NIGUEL SUMMIT HOMEOWNERS ASSOCIATION DHLA PROJECT 15.028.05 % LAW OFFICES OF RuTAN & TUCKEr NOVEMBER 27, 2022
2014. The instrument used to read the casings is an inclinometer probe comprised of two orthogonally-oriented accelerometers. We are using a) the same type of inclinometer probe used by AGI, and b) updated DigiPro2 software developed by the probe manufacturer, the Durham Geo Slope Indicator Company.
A Site Location Map is shown on Plate 1. The locations of the inclinometer casings and piezometers are shown on Plate 2 - Geotechnical Map, based on the original Plate 1 Site Plan prepared by AGI.
REFERENCES
A list of the documents reviewed as part of our preparation of this monitoring report is included in Appendix A.
DISCUSSION
For reference, the 19 slope indicators were read after an approximate ten-to-twelve-month hiatus between late 2021 and November 2022. During our data reduction of those readings, four of the inclinometer casings were found to have exhibited new movement at varying depths.
Those casings were numbers AGI-25, - 26, -27, and -30.
Because the casings are not watertight, we feel that the water levels within each casing will not be representative of the actual water table below the ground surface. Accordingly, for this monitoring report, we have read only the piezometers to establish the present groundwater levels. All of the inclinometer casings were read in November 2022. Changes between the initial and subsequent readings were tabulated during the data processing. The changes between the initial and subsequent readings are displayed on our printouts as linear displacements. Our readings of all of the inclinometer casings done for this sixth monitoring report are included as Appendix B. The piezometer readings are updated in Table 2 below.
We have also included as Appendix C a Top View plot for inclinometers AGI-25, AGI-26, AGI-27, and AGI-30 showing a "birds-eye" view of the movement trends of these four casings between our November 2021 and November 2022 readings, as these casings were the only ones to exhibit some minor movement.
Slope Indicator Readings
Summarized below are the dates the slope inclinometers were read, the casing depths we measured for each inclinometer and other pertinent information. We have kept the same inclinometer identification number as the previous consultant for ease of reference and used their ground surface elevations.
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Table 1: Casing Identification, Length and Casing Tip Elevation Casing Reading Date Length (ft.) Ground Surface Elevation (ft.) Casing Tip Elevation ID (ft.)
AGW-1 11/20/2022 100 518 418
AGW-2 11/20/2022 100 518 418
AGW-3 11/20/2022 104 518 414
AGW-4 11/20/2022 102 518 416
AGW-5 11/20/2022 104 518 414
AGI-10 11/20/2022 65 517 452
AGI-12 11/20/2022 138 517 379
AGI-13 11/20/2022 158 545 387
AGI-14 11/19/2022 128 466 338
AGI-16 11/17/2022 27 538 511
AGI-17 11/17/2022 75 520 445
AGI-18 11/17/2022 74 518 444
AGI-25 11/19/2022 118 460 342
AGI-26 11/19/2022 133 440 307
AGI-27 11/19/2022 139 380 241
AGI-28 11/19/2022 118 461 343
AGI-29 11/19/2022 126 458 332
AGI-30 11/20/2022 34 496 462
AGI-31 11/19/2022 98 422 324
• AGW-1: Our November 20, 2022, reading reveals that our latest data set virtually overlies our original July 24, 2015, reading, and the January 10, 2022, reading indicating virtually no displacement since we began the monitoring in 2015. AGI reported that this casing had cumulative deflections of about 0.25-inch in the upper 60 feet since July 2001. • AGW-2: Our November 20, 2022, reading also overlies our prior data sets and also indicates no displacement. AGI reported that the casing originally hinged at 45 feet deep and, as of 2014, had an into-slope displacement of 0.3-inch since July 2001. • AGW-3: The most current reading (November 20, 2022) lies virtually on our initial July 2015 reading and is essentially the same as our January 10, 2022, data set indicating no displacement compared to our earlier. AGI had reported cumulative displacement of up to 0.2-inch into-slope between July 2001 and May 2014.
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• AGW-4: Our November 20, 2022, reading is basically unchanged from previous data sets, indicating no movement. Below about 26 feet the casing is essentially unchanged from our initial reading on July 25, 2015. AGI reported into-slope cumulative displacement of between 0.15 and 0.20-inch in the upper 10 feet from July 2001 until May 2014.
• AGW-5: Our November 20, 2022, data set overlies the October 2020 reading with a very slight change between about 22 and 46 feet. Movement of the casing of a little over 0.2- inch has developed at a depth of approximately 50 to 68(‡) feet, with the latest reading overlying all previous readings from about 68 feet to the bottom of the casing. AGI reported into-slope cumulative displacement of 0.20-inch in the upper 20 feet from November 1998 until May 2014.
• AGI-10: Our November 20, 2022, reading has moved inward in the upper 59() feet less than 0.1-inch compared to the January 3, 2022, reading on the A-axis. The movement remains less than 0.2-inch at the top of the casing. AGI reported into-slope cumulative displacement of 0.20-inch in the upper 35 feet from November 1998 until May 2014.
• AGI-12: November 20, 2022, reading has moved into slope less than 0.1-inch compared to the January 3, 2022, reading showing that the slight out-of-slope displacement (about ¼-inch at the top of the casing in January 2022) has decreased to about 0.15-inch from our initial July 2015 reading. The A and B axes show a very gradual hinging of the casing from 90 feet deep up to the surface. AGI reported into-slope cumulative displacement of
0.20-inch from 100 to 40 feet deep, where the casing hinged and moved out-of-slope around 0.30-inch from April 1998 until May 2014.
• AGI-13: The November 20, 2022, data exhibit a slight into-slope movement along the A-axis from approximately 140 (*) feet to the ground surface. The movement is a maximum of about 0.1-inch at the top of the casing, tapering gradually to zero at about the 140(÷)-foot depth. AGI reported into-slope cumulative displacement of 0.20-inch in the upper 45 feet from June 1998 until May 2014.
• AGI-14: This inclinometer casing exhibits an out-of-slope casing displacement of about
0.45-inch at a depth of six feet since the July 30, 2015, readings. The most recent reading shows virtually no movement when compared to our November 24, 2021, reading. Our review of the inclinometer data included in the AGI reports shows that the casing had moved out about 2.2 inches between July 1998 and May 2014. The hinge point during that period was roughly about 60 feet below the ground surface. Thus, the accumulative total movement is about 2.7 inches.
• AGI-16: The November 17, 2022, reading shows the trend to be within a few hundredths of an inch into slope from the previous January 11, 2022, reading with about 0.1-inch into-slope movement within the upper three feet. AGI reported out-of-slope cumulative displacement of just over 0.40-inch in the upper 17 feet from November 1999 until May 2014.
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• AGI-17: Our November 17, 2022, reading overlies the January 12, 2022, reading and shows that the casing has not moved further outward since the ¼-inch movement that developed between the September 21, 2020, and January 12, 2022, readings. AGI reported out-of-slope cumulative displacement of 0.30-inch in the upper 25 feet from June 1999 until May 2014. Thus, the total out-of-slope movement of the casing would be on the order of about 0.4 to 0.5-inch. It should be noted that AGI-17 is outside the limits of the repair area.
• AGI-18: The latest reading of this inclinometer (November 17, 2022) shows that the current trend completely overlies the January 12, 2022, reading which had moved into- slope about 0.2-inch compared to the September 21, 2020, reading. AGI reported out- of-slope cumulative displacement of 0.60-inch in the upper 65 feet from May 1999 until May 2014. Thus, the total cumulative displacement has now reduced to about 0.5-inch between 32 and 65 feet. However, the outward bend in the casing is still prevalent between about 16 feet and the top of the casing.
• AGI-25: This inclinometer has moved about 0.35(‡)-inch out-of-slope between July 30, 2015, and November 19, 2022, over a depth of 10 to 48 feet. The trend necks down to a hinge point at 62 feet below the ground surface. Our November 2022 reading has noved slightly outward (about 0.1-inch) since the November 24, 2021, reading. AGI reported out-of-slope cumulative displacement of 0.75-inch in the upper 75 feet from June 2002 until May 2014. The cumulative movement of the casing up to the present is thus a little over one-inch. AGI's cross section D-D' shows that the outward movement, or "possible kickout" (as denoted by AGI), was in the then-active landslide they designated as Qls1, and at a depth of about 38 feet. Where AGI projected the possible kickout onto their cross-section C-C' the "possible kickout" was about 56 (*) below the ground surface, roughly where it is now.
