O17 West_Essex_Highlands_Geotech_Slope_Stability_Review_20250716

Princeton Hydro, LLC Page | 2 Boring Cross Section Slope Location Sample/ Depth (ft) REC % RQD % LB-1 A Upper C-1 / 14-19 C-2 / 19-24 97 97 58 82 LB-2 A Middle n/a n/a n/a LB-3 B Upper C-1 / 9-14 C-2 / 14-19 93 87 77 67 LB-4 B Middle n/a n/a n/a Average (LB) 94 71 Highest Value (LB) 97 82 Lowest Value (LB) 87 58 NLB-1 C Middle C-1 / 17-22 C-2 / 22-26 78 100 0 23 NLB-2 C Upper C-1 / 10-15 C-2 / 15-20 100 93 72 93 NLB-3 D Middle C-1 / 22-27 C-2 / 27-32 100 75 42 48 NLB-4 D Upper C-2 / 12-17 C-3 / 17-22 95 97 52 83 Average (NLB) 92 52 Highest Value (NLB) 100 93 Lowest Value (NLB) 75 0 Average (LB and NLB) 92 58 Highest Value (LB and NLB) 100 93 Lowest Value (LB and NLB) 75 0 1. As stated above, the rock core samples obtained from the boring investigation used two rock samples to test for compressive strength from the most competent rock found above the top of the subject slope. For example, the cores chosen had RQD values of 77% and 67”, which are greater than the average values, and significantly greater than the lowest values obtained from the site. And, when tested for compressive strength, even the values obtained were found to have strengths indicative of a lower strength type rock than basalt. As stated in the subject report (pdf page 17), Unconfined compressive tests were performed on 2 rock core samples taken from boring LB-3 located at the upper portion of the slope. The tests suggest that the unconfined compressive strength of the basalt rock samples varied between approximately 2,200 pounds per square inch (psi) and 3,500 psi or approximately 316,800 pounds per square foot (psf) and 504,000 psf. These values equate to 15 Megapascals (MPa) and 24 MPa, respectively. When compared to known strengths of rock material, as shown in the table below (table source from Rockscience slope stability program), the material has more of a quality of chalk, rocksalt, or potash material. This is an indication that the basalt is significantly weathered, even in the intact portions of the rock than typically found. Typical un-weathered basalts are normally almost 10 times the values obtained from the testing of the specimens chosen.