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  • 4. Environmental Setting (Affected Environment), Impacts, and Mitigation Measures 4.3 Surface Water Hydrology and Water Quality

    CalAm Monterey Peninsula Water Supply Project 4.3-1 ESA / 205335.01 Final EIR/EIS March 2018

    4.3 Surface Water Hydrology and Water Quality Sections

    4.3.1 Setting/Affected Environment 4.3.2 Regulatory Framework 4.3.3 Evaluation Criteria 4.3.4 Approach to Analysis 4.3.5 Direct and Indirect Effects of the Proposed Project 4.3.6 Cumulative Effects of the Proposed Project

    Figures Tables

    4.3-1 Surface Water Resources in the Project Area 4.3-2 Flood Hazards in the Project Area 4.3-3 Areas Subject to Sea Level Rise in the Project

    Area 4.3-4 Illustrations of Trajectory and Behavior of a

    Plume Discharge 4.3-5 Illustrations of the Trajectory of a Dense Brine

    Discharge Plume 4.3-6 Typical Graphics Output of Jet Trajectory from

    VP Method: Brine Only Discharge Scenario 4.3-7 Brine Mixing Zone (BMZ) and Diffuser

    Overview 4.3-8 Non-merging Dense Discharge Plumes from

    Diffuser Ports (Near Field) 4.3-9 3DLIF Image of Horizontal Dense Jet 4.3-10 UM3 Graphical Output for Scenario 2 (Pure

    Brine at 13.98 mgd) 4.3-11 Summary of Approach to Analysis for

    Determining Ocean Plan Compliance

    4.3-1 Seasonal Average Temperature, Salinity, and Density Properties at MRWPCA Outfall Diffuser

    4.3-2 303(d) List of Impaired Water Bodies in the Project Vicinity

    4.3-3 Designated Beneficial Uses of Surface Water Bodies in the Project Vicinity

    4.3-4 Water Quality Objectives in the 2016 Ocean Plan 4.3-5 Water Quality in Monterey Bay (Constituent

    Concentrations Reported Under CCLEAN 2008-2015) 4.3-6 Overview of Post-Construction Requirements for

    Stormwater Management 4.3-7 Applicable Regional and Local Land Use Plans,

    Policies, and Regulations Pertaining to Surface Water Hydrology and Water Quality

    4.3-8 Summary of Impacts Surface Water Hydrology and Water Quality

    4.3-9 Monthly Average Flows of Secondary-Treated Wastewater from the MRWPCA Regional Wastewater Treatment Plant (19982012 and Projected 2017) and the Estimated Brine Stream under the MPWSP

    4.3-10 Proposed Project Discharge Scenarios Modeled 4.3-11 Effluent Water Quality Characteristics Assumed for All

    Modeled Scenarios 4.3-12 Operational Discharge Flow, Salinity, and Density 4.3-13 Dilution Model Results for Dense Discharge

    Scenarios 4.3-14 Dilution Results for Buoyant Discharge Scenarios 4.3-15 MPWSP Operational Discharge Scenarios: Estimated

    Concentrations at the Edge of the ZID for Ocean Plan Constituents of Concern

    4.3-16 MPWSP Operational Discharge Scenarios: Estimated Concentrations at the Edge of the ZID Expressed as Percentage of Ocean Plan Objective for Ocean Plan Constituents of Concern

    4.3-17 Effect of Nozzle Angle on dilution for Select Operational Discharge Scenarios

  • 4. Environmental Setting (Affected Environment), Impacts, and Mitigation Measures 4.3 Surface Water Hydrology and Water Quality

    CalAm Monterey Peninsula Water Supply Project 4.3-2 ESA / 205335.01 Final EIR/EIS March 2018

    This section analyzes the potential for the Monterey Peninsula Water Supply Project (MPWSP or proposed project) which includes 10 slant wells at CEMEX, to adversely affect surface water hydrology and water quality in inland freshwater bodies and in Monterey Bay National Marine Sanctuary (MBNMS) ocean waters1 in the southern portion of Monterey Bay. Impacts on groundwater resources are evaluated in Section 4.4, Groundwater Resources. The secondary effects of potential project-related changes in ocean water quality on marine biological resources are evaluated in Section 4.5, Marine Biological Resources. Impacts related to coastal erosion are evaluated in Section 4.2, Geology, Soils, and Seismicity.

