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HomeMy WebLinkAboutCDP 99-04; Day Residence; Soils Investigation and Geologic Reconnaissance; 1999-01-04REPORT OF SOILS INVESTIGATION and GEOLOGIC RECONNAISSANCE DAY RESIDENCE SITE 2479 Ocean Street Carlsbad, California Job No 98-2611 January 4,1999 Prepared For: Davis Group, Architecture & Planning Prepared By: C.W. LA MONTE CO. 4350 Palm Avenue, Suite 25 La Mesa, CA. 91941 <$^, / C.W. LA MONTE CO. Soil and Foundation Engineers January 4, 1999 Job No. 98-2611 TO: The Davis Group, Architecture & Planning 344 Seventh Avenue San Diego, Ca. 92101 Attn: Mr. Wayne Davis SUBJECT: Report of Soils Investigation and Geologic Reconnaissance Day Residence Site 2479 Ocean Street Carlsbad, CA Dear Mr. Davis: In accordance with your request, in conjunction with M.W. Hart, RG, CEG, we have performed a soils investigation and geologic reconnaissance for your proposed residential project. We are presenting herein our findings and recommendations. In general, we found the site suitable for the proposed project provided that the recommendations contained herein are adhered to. Minor items of concern when developing the project include the presence of loose topsoil ranging up to 2 feet in thickness overlying the medium dense to dense terrace deposits. Therefore penetration with proposed foundations or a removal and re-compaction grading operation will be required to mitigate this condition. If you should have any questions after reviewing this report, please do not hesitate to contact our office. This opportunity to be of professional service is sincerely appreciated. Respectfully submitted, C.W* LA MONTE *£ k) *c i W. LA MONTE RCE 25241, GE 495 Job No. 98-2611 January 4, 1999 TABLE OF CONTENTS SCOPE OF WORK AND PROJECT DESCRIPTION 1 FINDINGS 1 SITE DESCRIPTION 1 FIELD INVESTIGATION 2 DESCRIPTION OF SOILS 2 GROUND WATER 2 TECTONIC SETTING 3 GEOLOGIC HAZARDS 3 GENERAL 3 GROUND SHAKING ."....3 LANDSLIDES 4 LIQUEFACTION 4 FLOODING 4 TSUNAMIS 4 SEICHES 4 LABORATORY TESTS AND SOIL INFORMATION 4 RECOMMENDATIONS 5 GENERAL SITE DEVELOPMENT 5 EARTH WORK AND GRADING 5 Fill Suitability 6 Earthwork 6 Excavation Characteristics 6 FOUNDATIONS 6 Dimensions and Embedment 6 Soil Bearing Value 6 Foundation Reinforcement 6 Foundations Near Tops of Slopes 7 Anticipated Settlements 7 Foundation Excavation Observation 7 Concrete Slabs-on-grade 7 Expansive Characteristics 8 DESIGN PARAMETERS FOR EARTH RETAINING STRUCTURES 8 Active Pressure 8 Lateral Pressure 8 Waterproofing and Subdrain Observation 8 Backfill 8 Factor of Safety 9 FOUNDATION AND GRADING PLANS RE VIEW 9 SLOPE STABILITY 9 SITE DRAINAGE CONSIDERATIONS 9 GRADING NOTES 9 LIMITATIONS 10 FIGURES Figure No. 1 - Plot Plan Figure No. 2 Site Plan Figure No. 3a through 3d Test Excavation Logs Figure No. 4 Laboratory Test Results Figure No. 5 Slope Setbacks Appendix "A" Geologic Reconnaissance - M. W. Hart, RG., CEG. 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 REPORT OF SOILS INVESTIGATION and GEOLOGIC RECONNAISSANCE Day Family Residence 2479 Ocean Street Carlsbad, CA The following report presents the findings and recommendations of the C.W. La Monte Company and M. W. Hart, Engineering Geologist for the subject project. SCOPE OF WORK AND PROJECT DESCRIPTION It is our understanding that the site is being developed to receive a new single family residence. The proposed two-story structure will be of wood-frame construction and founded on conventional shallow stepped continuous foundations, concrete with wood framed diaphragm and concrete slab-on-grade floors. The structures will be constructed near the existing grade utilizing moderate sized retaining walls. A swimming pool will be placed in the area of the existing stone gazebo. With the above in mind our scope of work consisted of the following: Identify and classify the surface and subsurface soils to depths, in conformance with the Unified Soil Classification System (refer to Appendix A). Determine the allowable presumptive bearing pressures for the natural ground and any soils to be used in compacted fill, based on their assumed shear-strength characteristics. Recommend treatment for any expansive soils and/or uncompacted fill or compressible alluvial soils that, if left in place and unmodified, could result in structure and cosmetic damages to the structure and proposed additions. Predict the settlement potential of re-compacted fill soils under the proposed structural loads. Recommend active and passive earth pressures to be utilized in design of any proposed retaining walls and foundation structures. Preparation of this report and appropriate graphics, presenting our findings, conclusions and recommendations. It was not within our scope of work to evaluate the site for hazardous materials contamination. 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4,1999 Page 2 FINDINGS SITE DESCRIPTION The project site consists of a rectangular shaped parcel of land with an existing wood frame and block residential structure, approximately 0.23 acres in size. The site is located on the southwest side of Ocean Street near the intersection with Rue Des Chateaux in the city of Carlsbad. The site is further, bounded on the easterly and westerly sides with existing single family residences . A description of the property is Assessor's Parcel Number 203-021-04-00**. Refer to the attached Plot Plan (Figure 1) for a layout of the site and location of proposed improvements. The property is moderately steep and appears to drain, by sheet flow, to the southwest towards the pacific ocean. Vegetation consists of lawn grass, shrubs and ice plant . A rock and mortar seawall approximately 8 feet in maximum height is located near the southwest property line. Elevations on-site range from approximately 6 feet at the southwest end of the site to 26 feet at the northeast end. FIELD INVESTIGATION Four hand augured test borings were placed on the site, specifically in areas where representative soil conditions were expected and where the proposed structure will be located. Our investigation also included a geologic site reconnaissance included as Appendix "A". The excavations were visually inspected and logged by our field geologist, and samples were taken of the predominant soils throughout the field operation. Test boring logs have been prepared on the basis of our inspection and the results have been summarized on Figure 3, a through d. The predominant soils have been classified in conformance with the Unified Soil Classification System (refer to Appendix A). DESCRIPTION OF SOILS The site is underlain with terrace deposits and associated, surficial topsoil. These soils and subsurface conditions are described individually below, also refer to the attached Test Boring Logs for more detailed information on the encountered soil conditions. Bay Point Terrace Formation: The site is underlain by the Pleistocene-aged Bay Point formation. The Bay Point Formation on the site consists of moderately well cemented, massively bedded, brown, fine, silty sands. (See Geologic Reconaissance App. "A"). Topsoil: The Bay Point formation is overlain with approximately 1 to 3 feet of natural ground topsoil. The topsoil's consists primarily of loose to medium dense, dark brown, silty medium sands . ( See Geologic Reconaissance App. "A"). 