O30 Princeton Hydro Report Dated 9 3 25

West Essex Highlands Review 4 West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 During the water quality storm, BMP 3 infiltrates 880 cf of runoff. The area of the infiltration basin is 5,558 sf. 880 cf of water is equivalent to about two inches of water over the area of the basin. That means that two vertical inches of water will be held above the SHWT and slowly infiltrate. Assuming a porosity of 0.4 for the sand layer, the two inches of vertical water turns into five inches. That means that there is five inches of water in the sand layer between the SHWT and the bottom of the storage for PP3. The system works under this scenario because the soil replacement area is two feet deep. However, during the 100-year storm, the model assumes that 10,971 cf of water will infiltrate through the system (page 529 of 946 in drainage report). That is because the model is assuming the runoff is infiltrating at a constant rate of five inches per hour. The reality is that at the surface of the basin at the beginning of the storm, the runoff will infiltrate at that rate but once it hits the SHWT it will infiltrate at the much slower rate of 0.25 inches/hour (assuming a factor of safety of 2, based on the soil testing results) that will cause water to back up into the sand layer. Once the system is under the influence of a groundwater mound the rate of infiltration could be expected to decrease by orders of magnitude as the system will rely on horizontal groundwater flow. There needs to be thick enough layer of sand to prevent that runoff from backing up into the storage area of the BMP3. 10,971 cf of water over the area of the basin is equal to 1.97 ft of water. As noted above when you apply the 1.97 feet of water to the anticipated porosity of sand (0.4), the height of the sand and the water is 4.9 feet (59 inches) from the SHWT. BMP 3 (see Figure 4) only provides two feet of sand storage and an additional 26 inches of stone storage (see Figure 7). The system will become overwhelmed during a 100-year storm and the peak flow rates will not be reduced. Instead of infiltrating, a large portion of the 10,971 cf that the model says will infiltrate will discharge through the stormwater system. The design will fail and potentially create higher peak flow runoff rates than currently exist. Furthermore, this design issue is not isolated to BMP 3 since any unanticipated

h the stormwater system. The design will fail and potentially create higher peak flow runoff rates than currently exist. Furthermore, this design issue is not isolated to BMP 3 since any unanticipated surcharge from the BMP will be captured by inlets further downstream and will potentially overwhelm those inlets. If the excess runoff is captured by the inlets, the runoff will enter either BMP 1 or 2, it could overwhelm those systems and increase the peak flow rates from those BMPs as well. Princeton Hydro, LLC Page | 14

West Essex Highlands Review West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 POROUS PAVEMENT #3 SECTION ‘SORE NTS Figure 4: Cross Section of BMP 3. 2.5 IMPACTS TO WETLANDS In the existing conditions, the stormwater runoff generated from the existing topography travels over the surface and reaches the upgradient wetlands providing valuable water to the wetland ecosystem. In the proposed condition, the discharge locations for each of the drainage areas are at the bottom of the project area. This is illustrated in Figure 5. The blue arrows show the existing flow paths and the fuchsia arrows represent the proposed flow paths. The proposed stormwater system intends to route the stormwater runoff through a pipe network to basins where all the surface runoff will discharge much further downstream. The drainage area to the wetlands uphill of the discharge locations will have a smaller drainage area and collect less stormwater runoff. Princeton Hydro included two attachments that show the existing drainage areas for eastern and western wetlands. The western wetlands have a drainage area of approximately 32 acres. The proposed improvements to DA for the western wetlands will reduce the drainage area by nine acres or 28% of the total existing drainage area. The eastern wetlands have a drainage area of 48 acres. The proposed improvements to the DA for the eastern wetland will reduce the drainage area by 16 acres or 33% of the total existing drainage area. In addition, to the modified drainage areas to the wetlands there are at least two instances where the proposed design will result in the hydrologic gradient of groundwater to the wetlands being modified and redirected toward two of the proposed infiltration basins, BMP 2 and BMP 7. For example, the bottom of BMP 2 is at elevation 544 (this is incorrectly identified as being 544.5 on plan sheet SP-55 as the bottom of the basin should be the base of the 6-inch sand layer). Figure 6 shows a cross section of BMP 2 with the elevations of the adjacent wetland. In this case, the basin bottom is situated as much as six feet below the elevation of the wetland which is less than 75 feet from the wetland to the east (see Figures 6 and 7). More importantly, the groundwater data indicates that the SHWT for boring six is approximately ten feet lower than that of the surface of the nearby wetland. In addition,