• AGI-26: This inclinometer has developed an out-of-slope movement of about 0.45-inch since our initial July 30, 2015, reading through November 19, 2022. Our latest data set shows that the new casing trend has moved out from a few hundredths of an inch up to about 1/8-inch at the top of the casing, indicating there has been An ongoing, slight, outward displacement. The main hinge in the displacement developed at a depth of about 45 feet. AGI reported out-of-slope cumulative displacement of over 0.60-inch in the upper 50 feet from June 2000 until May 2014. Thus, the total displacement from March 2001 to November 19, 2022, is a little over one inch. Looking at AGI's section D-D' the outward movement appears to be creep-associated movement within the buttress fill. • AGI-27: Below a depth of 31 feet this inclinometer has not moved since our initialization reading in July 2015. Beginning in December 2019, the upper 30 feet of the casing rotated outward sharply almost one inch at the top of the casing for the A-axis and about 0.65-inch along the B-axis over the same depth. The October 24, 2020, reading showed the top of the casing had moved out-of-slope a further 0.3-inch, the November 24, 2021, reading exhibited another 0.33(‡)-inch of movement, and our current (November 19, 2022) reading shows close to an additional 0.2-inch of creep movement for a total July 2015 through November 19, 2022, displacement of https://dbla-my.sharepoint.com/persone1/davidr1_dhla_cov/Documents/PUBLIC/PRQJBCTS/15.028.05 VIA ESTORIL MONITORING REPORT #6/REPQRT/15.028-05 MONITORING REPORT NO 5.docx Page 5
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approximately 1.8 inches along the A-axis and now one inch along the B-axis. AGI reported out-of-slope cumulative displacement of over 0.50-inch in the upper 20 feet from March 2001 until May 2014. Our readings indicate that the upper 20 feet of the casing has moved over 0.8-inch since July 2015 and about 1.4 inches from March 2001 until November 19, 2022, adding in the AGI measured movement. The outward distortion hinges at about 31 feet in the underlying, older landslide debris left in-place that AGI identified as Q|sz. Nearby piezometers AGPZ-5 and "Un-Named #1" both reflect groundwater surfaces within the Qis slide mass, based on the AGI cross section D-D' from the referenced July 2002 AGI report.
• AGI-28: The November 19, 2022, A-axis reading shows that the upper 20 feet of the casing hinges at a depth of about 18(*) feet, displacing outward in a uniform curve to an approximate one inch at the top of the casing. Below about 20 feet the current reading overlies last year's reading. Movement of the B-axis is demonstrating an into-slope movement of an estimated 0.1-inch to 0.15-inch from about 15 to 67 (÷) feet with the upper 15 feet overlying the November 24, 2021, reading. The out-of-slope movement hinges at 52 feet on the A and B axes, with additional southeasterly movement of the casing along the B-axis from 52 feet down to the casing bottom. The inclinometer readings for December 17, 2012, and May 13, 2014 (in the AGI May 19, 2014, report) show a lateral displacement of the casing of about 0.7 to 0.8-inch when compared to their prior March 30, 2004, reading, indicating horizontal movement within the O|s1 landslide mass left in-place. In their November 2002 report, AGI shows the casing in this zone as exhibiting "Possible kickout." The total horizontal movement up to November 19, 2022, is thus nearly two inches.
• AGI-29: Presently, the November 19, 2022, reading virtually overlies the previous two readings from November 2020 and November 24, 2021, and is considered to have had no casing displacement. AGI reported out-of-slope cumulative displacement of over 0.90- inch beginning at a depth of 81 feet from March 2000 and extending up to May 2014, but AGI shows the "Possible kickout" as occurring at a depth of about 65 feet at the contact between slide masses Qls1 and Qls. The total out-of-slope cumulative movement to- date is still about one inch, although the hinge-point is at about the 86-foot depth. • AGI-30: Our present November 20, 2022, reading shows it overlaying the September 21, 2020, reading in the upper five (‡) feet on the A axis, then exhibiting a slight into- slope displacement since 2020. The magnitude is about 1.3 inches since our initial August 2015 reading, beginning at a depth of 12 feet. This upper distortion is within the buttress fill shown on AGI's section E-E'. AGI reported that a lower hinge point had developed at about 26 feet in depth, with an out-of-slope cumulative displacement of about 1.80 inches, hinging at 21 feet from November 2001 until May 2014. This lower hinge point was in the Qls1 slide mass and AGI designated this area as within a "slope creep zone." However, our monitoring since August 2015 has not shown any outward displacement in this lower creep zone.
• AGI-31: Our latest reading on November 19, 2022, overlies the reading from December 27, 2021, and displays a slight into-slope movement. The outward movement is still httpe://dhla-my.ghazeposnc.com/persora1/davidhl_chla_com/Documents/PUBLIC/PRQJ5CTS/15.028.05 VIA ESTORTE MONITORIIG REFORT #6/REPORT/15.028. 05_MONITORING REPORT NO G.DOCX Page 6 NIGUEL SUMMIT HOMEOWNERS ASSOCIATION DHLA PROJECT 15.028.05 % LAW OFFICES OF RUTAN & TUCKER NOVEMBER 27, 2022
about ¼-inch from July 30, 2015, to the present. AGI reported an out-of-slope cumulative displacement of about 0.50-inch in the upper 60 feet from June 2003 until May 2014 with the location of the hinge in the lower area of landslide Qls above the contact between Qls1 and Qisz. Combining the recorded totals indicates that the casing has moved about 0.8-inch since June 2003.
Piezometer Readings
We have previously located six open-standpipe piezometers within the stabilization area.
However, on November 20, 2022, only four piezometers were able to be sounded using an electronic water sounder to measure the depths to the groundwater table (GWT) or perched zones of groundwater. The present water surface is located at or below the water level readings measured in 2020. We still have no additional information regarding the installation of the three additional, unnamed piezometers we discovered in 2016, but they have been located on our Geotechnical Map and are being sounded as part of the monitoring work.
Table 2: Piezometer Reading Summary
Casing ID Reading Date Water Level (fbgs*) 11/2020 Water Level (fbgs*) 11/20/2022
AGP-9 -- 36.4 N/A
AGP-10 11/20/2022 47.7 48.6
AGPZ-5 11/20/2022 34.9 38.8
Un-Named #1 11/20/2022 27.9 32.1
Un-Named #2 11/20/2022 32.0 35.5
Un-Named #3 - 35.0 N/A
fbgs* = feet below ground surface
CONCLUSIONS AND RECOMMENDATIONS
Based on our a) site observations, b) reading of the slope inclinometer casings and piezometers, c) analysis of the data collected and d) review of the referenced reports, we can provide the following conclusions and recommendations regarding the Niguel Summit Landslide Stabilization Area:
1. We did not observe signs of ground cracking or distress in the (a) sidewalk, curb and gutter or pavement wearing surface in Via Estoril or (b) visible portions of the gunite terrace drains on the slopes (appearing largely intact). However, there does appear to be some slight, vee-ditch gunite displacement near AGI-27. Where the gunite was distressed, a filler has been placed into the cracks and it is largely intact.
2. Four of the inclinometers (AGI-25, - 26, - 27, and - 30) show slight, continued, patterns of out-of-slope movement that appear to have developed in the 12 months since we last read these casings. The most logical causes are believed to be a) ongoing movements within the slide masses left in-place during the creation of the buttress stabilization fill and b) slope creep exacerbated by the prior drought years and then re-wetting of the slopes in winter storms.
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3. Inclinometer AGI-28 is showing a deeper hinge point, which suggests deep-seated movement is occurring. As noted in December 2019, our review of the AGI reports mentioned above indicated that significant amounts of landslide debris from the 1998 landslide (Qls1), and an older landslide (Qls2) underlying the 1998 slide, were left in- place. These materials were described as very weak, compressible, soft, and saturated at the time of AGI's exploration just after the 1998 landslide. Our comparison of the hinge points exhibited in some of the inclinometer plots with the AGI cross sections through the stabilization area show that the movement is generally occurring in the upper, newer 1998 landslide along with minor movement in the Qls slide mass and some creep movement within the stabilizing buttress fill.
4. As we have previously noted, the amount of future movement within the landslide masses cannot be established in view of the thicknesses of those materials and their characteristics as noted above. It is likely that several of the casings will "kink" to the point that they can no longer be read. Presently, this would include inclinometers AGI-27, - 28, and -30.
5. It is still our opinion that consideration should be given to continuing an annual geologic reconnaissance of the landslide stabilization area to observe the condition of the vee-ditches and downdrains, whether creep-associated movement in the slopes is affecting those structures, and if there are signs in the slopes of adverse soil or geologic conditions developing.
6. We recommend that the ditches and downdrains be cleaned out as soon as practical considering that we are now in the rainy season. Clogged vee-ditches can lead to over-topping resulting in surficial slope failures.
