SAN DIEGO REGIONAL BEACH SAND PROJECT

F I N A L

R E P O R T 24 Hour Vibracoring Off Southern California Coast

OFFSHORE SAND INVESTIGATIONS

Prepared For: San Diego Association of Prepared by: Sea Surveyor, Inc. Governments (SANDAG) 960-C Grant Street 401 B Street., Suite 800 Benicia, CA 94510 San Diego, CA 92101 TEL: (707) 746-1853 (619) 595-5300 FAX: (707) 746-0184

APRIL 1999 Table of Contents

SECTION TITLE Page 1. EXECUTIVE SUMMARY 3

2. SURVEY METHODS, LABORATORY TESTING, AND ANALYTICAL TECHNIQUES 8 2.1 Field Survey Methodology 2.1.1 Geophysical Survey Methods 2.1.1.1 Survey Vessel 2.1.1.2 Navigation & Hydrographic Equipment 2.1.1.3 Side Scan Sonar and Magnetometer 2.1.1.4 Shallow Seismic Subbottom Profilers 2.1.2 Vibratory Coring 2.1.2.1 Vessel 2.1.2.2 Vibratory Corers 2.1.2.3 Penetration Recorder 2.2 Laboratory Testing 15 2.2.1 Grain Size Analyses 2.2.2 Chemical Analyses 2.3.2 Petrographic Analyses 2.3 Analytical Techniques 17 2.3.1 Trackline Chart and Seafloor Features Map 2.3.2 Subbottom Isopach Maps 2.3.3 Volume Computations

3. RESULTS AND SITE DESCRIPTIONS 20 3.1 Regional Results 3.1.1 Sediment Chemistry 3.1.2 Lithologic Analyses 3.1.3 Tide Data 3.2 Site Descriptions 23 3.2.1 Site SO-9 3.2.2 Site SO-8 3.2.3 Site AH-1 3.2.4 Site SO-7 3.2.5 Site SO-6 3.2.6 Site SO-5 3.2.7 Site SO-4 3.2.8 Site MB-1 3.2.9 Site SS-2 3.2.10 Site SS-1

4. BIBLIOGRAPHY 63

A. TRACKLINE CHARTS B. GRAIN-SIZE and CHEMISTRY TABLES C. GEOTECHNICAL CORE LOGS. D. PHOTOGRAPHS OF SEDIMENT CORES. E. GRAIN SIZE DISTRIBUTION CURVES

SECTION 1

EXECUTIVE SUMMARY

San Diego County is experiencing a net loss of sand from numerous beaches along its coastline. To address and remedy this problem, the San Diego Association of Governments (SANDAG) instituted the San Diego Regional Beach Sand Project to evaluate the possibility of using offshore sand borrow sites to replenish the beaches.

SANDAG has established the following criteria for selecting the offshore sand borrow sites:

• The offshore borrow sites should be close to the beaches requiring sand nourishment.

• Based on guidelines specified by the US Army Corps of Engineers (USEPA/USACE, 1991), sand suitable for beach replenishment shall be fine- to coarse-grained with a

narrow size gradation. The mean grain size diameter (d50) shall range from between 0.2 and 0.6 mm. A maximum of 10% by weight can be silt or clay (0.074 mm), and a maximum of 10% by volume of the material may be larger than sand and no larger than cobble. To add an intermediate level, this report classifies as "marginal" any material that contains a silt or clay content of 10-15% .

• The offshore sand borrow sites should be located deeper than 30' to 50' of water because in the San Diego region the "depth-of-closure" for seasonal bathymetric profile changes occurs between these depths (SANDAG, 1998). Dredging shallower than the depth-of- closure merely relocates material already within the littoral zone; conversely, dredging deeper than the depth-of-closure results in introducing new material on to the beaches.

• The offshore boundaries for the proposed borrow sites should be no deeper than approximately 80'-90', which is believed to represent the limit for offshore dredge operations (Moffatt & Nichol, 1999).

Based upon these criteria and review of the historical data collected along the San Diego coastline, SANDAG has preliminarily selected 10 offshore borrow sites (Figure 1) that are located adjacent to beaches requiring sand nourishment between Oceanside and the US-Mexico Border. To update and expand upon the historical investigations, SANDAG contracted Sea Surveyor, Inc. of Benicia, California to conduct offshore field investigations at the 10 proposed borrow sites. The objective of this offshore sand investigation is to: 1) map the horizontal and vertical extent of suitable beach sand within the 10 proposed borrow sites, and 2) compute the volume of suitable beach replenishment material contained within each site.

During January 1999, geophysical surveys were conducted at 9 of the 10 proposed borrow sites and vibracore sediment samples were collected at all 10 sites. The geophysical surveys used differential GPS navigation to map each site with a sidescan sonar, a marine magnetometer,

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FIGURE 1: Location of the 10 Proposed Offshore Sand Borrow Sites.

TABLE 1: Borrow Site Dimensions, Extent of Field Investigations, and Sand Volumes.

Surface Geophysical Number of Sand Volume Site Location Area (acres) Survey Area Vibracores (million cubic yds) SO-9 Offshore of Santa Margarita River 344 3,000' x 5,000' 12 0.9 SO-8 Offshore of San Luis Rey River 459 4,000' x 5,000' 23 4.7 AH-1 Offshore Agua Hedionda Lagoon 275 3,000' x 4,000' 10 0.0 SO-7 Offshore of Batiquitos Lagoon 287 2,500' x 5,000' 20 1.1 SO-6 Offshore of San Elijo Lagoon 230 2,500' x 4,000' 5 0.8 SO-5 Offshore of San Dieguito Lagoon 275 3,000' x 4,000' 10 6.2 SO-4 Offshore Los Penasquitos Lagoon 230 2,500' x 4,000' 10 1.5 MB-1 Offshore of Mission Beach 413 4,000' x 4,500' 10 26.0 SS-2 Offshore of Imperial Beach 482 3,000' x 7,000' 10 0.9 SS-1 Adjacent to US-Mexico Border 631 None 15 7.6 Page 5

2 types of subbottom profilers, and a survey-grade depthfinder. After interpreting the geophysical data, a recommendation was presented to SANDAG regarding the number and location of sediment core samples that should be collected in each site. After SANDAG accepted the vibracoring plan, a total of 125 sediment cores were collected in the sites using a 20' ALPINE vibratory corer. The collected core samples were transported to Oceanside Harbor on a daily basis, where geotechnical personnel split, logged, photographed, subsampled, and archived the sediment cores. The subsamples from the vibracores were analyzed for grain-size, lithology, and chemical constituents by MEC Analytical Systems of Carlsbad, California.

Table 1 summarizes the location and dimension of the sites, the field investigations that were conducted in each, and the estimated volume of suitable beach nourishment material which they contain. Chemical testing of the composited sediments collected at the offshore borrow sites were conducted to determine the suitability of the material for beach replenishment. The results from the chemical testing were compared to sediment samples collected in the tidal and intertidal zones of 6 receiver beach sites (Imperial Beach, Torrey Pines, San Dieguito Lagoon, Batiquitos Lagoon, Buena Visa Lagoon, and Oceanside), with no significant difference found. Total organic carbon concentrations in the proposed borrow site sediment ranged from 0.017 to 0.216%. Total sulfide concentrations ranged from 0.2 to 1.1 mg/Kg and dissolved sulfides were mostly non-detectable. Concentrations of pesticides, polychlorinated biphenyls, polynuclear aromatic hydrocarbons, or phenol were also not found. Concentrations of metals, arsenic, chromium, copper, lead, nickel, selenium, and zinc were detected. Results from the chemical analyses are expressed in dry weight, and presented in Appendix B.

The following sections present a brief description of the proposed offshore borrow sites.

SITE SO-9: Site SO-9 is located north of Oceanside Harbor and offshore of the Santa Margarita River in 50' to 80' water depths. This site is the northern-most sand borrow site, and it lies within the Oceanside Littoral Cell. Eight (8) artificial reef habitats, comprised of piles of quarry rock, are located near the center of the site and may present an obstruction to dredging. Three (3) layers of sediments occur inshore of the artificial reefs within Site SO-9: 1. The top (surficial) layer consists of sandy silt that is unsuitable for beach nourishment material. The thickness of this silt layer measures about 12' in the central region of the site and gradually thins out before reaching the nearshore boundary of the site. This surficial layer of unsuitable sandy silt has an estimated volume of 0.4 million cubic yards. 2. Buried beneath the surficial layer of sandy silt is a layer of fine- to medium-grained sand that is suitable for beach nourishment. This sand layer is 3' to 23' thick, and is exposed on the seafloor surface along the nearshore boundary of the site. An estimated 0.9 million cubic yards of suitable beach nourishment material is contained within this layer. 3. A third sediment layer, consisting of fine-grained silty sand that is unsuitable for beach nourishment, was found under the sand layer.

SITE SO-8: SO-8 is located south of Oceanside Harbor and offshore of the San Luis Rey River in 50' to 90' water depths. The seafloor within the site is covered by a 4'-13' thick layer (average 10') of sandy-silt or very fine-grained silty sand that is unsuitable for beach nourishment purposes. In the northeast corner of the site, buried beneath an estimated 2.5 million cubic yards of unsuitable material, lies approximately 4.7 million cubic yards of fine-grained sand that, although quite silty, has been determined to be suitable for beach nourishment material.

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SITE AH-1: This site is located offshore of Aqua Hedionda Lagoon in 60' to 130' of water. Approximately 50% of Site AH-1 is deeper than 90', which may be too deep for dredging with conventional equipment. The very fine-grained sand found in Site AH-1 has a high silt content that makes it unacceptable for beach nourishment. Since no acceptable beach nourishment material was found in Site AH-1, no volumes of beach-quality sand could be computed.

SITE SO-7: Site SO-7 is located offshore of Batiquitos Lagoon in 50' to 100' water depths, and was the most geologically-complex site surveyed. In general, Site SO-7 can be divided into 4 regions: 1. The northern region contains 1' to 4' of fine- to medium-grained sand overlying a hard (rock) substrate. Although the sand overlying the bedrock in this region is suitable for beach nourishment purposes, the surficial layer may be too thin to dredge economically. 2. The central region of Site SO-7 is predominantly medium- to coarse-grained sand that is ideal for beach nourishment, and the layer is thick enough (up to 13') for efficient and economical dredging. The estimated volume of suitable beach sand within this central region is 1.1 million cubic yards. 3. The southern region is characterized as having 1' of fine-grained silty sand overlying 1' to 7' of fine-grained sand. The overlying layer of silty sand is not suitable for placement on the beach. Although the underlying layer of sand is acceptable for beach nourishment, it probably has insufficient volume for economical dredging. 4. The western region along the offshore boundary of the site has a layer of silty sand that is 2'-30' thick and unsuitable for beach nourishment.

SITE SO-6: This site is located offshore of San Elijo Lagoon in 60' to 120' of water. The southern boundary of the site will need to be re-defined to avoid an armored pipe lying on the seafloor. The sediments in Site SO-6 consist of a single, wedge-shaped layer of fine-grained sand with low- to marginal-silt content overlying shale bedrock. This wedge of surficial material is less than 5' thick along the east (nearshore) boundary of the site and uniformly increases to a maximum thickness of 27' towards the site's west (offshore) boundary. A total of 5.3 million cubic yards of material lies within this surficial wedge-shaped layer; unfortunately, only 0.8 million cubic yards may be available for beach nourishment purposes. Approximately 2.9 million cubic yards of the total material in the site has a silt content that is marginal for placement on the beach, and another 0.4 million cubic yards of the beach-quality material is located in water depths that may exceed conventional dredging methods. Additionally, dredging may be prohibited within 1,000' of the submerged pipe, which deducts an additional 1.2 million cubic yards of beach-quality material from the total volume of material in the site.

