4

Use of OST Within the Environmental Impact Statement for Modifications to the Catalum SPDES Permit

The study Statement of Task requests the National Academies Committee to review the City’s plan for use of the Operations Support Tool (OST) in evaluating proposed modifications to the Catalum State Pollutant Discharge Elimination System (SPDES) permit, as well as alternatives to be considered in the associated environmental review. The New York City Department of Environmental Protection (NYC DEP) has proposed modifications to its SPDES permit for adding alum to the Catskill Aqueduct just prior to Kensico Reservoir for the purpose of controlling high turbidity. These modifications, including operation of the Ashokan Release Channel, the dredging of alum floc from Kensico Reservoir, and the addition of alum to the Catskill Aqueduct, will undergo a review to determine their environmental impacts. As part of the analysis of environmental impacts, NYC DEP will also evaluate a range of structural, nonstructural, and operational alternatives. OST is anticipated to be one of many tools that will be used during the analysis and drafting of the environmental impact statement (EIS), which is scheduled to be completed six months after publication of this report. This chapter focuses on the use of OST in the EIS analysis, not on the EIS generally.

BACKGROUND ON ENVIRONMENTAL IMPACT STATEMENTS

The federal government passed the National Environmental Policy Act (NEPA) in 1970 to establish a process and regulations for how to evaluate the impacts of federal projects. It required an environmental impact assessment (EIA) to determine if potential impacts from a project might result,

and then a more comprehensive EIS to document potential impacts, explore alternatives, and set a course of action to minimize impacts. The State of New York passed a companion piece of legislation termed the State Environmental Quality Review (SEQR) Act, initially legislated in 1976 and last amended in 2005. An EIS under SEQR requires five basic elements:

1. description of the action, including its need and benefits;
2. description of the environmental setting and areas to be affected;
3. analysis of all environmental impacts related to the action;
4. analysis of reasonable alternatives to the action; and
5. identification of ways to reduce or avoid adverse environmental impacts.

Not all actions require an EIS; it depends on the nature and scope of the proposed action as well as the potential for the action to have adverse impacts.

Although the term EIS specifically references “environmental,” the assessment and analysis is broad. In general, an EIS must address traditional environmental factors such as air, water quality, and biological conditions, especially for endangered species. However, the EIS must also examine potentially affected historical and cultural features, as well as socioeconomic conditions. An approved EIS must examine the impacts to all these factors for a specific action plus a range of reasonable alternatives, comparing each and performing a cost-benefit analysis.

The regulations for an EIS are quite involved to ensure that the EIS is comprehensive, interdisciplinary, and scientifically robust. The regulations also provide for ample time for agency and public input. The schedules, format, content, and requirements are quite prescriptive ([6 New York Codes, Rules and Regulations Part 617 SEQR Statutory authority: Environmental Conservation Law §§ 3-0301(1)(b), 3-0301(2)(m), and 8-0113]). In the case of the Catalum permit, the EIS also must comply with New York City’s Environmental Quality Review (CEQR) as set forth in 62 Rules of the City of New York Chapter 5 and Executive Order 91 and its amendments.

EIS AND THE CATALUM SPDES PERMIT

A SPDES permit was issued to NYC DEP on January 1, 2007, in order to permit the addition of alum (more specifically aluminum sulfate) and sodium hydroxide to the Catskill Aqueduct and essentially in turn to the Kensico Reservoir. The purpose of alum addition is to decrease the impact of Catskill Aqueduct high turbidity loading on Kensico Reservoir diversion turbidity, primarily to protect public health but also to avoid the need for filtration. The federal Clean Water Act (CWA) and companion state rules

require a SPDES permit for the discharge of pollutants and in turn compliance with state water quality standards. SPDES requirements can have many provisions including discharge restrictions, monitoring, studies, and plans. The Catalum SPDES permit was no different: it required NYC DEP to reduce the amount of alum discharged by evaluating structural, operational, and erosion control measures to reduce turbidity in the incoming water and hence the need for alum. These measures are discussed at length in the Catskill Turbidity Control Study reports (see Box 1-1 and Chapter 3).

