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Home My WebLink AboutCT 13-05; STATE STREET TOWNHOMES; GEOTECHNICAL UPDATE; DWG 484-2, DWG 484-2A; 2014-02-04Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY February 4, 2014 To: lntracorp Companies 4041 MacArthur Blvd. Suite 250 Newport Beach, CA 92660 Attention: Mr. Ken Benson r. : ' ,i O 3 2014 Project No. 10552.004 Subject: Geotechnical Update, Proposed Redevelopment of 2531 -2589 State Street, Carlsbad, California References: California Building Standards Commission (CBSC), 2013, California Building Code (CBC) Leighton and Associates, Inc., 2005, Preliminary Geotechnical Investigation, Proposed Redevelopment of 2531, 2541, and 2551 State Street, Carlsbad, California, Project No. 041742-001, dated December 7, 2005 Leighton and Associates, Inc., 2014, Phase I and Limited Phase II Environmental Site Assessment for 2531 through 2601 State Street, Carlsbad, California, Project No. 10552.001, dated January 9, 2014 RBF Consulting, 2014, Preliminary Grading Plans for State Street Townhomes, Carlsbad, California, Sheet C5, dated January 2014 In accordance with your authorization, this letter presents Leighton's geotechnical update for the proposed State Street residential redevelopment, located at 2531 -2589 State Street, in Carlsbad, California. The purpose of this update study was to review our previous geotechnical report and site environmental documentation (Leighton, 2006 and 2014), and to provide seismic design parameters in accordance with the 2013 CBC. We also performed a site visit on January 31, 2014 to observe current conditions. Currently, the site, approximately 1.89 acres, is utilized as commercial and light industrial property. 3934 Murphy Canyon Road, Suite 8205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 10552.004 As background, Leighton performed the initial geotechnical investigation of the subject site in 2005 (Leighton, 2005). Recently, Leighton performed a Phase I and Limited Phase II Environmental Site Assessment (ESA) Report for the site. The purpose of the Limited Phase II ESA was to assess the soil and soil vapor throughout the subject site for the presence of contaminants originating from current and historical site uses, such that the potential health risks can be evaluated prior to residential development. The environmental study included eight (8) subsurface borings across the subject site. For the findings and results of the environmental study, please refer to referenced document (Leighton, 2014). Based on our understanding of the site conditions and review of the referenced geotechnical and environmental documents, the geotechnical conditions of the subject site have not changed. Therefore, it is our professional opinion that the geotechnical recommendations presented in the referenced geotechnical report are still applicable for its intended use, provided the following recommendations are incorporated into the design and construction of the proposed buildings and improvements. In addition, the following items should be noted: • The undocumented fill associated with the former development is potentially compressible and should be removed down to the dense competent fonnation material. The depth of the removal is generally anticipated to be on the order of 3 to 5 feet below the existing ground surface. However, deeper undocumented fill associated with buried utilities, old septic systems, basements and underground storage tanks should be anticipated. • Impacted soil may be encountered during grading. Please refer to the referenced environmental study (Leighton, 2014). Note that special handling and waste profiling may be required for the excavation and disposal of this impacted soil. Seismicity The following seismic design parameters for the site (latitude 33.164299, longitude -117.35299) are the risk-targeted spectral acceleration parameters for the project determined in accordance with