SITE SO-5: Site SO-5 is located offshore of San Dieguito Lagoon in 50' to 95' of water. The majority of Site SO-5 contains suitable beach nourishment sand. The suitable sand is contained within a surficial sediment layer that measures 2' to 5' thick along the eastern (nearshore) boundary and increases uniformly in thickness to approximately 25' along the west (offshore) boundary of the site. A layer of shale may underlie the surficial sand layer. At vibracore station SDG-78 a sample of shale was collected 9.5' below the seafloor, which corresponds to the seismic reflection data showing the unconsolidated sediments to be 10' thick at that location. The estimated volume of suitable beach nourishment sand within Site SO-5 is 6.2 million cubic yards.

SITE SO-4: Site SO-4 is located offshore of Los Penasquitos Lagoon in 40' to 90' of water. This site is the southern-most sand borrow site within the Oceanside Littoral Cell. Within the site, a 50-acre area along the eastern (nearshore) boundary contains 1.5 million cubic yards of very fine- Page 7 grained sand that is suitable for beach nourishment. Approximately 75% of the site (including half of the seafloor that is less than 60' deep and all of the seafloor deeper than 60') contains silty, very fine-grained sand that is unsuitable for beach replenishment.

SITE MB-1: Site MB-1 is located within the Mission Beach Littoral Cell in water depths ranging from 60' to 110'. This site contains over 26 million cubic yards of uniquely-colored beach sand that has been described as "red-yellow-brown" or "golden". With the exception of a 2' layer of silty material in the northeast corner of the site, the seafloor is blanketed with a very thick (15' to 60') surficial layer of medium- to coarse-grained sand. Although the MB-1 site contains an impressive volume of beach-quality sand, approximately 25% of the site (and 30% of the sand volume) may be deeper than the 90' depth limitations of conventional dredges.

SITE SS-2: Site SS-2 is located offshore of Imperial Beach, approximately 4.5 miles north of the US-Mexico Border. This site is located within the Silver Strand Littoral Cell. The seafloor is nearly flat, with depths ranging between 50' and 60'. The geophysical and vibracore investigation found a buried layer of sand in the central region of Site SS-2 that is 4' to 11' thick and contains 0.9 million cubic yards of suitable beach replenishment material; however, this layer of suitable sand is covered by as much as 12' of unsuitable silty sand that is thickest in the middle of the site, and thins to 4' thick towards the west. The buried layer of suitable sand also thins to 4' towards the west, and uniformly increases in thickness towards the eastern (nearshore) boundary of the site. Future surveys may find that this buried layer of sand contains a considerable volume of beach nourishment material closer to shore past the eastern boundary of the site.

SITE SS-1: Located adjacent to the US-Mexico Border in 40' to 70' of water, Site SS-1 is the southern-most borrow site studied. No geophysical surveying was conducted at this site, so the volume of available beach sand was calculated using only the vibracore logs. It is estimated that at least 7.6 million cubic yards of suitable sand is available within Site SS-1, and the total may be considerably higher if the layer of suitable material extends deeper than the vibracores penetrated. Suitable beach replenishment sand is exposed on the seafloor in the northeast corner of Site SS-1 and in an area extending from the center of the site to the southeast corner. Most of the suitable sand within the site, however, is buried under a 2' to 6' thick surficial layer (3.4 million cubic yards) of silty sand that is not suitable for beach replenishment.

This report contains the results of the Offshore Sand Investigations conducted by Sea Surveyor, Inc. Section 2 describes the field survey methods, laboratory testing, and analytical techniques used to conduct the offshore sand investigation. Section 3 presents the results from the geophysical and vibracoring investigation with detailed descriptions of the sites. A bibliography of the references and historical investigations referenced in this report is presented in Section 4. The trackline charts, analytical results (grain-size and chemical), vibracore sediment logs and photographs of the sediment core samples are included in the appendix of this report.

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SECTION 2

SURVEY METHODS, LABORATORY TESTING, AND ANALYTICAL TECHNIQUES

2.1 FIELD SURVEY METHODOLOGY

During January 1999, Sea Surveyor, Inc. conducted marine geophysical surveys and vibracore investigations along the San Diego coastline to map the horizontal and vertical extent, and compute the volume, of beach-quality sand in 10 proposed borrow sites. The following sections describe the field methods and survey equipment used to map the distribution and compute the volume of suitable beach nourishment material within the 10 proposed sites.

2.1.1 Geophysical Survey Methods

A series of marine geophysical surveys was conducted on 4-12 January 1999 in 9 of the 10 offshore areas being proposed as borrow sites for beach sand nourishment material. Mr. Phillip Torres of Sea Surveyor, Inc. was responsible for managing the geophysical field surveys. Golder Associates provided the side-scan sonar, subbottom profilers, and 2 geophysical technicians, while Sea Surveyor provided the fathometer, marine magnetometer, GPS navigation, and a navigator. The following sections describe the equipment and methods used to conduct the geophysical surveys, as well as the data processing methods used to interpret the results from the field surveys.

2.1.1.1 Survey Vessel: The geophysical surveys of 9 proposed sand borrow sites were conducted using the 48' survey boat "WESTWIND" (Figure 2) that is permanently berthed in Newport Beach, California. The "WESTWIND" is a US Coast Guard inspected vessel certified for use in oceanographic research.

The “WESTWIND” has twin propellers powered by two turbo-charged D333 Caterpillar engines. The vessel has 182 square feet of unobstructed aft deck space, ample table space inside the cabin, and an aft A-frame for launching towed sensors. The "WESTWIND" was mobilized to Oceanside Harbor, where it was based until the completion of the geophysical survey.

Figure 3 shows the configuration for the geophysical sensors deployed from the survey vessel "WESTWIND". The 200kHz transducer for the survey-grade echosounder was installed in a well in the center of the vessel. The differential GPS antenna was installed on the mast of the vessel, directly over the transducer well. The towfish for the side scan sonar was towed 80' behind the GPS navigation antennae from the port (left) side of the vessel, and the sensor for the marine magnetometer was towed 130 behind the GPS antennae from the starboard (right) side of the vessel. The subbottom profiling acoustic source and hydrophones were towed alongside the vessel and 17' behind the GPS navigation antenna. The location of each geophysical sensor was post-calculated by applying the appropriate offset for that sensor to the coordinates determined by the GPS navigation system. Page 9

Figure 2: The survey vessel “WESTWIND” returning to Oceanside Harbor.

Figure 3: Arrangement of hydrographic and geophysical sensors on the WESTWIND. Page 10

2.1.1.2 Navigation and Hydrographic Equipment: The hydrographic survey methods and equipment used for the offshore sand investigation meets the highest (Class 1) standards of the US Army Corps of Engineers. as described in their HYDROGRAPHIC SURVEYING MANUAL (USACE, 1994).

Navigation during the geophysical and vibracoring surveys was provided using the OMNISTAR LR-8 differential GPS navigation system (+1m accuracy). The differential GPS navigation system recorded the survey vessel's location at 1-second intervals. The navigation data was input to a dedicated navigation computer that was running Trimble’s HYDRO navigation software. The navigation computer recorded real-time data from a variety of sensors along with the navigation data, and the computer sent a "fix mark" to each device’s paper record simultaneously every 20 seconds to ensure synchronization of all survey instruments. The navigation computer also provided an onscreen helmsman display that showed the survey vessel's location relative to the intended survey course.

Water depths were recorded using an INNERSPACE Model 448 survey-grade fathometer. The INNERSPACE fathometer records water depths digitally by transmitting data 20-times each second into the navigation computer. The fathometer also creates a continuous stripchart recording of the water depth. The fathometer is interfaced with the navigation computer to allow automated fix marks triggered from the navigation computer to be displayed on the graphic recorder. This interface allows accurate correlation of position and depth information.

Calibration is one of the most critical factors in acquisition of accurate sounding data. The fathometer was calibrated at the beginning and end of each survey day using the bar check procedure. The bar check procedure consists of lowering an acoustic target (a circular metal plate) on a measured sounding line to the maximum project depth. The fathometer's speed-of- sound control is then adjusted until the target reflection is printed precisely at its known depth. After calibrating the fathometer for the maximum practical depth, the target was raised to shallower depths, at 5' intervals, and the calibration readings at these depths were recorded.

In order to correct the water depth measurements for fluctuations in the water surface elevation caused by tides, two self-recording tide gauges were installed at Oceanside Harbor for the duration of the geophysical survey. The tide gauges were referenced to National Ocean Service benchmark #0396A, 1979 (elevation 16.54' MLLW) set in the concrete base of the flagpole in front of the Oceanside Harbor Headquarters.

2.1.1.3 Side Scan Sonar and Magnetometer: A dual-frequency (100 and 500kHz) GEOACOUSTICS digital side scan sonar (Figure 4) was used to produce acoustic images of the seafloor 100-150m on each side of the survey lines. The acoustic images were graphically- displayed on an EPC Model 1086 thermal recorder. The acoustic images were interpreted to produce maps that show the lateral extent of surficial lithology (silt, sand, gravel, cobble etc.) and natural (bedrock exposures) or cultural (boats, pipelines etc) features on the seafloor that may have an impact on dredging activities. The layback of the side scan sonar towfish was calculated by recording the amount of cable deployed, using a digital cable counter.

The presence of ferrous-metal on or below the seafloor was determined using a GEOMETRICS Model G-881 cesium-vapor marine magnetometer (Figure 5). The magnetometer recorded local variations in the total magnetic field as measured by the marine sensor towed 200' behind the survey boat. The magnetometer data was displayed on the navigation monitor aboard the Page 11

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vessel, and the digital data was recorded in the navigation computer at 1-second intervals along with the navigation data. The magnetometer has a sensitivity of one gamma, with instrument noise-level no greater than 3 gamma, peak to peak.

2.1.1.4 Shallow Seismic Subbottom Profilers: Two (2) high-frequency subbottom profiling systems were used to map cross-sectional profiles of the sediment layers within the borrow sites. These seismic reflection systems use acoustic pulses, emitted at regular intervals by an acoustic source, to image subbottom stratigraphy and geology. The transmitted acoustic pulses are reflected from the seafloor and from density boundaries separating underlying sediment layers. The reflections are received by either a transducer (subbottom profiler) or a surface-towed hydrophone (high-resolution seismic reflection profiler). The transducer or hydrophone converts the reflected acoustic signals into electrical signals that are processed and displayed on a graphic recorder on board the survey vessel.

One of the subbottom profiling system, a DATASONICS Model CHIRP II, was used to map the sediment layers in the top 10'-30' of the seafloor. This system operates at a frequency of 3-16 kHz, and includes a swell filter. The transducer was mounted on the starboard (right) side of the survey vessel 17' behind the GPS navigation antennae.

While the CHIRP II subbottom profiling system was mapping sediment layers down to 30' below the seabed, a second system was recording sediment layers down to 80-100' below the seafloor. The deeper-penetrating high-resolution seismic reflection data was collected with an APPLIED ACOUSTIC ENGINEERING Geopulse system. This system produces low frequency acoustic signals (0.8-2 kHz) that penetrated approximately 100' below the seabed at the proposed borrow sites. The acoustic source for the Geopulse subbottom profiler was mounted on a surfboard that was towed next to the survey vessel (Figure 6) and a towed hydrophone was used to receive the reflected acoustic signal.

The seismic reflection data from both subbottom profiling systems were displayed on an EPC Model 1086 thermal graphic recorder, and permanently archived on a Sony Model 8000 DAT digital recorder. The subbottom profiling data was also stored digitally on a high density disk drive. Both the graphic recorder and the digital recorder were interfaced with the navigation computer, which provided fix marks at 20-second intervals.

2.1.2 Vibratory Coring

Sea Surveyor used the 165' vessel "AMERICAN PATRIOT" and our 20' ALPINE vibratory corer to collect sediment core samples at 125 locations in 10 proposed sand borrow sites during 18-24 January 1999. Mr. Steve Sullivan of Sea Surveyor was responsible for supervising the collection of the vibracores. The ALPINE vibracore were operated by two 4-person crews that worked alternating 12-hour shifts, with each crew comprised of 2 Sea Surveyor personnel (crew chief and vibracore operator) and 2 chemical technicians provided by MEC Analytical Services.

