January 14, 2026, Planning Board Special Meeting - WEHI Transcript

27 of 53 sheets Page 105 to 108 of 122 02/03/2026 04:49:05 PM 105 recommendations was that the applicants engineer should1 perform a stability analysis using conservative2 piezometric surface that would reflect the response of3 groundwater to heavy storm induced rainfall. In other4 words, the analysis must assume a severe storm where the5 ground becomes saturated with water, the ground surface,6 and demonstrate that there's sufficient factor of safety7 to ensure slope stability under those very wet8 conditions.9 Langan Engineering provided additional data10 that was to address CMEs request, the data however11 raised significant concerns that I will discuss in12 detail. Their submission included a map showing the13 location of borings and showed four cross sections in14 which he performed a slope stability analysis under15 extensive rainfall events. These are the four sections,16 one near Howell Drive, another near 12 Howell Drive and17 then several that sloped into Rosemont Terrace and then18 also Mayfair Terrace. So under elevated groundwater19 factors of safety were calculated for each of the cross20 sections. The factor of safety tells you how much21 stronger the slopes natural resistance to sliding is22 compared to the forces pushing it to slide. In essence23 it's a safety buffer that considers uncertainty both24 spatially and overtime.25 106 The general accepted factor of safety1 utilized by the Corps of Engineers and others is 1.5.2 While the 1.5 is a common baseline it is not a universal3 constant and experienced geotechnical engineers use risk4 base approach to select an appropriate factor of safety5 for a specific project. For Section C the accumulated6 -- the calculated factor of safety under elevated7 groundwater is 1.5, which barely meets the safety8 standard. Similarly for Section DD. In each of these9 cases the analysis seemed to have been based on just two10 borings. For Sections A and DD they calculated 1.7 and11 1.67. So I recently became aware that Langan is now12 suggesting that a factor of safety be lowered to 1.2.13 To my knowledge there was no rigorous technical analysis14 that was performed to support this. As I mentioned, the15 generally accepted 1.5 factor of safety for slope16 stability in the literature, and I quote, "Is a minimum17 requirement for permanent slopes under normal static18 loading conditions." It can vary based

erally accepted 1.5 factor of safety for slope16 stability in the literature, and I quote, "Is a minimum17 requirement for permanent slopes under normal static18 loading conditions." It can vary based on-site specific19 project conditions, the type of analysis and level of20 risk or uncertainty. Ultimately the 1.5 is a standard21 minimum but the responsibile design engineer has the22 flexibility and responsibility to select the appropriate23 factor of safety based on a thorough documented analysis24 of site specific risks and conditions as guided by the25 107 principles in engineering manuals such as EM 1110-2-19021 by the Corps of Engineers. To my knowledge this has not2 been done. Given the proximity to the neighbors on3 Howell Drive these marginal factors of safety should be4 of grave concern to the Planning Board and at a minimum5 warrant additional analysis to demonstrate that there is6 no risk of slope failure.7 The analysis should also consider climate8 change and the likelihood of more extreme weather9 events.10 Another concern is the extensive tree11 removal that would take place. Tree roots are known to12 enhance slope stability by physically binding the soil13 with a strong interlocking network anchored to the14 bedrock and by absorbing excess water. The removal of15 trees and deep rooted vegetation can decrease the factor16 of safety over short to medium time scales. This also17 applies to trees in the vicinity of steep slopes.18 CHAIRMAN BAGOFF: Can you wrap it up, sir.19 THE PUBLIC: Yeah. Since tree roots are20 interconnected the loss of vegetation should be21 addressed as part of a more rigorous slope stability22 analysis.23 CHE also -- CME also provided 1124 requirements that must be followed during construction25 108 should the project be approved. These are comprehensive1 but could easily be forgotten or misapplied unless2 there's a full-time monitoring by experts with the3 ability to stop work.4 I also have concerns about the footprint5 being so close to the ridge top.6 In conclusion, as an engineer I see the7 following serious concerns for both Sections CC and DD8 near Howell Drive. The factor of safety is below 1.59 under certain conditions. As I mentioned, 1.5 is a10 standard minimum and the appropriate factor of safety11 should be based on assessment of risk and other factors.12 Given the potential for serious impacts to

ain conditions. As I mentioned, 1.5 is a10 standard minimum and the appropriate factor of safety11 should be based on assessment of risk and other factors.12 Given the potential for serious impacts to nearby13 properties, I would argue that the higher factor of14 safety is warranted. CME also considered --15 CHAIRMAN BAGOFF: Sir, you're done. Thank16 you. You extended your time.17 THE PUBLIC: Okay. Thank you.18 CHAIRMAN BAGOFF: Thank you very much.19 Any other members of the public who have a20 comment?21 Go right ahead.22 THE PUBLIC: Donald Ershow, Home Hill Lane.23 I'm also the president of the homeowners association.24 67 homes.25