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 3 GROUND WATER No ground water was encountered during the course of our investigation, however, it should be kept in mind, that any required grading operations may change surface drainage patterns and/or reduce permeability due to the densification of compacted soils. Such changes of surface and subsurface hydrologic conditions, plus irrigation of landscaping or significant increases in rainfall, may result in the appearance of minor amounts of surface or near-surface water at locations where none existed previously. The damage from such water is expected to be minor and cosmetic in nature, if good positive drainage is implemented at the completion of construction. Corrective action should be taken on a site-specific basis if, and when, it becomes necessary. TECTONIC SETTING No major faults are known to traverse the subject site but it should be noted that much of Southern California, including the San Diego County area is characterized by a series of Quaternary-age fault zones which typically consist of several individual, en echelon faults that generally strike in a northerly to north-westerly direction. Some of these fault zones (and the individual faults within the zones) are classified as active while others are classified as only potentially active, according to the criteria of the California Division of Mines and Geology. Active fault zones are those which have shown conclusive evidence of faulting during the Holocene Epoch (the most recent 11,000 years) while potentially active fault zones have demonstrated movement during the Pleistocene Epoch (11,000 to 2 million years before the present) but no movement during Holocene time. Refer to the Geologic Reconnaissance by M. W. Hart for a description of the Geologic and Seismic setting. SEISMIC SAFETY STUDY As part of our investigation, we have reviewed the current City of Encinitas Seismic Safety Study. This study is the result of a comprehensive investigation of the city and surrounding areas, which identifies any potential geotechnical hazards and/or describes geomorphic conditions. ( See Geologic Reconnaissance Appendix "A" ) GEOLOGIC HAZARDS GENERAL No geologic hazards of sufficient magnitude to preclude development of the site as we presently contemplate it are known to exist. In our professional opinion and to the best of our knowledge, the site is suitable for the proposed development. GROUND SHAKING A likely geologic hazard to affect the site is ground shaking as result of movement along one of the major active fault zones mentioned above. Probable ground shaking levels at the site could range from slight to moderate, depending on such factors as the magnitude of the seismic event and the distance to the epicenter. It is likely that the site will 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 4 experience the effects of at least one moderate to large earthquake during the life of the proposed structure. ( See Geologic Reconnaissance Appendix "A"). LANDSLIDES Geologic Maps indicate there are no landslides on this site. (See Geologic Reconnaissance Appendix "A"). LIQUEFACTION The materials at the site are not subject to liquefaction due to such factors as soil density, grain-size distribution, and groundwater conditions. FLOODING Flooding is not expected to present a hazard to the proposed development, assuming structures are constructed at elevations above the design historical flood. TSUNAMIS Tsunamis are great sea waves produced by a submarine earthquake or volcanic eruption. The highest historical waves to affect the San Diego coastal area has been slightly over six feet. There is a possibility that the site could be subject to tsunami-related hazards in the event of a large earthquake along one of the offshore fault zones. SEICHES Seiches are periodic oscillations in large bodies of standing water such as lakes, harbors, bays, or reservoirs. There is a possibility that the site could be subject to seiche-related hazards in the event of a large earthquake. LABORATORY TESTS AND SOIL INFORMATION Tests were performed on the disturbed and undisturbed soil samples in order to determine their physical and mechanical properties and their ability to support the proposed structure. Laboratory test results are presented on the attached Figure No. 8. The following tests were conducted on the sampled soils: 1. Moisture Content (A.S.T.M. D2216-71) 2. Density Determinations 3. Mechanical Analysis (A.S.T.M. D422) 4. Expansion Index Tests (UBC 18-1) 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 5 The relationship between the moisture and density of undisturbed and remolded soil samples give qualitative information regarding the soil strength characteristics and soil conditions to be anticipated during any future grading operation. The mechanical analysis was used to aid in the classification of the soils according to the Unified Soil Classification System. The expansion potential of clayey soils was determined utilizing the UBC Expansion Index Test. Expansive soils are classified as follows: Expansion Index Potential Expansion 0-20 Very Low (or considered "Non-expansive") 21-50 Low 51-90 Medium 91-130 High 13 0-Above Very High RECOMMENDATIONS GENERAL SITE DEVELOPMENT The major consideration when re-developing the site is the presence of loose topsoil subject to possible creep overlying the site. The thickness of these materials ranges to approximately 1 to 3 feet below the existing ground surface. These materials are unsuitable in there present condition to support the proposed structures. In order to mitigate this potentially adverse conditions we recommend the complete penetration with continuous foundations or removal and re-compaction the loose material. The loose topsoil shall be removed to an approximate depth of 3.0 feet. Loose topsoils will require recompacting or penetration and/or removal due to there present condition. Any excavation/recompaction should extend laterally a minimum distance of ten feet outside the building perimeters or to a distance equal to the depth of removal below footings (whichever is greater). Lateral constraints (due to existing utilities, structures etc.) may prevent the recommended lateral removals and therefore, specialized foundation design may be required in these areas. Prior to receiving fill, the bottoms of the