2.1.2.1 Vessel: Choosing the proper vessel is critical to the success of any vibracoring project. For vibracoring, the most common mistake is to anchor at each sampling location. Anchoring is inefficient, inaccurate, and dangerous. Conversely, the most efficient and safest method for vibracoring is to set the free-standing vibracore on the seafloor with the vessel maintaining station nearby using dynamic positioning systems. Collecting vibracores while "live-boating" is very easy and efficient if the vessel has a bow thruster and dynamic positioning system. Page 13

Sea Surveyor collected 125 sediment core samples using the research vessel “AMERICAN PATRIOT" (Figure 7) based in Long Beach, California. The “AMERICAN PATRIOT” is a 165' vessel with twin engines and a 40-ton pedestal crane. The “AMERICAN PATRIOT” has a large, open deck for handling the vibracores, and has sufficient living quarters for over 20-personnel.

Positioning the vessel on-station efficiently was the most critical component of this successful vibracoring project. Using differential GPS navigation, the vessel's position was displayed on a computer screen superimposed over a digital nautical chart showing the San Diego County coastline. The ship's captain used the computer display as a helmsman's aid to position the vibracore directly over the intended coring station. The trackline control system provided a real- time display of vessel position in relation to intended coring location, and digitally displayed range and bearing to the intended coring station, vessel speed, and station approach speed. The DGPS location of each core was determined when the vibracorer was set on the seafloor at each location.

2.1.2.2 Vibratory Corers: Sea Surveyor provided two different vibratory corers aboard the vessel, but we used only the ALPINE vibracorer to collect sediment cores at the 125 locations. The 2 vibratory corers provided aboard the ship included:

• Mini-Vibracorer: The pneumatic Mini-Vibracorer is a versatile, lightweight coring device capable of collecting sediment cores of up to 15’ length. The Mini-Vibracorer comes complete with a seafloor stand and penetration recorder. Sea Surveyor provided the Mini- Vibracorer as a backup corer if the larger and more powerful ALPINE vibracorer failed; however, the Mini-Vibracorer was never needed or used.

• ALPINE Vibracorer: The ALPINE vibracore (Figure 8) is the largest and most powerful vibratory corer ever manufactured. The ALPINE vibratory corer comes complete with seafloor stand and penetration recorder and can obtain continuous cores of up to 20’ length. The ALPINE vibracorer was used exclusively to collect 125 sediment cores in the 10 proposed sand borrow sites.

Both the ALPINE and Mini-Vibracorer are pneumatic units and use 4”-diameter steel barrels for collecting the core samples. Both vibratory corers collect 3.5” diameter cores in clear cellulose acetate butyrate (CAB) liners, which can be easily split laterally or longitudinally for inspection and geotechnical logging and subsampling. The transparent plastic rigid tubes permit visual inspection of the cored material. After the vibracore collected a sediment sample, the sediment cores were extracted from the vibracore barrel, and the liner was cut at 5' intervals, capped, taped, and labeled. The collected cores were then shuttled to Oceanside Harbor, where geotechnical personnel split, inspected, described, logged, and subsampled the core samples for laboratory analyses. Subsamples from the sediment cores were transported to MEC Analytical Systems' laboratory in Carlsbad, California for grain-size and chemical analyses. The sediment cores were then re-sealed and stored in racks of 4"-diameter PVC pipe for archival (Figure 9).

2.1.2.3 Vibracore Penetration Recorder: Sea Surveyor’s vibracorers come complete with a penetration recorder to monitor and record the rate at which the vibracorer penetrates the seafloor. Monitoring the penetration rate of the vibracorer is important because penetration vs. time is an indirect measure of the dredgability of the soils. Monitoring the penetration rate also ensures that the vibracorer reaches its refusal depth.

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Figure 7: Research vessel “AMERICAN PATRIOT”

Figure 8: ALPINE vibracore in 20’ configuration.

Figure 9: Sediment core samples being archived.

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The penetration recorder consists of a 360-degree potentiometer housed in a waterproof case mounted to the vibrator slide. The potentiometer is turned by a sprocket drive and roller chain stretched the length of the mast. The potentiometer makes one revolution for each foot of penetration into the sediment. An electrical signal cable transmits the data to a single-channel strip chart recorder on the support vessel.

While collecting vibracore samples, the vibracore operator aboard the vessel continuously monitored the penetration recorder. Vibracoring continued until the penetration recorder showed no downward movement of the vibracore for a minimum of 5-minutes.

2.2 LABORATORY TESTING

The vibracore sediment samples were transported daily from the vessel "AMERICAN PATRIOT" to a temporary geotechnical facility at Oceanside Harbor using Sea Surveyor's 26' survey vessel "BETTY JO". In Oceanside, the vibracore samples were split longitudinally, logged, photographed, and subsampled for grain-size and petrographic analyses by Dr. Peter Fischer and other geotechnical personnel provided by MESA-CUBED. Sediment subsamples were collected from all the vibracores and composited for chemical analyses by representatives from MEC Analytical Systems.

2.2.1 Grain-Size Analyses

After the sediment cores were split longitudinally, logged, and photographed, the geotechnical personnel collected one or more representative subsamples from the top 1-3 layers of the core. The sediment subsamples were sealed within transparent ziplock bags, labeled, and transported to MEC Analytical Systems' Carlsbad laboratory for grain-size analyses. A total of 235 sediment samples were analyzed for grain-size.

In the laboratory, approximately 40 grams of sediment from each subsample was weighed into a coors dish and placed into an oven to dry overnight. Once dry, the sample weight was determined by first weighing the sample in the coors dish, followed by weighing the dish after the sediment sample had been placed in the sieves. The sieves were stacked on top of one another with the sieve having the largest screen mesh diameter above sieves having progressively smaller screen mesh diameters. The sample was shaken for 10-minutes to sieve the sediment, which left the coarsest material on the upper screens and allowed the finer particles to fall through to the bottom. Once shaken, the contents of each sieve were weighed and the results were entered onto a data sheet. The data sheet was then entered into a computer spreadsheet, and the percentage (by weight) of gravels, sands, and silts were calculated.

2.2.2 Chemical Analyses

2.2.2.1 Chemical Testing Procedures: The sediments collected at the proposed offshore sand borrow sites were tested for their chemical constituents to determine the suitability of the material for beach replenishment. Sediments were tested according to guidelines provided in the Ocean Disposal Manual (USEPA/USACE 1991) and the California Ocean Plan using analytical methods accepted by the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers.

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Sediments were composited from the multiple vibracores collected within each borrow site into a single sample for chemical analysis. The composites for each borrow site were collected by extracting sediment from the entire length of each vibracore using a stainless-steel scoop. The collected sediments were then placed in a stainless steel mixing vessel, thoroughly homogenized, and placed in sample containers that were sealed in plastic bags, wrapped in bubble wrap, and securely packed inside the cooler with ice packs or crushed ice. Chain-of-custody (COC) forms were filled out, and the original signed COC forms were sealed in a plastic bag and placed inside the cooler. Samples were then hand-delivered to Pacific Treatment Analytical Service for chemical analysis following sample handling and custody procedures.

All samples were stored at 4°C until tested, and testing was begun as soon as possible (within two weeks) from the end of collection. Chemical analysis of the sediments was conducted by Pacific Treatment Analytical Service and included metals, pesticides, polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (PAHs), and phenols. Additional analyses were performed to determine total organic carbon (TOC), total and water-soluble sulfides, and percent solids. All methods and procedures were in accordance with procedures set forth in the OTM (USEPA/USACE 1991). Any remaining sediment from samples was retained at the laboratory and archived at 4° C in the event further chemical characterization is required.

All chemical analyses were performed using U.S. EPA (SW-846), National Oceanic and Atmospheric Administration (NOAA), Standard Methods for Examination of Water and Wastewater (SMEWW), or American Association for Testing and Materials (ASTM) methods. However, validated method modifications were used to obtain detection limits that were lower than those specified in the prescribed methodologies. Sediments were analyzed for arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc following sample digestion using EPA 3050. After digestion, samples were analyzed for metals using an inductively coupled plasma spectroscopy instrument with a mass spectral detector (ICPMS) (EPA 6020) and atomic absorption/graphite furnace methods (AA/GF) (EPA 7000 Series). Samples were analyzed for total and dissolved sulfides following methods SMEWW 4500D and Plumb 1981. Chlorinated pesticides and polychlorinated biphenyl (arochlors) (Pesticides and PCBs) were performed in accordance with EPA 3550/8081. Polynuclear aromatic hydrocarbons (PAH’s), and phenols were analyzed by gas chromatography/mass spectrometry using EPA 8270. Total organic carbon (TOC) was performed using modified ASTM D2579.

2.2.2.2 Quality Assurance Procedures: Chemical analysis were performed using quality control criteria specified in the CFR (1983) and USEPA (1986 and updates). Grain size and Total Organic Carbon analysis were consistent with MEC’s internal quality control criteria. Performance was evaluated via the use of laboratory control samples, method blanks, surrogates, spiked samples, duplicate samples, and internal quality control samples. Precision and accuracy objectives were established for method reporting limits, spike recoveries, and duplicate analyses.

Chain-of-custody forms were prepared in the field during sediment collection. Field personnel maintained custody of the samples until they were returned to the laboratory. Once sediments were composited, a new chain of custody was prepared for the transfer of sediments for chemical and physical analyses.

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2.3 Petrographic Analyses

After the sediment cores were split longitudinally, logged, and photographed, the geotechnical personnel collected one representative subsample for lithologic analysis from two vibracores from each of the 10 borrow sites, for a total of 20 subsamples. The lithologic analysis was conducted at California State University Northridge by Dr. Peter Fischer, Professor of Geology. The lithologic analyses was accomplished by lithologically identifying and counting 150-200 grains from each subsample. During counting, grain size was ignored. Replicated counts were made for different portions of the lithologic samples to verify the original count. The three most common lithologic grain types (quartz, feldspar, and lithic fragments) were counted and plotted on a triangular diagram. In addition, carbonates (shell fragments) were counted, but were found to be rare.

2.3. ANALYTICAL TECHNIQUES

2.3.1 Trackline Chart and Seafloor Features Map

After completing the field geophysical survey, a trackline chart was prepared for each site that showed the location of the survey vessel and all towed sensors at each navigation “event mark". These trackline charts, presented in Appendix A, were used to interpret the seismic, sidescan, magnetometer, and sounding records.. The coordinate system used to prepare the trackline charts, and all subsequent charts, was the California State Plane Coordinate System, Zone 6. All charts are referenced to both NAD 1927 and NAD 1983.

In the office, water depths recorded during the geophysical surveys were edited and corrected for tides to reference the soundings to the Mean Lower Low Water (MLLW) datum. The corrected soundings were imported into AutoCAD Version 14 drafting software in order to create the bathymetric chart. The bathymetric chart was then contoured at 5’-10' depth intervals, and the contours were annotated.

Side-scan records were manually interpreted to classify the seafloor sediment. A mosaic was created by pairing the stripchart records from adjacent survey lines in order to identify seafloor sediment more efficiently. The surficial sediment-type is represented on the Seafloor Features Maps as a unique hatch pattern according to classification. The location of significant bottom features that represent possible obstructions to dredging were depicted on the Seafloor Features Maps.

Seafloor features having an associated magnetic signature were identified by processing the data collected by the marine magnetometer during the surveys. The resulting data was used to calculate the location and size of any magnetic anomalies and depict them on Seafloor Features Maps. Each anomaly was reviewed to determine whether it has an acoustic (side-scan or subbottom) signature associated with it.

A Seafloor Features Map was prepared by compiling the bathymetric, magnetic, and sidescan data together for each site on a basemap prepared from a digital USGS topographic map using AutoCAD Version 14 software. Each Seafloor Features Map graphically depicts the bathymetric contours, sediment classification, magnetic anomalies, and possible dredge obstructions in plan- view format.

