Greenwood Lake Watershed Implementation Plan

Greenwood Lake is located on the border of Orange County, New York and Passaic County, New Jersey, and is a highly valued recreational, ecological, and potable water resource. It is one of the headwater systems that feeds the Wanaque Reservoir, which provides drinking water to over 2.3 million people. Greenwood Lake is on both States’ 303(d) list for being impaired by phosphorus. A phosphorus Total Maximum Daily Load (TMDL) was completed and proposed by NJDEP in June 2004 and established in September 2004. The NYSDEC reviewed the TMDL and formally agreed with the existing and targeted loads in 2005.

Princeton Hydro staff have been working on Greenwood Lake since the early 1980s when the Phase I Diagnostic and Feasibility study was completed. Princeton Hydro completed a prioritized Stormwater Implementation Plan, approved by NJDEP in 2006, which identified a series of stormwater projects to comply with the NJ contribution to the phosphorus TMDL. A similar Stormwater Implementation Plan was developed for the New York end of the watershed in 2008.

As part of a 319(h) grant, Princeton Hydro conducted engineering analyses and design work for the installation of six stormwater Best Management Practices (BMP) to reduce the Total Phosphorus (TP) and Total Suspended Solid (TSS) loads entering Greenwood Lake and comply with the TMDL. These BMPs include the installation of two vegetated bioretention swales; a baffle box and polisher Manufactured Treatment Device (MTD) unit by Suntree Technologies Inc; two Bay separator MTD devices by Baysaver Technologies, Inc; and a VORTECHS model 3000 MTD by Vortechnics, Inc. Princeton Hydro oversaw the installation of the structures and monitored stormwater upgradient and downgradient of the installed BMPs to measure their efficacy in TP and TSS reductions.

Princeton Hydro has conducted extensive in-lake, stream, and stormwater monitoring in accordance with the Quality Assurance Project Plans approved by NJDEP. Sampling included measurements of flow at eight tributary sites (six in the New Jersey end and two in the New York end), the collection of water samples for analysis, and collecting in-situ data (dissolved oxygen, temperature, pH, and conductivity).

As part of a NJ Highlands Council grant, Princeton Hydro updated Greenwood Lake’s Restoration Plan for the NJ end of the lake to a 9-Element Watershed Implementation Plan (WIP) to further identify NPS reduction. The updated WIP was completed in early 2020. Princeton Hydro recently modeled flow discharge and pollutant load from Belcher Creek, Greenwood Lake’s main input and source of nutrient loading, in order to evaluate the feasibility of a ferric sulfate infusion system to address phosphorus inputs. Such a system would decrease the amount of phosphorus being introduced into the lake and prevent HABs from occurring. This project was funded by NJDEP Harmful Algal Bloom (HAB) grants and was completed in 2021.