excavations (as prepared above) should be scarified to a depth of approximately 8 inches, moisture conditioned to slightly over optimum moisture content, and then recompacting the soils to at least 90 percent of their maximum dry density. Excavated and/or imported soils should then be placed back in the excavation in thin compacted layers at slightly over optimum moisture contents to the proposed finish grade. EARTH WORK AND GRADING 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 6 Fill Suitability On-site excavated materials may be used as compacted fill material or backfill. This fill should be placed in compacted layers not exceeding eight inches in thickness at slightly over optimum moisture content and at least 90 percent of the maximum dry density. The on-site materials, typically, posses a low to non expansive expansion potential. Any imported soil materials shall posses an expansion index of less than 30 and be obtained from an approved borrow pit or stockpile. Earth Work All earthwork and grading contemplated for site preparation should be accomplished in accordance with the attached Recommended Grading Specifications and Special provisions. All special site preparation recommendations presented in the sections above will supersede those in the standard Recommended Grading Specifications. All embankments, structural fill and fill should be compacted to at least 90 percent relative compaction at or slightly over optimum moisture content. Utility trench backfill within five feet of the proposed structures and beneath asphalt pavements should be compacted to at least 90 percent of its maximum dry density. The upper twelve inches of subgrade beneath paved areas should be compacted to 95 percent of its maximum dry density. This compaction should be obtained by the paving contractor just prior to placing the aggregate base material and should not be part of mass grading requirements. The maximum dry density of each soil type should be determined in accordance with ASTM Test D-1557-91, Method A or C guidelines. Excavation Characteristics The on-site material should be excavated with easy to moderate effort. FOUNDATIONS Dimensions and Embedment Conventional shallow foundations may be utilized in the support of the proposed structure and retaining walls (assuming loose fills and colluvial soils are removed and recompacted). Continuous footings should have a minimum depth of 15 inches below lowest adjacent finished grade for the proposed two-story structure. Two story structures require a 15-inch minimum foundation width per the Uniform Building Code. Soil Bearing Value A bearing capacity of 2000 psf may be assumed for said footings when founded a minimum of 18 inches into properly compacted fill or firm formational ground. This bearing capacity may be increased by one-third, when considering wind and/or seismic loading. Foundation Reinforcement It is recommended that continuous footings be reinforced with at least two No.5 steel bars; one reinforcing bar shall be located near the top of the foundation, and one bar near the bottom. The steel reinforcement will help prevent damage due to normal, post construction settlement, resulting from variations in the subsurface soil conditions. This recommendation does not supersede reinforcement required for structural considerations. 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 7 Foundations Near Tops of Slopes Foundations and footings of proposed structures, walls, et cetera, when located five feet and further away from the top of compacted fill slopes, may be of standard design in conformance with the recommended soil bearing value. If proposed foundations and footings are located closer than five feet from the top of slopes, they shall be deepened at least one foot below an imaginary plain projected from a point five feet horizontally inside the top of the fill slope and parallel to the face of the fill slope. Anticipated Settlements Based on our experience with the soil types on the subject site, the soils should experience settlement in the magnitude of less than 0.75 inch under a structural load of 2,000 pounds per square foot on a compacted fill mat. It should be recognized that minor hairline cracks normally occur in concrete slabs and foundations due to shrinkage during curing and/or redistribution of stresses and some cracks may be anticipated. Such cracks are not necessarily an indication of excessive vertical movements. Foundation Excavation Observation In order to minimize any work delays at the subject site during site development, this firm should be contacted 24 hours prior to any need for inspection of footing excavations or to perform grading observation or field density testing of compacted fill soils. If possible, placement of forms, templates and steel reinforcement in footing excavations should not occur prior to our inspection of the excavations. Sometimes foundation excavation observation reveals the need to deepen, redesign or otherwise mitigate unanticipated or adverse conditions. Therefore, prior observation would eliminate the need to remove any form work or steel reinforcement in the affected footing excavation in order to correct the observed problem. Concrete Slabs-on-grade Concrete floor slabs, if used shall be a minimum thickness of four inches and shall be underlain by two inches of clean sand overlying 6 mil visqueen, overlying an additional two inches of clean sand. Four inches of clean sand overlying 6 mil visqueen may be substituted if extreme care is taken not to puncture the visqueen vapor barrier during installation The slab should be reinforced #3 reinforcing bars placed at 18 inch centers, each way or with 6x6-6/6 steel wire mesh. The reinforcement should be placed on concrete "chairs" or spacers, to within the middle third of the slab. Theoretically, the above-recommended rebar and wire mesh options provide similar reinforcement strength. However, based on our past experience, we have found that the wire mesh is often and is more easily pushed to the bottom of the slab during the finishing process, thus significantly reducing its intended reinforcing, function. The rebar grid, if properly supported, is less likely to be dislodged during the finishing process. Thus, unless the concrete finisher is diligent in this regard, the rebar option is the preferred method of slab reinforcement. 