the 2013 California Building Code (CBSC, 2013) and the USGS Worldwide Seismic Design Values tool (Version 3.1.0). -2 - Leighton 10552.004 Table 2 2013 CBC Risk-Targeted Mapped Spectral Acceleration Parameters Site Class D Fa = 1.035 Site Coefficients Fv = 1.554 Ss = 1.163g Mapped MCER Spectral Accelerations S1 = 0.446g SMs = 1.203g Site Modified MCER Spectral Accelerations SM1 = 0.693g Sos = 0.802g Design Spectral Accelerations S01 = 0.462g Utilizing ASCE Standard 7-10, in accordance with Section 11.8.3, the following additional parameters for the peak horizontal ground acceleration are associated with the Geometric Mean Maximum Considered Earthquake (MCE0 ). The mapped MCE0 peak ground acceleration (PGA) is 0.463g for the site. For a Site Class D, the FPGA is 1.037 and the mapped peak ground acceleration adjusted for Site Class effects (PGAM) is 0.48g for the site. Site Grading All undocumented fill associated with the former development should be removed down to the dense competent formation material. To reduce the potential for differential settlement beneath the proposed buildings (i.e., cut/fill transitions), we recommend the entire building pad be overexcavated at least 3 feet below the lowest foundation and replaced with properly compacted fill. In addition, we recommend that the overexcavation extend laterally at least 10 feet beyond the building perimeter or footprint. Imported soil, if needed to raise the site grades, should be granular and have an expansion index less than 50 (per ASTM Test Method D4829). Import soils and/or the borrow site should be evaluated by the geotechnical consultant prior to importation. - 3 - Leighton 10552.004 Foundation and Slab Design for Residential Buildings The proposed residential buildings may be supported by conventional, continuous or isolated spread footings. Footings should extend a minimum of 24 inches beneath the lowest adjacent soil grade. At these depths, footings may be designed for a maximum allowable bearing pressure of 2,000 pounds per square foot (psf) if founded in properly compacted fill soils. The allowable pressures may be increased by one-third when considering loads of short duration such as wind or seismic forces. The minimum recommended width of footings is 18 inches for continuous footings and 24 inches for square or round footings. The interior and garage slab-on-grade floors for the residential buildings should be at least 4 inches and 5 inches thick, respectively, and be reinforced with No. 3 rebars 18 inches on center, each way (minimum), placed at mid-height in the slab. Slabs should be underlain by a 2-inch layer of clean sand (sand equivalent greater than 30), which is in-turn underlain by a minimum 10-mil plastic sheeting (moisture barrier) and an additional 2 inches of clean sand. We recommend that control joints be provided across the slab at appropriate intervals as designed by the project architect. Some moisture sensitive flooring may require additional measures to mitigate moisture migration through the slab as designed by the project architect. Limitations Recommendations contained in this limited report are based on our site reconnaissance, background review, and present knowledge of the proposed construction. It is possible that soil conditions vary between or beyond the points explored. If soil conditions are encountered during grading or foundation excavation, which differ from those described in the original geotechnical reports, our firm should be notified immediately in order that a review may be made and any supplemental recommendations provided. Our firm has performed our services in substantial accordance with the generally accepted geotechnical engineering practice 1as it exists in the site area at the time of our study. No warranty is made or intended. -4- Leighton 10552.004 We appreciate the opportunity to be of service on this project. Should you have any questions related to this report, please contact our office at your convenience. Respectfully submitted, LEIGHTON and ASSOCIATES, INC. William D. Olson, RCE 45283 Associate Engineer Distribution: (4) Addressee -s - Michael R. Stewart, CEG 1349 Vice President I Principal Geologist Leighton Proposal * Contract All Types of Fencing CORPORATE OFFICE 870 N Main St Riverside, CA 92501 951. 