7. We recommend that any ground subsidence along the top of slope paralleling Via Estoril be monitored, and that we be notified immediately if, or when, it becomes necessary to place more soil on the top of slope portion adjacent to the Via Estoril sidewalk.
8. We further recommend that (a) the inclinometers be read in November 2023, and (b) the landscape maintenance company continue to keep the trails open so that all inclinometers and piezometers on the Association's property can be accessed. This also might entail getting permission from the property owners in the planned development below.
LIMITATIONS
This sixth monitoring report has been prepared for the exclusive use of the Niguel Summit Homeowners Association and the Law Offices of Rutan and Tucker in reference to slope inclinometer and piezometer readings taken within and adjacent to the Niguel Summit Landslide Stabilization Area in Laguna Niguel, California. Our work to prepare this report has been done in accordance with generally accepted geotechnical engineering practices. No other warranty, either expressed or implied, is given.
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DHLA
DHLA PROJECT 15.028.05
NOVEMBER 27, 2022
ATTACHMENTS
The following are attached and complete this report:
Plate 1 -- Site Location Map
Plate 2 Geotechnical Map
Appendix A -- References
Appendix B - Plots for all Inclinometers
Appendix C Top View of AGI-25, 26, - 27, & -30
We appreciate this opportunity to be of continued service, Please call if there are any questions or comments regarding this report.
Respectfully submitted,
David H. Cee & Asaristons na DAVID H. LET
NO ELLIOTY
NO. GE 510
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CIVIL
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David Elliott Lee, PE
Project Engineer Principal Geotechnical Engineer
Distribution: Addressee (1) Via Electronic Mail
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REFERENCE: American Geotechnical Incorporated, ESTIMATED LOCATION OF INCLINOMETER CASING Inclinometer Monitoring Sumary of Findings Niguel NOT TO SCALE PLATE Summit Landslide Stabilization Area, File Number AGP-10 31515-80, dated May 19, 2015. FOR ILLUSTRATIVE PURPOSES ONLY ESTIMATED LOCATON OF PIEZOMETER
APPENDIX A
NIGUEL SUMMIT COMMUNITY ASSOCIATION DHLA PROJECT 15.028.05 % TINNELLY LAW GROUP NOVEMBER 2022
Appendix A
REFERENCES
American Geotechnical, Inc, Inclinometer Monitoring Summary of Findings: Niguel Summit Landslide Stabilization Area, Via Estoril, Laguna Niguel, California, dated May 19, 2014 (Their File No. 31515-80).
- Inclinometer Monitoring Summary of Findings: Nigue/
Summit Landslide Stabilization Area, Via Estoril..., dated January 29, 2013 Their File No. 31515-71).
- Inclinometer Monitoring Summary of Findings: Nigue/
Summit Landslide Stabilization Area, Via Estoril, dated January 14, 2011 (Their File No 31515-70).
,. Long-Term Monitoring Results: Niguel Summit Landslide Stabilization Area Below Via Estoril, Laguna Niguel, California dated September 12, 2005 (Their File No 31515-19).
David H. Lee & Associates, Inc, Initial Monitoring Report for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area of Findings: Niguel Summit Landslide Stabilization Area, Via Estoril, Laguna Niguel, California, dated September 10, 2015 (Our Project No. 15.028.00).
- Monitoring Report for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California, dated June 20, 2016 (Project No. 15.028.00).
_, Monitoring Report for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California, dated April 22, 2019 (Project No. 15.028.01).
_, Monitoring Report for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California, dated January 30, 2020 (Project No. 15.028.02).
, Monitoring Report No. 4 for the Slope Inclinometers
Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California, dated November 7, 2020 (Project No. 15.028.03). -1-
NIGUEL SUMMIT COMMUNITY ASSOCIATON DHLA PROJECT 15.028.05 % TINNELLY LAW GROUP NOVEMBER 2022
Appendix A
REFERENCES
_, Monitoring Report No. 5 for the Slope Inclinometers
Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California, dated January 25, 2022 (Project 15.028.04). -2-
APPENDIX B
152800 AGW_1 A 152800 AGW_1 B
-- 7124/2015 - 6/19/2019 - 9/23/2020 —- 7/24/2015 • 6/19/2019 9/23/2020 - 1/10/2022 - 11/20/2022 → 1/10/2022 → 11/20/2022
0 0
10- 10 -
20 20-
30 30
40 - 40 -
50 - 50 -
Depth in Feet
60 - 60 -
70 70 -
80 - 80 -
90 - 90 -
100 - 100 -
110 + T 110 +
-1 -0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGW_2 A 152800 AGW_2 B
- 7/24/2015 - 6/19/2019 do 9/23/2020 -- 7124/2015 - w 9/23/2020 → 1/10/2022 → 11/20/2022 → 1/10/2022 - 11/20/2022
0 10- 10-
вА..
20 - 20-
30 30
40 40•
50 50 -
Depth in Feet
60 60
70 70
80- 80-
90 90 -
100- 100-
110 + 110 +
-0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGW_3 A 152800 AGW_3 B
- 7125/2015 - 1/10/2022 — 11/20/2022 •- 7/25/2015 - 1/10/2022 - 11/20/2022 0 0
10 - 10-
20-
30 -
40 40-
50 50 -
Depth in Feet Depth in Feet
60 60-
70 70 -
80 - 80 -
90 90 -
100 100 -
110 + 110 +
T T
-1 -0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGW_4 A 152800 AGW_4 B
- 7/25/2015 - 6/20/2019 wai 10/10/2020 - 7/25/2015 - 6/20/2019 s 10/10/2020 — 1/10/2022 -- 11/20/2022 — 1/10/2022 - 11/20/2022
0 H
10 - 10 -
20-
30 30
40 - 40 -
50 50 -
Depth in Feet
60 60 -
70 70
80 - 80 -
90 90 -
100 100 -
110 + 110 -
-1 -0.5 0 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGW_5 A 152800 AGW_5 B
- 7127/2015 - 6/20/2019 readya: 10/10/2020 - 7127/2015 6/20/2019 enders 10/10/2020 - 1/10/2022 → 11/20/2022 → 1/10/2022 11/20/2022
0 0
10. 10 -
20-
30 -
40. 50 -
Depth in Feet Depth in Feet
60 -
70 80- 80-
90 90-
100- 100 -
110 + 110 +
- 1 -0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_10 A 152800 AGI_10 B
- 7129/2015 - 6/20/2019 10/10/2020 I- 7/29/2015 - - 6/20/2019 xia 10/10/2020 → 1/3/2022 → 11/20/2022 - 1/3/2022 → 11/20/2022
10-
Depth in Feet Depth in Feet
ALLELLL
50 50 -
52 52-
54 54 -
56 56 -
58 58
60 60 -
62 - 621
64- 64-
66 66-
68 + T 68 -
-1 -0.5 0 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_12 A 152800 AGL_12 B
- 7128/2015 - 6/21/2019 arms/pc 10/24/202 - 7/28/2015 - 6/21/2019 10/24/2020 - 1/3/202 - 11/20/2022 - 1/3/2022 -pa 11/20/2022
0 10. 10-
20-
30 40
50 Depth in Feet Depth in Feet
80 90 90
100- 100 -
110- 110-
120- 120-
130- 130 -
140 + T 140 +
-1 -0.5 0 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_13 A 152800 AGI_13 B
- 8/1/2015 - 6/21/2019 master. 10/24/2020 --8/1/2015 - 6/21/2019 10/24/2020 - 1/10/2022 - 11/20/2022 + 1/10/2022 про 11/20/2022
70 70
Depth in Feet 80
90 -
100 100 -
110
120
130 - 130 -
140- 140 -
150 - 150-
160 + 160 7
T
-1 -0.5 0 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_14 A 152800 AGI_14 B
- 7/30/2015 - 12/6/2019 11/1/2020 -7/30/2015 в-12/6/2019 11/1/2020 - 11/24/2021 : - 11/19/2022 - 11/24/2021 - 11/19/2022
0 0
10- 10 -
20. 20 -
30 40
50 60
Depth in Feet Depth in Feet
70 80 -
90 -
100 - 100 -
110 - 110 -
120- 120 -
130 + T 130 +
-1 -0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_16 A 152800 AGI_16 B
- 7128/2015 •- 7/6/2019 oran 10/10/2020 - 7/28/2015 - 7/6/2019 • 10/10/2020 -в- 1/11/2022 - 11/17/2022 + 1/11/2022 - 11/17/2022
1 1
2-
3-
5 -
12 TELL
13 Depth in Feet Depth in Feet
19 20 -
211
8₫]873Ñ3800
28-
29 ł
T
-1 -0.5 0.5 1 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_17 A 152800 AGI_17 B
-I- 7/31/2015 --- 127/2019 we 9/21/2020 -- 7/31/2015 -- 12/7/2019 9/21/2020 → 1/12/2022 → 11/17/2022 — 1/12/2022 → 11/17/2022
0 ₫ ₫ ₫₫₫₫ ₫ 9 9 ₫ ₫ 9 9 9 ¿ Depth in Feet
62•
66-
TT 78 -
-1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_18 A 152800 AGI_18 B
-- 7/31/2015 - 12/7/2019 - 9/21/2020 -- 7/31/2015 - 12/7/2019 - 9/21/2020 → 1/12/2022 -p- 11/17/2022 - 1/12/2022 -p 11/17/2022
2 4.