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 8 Following placement of concrete floor slabs, sufficient drying time must be allowed prior to placement of floor coverings. Premature placement of floor coverings may result in degradation of adhesive materials and loosening of the finish floor materials. Prior to installation, standardized testing can be performed to determine if the slab moisture emissions are within the limits recommended by the manufacturer of the specified floor-covering product. Expansive Characteristics The recommendations of this report reflect a non to low expansive condition resulting from topsoil and formational materials. DESIGN PARAMETERS FOR EARTH RETAINING STRUCTURES Active Pressure The active earth pressure to be used in the design of retaining walls, shall be based on an Equivalent Fluid Weight of 30 pcf (pounds per cubic foot) at any depth. This active pressure is for level backfill and assumes an unrestrained condition, using select backfill and that proper drainage is provided behind the wall. For a restrained condition an active pressure of 8 H shall be used over the depth of the wall. Lateral Pressure The passive earth pressure of the encountered natural-ground soils and any recompacted fill soils (to be used for design of building foundations and footings to resist the lateral forces) shall be based on an Equivalent Fluid Weight of 300 pcf (pounds per cubic foot). This passive earth pressure shall only be considered valid for design if the ground adjacent to the foundation structure is essentially level for a distance of at least three times the total depth of the foundation. We recommend that the upper 1-foot of soil not protected by pavement or concrete slabs be neglected when calculating passive resistance. A Coefficient of Friction of 0.4 times the dead load may be used between the bearing soils and concrete wall foundations or structure foundations and floor slabs founded on formational or similar materials. When combining frictional and passive resistance, the former should be reduced by one-third. Waterproofing and Subdrain Observation The geotechnical engineer should be requested to verify that waterproofing has been applied and that subdrains are properly installed. However, unless specifically asked to do so, we will not verify proper application of the waterproofing. Backfill All backfill soils should be compacted to at least 90% relative compaction. Expansive or clayey soils should not be used for backfill material. The wall should not be backfilled until 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 9 the masonry has reached an adequate strength. Pea gravel or equivalent if utilized as backfill will not require testing for relative compaction. Factor of Safety The above values, with the exception of the allowable soil bearing pressure, do not include a factor of safety. Appropriate factors of safely should be incorporated into the design to prevent the walls from overturning and sliding. FOUNDATION AND GRADING PLANS REVIEW The foundation and grading plans should be submitted to this office for review to ascertain that the recommendations provided in this report have been followed and that the assumptions utilized in its preparation are still valid SLOPE STABILITY Although no major slopes are anticipated, it is our opinion that cut and or fill slopes constructed at 2:1 (horizontal to vertical) inclination will possess an adequate factor-or-safety to heights of at least fifteen feet. SITE DRAINAGE CONSIDERATIONS Adequate measures shall be taken to properly finish-grade the site after the structures and other improvements are in place. Drainage waters from this site and adjacent properties which already show indications of potential problems, are to be directed away from foundations, floor slabs and footings, onto the natural drainage direction for this area or into properly designed and approved drainage facilities. Proper subsurface and surface drainage will ensure drainage that no waters will seek the level of the bearing soils under the foundations, footings and floor slabs. Failure to observe this recommendation could result in uplift or undermining and differential settlement of the structure or other improvements on the site. In addition, appropriate erosion-control measures shall be taken at all times during construction to prevent surface runoff waters from entering footing excavations, ponding on finished building pad or pavement areas, or running uncontrolled over the tops of newly-constructed cut or fill slopes. Planter areas and planter boxes shall be sloped to drain away from the foundations, footings, and floor slabs. Planter boxes shall be constructed with a subsurface drain, installed in gravel, with the direction of subsurface and surface flow away from the foundations, footings, and floor slabs, to an adequate drainage facility. Structure retaining walls shall be properly water proofed and provided with a subdrain system. Our firm prior to implementation should review the water proofing system and drainage design. 4350 Palm Avenue, Suite25, La Mesa, Ca, 91941 Job No. 98-2611 January 4, 1999 Page 10 GRADING NOTES Any required grading operations shall be performed in accordance with the requirements of local Grading Ordinances, under the observation of a qualified Soils Engineer or supervised Field Soils Technician. It is the responsibility of the Owner and/or Developer to ensure that the recommendations summarized in this report are carried out in the field operations. This firm does not practice or consult in the field of safety engineering. We do not direct the Contractor's operations, and we cannot be responsible for the safety of personnel other than our own on the site; the safety of other is the responsibility of the Contractor. The Contractor should notify the Owner if he considers any of the recommended actions presented herein to be unsafe. LIMITATIONS Our conclusions and recommendations have been based on all available data obtained from our field investigation and laboratory analysis, as well as our experience with the soils and formational materials located in the area. Of necessity, we must assume a certain degree of continuity between exploratory excavations and/or natural exposures. It is, therefore, necessary that all observations, conclusions, and recommendations be verified at the time grading operations begin or when footing excavations are placed. In the event discrepancies are noted, additional recommendations may be issued, if required. The work performed and recommendations presented herein are the result of an investigation and analysis, which meets the contemporary standard of care in our profession. No other warranty is expressed or implied. This report should be considered valid for a period of three (3) years, and is subject to review by our firm following that time. If significant modifications are made to the building and/or grading plans, especially with respect to the height and location of any cut and fill slopes, and the height and location of any proposed structures, this report must be presented to us for immediate review and possible revision. The firm of C.W. La Monte Co. shall not be held responsible for changes to the physical condition of the property, such as addition of fill soils or changing drainage patters, which occur subsequent to the issuance of this report. Once again, should any questions arise concerning this report, please do not hesitate to contact us. Respectfully submitted, C.W. La Monte Company ClifFocqW. La Monte, R.C.E. 25241, G.E. 0495s ' 4350 Palm Avenue, Suite255 La Mesa, Ca, 91941 i i .1 NOTE: This Site Plan is not to be used for legal purposes. Locations and dimensions are approx- imate. Actual property dimensions and locations of utilities may be obtained from the Approved Building Plans or the "As Built" Grading Plans. LEGEND: APPROXIMATE LOCATION OF TEST BORING B-l PLOT PLAN JOB NO. 98-2611 FIGURE NO. I I J I i i I i I I t * i s % * i I i I I I i t i N. g 2479 Ocean St, Carlsbad, 92008, Page & Grid 1106 D5 SITE PLAN JOBNO.98-2611 FIGURE NO. 2 EQUIPMENT DIMENSION ft TYPE OF EXCAVATION DATE LOGGED Hand Auger .5' x 6' 12/10/98 SURFACE ELEVATION GROUNOWATER DEPTH LOGGED BY Not Avialable Not Encountered MH t klO - r. . 