788.5620 Fax 951.788.5649 2861 La Cresta Ave Anaheim, CA 92806 714.238.0091 Fax 714.238.0096 707 Industrial Park Dr. Manteoa, CA 95337 209.239.1282 Fax 209.823.6985 35656 N Sierra Hwy Palmdale, CA 93550 661.265.0082 Fax 661.265.0179 Quoted to: TAYLOR MORRISON HOMES 8105 IRVINE CENTER DRIVE SUITE 1450 IRVINE, CA 92618 CHIP WALKER 891 Corporation St Santa Paula, CA 93060 805.933.4522 Fax 805.933.4521 Quotation 186 Quantico Avenue Bakersfield, CA 93307 661.325.2800 Fax661.325.2810 Quote: Date: 6837 Power Inn Road Sacramento, CA 95828 916.383.2853 Fax 916.383.2854 Phone:949-533-4168 Fax: Job: PALISADES YORBA LINDA 2397 Nov 3, 2014 1250 N Backer Avenue Fresno, CA 93703 559.454.1712 Fax 559.454.1713 Page: "Proud Member of the US Department of Homeland Security E-Verijj, program" Customer ID Terms Salesman -~--- 1 ·--····- TAY001PALISADES ,, Valid for 5 Days ! ORANDS ,,, .. Quantity Description Unit Price Extension 1.00 REMOVE GATE, CUT OUT POST AND SIDE PANELS, PATCH CONCRETE 1,475.00 1,475.00 BEST AS POSSIBLE SET (1) NEW POST, BUILD (1) NEW SIDE PANEL, NEW METAL SCREEN ON BACK SIDE OF PANEL, ZINC WELDS, SPOT PRIME AND POLYURETHANE PAINT. THIS WILL TAKE A FULL DAY PLUS PAINT AND MATERIAL. NOTE.: GATE HAS ELECTRIC KEY FOBS, ELECTRICIAN WITH NEED TO CHANGE ELECTRIC STRIKE POST DUE TO MOVING GATE. FENCEWORKS INC MUST HA VE PROPER BILLABLE PAPERWORK PRIOR TO WORK BEING STARTED. THANK YOU! NOTE FOLLOWING OONDITIONS: PENDING CREDIT APPROVAL. PRICE INO..UDESALL LABOR, MATERIAL. TAXES, ETC. NECESSARYTOCOMPLE1E JO FIELD MEASURED UPON OOMPLET!ON AND BILLED TO AGREED PRICES. ALL GATES ARE BILLED AT CONTRACT PRICE PLUS FOOTAGE. PRICING DO! NOT INCLUDE ANY OCIPNVRAP INSURANCE PROGRAMS. LUMBER PROD IZES SET BY 1HE MFRS. WORK MUST BE COMMENCED WITHIN 30 DAYS OF ACCEPTAIICE. WE ARE A N SHOP. PRICES SUBJEC DUE TO ALTERNATIVE PIGG ING REQUIREMENTS AFTER DIG ALERT. CORE DRILLING O..UDED UNLESS NOTED ABOVE. Total: 1,475.00 ACCEPTANCEOFPROP :SA~~~L~S~i~n~a~t~~re§§§~~§?:;r~~~~~ AUTHORIZED SIGNAT ~ 7 « STEVE ANDERSON *In the event that ekher party becomes involvediin;,,;;;,;;:;a -~,o;;in,~air ;,, ;;a;;,oiifn ~or;;;' rnyu1;;:;'.:;11;:e,;:a:;;1te:11;:1a;;:te;:;;;;;;;-;;;:;:;;;~;;;:;;;;;;;;;:;:;;;;o;,:;;,e;r,ai"iltingMt<to this contract or the performance of It, the court or tribunal in such arbitration or litigaUon shall award reasonable fees and cosls incurred to the prevailing party including attorneys fees, expert witness fees, court costs and other costs arising out of or relating lo resolution ofthe dispute . .. Payment to be made as follows: All materials is guaranteed to be as specified. All work to be completed in a workmanlike manner according to standard practices. Any alteration or deviation from above specifications Involving extra costs will be executed only upon written orders, and will become an extra charge over and above the estimate. All agreements contingent upon strikes, accidents or delays beyond our control. Owner to carry fire, tornado, and othernecessary insurance. Our workers are fully covered by Workmen's Compensation Insurance. All property markers must be visible at the start of construction or otherwise we do not assume any responsibility whatsoever for any fences in their wrong looation. •'*Notice: "Under the Mechanics' Lien Law (California Code of Civil Procedure, Section 1181 et seq.) any conlractor, subcontractor, laborer, supplier, or other person who helps to improve your property but Is not paid for his work or supplies, has a right to enforce a claim against your property. This means that, after a court hearing, your property could