In 2005 and 2006, there was extreme weather and at times exceptionally high turbidity entering the Ashokan and Kensico reservoirs. To deal with these issues, the NYC DEP under emergency authorization from the New York State Department of Environmental Conservation (NYS DEC) added alum into the Catskill Aqueduct to increase the removal of turbidity from the Catskill water as it enters the Kensico Reservoir. They also were authorized to release highly turbid Ashokan Reservoir waters to the Lower Esopus Creek. Following the expiration of the emergency authorization, NYC DEP applied for and was granted a SPDES permit in 2007 (herein referred to as the Catalum SPDES permit) that permitted these procedures but also required a number of studies, reports, and actions including removal of “alum floc” deposits in Kensico Reservoir (the deposits are aggregates of precipitated aluminum hydroxide from alum and the mineral particles that cause elevated turbidity in the Catskill Aqueduct water).

In 2010 and 2011, extreme events recurred and exceptionally turbid waters were released to the Lower Esopus Creek. The reaction from many downstream stakeholders was very negative, which placed increased critical inquiry on the release strategies and the terms of the SPDES permit. A Consent Order was issued by the NYS DEC to the NYC DEP on October 4, 2013, requiring the preparation of an EIS surrounding proposed modifications to the SPDES permit.

Analytical Framework for the EIS

The modifications to the permit that NYC DEP currently seeks include the use of the Ashokan Release Channel under the Interim Release Protocol (IRP) and a delay in dredging of Kensico Reservoir until certain infrastructure projects are completed. As documented in the Final Scope for the Modification of the Catalum SPDES Permit Environmental Impact Statement (NYC DEP, 2017), the EIS will address the following proposed actions:

• Operation of the Ashokan Release Channel under the IRP. The IRP specifies community minimum releases to protect minimum flow downstream in the Lower Esopus, spill mitigation releases

• to maintain storage and reduce flooding risks, and operational releases to reduce turbidity in diversions from Ashokan to the Catskill Aqueduct;

• Delay of dredging of alum floc from Kensico Reservoir to accommodate completion of ongoing and future infrastructure changes; and
• Addition of alum in the Catskill Aqueduct just prior to the water entering Kensico Reservoir.

Various operational alternatives proposed for Ashokan and Kensico reservoirs and for the Catskill Aqueduct do not require environmental impact reviews. Also, the proposed structural alternatives at Ashokan and Kensico reservoirs already have had environmental reviews completed (NYC DEP, 2017). Other alternatives will require analysis as part of the EIS.

The dredging of alum floc is not part of the long-term ongoing operational plan, like the other actions. Nonetheless, the EIS will include the environmental impacts of delaying the dredging of alum floc until 2024, and of the dredging itself once it starts. It should also be noted that the EIS is intended to look not just at identified alternatives and the existing IRP but also at potential modifications to the IRP and other possible alternatives not identified in the EIS scoping document.

Table 4-1 summarizes the analysis framework for the EIS, which shows how each program element will be considered under the baseline conditions, in the future (2019 and 2024) if no action is taken and in the future (2019 and 2024) if the action is taken. NYC DEP proposed 2019 and 2024 as the analysis/build years of the EIS for several reasons. First, in 2019 two projects that will increase operational flexibility and reduce the potential need for alum addition—the Shaft 4 Interconnection and the Croton Water Filtration Plant—are anticipated to be online. By 2024, the Rondout-West Branch Tunnel is anticipated to be repaired, and dredging of alum at Kensico Reservoir is planned. In addition, the potential effects of delaying dredging until 2024 will be evaluated. Despite designating 2019 and 2024 as the primary years of analysis, the NYC DEP indicated that the hydraulic and hydrologic modeling for the EIS will consider the long-term potential for impacts from the proposed action and not be limited to these two analysis years, which essentially represent operating scenarios. The final EIS scope (NYC DEP, 2017) goes on to say, “The analyses would consist of long term assessments based on a range of hydrologic conditions.”

The actions under consideration are listed in the first column of Table 4-1. Operation of the Ashokan Release Channel is the main action. Alum treatment is also being considered, but the exact amounts that will be used are dependent on other factors and cannot be specified at this time. Dredging of alum floc is the third action. The table suggests that the

TABLE 4-1 Analysis Framework for the EIS

^aAll scenarios assume use of OST and administration of NYC DEP’s Watershed Protection Programs.

^bIn all scenarios, alum addition would be considered, if needed, to comply with New York State Department of Health drinking water quality standards. The total alum applied as part of the analyses depends on infrastructure and operational protocols for the applicable scenario. The quantity, duration, and frequency of alum use for the future with the proposed action would be compared to the future without the proposed action for both scenarios.

