Feasibility Study of Subsurface Seawater Intakes West Basin Municipal Water District s Proposed El Segundo Desalination Facility

Transcription

1 Feasibility Study of Subsurface Seawater Intakes West Basin Municipal Water District s Proposed El Segundo Desalination Facility November 16, 2015 Bureau of Reclamation Project No. R14AP

2 Outline Health and Safety Moment Project Overview and Objective Subsurface Seawater Intake (SSI) Technologies Discussion of Feasibility Hydrogeological Setting Phase 1 Evaluation of SSI Feasibility using Guidance Tool Phase 2 Evaluation of SSI Feasibility Findings and Conclusions 2

3 Health and Safety Moment 600% increase in accidents during rain* Impaired Visibility and Traction Slow Down in the Rain Make sure your windshield wipers and tires are in good shape. * Ottenheimerl,

4 Objective Evaluate feasibility of Subsurface Seawater Intakes (SSIs) for a proposed desal facility at El Segundo. 4

5 Overview of Project Scope Develop general Guidance Tool to evaluate technical feasibility of SSIs Prepare document presenting overview of SSIs Use Guidance Tool for a Phase 1 Evaluation of technical feasibility of SSIs for a proposed desal facility at El Segundo Conduct a Phase 2 Evaluation of feasibility of SSIs at El Segundo Findings generally applicable to AES Facility at Redondo Beach 5

6 Overview of SSI Technologies 1. Vertical Wells 2. Slant Wells 3. Radial Collectors (e.g. Ranney Wells) 4. Horizontal Directionally Drilled Wells (HDD) 5. Beach Infiltration Gallery (BIG) 6. Seabed Infiltration Gallery (SIG) 7. Deep Infiltration Galleries (DIG) (off-shore tunnel system with vertical wells). 6

7 Overview of SSI Technologies 1. Vertical Wells Adapted from DRAFT CCC Poseidon ISTAP Phase I Report 7

8 Overview of SSI Technologies 2. Slant Wells (e.g. Dana Point Test SSI Slant Well: ~325 ft long) Adapted from DRAFT CCC Poseidon ISTAP Phase I Report 8

9 Overview of SSI Technologies 3. Radial Collector Wells (e.g. Ranney Wells) (In some settings) Horizontal wells radiating out ft from vertical caisson. (up to 100 ft deep) Commonly used beneath rivers. Adapted from DRAFT CCC Poseidon ISTAP Phase I Report 9

10 Overview of SSI Technologies 4. Horizontal Directionally Drilled Wells (HDD Wells) c 10 a & b adapted from Missimer (2013). c adapted from DRAFT CCC Poseidon ISTAP Phase I Report

11 Overview of SSI Technologies 5. Beach Infiltration Gallery (BIG) A B A adapted from Missimer (2013). B adapted from DRAFT CCC Poseidon ISTAP Phase I Report 11

12 Overview of SSI Technologies 6. Seafloor Infiltration Gallery (SIG) Adapted from DRAFT CCC Poseidon ISTAP Phase I Report 12

13 Overview of SSI Technologies 7. Deep Infiltration Galleries (DIGs) or Water Tunnels (off-shore tunnel system connecting wells). Adapted from DRAFT CCC Poseidon ISTAP Phase I Report and 13 Adapted from DRAFT report by Missimer to Poseidon

14 What is Feasibility? Definition of feasible, CEQA Statute / Coastal Act: Can be accomplished successfully within a reasonable period of time, taking into account economic, environmental, social, and technological factors. The SSI Feasibility Guidance Tool focuses on Technical Feasibility (ISTAP HB SSIs FS, 2014) Construction and operation possible given site conditions using currently available methods. 14

15 Economic Feasibility Amended Ocean Plan (May 2015, State Water Board) Subsurface intakes may be determined to be economically infeasible if additional costs associated with SSIs, as compared to surface intakes, would result in the desalination facility not being economically viable. 15