2- 3^ 4- 5- - 7- 8- 9- 10- 11 : 12 - 13- 3a a X FIELD DESCRIPTION AND CLASSIFICATION • DESCRIPTION AND REMARKS (CONSISTENCY, MOISTURE, COLOR, ORAIN till) Loose, brown, moist silty fine sand Medium dense, brown, damp, medium to coarse sand ( cemented) Terrace Deposit Bottom of Boring - U.S.C.I. SW SP B IN-PLACEMOISTURE7.4 i!IN-PLACEDENSITYe OPTIMUMMOISTURE8.8 5S MAXIMUMDENSITY117.1 JOB NAME DAY RESIDENCE b n DENSITY( % OF HI. 1 EXPAN. 1CONSOL.• t •LOWCOUNTS Iao SAMPLERY WATER TABLE SITE LOCATION 2479 Ocean Street «-» Carlsbad, CA.E] LOOSE BAG SAMPLE r-i JOB NUMBER Li] IN PLACE SAMPLE QR ?fi11 • DRIVE SAMHLt F|QURE NUMB£R 3-a REVIEWED BY LOG. NO. cl B - 1 EQUIPMENT DIMENSION ft TYPE OF EXCAVATION DATE LOGGED Hand Auger .5' x 6' 12/10/98 SURFACE ELEVATION GROUNOWATER DEPTH LOGGED BY Not Available Not Encountered MH t &kla _ i: - - 3- 4- 5- -7- 8- 9- 10- 11 : 12 - 13- s 6 "-' ,/ ^ • /. / 'X/ «# a ? E 1 FIELD DESCRIPTION AND CLASSIFICATION * DESCRIPTION ANO REMARKS (CONSISTENCY, MOISTUMC, COLOM, ORAIN IIZI) Very Loose, brown, moist, fine sand Fill and Topsoil \ Medium dense, brown, moist to wet, medium sand slight color change refusal on cobbles Bottom of Boring — - U.S.C.S. SP SP e 3?<:£ sS IN- PLACE DMTDENSITY (M'tOPTIMUMMOISTUMC (%)MAXIMUM OMYDENSITY (»c'lDENSITY(%OF It 0.0.)iiX OIM O JOB NAME DAY RESIDENCE k. ns|SAMPLER 00.WATER TABLE SITE LOCATION 2479 Ocean Street Carlsbad, CA.LOOSE BAG SAMPLE JOB NUMBERIN PLACE SAMPLE QQ OA1 ,yo-zoll 3-b REVIEWED BY LOG. NO. cl B 2 EQUIPMENT Hand Auger SURFACE ELEVATION Not Available t f kla - 1 . . 2- 3J 4- 5- 6 , 7- 8- 9- 10- 11 : 12 • L3- 2 . / / / // / / S / / / \ DIMENSION ft TYPE OF EXCAVATION .5' x 6' GROUNOWATER DEPTH Not Encountered FIELD DESCRIPTION AND CLASSIFICATION * DESCRIPTION AND REMARKS I CONSISTENCY, MOISTURE, COLOR, ORAIN SIZE) Loose, brown, dry, silty Medium dense, brown, dry, sand silty medium sand (lightly cemented) (Terrace J Deposit) Medium dense to dense, light brown, dry, medium sand (moderately cement (Terrace Bottom of Boring - Y WATER TABLE IT")| £J LOOSE BAG SAMPLE S IN PLACE SAMPLE • DRIVE SAMPLE Deposit) O.S.C.8. >d) ?IN -PL ACEMOISTUREi!IN- PL ACEDENSITYDATE LOGGED 12/10/98 LOGGED BY MH ?OPTIMUMMOISTUREi!MAXIMUMDENSITY6ri DENSITY( % OF HI? _ 1 EXPAN. 1CONSOL.K • LOWCOUNTS /bo SAMPLERJOB NAME DAY RESIDENCE SITE LOCATION 2479 Ocean Street Carlsbad, CA JOB NUMBER 98-2611 FIGURE NUMBER 3 -c REVIEWED BY LOG. NO. cl B- 3 EQUIPMENT DIMENSION ft TYPE OF EXCAVATION Hand Auger .5' x 6' SURFACE ELEVATION GROUNDWATER DEPTH Not Available DEPTH FT._ i: 2- 3. 4- 5- 6-; 7- 8- 9- 10- 11 : 12 - 13-SYMBOL"•• f V / // / a Not Encountered FIELD DESCRIPTION AND CLASSIFICATION DESCRIPTION AND REMARKS (CONSISTENCY, MOISTURE, COLOR, BRAIN SIZE) Loose, brown, moist, silty fine sand ( Topsoil) i Medium dense, brown, moist , medium sand (Terrace Deposit ) 1 ' Bottom of Boring — - ^ WATER TABLE £3 LOOSE BAG SAMPLE S IN PLACE SAMPLE | DRIVE SAMPLE U.B.C.S.IN -PL ACEMOISTURE (%)IN- PLACE ORYDENSITY (»«()DATE LOGGED 12/10/98 LOGGED BY MH OPTIMUMMOISTURE (%)MAXIMUM ORYDENSITY (»cf)rDENSITY(%OF M.0.0.)EXPAN. * .^CONBOL. -IL n 11 SAMPLER 00.JOB NAME DAY RESIDENCE SITE LOCATION 2479 Ocean Street Carlsbad, CA JOB NUMBER 98-2611 FIGURE NUMBER 3-d • REVIEWED BY LOG. NO. cl B - 4 1 30 i?n — i HO IUO 50 D — •5 Jj t- ^ tr \ \ V \ \ \ \ 7 \> \ \ \ \ \ <*• \ \ \ \ \_ \ V MAXIMUM DF DENSITY (pcf) LABORATORY SOIL DATA SUMMARY ASSUMED SHEAR \ \ VV\\ — Y OPTIMUM MOISTURE (%) \ A \\ V A5xAvA AX\ v \\ V \\ r\ A\\X 1 Al Anenr conc3i DATA ON (p<f) APPARENT FRICTION AMOLE i iuka 117.1 8.8 MOISTUnE CONTENT 7o 00 0 10 • 20 LABORATORY COMPACTION SOILTYPE 1 \ \ \ a.ivii :i nn • M ^ \ — 300 30° 3.,.d < L j fi fl (Ij !|ii COKKI Id r.n. fln.i S.ll U S tlfndod 1 •«• lil» 2 R 3 * V. / » / \ I \ : \ i1 ii ij i i1 i i | \ I \ijl j« \ i i i !l 2 5 •5oS;!=§ 5 2.70^^ 2 6(/>]-SPECIFIC GRAVITY K IXV2.50 \x<r a., 8ft 11 liII 8i ZERO AIR VOIDS CURVES 30 10 TEST SOIL CLASSIFICATION BROWN MEDIUM TO COARSE SAND BC i 1 • — SWELL TEST DATA INITIAL OUT OEMS TY pcf) INITIAL WA T En CONTENT (%) LOAD (p « I) PERCENT SWELL nine NO. 1 THEN NO CH OEPT, 3' 1 JOn NO' 98-2611 rinunf no 4 FOUNDATION REQUIREMENTS NEAR SLOPES PROPOSED STRUCTURE CONCRETE FLOOR SLAB 8' REINFORCEMENT OF FOUNDATIONS AND FLOOR 8LASSFOLLOWINGTHE • RECOMMENDATIONS OF THE ARCHITECT OR STRUCTURAL ENGINEER — • CONCRETE FOUNDATION s» ^ X ^r X TOP OF COMPACTED FILL SLOPE (LOOSE OVERBURDEN SOIL IS IGNORED) COMPACTED FILL SLOPE WITH MAXIMUM INCLINATION AS PER SOILS REPORT TOTAL DEPTH OF FOOTING MEASURED FROM FINISH SOIL SUB-GRADE COMPACTED FILL OUTER MOST FACE FOOTING ~ • ' \ \^ 12-MINIMUM OR AS DEEP AS REQUIRED FOR LATERAL TYPICAL SECTION STABILITY (SHOWING PROPOSED FOUNDATION LOCATED WITHIN 5 FEET OF TOP OF SLOPE) 12" FOOTING / 5' SETBACK TOTAL DEPTH OF FOOTING DISTANCE FROTOP OF SLOPEo 1' 2' 3' 4' 8' 1.8 : 1.0 S L O P E * 82" 48" 38" 28" 20" 12" 2.0 : 1.0 SLOPE 42" 38" 30" 24" 18" 12" wh.n .ppllc.bl.FIGURE NUMBER 5 JOB NUMBER98_26n MICHAEL W. HART, ENGINEERING GEOLOGIST GEOLOGIC RECONNAISSANCE DAY RESIDENCE SITE 2479 OCEAN STREET CARLSBAD, CALIFORNIA FOR DAVIS GROUP, ARCHITECTURE AND PLANNING SAN DIEGO, CALIFORNIA JANUARY, 1999 MICHAEL W. HART ENGINEERING GEOLOGIST File No. 367-99 January 4, 1999 Davis Group, Architecture and Planning 344 Seventh Avenue San Diego, California 92101 Attention: Mr. Wayne Davis Subject: Day Residence Site 2479 Ocean Street Carlsbad, California GEOLOGIC RECONNAISSANCE Gentlemen: In accordance with your request, I have completed a geologic reconnaissance of the subject site. It is concluded that erosion and bluff retreat potential at the site can be classified as low. The potential for further erosion has been reduced by construction of a sea-wall. Accordingly, it is concluded that if the sea-wall is properly maintained, the proposed residence should have a useable life span of at least 75 years. Detailed geologic