be sold by a court officer and the proceeds of the sale used to satisfy lhe indebtedness. This can happen even ii you have paid yourowncontractorinfull, if the subcontractor, laborer, orsupplierremainsunpaid." Form #1017 Rev. 6112 Cobb's Printing (909) 795_2318 Proposal * Contract CORPORATE OFFICE 870 N Main St Riverside, CA 92501 951.788.5620 All Types of Fencing Quotation Fax 951.788.5649 2861 La Cresta Ave Anaheim, CA 92806 714.238.0091 Fax 714.238.0096 707 Industrial Park Or. Manteca, CA 95337 209.239.1282 Fax 209.823.6985 35656 N Sierra Hwy Palmdale, CA 93550 661.265.0082 Fax 661.265.0179 Quoted to: TAYLOR MORRISON HOMES 8105 IRVINE CENTER DRIVE SUITE 1450 IRVINE, CA 92618 CHIP WALKER 891 Co!J)Oration St Santa Paula. CA 93060 805.933.4522 Fax 805.933.4521 186 Quantico Avenue Bakersfield. CA 93307 661.325 .2800 Fax661.325.2S10 Quote: Date: 6837 Power Inn Road Sacramento, CA 95828 916.383.2853 Fax 916.383.2854 Phone:949-533-4168 Fax: Job: PALISADES YORBA LINDA 2397 Nov 3, 2014 1250 N Backer Avenue Fresno, CA 93703 559.454.1712 Fax 559.454.1713 Page: "Proud Member of the US Department of Homeland Security E-Verijj, program" Customer ID .Terms Salesman TAY001PALISADES ,, Valid for 5 Days ! ORANDS . Quantity Description Unit Price Extension 1 1.00 REMOVE GATE, CUT OUT POST AND SIDE PANELS, PATCH CONCRETE 1,475.00 1,475.00 BEST AS POSSIBLE SET (1) NEW POST, BUILD (1) NEW SIDE PANEL, NEW METAL SCREEN ON BACK SIDE OF PANEL, ZINC WELDS, SPOT PRIME AND POLYURETHANE PAINT. THIS \NILL TAKE A FULL DAY PLUS PAINT AND MATERIAL. NOTE: GATE HAS ELECTRIC KEY FOBS, ELECTRICIAN WITH NEED TO CHANGE ELECTRIC STRIKE POST DUE TO MOVING GATE. FENCEWORKS INC MUST HA VE PROPER BILLABLE PAPERWORK PRIOR TO WORK BEING STARTED. THANK YOU! NOTE FOLLOWING CONDITIONS: PENDING CREDIT APPROVAL. PRICE INQ.UDES ALL LABOR, MATERIAL, TAXES, ETC. NECE55ARYTOCOMPLETE JO FIELD MEASURED UPCN COMPLETION AND BILLED TO AGREED PRICES. ALL GATES ARE BILLED AT CONlRACT PRICE PLUS FOOTAGE. PRICING 00£ NOT INCLUDE ANY OCIPIWRAP INSURANCE PROGRAMS. LUMBER PROD ZES SET BY 1HE MFRS. WORK MUST BE COMMENCED WITHIN 30 DAYS OF ACCEPTAIICE. WE ARE A N SHOP. PRICES SUBJECT DUE TO AL TERN/(TIVE OIGG 11113 REQUIREMENTS AFTER DIG ALERT. CORE DRILLING QUDED UNLESS NOTED ABOVE. Total: 1,475.00 ACCEPTANCEOFPRO;(.P,~~~S~i~n~a~tu~r~e~~~~;,;:--~~~-- A.~~~v~~~!:~!!!~!~1v,:e~d ;in~, ~;=~1on~·.ia,i,;;;ra;,;jon~o~r;an;y~ot;;:1,e:,:al~te;:111::;ate;::;::;;;:;:;;;;;::;;;;;;;:;;;;;;;:;:;;;o;;;rr;ier,,;atiiring;;;'"tctothis contrac\~!e~:!~an~~t.~e~~~t~u~ in such arbitration or litigation shall award reasonable fees and costs incurred to the prevailing party including attorneys fees, expert witness fees, court oosts and other costs arising out of or relating to resolution of the dispute. "Payment to be made as follows: All materials is guaranteed to be as specified. All work to be completed in a workmanlike manner according to standard practices.Any alteration or deviation from above specifications Involving extra oosts will be esecuted only upon written orders, and will become an extra charge over and above the estimate. All agreements contingent upon strikes, accidents or delays beyond our control. Owner to carry fire, tornado, and othernecessary insurance. Our workers are Mly covered by Workmen's Compensation Insurance. All properly markers must be visible atthe start of construction or otherwise we do not assume BM responsibility whatsoever for any fences in their wrong location . .. *Notice: 'Under the Mechanic.~· Lien Law (California Code of Civil Procedure, Section 1181 et seq.) any contractor, subcontractor, laborer, supplier, or other person who helps to improve your property but Is not paid for his work or supplies, has a right to enforce a claim against your property. This means that, after a court hearing, your property could be sold by a court officer and the proceeds of the sale used to satisfy the indebtedness. This can happen even if you have paid your own contractor in full, if the subcontractor, laborer, or supplier remains unpaid.