DeepWater Desalination Plant, Moss Landing, California Hydrogeological Literature Review and Analysis
TABLE OF CONTENTS 1.0
INTRODUCTION................................................................................................................................................. 1
2.0
GEOLOGIC SETTING.......................................................................................................................................... 4
3.0 AQUIFER SYSTEMS IN THE VICINITY OF MOSS LANDING .......................................................................... 11 3.1 PAJARO VALLEY – SPRINGFIELD TERRACE, NORTH OF ELKHORN SLOUGH ............................ 11 3.2 SALINAS VALLEY – PRESSURE SUBAREA, SOUTH OF ELKHORN SLOUGH ................................ 12 3.3 DISCUSSION AND RECOMMENDATIONS ............................................................................................ 14 4.0 GROUNDWATER CHARACTERISTICS ............................................................................................................ 26 4.1 STUDY AREA.............................................................................................................................................. 26 4.2 SAMPLING .................................................................................................................................................. 27 4.3 RESULTS ..................................................................................................................................................... 27 5.0 GEOLOGIC HAZARD ANALYSIS ..................................................................................................................... 40 5.1 EARTHQUAKE HAZARDS ........................................................................................................................ 40 5.2 LIQUEFACTION HAZARDS AND EFFECTS ON VERTICAL FLUID FLOW ...................................... 41 5.3 LANDSLIDE HAZARDS ............................................................................................................................. 42 5.4 TSUNAMI HAZARDS ................................................................................................................................. 42 6.0 SUB-SURFACE INTAKE SYSTEMS .................................................................................................................. 51 6.1 TYPES OF SUBSURFACE INTAKE SYSTEMS ....................................................................................... 51 6.2 ADVANTAGES AND DISADVANTAGES ............................................................................................... 51 6.3 DATA FROM SELECTED SUBSURFACE INTAKE SYSTEMS IN OPERATION ................................. 52 7.0
SUMMARY AND CONCLUSIONS .................................................................................................................... 58
8.0
REFERENCES ................................................................................................................................................... 61
LIST OF APPENDICES Appendix A. Coastal Aquifers and Seawater Recharge …………………………….……….A-1 LIST OF FIGURES Figure 1-1. Shaded relief bathymetry/topography map showing the location of Moss Landing on the eastern shoreline of Monterey Bay in central California ...................2 Figure 1-2. Map showing Moss Landing Harbor and locations of geophysical data used to describe the geological setting and subsurface character of the aquifer system .........................................................................................................................3 Figure 2-1. Geological map from Greene and Clark (1979) showing the major surficial rock units and tectonic structure (faults) .....................................................................6 Figure 2-2. Stratigraphic column published by Greene and Clark (1979) for the offshore area south of Monterey Canyon ..................................................................................7 Figure 2-3. Geology and selected wells used to estimate aquifer thicknesses, geologic outcrops, and sites for geophysical logging in the Pajaro Valley, Santa Cruz and Monterey Counties ...............................................................................................8 Figure 2-4. Geology of the Moss Landing area from the 100:000-scale U.S. Geological Survey digital map ......................................................................................................9 Figure 2-5. Isopach map of Pleistocene sediments in Monterey Bay..........................................10 EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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Figure 3-1. Map showing the Salinas Valley Water Project in the vicinity of Moss Landing. Modified from the Monterey County Water Resources Agency (2003) ........................................................................................................................15 Figure 3-2. Cross-section showing relation between geology and selected water quality attributes along the coast in the Pajaro Valley, Santa Cruz and Monterey Counties, California ..................................................................................................16 Figure 3-3. Map and diagrams showing seawater intrusion within the Pajaro Basin. Hydrologic modeling suggests that seawater intrusion occurs as a landward thinning wedge of saline water .................................................................................17 Figure 3-4. Map showing the distribution of pumping wells with depth to top of perforations in the Pajaro Valley, California ............................................................18 Figure 3-5. Geophysical logs and well construction for selected monitoring wells and test holes in the Pajaro Valley, Monterey County, California ..................................19 Figure 3-6. Geophysical logs for selected monitoring wells and test holes in the Pajaro Valley, Monterey County, California .......................................................................20 Figure 3-7. Cross-section across Elkhorn Slough at the Highway 1 bridge based on Caltrans boreholes .....................................................................................................21 Figure 3-8. Shallow geophysical log section from abandoned oil well “Vierra #1” drilled in 1946 and located near Moss Landing ........................................................22 Figure 3-9. Shallow geophysical log section from abandoned oil well “Pieri #1” drilled in 1949 and located near Moss Landing ...................................................................23 Figure 3-10. Seawater intrusion in the Salinas Valley Groundwater Basin – 180-Foot Aquifer ......................................................................................................................24 Figure 3-11. Seawater intrusion in the Salinas Valley Groundwater Basin – 400-Foot Aquifer ......................................................................................................................25 Figure 4-1. The Monterey Bay and Salinas Valley GAMA study unit, locations of study areas, major cities, rivers, creeks, groundwater basins, and subbasins .....................29 Figure 4-2. Monterey study area; public supply wells sampled are shown in black; flowpath wells are shown in blue; monitoring wells 1-3 are shown in green ..................30 Figure 4-3. Blue circles show wells where conductivity is >700 uS/L .......................................31 Figure 5-1. Map showing earthquake epicenters (seismicity) and major faults in the vicinity of Moss Landing, California ........................................................................44 Figure 5-2. Map showing distribution of liquefaction-induced ground failures in the Moss Landing area following the October 18, 1989 Loma Prieta earthquake .........45 Figure 5-3. CPT profiles of the subsurface deposits at the Moss Landing Marine Laboratory where liquefaction occurred following the 1989 Loma Prieta earthquake .................................................................................................................46 Figure 5-4. Marigram from the Monterey Tide Gauge showing the first 12 hours of the tsunami from the Prince William Sound, Alaska, Good Friday earthquake of March 28, 1964 .........................................................................................................47 Figure 6-1. Selected subsurface intake well systems...................................................................54 Figure 6-2. Feed water supply (mgd) and number of wells for each desalination plant presented in Table 6-1...............................................................................................55 Figure 6-3. Average well feed water supply (mgd) for each desalination plant presented in Table 6-1 ...............................................................................................................56 EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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LIST OF TABLES Table 4-1. Table 4-2. Table 4-3. Table 4-4. Table 4-5a. Table 4-5b. Table 4-6. Table 4-7 Table 5-1. Table 5-2. Table 5-3. Table 6-1.
Analyte list ................................................................................................................32 Water quality parameters ..........................................................................................33 Major and minor ions ................................................................................................34 Nutrients and DOC and radioisotopes ......................................................................35 Trace elements - A ....................................................................................................36 Trace elements - B ....................................................................................................37 Volatile organic compounds .....................................................................................38 Pesticides...................................................................................................................39 Significant historical earthquakes affecting the Monterey Bay area ........................48 Major faults affecting the Moss Landing area (within 100 km of site). ...................49 Modified Mercalli Intensity Scale (1931) .................................................................50 Selected subsurface beach well intake systems for seawater desalination currently in operation ................................................................................................57
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DEEPWATER DESALINATION PLANT MOSS LANDING, CALIFORNIA HYDROGEOLOGICAL LITERATURE REVIEW AND ANALYSIS
1.0
INTRODUCTION
Moss Landing is located in Monterey County on the central California coast near the center of Monterey Bay (Figure 1-1). The harbor at Moss Landing is bisected by the Elkhorn Slough where the Salinas River empties into the Pacific Ocean via Monterey Bay (Figure 1-2). Monterey Canyon, one of the largest active submarine canyons in western North America, lies directly west offshore of the mouth of Elkhorn Slough. Moss Landing and Elkhorn Slough lie between two major watersheds – the Pajaro River and the Salinas River – and both groundwater basins suffer from seawater intrusion along the coast. DeepWater Desal (DWD) is planning to construct a seawater desalination plant at Moss Landing to address the growing demand for freshwater in the Monterey Bay area. This report describes the hydrogeology of the area and the available background literature that is being used to evaluate the feasibility of subsurface intake systems for the project. The DWD facility is expected to have the capacity of 25 mgd (milliongallons-per-day). This report consists of six chapters. Chapter 1: Chapter 2: Chapter 3:
Chapter 4:
Chapter 5: Chapter 6:
Chapter 7:
General introduction to the project site and the proposed desalination plant. Gives a historical evaluation of the geological character and formation of the project site. Provides a description of the two major groundwater basins, the Pajaro Valley and the Salinas Valley, which exist on opposite sides of the Elkhorn Slough. In this chapter, the main water-bearing units, the upper 180-foot Aquifer and the lower 400-foot Aquifer, were discussed, along with the 900foot Aquifer. This chapter also describes the shallow alluvial aquifer, including Dune Sand Aquifer, which may be used for subsurface intake at other desalination plants. Discussion of the groundwater chemical characteristics for the wells located near the coast. Several tables are presented to provide qualitative values for various water quality parameters, ions, nutrients, DOC and radioisotopes, trace elements, volatile compounds, and pesticides. Discussion of historical and potential future hazards from earthquakes and tsunamis. Brief description of various types of subsurface intake systems, as well as a discussion of their advantages and disadvantages. The intake capacities of selected desalination plants in operation are presented in graphical and tabular forms. Summary and conclusions of the study.
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Figure 1-1. Shaded relief bathymetry/topography map showing the location of Moss Landing on the eastern shoreline of Monterey Bay in central California. Monterey Canyon is one of the largest active submarine canyons along the U.S. West Coast. (USGS, 2005)
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Figure 1-2. Map showing Moss Landing Harbor and locations of geophysical data used to describe the geological setting and subsurface character of the aquifer system. Seismic reflection profiles and offshore backscatter images are provided by the U.S. Geological Survey, National Archive of Marine Seismic Surveys (NAMSS) and the Coastal and Marine Geology Branch (InfoBank). Bathymetry data used in this study were acquired, processed, archived, and distributed by the Seafloor Mapping Lab of California State University Monterey Bay. The oil well data are provided by the State of California Division of Oil, Gas, and Geothermal Resources (DOGGR). The water well data are provided by the Pajaro Valley Water Management Agency and published in Hanson (2003). The coastline and inland waterways boundaries are provided by Bureau of Ocean Energy Management (BOEM).