    Comments received on the April 2015 Draft EIR expressed concerns over the potential for hypoxia2 to occur near the seabed as a result of proposed MPWSP operational discharges. Specifically, there was concern that high salinity discharges from the MRWPCA outfall would restrict oxygen supply near the seabed and result in stress or mortality to benthic organisms and other marine resources. Additionally, comments raised concerns regarding the adequacy of model analyses related to salinity and water quality; the travel path of the operational discharge plume; salinity levels within and beyond the area of initial dilution following discharge; and the potential for a dense operational discharge plume to travel along the sea floor and result in impacts on marine resources as a result of elevated salinity and associated toxic effects to habitat and wildlife. These issues are addressed in Section 4.3.5.2 under Impact 4.3-4 and Impact 4.3-5. Comments related to impacts on marine biological resources resulting from operational discharges are addressed in Section 4.5, Marine Biological Resources and are based, in part, on the water quality analyses presented in Impacts 4.3-4 and 4.3-5. Additional sampling and modeling were conducted to address many of these concerns and are addressed in Section 4.3.5.2.

    As a result of comments received on the January 2017 Draft EIR/EIS, revisions have been made to this EIR/EIS section. Those changes include:

    Clarifications and revisions to Setting/Affected Environment and Regulatory Setting sections.

    Additional dilution model analysis to assess dilution and water quality impacts for a wider range of potential operational discharge scenarios.

    Incorporation of additional water quality data into the assessment of potential water quality impacts from operational discharges.

    Revisions relating to compliance with Ocean Plan water quality objectives for two constituents for certain operational discharge scenarios based on revised model analysis and additional water quality data.

    Removal of biologically active filtration from Mitigation Measure 4.3-5.

    Addition of end gate modification for the existing diffuser outfall structure in Mitigation Measure 4.3-5.

    1 Ocean water is defined as water located above the seafloor. 2 Hypoxia, or oxygen depletion, is an environmental phenomenon where the concentration of dissolved oxygen in

    the water column decreases to a level that can no longer support living aquatic organisms. The impacts of hypoxia are often described as creating a so-called dead zone in the marine environment.

  • 4. Environmental Setting (Affected Environment), Impacts, and Mitigation Measures 4.3 Surface Water Hydrology and Water Quality

    CalAm Monterey Peninsula Water Supply Project 4.3-3 ESA / 205335.01 Final EIR/EIS March 2018

    Addition of an assessment of the efficacy of end gate modification to increase dilution for operational discharges.

    Addition of an assessment of secondary impacts from implementing end gate modification under Mitigation Measure 4.3-5.

    Additional model assessment to determine the feasibility of retrofitting the existing outfall diffuser with incline jets to achieve compliance with all Ocean Plan water quality objectives.

    Revision of Mitigation Measure 4.3-5 such that retrofit of the diffuser is elevated to the primary mitigation strategy for mitigating water quality impacts based on model assessment.

    4.3.1 Setting/Affected Environment The study area for evaluation of surface water hydrology and water quality impacts is the Salinas River watershed, Carmel River watershed, and the southern portion of Monterey Bay south of Elkhorn Slough within MBNMS.

    4.3.1.1 Climate and Topography The climate in the study area is moderate throughout the year with warm, dry summers and cool, moist winters. The average temperature is approximately 60 degrees Fahrenheit (F) (Monterey County, 2008). Rainfall occurs primarily between November and April. Average annual rainfall in the county is approximately 18 inches.

    The study area lies within the southern portion of the Coast Ranges province. The topography in the study area is dominated by a rugged coastline and the Diablo, Gabilan, and Santa Lucia mountain ranges with peaks of up to 5,844 feet above mean sea level (msl). Elevations in the project area range from approximately 10 feet above msl in the CEMEX active mining area to roughly 300 feet above msl along General Jim Moore Boulevard in Seaside. The topography of the project area results in part from the gently to moderately rolling sand dunes that are present along the coastal areas in the north to the city of Monterey in the south. Active, wind-blown dunes generally extend less than a 0.5-mile inland, and older, more stabilized dunes extend up to 4 miles inland.

    4.3.1.2 Regional Surface Water Hydrology The project area is located in the Salinas River and Carmel River watersheds (see Figure 4.3-1), which are discussed below. The headwaters of the Salinas and Carmel Rivers, the primary watercourses in the region, originate in the Santa Lucia and Gabilan Mountains (Monterey County, 2008). In general, the overall drainage pattern in the county is from southeast to northwest. The Salinas River drains into Monterey Bay and the Carmel River drains into Carmel Bay both of which are within MBNMS. A third major watershed in the region, the Pajaro River watershed, lies north of the project area and includes the Elkhorn Slough subwatershed. The Pajaro River enters Monterey Bay at the northern tip of Monterey County. The Pajaro River Watershed lies north of and outside of the project area and is not discussed further.

  • 4. Environmental Setting (Affected Environment), Impacts, and Mitigation Measures 4.3 Surface Water Hydrology and Water Quality

    CalAm Monterey Peninsula Water Supply Project 4.3-4 ESA

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