10-
12-
Depth in Feet
76 4
-1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGL 25 A 152800 AGI_25 B
- 7130/2015 12/6/2019 amale 11/1/2020 - 7/30/2015 - 12/6/2019 - 11/1/2020 - 11/24/2021 - 11/19/2022 → 11/24/2021 - 11/19/2022
0 0
10 - 10-
20 - 20 -
30 40
50 -
Depth in Feet Depth in Feet 60
70 80
90 90
100- 100 -
110 - 110-
120 + 120 + T
T
-1 -0.5 0 0.5 1 -1 -0.5 0.5 1
Profile Change in inches Profile Change in Inches
152800 AGI _26 A 152800 AGI_26 B
- 7/29/2015 • 12/6/2019 my 11/1/2020 •- 7129/2015 - 12/6/2019 - 11/1/2020 - 11/24/2021 - 11/19/2022 - 11/24/2021 - 11/19/2022
0 10-
20-
****
1-0-0-
40 40
50 50
60 60
Depth in Feet Depth in Feet 70
80 90 90
100 - 100-
110 -
120-
130 -
130
140 + 140 -
- T T
-0.5 0.5 1 -1 -0.5 0.5 1
Profile Change in inches Profile Change in Inches
152800 AGI_27 A 152800 AGI_27 B
- 7/29/2015 - 12/7/2019 10/24/2020 - 7/29/2015 - 12/7/2019 10/24/2020 - 11/24/2021 - 11/19/2022 → 11/24/2021 - 11/19/2022
0 10 10-
20 20•
50 50
60 60
70 Depth in Feet Depth in Feet
80 90
100
110 110-
120 120 -
130 130-
140 - 140
150 150 +
T
0.5 1.5 - 1.5 -1 -0.5 0.5
Profile Change in Inches Profile Change in Inches
152800 AGI_28 A 152800 AGI_28 B
- 7130/2015 - 12/6/2019 11/1/2020 -- 7/30/2015 12/6/2019 - 11/1/2020 — 11/24/2021 - = 11/19/2022 → 11/24/2021 - 11/19/2022
0 10 - 10 -
20- 20-
30 - 30
40 - 40
50 50
Depth in Feet 60 Depth in Feet 60
70 70-
80 80
90 90 -
100 100 -
110 - 110 -
120 + T 120+
-1 -0.5 0.5 1 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_29 A 152800 AGI_29 B
- 7/30/2015 - 12/6/2019 * 11/1/2020 - 7/30/2015 - 12/6/2019 bon 11/1/2020 - 11/24/2021 - 11/19/2022 - 11/24/2021 - → 11/19/2022
0 0
10- 10-
20 -
20. 30 30 -
40 40-
50 50
60 60
Depth in Feet Depth in Feet
70 80 80
90 90-
100 - 100 -
110 - 110 -
120 - 120 -
130 + 130 +
-1 -0.5 0.5 1 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGI_30 A 152800 AGI_30 B
8/1/2015 - 127/2019 9/21/2020 - 8/1/2015 → 1277/2019 ma 9/21/2020 → 1/11/2022 - 11/20/2022 - 1/11/2022 - 11/20/2022
2 2
3-
4 5 or
6 7
8 9
Depth in Feet Depth in Feet
LL
4725%
36 0 0.5 1 1.5 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
152800 AGL_31 A 152800 AGI|_31 B
- 7/30/2015 -- 12/6/2019 ma 10/10/2020 -- 7/30/2015 - 12/6/2019 10/10/2020 → 12/27/2021 - 11/19/2022 —- 12/27/2021 -p— 11/19/2022
Depth in Feet
75 h
80 -
85 -
90-
95- 95 1
100 + T 100 +
-1 -0.5 0 0.5 -1 -0.5 0 0.5 1
Profile Change in Inches Profile Change in Inches
APPENDIX C
152800 AGI_25 Top View
- 12/6/2019 11/1/2020 - 11/24/2021 → - 11/19/2022
350 10
340- 20
330 30
320 Y 40
310 50
300
60 290 70
280 •80
270 90
0/5 0.25
260 - 100
250• -110
240 \ / 120
230 130
220 140
210 150
200 160
190 180 170
Resultant Profile_Change in Inches
152800 AGI_26 Top View
- 12/6/2019 11/1/2020 - 11/24/2021 - 11/19/2022
350 0 10
340 20
330 30
320 40
310 50
300
60 290 - 70
280-
- 80
270 90
0/5 0.25
260 - - 100
250 - 110
240 < 120
230 130
220 140
210 150
200 160
190 180
Resultant Profile_Change in Inches
152800 AGI_27 Top View
- 12/7/2019 10/24/2020 — 11/24/2021 - 11/19/2022
350 0 10
340 20
330 30
320 / 40
310 50
300
60 290 - 70
280 - - 80
270 90
2 1.5 1 0.5
260 - 100
250 - 110
240 < 120
230 130
220 140
210 150
200 160
190 170
180
Resultant Profile_Change in Inches
152800 AGI_30 Top View
- 12/7/2019 9/21/2020 → 1/11/2022 - 11/20/2022
350 0 10
340 20
330 30
320 40
310 50
300
• 60
290 - 70
280 - 80
270 90
1 0.5
260 -100
250 - 110
240- - 120
230 130
220 140
210 150
200 160
190 180 170
Resultant Profile_Change in Inches
ATTACHMENT F
Slope Monitoring Report Comments by AGI,
November 30, 2022
American Geotechnical, Inc.
GEOTECHNICAL/CIVIL ENGINEERING, TESTING & INSPECTION
November 30, 2022 File No. 33348-08
The Cove at El Niguel
c/o Laguna Niguel Properties, Inc.
27422 Portola Parkway, Suite 300
Foothill Ranch, CA 92610
Attention: Ms. Deborah Hon
Mr. Michael Recupero & Mr. Brian Diaz, Recupero and Associates, Inc.
Subject: COMMENTS TO SLOPE MONITORING REPORT NO. 6 BY DAVID H. LEE AND ASSOCIATES DATED NOVEMBER 27, 2022
The Cove at El Niguel Project
30667 Crown Cove Parkway
Laguna Niguel, California
References: MONITORING REPORT NO. 6 FOR THE SLOPE INCLINOMETERS INSTALLED WITHIN THE NIGUEL SUMMIT LANDSLIDE STABILIZATION AREA. LAGUNA NIGUEL,
CALIFORNIA
By David H. Lee and Associates (DHLA)
Dated: November 27, 2022
SUPPLEMENTAL LETTER OF OPINIONS
By: American Geotechnical, Inc. (File No.: 33348-08)
Dated: November 22, 2022
Dear Ms. Hon:
The undersigned and American Geotechnical, Inc. (AGI) have appreciated the opportunity to review the above referenced report pertaining to David H. Lee and Associates' (DHLA's) most recent readings of nineteen (19) inclinometers on the Niguel Summit Property and also those located on The Cove at El Niguel (The Cove) property as well as four (4) piezometers on The Cove property. The purpose of this report is to provide our peer review comments to DHLA's slope monitoring report No. 6 on the readings of the 19 inclinometer casings and 4 piezometers taken by DHLA from July/August of 2015 to November of 2022.
