60-25 Attachment.pdf

December 6, 2024 Proposal for Professional Services –Groundwater Monitoring and Reporting Re: Department of Public Works at 25 Lakeside Avenue – UST Case Page 2 of 6 Monitored Natural Attenuation (MNA) as an effective Ground Water Remedial Action for the site. (N.J.A.C. 7:26C-7.5(c)3i). Four quarterly sampling events were completed (were included in the previous proposal), therefore four (4) additional rounds are required by the NJDEP Regulations. BACKGROUND A groundwater and soil delineation program and additional groundwater investigations were implemented at the Site to evaluate the impacts resulting from an on-Site 4,000-gallon gasoline underground storage tank (UST) discharge. Based on analytical results, it appeared that benzene, toluene, ethylbenzene, and xylenes (BTEX), methyl tertiary butyl ether (MTBE) and lead are the contaminants of concern in the groundwater. Furthermore, it appeared that the contamination plume originated in the vicinity of the UST and migrated along the general direction of groundwater flow which was determined to be easterly towards the nearby Brook. Two additional wells MW-11 and MW-12 were installed to complete delineation of the horizontal extent of gasoline impacts in the eastern direction as required in the NJDEP Notice of Technical Deficiency, dated April 14, 2021. The NJDEP required the removal of impacted soil that acts as a source of groundwater contamination. Excavation and backfilling activities at the West Orange DPW were completed on November 29 and 30, 2022 by Environmental Management Associates, Inc. (EMA) of Farmingdale, NJ. The excavation area was located based on the previous soil sampling analytical results that identified the limits of the impacted soil at the source area. The remedial action goal is the removal of impacted soil that acts as a source of groundwater contamination at a limited area located to the south-west of the former location of the UST and close to the pump island. MW-1 was abandoned and we re-installed MW-1R after completing the excavation. The monitoring wells sampling was conducted to monitor the effectiveness of the remedial action. A re-bound in benzene concentration levels was noticed in MW-1R (located at the edge of the pump island) as it was not possible to extend the excavation beyond the edge of the concrete pad.