Kensico Reservoir Project Description 8. PROPOSED ACTION IN THE KENSICO RESERVOIR STUDY AREA 8.1 KENSICO RESERVOIR PROJECT DESCRIPTION 8.1.1 BACKGROUND As discussed in Section 1.2.3, “Emergency Authorizations for Alum Application,” NYSDEC, in coordination with NYSDOH issued several emergency authorizations to DEP, which allowed for the application of alum to water in the Catskill Aqueduct upstream of Kensico Reservoir1 to address episodic turbidity. Specifically, alum was applied to coagulate the suspended solids to improve settling and reduce turbidity in flows of water from Ashokan Reservoir.2 Following the expiration of these emergency authorizations, DEP applied for a permit and NYSDEC issued the Catalum SPDES Permit. This permit authorizes DEP to apply alum and sodium hydroxide to reduce turbidity in the Catskill Aqueduct upon NYSDEC receipt of a copy of a notice from the NYSDOH that there is a potential imminent development of a public health hazard related to the discharge of turbid water from Kensico Reservoir. The Catalum SPDES Permit issued by NYSDEC to authorize alum application included a condition that DEP dredge accumulated alum floc from the Reservoir in a manner that minimizes adverse impacts to the environment within Kensico Reservoir. In 2011, the Catalum SPDES Permit was administratively extended. In June 2012, DEP requested a modification to the NYSDEC Catalum SPDES Permit to incorporate measures to address episodic turbidity in water diverted from Ashokan Reservoir, and delay of dredging of alum floc from Kensico Reservoir until completion of RWBT repairs. Repairs to the RWBT are underway and are part of a broader program to ensure the continued reliability of the drinking water system: DEP’s Water for the Future (WFF) Program. When the RWBT will be shut down (RWBT shutdown) to facilitate these repairs, DEP will be more heavily reliant upon the water in the Catskill System to meet its customers’ daily demand as water from the Delaware System will be unavailable. More reliance on the Catskill System increases the likelihood that the City would need to apply alum and sodium hydroxide to address turbidity to water in the Catskill Aqueduct upstream of Kensico Reservoir during the RWBT shutdown. As discussed in Section 1, “Introduction,” NYSDEC issued a Consent Order delaying the commencement of dredging design until the RWBT repairs are complete. In addition, and also as part of the WFF Program, DEP has commenced a project to repair and rehabilitate the Catskill Aqueduct (CAT-RR) to restore its historic capacity. As such, DEP expects that it may also be necessary to apply alum to water in the Catskill Aqueduct upstream of Kensico Reservoir during brief periods of aqueduct start-up after shutdowns associated with the CAT-RR project. DEP evaluated the potential for the application of alum during the RWBT shutdown and the CAT-RR project in the Water for the Future: Upstate Water Supply Resiliency Final Environmental Impact Statement (FEIS) (CEQR No. 5DEP006U) issued on December 15, 2017. Pursuant to the 2018 Modification to the Catalum Administrative Order on Consent, DEP is authorized to add alum in accordance with the WFF Alum Treatment Plan (ATP) and requires that the associated alum floc be included in the Total Dredging Mass.3 1 Aluminum sulfate (alum) and sodium hydroxide are added at the Pleasantville Alum Plant to water in the Catskill Aqueduct upstream of Kensico Reservoir (alum application). 2 Alum attaches to particles suspended in the water column that cause turbidity and causes them to sink and settle on the floor of the water body. These coagulated/flocculated particles are referred to as “alum floc.” 3 The 2018 Modification defines the Total Dredging Mass as the mass of alum floc deposited in Kensico Reservoir under two Emergency Orders in 2005, under authority of the Catalum SPDES Permit, and in accordance with the WFF ATP. Modification of the Catalum SPDES Permit EIS 8-1 Kensico Reservoir Project Description Therefore, any dredging in the future would be focused on the dredging of alum floc deposited since 2005, as well as any alum floc deposited in accordance with the WFF Alum Treatment Plan. Alum applied to water in the Catskill Aqueduct upstream of Kensico Reservoir forms alum floc, which is deposited and accumulates in the vicinity of the Catskill Influent Chamber (CATIC) Cove where water from the Catskill Aqueduct discharges into Kensico Reservoir. DEP conducted extensive bathymetric and sediment sampling studies in 2006 and 2014 to determine the depth, areal distribution, and chemical make-up (total and dissolved aluminum content) of the alum floc deposition within the area of CATIC Cove and the adjacent area of the Reservoir. Analysis of the physical characteristics of collected samples included grain size, percent moisture, percent solids, and percent organic matter. In addition, DEP sampled the Kensico Reservoir benthic community in proximity to the areas of alum deposition in April and July 2007. The 2007 surveys followed a period of alum application in 2005 and 2006. In July 2014, a representative subset of the stations sampled in 2007 were selected and resampled. The 2014 sampling also followed a period of alum application in 2011 and 2012. 