16 Environmental and Social Feasibility Must be considered in the context of the project and site-specific setting. Examples include: impacts to habitats of sensitive species, construction noise, traffic and emissions, visual aesthetics, disturbance of recreation and business Detailed evaluation required in an EIR. 16

17 SSI Feasibility Guidance Tool Guidance tool developed for screening-level evaluation of feasibility of subsurface intakes. User inputs: Required Intake Flow Rate (Proposed El Segundo Facility 40 MGD) Site-Specific Characteristics Based on the User Inputs the Guidance Tool Provides: Indication of Potential Fatal Flaws for SSI Options, Assessment and Rating of Challenges for SSI Options, Suggestions of Potential Level 2 & 3 Investigations. The guidance tool, which was reviewed and presented earlier this year, was used for a screening-level (Phase 1) feasibility evaluation of SSIs at the El Segundo Site. 17

18 Hydrogeologic Setting at El Segundo Coastal margin of West Coast Groundwater Basin. Thick sequence of unconsolidated interbedded clays, silts, sands and gravels. Stratigraphic Column * Injection Barrier (major aquifer) 18

19 Compilation of Existing Data Onshore boring logs Shallow seafloor borings (800 to 2,500 ft offshore) Seafloor sediment samples (1,000 to 6,000 ft offshore) Existing Reports (NRG, and Chevron Refinery, USGS regional studies, etc.) 19

20 Locations of Existing Data E W 20

21 Compilation of Existing Data Site-Specific Cross-Section 21 Shallow clayey intervals are potential limitation to hydraulic connection between SSIs and the ocean. Key data gap was offshore extent and continuity.

22 Phase 1 Evaluation Using Guidance Tool Assumed eight miles of beach front are available for siting of infrastructure for SSIs. Marina Del Rey Harbor ~8 miles Between Redondo Beach Marina Del Rey Harbors and Ballona Creek. 22 Redondo Beach Harbor

23 Results of Phase 1 Evaluation with Guidance Tool Assuming no constraints on siting of infrastructure and availability of approx eight miles of beach front, Phase 1 Evaluation using the Guidance Manual indicates all SSI technologies are technically feasible at El Segundo. Normalized Challenge Scores of SSIs at El Segundo (100 = most feasible; 0 = most challenging) 23

24 Phase 2 Evaluation Site-Specific Investigation & Analysis Onshore Cone Penetrometer Testing (CPT) Onshore stratigraphy and permeability Offshore geophysical survey Offshore stratigraphy (extent and continuity of clay layers) Groundwater Modeling of SSIs Evaluate sustainable yield and influence on inland aquifers Other feasibility factors (economic, environmental, social) considered in accordance with the Amended Ocean Plan (State Water Board, May 2015) 24

25 Phase 2 Evaluation Additional Site-Specific Investigation Onshore CPTs Beach sand samples Offshore geophysical survey 25

26 Phase 2 Evaluation Onshore CPT Investigation Cone Penetrometer Testing (CPT) at NRG August 31, 2015 Refusal encountered in cobbles and gravel at depth of ~27 ft at two locations. CPT-3 completed to depth of 80 ft Confirms presence two clayey intervals Provided local permeability data 26 26

27 Phase 2 Evaluation Onshore CPT Investigation CPT profile of soil permeability. Confirms presence of two clayey, low-permeability intervals Refusal encountered at two locations in cobbles and gravel at depth of 27 ft (~elev -10ft). 27

28 Phase 2 Evaluation Offshore Geophysical Survey September 3, 2015 (Fugro) Seismic reflection surveys along 5 lines (~20,000 ft total) 1. Edgetech SB-512 Chirp singlechannel sub-bottom profiler for optimum imaging of shallow seds (45 ft below seafloor) 2. Multi-channel survey with single-plate boomer system provided deeper imaging of offshore stratigraphy (700 ft)

29 Phase 2 Evaluation Offshore Geophysical Survey - Chirp 29 Chirp Sub-bottom Profiler single-channel seismic reflection. Images shallow seds (~45 ft below sea floor) Edgetech SB-512 Sub-bottom profiler