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2.0
GEOLOGIC SETTING
The Monterey Bay region of central California lies within the California Coast Ranges geomorphic province along the Pacific continental margin of North America (Greene, 1977; Greene and Clark, 1979). The Coast Ranges in central California have undergone a complex geological history related to the transition of the margin from Mesozoic to early Tertiary subduction of the Farallon plate beneath North America to the late Cenozoic evolution of the Pacific-North America transform fault plate boundary (Atwater, 1970). Active northwesttrending strike-slip faults of the San Andreas system accommodate the right-lateral shear between the Pacific and North America tectonic plates at present (Wallace, 1990). A component of northeast-directed convergence is also evident based on earthquake focal mechanisms, folding and thrust faulting within the Coast Ranges (Plafker and Galloway, 1989). The Monterey Bay region is located on Cretaceous granitic rocks of the Salinian block (Page, 1970), which is flanked by two major fault zones – the San Andreas to the east and the San Gregorio offshore to the west (Figure 2-1). The relatively impermeable basement rocks are estimated to be about 1 km below the surface in the coastal area (Greene and Clark, 1979). A well located a few kilometers south of Moss Landing may have reached basement at a depth of 989 meters (3245 ft). However, exploratory oil and gas wells drilled to the north of Elkhorn Slough found a large erosional “gorge” cut into the Salinian granitic rocks nearly 2.5 kilometers below the ground surface (Greene, 1977; Schwartz, 1983). The well log for Vierra #1 (DOGGR, 2003) drilled near Moss Landing recorded hard sand at a total depth of 7916 feet (2413 m; Figure 1-2). The thick sand layers above the bottom of the well were described as granitic debris and may represent decomposed granite, so the true depth to basement is uncertain. A sequence of poorly permeable consolidated rocks of Miocene age, described as the Monterey formation, overlie the basement in the Monterey Bay region (Figure 2-2, Greene and Clark, 1977). The Monterey formation in the coastal area near Moss Landing consists of marine mudstones, shales, siltstones, and to the south, basal sandstone. Thickness of the Monterey unit in Monterey Bay is about 550 to 640 m (1800-2100 ft; Figure 2-2). Marine sediment deposition continued into the Pliocene epoch with the semi-consolidated to consolidated sandstone, siltstone, and shale of the Purisima formation. The Purisima formation dips to the west or northwest in southern Monterey Bay and crops out on the seafloor to the north near Santa Cruz and along the walls of the Monterey Canyon, near the 200 m (656 ft) contour a few miles west of Moss Landing (Figure 2-1, Greene and Clark, 1979; Figure 2-3, Hanson, 2003). Strata of the Purisima formation are about 400 m thick (1312 ft) along the coast from north of Moss Landing (Figure 2-2, Greene and Clark, 1979) and thin to zero at the erosional edge in southernmost Monterey Bay. Upper Pliocene to Holocene sediments along the coast of Monterey Bay include the PlioPleistocene Paso Robles formation, the Pleistocene Aromas Sand, and surficial deposits including Quaternary deltaic sediments of the Salinas River, submarine canyon fill, slump and landslide deposits, and Holocene marine sediments (Figure 2-2, Greene and Clark, 1979). Onshore deposits of eolian, older dune sands, and marine terraces are exposed, and basin sediments of sand and mud are submerged in parts of the Elkhorn Slough (Figure 2-4, Wagner et al., 2002). The Aromas Sand shows cross-bedding in seismic reflection profiles, appears to EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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unconformably overlie the Purisima formation north of Monterey Canyon, and extends more than 10 km seaward from the mouth of the Pajaro River (Figure 2-1, Greene and Clark, 1979; Figure 2-3, Hanson, 2003; Figure 2-4, Wagner et al., 2002). South of the submarine canyon, the undifferentiated Aromas-San Pablo units are poorly defined in seismic reflection profiles and lap onto the folded and faulted Monterey strata offshore in the Monterey Bay fault zone (Greene, 1977; Greene and Clark, 1979). The Aromas Sand is more than 255 m thick (837 ft; Figure 2-5) near the coast north of the submarine canyon, and less than about 75 m thick (246 ft) south of the canyon. Quaternary deltaic deposits of the Salinas River extend up to eight kilometers offshore south of the canyon, whereas Holocene marine surficial deposits extend as a west-northwest elongate mass from the mouth of the Pajaro River for more than 25 km toward the northwest corner of Monterey Bay (Figure 2-5, Greene and Clark, 1979). The surficial deposits are about 25 m (82 ft) thick near the coast between Moss Landing and the Pajaro River (Figure 2-5) and likely represent deltaic deposits from the Pajaro River.
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Figure 2-1. Geological map from Greene and Clark (1979) showing the major surficial rock units and tectonic structure (faults). Granitic basement rocks of the Salinian crustal block outcrop near Monterey and in the Santa Cruz Mountains. Moss Landing (ML) lies on the coastal plain near the head of Monterey submarine canyon.
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Figure 2-2. Stratigraphic column published by Greene and Clark (1979) for the offshore area south of Monterey Canyon (see Figure 2-1 for general location #4).
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Figure 2-3. Geology and selected wells used to estimate aquifer thicknesses, geologic outcrops, and sites for geophysical logging in the Pajaro Valley, Santa Cruz and Monterey Counties (Source: Hanson, 2003). Profile A-A’ is shown in Figure 3-2.
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Figure 2-4. Geology of the Moss Landing area from the 100:000-scale U.S. Geological Survey digital map (Wagner et al., 2002). The red line shows the approximate location of the proposed intake pipe. Onshore wells (oil in red, water in green) with geophysical and descriptive logs are shown. The blue line labeled Caltrans shows the location of a borehole cross-section that was used to determine the subsurface stratigraphy beneath the Highway 1 bridge across Elkhorn Slough (Figure 3-7).
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Figure 2-5. Isopach map of Pleistocene sediments in Monterey Bay (Source: Greene and Clark, 1979). See Figure 2-2 for stratigraphic column offshore southern Monterey Bay.
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3.0
AQUIFER SYSTEMS IN THE VICINITY OF MOSS LANDING
Two major groundwater basins, the Pajaro Valley and the Salinas Valley, exist on opposite sides of the Elkhorn Slough at Moss Landing (Figure 2-3, Hanson, 2003; Figure 3-1, MCWRA, 2003; PVWMA, 2003). The Pajaro Valley is the coastal part of the Pajaro River Basin located in southern Santa Cruz County and Monterey County north of Elkhorn Slough. The Springfield Terrace subarea comprises the region between the Pajaro River and Elkhorn Slough (Figure 2-3). The coastal part of the Salinas Valley Basin includes the Pressure subarea (Figure 3-1, MCWRA, 2003) located south of Elkhorn Slough and adjacent to Moss Landing. 3.1
PAJARO VALLEY – SPRINGFIELD TERRACE, NORTH OF ELKHORN SLOUGH
The principal aquifers described by the Pajaro Valley Water Management Agency (PVWMA, 2000; Hanson, 2003) are based on the major geologic units, including the Purisima formation, Aromas Sand and Quaternary Alluvium (Figure 3-2). The Aromas Sand is subdivided based on lithology and geophysical characteristics into upper and lower parts. The upper-aquifer system may include both the alluvial deposits and the upper Aromas Sand, whereas the loweraquifer system may include both the lower Aromas Sand and Purisima Formation (Hanson, 2003). Hanson states that “the geologic factors that, in part, control the distribution of recharge, pumpage, and related seawater intrusion include the layering of the sediments, the potential connectivity of the coarse-grained deposits that allows deep percolation of recharge to replenish pumpage, and the potential barriers to groundwater flow or infiltration of recharge.” Coarse-grained deposits that exist over large areas control and define the aquifer where pumpage and related seawater intrusion occur (Hanson, 2003). The upper alluvial sediments include eolian, terrace, and fluvial deposits onshore and deltaic deposits offshore (Figure 2-2, Greene and Clark, 1979; Figure 2-4, Wagner et al., 2002; Dupré, 1975). Water wells in the Springfield Terrace subarea of the Pajaro Valley are widespread and generally tap the upper aquifer in the coastal area (Figure 3-4, Hanson, 2003). The upper Aromas Sand in the Pajaro Valley is considered to connect to the 180-foot aquifer in the Salinas Valley (Pressure subarea, Figure 3-1). The lower aquifer is mostly within the Aromas Sand (Johnson, 1982) and includes fluvial sand and gravels (Figure 3-5, Hanson, 2003). More widely-spaced wells pumping in the 300-600 ft interval tap the lower aquifer in the coastal area (Figure 3-4, Hanson, 2003). The lower aquifer may correspond to the 400-ft aquifer of the Salinas Valley. The upper aquifer has seawater intrusion which intrudes at a depth near the coast of 100200 ft below sea level (Figure 3-2, Hanson 2003, quoting Johnson, 1982; Figure 3-3, PVWMA, 2000). Saline water has intruded through most of the coastal area north of Moss Landing (Figure 3-3, PVWMA, 2000), progressing farther east in the upper-aquifer system. Hydrologic modeling suggests that seawater intrusion occurs as a landward-thinning wedge of saline water within the major aquifer systems (Figure 3-3, PVWMA, 2000). The lower aquifer, in particular the lower Aromas Sand, might be considered as an area of potential seawater intrusion, but the data north of the Pajaro River show distinct zones of “older sea water” based on geochemical analysis (Figure 3-2, Hanson, 2003). EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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Large areas of fine-grained deposits have been mapped as a continuous layer in the Pajaro River floodplain (Hanson, 2003). However, drillers’ logs and geophysical logs from wells in the area show variable thickness of shallow fine-grained deposits (Figures 3-5 and 3-6, Hanson, 2003). Boreholes drilled by Caltrans for construction of the Highway 1 Bridge across Elkhorn Slough also show this complex layering of fine-grained and coarse-grained units in the shallowest deposits (Figure 3-7, SEI, 2006). Here at Moss Landing, a distinct fining-upward sequence is recognized and considered to represent the filling of the Elkhorn Valley paleochannel and onshore extension of Monterey Canyon as sea level rose following the last ice age. These fine-grained layers that separate the coarse-grained aquifers are called “aquitards” and appear to be laterally extensive parallel to the coast (Figure 3-2, Hanson, 2003; Figure 3-7, SEI, 2006). Massive fine-grained layers in the shallow subsurface near the Moss Landing area are exemplified in the well log from test hole PV-5 (Figure 3-6, Hanson, 2003) and from the abandoned oil well “Vierra #1” (Figure 3-8). Surficial sediments in the area around Moss Landing include unconsolidated marine and non-marine gravel, sand, silt, and clay deposits. Recently stabilized coarse-grained sand dunes that surround the salt marshes of Elkhorn Slough facilitate rapid penetration of water delivered by local storms. However, widespread layers of fine-grained material in the shallow alluvium and Aromas Sand create aquitards that limit recharge of the deeper aquifers. Deep saline waters encountered in wells of the Pajaro Valley represent recharge from thousands of years ago (Hanson, 2003). Layered strata in the coastal aquifer systems restrict vertical migration of water resulting in seawater intrusion that is vertically restricted. Rather than a wedge of saline water, discrete layers of coarse-grained water-bearing units from 10-150 feet thick accommodate the lateral migration of seawater (Hanson, 2003). Seawater intrusion was recognized as early as 1943 in Santa Cruz and Monterey Counties; seasonal pumping troughs of 15 ft below sea level were considered to drive the intrusion (California State Water Resources Board, 1953). The most extensive seawater intrusion has been in the aquifers from 100 to 200 ft depths below sea level, and less severe in the lower Aromas Sand (Muir, 1974). Long-term declines of groundwater levels in the Springfield Terrace subarea exceed 20 ft prior to the 1990s, and increasing water-level differences exceeding 10 ft are occurring in the Aromas Sand relative to shallow aquifers (well PV-4A, Figure 3-2, Hanson, 2003). Droughts exacerbate the decline in groundwater levels and may increase seawater intrusion. However, depressed groundwater levels in the coastal areas suggest that seawater intrusion may be unable to recharge the aquifer at depth if subsurface intakes for desalination plants are installed. The fine-grained layers that restrict vertical fluid movement for seawater intrusion would also restrict recharge of offshore aquifers with fresh seawater for desalination projects. 3.2