e east (see Figures 6 and 7). More importantly, the groundwater data indicates that the SHWT for boring six is approximately ten feet lower than that of the surface of the nearby wetland. In addition, TP22 is located approximately fifty to the Princeton Hydro, LLC Page | 15

West Essex Highlands Review West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 northwest of the basin and the SHWT is indicated to be at an elevation of 545, a foot above the basin bottom. It is important to reiterate that no redoximorphic features were identified by the applicant's professionals in any of the borings. Figure 5: Proposed Grading Plan with Blue Arrows showing the existing drainage path and the Fuchsia arrows showing the proposed drainage paths and how the runoff is being diverted from the wetlands. Both BMP 2 and 7 are proposed to be excavated to an elevation below nearby wetlands. In these cases, the proposed BMP would result in the disruption of the current hydrologic gradient toward the wetland to one that redirects the hydrologic gradient toward the BMPs from the wetland. This will not only impact the wetland but will add an additional source of water to the BMPs that has not been identified by the applicant. This is especially relevant for BMP 7 where the basin is proposed to be excavated to an elevation approximately 16.5 feet lower than the delineated wetland located a little over 50 feet to the north of the basin. The relationship of wetlands and state open waters to infiltration basins should have been considered in the design of the proposed stormwater BMPS as the current design will not just impact the function of the BMPs but also impact the wetlands. The impacts to the wetlands related to changes in hydrology also warrants reconsideration by the NJDEP as it relates to the 401 Water Quality Certification the NJDEP granted to this applicant. Princeton Hydro, LLC Page | 16

West Essex Highlands Review West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 ———BASIN-2- OUTLET STRUCTURE #2 SCALE NTS ANISMED GRADE: 546.5 2s Paks Se AF 56 1s BS, Led 545.62 R ra / 545.18 10 ¥R sus TPs 544.96 2.R 544 2 544.5 BASIN 6” SANO LAYER SOL REPLACEMENT PERMEBILITY = 8 IN/HR INFILTRATION BASIN #2 SECTION ‘SCALE NTS Figure 6 Cross section of BMP 2 from the construction plans. The red lines mark the surface elevation of the nearby wetland. Figure 7 Plan view of BMP 2 from the construction plans. The red lines show the relationship of adjacent wetland to BMP. Princeton Hydro, LLC Page | 17

West Essex Highlands Review = West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 Figure 8 Plan view of BMP 7from the construction plans showing 16.5 foot cut downgradient of mapped wetland to the north. 2.6 TIME OF CONCENTRATION Existing conditions were incorrectly calculated for this project. The time of concentration (TC) is the time it takes for runoff to travel through the watershed on the longest hydrologic flow path. The designer used an outdated method to determine the TC for the drainage areas POA | and 2. Due to the very small size of the drainage area for POA 3, it was not included in this analysis. The plans describe the land use as “unpaved” which is an older land use classification that is not used in the latest method. Princeton Hydro would note that this method was not issued during the last update to the stormwater rules which NJDEP ruled did not apply to this project, but it was updated on the previous rule change in 2021 which do apply to this application. TC for this system was broken down into two different flows: sheet flow and shallow concentrated flow. Runoff then transitions from sheet flow to shallow concentrated flow. Shallow concentrated flow Princeton Hydro, LLC Page | 18