8.1.2 PROJECT OVERVIEW This EIS includes an analysis of the potential effects of delay of dredging, as well as an assessment of environmental considerations associated with this dredging by comparing the future without the Proposed Action (no dredging) to the future with the Proposed Action (delay of dredging).4 As described in Section 8.2, “Kensico Reservoir Dredging Analysis,” dredging in the future would involve removal of approximately 91,000 to 98,400 cubic yards (cy) of accumulated alum floc from the bottom of Kensico Reservoir. As shown on Figure 8.1-1, dredging would occur within the approximate limits of historical and anticipated future floc deposition in the vicinity of the CATIC Cove. Dredging would be performed using a barge-based hydraulic dredge, with the pumping of dredged materials via temporary piping to an upland site. A separate dewatering operation to remove excess water from the dredged material would be established approximately 2.3 miles south of the CATIC site on property owned by the City and operated by DEP. The dewatering site would be located on the west side of the Reservoir off of Westlake Drive. Two adjacent temporary above-ground pipelines would be installed between the CATIC and dewatering sites. One pipeline would transport dredged material pumped from the CATIC site to the dewatering site for dewatering and off-site disposal of processed dredge materials, and the other would transport filtrate water generated from the dewatering process to the CATIC site for discharge back into the Reservoir. Descriptions of these activities are provided below. Dredging activities within Kensico Reservoir would be further refined in the future based on the detailed plans for dredging, and supplemental environmental analysis would be conducted, as applicable. 4 As described, the Proposed Action would modify the Catalum SPDES Permit to incorporate: (1) Turbidity control measures, including operation of Ashokan Reservoir in accordance with the IRP; and (2) Delay of dredging accumulated material (alum floc) from Kensico Reservoir until the completion of certain infrastructure projects. The Kensico Reservoir Study Area assessment focuses on delay of dredging. Modification of the Catalum SPDES Permit EIS 8-2 Kensico Reservoir Project Description Figure 8.1-1 Kensico Reservoir Project Location Modification of the Catalum SPDES Permit EIS 8-3 Kensico Reservoir Dredging Analysis 8.2 KENSICO RESERVOIR DREDGING ANALYSIS As set forth in the Final Scope of Work, the EIS assesses the potential impacts associated with a delay of dredging until certain DEP infrastructure projects, such as the RWBT repairs, have been completed, while also evaluating potential environmental considerations for the dredging of alum floc from Kensico Reservoir. This section analyzes the potential for significant environmental impacts associated with the delay of dredging and identifies environmental considerations associated with dredging activities. As the dredging design would be further refined in the future, DEP would review the need for additional environmental review of the potential effects of dredging that would be completed in the future, if required. 8.2.1 DELAY OF DREDGING In the future with the Proposed Action (delay of dredging), existing alum floc would continue to remain in place and the deposition of new alum floc in Kensico would increase as a result of alum application in accordance with the WFF ATP. In the future with the Proposed Action, general compliance with water quality standards would remain unchanged. NYSDEC-designated best uses for Kensico Reservoir, including use as a drinking water supply, would continue to be achieved as has been the case for many years. New deposition is anticipated to occur within the same lateral extent of the Kensico Reservoir CATIC Cove associated with alum floc deposition since 2005 and not beyond, as shown on Figure 8.2-1. The diversity and presence of existing benthic communities within previously deposited alum floc are anticipated to continue to persist, as documented from a comparison of 2007 and 2014 benthic sampling events that were completed after several larger previous alum applications. Likewise, impacts to other aquatic species, specifically fish, would also not be expected due to existing or newly deposited alum floc. No impacts to water quality or wetlands are expected to occur, as these would remain comparable to current conditions. Similarly, adverse impacts from existing floc have not been observed and potential impacts associated with aluminum within alum floc would not be expected, as the long-term water quality characteristics of Kensico Reservoir (i.e., neutral pH levels) do not support the conditions necessary for the bioavailability of aluminum that would potentially result in adverse impacts to benthos or fish.