SALINAS VALLEY – PRESSURE SUBAREA, SOUTH OF ELKHORN SLOUGH
The principal aquifers within the Pressure subarea of the Salinas Valley are based on the typical depth of the aquifer tapped by wells (Figure 3-1, MCWRA, 2003). The primary aquifer system is called the 180/400-Foot Aquifer Subbasin, which includes the lower reaches of the Salinas River and the coastal area south of Moss Landing. As stated in DWR Bulletin 118 (2004), “The northern boundary of the 180/400-Foot Aquifer Subbasin is shared with the Pajaro EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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Valley Groundwater Basin and coincides with the inland projection of a 400-foot deep, buried and clay-filled paleodrainage of the Salinas River. This acts as a barrier to groundwater flow between these subbasins (DWR, 1969; Durbin et al., 1978).” Two main water-bearing units, the upper 180-Foot Aquifer and the lower 400-Foot Aquifer, exist within the Aromas Sand with the names based on their average depth. A complex zone of interconnected sands, gravels, and clay lenses, varying from 50-150 feet in thickness and averaging 100 ft comprise the 180-Foot Aquifer (DWR, 2004). The 400-Foot Aquifer also consists of sand, gravel, and clay lenses with a greater average thickness of about 200 ft (DWR, 2004). As observed in the Pajaro Valley, the two main aquifers are separated by a zone of discontinuous aquifers and aquitards with thicknesses varying from 10 to 70 ft. A near-surface water-bearing zone exists as a minor source of poor quality water, and corresponds to the shallow alluvial aquifer in the Pajaro Valley north of Elkhorn Slough. The Dune Sand Aquifer within recent dune sands along the shoreline of Monterey Bay south of Moss Landing may correspond to the shallow alluvial aquifer. The Dune Sand Aquifer extends from the ground surface to 160 ft below mean sea level and consists of silty, fine to medium sand with some paleosols (ancient soil horizons) at various levels. A deeper aquifer consisting of alternating layers of sand-gravel mixtures and clays, up to 900-ft thick, exists and is referred to as the 900-Foot or Deep Aquifer (DWR, 2004). The 400Foot and 900-Foot aquifers are separated by a blue marine clay aquitard. The 900-Foot Aquifer may correspond to the Paso Robles Formation (Figure 2-2) or the Purisima Formation aquifer of the Pajaro Valley, which crops out on the south wall of Monterey Canyon offshore (Figure 2-1) at seafloor depths of 500-1000 ft. The 900-Foot Aquifer has been used to replenish groundwater from the 180-Foot and 400-Foot aquifers that were contaminated by seawater intrusion (Monterey County Planning Department, 2012). Massive fine-grained layers in the shallow subsurface south of Moss Landing are exemplified in the well log from the abandoned oil well “Pieri #1” (Figure 3-9). According to DWR Bulletin 118 (2004), “Heavy pumping of the 180- and 400-Foot Aquifers has caused significant seawater intrusion into both these aquifers, which was first documented in the 1930s (DWR, 1946). Groundwater flow in the northernmost subbasin has been directed from Monterey Bay inland since at least this time. By 1995, seawater had intruded over five miles inland through the 180-Foot Aquifer, including the area beneath the towns of Castroville and Marina. Seawater has also intruded over two miles into the 400-Foot Aquifer by 1995.” The Monterey County Water Resources Agency (MCWRA, 2003) mapped the time history of seawater intrusion within these two aquifers (Figures 3-10 and 3-11). Elongate “tongues” of intrusion appear to coincide with the surface stream channels and are likely to follow the buried Pleistocene paleochannels of the Salinas River. Seawater intrusion does not appear to have progressed farther inland along the south side of Elkhorn Slough, perhaps due to the fine-grained sediment layers that filled the Elkhorn Slough paleochannel; these may represent estuarine deposits similar to the modern sediments in Elkhorn Slough (basin deposits in Figure 2-4, Wagner et al., 2002). In contrast, seawater intrusion to the north in the Pajaro Valley does appear to reach farther inland along the north side of Elkhorn Slough (Figure 3-3). This EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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observation may indicate a more continuous coarse-grained aquifer to the north of Elkhorn Slough than there is to the south. Continuing with DWR Bulletin 118, “Due to the impermeable nature of the clay aquitard above the 180-Foot Aquifer, subbasin recharge (including that from precipitation, agricultural return flows, or river flow) is nil. Instead, recharge is from underflow originating in upper valley areas such as the Arroyo Seco Cone and Salinas River bed or the adjacent Eastside Subbasin, and more recently, from seawater intrusion. Historically, groundwater flowed from subbasins to the south and east through the subbasin and seaward to discharge zones in the walls of the submarine canyon in Monterey Bay (Durbin and others, 1978; Greene, 1970). With increased pumping in the adjacent Eastside Subbasin since the 1970s, groundwater flow is dominantly northeastward in the central and southern subbasin.” If historical discharge zones of fresh groundwater were in the walls of the Monterey Canyon, then one could infer that recharge for seawater intrusion is derived mainly from the canyon walls; vertical recharge from the seafloor into the 180-Foot Aquifer may be negligible. Careful mapping of the blue clay aquitard above the 180-Foot Aquifer would be necessary to identify the likely areas of seawater recharge. Hydrologic modeling would be necessary to determine what flow rates could be achieved for a desalination intake system. The observations of seawater intrusion over time may provide a calibration for the hydrologic modeling for the intake system. According to the California Department of Water Resources (DWR Bulletin 160-93), during the drought of 1987-1992, seawater intrusion rates accelerated due to “decreased ground water recharge and increased ground water extraction.” The current drought may create similar problems with increased rates of seawater intrusion. Some important questions arise: Would seawater extraction from subsurface intakes for desalination alleviate this problem? Would injection of brines resulting from desalination make the problem worse? Would denser brines flow seaward within the aquifer and act as a barrier to seawater intrusion? Or would that create greater depression of groundwater levels inland? In the absence of a natural barrier, like the Newport-Inglewood fault zone in the LA-Orange Counties region, would a line of injection wells to produce a barrier to seawater intrusion be infeasible? 3.3
DISCUSSION AND RECOMMENDATIONS
Careful hydrologic modeling and analysis must be conducted to evaluate the feasibility and consequences of potential subsurface seawater intake systems. Abundant data exist onshore to describe the subsurface geology as described above, and there are abundant data farther offshore, >1-km to the seismic profiles (Figures 1-2 and 2-4) where the U.S. Geological Survey and other scientists have been mapping the Monterey Bay Marine Sanctuary. However, there are few subsurface data in the nearshore region where tidal currents, ocean waves, and littoral drift may have eroded and removed the fine-grained deposits. A layer of coarse material that may be well-suited for an offshore subsurface intake system may exist in the nearshore area.
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Figure 3-1. Map showing the Salinas Valley Water Project in the vicinity of Moss Landing. Modified from the Monterey County Water Resources Agency (MCWRA, 2003).
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Figure 3-2. Cross-section showing relation between geology and selected water quality attributes along the coast in the Pajaro Valley, Santa Cruz and Monterey Counties, California. Profile location is shown in Figure 2-3. (Source: Hanson, 2003).
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Figure 3-3. Map and diagrams showing seawater intrusion within the Pajaro Basin. Hydrologic modeling suggests that seawater intrusion occurs as a landward thinning wedge of saline water. (Source: PVWMA, 2000).
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Figure 3-4. Map showing the distribution of pumping wells with depth to top of perforations in the Pajaro Valley, California (modifed from Hanson, 2003). ML = Moss Landing.
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Figure 3-5. Geophysical logs and well construction for selected monitoring wells and test holes in the Pajaro Valley, Monterey County, California. (Source: Hanson, 2003) Well locations are shown in Figure 2-3.
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Figure 3-6. Geophysical logs for selected monitoring wells and test holes in the Pajaro Valley, Monterey County, California. (Source: Hanson, 2003) Well locations are shown in Figure 1-2.
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Figure 3-7. Cross-section across Elkhorn Slough at the Highway 1 bridge based on Caltrans boreholes (Source: SEI, 2006). Location of cross-section is shown on Figure 2-4.
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Figure 3-8. Shallow geophysical log section from abandoned oil well “Vierra #1” drilled in 1946 and located near Moss Landing (location shown on Figure 1-2). A prominent resistivity kick between 150 and 200 ft is in a layer described as “Clay, sticky with streaks sand and oyster shells” on the drillers’ log. (Data from DOGGR, 2003).
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Figure 3-9. Shallow geophysical log section from abandoned oil well “Pieri #1” drilled in 1949 and located near Moss Landing (location shown on Figure 1-2). (Data from DOGGR, 2003).