^cNote that this row was implicit in the EIS framework and added to the table herein by the Committee after discussion with NYC DEP.

SOURCE: Modified from NYC DEP (2017, Table 3).

“future without the proposed action” has no use of the IRP, substantial alum addition, and no dredging in 2024. The “future with the proposed action” is characterized by use of the IRP, potentially little to no alum addition, and dredging of alum floc in 2024. The latter three items in Table 4-1 (Catskill and Delaware interconnection at Shaft 4, Improvements to Catskill Aqueduct—stop shutters, and repaired Rondout-West Branch Tunnel) are listed as program elements, but they are not “actions” for the purpose of considering their impacts. Rather, they represent infrastructure issues that have to be taken into account during the analysis.

The EIS will address potential environmental impacts in 19 topic areas:

1. Land use, zoning, and public policy;
2. Socioeconomic conditions;
3. Community facilities and services;
4. Open space and recreation;
5. Critical environmental areas;
6. Historical and cultural areas;
7. Aesthetic resources;
8. Water resources and water quality;
9. Natural resources;
10. Hazardous materials;
11. Infrastructure and energy;
12. Solid waste;
13. Transportation;
14. Air quality;
15. Greenhouse gas emissions;
16. Noise;
17. Public health;
18. Construction analysis; and
19. Environmental justice.

The use of OST in the EIS obviously relates directly to impact area 8, water resources and water quality, but OST will also be used, in part, to help analyze several of the other impact areas as well.

There are two main locations (study areas) where the impacts will be considered. The first area is the Ashokan Reservoir and the 30-mile extent of the Lower Esopus Creek (shown in Figure 5 of NYC DEP, 2017), extending to the Lower Esopus Estuary where the river merges with the Hudson River. It is in this area that the EIS will evaluate the impacts of the operation of the Ashokan Release Channel (and the IRP). The second study area is the Kensico Reservoir near the location where the Catskill Aqueduct enters the reservoir (Catskill Infleunt Chamber [CATIC]). The EIS will also consider a potential dewatering site near Kensico Reservoir about

2.5 miles from CATIC (see Figure 7 of NYC DEP, 2017). The activities near Kensico Reservoir for which impacts will be examined include dredging of alum floc, alum floc disposal at dewatering facilities, and alternatives that minimize the floc deposition. For each of the proposed actions (use of IRP, alum use, floc dredging, and dewatering), all 19 areas of impact previously listed will be investigated, even if impacts are expected in only a few areas.

For example, for the Lower Esopus Creek study area, the major focus will be on how much water may be introduced to the system from the Ashokan Release Channel and its quality (focusing mainly on turbidity). However, use of the IRP may be expected to also have some indirect impacts to land use, zoning, and public policy. Recreational activities, tourism, fisheries, agriculture, and other local businesses near the Lower Esopus Creek may also be affected by the IRP.

For impacts in the Kensico study area due to alum use, floc dredging, and floc dewatering, a different set of concerns arises. With respect to impacts to water resources, it will be necessary to predict how the proposed actions will affect turbidity. There may also be impacts to natural resources, such as the effect of aluminum in the water column on fish health and specifically the effects of floc deposits and dredging (or not) on the benthos of Kensico Reservoir. There could be some temporary construction impacts from the dewatering facility.

As part of the consideration of impacts, the EIS will take into account a suite of structural, nonstructural, and operational alternatives that might achieve the same goals and objectives as the proposed actions and reduce, eliminate, or minimize potential impacts. It should be clarified that the “alternatives,” which deal mainly with a multitude of already-proposed structural changes, are not the subject of the EIS themselves because either they had already been subjected to an EIS, or they represent in-system changes that do not have to undergo review, according to New York State regulations. These alternatives can impact the conditions that will determine turbidity levels. If the alternative has already been implemented, it will be considered as part of the baseline conditions. If it will be implemented in the near future, it will be considered part of the “future with or without the proposed action.” The 18 alternatives can be grouped into three categories:

Ashokan Reservoir alternatives

1. West Basin outlet,
2. Dividing weir crest gates,
3. East Basin diversion wall and channel improvements,
4. Upper gate chamber modifications,
5. East Basin intake,
6. Changes to release channel operations,

7. Bypass of low-turbidity Upper Esopus Creek water directly to the Ashokan East Basin,
8. Bypass of Upper Esopus directly to the Lower Esopus Creek.

