Langan Rebuttal Report 9 15 2025

Global Stability Study for Eastern Slope near Building D West Essex – Highlands Development West Orange, New Jersey Langan Project No.: 101049801 15 September 2025 Page 3 of 7 Princeton Comment: Parameters of Slope Stability Analysis Do Not Match Actual Conditions Langan Response: Princeton initially identified seven subparts associated with their position. Five of 7 relate to rock properties used in our model, one relates to building loading, and one relates to the presence of a sewer. In Princeton’s 12 August letter they provided analyses using their interpretation of our data. Overall, Princeton repeatedly claims our design values are incorrect, yet they clearly misinterpret the data and mis-apply it. Princeton is mistakenly focused on the rock parameters as being the primary controlling factor in the slope stability analysis. Although rock strength is important, the soil properties control the stability of this slope. Princeton implies that the critical section for slope stability would extend through the underlying rock stratum. Our output files, provided in our 18 June report, clearly demonstrate that all slope stability critical surfaces (i.e., lowest factors of safety) pass through the overlying soil. Princeton’s slope stability output files also clearly demonstrate that the overlying soil properties control the slope stability. The only way for the rock to govern the stability under the design loading conditions would be if the rock strength were lower than the overlying soil strength. Despite both Langan and Princeton proving that point, Princeton incorrectly maintains the rock strength is the primary controlling factor in the slope stability analysis. As there is no grading proposed on the slope, the soil properties do not change between the existing and post development conditions (i.e., no change in the stability). Princeton also incorrectly stated that Rock Quality Designation (RQD) defines rock mass quality. ASTM D6032 is the Standard Test Method for Determining Rock Quality Designation of Rock Core. The significance and use of this standard is to provide a "simple and inexpensive general indication of rock mass quality". However, RQD, which is determined from 2-inch diameter rock cores, is one basic component of rock mass classification systems which are used in engineering analysis and design to better understand rock mass

r, RQD, which is determined from 2-inch diameter rock cores, is one basic component of rock mass classification systems which are used in engineering analysis and design to better understand rock mass quality. Fundamentally, RQD is used to identify potential problems within a rock mass and to provide a basis for making preliminary decisions. The Standard clearly states that RQD alone is not sufficient to provide an adequate description of rock mass quality; and, RQD must be used in combination with other geological and geotechnical input. The Rock Mass Rating (RMR) System (aka, Geomechanics Classification System by Bieniawski, 1989) is a widely accepted and utilized method of classifying/categorizing rock masses in terms of general “quality” based on physical and mechanical properties and is used to aid in the prediction of rock mass behavior. The RMR System assigns numerical values to six important parameters (UCS, RQD, Joint Spacing, Joint Condition, Groundwater, and Joint Orientation). It is universally agreed that the RMR system is appropriate for rock mass of good to reasonable quality (i.e., GSI>25, per Hoek and Brown). We assigned values to the RMR System (see Exhibit A) and find the rock mass to be predominantly Fair to Good Quality, not Very Poor Quality as erroneously suggested by Princeton. Princeton claimed we chose the most competent rock to select model properties, yet our model clearly shows we assigned design values (GSI, UCS, Disturbance, etc.) in our slope stability analysis that are appropriate based on our borings, laboratory testing and evaluation of the rock mass quality and characteristics. Princeton recognized that basalt should have considerably higher uniaxial compressive strength values, but they incorrectly correlated the