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2.3.2 Subbottom Isopach Maps

Information regarding geologic layering below the seafloor was derived from data collected by the seismic reflection equipment during the geophysical survey. The data collected from the seismic reflection systems were used to determine the location and subbottom elevation of geological features. These features were transferred into digital form by manual digitization and incorporated with the navigation data in order to create a geological profile for each survey line. The cross-sectional profiles derived from this process were used to create a 3-dimensional terrain model used to produce isopach maps and compute sediment volume.

2.3.3 Volume Computations

Estimates of available beach replenishment material were computed for each site based on vibracore and geophysical survey results. Each site was reviewed independently to determine the most appropriate method for performing the computation.

The vibracore logs and grain-size results were used to give an indication of the suitability of the sediment collected during vibracoring. The vibracore logs identified the elevations of geological unit boundaries within each vibracore sample. Sediment sub-samples were correlated with the vibracore logs in order to ascertain the vertical extent of material that each sub-sample represents. The sediment type found within a sub-sample was assumed to extend vertically to the boundaries of the geological unit that the sub-sample was extracted from. The results of this correlation were entered into a computer database.

A 3-dimensional terrain model was created using data collected from the seismic reflection systems during the geophysical survey. Sediment wedges within a site were identified from the model, and the vibracore logs were used to identify the sediment type within these wedges. In most cases, a single sediment wedge was identified by the geophysics.

Quantity computations of available beach replenishment materials were computed within the site boundaries using the geophysical terrain model where possible. When the geophysics was unable to confirm the geology of the vibracore logs, a terrain model was created from the vibracore logs and used instead. This was the case at sites SO-9 and SS-2. The silt overburden layer at site SO- 8 was also determined using the vibracore logs. At site SS-1, having no geophysical data to use, the computation was also performed using the vibracore logs.

A layer of silt was found overlying suitable beach sand at sites SO-9, SO-8, MB-1, SS-2 and SS- 1. Quantity computations were performed to estimate the volume of silt overburden within these sites. In each case, the vibracore logs were used to determine the thickness of this layer, as the geophysics could not be used to measure it.

In all quantity computations, the sediment type in between vibracore locations was assumed to be of the type found in the surrounding cores. In cases where the geophysics was used for quantity computations, the sediment was assumed to be uniform vertically throughout the sediment wedge described by the geophysics, and of the same type identified by the core logs. At sites SO-9, SS- 2 and SS-1 where geophysics was not used, the bottom elevation of the vibracore sample was used as the limit of the quantity computation for those sites.

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Sub-regional boundaries were created within sites SO-9, SO-8, SO-7, SO-6, SO-4 and SS-2 and are depicted on the Isopach maps for those sites. These sub-regions were created in sites in which not all core samples contained suitable beach replenishment materials. The sub-regional boundaries in these sites enclose only the vibracore stations where suitable beach sand was identified, and the quantity computation results reflect only the material within these sub-regions. A few exceptions are as follows:

1) At site SO-9, vibracore samples 6, 7 and 9 were included on the sub-regional border because their silt/gravel content were within 5% of passing.

2) At site SO-8, vibracore samples 18, 24 and 27 were included within the sub- regional border because the vibracore logs and core photos suggest that acceptable sand exists deeper than where sub-samples were collected. Vibracore sample 23 at SO-8 was included because the silt content was within 6% of passing, and because of its lateral proximity to passing samples.

3) At site SO-7, vibracore sample 59 was included on the sub-regional border because the silt content was within 4% of passing. Vibracore 58 was included because the core was only 1.4’ long and no sub-sample was taken (Isopach was limited to 1.4’ thick here).

4) At site SO-6, vibracore sample 68 was excluded from the sub-regional border because the geophysical results suggest that it may be in an area of silty sediment, and the silt content was within 1% of failing.

5) At site SS-2, vibracore sample 106 was included on the sub-regional border because the gravel content was within 6% of passing.

6) The sub-regional boundary at site SO-6 was created using the seafloor features gathered during the geophysical survey. The geophysics suggests that the surficial sediment contain more silt toward the west of this boundary, and more sand to the east.

SECTION 3

SURVEY RESULTS AND SITE DESCRIPTIONS

The results from the Offshore Sand Investigation can be divided into regional results and site- specific results. Section 3.1 presents the results that apply to all of the proposed offshore borrow sites, including the chemical testing, lithologic analyses, and tide measurements. Section 3.2 presents a detailed, site-specific description of the results for each of the proposed offshore sand borrow sites. Page 20

3.1 REGIONAL RESULTS

3.1.1 Sediment Chemistry

The sediments collected at the proposed offshore sand borrow sites were tested for their chemical constituents to determine the suitability of the material for beach replenishment. Sediments were composited from multiple vibracores collected within each borrow site into a single sample for chemical analyses. Results from the chemical analyses of the sediment are expressed in dry weight, and presented in Appendix B.

Total organic carbon concentrations in the proposed borrow site sediments ranged from 0.017 to 0.216%. Total sulfide concentrations ranged from 0.2 to 1.1 mg/Kg and dissolved sulfide ranged from non-detectable to just at the detection limit of 0.1 mg/Kg.

No concentrations of pesticides, polychlorinated biphenyls, polynuclear aromatic hydrocarbons, or phenols were detectable in borrow site sediments. Concentrations of the metals arsenic, chromium, copper, lead, nickel, selenium, and zinc were detected in the sediment. Arsenic concentrations ranged from 0.8 to 2.1 mg/Kg. Chromium concentrations ranged from 1.4 to 9.7 mg/Kg. Copper concentrations ranged from 0.4 to 4.1 mg/Kg. Lead concentrations ranged from 0.3 to 1.6 mg/Kg. Nickel concentrations ranged from 0.4 to 4.0 mg/Kg. Selenium concentrations ranged from non-detectable to 0.3 mg/Kg. Zinc concentrations ranged from 2.2 to 18.9 mg/Kg.

The results from the chemical testing of the proposed offshore borrow site sediments were compared to sediments collected at 6 receiver beach sites (Imperial Beach, Torrey Pines, San Dieguito Lagoon, Batiquitos Lagoon, Buena Vista Lagoon, and Oceanside) by Ogden (1995). The chemical characteristics of the sediments collected at the proposed offshore borrow sites were not significantly different than the chemical characteristics of the sediments at the 6 receiver beach sites.

The total organic carbon concentrations from borrow site sediments (0.04 - 0.22%) were similar to the concentrations of total organic carbon detected at the beach receiver sites (0.04 - 0.28%). Total sulfide concentrations from borrow site sediments did not exceed 1.1 mg/Kg and the highest concentration of total sulfide at the receiver beach sites was 1.8 mg/Kg (subtidal sediment at Oceanside).

Arsenic concentrations at borrow site sediments ranged from 2.1 mg/Kg (AH-1) to 0.7 mg/Kg, whereas the greatest concentration of arsenic at receiver beaches was at 1.7 mg/Kg (subtidal at Oceanside). However, these data points are within 21% of each other and both concentrations are less than the ER-L and ER-M (Effects Range-Low and Median) guideline values (Long,et.al, 1995) and less than the TELs and PEL (Threshold and Probable Effects Level) guideline values (MacDonald, et. al., 1996). Chromium, copper, lead, nickel, selenium, and zinc concentrations in borrow site sediments did not exceed those concentrations detected at the receiver beaches.

3.1.2 Lithologic Analyses

The results from the Lithologic analyses is presented in Table 2. The three most common lithologic grain types (quartz, feldspar, and lithic fragments) are plotted on a triangular diagram in Figure 10. In addition, carbonates (shell fragments) were counted, but were found to be rare. Page 21

The most common component of the sands was quartz, which increased in abundance with a reduction in grain-size (51-90%). The percentage of feldspars ranged from 0-15%, and was most abundant in medium to coarse-grained sand. Lithic fragments ranged in percentage from 8-64%, with the highest concentrations found in mica sand. The lithic fragments included rock fragments and minerals (e.g., mica and magnetite/ilmenite). Carbonates or shell fragments were generally scarce in all samples, with the percentage of these fragments ranging from 0-2%, with the highest abundance in the coarse-grained sands.

FIGURE 10: Triangular Diagram of Sediment Lithology.

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TABLE 2: Tabulated Results from Lithologic Analyses.

Depth Lithic Sample Site In Core Quartz Feldspar Frags Carbonate SDG-2 SO-9 7' 76% 0% 24% 0% SDG-11 SO-9 7' 59% 0% 41% 0% SDG-30 SO-8 6' 64% 4% 32% 0% SDG-35 SO-8 2' 63% 2% 35% 0% SDG-38 AH-1 2' 69% 9% 22% 0% SDG-43 AH-1 4' 90% 2% 8% 0% SDG-52 SO-7 5.5' 72% 9% 19% 0% SDG-55 SO-7 3' 64% 10% 25% 1% SDG-70 SO-6 1' 51% 7% 37% 5% SDG-78 SO-5 8' 79% 0.5% 20% 0.5% SDG-79 SO-5 5.5' 60% 11% 27% 2% SDG-81 SO-4 3' 67% 0% 33% 0% SDG-84 SO-4 3' 63% 3% 34% 0% SDG-93 MB-1 4' 55% 15% 27% 3% SDG-100 MB-1 6.5' 60% 13% 27% 0% SDG-107 SS-2 6' 77% 3% 20% 0% SDG-110 SS-2 6.5' 65% 0% 33% 2% SDG-117 SS-1 4.5' 35% 1% 64% 0% SDG-121 SS-1 4.5' 79% 0% 21% 0% SDG-124 SS-1 5' 57% 9% 34% 0%

3.1.3 Tide Data Comparisons

A self-recording tide gauge was installed at Oceanside Harbor for the duration of the geophysical survey. The tide gauge was referenced to National Ocean Service benchmark #0396A, 1979 (elevation 16.54' MLLW) set in the concrete base of the flagpole in front of the Oceanside Harbor Headquarters. Tides were also monitored during the survey by the National Oceanic and Atmospheric Administration (NOAA) at Scripps Pier in La Jolla, California. A plot comparing the tide measurements collected at Oceanside Harbor and Scripps Pier is presented in Figure 11.

The tide measurements recorded at Oceanside Harbor and at Scripps Pier are nearly identical, except surge is evident in Oceanside Harbor. The elevation of the high and low tides at Oceanside Harbor and at Scripps Pier match within +0.2'. The time of high and low tides at Oceanside Harbor and Scripps Pier match within +5 minutes.

Comparison of these two sets of tide records suggest that the offshore tides are identical anywhere along the open coastline of San Diego County. Consequently, the water depth measurements collected at the 10 proposed offshore sand borrow sites between Oceanside and the US-Mexico Border were corrected for changes in tide using only the NOAA tide data collected at Scripps Pier in La Jolla.

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FIGURE 11: Comparison of Tide Data Collected at Oceanside Harbor and Scripps Pier.

3.2 SITE DESCRIPTIONS

The results from the geophysical surveys and vibracore investigations at each of the proposed offshore sand borrow site are presented in the following sections. The site descriptions are presented from north-to-south, beginning with the northern-most site (SO-9).

3.2.1 Site SO-9

Site S0-9 is located north of Oceanside Harbor and offshore of the Santa Margarita River in 50 to 80 feet of water. The site measures 3,000' x 5,000' and has a surface area of 15 million square feet (344 acres). Because the Santa Margarita River is a potential source for coarse sediment and the offshore area is a likely location for paleochannels or terraces, the area surrounding Site SO-9 has been previously explored by vibracore investigations. Historical vibracore investigations have found areas of suitable beach replenishment material just inshore of Site SO-9 (Osbourne et al., 1983). A second historical vibracore investigation identified an area just inshore of Site SO-9 that had 1-2 feet of silty fine sand overlying poorly-graded medium sand with gravel (USACE, 1993).