Alternatives along the Catskill Aqueduct

9. Use of the Hudson River drainage chamber,
10. Use of the Croton Lake siphon,
11. Use of the Rondout pressure tunnel,
12. Use of Wallkill pressure tunnel siphon drain or the Wallkill blow-off chamber.

Alternatives at Kensico Reservoir

13. Perforated target baffle,
14. Sedimentation basin,
15. Perforated baffle wall,
16. Submerged weir,
17. Boom and silt curtains,
18. Large settling basin.

USE OF OST IN THE EIS

As previously described, the EIS requires an assessment of 19 different potential impact areas for a large number of actions and alternatives under a range of conditions. The charge for this Committee is much narrower, to “review the City’s plan for use of OST in evaluating proposed modifications to the Catalum State Pollutant Discharge Elimination System permit, as well as alternatives to be considered in the associated environmental review.” Hence this chapter focuses only on those elements of the EIS that relate to the City’s plan to use OST.

The primary functions of OST with regard to the Catalum EIS are to simulate reservoir operations and conditions consistent with the framework and scenarios outlined in Table 4-1 and to provide simulated reservoir volumes, water quality information, spills, releases, and diversions for the EIS analysis, some of which will feed into other models and analyses. The final EIS scope document (NYC DEP, 2017) has only limited comments on the use of OST. However, the NYC DEP study team (including consultants Hazen and Sawyer) presented a plan to the Committee at its April 2017 meeting on how OST will be used to examine the impacts of the three main actions (operation of the Ashokan Release Channel, alum addition, and dredging alum floc), along with the 18 alternatives, for the three scenarios of baseline conditions, 2019 conditions, and 2024 conditions.

Unlike the use of OST in position analysis mode for day-to-day operations in which the input consists of an ensemble of streamflow forecasts

from the National Weather Service (see Chapter 2), the EIS analysis will use OST in simulation mode, using the historical streamflow record at relevant locations as input. The NYC DEP EIS team proposes to use the historical data from 1948 through 2013 to capture the range of climate fluctuations and conditions that could be experienced in the near future (Kimberlee Kane, personal communication, NYC DEP, June 27, 2017). It is also assumed (but not explicitly stated by the EIS team) that W2 will be “turned on” for the entire OST simulation, which is necessary and appropriate.

The three main actions and 18 alternatives will be separately coded into OST. That is, OST operational rules (constraints, goals, etc.) will be specified to best represent current operations and/or conditions consistent with the proposed alternative. Each alternative will be simulated using the same input conditions (hydrology, demands, infrastructure configuration, etc.), varying only those components related to the specific alternative. For example, the alternative to bypass the Ashokan West Basin completely (No. 7) will require changes in the hydrologic routing in the OASIS portion of the model. The results from OST for each alternative will simulate overall water supply operations, Ashokan and Kensico Reservoir conditions, and conditions of the flow entering the Lower Esopus Creek (for the Lower Esopus Creek study area).

NYC DEP proposes to use sensitivity analyses in OST to help understand model uncertainty, although details of this activity have yet to be explicitly stated.

In their April 25, 2017, presentation (Iyer and Wright, 2017), the NYC DEP EIS team proposed to use certain select performance metrics in the EIS for initial screening of alternatives. These relate to:

• Reducing the frequency of alum treatment,
• Reducing the depth and extent of alum floc deposition in Kensico Reservoir,
• Achieving Ashokan Reservoir storage objectives,
• Maintaining downstream Lower Esopus flow objectives as stated in the IRP (e.g., sufficient community release and flood mitigation).

Results for each of these performance metrics can be adequately simulated by OST. These are derived directly from principal outputs of OST. Only those alternatives that meet minimum criteria for these performance metrics will be further considered and undergo a complete EIS analysis for all impact areas.

Output from OST will be used directly in evaluating some impacts and as input to other models and analyses for evaluating other impacts. For example, output from OST will be used as input to the Army Corps

of Engineers Hydrologic Engineering Center models (HEC-HMS and HEC-RAS), which will evaluate erosion in the Lower Esopus Creek by simulating peak hydraulic conditions of flow, depth, and velocity. Similarly, the U.S. Fish and Wildlife Service Instream Flow Incremental Methodology (IFIM) will use OST output to assess low-flow impacts on fish habitat. These other models and analyses are outside the scope of this report.