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Figure 3-10. Seawater Intrusion in the Salinas Valley Groundwater Basin – 180-Foot Aquifer, August 6, 2012. (Source: Monterey County Water Resource Agency, http://www.MCWRA-CO.Monterey.ca.us)
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Figure 3-11. Seawater Intrusion in the Salinas Valley Ground Water Basin – 400-Foot Aquifer, August 7, 2012. (Source: Monterey County Water Resource Agency, http://www.MCWRA-CO.Monterey.ca.us)
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4.0 4.1
GROUNDWATER CHARACTERISTICS
STUDY AREA
The Salinas River is the Central Coast’s largest river and has the fourth largest watershed in California. Most rivers in California flow west or south. River water is used for irrigation. The river and the underground flow catch agricultural discharges, precipitation percolated through surface soils, and river and stream infiltration, all potential sources of contaminants. In considering subsurface intake systems for desalination plans, it is important to know the quality of the underground water in the vicinity of the plant. A large database exists as a result of the Groundwater Ambient Monitoring and Assessment program (GAMA) carried out by the U.S. Geological Survey (USGS), in collaboration with the California State Water Resource Control Board and Lawrence Livermore National Laboratory (LLNL). The GAMA program is a statewide groundwater quality monitoring and assessment program designed to help better understand and identify risks to groundwater resources (Hanson et al., 2002; RMC, 2006; Kulongoski and Belitz, 2007). Groundwater quality in the approximately 1,000-square-mile Monterey Bay and Salinas Valley study unit (Figure 4-1) was investigated in order to provide a spatial assessment of raw groundwater quality. Samples were collected from public-supply wells and monitoring wells. These wells were located in Monterey, Santa Cruz, and San Luis Obispo Counties. The samples were analyzed for volatile organic compounds (VOCs), pesticides, nutrients, metals, major and minor ions, trace elements, radioactivity, microbial indicators, and dissolved noble gases. Naturally occurring isotopes (tritium, carbon-14, helium-4, and the isotopic composition of oxygen and hydrogen) were also measured to help identify the source and age of the sampled groundwater. Figure 4-2 shows the wells at Monterey Bay study area. Those wells located nearby the coast at Moss Landing are most likely to impact the subsurface intake system of the desalination plant. The Monterey Bay (MSMB) study area extends from east of Santa Cruz south along Monterey Bay to the Forebay of the Salinas Valley. It covers approximately 450mi2 and includes most of the Quaternary sediment-filled basins in this area, which includes the Pajaro Valley, Carmel Valley, and the following subbasins of the Salinas Valley: 180/400Foot Aquifer, Eastside Aquifer, Seaside Area, Langley Area, and Corral de Tierra Area. The sampling stations penetrate several water-bearing geologic units. The geologic units located to the north in the Pajaro Valley (Figure 4-1) are the Purisima Formation, the Aromas Sands, the Terrace Deposits, the Quarternary alluvium, and the Dune Deposits (Johnson et al., 1988). The geologic units located to the south are the Salinas Valley formations (Figure 4-1): the 180/400-Foot Aquifer and Langley Area subdivisions. The 180/400-Foot Aquifer also extends to the southeast and is referred to as the East Side Aquifer in Figure 4-1. To the south, the 180/400-Foot Aquifer joins the Forbay and Upper Valley aquifers located in the Salinas Valley groundwater basin. EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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4.2
SAMPLING
Groundwater samples were collected and analyzed for the constituents listed on either the fast, slow, or monitoring-well sampling schedules. Table 4-1 gives a summary list for the major parameters analyzed per sample for fast, slow and monitoring well schedules. A complete list of these analytes is given by Kulongoski and Belitz (2007). All wells were sampled between August and September 2005. For the fast schedule, samples were collected at the well head using a foot-long length of Teflon tubing. For the slow schedule, the samples were collected inside an enclosed flowthrough chamber located inside a mobile laboratory and connected to the well head by a 10-50 ft length of the Teflon tubing. For the field measurements groundwater was pumped through a flow-through chamber fitted with a multi-probe meter that simultaneously measures pH, DO, temperature, conductivity, and turbidity. 4.3
RESULTS
The results presented here are for the 26 Monterey Bay sampling stations in the area within 10 miles of the desalination plant (Figure 4-2). Table 4-2 presents the results of the water quality parameters; Table 4-3 shows the concentration of major and minor ions near the proposed plant; Table 4-4 lists nutrients, dissolved organic matter (DOC), and radio isotopes; Table 4-5 lists the trace elements; Table 4-6 lists volatile organic carbons and gasoline additives; and Table 4-7 lists the pesticides. Tables 4-2 and 4-6 list the results for selected stations measured under the “fast” and “slow” sampling schedule within 10 miles of the coast, while Tables 4-3, 4-4, 4-5, and 4-7 show the additional analytes measured under the monitoring program for selected stations. Tables 4-2 through 4-7 show that there can be discrepancies between stations even though they are all from within the same 10-mile radius. However, one should takes into account the fact that the area contains several aquifers of different origin with different geochemistries, and samples may be taken at different depths. A second observation that can be made is that most of the measured analytes in Tables 43 through 4-7 have values considerably below their threshold values (TV). The same can be said for two of the three radioisotopes measured (Table 4-4). Only Rn-222 is elevated above TV in many samples, and in the study zone, values range from 170 pC/L to 1,610 pC/L (TV = 300 pC/L). The human health effects of the higher levels are unknown. The samples provide evidence of saltwater intrusion into the aquifers. Stations MSB4, MSB17, MSB22, and MSB35 show conductivities above the TV of 900 u/s/cm. These observations are supported by higher Cl-and SO4= values. Three of the stations, MSB4, MSB22, and MSB35, all lie along the Pajaro River from the coast to 15 mi inland. Conductivity values above 700 uS/L characterize six stations in the same area (Figure 4-3). The lower threshold also points to another high-salinity cluster in the central portion of the studied area. EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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An additional comment may be made about atmospheric CO2(g) in the Monterey Bay zone. Pure water in equilibrium with the present atmosphere (pCO2 = 390 µatm) has a pH of about 5.5; the pH increases with increased alkalinity. Groundwater has a pH ≈ 7.5 because of its alkalinity. If pCO2 is calculated for a pH = 7.5 and an alkalinity of 300 mg/L (as CaCO3-Table 4-1), a value of ≈ 3,600 µatm is obtained, e.g., considerably above atmospheric CO2(g) (Pierrot and Wallace, 2006; Jahangir et al., 2012) and ultimately cause this gas to be vented to the atmosphere.
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Figure 4-1. The Monterey Bay and Salinas Valley GAMA study unit, locations of study areas, major cities, rivers, creeks, groundwater basins, and subbasins (Kulongoski and Belitz, 2007).
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10 mi Figure 4-2. Monterey study area; public supply wells sampled are shown in black; flowpath wells are shown in blue; monitoring wells 1-3 are shown in green. The oval highlights stations within ten miles of the coast.
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Figure 4-3. Blue circles show wells where conductivity is >700 uS/L.
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Table 4-1. Analyte list.
Fast pH, conductivity, DO, and temperature Volatile organic compounds Gasoline additives Pesticides and pesticide degradates Chromium abundance and speciation Stable isotopes of hydrogen and oxygen Tritium Noble gases
Schedule Slow Fast schedule analyte list, plus: Arsenic and iron speciation perchlorate, NDMA, 1,2,3trichloropropane Nutrients and dissolved organic carbon Major and minor ions and trace elements Carbon isotopes Radium isotopes Radon-222 Gross alpha and beta radiation Microbial constituents
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Monitoring Well Fast schedule analyte list, plus: Perchlorate, NDMA, 1,2,3trichloropropane Nutrients and dissolved organic carbon Major and minor ions and trace elements Arsenic and iron speciation Gross alpha and beta radiation
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Table 4-2. Water quality parameters. Water Quality Parameters Well
Mode
Turbid.
DO
Depth
NTU
mg/L
Threshold
na
na
pH 8.5
Conduct.
Alkal.
Bicarb.
Carbon.
uS/cm
mg/L
mg/L
mg/L
900
na
na
na
163
199
2
173
211
0
135
161
2
138
168
0
300
366
0.5
311
378
0.8
180
219
0
148
180
0.2
330
401
0.5
Sched.
feet
MSMB-2
Fast
288
2.2
885
MSMB-3
Fast
1364
1.9
338
MSMB-4
Slow
800
MSMB-5
Slow
nd
MSMB-9
Slow
466
MSMB-10
Fast
600
4.3
708
MSMB-11
Fast
590
1.3
591
MSMB-12
Slow
nd
MSMB-13
Fast
557
3.9
648
MSMB-16
Fast
552
4.1
651
MSMB-17
Fast
630
1.8
953
MSMB-18
Slow
nd
0.1
0.1
8.1
7.8 0.1
0.2
2.9
0.2
0.1
3.5
0.2
0.9
1210 397
7.3
8.8
435
538
7.3
499
7.3
753
MSMB-19
Fast
518
MSMB-20
Slow
177
2.9
622
MSMB-21
Fast
nd
MSMB-22
Slow
nd
MSMB-23
Fast
nd
2.7
693
MSMB-24
Fast
600
7.5
555
MSMB-25
Fast
nd
4.5
562
MSMB-26
Fast
650
2.7
777
MSMB-30
Slow
668
MSMB-31
Fast
619
5.2
595
MSMB-32
Fast
214
8.4
353
MSMB-33
Slow
nd
MSMB-34
Fast
510
MSMB-35
Slow
nd
MSMB-36
Fast
640
0.2 0.1
0.1
0.2
0.3
4
1.4
534 7.4
6.7
7.2
0.2 0.2
894
567 711
7.3 0.4
985
1260 568
Note: Values exceeding the drinking water threshold are shown in red.
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Table 4-3. Major and minor ions. Major and Minor Ions Ca
Mg
K
Na
Br
Cl-
F-
I-
SiO2
SO4=
TDS
Well
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
Threshold
na
Na
na
na
na
250
2
na
na
250
500
MSMB-4
40.2
52.4
16.9
112
1.01
241
0.1
0.015
31.2
61.9
658
MSMB-9
49.5
20.8
1.85
20.3
17
0.3
0.004
34
31.6
281
MSMB-12
15.4
0.64
3.78
1.3
0.42
123
0.1
0.049
39
46.4
446
MSMB-18
34.8
14.6
1.97
45.7
0.01
61.2
0.2
51.1
14.4
302
MSMB-20
78.9
32.7
2.53
39
0.28
31.3
0.2
0.008
37.5
54.3
464
MSMB-22
69.2
53.2
2.56
69.1
0.27
73.9
0.2
0.041
30.9
125
619
MSMB-30
84
30.9
2.21
58.4
0.38
112
0.3
0.002
45.5
88.1
547
MSMB-33
27.7
11
1.93
69.7
0.22
71.2
0.4
0.029
31.4
6.8
312
MSMB-35
100
57.9
2.36
89.5
0.92
98.2
0.3
0.03
31.5
216
828
Note: Values exceeding the drinking water threshold are shown in red.
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Table 4-4. Nutrients and DOC and radioisotopes. Nutrients and DOC Well Threshold
Radioisotopes
NH3
DOC
NO2
NO2+
TN
PO4
Ra-228
Rn-222
Tritium
mg/L
mg/L
mg/L
mg/L
mg/l
mg/L
pC/L
pC/L
pC/L
30
na
1
10
na
na
5
300
20000
MSMB-2
4.5
MSMB-4 MSMB-9 MSMB-12
0.09 0.5
MSMB-18
0.4
0.011
0.37
300
2.2
0.13
0.079
0.41
210
1.6
0.55
0.013
0.61
1450
0.057
0.7
360
0.3
0.67
0.7
MSMB-20
0.4
1.6
1.75
MSMB-22
1.8
MSMB-30
0.3
MSMB-33
0.4
MSMB-35
0.07
0.005
0.08
0.67
480
0.014
0.48
250
2.6
3.87
4
0.06
0.31
560
0.3
1.52
1.55
0.039
0.58
1610
1.6
0.17
0.048
0.29
170
8
1.8
Note: Values exceeding the drinking water threshold are shown in red.
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Table 4-5a. Trace elements - A. Trace Elements - A Al
Sb
As
Ba
Be
B
Cd
Cr
Co
Cu
Fe
Well
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
Threshold
1000
6
10
1000
4
1000
5
50
na
1300
300
0.073
4.4
48
0.059
0.4
18
0.3
11
MSMB-2 MSMB-4
1
MSMB-9
0.9
0.6
26
MSMB-12
7
2.3
23
131
MSMB-18
1.4
51
32
MSMB-20
0.7
59
162
0.56
96
463
0.11
3.3
89
0.39
7.3
87
0.14
0.5
191
MSMB-22
1
MSMB-30
0.9
MSMB-33 MSMB-35
1
4
88
1.28
0.04 13.1
0.059
0.7
7.4
0.126
0.8
0.02
0.07
0.161
46
0.04
3.5
0.183
4
9
168
0.07
0.2
0.127
0.2
87
0.03
1.2
2
35
427
0.03
90
Note: Values exceeding the drinking water threshold are shown in red.