A marine geophysical survey was conducted in Site SO-9 during January 1999 along tracklines spaced at nominal 500' intervals parallel to shore and nominal 1,000' intervals perpendicular to shore (Appendix A). A Seafloor Features Map depicting the results of the geophysical survey is presented in Figure 12. The side-scan sonar showed the seabed within Site SO-9 to be uniform and comprised of fine- to medium-grained sediment. The side-scan records also showed eight artificial reef habitats, comprised of piles of quarry rock, on an otherwise featureless seafloor within Site SO-9.

The seismic reflection records collected in Site SO-9 were complex, particularly in the nearshore, shallow waters. The seismic reflection data indicates the presence of a paleochannel buried beneath 30'-55' of sediment (Figure 13); however, this buried feature is too deep for correlation with the vibracore data. In nearshore waters, a 30' thick layer of sediment is seen with

FIGURE 12: Seafloor Features Map of Site SO-9.

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FIGURE 13: Typical Cross-Sectional Profile of Subbottom Features in Site SO-9. discontinuous, horizontal and sometimes dipping stratigraphy. This surficial layer of sediment is underlain by an angular unconformity. Seaward of the 70' bathymetric contour, a well defined 20'-30' thick sediment prism is present.

After preliminary interpretation of the geophysical records, twelve vibracore stations were selected at the intersection of the crossing survey lines (Appendix A). Most of the vibracore stations were located inshore of the artificial reefs, but 2 vibracore stations were located between the 4 inshore reefs and 4 offshore reefs in order to define the resource potential of the region surrounded by the artificial reefs.

The vibracores collected within Site SO-9 penetrated from 4.7' to 17.3'. In general, the vibracore logs indicate that the nearshore border of the site has fine- to medium-grained sand, while the offshore border of the site has fine-grained sand to fine-grained silty sand overlying poorly-sorted fine- to medium-grained sand offshore. Confirming the vibracore logs, results from the grain-size analyses (Table 3) also indicate the presence of fine- to medium-grained sand along the nearshore border of Site SO-9 grading to sandy silt and very-fine silty sand overlying fine- to medium- grained sand at the offshore border of the site.

The vibracore logs and grain-size analyses identify three layers of sediments within Site SO-9:

1. The top (surficial) layer consists of sandy silt and is wedge-shaped. The thickness of this silt layer measures about 12' in the central region of Site SO-9 and gradually thins out before reaching the nearshore boundary (Figure 14). The offshore extent of this wedge-shaped surficial layer could not be determined past the 8 artificial reefs, but the grain-size analyses showed this surficial layer to be unsuitable for beach nourishment material.

2. Beneath the surficial silt layer is a layer of fine- to medium-grained sand that is suitable for beach nourishment. This sand layer is 3'-13' thick, and is exposed on the seafloor surface along the nearshore boundary of the site (Figure 15). This sand layer is not quite wedge-shaped due to the thick deposit located near the northeast corner, but tends to grow thicker as it moves offshore.

3. A third layer, consisting of fine-grained silty sand, was found under the sand layer. Page 26

Since it is unlikely that dredging will be allowed in the offshore half of Site SO-9 because of interference with the 8 artificial reef habitats, volume calculations were performed only for the top two sediment layers limited to an area inshore of the eight artificial reefs. The estimated volume of suitable beach nourishment material in Site SO-9 is 0.9 million cubic yards buried under 0.8 million cubic yards of unsuitable silty material. To dredge the estimated 0.9 million cubic yards of suitable sand, excavation of up to 13 feet below the seafloor would be required.

Most of the volume of suitable sand is located along the nearshore boundary of Site SO-9. Historical vibracore explorations identified suitable beach material just inshore of Site SO-9. Therefore, it is recommended that Site SO-9 be moved towards the northeast to take advantage of the suitable sand located inshore, and to avoid impacts associated with dredging near the 8 artificial reef structures. Additional geophysical surveys should be conducted after the site has been relocated in order to provide the necessary information to revise the borrow volume computations.

Figure 14: Isopach map showing thick- Figure 15: Isopach map showing thick- ness of silt overburden in Site SO-9. ness of underlying sand in Site SO-9. Page 27

TABLE 3: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-9.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 1-1 0.889 89.228 9.883 0.181 0’ - 4’ SP Suitable SDG 1-2 31.649 66.589 1.762 1.204 4’ - 7.4’ SP Unsuitable SDG 2-1 5.328 91.657 3.014 0.215 0’ - 5.3’ SP Suitable SDG 2-2 0.000 98.32 1.678 0.180 5.3’- 9.2’ SP Suitable SDG 3-1 0.019 48.473 51.508 0’ - 2’ ML Unsuitable SDG 3-2 0.904 91.067 8.029 0.119 2’ - 4’ SP Suitable SDG 4-1 0.123 49.012 50.866 0’ - 3.5’ ML Unsuitable SDG 4-2 4.833 69.231 25.936 0.136 3.5’ - 4.5’ SM Unsuitable SDG 4-3 0.396 98.833 0.771 0.289 4.5’ - 12.6’ SP Suitable SDG 5-1 0.147 92.551 7.302 0.179 0’ - 6’ SW Suitable SDG 5-2 21.771 48.535 29.694 0.463 6’ - 8.2’ SM Unsuitable SDG 6-1 0.027 88.618 11.355 0.163 0’ - 3.4’ SP Marginal SDG 6-2 0.163 89.351 10.486 0.181 3.4’ - 13’ SW Marginal SDG 6-3 20.449 72.036 7.515 0.525 13’ – 15.3’ SP Unsuitable SDG 7-1 0.656 45.760 53.585 0’ - 6’ ML Unsuitable SDG 7-2 14.328 82.451 3.221 0.435 6’ - 7’ SP Marginal SDG 8-1 0.000 42.932 57.068 0’ - 4’ ML Unsuitable SDG 8-2 0.109 43.725 56.166 4’ - 6’ ML Unsuitable SDG 8-3 0.000 93.480 6.520 0.119 6’ - 9’ SW Suitable SDG 8-4 31.640 66.865 1.495 1.024 9’ – 17.3’ SP Unsuitable SDG 9-1 0.000 35.600 64.400 0’ - 2.5’ ML Unsuitable SDG 9-2 0.000 50.030 49.970 0.084 2.5’ – 4.5’ SM Unsuitable SDG 9-3 0.055 85.700 14.245 0.109 4.5’ –11.2’ SP Marginal SDG 10-1 0.035 47.375 52.591 0’ - 6’ ML Unsuitable SDG 10-2 0.000 96.704 3.296 0.123 6’ – 10’ SP Suitable SDG 10-3 0.000 95.154 4.846 0.121 10’ – 13.7’ SP Suitable SDG 11-1 0.000 36.753 63.247 0’ - 5’ ML Unsuitable SDG 11-2 1.897 68.441 29.662 0.103 5’ – 10’ SM Unsuitable SDG 11-3 0.117 57.251 42.632 0.090 10’ – 14.4’ SM Unsuitable SDG 12-1 0.000 19.199 80.801 0’ - 4’ ML Unsuitable SDG 12-2 0.175 76.274 23.551 0.109 4’ – 10.9’ SM Unsuitable

3.2 Site SO-8

Site SO-8 is located south of Oceanside Harbor, and offshore of the San Luis Rey River, in 50' to 90' of water. The site measures 4,000' x 5,000' and covers 20 million square feet (459 acres). The offshore area near Site SO-8 was investigated in 1983 and 1993. Two vibracore sediment samples collected in 1983 contained marginally-suitable fine-grained sediment (Osbourne et al., 1983), and 8 vibracore samples collected in 1993 found only 1 core with marginally-promising sand and one core with promising beach replenishment material (USACE, 1993).

A geophysical survey of Site SO-8 was conducted in January 1999 along tracklines spaced at nominal 500' intervals in a north-south direction and nominal 1,000' intervals in an east-west direction (Appendix A). A Seafloor Features Map showing the location of the site and the results of the geophysical survey is presented in Figure 16. The side-scan sonar found four (4) piles of debris on the seafloor that are probably the remains of artificial reef habitats. Except for the artificial reef remnants, the seafloor in Site SO-8 is uniform and featureless. The seismic reflection records show a well-defined prism of sediment that varies in thickness from FIGURE 16: Seafloor Features Map of Site SO-8. Page 29

approximately 10'-35'. An example cross-sectional profile from the seismic reflection records is presented in Figure 17. In general, the sediment layer is 10'-20' thick nearshore and increases to 25'-35' thick along the western (offshore) boundary. Within this sediment prism are several discontinuous horizontal reflectors with low signal returns.

After preliminary review of the geophysical records, 24 vibracore stations were selected in locations that coincided with the intersection of the north-south and east-west survey lines. Vibracore penetration was between 4'-17' within Site SO-8. The vibracore logs indicate that the predominant surficial sediment within this area is dark olive-gray very fine- to fine-grained silty sand. Underneath this silty fine sand is a layer of gray poorly sorted fine-grained sand. The thickness of this silty sand layer was not visible on the seismic reflection records and therefore cannot be defined in areas where sediment samples were not collected.

The grain-size analyses (Table 4) confirmed that unsuitable beach material overlies marginally suitable material in Site SO-8. The surficial sediment layer in Site SO-8 is 4'-13' thick (average=10') and comprised of sandy-silt or very fine-grained silty sand that is unsuitable for beach nourishment purposes (Figure 18). An underlying layer of fine-grained sand, although quite silty, has been determined to be suitable for nourishment material. This underlying layer of marginally suitable material varies in thickness from 6'-25' (Figure 19).

Although the bottom of the suitable sand layer was identified on the seismic reflection data, the thickness of the overlying unsuitable silty sand layer cannot be defined where vibracore sediment samples were not collected. Volume computations were thus limited to areas with sufficient data, as depicted in the isopach charts mentioned above.

In Site SO-8, approximately 5.8 million cubic yards of marginally suitable beach sand is buried under 3.1 million cubic yards of unsuitable silty sand. The dredge will need to excavate between 4 to 35 feet below the seafloor to produce the estimated 5.8 million cubic yards of suitable sand.

FIGURE 17: Typical Cross-Sectional Profile of Subbottom Features in Site SO-8.

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FIGURE 18: Isopach Chart Showing Thickness of Silt Overburden in Site SO-8.

FIGURE 19: Isopach Chart Showing Thickness of Suitable Sand Layer in Site SO-8. Page 31

Removing the unsuitable material to dredge the suitable sand underneath may be impractical. Unfortunately, the coastline surrounding Site SO-8 is believed to contain similarly unsuitable fine-grained sediment. To the north, unsuitable silty material was collected along the southern region of Site SO-9. Inshore of Site SO-8, historical studies have shown than only one out of eight cores collected contained promising beach replenishment material (USACE, 1993). To the south, no suitable sand was found in Site AH-1.

It is recommended that an exploratory geophysical survey be conducted along a broad reach of coastline near Oceanside in order to locate a new borrow site to replace Site SO-8.