conditions of the site and the potential for bluff retreat is discussed in the following report. Michael W. Hart CEG 706 OT.CEG7C3 CERTIFIED ENGINEERINGGEOLoer" P.O. Box 261227 • SAN DIEQO CALIFORNIA 92196* (619) 57B-4672 Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 GEOLOGIC RECONNAISSANCE DAY RESIDENCE SITE 2479 OCEAN STREET CARLSBAD, CALIFORNIA Purpose and Scope; This report presents the findings of a engineering geologic reconnaissance of the residential site located at 2479 Ocean Street in Carlsbad, California. The purpose of this study is to: 1) describe the general geologic characteristics of the site; and 2) to address the potential for the property to be impacted by erosion and sea-bluff retreat. The scope of work included a site inspection, observation of soil test pits excavated for the Soil Investigation performed by the C.W. La Monte Company, review of aerial photographs and published geologic reports; and preparation of this written report summarizing findings and recommendations. Site Description; The site consists of an approximately rectangular residential lot located on a low sea-bluff west of Ocean Street in Carlsbad, California (Figure 1). The lot has a frontage of approximately 75 feet along Ocean Street and extends 135 feet westerly to a point on the beach near an approximately eight feet high stone sea-wall. It is my understanding the existing residential structure is to be removed and will be replaced with a new residence of wood-frame and stucco construction. The sea bluff west of the existing residence is moderately steep and covered with ice-plant. The building pad appears to drain primarily by sheet flow to the west towards the ocean. Vegetation consists of grass, shrubs and ice-plant. Elevations on site range from approximately 6 feet at the southeast end of the site to 26 feet at the northeast property line. 1 MICHAEL. W. HART, ENGINEERING GEOLOGIST Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 General Geology and Geologic Structure: The site is underlain by a late Pleistocene marine terrace deposit which constitutes the underlying bedrock, and thin surficial deposits consisting of shallow topsoils and fill. The marine terrace deposits are comprised of massive sandstones that may be correlatable with the Bay Point Formation whose type area is located near Mission Bay in San Diego. Weber (1982) maps these same deposits as unnamed "younger coastal terrace deposits" of Pleistocene age. Mapping by Weber also indicates that no faults are present on or adjacent to the site. The presence of the sea- wall on the property as well as other similar sea-walls on adjacent properties to the north and south precludes geologic observations at the extreme west edge of the site near the beach. Based on observations of shallow borings placed in this area by The C.W. LaMonte Company for the soils investigation, it is likely that the terrace deposits extend in depth to at least beach level in this area. The closest outcrop of densely cemented Eocene-aged bedrock lies approximately one mile to the south (Weber, 1982). Shallow fill soils are present as backfill behind the sea-wall and topsoils consisting of loose to medium dense, dark brown, silty, medium-grained sands extending to depths of approximately two to three feet are present over most of the remainder of the property. Groundwater; No groundwater was encountered during the course to the soils investigation and no seepage was observed on the face of the sea-wall. It may be expected however, that the ground water level in the proposed building area lies at, or slightly above, mean sea-level. Coastal Erosion The coastal zone in the Ocean Street area of north Carlsbad is somewhat atypical of the San Diego County coastline. The coast is not typified by a high sea-cliff being eroded into a flat-topped ancient marine terrace. In this location, the backshore zone, prior to construction of the sea-wall was characterized by a broad, low slope that terminated near the west side of Ocean Street. The particular coastal segment on which the site is located is characterized by a "fine-grained sand and cobble beach backed by (gentle to moderate) 30 to 60 feet high cliffs comprised of the 80,000 to 120,000 yr. old Bay Point Formation. In this area, the Bay Point forms fairly stable slopes, with little evidence of sliding, but is MICHAEL W. HART, ENGINEERING GEOLOGIST Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 susceptible to extensive erosional rilling" (Shoreline Erosion Assessment and Atlas of the San Diego Region, Vol. II ,1994). Such rilling is not now occurring at the site due to a well-developed ground cover of iceplant and the presence of the seawall. A comparison of vertical aerial photographs taken in 1928 and 1953, with current bluff conditions indicate that coastal recession rates in this area have been slow compared to other sites in nearby Leucadia and Encinitas. According to the U.S. Corps of Engineers Reconnaissance Report (1996) on the Encinitas coastline several miles south of the site, the rate of horizontal bluff-top recession in that area varies from 0.15 to 1.0 feet per year. The average rate in that area is probably on the order of 0.1 to 0.2 feet per year. Unprotected areas of the Carlsbad coastline likely have similar erosion rates. The above-referenced recession rates apply to sections of the coast that are not protected from erosion by sea-walls or rock-revetment. In areas where such walls exist, erosion of the back beach slopes is essentially halted as long as the sea-wall is properly maintained. One of the factors controlling erosion of the beach bluffs and to a degree, the life-span and maintenance requirements of the sea-wall is the condition of the beach and whether the beaches are being narrowed by loss of sand or whether the beaches are widening by artificial sand nourishment. The Corps of Engineers report (1996) indicates that the beaches in the northern part of Encinitas, and presumably Carlsbad as well, have been accreting due to the downcoast propagation of recently placed fill from lagoon dredging operations. Dredging operations in Oceanside harbor during the period from 1963 to 1984 resulted in the placement of 2,400,000 cubic yards of sand on the beach in that area that due to littoral drift, eventually is redeposited along the coast to me south. Much of this sand has migrated into deeper water as a result of recent storms. Currently, the beach in front of the sea-wall is characterized by a high cobble berm that is providing temporary protection from bluff toe erosion. Faulting. Local and Regional Published geologic maps (Weber, 1982) indicate that the closest faults inland of the site are minor inactive faults that cut Eocene-aged bedrock. Similar faults cutting the Eocene bedrock but not the overlying terrace deposits are exposed in