30 Phase 2 Evaluation Offshore Geophysical Survey Boomer Multi-channel seismic reflection, imaging of stratigraphy to depths of ~700 ft 30

31 Phase 2 Evaluation Offshore Geophysical Survey W Processed Seismic Reflection Image E W Interpreted Seismic Reflection Image E Confirms continuity offshore of shallow clayey intervals, which are a key limitation to hydraulic connection of SSIs to the ocean

32 Problematic Influence of SSIs on Coastal Margin Aquifers contaminated groundwater aquifer de-designated for municipal use by State Water Board (Resolution 98-18) adjudicated basin interference with injection barrier 32 Injection Barrier

33 Phase 2 Evaluation Groundwater Modeling of SSIs Conducted groundwater modeling to assess sustainable yield and inland impacts of SSIs. Accounts for limited hydraulic connection of SSIs to ocean due to the shallow clay intervals. Calculates inland drawdown of groundwater and portion of flow from inland aquifers. 33

34 Groundwater Modeling of SSIs SSIs at NRG Facility Injection Barrier closer to coast to south 12 Layer Model 30,000 ft by 16,500 ft domain SSIs up to 200 ft deep 34 Site-specific groundwater model developed to help evaluate SSI feasibility sustainable yields and inland influence

35 Groundwater Model Cross Section 35 Model layering consistent with onshore and offshore stratigraphy based on borings and geophysics

36 Vertical Wells Groundwater Model Cross-Section Gage Aquifer Silverado Aquifer 36

37 Vertical Wells Groundwater Contours and Flow Paths 10 Vertical wells pumping a total of 10 MGD Higher flow rates not sustainable. 56% from inland aquifers 37

38 Vertical Wells Contours of Groundwater Drawdown 10 Vertical wells pumping a total of 10 MGD Higher flow rates not sustainable. 56% from inland aquifers Drawdown in coastal margin aquifer extends 1000s of ft inland 38

39 Vertical Wells Not Feasible Impact to inland aquifers would violate State Water Board Resolution (98-18) violate aquifer adjudication draw contaminated groundwater interfere with performance of injection barrier Extent of wells to achieve design flow rate would impact protected habitat and residential properties. 39

40 Increased Extent of SSIs to Achieve 40 MGD - Not Feasible Extend well heads beyond the NRG Facility Still violate SWB Resolution Still violate aquifer adjudication Still draw contaminated water Still interfere with performance of injection barrier (larger impacts to the south) Additional construction, operations, and maintenance impacts: Protected snowy-plover habitat to the north Residential property to the south 40 40

41 Slant Wells Groundwater Model Cross-Section Gage Aquifer Silverado Aquifer 41

42 Slant Wells Groundwater Contours and Flow Paths 10 Slant wells pumping a total of 16 MGD Higher flow rates not sustainable. 55% from inland aquifers 42

43 Slant Wells Contours of Groundwater Drawdown 10 Slant wells pumping a total of 16 MGD Higher flow rates not sustainable. 55% from inland aquifers 43 Drawdown in coastal margin aquifer extends 1000s of ft inland

44 Slant Wells Not Feasible Impact to inland aquifers would violate State Water Board Resolution (98-18) violate aquifer adjudication draw contaminated groundwater interfere with performance of injection barrier Extent of wells to achieve design flow rate would impact protected habitat and residential properties. No precedence at project scale. 44

45 Radial Collector Wells in Gage Aquifer Groundwater Contours and Flow Paths 18 Collector Wells (6 caissons with 3 wells) pumping a total of 5 MGD from Gage Aquifer Higher flow rates not sustainable. 45

46 Radial Collector Wells in Gage Aquifer Contours of Groundwater Drawdown 18 Collector Wells (6 caissons with 3 wells) pumping a total of 5 MGD from Gage Aquifer Higher flow rates not sustainable. Drawdown in coastal margin aquifer extends 1000s of ft inland 46