TABLE 4: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-8.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 13-1 0.000 83.257 16.743 0.104 0’ - 8’ SM Unsuitable SDG 13-2 0.016 43.337 56.647 8’ – 13’ ML Unsuitable SDG 13-3 4.179 89.591 6.230 0.118 13’ – 16.5’ SP Suitable SDG 14-1 0.000 50.767 49.233 0.079 0’ – 8’ SM Unsuitable SDG 14-2 0.906 84.945 14.149 0.114 8’ – 12’ SP Marginal SDG 14-3 0.000 90.656 9.344 0.106 12’ – 16.5’ SP Suitable SDG 15-1 0.000 47.390 52.610 0’ – 5.5’ ML Unsuitable SDG 15-2 0.204 66.416 33.380 0.098 5.5’ – 10’ SM Unsuitable SDG 15-3 0.000 92.892 7.108 0.107 10’ – 17.1’ SP Suitable SDG 16-1 0.535 49.333 50.131 0’ – 7’ ML Unsuitable SDG 16-2 3.877 83.100 13.022 0.126 7’ – 10’ SP Marginal SDG 16-3 0.388 92.067 7.545 0.109 10’ – 16’ SP Suitable SDG 17-1 0.571 45.585 53.844 0’ – 10’ ML Unsuitable SDG 17-2 0.000 93.769 6.231 0.116 10’ – 13.1’ SP Suitable SDG 18-1 0.000 33.635 66.365 0’ – 4’ ML Unsuitable SDG 18-2 0.672 45.620 53.708 4’ – 12.2’ ML Unsuitable SDG 19-1 0.000 35.709 64.291 0’ – 4’ ML Unsuitable SDG 19-2 0.328 47.431 52.241 4’ – 13.1’ ML Unsuitable SDG 19-3 5.986 89.495 4.519 0.122 13.1’ – 14’ SP Suitable SDG 20-1 0.000 35.655 64.345 0’ – 7.5’ ML Unsuitable SDG 20-2 0.118 56.687 43.195 0.090 7.5’ – 11’ SM Unsuitable SDG 20-3 0.000 92.201 7.799 0.108 11’ – 16.3’ SP Suitable SDG 21-1 0.812 44.964 54.224 0’ – 6’ ML Unsuitable SDG 21-2 0.419 90.949 8.633 0.116 6’ – 13.6’ SP Suitable SDG 22-1 0.000 41.928 58.072 0’ – 6.5’ ML Unsuitable SDG 22-2 0.012 81.830 18.157 0.111 6.5’ – 9.5’ SM Unsuitable SDG 22-3 0.000 94.553 5.447 0.107 9.5’ – 17’ SP Suitable SDG 23-1 0.000 32.939 67.061 0’ – 7.5’ ML Unsuitable SDG 23-2 0.368 83.543 16.089 0.116 7.5’ – 9.8’ SM Unsuitable SDG 24-1 0.000 34.096 65.904 0’ – 8’ ML Unsuitable SDG 24-2 0.045 61.549 38.406 0.094 8’ – 14.5’ SM Unsuitable SDG 25-1 0.000 41.893 58.107 0’ – 3’ ML Unsuitable SDG 25-2 3.863 86.688 9.449 0.119 3’ – 10’ SP Suitable SDG 26-1 0.053 42.098 57.849 0’ – 10’ ML Unsuitable SDG 26-2 9.852 85.711 4.437 0.176 10’ – 15.5’ SP Suitable SDG 27-1 0.226 41.953 57.821 0’ – 9’ ML Unsuitable SDG 27-2 0.034 76.998 22.969 0.104 9’ – 11.3’ SM Unsuitable SDG 28-1 0.000 38.899 61.101 0’ – 9’ ML Unsuitable SDG 28-2 0.000 93.087 6.913 0.117 9’ – 12.2’ SP Suitable SDG 29-1 0.000 27.295 72.705 0’ – 7’ ML Unsuitable SDG 29-2 0.000 92.370 7.630 0.120 7’ – 9.7’ SP Suitable

Page 32 Table 4:cont. SDG 30-1 0.000 32.596 67.404 0’ – 5.5’ ML Unsuitable SDG 30-2 0.405 63.667 35.928 0.095 5.5’ – 11.5’ SM Unsuitable SDG 31-1 0.132 38.464 61.405 0’ – 7’ ML Unsuitable SDG 31-2 0.813 75.064 24.123 0.102 7’ – 11’ SM Unsuitable SDG 32-1 0.122 46.817 53.061 0’ – 6’ ML Unsuitable SDG 32-2 0.000 39.843 60.157 6’ – 9.9’ ML Unsuitable SDG 33-1 0.000 44.064 55.936 0’ – 3.6’ ML Unsuitable SDG 34-1 0.000 35.664 64.336 0’ – 3.9’ ML Unsuitable SDG 35-1 0.575 41.494 57.931 0’ – 4’ ML Unsuitable SDG 35-2 0.000 39.901 60.099 4’ – 6.1’ ML Unsuitable

3.3 Site AH-1

Site AH-1 is located offshore of Agua Hedionda Lagoon in 60 to 130 feet of water. The proposed site measures 3,000' x 4,000' and covers 12 million square feet (275 acres), but only approximately 5-6 million square feet (or 50% of the site) is shallower than the 80 foot contour. Historical data available for Site AH-1 indicates that the surficial sediment is unsuitable for beach nourishment purposes. Soil samples collected for the Encina Power Plant Offshore Pipeline (Woodward-Gizienski, 1974) found very fine silty sand as the predominant sediment in this area, and two vibracore samples collected inshore of Site AH-1 contained unsuitable material for beach nourishment (USACE, 1993).

A geophysical survey was conducted in January 1999 that included tracklines spaced at nominal 300' intervals in a north-south direction (parallel to shore) and nominal 1,000' intervals in an east- west direction (Appendix A). The side-scan sonar records showed the seafloor in Site AH-1 to be very uniform, with fine-grained surficial sediments and occasional boulders, cobbles, and rock with kelp (Figure 20). The seismic reflection data indicated that the thickness of the surficial sediment in Site AH-1 is only approximately 1' thick along the near-shore boundary, but increases to approximately 35' thick at the offshore boundary of the site.

Ten (10) sediment cores were collected in Site AH-1 between the 60 and 80 depth contours. The vibracore locations were selected to coincide with the intersection of the geophysical survey lines within the optimal water depth range for dredging. All sediment cores penetrated between 5'-7' below the seafloor, with the longest cores collected in deeper water. The vibracore logs indicate that very fine silty sand is the predominant sediment type in this area. Results from the grain-size analyses (Table 5) show that the surficial sediment is fine sand with a high silt content (10.7- 42.5%) that is unacceptable for beach nourishment. The silt content is highest for subsamples collected near the top of the vibracore, and the percent silt decreases with depth. The sediment samples with the lowest (10-12%) silt content in Site AH-1 may be of marginal use for beach nourishment purposes, but are located 4'-6' under a mantle of sediments containing 30% silt.

There is no material within Site AH-1 that is suitable for beach nourishment purposes; therefore, the volume of available beach sand could not be computed for this site. Since the available historical data also did not show any acceptable material near Site AH-1, it is recommended that a exploratory geophysical survey be conducted between the 40'-80' depth contour over a broad reach of the coastline in order to locate the nearest alternate offshore borrow site for beach nourishment material. FIGURE 20: Seafloor Features Map of Site AH-1.

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TABLE 5: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site AH-1.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 36-1 0.427 64.053 35.520 0.089 0’ – 2’ SM Unsuitable SDG 36-2 0.086 84.066 15.847 0.100 2’ – 4.2’ SM Unsuitable SDG 37-1 0.000 60.259 39.741 0.102 0’ – 3’ SM Unsuitable SDG 37-2 0.444 84.541 15.015 0.097 3’ – 6.3’ SM Marginal SDG 38-1 0.622 56.906 42.472 0.085 0’ – 4.5’ SM Unsuitable SDG 38-2 1.593 72.722 25.685 0.093 4.5’ – 7.2’ SM Unsuitable SDG 39-1 0.000 62.876 37.124 0.086 0’ – 3’ SM Unsuitable SDG 39-2 0.000 86.480 13.520 0.097 3’ – 5’ SP Marginal SDG 40-1 0.000 67.685 32.315 0.090 0’ – 3’ SM Unsuitable SDG 40-2 0.748 70.120 29.132 0.091 3’ – 5.5’ SM Unsuitable SDG 41-1 0.000 68.327 31.673 0.089 0’ – 4’ SM Unsuitable SDG 41-2 0.751 86.955 12.294 0.098 4’ – 5.1’ SP Marginal SDG 42-1 1.316 69.209 29.475 0.091 0’ – 5’ SM Unsuitable SDG 42-2 0.515 88.806 10.679 0.104 5’ – 6.7’ SP Suitable SDG 43-1 0.925 66.101 32.974 0.091 0’ – 4’ SC Unsuitable SDG 43-2 0.000 77.407 22.593 0.093 4’ – 5.5’ SM Unsuitable SDG 44-1 0.551 74.850 24.599 0.092 0’ – 4.7’ SM Unsuitable SDG 45-1 0.000 82.207 17.793 0.095 0’ – 5’ SM Unsuitable

3.4 Site SO-7

Site SO-7 is located offshore of Batiquitos Lagoon in 50 to 100 feet of water. Site SO-7 has dimensions of 2,500' x 5,000', and covers an area of 12.5 million square feet (287 acres). Approximately 35% of Site SO-7 is deeper than the 80 foot contour. The available historical data near Site SO-7 include three vibracores collected directly offshore of Batiquitos Lagoon that contained suitable beach nourishment material, and three vibracores collected further offshore that contained unsuitable material (USACE, 1993).

A marine geophysical survey was conducted at Site SO-7 during January 1999 along survey lines spaced at nominal 300' intervals in a north-south direction and nominal 1,000' intervals in an east- west direction (Appendix A). The results from the geophysical survey indicated that Site SO-7 is the most geologically-diverse of all the borrow sites surveyed. The side-scan sonar records show a great deal of variability in the surficial sediments within Site SO-7 (Figure 21). There appears to be several small zones of cobbles, including one near the site's southern border and one near the center of the eastern boundary of the site. A small region of exposed bedrock located near the center of the northern boundary of the site appears to be adjacent to very coarse sediments located in the northwest corner of the site. In the northeast corner or the site, and along the western (offshore) boundary, the side-scan records exhibit low-amplitude sandwaves characteristic of fine-grained material. Similarly, the southern half of the site appears to be fine-grained sediments, with some sand waves along the southern boundary of the site.

Like the side-scan records, seismic reflection data collected during the January 1999 geophysical survey show variability in the sediment type and thickness of layers within Site SO-7. The seismic reflection records clearly show that shallow bedrock underlies most of Site SO-7. In the central region of the site, up to 13' of unconsolidated fine- and medium-grained material has accumulated in pockets and terraces within the bedrock. The bedrock is very shallow along the northern and southern boundaries of Site SO-7, covered by only 1'-3' of unconsolidated sediment. FIGURE 21: Seafloor Features Map of Site SO-7. Page 36

A sediment prism, probably fine-grained sand with silt, develops offshore (west) of the 80' contour.

After reviewing the geophysical data collected at Site SO-7, a total of twenty (20) vibracore sample locations were selected. The vibracore locations were selected to coincide with the intersection of north-south and east-west survey lines (Appendix A), and to sample within discrete regions of surficial sediments types mapped by the geophysical survey. Vibracore penetration at these 20 locations varied from 1'-15', and confirmed the presence of confined pockets of sediments within a region of very thin layers of unconsolidated sediments overlying bedrock. The predominant sediment within Site SO-7 is olive-gray fine- to medium-grained silty sand, except for an area of brownish-gray medium- to coarse-grained sand in the central region of the site.

Within the central region, a deep pocket or terrace of sand overlies the bedrock (Figure 22). Within this central pocket, a layer of compacted medium- to coarse-grained sand was found buried under 3'-13' of fine- to medium-grained sand, with both layers suitable for beach replenishment (Figure 23). The vibracore could not penetrate far into the compacted underlying sand, therefore the characteristics of the underlying layer is still not clear. Occasional lenses of pebbles and gravel were found within the sand in the central region. Surrounding this central pocket, in all directions, the hard bottom becomes very shallow, especially to the north and west with only 1'-3' of overlying unconsolidated sand. Another pocket of sediment is located at the southeast corner of the site, but the results from the grain-size analyses indicate the material is unsuitable for beach replenishment.

To the west, beyond the 80' bathymetric contour, another sediment prism exists. This prism is approximately 2'-3' thick just west of the large pocket of sand in the central region of the site, and rapidly increases in thickness to 30' as it approaches the western boundary of Site SO-7. The single vibracore sample that was collected within this sediment prism found unsuitable material.

The results of the grain-size analyses (Table 6) show that the majority of Site SO-7 contains suitable sand for beach nourishment. Only the southeastern corner of Site SO-7, and a region along the western boundary, were found to contain fine-grained material with silt percentages too high for beach nourishment purposes.