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Table 4-5b. Trace elements - B. Trace Elements - B Pb
Li
Mn
Hg
Mo
Ni
Se
Ag
Sr
Tl
U
V
Zn
Well
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
Threshold
15
na
50
2
40
100
50
na
4000
2
30
50
5000
MSMB-4
0.55
10.9
13.3
2.1
1.22
276
0.74
0.3
3
MSMB-9
0.25
13.2
0.6
5
1.8
0.9
248
0.5
3.7
6.5
45
5.5
4.5
0.42
0.1
284
0.03
0.9
1.35
0.9
239
0.91
2
MSMB-2
MSMB-12 MSMB-18
0.14
16.1
MSMB-20
0.85
18.2
1.6
2.3
2.68
12.8
60.8
4.2
1.41
2.7
4.26
4.8
494
MSMB-22
0.01
0.38 12.6
0.8
504
1.72
4.4
1.4
698
2.38
4.8
0.9
5.94
7.1
4.5
MSMB-30
0.94
29
1.3
0.02
MSMB-33
0.46
5.8
208
42.6
0.87
0.2
245
0.21
1
4
MSMB-35
0.15
19.3
2410
3.7
7.24
0.1
699
1.35
3
6.6
Note: Values exceeding the drinking water threshold are shown in red.
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Carbon Disulfide
1,2,4 Trimethylb.
MTBE
Trichloroethe.
Bromodichloro
1,2-dichlo.ethy.
C.Tetrachloride
Bromoform
Dibromochl.me.
1,1Dichloroeta.
1,1Dichloroete
Ethylbenzene
T-Butylbenzene
Xylene,m&p
Trans-1,2-Dichl.
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
ug/L
Threshold
80
10
160
330
13
5
80
6
0.5
80
80
1
1200
300
na
1750
10
MSMB-1
0.17
0.84
0.2
Well
Chloroform
Tetrachloroethe.
Table 4-6. Volatile organic compounds.
0.1
MSMB-2
0.17
0.48
0.1
MSMB-5
0.09
0.09
0.1
MSMB-8
0.02
MSMB-11 MSMB-13
0.06
0.08
0.1
0.04
0.01 0.04
0.07
0.03
0.03
0.01 0.08
0.43
MSMB-15
0.8
0.38
0.03
0.41
0.04
0.06
0.23
0.56
0.02
0.22
MSMB-16
0.04
MSMB-18
0.02
0.04 0.05
MSMB-20
0.07
0.24
MSMB-24
0.14
0.08
0.02 0.02
MSMB-29
0.02
MSMB-30
0.07
MSMB-31
0.02
MSMB-32
0.03
MSMB-33
0.12
2.05
0.02
0.07
0.02
Note: Values exceeding the drinking water threshold are shown in red.
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Metolachlor
ug/L
ug/L
1
na
100
na
Threshold
4
na
MSMB-1
0.01
MSMB-2
0.2
ug/L
ug/L
ug/L
100
na
0.035
0.01
0.007
MSMB-5
0.004
MSMB-19
0.004
0.006 0.008
MSMB-20 MSMB-30
Terbutylazine
Caffeine
ug/L
Prometon
Atrazine
ug/L
ug/L
Dieldrin
Diethylatrazine.
Well
Simazine
Table 4-7. Pesticides.
0.004 0.004
MSMB-35
0.008
Note: Values exceeding the drinking water threshold are shown in red.
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5.0 5.1
GEOLOGIC HAZARD ANALYSIS
EARTHQUAKE HAZARDS
Moss Landing is located within the lower Salinas Valley of central California adjacent to Monterey Bay and within the Coast Ranges structural province. The Santa Cruz Mountains form the northern boundary of the Salinas Valley, the Gabilan Range rise to the east and the rugged Santa Lucia Mountains rise to the south of Monterey Bay. The region lies on a major crustal sliver called the Salinian Block bounded by major faults of the San Andreas fault system. The Coast Ranges region has high seismicity (Figure 5-1), but the Moss Landing area has moderate seismicity with only about 506 earthquakes, Magnitude (M) > 3.5, occurring within 50 km of the subject site during the 104-yr interval between 1910 and 2013. Many smaller (3.0) were located in this area during the 18-yr interval between 1996 and 2013. There have been four moderate earthquakes striking the central Coast Ranges area since 1910 (Table 5-1) within about 50 km of the subject site. The July 1, 1911 event (Magnitude1 = 6.6) was associated with the Calaveras fault, caused slight damage (Modified Mercalli Intensity2 (MMI) = V-VI) in the Monterey Bay area. Two events located offshore on October 26, 1926 (Magnitude = 6.1 each) were damaging in the Monterey Bay area, especially at Santa Cruz. The October 18, 1989 Loma Prieta earthquake (Magnitude = 7.1) produced only moderate shaking damage (MMI = VII) in the Moss Landing area, but produced severe liquefaction and ground failure damage (Greene et al. 1991; Mejia, 1998; Dupré and Tinsley, 1998). The latter part of the 19th century saw substantially greater earthquake activity in the San Francisco Bay area, culminating in the 1906 San Francisco (Magnitude = 7.8) earthquake on the northern San Andreas fault. The San Francisco earthquake also produced severe liquefaction and ground failure in the Moss Landing area (Lawson, 1908)/ The activity in this region has again been building up with several moderate events occurring since about 1980, including the 1989 Loma Prieta earthquake. For a 10% chance of exceedance during a 50 year interval, earthquakes as large as M = 7.25 may be expected to strike within 50 km of the site, resulting in damaging levels of shaking. Many active and potentially-active faults lie within 100 km of the subject site, and most are capable of generating moderate to large (Magnitude > 6.5) earthquakes. Table 5-2 lists the more significant faults near the site. No California Earthquake Fault Rupture Zones are located in the Moss Landing area. For shaking and secondary ground failure hazards, the greatest threat to the subject site are active faults of the San Andreas fault system including the northern San Andreas and Calaveras fault located east of the site, and the San Gregorio fault located offshore to the west. The rates of earthquake activity for these major faults is high with moderate earthquakes (Magnitude = 5.5-6.5) striking every few decades, and large earthquakes (Magnitude > 6.5) striking at least once per century. The San Andreas fault is about eleven (11) miles east of the site. Other nearby faults including the Monterey Bay fault zone may sustain moderate earthquakes, but with lower recurrence frequency, perhaps several hundred or thousands of years between events. Scientists estimate the likelihood of a large earthquake (Magnitude > 6.7) along 1
Magnitude listed here is generally surface wave magnitude, MS, or moment magnitude MW for more recent events. 2 See Table 5-3. EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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the San Andreas fault, in the Santa Cruz Mountains region, at about 21% during the 30-year interval from 2000 to 2030 (WGCEP, 1999). At present, however, no one can predict when or where the next damaging earthquake will occur. Because there are many active faults within 100 km of the site, the combined hazard from all sources is estimated to pose shaking levels of about 38% of gravity at the site with the 10% chance of exceedance during a 50-year interval (NSHMP, 2002, 2008). This probability level corresponds to a 475-year average recurrence interval for this level of shaking. This level of shaking corresponds to Modified Mercalli Intensity (MMI) VIII. The Moss Landing area experienced shaking of MMI = VII during the 1989 Loma Prieta earthquake (Plafker and Galloway, 1989), with estimated Peak Horizontal Ground Acceleration (Pga) of 25% of gravity (Mejia, 1998). The site experienced shaking of MMI = VIII during the 1906 San Francisco earthquake. Damage from direct shaking effects for both events was minor. However, liquefaction-induced ground failure including settlement and lateral spreading destroyed the Moss Landing Marine Laboratories (Greene et al., 1991; Mejia, 1998; Dupré and Tinsley, 1998). The subject site does not lie within any Alquist-Priolo Earthquake Fault Zone (EFZ). Also, no Active Fault Near-Source Zones are located in the vicinity of the property according to the 1997 Uniform Building Code (no faults closer than 10 km). 5.2
LIQUEFACTION HAZARDS AND EFFECTS ON VERTICAL FLUID FLOW
Ground failure induced by liquefaction of water-saturated cohesionless soils and sensitive clays is typically caused by earthquake strong ground-motion, but may also be triggered during heavy flooding. The Moss Landing area has a high to very high susceptibility to liquefaction based on mapping by U.S. Geological Survey scientists (Dupré and Tinsley, 1980, 1998). Both the 1989 Loma Prieta (Magnitude = 7.1) and the 1906 San Francisco (Magnitude = 7.9) earthquakes triggered severe liquefaction-related ground failures (Figure 5-2, Dupre and Tinsley, 1998, modified from Green et al., 1991; Lawson, 1908; EERI, 1990; Mejia, 1998). A large-scale lateral spread occurred following the 1989 earthquake that resulted in slumping at the head of Monterey Canyon and destruction of the Moss Landing Marine Laboratory (Greene et al., 1991). An investigation of the liquefaction at Moss Landing determined that liquefaction occurred in loose to medium-dense sand at about 10- to 20-ft depth beneath the Moss Landing Marine Laboratory (Figure 5-3, Mejia, 1998). Seafloor geophysical surveys after the earthquake identified sand boils and possible mud volcanoes, evidence of submarine liquefaction in water depths of 9-12 m (30-40 ft) at the head of Monterey Canyon (Greene et al., 1991). Liquefaction occurred at the Monterey Bay Aquarium Research Institute (MBARI) technology building and pier, too. However, damage was minor. Mejia (1998) concluded that the pier and its pile foundations helped to buttress the liquefied soils and prevent larger deformations. Also, the settlement and permanent ground deformation at the MBARI technology building were small, which “suggest that limited liquefaction may have occurred in the mediumdense to dense sand underlying the building to about 25-ft depth.” (Mejia, 1998). EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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The subsurface profiles from the liquefaction investigations at Moss Landing show that layers of fine-grained material exist within the beach and dune sands of the shallow (3 ft), and subsequent waves showed peak-to-trough amplitudes of about 2.5 m (8.3 ft) that persisted for more than five hours. Recent tsunamis recorded at Monterey include the March 11, 2011, Tohoku, Japan (Magnitude 9.0) event at about 1.5 m peak-to-trough (5 ft) and the October 27, 2010 Chile (Magnitude 8.8) event at about 0.6 m peak-to-trough (2 ft). Tsunami wave activity from these extreme events persist for more than four days and may involve significant bottom currents. As described in the liquefaction section, the 1989 Loma Prieta earthquake triggered a submarine slump at the head of Monterey Canyon that destroyed the Moss Landing Marine Laboratory. The wave height measured at the Monterey tide gauge was about 0.4 m peak-to-trough (1.3 ft) arriving about 20 minutes after the earthquake origin time (Lander et al., 1993).
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The State of California has published Tsunami Inundation Maps for emergency planning along the populated coastal areas (CalEMA, 2009). The map for the Moss Landing 7.5-minute quadrangle shows inundation over most of the low-lying coastal areas and up into the Elkhorn Slough. The estimated wave heights above mean sea level are about ten feet, which is comparable to the predictions made by Garcia and Houston (1975). Their estimates were 6.0 ft for the 100-yr and 11.7 ft for the 500-yr recurrence intervals. The CalEMA tsunami inundation maps do not have a probability specified and represent all types of sources, distant and local, that were modeled by the USC Tsunami Research Center. Although wave height may be small compared to the disastrous waves observed in Alaska, Hawaii, Japan, and Sumatra, very strong currents that affect the entire water column due to the long-period wave character may be destructive for tsunami attack in California. Dr. Mark Legg measured currents of four knots in the Santa Ana River mouth from the 2011 Tohoku tsunami and was told by LA County sheriff’s deputies that 14 knot currents were observed at the entrance to King Harbor, Redondo Beach from that event. The San Diego Harbor police reported that severe scour to the pilings of their boat docks was observed following the 2011 tsunami and one of their rubber pilot boats was ripped apart by being dragged beneath the floating dock due to the strong currents almost six hours after the first wave arrival. Such currents may be amplified at the head of Monterey Canyon offshore and could be damaging to seafloor pipelines or other structures.