American Geotechnical, Inc. (AGI) received a copy of the referenced monitoring report from Mr. Michael Recupero at Recupero & Associates on November 28, 2022. The referenced monitoring report is entitled, "Monitoring Report No. 6 for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California," prepared by Niguel Summit HOA's geotechnical consultant, David H. Lee and Associates (DHLA) dated November 27, 2022. The referenced monitoring report by 22725 Old Canal Road, Yorba Linda, CA 92887 - (714) 685-3900 - FAX (714) 685-3909 4901 Morena Boulevard, Suite 1110, San Diego, CA 92117 - (858) 450-4040 - FAX (858) 457-0814 3100 Fite Circle, Suite 103, Sacramento, CA 95827 - (916) 368-2088 - FAX (916) 368-2188 5600 Spring Mountain Road, Suite 201, Las Vegas, NV 89146 - (702) 562-5046 - FAX (702) 562-2457 File No. 33348-08
November 30, 2022
DHLA presents the results of their sixth set of slope indicator readings for the nineteen (19) slope inclinometer casings and four (4) open standpipe piezometers installed in and adjacent to the Niguel Summit landslide stabilization area in the city of Laguna Niguel, California. AGI previously prepared a letter, entitled, "Supplemental Letter of Opinions", dated November 22, 2022 providing our comments on the readings of the nineteen (19) inclinometer casings taken by DHLA from 2015 to January 2022. The Monitoring Report No. 6 included the most recent readings of the 19 inclinometer casings and 4 piezometer readings taken by DHLA in November 2022.
A copy of DHLA's Monitoring Report No. 6 is attached in Appendix A for reference. DHLA's comments on the readings are repeated herein in Italic font followed by our peer review comments. Our more detailed analyses/rebuttal of DHLA's most recent findings is presented in the following report, but a brief executive summary is presented below.
EXECUTIVE SUMMARY
No concern is levied by DHLA with respect to the Niguel Summit property which is, of course, the key interest of their client. Not one of the four plots (i.e., AGI-25, AGI-26, AGI-27, and AGI-30) show even the slightest "blip" on the profile indicative of landslide creep at depth or any likelihood of a landslide reoccurrence like what happened in 1998 (i.e., the Via Estoril Landslide).
DHLA opines in the last sentence of their executive summary that, relative to the Cove project, "The present creep rates shown in these lower inclinometers indicate that ongoing creep will damage rear-yard appurtenances and ultimately the structures themselves." AGI does not believe that the data support this conclusion by DHLA.
It appears that DHLA largely relies on the readings of the inclinometers AGI-25, AGI-26, AGI-27, and AGI-30. The most recent DHLA data, read in November 2022, does show upper soil creep rates ranging from about 0.04-inches per year (AGI-25) to about 1/4-inch per year (AGI-27). These rates are within what we typically find in southern California and Orange County expansive soil hillsides. DHLA's emphasis is on the readings of the inclinometer AGI-27 with the rate of about 1/4-inch per year. A closer examination indicates a slowing of the rate to about 0.2-inches per year in the final reading set (i.e., November 2021-2022 readings). This rate is normal, but, as importantly, this inclinometer is at the toe of the buttress where an MSE (Mechanically Stabilized Earth) retaining wall will be built and the soil will be substantially reinforced with high-strength geogrids which provide more stability than exists in the current File No. 33348-08
Pagember 30, 2022
configuration. Logically, long-term creep rates will be slower. If for the sake of perspective, we assume the rate will continue at 0.2-inches per year (and we assume there was no mitigating work performed), we estimate that it would take approximately twelve hundred (1,200) years for the slope to creep to the back of the structures at the proposed The Cove property, roughly 20-feet away from the proposed MSE wall.
Simply stated, AGI is pleased to see that the recent DHLA data completely supports the conclusion that The Cove at El Niguel project can be built without risk of the 1998 Via Estoril Landslide reoccurrence or any other abnormal risks.
We believe this is the information that you require at this time. Should you have any questions regarding the information provided in this report, please do not hesitate to contact our office.
Respectfully submitted,
ORD PROTEISIONA No. GE103
AMERICAN GEOTECHNICAL, INCHIU HUANG
NEER
in / fua No. GE2601 SE OF CALA
keith
Rei chiu (Jerry) Huang, Ph.D. Gregory W. Axten
Principal Engineer A OPCAPOA President/CEO
G.E. 2601 G.E. 103
Distribution: Addressee (Email: [email protected]) Mr. Michael Recupero (Email: [email protected])
Enclosures: Appendix A - Monitoring Report No. 6 by David H. Lee and Associated Dated November 27,2022
SP/33348-08 Comments to Slope Monitoring Report No. 6 GWA JH 11-30-22 DL File No. 33348-08
November 30, 2022
1.0 AGI COMMENTS ON DHLA'S INCLINOMETER READINGS
Inclinometer AGW-1 (Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022,
Our November 20, 2022, reading reveals that our latest data set virtually overlies our original July 24, 2015, reading, and the January 10, 2022, reading indicating virtually no displacement since we began the moinitoring in 2015. AGI reported that this casing had cumulative deflections of about 0.25-inch in the upper 60 feet since July 2001.
AGI Response:
Our review of the profile change plots for inclinometer AGW-1 casing revealed that the displacement is about 0.1 inches at ground surface over about seven and one-third (7-1/3) years monitoring period by DHLA. The rate of movement is about 0.01 inches per year. Overall, no landslide-related displacement was noted in inclinometer AGW-1 readings.
Inclinometer AGW-2
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 3) Our November 20, 2022, reading also overlies our prior data sets and also indicates no displacement.
AGI reported that the casing originally hinged at 45 feet deep and, as of 2014, had an into-slope displacement of 0.3-inch since July 2001.
AGI Response:
Our review of the profile change plots for inclinometer AGW-2 revealed that the displacement is an into- slope displacement at ground surface. Overall, no landslide-related displacement was observed in inclinometer AGW-2 readings. It is worthy of note that likely pipe compression features were noted at various depths in both A-axis and B-Axis profile change plots of inclinometer AGW-2 readings.
File No. 33348-08
Pagember 30, 2022
Inclinometer AGW-3
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 3) The most current reading (November 20, 2022) lies virtually on our initial July 2015 reading and is essentially the same as our January 10, 2022, data set indicating no displacement compared to our earlier. AGI had reported cumulative displacement of up to 0.2-inch into-slope between July 2001 and May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGW-3 revealed that no displacement is noted at ground surface and at depths. Overall, no landslide-related displacement was noted in inclinometer AGW-3 readings. It is worthy of note that possible pipe compression features were also noted at depths in both A-axis and B-axis profile change plots of inclinometer AGW-3 readings.
Inclinometer AGW-4
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) Our November 20, 2022, reading is basically unchanged from previous data sets, indicating no movement. Below about 26 feet the casing is essentially unchanged from our initial reading on July 25, 2015. AGI reported into-slope cumulative displacement of between 0.15 and 0.20-inch in the upper 10 feet from July 2001 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGW-4 revealed essentially no displacement at ground surface and at depths. Overall, no landslide-related displacement was noted in inclinometer AGW-4 readings. It is worthy of note that possible pipe compression features were noted at various depths in both A-axis and B-axis profile change plots of inclinometer AGW-4 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGW-5
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) Our November 20, 2022, data set overlies the October 2020 reading with a very slight change between about 22 and 46 feet. Movement of the casing of a little over 0.2-inch has developed at a depth of approximately 50 to 68 (‡) feet, with the latest reading overlying all previous readings from about 68 feet to the bottom of the casing. AGI reported into-slope cumulative displacement of 0.20-inch in the upper 20 feet from Movember 1998 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGW-5 revealed into-slope displacement at ground surface for the most recent readings. The displacement of the casing of a little over 0.2-inch at a depth of approximately 50 to 68 (t) is most likely a result of pipe compression. Such pipe compression features were also noted in the readings at other inclinometer casings (e.g., AGW-2, AGW-3, AGW-4, etc.) Inclinometer AGI-10
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) Our November 20, 2022, readings has moved inward in the upper 59(+) feet less than 0.1-inch compared to the Janury 3, 2022, reading on the A-axis. The movement remains less than 0.2-inch at the top of the casing. AGI reported into-slope cumulative displacement of 0.20-inch in the upper 35 feet from November 1998 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGI-10 revealed that DHLA's November 20, 2022 readings into-slope displacement from the previous January 3, 2022 readings. Overall, no landslide- related displacement was noted in inclinometer AGI-10 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-12
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) November 20, 2022, reading has moved into slope less than 0. 1-inch compared to the January 3, 2022, reading showing that the slight out-of-slope displacement gabout ¼-inch at the top of the casing in January 2022) has decreased to about 0. 15-inch from our initial July 2015 reading. The A and B axes show a very gradual hinging of the casing from 90 feet deep up to the surface. AGI reported into-slope cumulative displacement of 0.20-inch from 100 to 40 feet deep, where the casing hinged and moved out-of-slope around 030-inch from April 1998 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGI-12 revealed no landslide-related displacement noted in inclinometer AGI-12 readings.