The NYC DEP EIS team detailed their approach to how information from the modeling analyses will be used to inform the impact evaluations for each impact category (Iyer and Wright, 2017). Their approach for the Ashokan Reservoir and Lower Esopus Creek area is illustrated with examples as follows:

• Land use, zoning, and public policy (1), community facilities and services (3), open space and recreation (4), and infrastructure (11). These areas are most likely to be affected by inundation, which will be calculated by HEC-RAS using inputs from OST.
• Socioeconomic conditions (2). These impacts will be informed by data and information on inundation (HEC-RAS using inputs from OST) and water quality (OST).
• Historic and cultural areas (6). This impact area will be informed by calculations of flooding and erosion potential determined by hydrologic information that will be used in computations with HEC-RAS (using inputs from OST) and stream geomorphologic assessments.
• Aesthetic resources (7). Impacts in this area will be informed by water quality predictions from OST complemented by erosion calculations.
• Water resources (8). Flow rates and flow velocity in the Lower Esopus Creek, as well as potential areas of inundation, will be determined using HEC-RAS, using hydrologic inputs from OST. Water quality conditions directly from OST will be used.
• Natural resources, wetlands (9). The anticipated inundation areas determined by HEC-RAS (using inputs from OST) will be investigated for wetlands using current federal delineation methods. Wetland function and value assessments will be performed at each redelineated wetland using the methods outlined in USACE (1995).
• Natural resources, fish (9). OST will provide information on water quality as well as hydrologic information, but flow velocity and depths needed for the analysis will be calculated by HEC-RAS, as needed, to determine impacts on fish.
• Natural resources, wildlife (9). Inundation will be calculated by HEC-RAS (using inputs from OST), and then impacts on wildlife assessed therein.

• Public health (17). This impact area relates primarily to water supply issues and will be informed by reservoir operations as predicted by OST.

In this fashion, the OST modeling output combined with other analyses will be used to calculate impacts and performance metrics to compare the various alternatives.

For the Kensico Reservoir study area, OST will be used to estimate the quantity of turbid water entering Kensico Reservoir, water quality in the reservoir, and depositional amounts and patterns in CATIC cove. This output can be used as inputs to analysis of impacts on fish and benthic organisms in the CATIC cove region under each scenario and for each alternative at Kensico Reservoir. As with the Ashokan and Lower Esopus Creek region, other models/analyses will be used in conjunction with OST to determine impacts. For example, the analysis of impacts to aquatic resources will build on recently completed benthic assessments of Kensico Reservoir. Kensico Reservoir bathymetry and changes over time will also be evaluated to approximate dredging quantities.

For the alternatives within the Catskill Aqueduct, OST will be used to estimate how the proposed actions and the alternatives impact the frequency, size, and duration of turbidity events; the use of alum; and operational measures related to discharges from the Catskill Aqueduct.

Critique of the Proposed Uses of OST for the EIS

In a presentation to the Committee on April 25, 2017 (Iyer and Wright, 2017), the NYC DEP EIS study team presented their approach for addressing the EIS requirements as outlined in the final scope document for the EIS, as well as describing where OST output will be used in the EIS analysis. Based on a review of the EIS scope and the presentation by Iyer and Wright (2017), the Committee agrees that using OST in the EIS analysis is appropriate and superior to approaches that would not use OST. By using OST, the NYC DEP can more easily examine a range of conditions, simulate the expected operational response, and observe the simulated outcomes, including the discharge of highly turbid waters and the need for alum use. The NYC DEP’s approach to using OST in the EIS seems well thought out and systematic. Nonetheless, some areas for improvement are discussed in the following section.

Disclosure and Transparency

How the OST output will be used in the analysis of each of the 19 impact areas and how the simulations are run need to be more completely

disclosed and fully transparent. OST provides output on water levels, flow, and water quality in the Catskill system; this output has direct relevance to some of the 19 impact areas (in that OST output could be used as input to other analyses) but no relevance to others. It will be important for the EIS team to provide details (perhaps an outline and a table) on how the specific OST outputs will be used in each impact area assessment beyond what was shown by Iyer and Wright (2017). For example, OST results on flow and turbidity releases to Lower Esopus Creek can be directly used in assessing part of impact area 17 (public health, as turbidity relates to water supply) and area 8 (water resources and quality). The OST results for flow and turbidity also have relevance to impact area 9 (natural resources) as an input to analyzing the impacts to biology (fish, wildlife, benthic invertebrates, and plants), wetlands, and stream geomorphology. For many of these impact areas, additional analyses using output from OST will be needed to quantify impacts. It is important that the EIS team clearly and explicitly outlines how OST output will be used as part of the methods, inputs, analyses, and quantification for each impact area.