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Figure 5-1. Map showing earthquake epicenters (seismicity) and major faults in the vicinity of Moss Landing, California. (Epicenters from the Northern California Seismograph Network; fault traces from the California Geological Survey, 2000).
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Figure 5-2. Map showing distribution of liquefaction-induced ground failures in the Moss Landing area following the October 18, 1989 Loma Prieta earthquake. (Source: Dupré and Tinsley, 1998, modified from Greene et al., 1991).
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Figure 5-3. CPT profiles of the subsurface deposits at the Moss Landing Marine Laboratory where liquefaction occurred following the 1989 Loma Prieta earthquake. The two profiles cross the sand spit on each side of the building which was located immediately south of the bridge that crossed from the mainland to the sand spit (see Figure 5-2) (Source: Mejia, 1998).
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Figure 5-4. Marigram from the Monterey Tide Gauge showing the first 12 hours of the tsunami from the Prince William Sound, Alaska, Good Friday earthquake of March 28, 1964. (Source: Lander et al., 1993).
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Table 5-1. Significant historical earthquakes affecting the Monterey Bay area. Time (UTC)
Lon
36.9
121.6
16:24
35.7
120.3
7.9
X
San Andreas (South-Central)
8
20:46
37.2
121.9
6.3
VIII
San Andreas (Sta Cruz Mtns)
Feb
17
20:12
37.2
122.1
5.8
VII
Near Santa Cruz
1882
June
27
13:32
37.2
122.0
VII
Near Santa Cruz
1883
Mar
30
15:45
36.9
121.6
5.6
VII
Near Gilroy (Calaveras?)
1885
Mar
31
7:56
36.7
121.3
5.5
VII
South of Hollister
1890
Apr
24
11:36
36.9
121.6
6.0
VIII
San Andreas? (Corralitos)
1897
June
20
20:14
37.0
121.1
6.2
VIII
Calaveras (Near Gilroy)
1899
Apr
30
22:41
36.9
121.7
5.6
VII
Near Watsonville
1899
July
6
20:10
37.2
121.5
5.8
VII
North of Watsonville
1906
Apr
18
13:12
37.7
122.5
7.8
XI
San Andreas (North)
1910
Mar
11
6:52
36.9
121.8
5.8
VI
Near Watsonville
1911
July
1
22:00
37.2
121.8
6.6
VIII
Near Coyote (Sta Clara Co.)
1926
Oct
22
12:35
36.6
122.4
6.1
VII
Offshore Monterey
1926
Oct
22
13:35
36.6
122.2
6.1
VII
Offshore Monterey
1939
June
24
13:02
36.8
121.4
5.5
VII
Southwest of Hollister
1949
Jan
1
1:18
36.9
121.6
4.5
VII
Near Watsonville
1949
Mar
9
12:29
37.0
121.5
5.2
VII
Near Hollister
1954
Apr
25
20:33
36.9
121.7
5.3
VIII
East of Watsonville
1959
May
26
15:58
36.7
121.6
4.6
VI
Near Salinas
1961
Apr
9
7:26
36.7
121.3
5.5
VII
South of Hollister
1966
June
28
4:26
36..0
120.5
6.0
VII
San Andreas (Parkfield)
1979
Aug
6
17:05
37.1
121.5
5.9
VII
Calaveras (Coyote Lake)
1984
Apr
24
21:15
37.3
121.7
6.2
VIII
Calaveras (Morgan Hill)
1989
Oct
18
0:04
37.0
121.9
7.1
IX
Mon
Day
1800
Oct
11
1857
Jan
9
1865
Oct
1870
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MS
MMI (max)
Lat
Year
VII
Fault or Zone Near San Juan Bautista
San Andreas? (Loma Prieta)
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Table 5-2. Major faults affecting the Moss Landing area (within 100 km of site). No.
Fault Name and Type
1 2 3 4 5
Zayante-Vergeles [SS] Monterey Bay [SS?] San Andreas [SS] - North Section Sargent-Berrocal [SS] Riconada [SS]
6
Calaveras [SS]
7 8 9 10 11 12 13 14 15 16 17 18
Paicines [SS] San Gregorio [SS] Quien Sabe [SS] Butano [SS] Monte Vista-Shannon [T] Hayward [SS] San Benito [SS] San Joaquin [T] Ortigalita [SS] Hosgri [SS] Greenville [SS] O’Neill [T?]
Date of Last Major Event
Mmax
1906 [M=7.8]
7.0 6.5 8.1 7.1 7.5
Distance (km) 12.2 12.8 17.8 22 30
Slip Rate (mm/yr) 0.1 0.5 17 3 3
1911,1979, 1984
6.8
33
15
6.7 7.2 6.4 6.5 6.7 7.5 6.7 6.6 7.1 7.5 6.6 6.5
33 33 39 39 45 52 54 60 63 60 68 69
15 3-7 1 ? 0.4 9 ? 1.1 1 2.5 2 1.1
1836,1868
1980
Faults in Bold Type are the closest to the subject site.
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Table 5-3. Modified Mercalli Intensity Scale (1931) I.
Not felt. Marginal and long-period effects of large earthquakes.
II.
Felt by persons at rest, on upper floors, or favorably placed.
III.
Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be recognized as an earthquake.
IV.
Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy ball striking the walls. Standing motor cars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In the upper range of IV wooden walls and frame creak.
VIII. Steering of motor cars affected. Damage to masonry C; partial collapse. Some damage to masonry B; none to masonry A. Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. Decayed piling broken off. Branches broken from trees. [Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes.] IX.
General panic. Masonry D destroyed; masonry C heavily damaged, sometimes with complete collapse; masonry B seriously damaged. (General damage to foundations.) Frame structures, if not bolted, shifted off foundations. Frames racked. Serious damage to reservoirs. Underground pipes broken. [Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters.]
V.
Felt outdoors; direction estimated. Sleepers wakened. Liquids disturbed, some spilled. Small unstable objects displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, change rate.
VI.
Felt by all. Many frightened and run outdoors. Persons walk unsteadily. Windows, dishes, glassware broken. Knickknacks, books, etc., off shelves. Pictures off walls. Furniture moved or overturned. Weak plaster and masonry D cracked. Small bells ring (church, school). Trees, bushes shaken (visibly, or heard to rustle).
X.
Difficult to stand. Noticed by drivers of motor cars. Hanging objects quiver. Furniture broken. Damage to masonry D, including cracks. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices (also unbraced parapets and architectural ornaments). Some cracks in masonry C. Waves on ponds; water turbid with mud. [Small slides and caving in along sand or gravel banks.]! Large bells ring. Concrete irrigation ditches damaged.
Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. [Large landslides.] Water thrown on banks of canals, rivers, lakes, etc. [Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.]
XI.
[Rails bent greatly. Underground pipelines completely out of service.]
XII.
Damage nearly total. [Large rock masses displaced. Lines of sight and level distorted.] Objects thrown into the air.
VII.
*
Abridged and Modified by C. F. Richter, 1958, Elementary Seismology: W. H. Freeman and Company, San Francisco, p. 137-138. ! Bracketed items describe ground failure effects which are less reliable for shaking intensity measurement. Masonry A. Good workmanship, mortar, and design; reinforced, especially laterally, and bound together by using steel, concrete, etc.; designed to resist lateral forces. Masonry B. Good workmanship and mortar; reinforced, but not designed in detail to resist lateral forces.
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Masonry C. Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither reinforced nor designed against horizontal forces. Masonry D. Weak materials, such as adobe; poor mortar; low standards of workmanship; weak horizontally.
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6.0 6.1
SUB-SURFACE INTAKE SYSTEMS
TYPES OF SUBSURFACE INTAKE SYSTEMS
While surface intake systems for seawater reverse osmosis (SWRO) desalination plants may improve feed water quality in some cases, the feasibility of subsurface intake systems for desalination plants depends on the local hydrological conditions, site location and available space, engineering concerns, hazards, and the proposed capacity of SWRO plans (Missimer et al., 2013; Dietrich, 2013). Subsurface intake systems for desalination plants is evolving technology having the advantage of no impacts to ocean environment in the form of entrainment or impingement to marine life; however, they have a short history and few successful surface intakes are in operation worldwide in comparison to open ocean intake plants. There are a number of different types of subsurface systems that can be used: (1) vertical beach wells; (2) Ranney collector wells; (3) horizontal directionally drilled (HDD) wells; (4) slant wells; (5) beach infiltration galleries; and (6) offshore infiltration galleries. Missimer et al. (2013) provide a good summary and discussion of various subsurface intake systems. An overview of desalination plant intake alternatives is also given in Water Reuse Association (2011) and Dietrich (2013). Figure 6-1 summarizes the various types of subsurface intake systems from Missimer et al. (2013). The selection of an appropriate intake system depends on geological and geotechnical characteristics of the site, engineering and construction of the subsurface intake system as facilities, possible impacts on the ground water, nearby wetlands and agricultures, reliability of the system and costs. 6.2
ADVANTAGES AND DISADVANTAGES
Advantages • • •
• •
Subsurface intakes have no impacts to the ocean environment in the form of entrainment or impingement to marine life. The need for pretreatment (in the case of well feedwater supply), is significantly reduced . Land water well technology has a very well developed technology over the last 70 years. Application of this technology to vertical wells, Ranney Wells, HDD wells and slant wells may ensure success of supply and the ability to maintain the supply with minimum maintenance, which is a major issue for such systems. Beach wells, Ranney Wells, HDD wells and slant wells have no ocean construction impacts. Beach wells, Ranney Wells, HDD wells and slant wells tapping subsea or near shore aquifers provide natural filtration of organic matter and suspended sediment,
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•
particularly during storm surges and periods of heavy precipitation and surface runoff. Both slant and vertical well intake systems can be completely buried such that there are no visible structures at the land surface, offering an acceptable solution to environmental concerns.
Disadvantages •
• • • • •
6.3
Research has shown that subsurface intake systems are site specific and a system which may work in one environment (and country) may or may not be successfully applied to other areas. As local geologic, hydrologic, oceanographic, and environmental conditions vary widely, success or failure of a particular system may also vary widely. Use of subsurface intake systems is an emerging technology with a relatively short history. All subsurface intake systems (wells and galleries) are in a minority as compared to open ocean intakes. As such, only a handful of successful subsurface intakes are in operation worldwide. In some coastal areas, obtaining permits is the number one constraint in constructing a near shore or offshore subsurface feedwater supply. Many of the operational intakes worldwide do not have the same stringent environmental requirements as required in the United States and especially along the coast of California. During construction, visual impacts may include unsightly facilities on the beach or in near shore areas where recreational or other high use occur.