Inclinometer AGI-13
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) The November 20, 2022, data exhibit a slight into-slope movement along the A-axis from approximately 140 (+) feet to the ground surface. The movement is a maximum of about 0.1-inch at the top of the casing, tapering gradually to zero at about the 140(+)-foot depth. A GI reported into- slope cumulative displacement of 0.20-inch in the upper 45 feet from June 1998 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGI-13 revealed no landslide-related displacement noted in inclinometer AGI-13 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-14
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) This inclinometer casing exhibits an out-of-slope casing displacement of about 0.45-inch at a depth of six feet since the July 30, 2015, readings. . The most recent reading shows virtually no movement when compared to our November 24, 2021, reading. Our review of the inclinometer data included the AGI reports shows that the casing had moved out about 2.2 inches between July 1998 and May 2014.
The hinge point during that period was roughly about 60 feet below the ground surface. Thus, the accumulative total movement is about 2.7 inches.
AGI Response:
Our review of the profile change plots for inclinometer AGI-14 revealed classic creep-related displacement. • Overall, no landslide-related displacement was noted in the inclinometer AGI-14 readings.
Inclinometer AGI-16
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 4) The November 17, 2022, reading shows the trend to be within a few hundredths of an inch into slope from the previous January 11, 2022, reading with about 0. 1-inch into-slope movement within the upper three feet. AGI reported out-of-slope cumulative displacement of just over 0.40-inch in the upper 17 feet from November 1999 until May 2014.
AGI Response:
Our review of the profile change plots for inclinometer AGI-16 revealed classic creep-related displacement in the inclinometer AGI-16 readings. Overall, no landslide-related displacement was noted in the inclinometer AGI-16 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-17
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 5) Our November 17, 2022, reading overlies the January 12, 2022, reading and shows that the casing has not moved further outward since the ¼-inch movement that developed between the September 21,2020, and January 12, 2022, readings. AGI reported out-of-slope cumulative displacement of
0.30-inch in the upper 25 feet from June 1999 until May 2014. Thus, the total out-of-slope movement of the casing would be on the order of about 0.4 to 0.5-inch. It should be noted that AGI-17 is outside the limits of the repair area.
AGI Response:
Our review of the profile change plots for inclinometer AGI-17 revealed classic creep-related displacement. Inclinometer AGI-17 is located outside the east boundary of the previous Via Estoril Landslide Repairs area. Overall, no landslide-related displacement was noted in the inclinometer AGI-17 readings.
Inclinometer AGI-18
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 5) The latest reading of this inclinometer (November 17, 2022) shows that the current trend completely overlies the January 12, 2022, reading which had moved into-slope about 0.2-inch compared to the September 21, 2020, reading. AGI reported out-of-slope cumulative displacement of 0.60-inch in the upper 65 feet from May 1999 until May 2014. Thus, the total cumulative displacement has now reduced to about 0.5-inch between 32 and 65 feet. However, the outward bend in the casing is still prevalent between about 16 feet and the top of the casing.
AGI Response:
Our review of the profile change plots for inclinometer AGI-18 revealed no displacement between DHA's latest readings taken on November 17, 2022 and previous readings taken on January 12, 2022. The displacement is classic creep-related displacement. Overall, no landslide-related displacement was noted in the inclinometer AGI-18 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-25
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 5) This inclinometer has moved about 0.35(+)-inch out-of-slope between July 30, 2015, and November 19, 2022, over a depth of 10 to 48 feet. The trend necks down to a hinge point at 62 feet below the ground surface. Our November 2022 reading has moved slightly outward (about 0. 1-inch) since the November 24, 2021, reading. AGI reported out-of-slope cumulative displacement of 0.75-inch in the upper 75 feet from June 2002 until May 2014. The cumulative movement of the casing up to the present is thus a little over one-inch. AGI's cross section D-D' shows that the outward movement, or "possible kickout" (as denoted by AGI), was in the then-active landslide they designated as Qls1, and at a depth of about 38 feet. Where AGI projected the possible kickout onto their cross-section C-C' the "possible kickout" was about 56 (+) below the ground surface, roughly where it is now.
AGI Response:
Our review of the profile change plots for inclinometer AGI-25 revealed classic creep-related displacement. The displacement of about 0.35(‡)-inch out-of-slope between July 30, 2015 and November 19, 2022 readings is equivalent to about 0.05 inches per year of creep-related movement.
Overall, no landslide-related displacement was noted in the inclinometer AGI-25 readings. The readings also show possible buckling pipe features at depths between 70 and 80 feet.
Inclinometer AGI-26
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 5) This inclinometer has developed an out-of-slope movement of about 0.45-inch since our initial July 30, 2015, reading through November 19, 2022. Our latest data set shows that the new casing trend has moved out from a few hundredths of an inch up to about 1/8-inch at the top of the casing, indicating there has been An ongoing, slight, outward displacement. The main hinge in the displacement developed at a depth of about 45 feet. AGI reported out-of-slope cumulative displacement of over
0.60-inch in the upper 50 feet from June 2000 until May 2014. Thus, the total displacement from March 2001 to November 19, 2022, is a little over one inch. Looking at AGI's section D-D' the outward movement appears to be creep-associated movement within the buttress fill.
AGI Response:
Our review of the profile change plots for inclinometer AGI-26 revealed classic creep-related displacement. The displacement of an out-of-slope movement of about 0.45-inch since DHLA's initial File No. 33348-08
November 30, 2022
July 30, 2015 readings through November 19, 2022 is equivalent of about 0.06 inches per year of creep- related movement. DHLA agrees that "the outward movement appears to be creep-associated movement within the buttress fill." Overall, no landslide-related displacement was noted in the inclinometer AGI-26 readings.
Inclinometer AGI-27
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 5-6) Below a depth of 31 feet this inclinometer has not moved since our initialization reading in July 2015.
Beginning in December 2019, the upper 30 feet of the casing rotated outward sharply almost one inch at the top of the casing for the A-axis and bout 0.65-inch along the B-axis over the same depth. The October 24, 2020, reading showed the top of the casing had moved out-of-slope a further 0.3-inch, the November 24, 2021, reading exhibited another 0.33(+)-inch of movement, and our current (November 19, 2022) reading shows close to an additional 0.2-inch of creep movement for a total July 2015 through November 19, 2022, displacement of approximately 1.8 inches along the A-axis and now one inch along the B-axis. AGI reported out-of-slope cumulative displacement of over 0.50-inch in the upper 20 feet from March 2001 until May 2014. Our readings indicated that the upper 20 feet of the casing has moved over 0.8-inch since July 2015 and about 1.4 inches from Marcy 2001 until November 19, 2022, adding in the AGI measured movement. The outward distortion hinges at about 31 feet in the underlying, older landslide debris left in-place that AGI identified as QIs. Nearby piezometer AGPZ-5 and "Un-Named #1" both reflect groundwater surfaces within the QIsz slide mass, based on the AGI cross section D-D' from the referenced July 2002 AGI report.
AGI Response:
Our review of the profile change plots for inclinometer AGI-27 revealed creep-related displacement from ground surface to depth of about 31 feet below ground surface (bgs). The approximately 1.8 inches of total creep-related movement measured from July 2015 through November 19, 2022 readings is equivalent to about 0.25 inches per year of creep-related movement. The overall rate of displacement at ground surface is about 0.2 inches per year. Creep at this location is likely aggravated by drying subsidence. This is also the area that the Cove development is planning an MSE retaining wall with the soil behind the wall highly reinforced. As such, future creep influence should be at a slower rate. Overall, no landslide-related displacement was noted in inclinometer AGI-27 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-28
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 6) The November 19, 2022, A-axis reading shows that the upper 20 feet of the casing hinges at a depth of about 18(+) feet, displacing outward in a uniform curve to an approximate one inch at the top of casing. Below about 20 feet the current reading overlies last year's reading. Movement of the B-axis is demonstrating an into-slope movement of an estimated 0. 1-inch to 0. 15-inch from about 15 to 67 (+) feet with the upper 15 feet overlying the November 24, 2021, reading. The out-of-slope movement hinges at 52 feet on the A and B axes, with additional southeasterly movement of the casing along the B-axis from 52 feet down to the casing bottom. The inclinometer readings for December 17, 2012, and May 13, 2014 (in the AGI May 19, 2014, report) show a lateral displacement of the casing of about 0.7 to 0.8-inch when compared to their prior March 30, 2004, reading, indicating horizontal movement within the Qis, landslide mass left in-place. In their November 2002 report, AGI shows the casing in this zone as exhibiting "Possible kickout." The total horizontal movement up to November 19, 2022, is thus nearly two inches.