the sea-bluffs south of the site in the Leucadia area. The closest active fault is the Rose Canyon fault that lies MICHAEL W. HART, ENGINEERING GEOLOGIST Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 approximately two miles off-shore. Recent studies have shown that the Rose Canyon fault is capable of producing an M 6.5 earthquake. Such an event on this fault or other regional active faults in the southern California area could subject the site to moderate to severe seismic shaking. Landsliding The results of the geologic mapping for this report and review of aerial photographs indicates that the site is not located on or adjacent to areas that have been subject to landsliding. In addition, the topography and geologic conditions at the site are such that future landsliding is not likely. Secondary Effects of Faulting Secondary effects of faulting include lateral spreading, liquefaction, and seismically induced settlement. Since the foundations of the proposed structure will be extend through loose surficial soils and into medium-dense terrace deposits, it will not likely be subject to secondary effects of faulting or seismic shaking. Tsunamis: Tsunamis are long period ocean surface waves that are generated by large submarine earthquakes that displace the seafloor over large areas. Tsunamis may also be caused by large submarine landslides. Measurable tsunamis generated by remote earthquakes strike the southern California coast on average about once every 4 to 5 years (Zeiser-Kling Consultants, 1994). Few locally generated tsunamis have been observed in the San Diego coastal area during the brief historical record over the last 200 years. Because of the strike slip nature of offshore faults, this area is unlikely to experience significant locally generated tsunamis in the future. According to Agnew ( 1979) San Diego has experienced only one tsunami caused by a local earthquake. It was associated with the earthquake of May 27, 1862 which caused intense shaking in the San Diego area. This tsunami resulted in a beach run-up of about 3 to 4 feet. According to the report for the city of Encinitas by Zeiser-Kling consultants, (1994), the run-up value for coastal inundation due to tsunami (in the past) are comparable to values for MICHAEL W. HART, ENGINEERING GEOLOGIST Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 extreme waves during storm surges. Since the site is located at an elevation of approximately 26 feet, it is considered unlikely that it will be subject to inundation due to tsunamis during the life of the structure. Conclusions and Recommendations 1. The results of this study indicate that the site is underlain by loose surficial soils and medium-dense terrace deposits consisting of medium-dense, horizontally-bedded, medium- grained sands of the Bay Point Formation. 2. It is concluded that long term bluff recession has been arrested or significantly reduced by installation of a sea-wall. It is further concluded that if the sea-wall is properly maintained throughout the project life, that the residence should have a usable life-span of at least 75 years. In addition, it is concluded that the proposed development will have no adverse effect on the stability of the coastal slope west of the building site. 3. Based on the findings of this report it is concluded that the project can be designed so that it will neither be subject to, nor contribute to, significant geologic instability. 4. Poor surface drainage can be a significant factor in erosion of coastal slopes. Therefore, it is recommended that all surface and roof water be directed via swales or subsurface drains that direct water to properly engineered outlets. MICHAEL W. HART, ENGINEERING GEOLOGIST Day Residence Site 2479 Ocean Street, Carlsbad, CA File No. 367-98 References Agnew, D.C., 1979, Tsunami history of San Diego, inJEarthquakes and other perils, San Diego region, eds., Abbott, P.L., and Elliott, W.J., Geological Soc. America Guidebook, p. 117-122. Kuhn, G.G. and Shepard, P.P., 1984, Sea Cliffs, Beaches, and Coastal Valleys of San Diego County, Univ. California Press, p. 193. Shoreline Erosion Assessment and Atlas of the San 'Diego Region, vol. II, 1994, ed. Reinhard E. Flick, pub. by Calif. Dept. Boating and Waterways, Map 12b. U. S. Corps of Engineers, 1996, Reconnaissance Report, Encinitas Shoreline, U.S. Corps of Engineers Los Angeles District. Weber, H.F., 1982, Recent slope failures, ancient landslides and related geology of the north-central coastal area, San Diego County, California, Calif. Div. Mines and Geology Open File Report 82-12 LA. Wilson, K., 1972, Eocene and related geology of a portion of the San Luis Rey and Encinitas Quadrangles, San Diego County, California, unpub. M.A. thesis, Univ. of California, Riverside. Aerial Photographs U.S. Department of Agriculture, 1953, 14M 19 & 20 San Diego County, 1928, Fit. # 22A, 3 & 4. MICHAEL W. HART, ENGINEERING GEOLOGIST NOTE. TOP Or EXISTING SEA nAU. IS APPROXIMATELY 8' ABOVE •BEACH SAND" LEVEUEXISTING SELP-CLOSINS ILATCHIN6 SATE • UANO9CAPE AKEA EX»TIN6 6A2CBOTO BE REMOVED STUCCO P1NISH GARDEN HAUL _. EXISTING CONCRETE r 6AZEBO OVER SP PROPOSED ABOVE < SHAPE BALCONYSTRJN&-UNE UUtTlHi., 9TRIN6-UNE STRU&TRUR! --a- I EXISTING SJ"X». TO BE REMOVED OR DEMOLISHED EXISTING HATER METER PROTECT PROM DAMASE eX»TIN» HATER METER RELOCATE Aft REQUIRES OCEAN STREET WET WEATHER MAINTENANCE AT RESIDENTIAL SITES* Southern Californians, unlike other residents of the nation, are unaccustomed to heavy rainfall. Whenever unusually wet weather occurs, San Diegans, particularly those living on slopes of filled land, become concerned (often unduly) about the conditions of their building site. They should not be, generally, The grading codes of the County of San Diego, and the various incorporated ciles in the County, concerning filled land, excavation, terracing, and slope construction, are among the most stringent in the stale, and adequate to meet almost any natural occurrence. This is the opinion of the San Diego Chapter of the California Council of Civil Engineers and Land Surveyors, whose members help prepare and review the codes. In 1967, the local Chapter of the California Council of Civil Engineers and Land Surveyors compiled a list of some precautions that homeowners can take to maintain their building sites. This updated pamphlet reiterates those precautions. Everyone is accustomed to maintaining his house. Everyone realizes that periodic termite inspections are a reasonable precaution, and that homes require a coat of paint from time to time. Homeowners are well used to checking and replacing wiring and plumbing, particularly in older homes. Roofs require occasional care. However, the general public regards the natural ground as inviolate. They ought to realize that Nature is haphazard in her creation of all land, some of which becomes building sites. Nature's imperfections have been largely compensated through careful engineering design and construction and enforcement of rigorous building and lot development ordinances. It is only reasonable to assume that an improved building site requires the approximate same care that the building itself does. In most instances, lot and site care are elementary steps that can be taken by the homeowner at considerably less cost that building maintenance. As a public service, engineers in private practice of the San Diego Chapter of the California Council of Civil Engineers and Land Surveyors have compiled this pamphlet of pertinent Do's and Don'ts as a guide to homeowners. The CCCELS respectfully advises that, in offering these guides, it accepts no responsibility for the actual performances of home sites or structures located thereon. * Pamphlet prepared by the San Diego Chapter California Council of Civil Engineers and Land Surveyors. 