DATA FROM SELECTED SUBSURFACE INTAKE SYSTEMS IN OPERATION
Information from worldwide desalination plants utilizing subsurface well intake systems are summarized in Table 6-1. Table 6-1 gives the name of the desalination plant: its location, the volume of the feed water supply (mgd), the number of the wells and the source of the information. On average the mean feed water supply from wells for desalination plants in operation is 14 mgd. The average number of wells per desalination plant is about 10. The data is presented graphically in Figure 6-2. Figure 6-3 gives the average feed water supply per well for each desalination plant. The mean feed water supply per well is about 1.3 mgd/well with a maximum feed water supply of 4 mgd/well. There is one offshore infiltration gallery currently in operation, at Fukoka desalination plant in Japan. This plant was begun in 2001 and became operational in 2005. The subsurface intake feed water supply is 27.2 mgd. The cost was approximately $400 million. This plant uses an Infiltration Gallery of perforated pipes below the seabed to draw in seawater (Figure 6-1). The Infiltration Gallery is located approximately 2100 ft offshore at a depth of 38 ft. The infiltration gallery is approximately 215,000 square feet in size. It has approximately 3 meters of engineered sand and crushed stone around the pipes. The sand has a D10 size of 0.4 mm. The infiltration EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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gallery was located in an area of the Genkai Sea where there is continual gentle wave action such that sand is neither eroded nor deposited in any significant amounts. The SDI of the seawater was between 4.3 and 5.7, but it decreased to 2 once it flows through the sand/crushed stone filter surrounding the perforated pipes. The feed water is filtered by an ultrafiltration membrane prior to entering the RO plant (www.niph.go.jp/soshiki/suido/pdf/h21JPUS/abstract/r9-2.pdf; Dietrich, 2013).
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Vertiical Beach Well W
Slant W Well
Horizontal Wells s
Radial Collector W Well
Ranney y Collector W Well
Figure 6-1. Selected su ubsurface in ntake well ssystems.
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*Slant well Figure 6-2. Feed water supply (mgd) and number of wells for each desalination plant presented in Table 6-1.
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*Slant well Figure 6-3. Average well feed water supply (mgd) for each desalination plant presented in Table 6-1.
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Table 6-1. Selected subsurface beach well intake systems for seawater desalination currently in operation. Site No. 1 2 3 4 5 6
Desalination Plant Al-Birk Alicante II Aruba SWRO-2 Arucas-Moya Bajo Almanzora Bay of Palma
Location
Feed Water Supply (MGD) 2.3 34.3 12.4 2.1 31.7 23.7
Number of Wells 3 30 14 1 14 16
Source of Information Missimer et al., 2013 Missimer et al., 2013 Dietrich, 2013 Bartak et al., 2012 Missimer et al., 2013 Missimer et al., 2013
14.4
12 ?
Missimer et al., 2013
1.4 6.6 3.0 11.9 4.0 15.9 2.1
4 15 1a 18 8 11 3
Missimer et al., 2013 Missimer et al., 2013 Bartak et al., 2012 Missimer et al., 2013 Missimer et al., 2013 Missimer et al., 2013 Missimer et al., 2013
7
Blue Hills
8 9 10 11 12 13 14
Britannia Dahab Dana Point Ghar Lapsi Ibiza Lanzarote IV Lower Valley
Saudi Arabia Alicante, Spain Aruba Gran Canaria Almeria, Spain Mallorca, Spain New Providence Island Grand Cayman Red Sea, Egypt Dana Point, CA Malta Spain Canary Islands Grand Cayman
15
Morro Bay
Morro Bay, CA
1.2
5
Dietrich, 2013
16
Nuweiba City
Sinai, Egypt
2.6
8
Djebedjian et al., 2007
17
Pemex Refinery
Salina Cruz, Mexico
11.9
3b
Bartak et al., 2012
Spain
39.6
10 c
Bartak et al., 2012
Sand City, CA
0.6
4
Water-technology.net
Canary Islands
13.2
8
Missimer et al., 2013
San Pedro del Pinatar Sand City Santa Cruz de Tenerife
18 19 20 21
SAWACO
22 23 24
Soslaires Canarias Sur Tordera Turks & Caicos Water Co. WEB
25 26
Jeddah, Saudi Arabia Gran Canaria Oman Blanes, Spain
8.3
10
Missimer et al., 2013
2.6 58 33.8
3 32 10
Rybar et al., 2005 Dietrich, 2013 Missimer et al., 2013
Turks and Caicos
6.1
6
Missimer et al., 2013
Aruba
21.1
10
Missimer et al., 2013
14.0
9.9
Mean Notes:
a
= Installed well is a Slant Well = 3 Rainey Collector Wells being used for intake c = 10 Horizontal Wells being used for intake b
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7.0
SUMMARY AND CONCLUSIONS
1. Major coarse-grained aquifers exist at about 180 ft and 400 ft below sea level in the coastal zone near Moss Landing. A shallow aquifer in alluvium, eolian, and older dune sands also exists along the coastal zone and has been considered as a saltwater source for a subsurface intake system. 2. Seawater intrusion has occurred in these aquifers since at least the 1930s. In the Moss Landing area, saline water has reached farther (1.75-2.5 miles) inland in the upper (180-Foot, or upper Aromas Sand) aquifer, and not as far (0.75-1.2 miles) in the lower (400-Foot, or lower Aromas Sand) aquifer. Thus, seawater transport from offshore to inland areas occurs by lateral flow within the aquifers. Rates of fluid flow and the character of saline water may be determined from pump tests in monitoring wells in the coastal zone. 3. Layers of fine-grained deposits between and within the major aquifers form aquitards that limit the vertical flow and recharge of the major aquifers. Recharge of groundwater into the 180Foot Aquifer is from underflow originating in upper valley areas, which demonstrates the impermeable nature of shallow aquitards. The depth of saline water observed in coastal wells is vertically restricted and not continuous throughout the main aquifer deposits. Therefore, vertical recharge of seawater into deeper aquifers is restricted and may be insufficient for a large-scale desalination plant subsurface intake system. 4. As described in Section 5, natural hazards, including the strong ground motion of earthquakes, liquefaction-induced ground failures, submarine landslides, and potential tsunami or storm surges, pose significant risks, including damaged intake systems and disrupted operations. Subsurface intake systems would be more difficult and costly to repair than seabed intake systems, which would result in the limited availability of source water for months. Existing data published by the U.S. Geological Survey (earthquake.usgs.gov/hazards), California Geological Survey (http://www.consrv.ca.gov/CGS/Pages/Index.aspx), and other sources (Greene et al., 1991; Dupre and Tinsley, 1998) are available to quantify the risks posed by these hazards. Additional data are necessary to map the seafloor hazards in the nearshore zone where the proposed intake system would be constructed. 5. The construction and operation of a subsurface intake system in or near the Monterey EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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Canyon may impact the stability of the canyon edges. Disturbance of the saturated cohesionless sediments on the seafloor and shallow sub-bottom may trigger liquefaction and downslope movement that could damage or destroy the intake system. It is known that spring sapping of groundwater in unconsolidated sediments along submarine slopes may trigger slope failure. 6. A borehole drilled by Cal Am at Moss Landing during 2013 found “intermittent clay layers mixed with silt and fine sand, without enough continuous sand layers to use any type of subsurface intake system efficiently” (“Monterey boreholes reveal good slant-well conditions,” The International Desalination & Water Reuse Quarterly website, 5 January 2014). Promising sites where boreholes have shown highly favorable conditions for subsurface slant well locations are located south of the Salinas River in the area of dune sands. Similar dune sands exist along the coast in a small area north of the Pajaro River. However, due to the variable layers of finegrained material without continuous sand layers, the coastal sediments at Moss Landing appear to be unsuitable for subsurface intake systems. 7. Subsurface intake systems are newly evolving technologies, and at present are suitable only for small desalination plants (about 10 mgd) unless very special hydrogeological conditions exist. Their success requires site-specific hydrogeological conditions relative to the recharge rate, water quality, engineering concerns, geological hazards, maintenance, reliability, and economic concerns. 8. Results from 26 operating desalination plants (Figures 6-2 and 6-3) that are using subsurface intake systems show that the maximum well production was 3.98 mgd. The average production of the wells from these plants was 1.5 mgd. These subsurface intake systems were located within different sediment types and grain sizes, which yield differing amounts of raw seawater. Based on this production range, approximately 20 to 37 wells will be required at Moss Landing to reliably and continuously produce the 51.6 mgd of raw seawater that would enable the production of the design capacity of 22.3 mgd of desalinated water. 9. Hydrologic modeling of the aquifer systems in the vicinity of Elkhorn Slough was used to estimate the leakage at about 3,000 to 5,000 acre-feet per year (2.7 to 4.5 mgd) of seawater into the groundwater system (Fugro, 1995). About 20 percent of this value is due to horizontal flow (seawater intrusion) and the rest to vertical leakage from Elkhorn Slough (Fugro, 1995). In order
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to sustain a 50 mgd desalination plant, the recharge area or infiltration rates must be increased by at least one order-of-magnitude. A summary of Fugro (1995) study is presented in Appendix A. 10 A larger area covered by seawater exists offshore and adjacent to the Monterey Canyon. If the shallow alluvial basin (paleochannel) has similar layering of coarse-grained aquifers interbedded with low-permeability clays and silts, as are found in wells onshore (Fugro, 1995), then the area for vertical infiltration systems must be at least ten times larger than the 1,000 to 2,000 acres assumed for the Elkhorn Slough hydrologic modeling. Alternatively, a thick, coarsegrained layer exposed at the seafloor (outcrop at Monterey Canyon) and laterally continuous to the coastal area near Moss Landing would be needed to provide sufficient lateral flow. It is also should be point out that the lateral flow rate assumed for the Elkhorn Slough model was only 20 percent of the vertical infiltration, so that the combination of surface exposure and enhanced conductivity must be about five times greater than that considered in the Slough model. 11. Based on the available information and literature we have reviewed, the hydrogeological conditions appear unfavorable for the large-scale (51.6 mgd) subsurface seawater intake system required to supply the proposed 22.3 mgd of desalinated water production at the proposed site. A hydrological analysis based on the geometry and character of the subsurface hydrogeological conditions in the Moss Landing area would be required to further evaluate candidate subsurface intake systems and quantify the potential capacity of such systems. In order to provide a more definitive assessment, significant additional data would need to be developed based on test borings and the construction of at least 1 pilot test well of a capacity sufficiently large to test the draw-down and recharge rates of the local aquifer penetrated. Additionally, given the uncertainty regarding surface water quality, the pilot well would need to be pumped for an extended period (6-12 months) to provide reliable data regarding sustainable flows, capacity and stable water quality. Only on this basis is it possible for us to provide a more definitive conclusion as to the feasibility of supplying the required volumes of raw water for subsequent desalination of a regional desalination plant with a design capacity of 25,000 acre-feet per year.