Other Methods and Models Used. In the Lower Esopus Creek, detail is needed on the methods that will be used for examining how changes in water quality and flow impact aesthetics, fish, habitat, and erosion, among others. Because OST provides turbidity and flow inputs to the Lower Esopus but does not simulate conditions downstream, the EIS team proposes using other methods and models such as HEC-RAS, IFIM, Rosgen methods, and other tools to evaluate downstream impacts. Although the selection and analysis of these models and tools is beyond the scope of this report, the Committee encourages the EIS team to critically review the models, tools, and methodologies (and the versions of these models or tools) for their suitability to the intended purposes. For example, Rosgen (1994, 2013) has had wide use but may not be appropriate for this particular application (see Simon et al., 2007; Palmer et al., 2014). Also, HEC-RAS is a long-established and well-regarded model supported by the Army Corps of Engineers. However, it has different versions and enhancements; Version 5.0.4 of HEC-RAS has the most recent improvements related to sediment suspension and scour. Downstream conditions in the Lower Esopus were a major impetus for the Consent Order and hence the requirement for doing an EIS, and therefore methods need to be clearly justified.

Parameters Considered. The water quality-related impacts of the proposed actions on public health, ecologic health, and aesthetics need to be assessed for a wider range of parameters than just turbidity. Suspended solids, aluminum (and the associated toxicity to fish), dissolved oxygen, pesticides, herbicides, and pathogens are examples of possible parameters

of concern. The EIS team has not detailed the inventory of water quality parameters they plan to consider and how, if at all, they will use OST output or other analyses to make their assessments. As currently configured, OST is not suitable for these other water quality considerations. A discussion of approaches to address these other water quality concerns is beyond this Committee’s charge, but should nonetheless be made more explicit by NYC DEP.

OASIS Configuration. Whether in position analysis mode or simulation mode, OST simulates operational decisions (e.g., diversions, releases, and alum additions) as it progresses through a year simulation. These simulations are based on the goals, constraints, and weights that are part of the OASIS programming and hence may implicitly favor certain outcomes over others. For example, in the present configuration of OASIS, maintaining low turbidity in the outlet from Kensico is the primary goal, and the weights have been set to reach that goal. If the weights stay the same when OST is used to conduct the EIS, these preferences will remain. If NYC DEP intends to change any of the weights when using OST to conduct the EIS, they need to be transparent about it. If nothing else this implicit expression of preferences should be disclosed and discussed.

Model Inputs

A second major area of concern relates to streamflow and other data that will be used as input to OST and whether they properly address the range of flow and environmental conditions required in the final EIS. In their April 2017 presentation, the EIS team indicated that the OST would be run in simulation mode using historical data on streamflow, supplemented by sensitivity analysis. The historical data were characterized as having sufficient variability to account for conditions that might be observed in the future. First, the historical data used as input to OST for the EIS analysis should include the most recent data available, not just through 2013. There is no reason to truncate the data at 2013 and potentially ignore the most recent hydrologic data that may represent changing conditions (e.g., see Appendix A).

In addition to using the historical streamflow record as input, the EIS team should consider creating simulated streamflow inputs to OST that might reflect climate change. The Final Scope calls for consideration of a “range of precipitation and climate events.” Yet, the EIS team has been vague about how it intends to factor climate change into the EIS exercise. It is theoretically possible that the actions found to have the fewest impacts under existing and historical conditions may not be effective or even functional under future climate change. For example, climate change may

alter turbidity conditions such that the trade-off between adding alum and sending water down the Ashokan Release Channel no longer suffices and both interventions are needed. A sensitivity scenario to test this possibility could span a range of increments of higher temperature and increased precipitation. These could be based on climate model results for the region (see Chapter 5) as well as include potential extreme scenarios. Scenarios could be developed for one or more future time periods such as mid-century (2041–2070) or late-century (2071–2090) and can be presented as a time series or a range for the time period. These scenarios could include two or more emissions scenarios (e.g., low- and high-end scenarios). Results from such tests could help determine whether new infrastructure may be needed.

