grained nature of the soils at depths below 10 feet, the systems should not be deeper than 10 feet below existing grades.
Infiltration systems should be designed and cons tructed in accordance with County/City of Riverside guidelines. Infiltration systems should have a minimum setback of 15 feet from proposed residential structures. The subgrade soil utilized as the infiltration surface should be reviewed and approved by the geotechnical consul tant prior to installation of a ny infiltration devices. Special care should be taken to limit disturbance to nati ve soils used as the infiltration surface. Proper maintenance will also be required to extend the op erational life and reduce siltation or reduction in infiltration performance. All infiltration devices should be provided with an overflow system.
3.16 Surface Drainage an d Irrigation
Maintaining adequate surface drainage, proper disposal of run-off water, and control of irrigation will help reduce the potential for future mois ture-related problems and differential movements from soil heave/settlement.
Surface drainage should be carefully taken into consideration during grading, landscaping, and building construction. Positive surface drainage s hould be provided to direct surface water away from structures and slopes and toward the street or suitable drainage de vices. Ponding of water adjacent to the structures should not be allowed. Buildings should have roof gutter systems and the run-off should be directed to parking lot/street gutters by area drainpipes or by sheet flow over paved areas. Paved areas should be provided with adequate drai nage devices, gradients, and curbing to prevent run-off flowing from paved areas onto adjacent unpaved areas.
Considering the climatic conditions in southern California and the rela tively low expansion potential of onsite soils, a two- percent slope away fro m structures should be provided and is in substantial compliance with the 2022 CBC. Also, swales with one-percent slopes are acceptable from a geotechnical standpoint and are common practice in this locale.
Construction of planter areas immediately adjacent to structures should be avoided if possible. If planter boxes are constructed adjace nt to or near buildings, the planters should be provided with controls to prevent excessive penetration of th e irrigation water into th e foundation and flatwork subgrades. Provisions should be made to drain ex cess irrigation water from the planters without saturating the subgrade below or adjacent to the planters. Raised planter boxes may be drained with weepholes. Deep planters (such as palm tree planters) should be drained with below-ground, water-tight drainage lines conne cted to a suitable outlet. Mois ture barriers should also be considered.
It is also important to maintain a consistent level of soil moisture, not allowing the subgrade soils to become overly dry or overly wet. Properly designed landscaping and irrigation systems can help in that regard.
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3.17 Maintenance of Graded Slopes
To reduce the erosion and slumping potential of graded slopes, all permanent manufactured slopes should be protected from erosi on by planting with appropriate ve getation, or suitable erosion protection should be applied as soon as is pr actical. Proper drainage should be designed and maintained to collect surface waters and direct them away from slopes. A rodent-control program should also be established and maintained to reduce the potential for damage related to burrowing.
In addition, the design and cons truction of improvements and la ndscaping should also provide appropriate drainage measures.
3.18 Additional Subsurface Explor ation and Laboratory Testing Additional subsurface exploration and laboratory testing may be necessary during the design phase of the project for determination/ confirmation of the percolation rates, depending on the location and depth of the proposed system(s). Also, ad ditional laboratory testing should be performed during and upon the completion of grading to confirm/update th e design parameters provided herein.
3.19 Review of Future Plans
The project grading, foundation, st reet improvement, wall, water quality management, and landscape plans should be reviewed and accepted by the geotechnical consultant prior to grading and construction. Additional recommendations should be provided upon the review of the project plans and as needed.
3.20 Observation and Testing during Grading and Construction Geotechnical observation and testing should be performed by SA GEO during the following phases of grading and construction:
During site demolition, preparation and clearing;
During excavations performed for remedial grad ing and to relocate or remove existing underground improvements;
During removal/abandonment of cesspits, septic tanks, wells, etc.; During earthwork, including observation and acceptance of remedial removal and overexcavation bottoms and fill placement, including import material (if any); Following the completion of gradin g, in order to verify soil properties for foundations, slab- on-grade and pavement areas;
Upon completion of any foundation or structural excavation, prior to pouring concrete; During slab and flatwork subgrade preparation in cluding pre-saturation, prior to pouring of concrete;
During placement of backfill for utility trenches;
During construction of infiltration/stormwater filtration systems; During placement of backfill for retaining structures; During installation and backfill of subdrainage systems; and When any unusual soil conditions are encountered.
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4.0 LIMITATIONS
This report has been prepared for the exclusive use of our client, Meritage Homes, within the scope of services requested for the subject property described herein. This report or its contents should not be used or relied upon fo r other projects or purposes, or by other parties without the acknowledgement of SA GEO and the consultation of a geotechnical professional. The means and methods used by SA GEO for this study are base d on local geotechnical st andards of practice, care, and requirements of governing agencies. No warranty or guarantee, expressed or implied, is given.
Our findings, conclusions, and recommenda tions are profession al opinions based on interpretations and inferences made from geolog ic and engineering data from specific locations and depths, observed or collected at a given time. By nature, geologic conditions can vary from point to point, can be very different in-between exploration points, and can also change over time.
Our conclusions and recommendations are, by na ture, preliminary and subject to verification and/or modification during grading and construction when more subsurface data is exposed.
Source: Google Earth
Site Location Map
Site Location
Meritage Homes
Proposed Residential Development
La Sierra Avenue/Alhambra Avenue
Riverside, California
Project Number: 23145-01
Date: December 22, 2023
Figure 1
Source: Geologic Map of the Corona North and Riverside West 7.5’ Quadrangles, (USGS, 2001 & 2002) Regional Geologic Map
Site Location
Meritage Homes
Proposed Residential Development
La Sierra Avenue/Alhambra Avenue
Riverside, California
Project Number: 23145-01
Date: December 22, 2023
Figure 2
Source: Fault Activity Map of California (Jennings and Bryant, 2010) Regional Fault Map
Site Location
Project Number: 23145-01
Date: December 22, 2023
Figure 3
Meritage Homes
Proposed Residential Development
La Sierra Avenue/Alhambra Avenue
Riverside, California