AGI Response:
Our review of the profile change plots for inclinometer AGI-28 revealed creep-related displacement from ground surface to depth of about 52 feet below ground surface (bgs). Overall, no landslide-related displacement was noted in inclinometer AGI-28 readings. DHLA indicated that the total horizontal movement up to November 19, 2022 readings is nearly two inches since 2002 readings, roughly 20 years monitoring period. As such, the rate of displacement is about 0.1 inches per year in the inclinometer AGI- 28 casings. It is worthy to note that the possible pipe buckling feature was noted at depths between 68 and 74 feet.
File No. 33348-08
November 30, 2022
Inclinometer AGI-29
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 6) Presently, the November 19, 2022, reading virtually overlies the previous two readings from November 2020 and November 24, 2021, and is considered to have had no casing displacement.
AGI reported out-of-slope cumulative displacement of over 0.90-inch beginning at a depth of 81 feet from March 2000 and extending up to May 2014, but AGI shows the "Possible kickout" as occurring at a depth of about 65 feet at the contact between slide masses Qls, and Qls2. The total out-of-sloe cumulative movement to date is still about one inch, although the hinge-point is at about the 86-foot depth.
AGI Response:
Our review of the profile change plots for inclinometer AGI-29 revealed creep-related displacement with creep zone at depths between 82 and 86 feet below ground surface (bgs). It is also noted that the creep zone is likely associated with pipe buckling. Overall, no landslide-related displacement was noted in inclinometer AGI-29 readings.
Inclinometer AGI-30
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 6) Our present November 20, 2022, reading shows it overlaying the September 21, 2020, reading in the upper five (‡) feet on the A axis, then exhibiting a slight into-slope displacement since 2020. The magnitude is about 1.3 inches since our initial August 2015 reading, beginning at a depth of 12 feet.
This upper distortion is within the buttress fill shown on AG/'s section E-E'. AGI reported that a lower hinge point had developed at about 26 feet in depth, with an out-of-slope cumulative displacement of about 1.80 inches, hinging at 21 feet from November 2001 until May 2014. This lower hinge point was in the Qls1 slide mass and AGI designated this area as within a "slope creep zone." However, our monitoring since August 2015 has not shown any outward displacement in this lower creep zone.
AGI Response:
Our review of the profile change plots for inclinometer AGI-30 revealed creep-related displacement in the inclinometer AGI-30 readings. Overall, no landslide-related displacement was noted in the inclinometer AGI-30 readings.
File No. 33348-08
November 30, 2022
Inclinometer AGI-31
(Excerpt from DHLA's Monitoring Report No. 6, dated November 27, 2022, Page 6-7) Our latest reading on November 19, 2022, overlies the reading from December 27, 2021, and displays a slight into-slope movement. The outward movement is still about ¼-inch from July 30, 2015, to the present. AGI reported an out-of-slope cumulative displacement of about 0.50-inch in the upper 60 feet from June 2003 until May 2014 with the location of the hinge in the lower area of landslide Qls, above the contact between Qls, and QIs2. Combining the recorded totals indicates that the casing has moved about 0.8-inch since June 2003.
AGI Response:
Our review of the profile change plots for inclinometer AGI-31 revealed creep-related displacement with creep zone at depths between 58 and 62 feet below ground surface (bgs). Overall, no landslide-related displacement was noted in the inclinometer AGI-31 readings.
2.0 AGI COMMENTS ON DHLA'S PIEZOMETER READINGS
Our review of DHLA's piezometer readings at four out of the six piezometers located within The Cove at El Niguel property revealed that the measured groundwater level is relatively stable when compared to previous readings. Minor variations in water levels occur, as can be expected. As DHLA pointed out that the present water surface is located at or below the water level readings measured by DHLA in 2020.
DHLA's piezometer readings indicate that the back drains previously installed during Via Estoril Landslide Repairs are performing rather well as designed and anticipated. Additionally, the existing storm drains within The Cove property is also functioning well with no blockage in the storm drain system within The Cove property.
3.0 AGI COMMENTS ON TOP VIEW PLOTS OF INCLINOMETER READINGS In addition to the detailed review of DHLS's profile change plots for the nineteen (19) inclinometer readings, AGI reviewed in detail the four (4) top view plots of the inclinometer readings for inclinometers AGI-25, AGI-26, AGI-27, and AGI-30. As indicated by DHLA in their November 27, 2022 report, these casings were the only ones to exhibit some minor movement, the movement in those casings is creep related to the upper soil horizons. There is absolutely no indication of landslide movement in the plots.
These four top view plots, in general, show a "birds-eye" view of the movement trends of these four casings between DHLA's November 2021 and November 2022 readings. Our review of these four top File No. 33348-08
lovember 30, 202
age 1!
view plots revealed that the direction of movement in these four inclinometers are pointing to various directions and are not pointing toward the same or similar direction suggesting that the horizontal displacements shown in these four top view plots are clearly related to slope creep influence and not landslide-related displacement.
4.0 CONCLUSION
Our review of the inclinometer and piezometer readings by Niguel Summit's geotechnical consultant, David H. Lee and Associates (DHLA) revealed that a total of nineteen (19) inclinometers and four out of the six piezometers were read by DHLA in November 2022. Sixteen (16) of these inclinometers (AGW-1 through AGW-5, AGI-10, AGI-12 through AGI-14, AGI-16 through AGI-18, AGI-25, AGI-28 through AGI- 30) are located within the Niguel Summit HOA property and three (3) of them (AGI-26, AGI-27, and AGI- 31) are located within The Cove at El Niguel property. All nineteen (19) inclinometers had a base reading taken by DHLA in July/August of 2015 and subsequent readings were taken in 2019 and 2020, as well as January and November of 2022. The last readings were taken in November of 2022. It appears that DHLA set up their own base readings in 2015 and continued their inclinometer readings through November of 2022. The inclinometers consist of profile change plots for all nineteen (19) inclinometers as well as four (4) top view plots of inclinometers at AGI-25, AGI-26, AGI-27, and AGI-30. These top view plots illustrate the direction of inclinometer movement of these four inclinometers.
Based on our review and detailed analyses of the nineteen (19) inclinometer profile change plots, it is our opinion that all readings taken by Niguel Summit HOA's geotechnical consultant, David H. Lee & Associates (DHLA), indicated no apparent, disruptive shear displacement in any of the readings performed by DHLA from 2015 to November of 2022. Given our prior experience with reading all of the inclinometers, we can safely say analysis of readings as far back as the year 2000 do not support the conclusion that there is any risk of landslide recurrence. Simply stated, the inclinometer data shows no indication of landslide-related movement. Four inclinometers (i.e., AGI-25, AGI-26, AGI-27, and AGI-30) as pointed by DHLA show some minor soil creep-related movement, but the rate of movement in these inclinometers show not more than about 1/4-inch per year which is consistent with typical, normal slope creep movement in southern California. Most recent readings indicate that even that rate has slowed to about 0.2-inches per year. Additionally, our review of the directions of inclinometer movement illustrated in the top view plots revealed that the direction of movement in these inclinometers are pointing to various directions and are not pointing toward the same or similar direction suggesting that the movement shown in these inclinometers are essentially related to slope creep influence.
File No. 33348-08
November 30, 2022
It is worthy of pointing out that further examination of these inclinometer plots revealed that we may be beginning to see the effect of moisture-loss related subsidence inducing casing compression. Such conditions could enlarge the apparent creep influence and sometimes even a little buckle may appear where the casing hits the harder material at depth. Throughout Orange County in the past approximately ten years or more, we have found that the drought and less irrigation are influencing slope behavior. As stated earlier, the inclinometer readings by DHLA were conducted from July/August of 2015 to November of 2022. It should be noted that in the years prior to 2015, when American Geotechnical, Inc. (AGI monitored these inclinometers, there was similarly no indication of landslide movement shown in the inclinometer readings taken by our office.
In summary, results of the nineteen (19) inclinometer readings taken within the Niguel Summit HOA and The Cove at El Niguel properties by Niguel Summit HOA's geotechnical engineer, David H. Lee and Associates (DHLA) clearly indicate that the subject slope, after the Via Estoril Landslide Repair, is performing rather well as designed and anticipated, and the inclinometer data shows no indication of landslide-related movement.
Furthermore, the piezometer readings taken by DHLA at four out of the six piezometers located within The Cove at El Niguel property show that the groundwater levels are at or below the water level readings measured by DHLA in 2020. Minor variations in water levels occur as can be expected. It's our opinion that the piezometer readings measured by DHLA further support our conclusion that the back drains previously installed during Via Estoril Landslide Repairs are performing rather well as designed and anticipated. The existing storm drain system within The Cove Project also performs rather well without any blockage in the storm drain system. These conditions further support AGI's opinion that there is no landslide-related movement occurred in the subject slope.