435O Palm Avc.. Suite 25. La Mesa. CA 91941 - (619) 462-9661 DO'S 1. Do clear surface and terrace drains with a shovel, if necessary, and check them frequently during the rainy season. Ask your neighbors to do likewise. 2. Do be sure that all drains have open outlets. Under the right conditions, this can be tested simply on a dry day with a hose. If blockage is evident, you may have to clear the drain mechanically. 3. Do check roof drains, gutters and down spouts to be sure they are clear. Depending on your location, if you do not have roof gutters and down spouts, you may wish to install them because roofs and their wide, flat space will shed tremendous quantities of water. Without gutters or other adequate drainage, water falling from the eaves ponds against foundation and basement walls. 4. Do check all outlets at the top of slopes to be sure that they are clear and that water will not overflow the slope itself, causing erosion. 5. Do keep drain openings (weep-holes) clear of debris and other material that could block them in a storm. 6. Do check for loose fill above and below your properly if you live on a slope or terrace. 7. Do watch hoses and sprinklers. During the rainy season, little, is any, irrigation is required. Over-saturation of the ground is not only unnecessary and expensive, but can cause subsurface damage. 8. Do watch for backup in interior drains and toilets during a rainy season, this may indicate drain or sewer blockage. 9. Do exercise ordinary precaution. Your house and building site were constructed to meet certain standards that should protect against any natural occurrences, if you do your part in maintaining them. 435O Palm Ave.. Suit* 25. la Mesa, CA 91941 - (6)9) 462-9061 DONTS 1. Don't block terrace drains and brow ditches on slopes or at the tops of cut slopes on sloping ground. These are designed to carry away runoff to a place where it can be safely distributed. Generally, a little shovel work will remove any accumulation of dirt and other debris that clogs the drain. If several homes are located on the same terrace, it is a good idea to check with your neighbors. Water backed up on their properly may eventually reach you. Water backed up in surface drains will tend to overflow and seep into the terraces, creating less stable slopes. 2. Don't permit water to gather above or on the edges of slopes (ponding). Water gathering here will tend to either seep into the ground, loosening fill or natural ground, or will overflow on the slope and begin erosion. Once erosion is started, it is difficult lo conlrol and severe damage may result rather quickly. 3. Don't connect roof drains and roof gullers and down spouts lo subdrains. Ralher, arrange them so thai ihey will flow out onto a paved driveway or Ihe slreet where the waler may be dissipated over a wide surface. Subdrains are conslrucled to lake care of ordinary subsurface waler and cannot handle the overload from roofs during a heavy rain. Overloading the subdrains lends to weaken Ihe foundalions. 4. Don't spill waler over slopes, even where this may seem a good way to prevent ponding. This tends lo cause erosion and, in Ihe case of fill, can eal away carefully engineered and compacled land. 5. Don't drop loose fill slopes. It is not compacled lo the same strength as the slop itself and will lend lo slide with heavy moislure. The sliding may clog terrace drains below, or may cause additional damage by weakening the slope. If you live below a slope, try to be sure thai no loose fill is dumped above your properly. 6. Don't discharge waler inlo French drains close lo slopes. French drains are sometimes used lo get rid of excess waler when oilier way of disposing waler are nol readily available. Overloading ihese drains salutales Ihe ground and, if Ihe drains are located close to slopes, may cause slope failure in their vicinity. 7. Don't discharge surface water inlo seplic lanks (leaching fields). Nol only are seplic lanks conslrucled for a differenl purpose, bul Ihey will lend, because of Iheir size, lo naturally accumulate additional waler from Ihe ground during a heavy rain. Overloading ihem articifially during the rainy season is bad for the 435O Palm Avc.. Suite 25. la Mcea, CA 91941 - (619) 462-9061 same reason as subdrains and French drains, and is doubly dangerous because their overflow can pose a serious health hazard. 8. Don't over-irrigate slopes. Naturally, ground cover of ice plant and other "*" vegetation will require some moisture during the hot summer months, but during the wet season, irrigation can cause ice plant and other heavy ground cover to pull loose, which not only destroys the cover, but also starts serious erosion. Planted slopes acquire sufficient moisture when it rains. xm - 9. Don't let water gather against foundations, retaining walls, and basement walls. These walls are build to withstand ordinary moisture in the ground and are, where necessary, accompanied by subdrains to carry off excess. If water is permitted to pond against them, it may seep through them, causing dampness and leakage inside the basement, more important, the water „, pressure can cause heavy structural damage to walls. 10. Don't try to compact backfill behind walls near slopes by flooding. Not only * is flooding the least efficient way of compacting fine-grained soil, but will also undermine or tip the wall. 11. Don't leave a hose and sprinkler remaining on or near a slope, particularly during the rainy season. This will enhance ground saturation and may cause ^ damage. 12. Don't block swales that have been graded around your house or the lot pad. •** These shallow ditches have been put there for the purpose of quickly removing water toward the driveway, street or other positive outlet. By all means, do not let water become ponded above by blocked swales. 435O Palm Avc.. Suit* 25. La Mesa. CA 91941 - (619) 462-9661