TMDL Considerations

Third, an issue that received limited discussion in the final scope document for the EIS is the Lower Esopus Total Maximum Daily Load (TMDL). The Lower Esopus has been listed as impaired due to high sediment and turbidity, and thus requires the development of a TMDL under the Clean Water Act. However, development of the TMDL has been deferred because the Lower Esopus is under category 3c for TMDL development where a “waterbody is awaiting the development/evaluation of other restorative measures.” To be conservative, the EIS team may want to assume that the TMDL will be developed in the near future, in which case the EIS analysis should take into consideration whether each alternative will meet the water quality standard and the TMDL. The narrative standards include many prohibitions such as not causing “visible contrasts to natural conditions” (Title 6 Section 703.2, New York Codes, Rules and Regulations). Determining compliance with narrative standards can be complex because there needs to be considerable interpretation on how turbidity loading to the Lower Esopus and high-flow conditions might impact what is more or less a judgment (and not a concentration criterion). Output from OST will not directly answer the question of whether water quality standards are being met and will require another level of interpretation. If the EIS analysis includes this consideration, more explanation will be needed on how the OST outputs relate to water quality standards comparison. Although this may be understood by the EIS team and already be implicit in their EIS approach, it is important to state this explicitly.

CONCLUSIONS AND RECOMMENDATIONS

The NYC DEP’s plans to use OST in the EIS are systematic and appropriate. The EIS team is on a good path and is applying OST appropriately. OST is particularly well suited for providing information on water qual-

ity and hydrologic conditions needed in the EIS analysis and is capable of simulating the proposed actions and relevant alternatives. OST can simulate a range of conditions for different actions and alternatives and can provide output that directly addresses the four performance metrics for screening alternatives in the EIS.

The EIS team needs to be more explicit and transparent in disclosing specifically how they intend to use OST in the EIS. For example, details are needed regarding how they will use the OST output as inputs with other tools to evaluate and quantify impacts for non-OST parameters and other considerations in the 19 impact areas. The EIS team is encouraged to critically review the models, tools, and methodologies that will be linked to the OST output for their applicability and reliability. The EIS team should also consider whether the specific goals, weights, and writing of the code within OASIS may introduce implicit bias when evaluating the various alternatives being considered in the EIS.

The EIS team needs to expand the range of hydrologic inputs it uses in OST and not be limited to historical data through only 2013. Input data should include all years up to the most recent available, because conditions are changing. In addition, it is important to add additional input scenarios that consider the potential impacts of climate change and sensitivity analyses. It is quite possible that the ranking or selection of an alternative might change under different climate conditions (e.g., more rain or extended droughts) or under different assumptions simulated in the sensitivity runs.

REFERENCES

Iyer, S., and B. Wright. 2017. Application of OST in the Modification of the Catalum SPDES Permit EIS. Presentation to the NASEM Committee to Review the NYC DEP Operations Support Tool for Water Supply. April 24.

NYC DEP. 2017. Final Scope for the Modification of the Catalum SPDES Permit Environmental Impact Statement. March. http://www.nyc.gov/html/dep/pdf/reviews/catskill_influent_chamber/catalum-spdes-modification-final-scope.pdf.

Palmer, M. A., K. L. Hondula, and B. J. Koch. 2014. Ecological restoration of streams and rivers: shifting strategies and shifting goals. Annual Review of Ecology, Evolution, and Systematics 45:247–269.

Rosgen, D. L. 1994. A classification of natural rivers. Catena 22(3):169–199.

Rosgen, D. L. 2013. Natural channel design: Fundamental concepts, assumptions, and methods. In: Stream Restoration in Dynamic Fluvial Systems: Scientific Approaches, Analyses, and Tools. A. Simon, S. J. Bennett, and J. M. Castro (eds.). America Geophysical Union, Vol. 194, pp. 69–93.

Simon, A., M. Doyle, M. Kondolf, F. D. Shields, B. Rhoads, and M. McPhillips. 2007. Critical evaluation of how the Rosgen classification and associated “natural channel design” methods fail to integrate and quantify fluvial processes and channel response. Journal of the American Water Resources Association 43(5):1117–1131.

USACE (U.S. Army Corps of Engineers). 1995. The Highway Methodology Workbook Supplement, Wetland Functions and Values: A Descriptive Approach. NEDEP-360-1-30a. USACE New England Division.