West Essex Highlands Review ? West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 occurs after sheet flow and the depths range from 0.1 to 0.5 ft. lo demonstrate the magnitude of how incorrect TC calculations are, Princeton Hydro recalculated the shallow concentrated flow portion of the TC for both POA 1 and 2. For POA1, the designer stated that it would take 7.2 minutes for the runoff to travel 1,625 ft via shallow concentrated flow. The average slope for that length is 5.5%. According to Chapter 5 of the New Jersey BMP manual, the velocity of runoff traveling through a forested area with heavy ground liter is 0.55 fps when the slope is 5.5% (Figure 5-13 of New Jersey BMP Manual). The travel length of 1,625 ft divided by 0.55 fps is equal to 49 minutes. The revised TC is almost seven times longer than what is shown on the stormwater report. For POA 2, the report states that it takes 1.9 minutes to travel 564 ft via shallow concentrated flow. The average slope for that length is 9.2%. That is an average velocity of 5 fps. The New Jersey BMP Manual states the velocity of runoff at a slope of 9.2% for wooded area is 0.75 fps (Figure 5- 13). Using that velocity the TC is 12.5 minutes. Again, the revised TC is almost seven times longer than what is shown on the stormwater report. Establishing the existing TC and peak flow rates are a crucial part of a compliant design. The TC has a significant impact on the existing peak flow rate. All development projects are required to have their peak flow rates leaving the site be less than the existing peak flow rate. In general, a shorter existing condition TC translates to a higher peak flow rate. The higher your peak flow rate, the easier it is to apparently meet your peak flow rate reduction requirements. An over- representation of the existing peak flow rate allows for a reduction in the size of your stormwater basins. The problem with this approach is that it does not reflect reality or site conditions and instead of reducing the peak flow rate generated by the project it will increase the rate in comparison to the existing conditions. The flow path shown on the Drainage area Map for POA 2s only 664 feet long and that matches what is shown on the model. The TC is meant to measure the time it takes for the water to travel the entire flow path. The actual flow path for POA 2 is greater than 664 ft. The

long and that matches what is shown on the model. The TC is meant to measure the time it takes for the water to travel the entire flow path. The actual flow path for POA 2 is greater than 664 ft. The discharge location is approximately 700 feet away from where the analysis ends (as the crow flies, see Figure 9). This analysis is incorrect and incomplete because it does not capture the entire flow path. This is similar to using the older TC calculation, as it artificially shortens TC so it shortens the peak flow rates for the existing conditions and potentially risks the proposed improvements increasing the flow rate leaving a site instead of decreasing as the regulations require. To understand the impact that the TC errors have on the design, Princeton Hydro calculated the TC for POA 2 using the correct method and included the entire flow path. The applicant's report has a total TC of 16.8 minutes. Princeton Hydro’s calculations show a TC of 60.8. That is about 3.5 times longer than that calculated by ACS. For the two-year storm, PH calculated a peak flow Princeton Hydro, LLC Page | 19

West Essex Highlands Review West Orange, NJ Permit No. 722-04-0001.1 LUP230001 April 2025 applicant's Figure 9: Existing Conditions Drainage Path for POA-2, demonstrating how the aie stops approximately 700 feet short of the POA location. model states 14.76 cfs (page 22) while their report states 17.53 cfs (page 14). Princeton Hydro also found that the existing peak flow rates in the report do not match the flow rates in the model results found in the report appendix. This should be corrected. For the purpose of this report, the he results found in the modeling calculation appendix were evaluated against Princeton Hydro's own calculations. Based on our calculations the peak flow rate for the development is 3.76 cfs under existing conditions for the two-year storm. Currently the design's peak flow rate under the post-development conditions is 7.24 cfs which is almost twice what should be permitted. Princeton Hydro calculated the peak flow rate for the 100-year storm at 37.7cfs but the applicant's model states the peak flow rate at 72.79. The peak flow rate for the proposed condition is 38.99 cfs. During the 100-year storm, the proposed Site will actually generate higher peak flow rate than what currently exists. This is an alarming situation especially considering there are flood prone areas immediately downstream. To meet the peak flow rate requirements state forth by the NJDEP and the local ordinance would require the volume storage for the BMPs to be dramatically increased. This would have a substantial impact on the current site design. Princeton Hydro, LLC Page | 20