Review of the New York City Department of Environmental Protection Operations Support Tool for Water Supply

by National Academies of Sciences, Engineering, and Medicine, Division on Earth and Life Studies, Water Science and Technology Board, Committee to Review the New York City Department of Environmental Protection Operations Support Tool

Overview

New York City's water supply system is one of the oldest, largest, and most complex in the nation. It delivers more than 1.1 billion gallons of water each day from three upstate watersheds (Croton, Catskill, and Delaware) to meet the needs of more than eight million people in the City, one million people in Westchester, Putnam, Orange, and Ulster counties, and millions of commuters and tourists who visit the City throughout the year. The Catskill and Delaware portions, which make up about 90 percent of the supply, receive no filtration or treatment other than disinfection, except for rare instances of high turbidity when a coagulant is added to increase deposition of suspended solids. The remaining 10 percent of the supply comes from the Croton watershed and receives treatment via filtration.

The drinking water supply is managed by the Bureau of Water Supply within the New York City Department of Environmental Protection (NYC DEP). To continue to avoid filtration of the Catskill/Delaware portion of the water supply, in 2007, NYC DEP reexamined its control of turbidity in the Catskill portion of the water supply, including both structural improvements to the system and operational changes. The Operations Support Tool (OST) was developed as part of these efforts. OST couples models of reservoir operations and water quality; it uses real-time data on streamflow, snow pack, water quality, reservoir levels, diversions, and releases; and it incorporates streamflow forecasts—all in order to predict future reservoir levels, water delivery to customers, and water quality within the system. These predictions inform the system operators, who then make decisions based on the most current data and forecasts.

This report reviews the use of OST in current and future reservoir operations. It considers potential ways in which the City can more effectively use OST, makes recommendations for additional performance measures, and reviews the potential effects of climate change on the City's water supply to help identify and enhance understanding of areas of potential future concern with regard to the use of OST.

Product Details

ISBN-13:	9780309482790
Publisher:	National Academies Press
Publication date:	01/11/2019
Pages:	214
Product dimensions:	6.00(w) x 9.00(h) x (d)

Table of Contents

Summary 1

1 Introduction 13

Description of the New York City Water Supply 13

Regulatory Framework 24

Overview of System Operations 33

Origin of the Study 36

References 40

2 Description of the Operations Support Tool 43

Overview of the Operations Support Tool 43

OST Data Flow and Outputs 53

Models Used in OST 56

How OST Is Used by NYC DEP 69

OST Data Input 75

Validation of OST 88

Conclusions and Recommendations 91

References 93

3 Metrics for the Catskill Turbidity Control Program 97

Background 98

Catskill Turbidity Control Study 101

Catskill Turbidity Control Program 103

Performance Measures 105

Conclusions and Recommendations 111

References 112

4 Use of OST within the Environmental Impact Statement For Modifications to the Catalum SPDES Permit 115

Background on Environmental Impact Statements 115

EIS and the Catalum SPDES Permit 116

Use of OST in the EIS 122

Conclusions and Recommendations 128

References 129

5 USE of OST in a Changing Climate 131

Observations of a Changing Climate: Impacts on Catskill and Delaware Watersheds in Context 132

Global- and Regional-Scale Projections of Climate Change 137

Improving the Utility of OST for Continued Use as an Operational Decision Support Tool 139

Using OST in Simulation Mode to Better Plan for Impacts of Climate Change on the NYC Water Supply 143

Coordination Beyond NYC DEP 151

Conclusions and Recommendations 152

References 153

6 Enhancements and Future Uses of OST 159

Use of OST to Capture Existing Staff Knowledge and Expertise 159

Use of OST as a Training Tool 161

Long-Term Planning Under a Range of Future Conditions 161

Use of OST to Support Compliance with the Filtration Avoidance Determination 162

Use of OST to Manage Other Water Quality Metrics 163

Use of OST to Help Illuminate and Frame Research Questions 164

Communication About OST and How It Is Used 165

References 165

Appendixes

A Observed Hydrologic Trends 167

B Use of Climate and Hydrologic Models for Projecting Future Water Resources 179

C Glossary of Terms 191

D Biographical Sketches of Committee Members and Staff 195