5.0 CLOSURE
The conclusion presented in this rebuttal comments report are based upon our detailed review of the most-recent Monitoring Report No. 6 by Niguel Summit HOA's geotechnical consultant, David H. Lee and Associates (DHLA), as well as our understanding of the previous Via Estoril Landslide Repairs project as well as the current proposed The Cove at El Niguel Project, as well as our professional experience and judgment. If new and/or additional monitoring reports are provided in the future, American Geotechnical, Inc. (AGI) is pleased to review and provide our comments on those new, additional information.
ATTACHMENT G
Geotechnical Review Memorandum by GMU,
December 1, 2022
CITY OF LAGUNA NIGUEL
30111 Crown Valley Parkway
Laguna Niguel, California 92677
Phone (949) 362-4300 | Fax (949) 362-4340
GEOTECHNICAL REVIEW SHEET
Reviewed by:
GMU GEOTECHNICAL, INC.
23241 Arroyo Vista
Rancho Santa Margarita, CA 92688
(949) 888-6513 • Fax: (949) 888-1380 • email: [email protected] Page 1 REFERENCE NO.: SP16-04 DATE: December 2, 2022
PROJECT DESCRIPTION: The Cove at El Niguel (multi-family residential development) LOCATION: 30667 Crown Valley Parkway
DEVELOPER/OWNER: Laguna Niguel Properties, Inc.,
GEOTECHNICAL FIRM: American Geotechnical. Inc.
THEIR JOB NO.: 33348-08
GEOTECHNICAL ENGINEER: Fei-chiu Huang (GE 2601) and Gregory Axten (GE 103) ENGINEERING GEOLOGIST: None
DOCUMENT REVIEWED: (1) "Comments to Slope Monitoring Report No. 6 by David H. Lee and Associates dated November 27, 2022, The Cove at El Niguel, 30667 Crown Valley Parkway, Laguna Niguel, California," prepared by American Geotechnical, Inc,. dated November 30, 2022; (2) "Monitoring Report No. 6 for the Slope Inclinometers Installed within the Niguel Summit Landslide Stabilization Area, Laguna Niguel, California," prepared by David H. Lee & Associates, Inc., dated November 27, 2022.
PREVIOUSLY REVIEWED: (1) "Geotechnical Review of Tentative Tract Map, Tenatative Tract No. 17721, The Cove at El Niguel, 30667 Crown Valley Parkway, Laguna Niguel, California," prepared by American Geotechnical, Inc,. dated January 8, 2021; (2) Tentative Tract Map No. 17721, The Cove at El Niguel, 30667 Crown Valley Parkway, Laguna Niguel, prepared by Hunsaker & Associates Irvine, Inc., dated January 21, 2021; (3) "Response to City of Laguna Niguel Geotechnical Review Sheet Dated February 15, 2021 and Notice of Incompleteness dated February 23, 2021, Tentative Tract No. 17721, The Cove at El Niguel, 30667 Crown Valley Parkway, Laguna Niguel, California," prepared by American Geotechnical, Inc,. dated April 2, 2021; (4) "Addendum Report - Adding Geology to Current Site Plan, The Cove at El Niguel, 30667 Crown Valley Parkway, Laguna Niguel, California," prepared by American Geotechnical, Inc,. dated April 2, 2021.
REVIEW TYPE: Planning Level Only
ACTION:
RECOMMENDED APPROVAL OF DOCUMENTS) SUBMITTED
CONDITIONAL APPROVAL OF DOCUMENTS) SUBMITTED - See Page 4.
REQUEST ADDITIONAL DATA FOR REVIEW.
CITY OF LAGUNA NIGUEL
30111 Crown Valley Parkway
Laguna Niguel, California 92677
Phone (949) 362-4300 | Fax (949) 362-4340
GEOTECHNICAL REVIEW SHEET
Reviewed by:
GMU GEOTECHNICAL, INC.
23241 Arroyo Vista
Rancho Santa Margarita, CA 92688
(949) 888-6513 • Fax: (949) 888-1380 • email: [email protected] Page 2 REFERENCE NO.: SP16-04 DATE: December 2, 2022
REVIEW OF CURRENTLY SUBMITTED DOCUMENTS
GMU has reviewed the recent slope inclinometer data, as well as the letters from David H. Lee & Associates, Inc. (DHLA) and American Geotechnical, Inc. (AGI) summarizing their interpretations and opinions regarding the inclinometer data.
Both letters concur that:
• Groundwater levels as measured are unremarkable.
• No deep-seated landslide movement is occurring.
• Slope creep-type movements are occurring in some installations. • The movements noted are not significant.
The DHLA letter states that:
• "New movement" is noted in AGI-25, AGI-26, AGI-27, and AGI-30. • Causal mechanism for this movement is either movement within the landslide mass or slope creep. • Creep rates indicate that rear-yard improvements and ultimately the structures will be damaged. • NOTE: There is no quantitative analyses within the letter to justify this statement.
The AGI letter states that:
• AGI-25, AGI-26, AGI-27, and AGI-30 does not show any landslide creep at depth or any landslide reoccurrence.
• DHLA's opinion that The Cove project will be damaged is not supported by the data. • Creep rates noted in the inclinometers are within typical limits for southern California and Orange County.
• Direction of creep movements are not consistent between installations. • "Moisture-loss related subsidence inducing casing compression" may be the cause of deflection of multiple inclinometer casings.
• If creep rate in AGI-27 is extrapolated (assumes 0.2 inches per year) in 1,200 years, the structures would be affected.
• Analyses of readings dating back to 2000 do not support any recurrence of landsliding. • The inclinometer data supports AGI's conclusion that The Cove is safe from risk of landslide reoccurrence or other abnormal risk.
CITY OF LAGUNA NIGUEL
30111 Crown Valley Parkway
Laguna Niguel, California 92677
Phone (949) 362-4300 | Fax (949) 362-4340
989
GEOTECHNICAL REVIEW SHEET
Reviewed by:
GMU GEOTECHNICAL, INC.
23241 Arroyo Vista
Rancho Santa Margarita, CA 92688
(949) 888-6513 • Fax: (949) 888-1380 • email: [email protected] Page 3 REFERENCE NO.: SP16-04 DATE: December 2, 2022
GMU concurs that:
• Deflections noted in the plots suggest creep-related movements. • There is no evidence of movement of the remnant landslide mass or the underlying bedrock. • Creep rates noted are generally typical for the area. • DHLA's conclusion of damage to The Cove project is not supported by the data and does not appear to be valid.
• AGI's conclusions regarding the feasibility of the proposed project are valid.
In summary, based on the inclinometer data presented in the DHLA letter dated November 27, 2022, the movement that has occurred is minor and there is no evidence that slope-related movements will adversely impact the proposed The Cove at El Niguel project. The letter provided by AGI (the Geotechnical Engineer of Record) dated November 30, 2022, states clearly that the proposed project is safe from risk of landslide reoccurrence. We concur with AGI's findings, and it is GMU's continued opinion that the proposed project is feasible from a geotechnical perspective.
GUNA
CITY OF LAGUNA NIGUEL
30111 Crown Valley Parkway
Laguna Niguel, California 92677
Phone (949) 362-4300 | Fax (949) 362-4340
989
GEOTECHNICAL REVIEW SHEET
Reviewed by:
GMU GEOTECHNICAL, INC.
23241 Arroyo Vista
Rancho Santa Margarita, CA 92688
(949) 888-6513 • Fax: (949) 888-1380 • email: [email protected] Page 4 REFERENCE NO.: SP16-04 DATE: December 2, 2022
CONDITIONS OF APPROVAL (Same As Previous)
Prior to issuance of the grading/construction permit, the consultant should review the precise rading plans, retaining wall plans and calculations, and MSE wall plans and calculations, an prepare a grading plan review letter/report with additional or revised recommendations, a necessary. If any major changes are made to the proposed grading, provide revised or additional slope stability calculations, as necessary.
In Section 8.24 of the Previously Reviewed document (3), the tentative tract map report states that cut/fill transitions and lot capping are not expected, and the need for lot capping should be further evaluated during grading. However, all of the geotechnical sections show a 5-foot over-excavation across all of the building areas. Please clarify the need for over-excavation as part of the precise grading plan review letter/report.
3. Page 10 of the Previously Reviewed document (3) recommends annual geotechnical/geologic monitoring of slopes, pavements, and common area improvements. This recommendation shall be added to the Homeowners' Association maintenance guidelines.
MESh
REVIEWED BY:
Lisa Bates, PG, CEG 2293 Greg Silver, M.Sc., PE, GE 2336 Associate Geologist Principal/Geotechnical Engineer
DISTRIBUTION: Amber Gregg, City of Laguna Niguel (email)