O17 West_Essex_Highlands_Geotech_Slope_Stability_Review_20250716

Princeton Hydro, LLC Page | 4 5. The model omitted the representation of the Feltville Formation, defined by the geologic map (Figure 2 of the Langan report). It is notable that contacts between rock formations (such as between the Preakness and Feltville Formations), are generally the location of significant access of surface water to the subsurface and resulting weathering at depth. Therefore, the marginal quality of the rock, such as in borings NLB-1 (RQDs 0% and 23%), NLB-3 (RQDs 42% and 48%), LB-2 (no RQDs due to deteriorated nature of rock4), and LB-4 (no RQDs due to deteriorated nature of rock5). 6. The analysis did not include the discontinuity in the subsurface cross section that results from the existence of the wastewater utility line that runs parallel to and at the toe of the steepest portion of the subject slopes. This utility, based on review of historic aerial photographs, was constructed in 1995 or earlier. Such a break in the subsurface conditions of the slope will have an impact and add to the probable failure mechanisms of the slope. 7. The depth of decomposed rock of a maximum of seven (7) feet is underestimated based on the extent of the depth of decomposed rock found in NLB-1, NLB-3, LB-2, and LB-4. Geologic Hazard Review Unjustified in Dismissing the Risks Langan dismissed the risk associated with the Landslide Class B III localized area directly below the building and on the slope due to their observation that the “typically favorable joint orientation in the outcrops”. It is our interpretation that their observation that the rock fracturing is tilted into the slope and therefore, would not be a hazard. However, based on the results of the borings and test pits completed for the site, on the downslope areas of the subject slope under analysis, the bedrock was found to have RQDs equivalent of “Fair” to “Poor”, based on the RQD analysis method, these slopes would, indeed, be susceptible to landslides. Below is a table of the classification of Landslide Susceptibility of Geologic Groups. A review of the soil borings with highly fractured and decomposed rock in the downhill formation of the subject slopes, it is highly probable that the rock acts as “weakly cemented” and does have a moderate chance of slope failure. And, as the application is proposing to impose significant excavations and likely, blasting to achieve the necessary garage

acts as “weakly cemented” and does have a moderate chance of slope failure. And, as the application is proposing to impose significant excavations and likely, blasting to achieve the necessary garage subgrade elevation of proposed Building D, this will further increase the probability of landslide activity in this location. Blasting Implications and Threats to Stability of the Slope Must be Addressed Before Approval Unless the Applicant provides sufficient information and defined specifications, simply adhering to “State regulations” as stated at the Planning Board meeting of June 30, such regulations only apply to the safety of conducting the blasting activities, not for the long-term stability and potential landslide potential that may occur because of changes to the bedrock condition adjacent to the site. Any rock stabilization and long-term stability is governed in NJ by the International Building Code, as adopted via NJAC 7:23, which requires that all site grading, excavation and foundation systems be designed based on property geotechnical investigation and engineering principles. A condition of approval stating that the Applicant will comply with the State regulations for blasting will not absolve the Applicant or Township from liability associated with the short and long term effects of blasting, or development, for that matter without blasting on the requirement to ensure that an approved project protects the health, safety, and welfare of the public from the result of landslides, rockfalls, and other related slope failures. 4 No RQDs as the rock was so deteriorated and fragmented as cores could not be progressed. 5 Same as previous footnote.