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REFERENCES
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DOGGR (Division of Oil, Gas, and Geothermal Resources), 2003. California Digital Map Data – Oil, Gas & Geothermal Well Locations, California Department of Conservation, Sacramento, CD-2. Well Finder web-site: http://maps.conservation.ca.gov/doggr/index.html# Duprė, W.R., 1975. Quaternary history of the Watsonville lowlands north-central Monterey Bay region, California. Unpublished Ph.D. dissertation, Stanford, University, 145 p. Duprė, W.R., 1998. Quaternary geology of the Monterey Bay Region, California. Duprė, W.R., and J.C. Tinsley III, 1980. Maps showing geology and liquefaction potential of northern Monterey and southern Santa Cruz counties, California. U.S. Geological Survey Miscellaneous Field Studies Map MF-1199, sheet 1, scale 1:62,500. Dupré, W.R., and J.C. Tinsley III, 1998. Evaluation of liquefaction-hazard mapping in the Monterey Bay region, central California. In: Holzer, T.L., ed., The Loma Prieta, California, Earthquake of October 17, 1989 – Liquefaction, U.S. Geological Survey Professional Paper 1551-B, B273-B285. Durbin, T.J., G.W. Kapple, and J.R. Freckleton, 1978. Two-dimensional and three-dimensional digital flow models of the Salinas Valley groundwater basin, California. U.S. Geological Survey, Water Resources Investigations Report 78-113. Prepared in cooperation with the U.S. Army Corps of Engineers, 134 p. Earthquake Engineering Research Institute (EERI), 1990. Loma Prieta Earthquake Reconnaissance Report, Supplement to Volume 6, Earthquake Spectra, El Cerrito, California, 448 p. Fugro West, Inc., 1995. North Monterey County Hydrogeologic Study: Volume I, Water Resources. Prepared for Monterey County Water Resources Agency, October 1995. 118 pp. + 9 appendices. Eittreim, S.L., R.J Anima, and A.J. Stevenson, 2002. Seafloor geology of the Monterey Bay area continental shelf. Marine Geology, Volume 181:3-34. Garcia, A.W., and J.R. Houston, 1975. Type 16 Flood insurance study: Tsunami predictions for Monterey and San Francisco Bays and Puget Sound. U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, Mississippi, Hydraulics Laboratory, Technical Report H-75-17. Greene, H.G., 1970. Geology of Southern Monterey Bay and its relationship to the groundwater basin and saltwater intrusion. United States Department of the Interior Geological Survey, Open File report 70-141. Greene, H.G., 1977. Geology of the Monterey Bay region: U.S. Geological Survey Open File Report 77-718, 347 p. EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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Greene, H.G., and J.C. Clark, 1979. Neogene paleogeography of the Monterey Bay area, California. In: Armentrout, J.M., Cole, M.R., and Terbest, H., Jr., Cenozoic Paleogeography of the Western United States, Pacific Section SEPM, Pacific Coast Paleogeography Symposium 3, Los Angeles, 277-323. Greene, H.G., J. Gardner-Taggert, M.T. Ledbetter, R. Barminski, T.E. Chase, K.R. Hicks, and C. Baxter, 1991. Offshore liquefaction and onshore liquefaction at Moss Landing spit, central California: Result of the October 17, 1989, Loma Prieta earthquake. Geology, v. 19, p. 945-949. Hanson, R.T., 2003. Geohydrologic framework of recharge and seawater intrusion in the Pajajo Valley, Santa Cruz and Monterey Counties, California. U.S. Geological Survey Water Resources Investigation Report 03-4096, 88 p. Hanson, R.T., R.R. Everett, M.W. Newhouse, S.M. Crawford, M.I. Pimentel, and G.A. Smith, 2002. Geohydrology of a deep-aquifer system monitoring-well site at Marina, Monterey County, California. U.S. Geological Survey, Water Resources Investigation Report 02400. Israel, K., and S. Watt, 2006. Elkhorn Slough: A Review of the geology, geomorphology, hydrodynamics and inlet stability. Technical Report by Sea Engineering Inc. Jahangir, M.J., P. Johnston, M.I. Khalil, J. Grant, C. Somers, and K.G. Richards, 2012. Evaluation of headspace equilibration methods for quantifying greenhouse gases in groundwater. Journal of Environmental Management, 111:208-12. Johnson, M.J., 1982. Public hearing regarding critical overdraft in the Santa Cruz-Pajaro groundwater basin. U.S. Geological Survey written testimony submitted to California Department of Water Resources at public hearings in Watsonville, California, October, 1982, 8 p. Johnson, M.J., C.J. Londquist, J. Laudon, and H.T. Mitten, 1988. Geohydrology and mathematical simulation of the Pajaro Valley Aquifer system, Santa Cruz and Monterey Counties, California. U.S. Geological Survey Water Resources Investigations Report 874281, 62 p. Kulongoski, J.T., and K. Belitz, 2007. Groundwater quality data in the Monterey Bay and Salinas valley basins, California, 2005: Results from the California GAMA Program. U.S. Geological Survey Data Series 258, 84 p. Lander, J.F., P.A. Lockridge, and M.J. Kozuch, 1993. Tsunamis affecting the West Coast of the United States 1806-1992. NOAA, National Geophysical Data Center, Geophysical Records Documentation No. 29, 242 p.
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Lawson, A.C., and others, 1908. The California earthquake of April 18, 1906: Report of the California State Earthquake Investigation Commission, Washington, Carnegie Institution, Publication 87, v. 1, 2 parts, 451 p. MCWRA, Monterey County Water Resources Agency, 2003. Salinas Valley Water Project. Website: http://mcsra.co.monterey.ca.us/welcome_svwp_n.htm. MCWRA, Monterey County Water Resources Agency, 2012. Map showing seawater intrusion in the Salinas Valley Groundwater Basin – 180-Foot Aquifer, August 6, 2012. Website: http://www.MCWRA-CO.Monterey.ca.us MCWRA, Monterey County Water Resources Agency, 2012. Map showing seawater intrusion in the Salinas Valley Groundwater Basin – 400-Foot Aquifer, August 7, 2012. Website: http://www.MCWRA-CO.Monterey.ca.us Mejia, L.H., 1998. Liquefaction at Moss Landing. In: Holzer, T.L., ed., The Loma Prieta, California, Earthquake of October 17, 1989 – Liquefaction, U.S. Geological Survey Professional Paper 1551-B, p. B129-B150. Missimer, T.M., N. Ghaffour, A.H.A. Dehwah, R. Rachman, R.G. Maliva, and G. Amy, 2013. Subsurface intakes for seawater reverse osmosis facilities: Capacity limitation, water quality improvement, and economics. Desalination 322 (2013) 37-51. Monterey County Planning Department, 2012. Ferrini Ranch Subdivision, Draft Environmental Impact Report. Muir, K.S., 1974. Seawater intrusion, groundwater pumpage, groundwater yield, and artificial recharge of the Pajaro Valley area, Santa Cruz and Monterey Counties, California. U.S. Geological Survey Water Resources Investigations Report 9-74, 31 p. National Seismic Hazard Mapping Project (NSHMP), 2008. Documentation for the 2008 update of the United States National Seismic Hazard Maps, U.S. Geological Survey Open-File Report 2008-1128, 60 p. Page, B.M., 1970. Sur-Nacimiento fault zone of California: Continental Margin Tectonics. Geological Society of America Bulletin, v. 81, p. 667-690. Pierrot, D., E. Lewis, and D.W.R. Wallace, 2006. MS Excel Program Developed for CO2 System Calculations. ORNL/CDIAC-105a. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee. Plafker, G., and J.P. Galloway, 1989. Lessons learned from the Loma Prieta, California, Earthquake of October 17, 1989. U.S. Geological Survey Circular 1045, 48 p.
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PVWMA, 2000. Pajaro Valley Water Management Agency, website: http://www.pvwma.dst.ca.us/ RMC, 2006. Salinas Valley integrated regional water management functionally equivalent plan summary document update. The Monterey County Water Resources Agency, May 2006. Rybar, S., M. Vodnar, F. Laurentiu, R.L. Méndez, and J.B.L. Ruano, 2005. Experience with renewable energy sources and SWRO desalination in Gran Canaria. International Desalination Association World Congress: SP05-100. Schwartz, D.L., 1983. Geological history of Elkhorn Slough, Monterey County, California. M.S. Thesis, San Jose State University, San Jose, CA. Sea Engineering Incorporated (SEI), 2006. Elkhorn Slough: A review of the geology, geomorphology, hydrodynamics and inlet stability. Prepared for Elkhorn Slough National Estuarine Research Reserve, May 31, 2006. 86 p. Toccalino, P.L., J.E. Norman, R.H. Phillips, L.J. Kauffman, P.E Stackelberg, L.H. Nowell, S.J. Krietzman, and G.B. Post, 2004. Application of health-based screening levels to groundwater quality data in a state-scale pilot effort. U.S. Geological Survey Scientific Investigations Report 2004-5174, 64 p. United States Geological Survey (USGS), 1995. Monterey Bay Geophysical Survey Data. Website: http://walrus.wr.usgs.gov/infobank/j295mb/html/j-2-95-mb.meta.html March 6 – April 15, 1995. United States Geological Survey (USGS), 2005. Status and understanding of groundwater quality in the Monterey Bay and Salinas valley basins, 2005: California GAMA Priority Basin Project. Scientific Investigations Report 2011-5058, U.S. Department of the Interior U.S. Geological Survey. Wagner, D.L., H.G. Greene, G.J. Saucedo, and C.J. Pridmore, 2002. Geologic map of the Monterey 30’ x 60’ quadrangle and adjacent offshore region, California: A Digital Database: California Department of Conservation, Division of Mines & Geology, DMG CD 2000-000. Wallace, R.E., ed., 1990. The San Andreas fault system, California, U.S. Geological Survey Professional Paper 1515, 283 p. Water Reuse Association, 2011. Overview of Desalination Plant Intake Alternatives, White Paper, June 2011. 17 p. Website: http://www.watereuse.org/sites/default/files/u8/Intake_White_Paper.pdf Water-Technology.net. Sand City coastal desalination plant, United States of America. http://www.water-technology.net/projects/sand-city-plant/ EcoSystems Management Associates, Inc. ECO-M Reference No. 14-04
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APENDIX A COASTAL AQUIFERS & SEAWATER RECHARGE FUGRO (1995) STUDY
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COASTAL AQUIFERS & SEAWATER RECHARGE The following is of summary of the main points from of Fugro (1995) report related to this study. 1. A deep late-Pleistocene channel (Figure 1) is inferred to exist beneath Elkhorn Slough in the vicinity of Moss Landing (Fugro, 1995). This has been called the Elkhorn Valley and was interpreted to be filled with marine and fluvial deposits near the coast. Isopachs of Holocene sediments mapped offshore north of Monterey Canyon project toward the Moss Landing area and appear to define the offshore buried paleochannel (ancestral valley). A well located at the center of the ancestral valley (well 13S/02E-07K) documented about 600 feet of lowpermeability materials. Adjacent wells document varying thicknesses of clay and lowpermeability materials, ranging from 10 to 70 feet thick, with some interbeds of sand, gravel, or sandy clay (Fugro, 1995). The thick clay layer (“mud plug”) restricts lateral migration (north-south) of fluids between the adjacent Salinas and Pajaro Valley aquifer systems. This boundary appears to account for different seawater intrusion rates in the two aquifer systems, with greater distance inland of the saline water on the north side of Elkhorn Slough. Fluvial channels with coarse-grained materials, including sand, gravel, and sandy clays, are documented in wells north of Elkhorn Slough (Figures 1, 2, and 3) 2. Figure 4 shows the geophysical section from abandoned oil well “Vierra #1”. In this geophysical section the shallow mud-logging is simplified up to depth