· Form #1017 Rev. 6112 Cobb's Printing (909) 795-2318 Proposal * Contract All Types of Fencing CORPORATE OFFICE 870 N Main St Riverside, CA 92501 951.788.5620 Fax951.788.5649 2861 La Cresta Ave Anaheim, CA 92806 714238.0091 Fax 714.238.0096 707 Industrial Park Dr. Manteca, CA 95337 209.239.1282 Fax 209.823.6985 35656 N Sierra Hwy Palmdale, CA 93550 661.265.0082 Fax 661.265.0179 Quoted to: TAYLOR MORRISON HOMES 8105 IRVINE CENTER DRIVE SUITE 1450 IRVINE, CA 92618 CHIP WALKER 891 Corporation St Santa Paula, CA 93060 805.933.4522 Fax 805.933.4521 Quotation 186 Quantico Avenue Bakersfield, CA 93307 661.325.2800 Fax 661.325.2810 Quote: Date: 6837 Power Inn Road Sacramento, CA 95828 916.383.2853 Fax 916.383.2854 Phone:949-533-4168 Fax: Job: PALISADES YORBA LINDA 2397 Nov 3, 2014 1250 N Backer Avenue Fresno, CA 93703 559.454.1712 !'ax 559.454.1713 Page: "Proud Member of the US Department of Homeland Security E-Verijy program" Customer ID Terms Salesman TAYOOlPALISADES Valid for 5 Days ORANDS ···-········ .. Quantity Description Unit Price Extension 1 1.00 REMOVE GATE, CUT OUT POST AND SIDE PANELS, PATCH CONCRETE 1,475.00 1,475.00 BEST AS POSSIBLE SET (1) NEW POST, BUILD (1) NEW SIDE PANEL, NEW METAL SCREEN ON BACK SIDE OF PANEL, ZINC WELDS, SPOT PRIME AND POLYURETHANE PAINT. THIS WILL TAKE A FULL DAY PLUS PAINT AND MATERIAL. NOTE: GATE HAS ELECTRIC KEY FOBS, ELECTRICIAN WITH NEED TO CHANGE ELECTRIC STRIKE POST DUE TO MOVING GATE. FENCEWORKS INC MUST HA VE PROPER BILLABLE PAPERWORK PRIOR TO WORK BEING STARTED. THANK YOU! NOTE FOLLOWING OJNDITIONS: PENDING CREDIT APPROVAL. PRICE INCLUDES ALL LABOR, MATERIAL, TAXES, E"!C. NECESSARYTOCOMPLElE JO FIELD MEASURED UPCN OOMPLETION AND BILLED TO AGREED PRICES. ALL GATES ARE BILLED AT CONTRACT PRICE PLUS FOOTAGE. PRICING DOE ~g~:::t-i'gf5 ~~H?Nc;/if¢; b~s~c~;~~~~ V:~~i:L~MBER PRo~ SHOP. PRICES suBJEles seT BY lHi:~t ,:ff~KN~¥i'v1 ~7GG 11\G Tota I: REQUIREMENTSAFfER DIG ALERT. CORE DRILLING C.UDED UNLESS NOTED ABOVE. 1,475.00 ACCEPTANCE OF PROP, S~nat~~e AUTHORIZED SIGNAT lij;E;_~~~/~§§'" ~~~;:-----STEVE ANDERSON *In the eventthat eijher party becomes involved in 1t1i-n:a,, ra 10n or' hera1tem one ating to this contract or the performance of it, !he court or tribunal in such arbitration or litigation shall award reasonable fees and costs incurred to the prevailing party including attorneys fees, expert witness fees, court costs and other costs arising out ofor relating to resolution of the dispute . .. Payment to be made as follows: All materials is guaranteed to be as specified. All work to be completed in a workmanlike manner according to standard practices.Any alteration or deviation from above specifications involving extra costs will be executed only upon written orders, and will become an extra charge over and above the estimate. All agreements contingent upon strikes, accidents or delays beyond our control. Owner to carry fire, tornado, and othernecessary Insurance. Our workers are fully covered by Workmen's Compensation Insurance. All property markers must be visible at the start of construction or otherwise we do not assume any responsibility whatsoever for any fences in theirwrong location. ••·Notice: 'Underthe Mechanics' Lien Law (California Code of Civil Procedure. Section 1181 et seq.) any contractor, subcontractor, laborer, supplier, or other person who helps to improve your property but Is not paid for his work or supplies, has a right to enforce a claim against your property. This means that, after a court hearing, your property could be sold by a court officer and the proceeds of the sale used to satisfy the indebtedness. This can happen even if you have paid your own contractor in full, If the subcontractor, laborer, or supplier remains unpaid.' l'orm #l 017 Rev. 6112 Cobb's Printing (909) 795_2318 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY February 4, 2014 To: lntracorp Companies 4041 MacArthur Blvd. Suite 250 Newport Beach, CA 92660 Attention: Mr. Ken Benson Project No. 10552.004 Subject: Geotechnical Update, Proposed Redevelopment of 2531 -2589 State Street, Carlsbad, California References: California Building Standards Commission (CBSC), 2013, California Building Code (CBC) Leighton and Associates, Inc., 2005, Preliminary Geotechnical Investigation, Proposed Redevelopment of 2531, 2541, and 2551 State Street, Carlsbad, California, Project No. 041742-001, dated December 7, 2005 Leighton and Associates, Inc., 2014, Phase I and Limited Phase II Environmental Site Assessment for 2531 through 2601 State Street, Carlsbad, California, Project No. 10552.001, dated January 9, 2014 RBF Consulting, 2014, Preliminary Grading Plans for State Street Townhomes, Carlsbad, California, Sheet C5, dated January 2014 In accordance with your authorization, this letter presents Leighton's geotechnical update for the proposed State Street residential redevelopment, located at 2531 -2589 State Street, in Carlsbad, California. The purpose of this update study was to review our previous geotechnical report and site environmental documentation (Leighton, 2006 and 2014), and to provide seismic design parameters in accordance with the 2013 CBC. We also performed a site visit on January 31, 2014 to observe current conditions. Currently, the site, approximately 1.89 acres, is utilized as commercial and light industrial property. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 10552.004 As background, Leighton performed the initial geotechnical investigation of the subject site in 2005 (Leighton, 2005). Recently, Leighton performed a Phase I and Limited Phase II Environmental Site Assessment (ESA) Report for the site. The purpose of the Limited Phase II ESA was to assess the soil and soil vapor throughout the subject site for the presence of contaminants originating from current and historical site uses, such that the potential health risks can be evaluated prior to residential development. The environmental study included eight (8) subsurface borings across the subject site. For the findings and results of the environmental study, please refer to referenced document (Leighton, 2014). Based! on our understanding of the site conditions and review of the referenced geotechnical and environmental documents, the geotechnical conditions of the subject site have not changed. Therefore, it is our professional opinion that the geotechnical recommendations presented in the referenced geotechnical report are still applicable for its intended use, provided the following recommendations are incorporated into the design and construction of the proposed buildings and improvements. In addition, the following items should be noted: • The undocumented fill associated with the former development is potentially compressible and should be removed down to the dense competent formation material. The depth of the removal is generally anticipated to be on the order of 3 to 5 feet below the existing ground surface. However, deeper undocumented fill associated with buried utilities, old septic systems, basements and underground storage tanks should be anticipated. • Impacted soil may be encountered during grading. Please refer to the referenced environmental study (Leighton, 2014). Note that special handling and waste profiling may be required for the excavation and disposal of this impacted soil. Seismicity The following seismic design parameters for the site (latitude 33.164299, longitude -117 .35299) are the risk-targeted spectral acceleration parameters for the project determined in accordance with the 2013 California Building Code (CBSC, 2013) and the USGS Worldwide Seismic Design Values tool (Version 3.1.0). -2 - Leighton 10552.004 Table2 2013 CBC Risk-Targeted Mapped Spectral Acceleration Parameters Site Class D Fa = 1.035 Site Coefficients Fv = 