In general, Site SO-7 can be divided into 4 regions:

1. The northern region of Site SO-7 contains 1'-4' of well- to moderately-sorted fine- to medium- grained sand overlying a hard (rock) substrate. Although the sand overlying the bedrock in this northern region is suitable for beach nourishment purposes, the surficial layer is probably too thin to dredge economically.

2. The central region of Site SO-7 is predominantly well-sorted medium- to coarse-grained sand with occasional pebbles and shell fragments. This material is ideal for beach nourishment, and the layer is thick enough (up to 13') for efficient and economical dredging. The estimated volume of suitable beach nourishment sand within this central region of Site SO-7 is 1.1 million cubic yards.

3. The southern region is characterized as having one foot of fine silty sand overlying 1' to 7' of moderately-sorted fine-grained sand. The overlying material is not suitable for Page 37

placement on the beach, and the volume of the underlying material is probably insufficient for economical or efficient dredging.

4. The western region along the offshore boundary has a layer of silty sand that is 2'-30' thick.

FIGURE 22: Typical Cross-Sectional Profile of Subbottom Features in Site SO-7.

FIGURE 23: Isopach Chart Showing Thickness of Surficial Sand in Site SO-7. Page 38

TABLE 6: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-7.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 47-1 0.000 96.445 3.555 0.248 0’ – 1.7’ SW Suitable SDG 48-1 0.000 95.849 4.151 0.179 0’ – 3.8’ SP Suitable SDG 50-1 0.000 95.303 4.697 0.168 0’ – 2’ SP Suitable SDG 50-2 0.131 95.531 4.338 0.282 2’ – 4’ SP Suitable SDG 51-1 0.000 96.520 3.480 0.297 0’ – 5’ SP Suitable SDG 52-1 9.077 90.871 0.052 0.803 0’ – 3.5’ SP Suitable SDG 52-2 4.817 95.065 0.118 0.779 3.5’ – 6’ SP Suitable SDG 52-3 0.986 98.861 0.152 0.605 6’ – 13.6’ SP Suitable SDG 53-1 6.586 93.176 0.238 0.731 0’ – 6’ SW Suitable SDG 53-2 5.910 93.946 0.144 0.703 6’ – 11.1’ SP Suitable SDG 54-1 5.871 93.730 0.400 0.875 0’ – 3’ SW Suitable SDG 54-2 0.218 99.192 0.590 0.420 3’ – 8’ SW Suitable SDG 54-3 0.000 98.642 1.358 0.205 8’ – 9.9 SP Suitable SDG 55-1 6.882 92.836 0.282 0.764 0’ – 6’ SW Suitable SDG 55-2 2.742 97.053 0.205 0.623 6’ – 9’ SW Suitable SDG 55-3 0.133 99.360 0.507 0.449 9’ – 14.9’ SW Suitable SDG 56-1 4.706 93.834 1.460 0.390 0’ – 4’ SW Suitable SDG 56-2 0.615 98.788 0.597 0.482 4’ – 8’ SW Suitable SDG 56-3 1.553 98.054 0.394 0.511 8’ – 12.9’ SW Suitable SDG 57-1 0.000 93.922 6.078 0.218 0’ – 4’ SP Suitable SDG 57-2 0.023 96.286 3.691 0.266 4’ – 5.5’ SP Suitable SDG 59-1 0.016 85.539 14.445 0.119 0’ – 4’ SP Marginal SDG 59-2 0.202 80.144 19.654 0.104 4’ – 6.5’ SM Unsuitable SDG 61-1 0.943 95.660 3.397 0.230 0’ – 5’ SP Suitable SDG 61-2 2.444 87.805 9.751 0.218 5’ – 14.3’ SP Suitable SDG 62-1 1.205 85.264 13.532 0.108 0’ – 6’ SP Marginal SDG 62-2 21.590 74.749 3.661 0.755 6’ – 10’ SP Unsuitable SDG 63-1 0.000 94.994 5.006 0.188 0’ – 3.4’ SP Suitable

3.5 Site SO-6

Site SO-6 is located offshore of San Elijo Lagoon in 60 to 120 feet of water. The site measures 2,500' x 4,000' and covers 10 million square feet (230 acres). The proposed location of Site SO-6 may need to be re-defined, because only approximately 45% of the site is shallower than the 80 foot contour and the San Elijo Outfall lies along the southern boundary of the site. The historical data available near Site SO-6 includes one vibracore sample that contained fine-grained sand marginally-acceptable for beach nourishment (Osbourne et al., 1983); however, additional historical data may be available from offshore surveys conducted during design/construction of the San Elijo Outfall.

A marine geophysical survey was conducted in January 1999 along tracklines spaced at nominal 500' intervals in a north-south direction and nominal 1,000' intervals in an east-west direction (Appendix A). The side scan sonar and marine magnetometer clearly recorded the San Elijo Outfall, covered with armor stone, that lies along the southern boundary of Site SO-6 (Figure 24). In addition, the side scan data showed a distinct, convoluted boundary between coarse-grained surficial sediments in the east (nearshore) side of the site and fine-grained sediments in the west (offshore) side of the site. The seismic reflection data indicates a single wedge-shaped layer of FIGURE 24: Seafloor Features Map of Site SO-6.

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unconsolidated material increasing uniformly in thickness towards the west (offshore). According to the seismic records, the thickness of this layer measures less than 5' along the eastern (nearshore) boundary of Site SO-6, and uniformly increases towards the west (offshore) to a thickness of approximately 27'. An example cross-section profile from the seismic reflection records is presented in Figure 25.

After reviewing the geophysical records, five (5) vibracore stations were selected for Site SO-6. including two vibracores in the north, two vibracores in the central, and one vibracore in the south part of the site. The vibracore locations were selected to coincide with the intersection of the geophysical survey lines (Appendix A), and to bracket the convoluted boundary between inshore coarse-grained and offshore fine-grained surficial sediments observed by the side scan sonar.

The vibracore logs confirm the seismic reflection results from the marine geophysical survey. Vibracore penetration at the 5 sampling locations in Site SO-6 ranged between 1'-10'. The two northern vibracores collected approximately 4' of very fine silty sand overlying bedrock. The two vibracores in the central region of Site SO-6 both collected 1.6' feet of medium grained sand with shell fragments overlying bedrock. The southern-most vibracore station (SDG-70) collected a 10.6' sediment core that included 3 feet of well-sorted coarse sand overlying 7 feet of moderately- sorted very fine- to fine-grained sand. The 10.6' of suitable beach nourishment material found at vibracore station SDG-70 corresponded well with the seismic reflection data, where the sediment thickness was interpreted to be 10'-11'.

The results from the grain-size analyses (Table 7) indicate that most, if not all, the sediment within Site SO-6 is acceptable for beach nourishment purposes. The largest volume of the most acceptable material for beach nourishment was found in the south central portion of Site SO-6 at vibracore station SDG-70. The vibracore sediment samples collected west (offshore) of the convoluted boundary observed on the side-scan records showed higher, and possibly unacceptable, silt concentrations of approximately 9-11%. Vibracore samples collected east (inshore) of the convoluted boundary observed on the side-scan records showed lower (1.1-7.8%) silt concentrations, with the silt concentrations decreasing with distance away from the convoluted boundary observed on the side-scan records.

The interpretation of the available data suggests that a single, wedge-shaped layer of fine-grained sand with a low content of silt overlies shale bedrock within Site SO-6. This wedge of material measures less that 5' thick along the east (nearshore) boundary of Site SO-6 and uniformly increases to a maximum of 27' towards the west (offshore) boundary of the site (Figure 26). The total volume of this wedge-shaped layer of sand is 5.3 million cubic yards; however, not all of this material may be available for dredging. Only approximately 2.4 million cubic yards of this wedge-shaped layer of sand is located east (shoreward) of the convoluted boundary observed on the side-scan records that may define the region of acceptable silt content. Within this area, an excavation of up to 20 feet below the seafloor is required to produce the estimated 2.4 million cubic yards of suitable sand. In addition, if dredging is prohibited near the San Elijo Outfall located along the southern boundary of Site SO-6, the total volume of beach sand available in the site will be reduced; for example, prohibiting dredging within 1,000' of the submerged pipe will reduce the volume of suitable beach sand within Site SO-6 to 1.2 million cubic yards. Finally, if the dredge is also limited to water depths of less than 90', the volume of beach sand available in Site SO-6 is reduced to a total of 0.8 million cubic yards.

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It is recommended that Site SO-6 be moved approximately 1,000' east (inshore) to encompass the 40-80' water depth contours and approximately 1,000' north to avoid impacting the existing submerged pipeline. A new geophysical survey of the revised site should be conducted so that potential borrow volumes can be computed.

FIGURE 25: Typical Cross-Sectional Profile of Subbottom Features in Site SO-6.

FIGURE 26: Isopach Chart Showing Thickness of Suitable Surficial Sand Layer in Site SO-6. Page 42

TABLE 7. Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-6.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 66-1 0.820 88.575 10.605 0.098 0’ – 3.5’ SP Marginal SDG 66-2 0.119 88.167 11.713 0.100 3.5’ – 4.5’ SP Marginal SDG 67-1 0.117 94.129 5.754 0.112 0’ – 3.3’ SP Suitable SDG 68-1 4.076 86.834 9.090 0.241 0’ – 1.6’ SW Suitable SDG 69-1 1.430 90.731 7.839 0.247 0’ – 1.6’ SP Suitable SDG 70-1 7.868 91.049 1.082 0.657 0’ – 3’ SW Suitable SDG 70-2 0.115 96.612 3.273 0.123 3’ – 10.6’ SP Suitable

3.6 Site SO-5

Site S0-5 is located offshore of San Dieguito Lagoon in 50 to 95 feet of water. Site SO-5 measures 3,000' x 4,000' and has a surface area of 12 million square feet (275 acres). Approximately 25% of the site is deeper than the 80' contour. There is no historical data available that defines the quality of beach nourishment material near Site SO-5.

A geophysical survey was conducted in Site SO-5 during January 1999. The geophysical survey lines were run at nominal 500' intervals in a north-south direction and at nominal 1,000' intervals in an east-west direction (Appendix A). The side-scan sonar records show that the majority of Site SO-5 is characterized by a very uniform, smooth seafloor (Figure 27), with sand waves in the northeast and southeast (inshore) corners of the site. The side-scan records exhibit a significant increase in seabed reflectivity in both the northeast and southeast corners of the site, which is indicative of medium- to coarse-grained sediment. The seismic reflection data identified a well- developed sediment prism measuring 2'-5' thick along the eastern (nearshore) boundary increasing uniformly in thickness to approximately 25' along the western (offshore) boundary of the site. An example cross-sectional profile from the seismic reflection records is presented in Figure 28.

After a preliminary review of the geophysical survey data, ten (10) sediment core locations were selected for Site SO-5. The location of the vibracore samples were selected to coincide with the intersection of the north-south and east-west geophysical survey lines (Appendix A), and to sample the various sediment types/layers observed in the geophysical data.

In general, the vibracore logs indicate a similar pattern as seen with the seismic reflection data. Vibracore penetration ranged from between 3'-12' within the site, with the short cores being collected nearshore and increasing in length offshore. At vibracore station SDG-78, shale was encountered at 9.5' below the seafloor which corresponds to the seismic reflection data indicating the sediment layer being 10' thick at that location. The only exception to the pattern was at vibracore station SDG-79, located along the eastern (nearshore) boundary of the site. At a penetration depth of 4.8', a 0.7' layer of pebbles and gravel was found to overlie a deeper layer of yellowish-gray well-sorted coarse sand.