47 Radial Collector Wells Not Feasible Impact to inland aquifers would violate State Water Board Resolution (98-18) violate aquifer adjudication draw contaminated groundwater interfere with performance of injection barrier Extent of wells to achieve design flow rate would impact protected habitat and residential properties. Vulnerable to sea level rise. 47

48 HDD Wells in Gage Aquifer Groundwater Contours and Flow Paths 13 HDD Wells pumping a total of 18 MGD from Gage Aquifer Higher flow rates not sustainable. 8% from inland aquifers 48

49 HDD Wells in Gage Aquifer Contours of Groundwater Drawdown 13 HDD Wells pumping a total of 18 MGD from Gage Aquifer Higher flow rates not sustainable. 8% from inland aquifers Drawdown in coastal margin aquifer extends 1000s of ft inland 49

50 HDD Wells below Shallow Clay Not Feasible Impact to inland aquifers would violate State Water Board Resolution (98-18) violate aquifer adjudication draw contaminated groundwater interfere with performance of injection barrier Extent of wells to achieve design flow rate would impact protected habitat and residential properties. No precedence for similar setting. 50

51 HDD Wells above Shallow Clay HDD wells above the shallow clayey interval (<20 ft below seafloor) Improves hydraulic connection to ocean Reduces impact to inland aquifers Adapted from Missimer (2013) 51

52 HDD Wells above Shallow Clay Drilling not viable due to gravel and cobbles. Davis (2008), D. Williams / DWR (2008), Nielson et al. (2013) No precedence in similar setting. Unacceptable risk and cost. $80 M to $120 M for 40 mgd source capacity Not feasible for West Basin 52

53 BIG Good hydraulic connection to ocean No impact on inland aquifers Adapted from Missimer (2013) 53

54 BIG Unstable beach Vulnerable to open ocean storm waves Vulnerable to sea level rise No precedence in similar setting Unacceptable risk and cost Not feasible for West Basin 54

55 SIG Good hydraulic connection to ocean No impact on inland aquifers SIG in Japan - protected low-energy coastal margin setting 55 Adapted from DRAFT CCC Poseidon ISTAP Phase I Report

56 SIG Susceptible to clogging by deposition of fines (e.g., turbid storm discharge from Ballona Creek) Vulnerable to open ocean storm waves No precedence in high energy setting Construction and maintenance pose major environmental impacts Unacceptable risk and cost >$774 M for 40 mgd source Not feasible for West Basin 56 Apr 2007

57 DIG (water tunnel) 57 Only one exists, and it is in a karst limestone setting Offshore subsurface at El Segundo is not stable soil Novel idea with no precedence in a marine unconsolidated alluvial setting Unacceptable risk and cost Not feasible for West Basin Apr 2007

58 Findings of Phase 2 Evaluation SSI Tech Vertical Wells Problems Inland aquifers, protected habitat, residential properties Slant Wells HDDs below shallow clay Inland aquifers, protected habitat, residential properties, no precedence at scale Inland aquifers, protected habitat, residential properties, no precedence in similar setting HDDs above shallow clay Gravel and cobbles, no precedence in similar setting, unacceptable risk and cost Radial collectors Inland aquifers, protected habitat, residential properties, vulnerable to sea-level rise 58

59 Findings of Phase 2 Evaluation SSI Tech BIG Problems Unstable beach, open ocean storm waves, vulnerable to sea level rise, no precedence in similar setting, unacceptable risk and cost SIG Clogging by sedimentation, open ocean storm waves, no precedence in high energy setting, construction and maintenance pose major environmental impacts, unacceptable risk and cost DIG Only one exists (karst limestone), no precedence in alluvial setting, subsurface at El Segundo is not stable soil, unacceptable risk and cost 59

60 Conclusions SSIs Not Feasible at El Segundo for West Basin s Proposed Desal Facility Shallow clayey intervals would limit hydraulic connection of SSIs to ocean. Pumping from SSI wells would influence coastal margin aquifers. Offshore infiltration galleries are without precedence in a high-energy coast margin setting. Too costly and risky for West Basin. 60