1.554 Ss = 1.163g Mapped MCER Spectral Accelerations S1 = 0.446g SMs = 1.203g Site Modified MCER Spectral Accelerations SM1 = 0.693g Sos = 0.802g Design Spectral Accelerations S01 = 0.462g Utilizing ASCE Standard 7-10, in accordance with Section 11.8.3, the following additional parameters for the peak horizontal ground acceleration are associated with the Geometric Mean Maximum Considered Earthquake (MCE0 ). The mapped MCE0 peak ground acceleration (PGA) is 0.463g for the site. For a Site Class D, the FPGA is 1.037 and the mapped peak ground acceleration adjusted for Site Class effects (PGAM) is 0.48g for the site. Site Grading All undocumented fill associated with the former development should be removed down to the dense competent formation material. To reduce the potential for differential settlement beneath the proposed buildings (i.e., cut/fill transitions), we recommend the entire building pad be overexcavated at least 3 feet below the lowest foundation and replaced with properly compacted fill. In addition, we recommend that the overexcavation extend! laterally at least 10 feet beyond the building perimeter or footprint. Imported soil, if needed to raise the site grades, should be granular and have an expansion index less than 50 (per ASTM Test Method D4829). Import soils and/or the borrow site should be evaluated by the geotechnical consultant prior to importation. - 3 - Leighton 10552.004 Foundation and Slab Design for Residential Buildings The proposed residential buildings may be supported by conventional, continuous or isolated spread footings. Footings should extend a minimum of 24 inches beneath the lowest adjacent soil grade. At these depths, footings may be designed for a maximum allowable bearing pressure of 2,000 pounds per square foot (psf) if founded in properly compacted fill soils. The allowable pressures may be increased by one-third when considering loads of short duration such as wind or seismic forces. The minimum recommended width of footings is 18 inches for continuous footings and 24 inches for square or round footings. The interior and garage slab-on-grade floors for the residential buildings should be at least 4 inches and 5 inches thick, respectively, and be reinforced with No. 3 rebars 18 inches on center, each way (minimum), placed at mid-height in the slab. Slabs should be underlain by a 2-inch layer of clean sand (sand equivalent greater than 30), which is in-tum underlain by a minimum 10-mil plastic sheeting (moisture barrier) and an additional 2 inches of clean sand. We recommend that control joints be provided across the slab at appropriate intervals as designed by the project architect. Some moisture sensitive flooring may require additional measures to mitigate moisture migration through the slab as designed by the project architect. Limitations Recommendations contained in this limited report are based on our site reconnaissance, background review, and present knowledge of the proposed construction. It is possible that soil conditions vary between or beyond the points explored. If soil conditions are encountered during grading or foundation excavation, which differ from those described in the original geotechnical reports, our firm should be notified immediately in order that a review may be made and any supplemental recommendations provided. Our firm has performed our services in substantial accordance with the generally accepted geotechnical engineering practice as it exists in the site area at the time of our study. No warranty is made or intended. - 4 -Leighton 10552.004 We appreciate the opportunity to be of service on this project. Should you have any questions related to this report, please contact our office at your convenience. Respectfully submitted, LEIGHTON and ASSOCIATES, INC. William D. Olson, RCE 45283 Associate Engineer Distribution: (4) Addressee -5 - Michael R. Stewart, CEG 1349 Vice President I Principal Geologist Leighton