The results of the grain-size analyses (Table 8) show that the majority of Site SO-5 contains suitable sand for beach nourishment. The predominant sediment within Site SO-5 is gray to olive-gray fine-grained sand with 3% silt content. Although 3 sediment samples contained marginally unsuitable material, two of these samples (SDG-71 and 79) were from vibracore stations located on the boundary of the site and the third sample (SDG-74) had a silt content of FIGURE 27: Seafloor Features Map of Site SO-5. Page 44

13.8% in the top 5' of the core. For purposes of volume calculations, Site SO-5 was assumed to contain a single, homogenous, wedge shaped layer of fine-grained sand, suitable for beach replenishment (Figure 29).

The estimated volume of suitable beach nourishment sand within Site SO-5 is 6.2 million cubic yards. Excavation required to produce the estimated 6.2 million cubic yards ranges from 2 to 25 feet below the seafloor. Because the thickness of the sand layer increases in deeper water, the amount of beach sand available for beach nourishment will be less if dredging is restricted to water depths less than 80'.

FIGURE 28: Typical Cross-Sectional Profile of Subbotom Features in Site SO-5.

TABLE 8: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-5.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 71-1 0.000 98.071 1.929 0.156 0’ – 1.5’ SP Suitable SDG 71-2 0.194 87.679 12.127 0.121 1.5’ – 3.1’ SP Marginal SDG 72-1 0.205 98.187 1.608 0.160 0’ – 4’ SP Suitable SDG 72-2 0.018 98.176 1.805 0.153 4’ – 6’ SP Suitable SDG 73-1 0.113 98.729 1.158 0.158 0’ – 6.3’ SP Suitable SDG 74-1 0.131 86.109 13.760 0.128 0’ – 3’ SP Marginal SDG 74-2 0.077 98.470 1.453 0.163 3’ – 8.3’ SP Suitable SDG 75-1 0.039 97.062 2.898 0.145 0’ – 3.3’ SP Suitable SDG 76-1 1.530 95.893 2.577 0.164 0’ – 3’ SP Suitable SDG 76-2 0.000 98.105 1.895 0.135 3’ – 6.3’ SP Suitable SDG 77-1 4.304 91.096 4.600 0.132 0’ – 5’ SP Suitable SDG 77-2 0.000 96.108 3.892 0.124 5’ – 7.6’ SP Suitable SDG 78-1 0.875 96.224 2.901 0.150 0’ – 5’ SP Suitable SDG 78-2 0.000 98.613 1.387 0.148 5’ – 10’ SP Suitable SDG 79-1 0.192 82.046 17.762 0.130 0’ – 3.5’ SM Unsuitable SDG 79-2 20.703 78.197 1.100 0.753 3.5’ – 5’ SP Unsuitable SDG 79-3 0.190 99.585 0.225 0.566 5’ – 10’ SW Suitable SDG 80-1 2.715 95.726 1.559 0.148 0’ – 9.5’ SP Suitable

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FIGURE 29: Isopach Chart Showing Thickness of Suitable Surficial Sand Layer in Site SO-5.

3.7 Site SO-4

Site SO-4 is located directly offshore of Los Penasquitos Lagoon in 40' to 90' of water. This site is the southern-most sand borrow area within the Oceanside Littoral Cell. Site SO-4 measures 2,500' x 4,000' and covers 10 million square feet (230 acres). The available historical data includes only one vibracore sample collected in the vicinity of SO-4, which found fine-grained sand that was marginally-suitable for beach nourishment (Osbourne et al., 1983).

A marine geophysical survey was conducted in Site SO-4 during January 1999, with north-south lines run at nominal 500' intervals and east-west survey lines at nominal 1,000' intervals (Appendix A). The side-scan records show Site SO-4 to be very uniform, with fine-grained surficial sediments (Figure 30). The seismic reflection data identified a well-developed sediment prism measuring approximately 10' in thickness along the eastern (nearshore) boundary that increases uniformly in thickness to approximately 30' along the western (offshore) boundary of SO-4 (Figure 31).

After preliminary review of the geophysical survey data, ten (10) vibracore sample locations were selected that coincided with the intersection of the north-south and east-west survey lines (Appendix A). The vibracore collected sediment samples of 4'-8' length; however, none of the vibracore samples were long enough to confirm the stratigraphic boundaries observed by the FIGURE 30: Seafloor Features Map of Site SO-4.

Page 47 seismic reflection data. In general, the vibracore logs indicate a single homogeneous layer of olive-gray, very fine-grained silty sand throughout the entire area.

The results of the grain-size analyses (Table 9) show that the majority of Site SO-4 contains silty, very fine-grained sand that is unsuitable for beach nourishment. However, a 50-acre area along the nearshore boundary contains surficial sediment that is suitable for beach nourishment (Figure 32). Within this nearshore area, vibracore samples SDG-84 and SDG-88 contained approximately 6' of suitable very fine-grained sand and SDG-90 contained marginally-suitable material.

The estimated volume of suitable beach nourishment sand within the 50-acre area of Site SO-4 is 1.5 million cubic yards. Required excavation would range from 10 to 20 feet below the seafloor. If the limited amount of material found within the small area along the eastern (nearshore) boundary of Site SO-4 is insufficient for beach nourishment, it is recommended that an alternate borrow site be identified by an exploratory geophysical survey within the 40'-80' depth contours along a broad reach of coastline.

FIGURE 31: Typical Cross-Sectional Profile of Subbottom Features in Site SO-4.

TABLE 9: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SO-4.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 81-1 0.041 77.762 22.196 0.093 0’ – 4.3’ SM Unsuitable SDG 82-1 0.052 76.876 23.073 0.093 0’ – 3’ SM Unsuitable SDG 82-2 1.386 84.869 13.745 0.114 3’ – 5.7’ SP Marginal SDG 83-1 0.000 75.597 24.403 0.091 0’ – 3’ SM Unsuitable SDG 83-2 0.219 82.270 17.512 0.097 3’ – 5.5’ SM Unsuitable SDG 84-1 0.100 95.240 4.660 0.121 0’ – 6.8’ SP Suitable SDG 85-1 0.000 77.591 22.409 0.092 0’ – 6.1’ SM Unsuitable SDG 86-1 0.048 78.490 21.463 0.093 0’ – 6.0’ SM Unsuitable SDG 87-1 0.270 85.907 13.823 0.096 0’ – 7.8’ SP Marginal SDG 88-1 1.599 89.397 9.004 0.105 0’ – 7’ SP Suitable SDG 89-1 0.051 81.440 18.508 0.094 0’ – 5.5’ SM Unsuitable SDG 90-1 0.200 89.648 10.152 0.096 0’ – 7.4’ SP Marginal Page 48

FIGURE 32: Isopach Chart Showing Thickness of Suitable Surficial Sand in Site SO-4.

3.8 Site MB-1

Site MB-1 is located offshore of Mission Beach and north of the San Diego River in 60' to 110' of water. The site measures 4,000' x 4,500' and covers 18 million square feet (413 acres). Site MB- 1 is the only proposed offshore borrowsite that is located within the Mission Beach Littoral Cell. Approximately 40% of Site MB-1 is deeper than the 80' depth contour. Historical data available near Site MB-1 include studies conducted for construction of the NOSC Tower (US Navy, 1965) and the proposed San Diego Clean Water ocean outfall (Kinnetic Laboratories, 1992). Both of these studies primarily identified the seafloor features and the presence/absence of archaeological sites, rather than the sediment type available in this area. However, the historical data contains 3 vibracore samples collected offshore of Mission Beach. One vibracore sample was identified as marginally-suitable fine-grained sand and the other two vibracore samples were identified as suitable medium-grained sand (Osbourne et al., 1983).

A marine geophysical survey was conducted in Site MB-1 during January 1999 along tracklines spaced at nominal 500' intervals in a north-south direction and nominal 1,000' intervals in an east- west direction (Appendix A). The side-scan sonar records from this survey show low-amplitude, short-wavelength sand waves characteristic of medium- to coarse-grained sand over most of the site (Figure 33). The side-scan records indicate that the northeast corner of the site has fine- grained surficial material, and a large pile of debris (reported to be the collapsed NOSC Tower) FIGURE 33: Seafloor Features Map of Site MB-1. Page 50 rests on the seafloor near the southeast corner of the site. The marine magnetometer recorded high magnetic anomalies associated with this debris field. The seismic reflection data shows a very uniform upper layer of sediment ranging in thickness from 15'-60' with occasional discontinuous, low-amplitude reflectors (Figure 34).

FIGURE 34: Typical Cross-Sectional Profile of Subbottom Features in Site MB-1.

After a preliminary review of the geophysical survey results, ten (10) vibracore locations were selected that coincided with the intersection of the north-south and east-west survey lines (Appendix A). Vibracore penetration within Site MB-1 ranged between 9' to over 19'. None of the vibracore samples were long enough to confirm the stratigraphic boundaries seen in the seismic reflection data.

The results from the grain size analyses (Table 10) show that the majority of Site MB-1 contains fine- to coarse-grained sand that is suitable for beach nourishment. The only exception was found in the northeast corner of the site, where a 2' layer of silty fine-grained sand overlies suitable beach sand. The suitable beach sand at Site MB-1 has a unique color that has been described as "golden" or "red-yellow-brown".

With the exception of a 2' layer of silty material found at the northeast corner, Site MB-1 contains a very thick layer of medium to coarse-grained sand covering the entire area and varying in thickness from 15' to approximately 60' (Figure 35). The volume of suitable beach nourishment sand within Site MB-1, excluding the two foot layer of silt in the northeast corner of the site, is estimated to be 26 million cubic yards.

MB-1 is an excellent borrow site for uniquely-colored beach sand. Of the 10 proposed borrow areas surveyed between Oceanside and the Mexican Border, Site MB-1 contains the largest overall volume of suitable sand. However, since approximately 40% of Site MB-1 is located in water depths greater than 80', a significant reduction in the amount of available beach replenishment sand can be expected if dredging is restricted to water depths less than 80'. Furthermore, to produce the estimated 26 million cubic yards of suitable sand, dredge excavations of up to 65 feet below the seafloor are required. An additional geophysical survey may be required if Site MB-1 is moved towards shore to bring the entire site within the 40'-80' depth contour.

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FIGURE 35: Isopach Chart Showing Thickness of Suitable Surficial Sand in Site MB-1.

TABLE 10: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site MB-1.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 91-1 0.000 67.634 32.366 0.090 0’ – 2.5’ SM Unsuitable SDG 91-2 0.612 99.201 0.187 0.572 2.5’ – 7’ SP Suitable SDG 91-3 0.000 99.294 0.706 0.298 7’ – 15.5’ SW Suitable SDG 92-1 0.073 99.808 0.119 0.495 0’ – 5.5’ SW Suitable SDG 92-2 0.000 99.821 0.179 0.482 5.5’ – 16’ SW Suitable SDG 92-3 2.415 96.576 1.009 0.572 16’ – 19.3’ SW Suitable SDG 93-1 1.783 97.616 0.601 0.581 0’ – 7’ SP Suitable SDG 93-2 0.334 99.323 0.343 0.625 7’ – 12.5’ SP Suitable SDG 94-1 0.549 99.301 0.150 0.573 0’ – 7’ SP Suitable SDG 94-2 0.000 99.575 0.425 0.585 7’ – 14.5’ SP Suitable SDG 95-1 0.860 98.981 0.159 0.614 0’ – 6.5’ SP Suitable SDG 95-2 1.940 97.961 0.100 0.635 6.5’ – 13.5’ SP Suitable SDG 96-1 0.284 99.611 0.105 0.593 0’ – 6.5’ SW Suitable SDG 96-2 0.000 99.909 0.091 0.445 6.5’ – 14.7’ SP Suitable SDG 97-1 1.909 97.924 0.167 0.736 0’ – 9’ SP Suitable SDG 97-2 0.043 99.595 0.362 0.356 9’ – 11.5’ SP Suitable SDG 98-1 0.123 99.784 0.093 0.474 0’ – 9.4’ SP Suitable SDG 99-1 3.096 96.377 0.527 0.512 0’ – 13.5’ SW Suitable SDG 100-1 1.575 97.706 0.719 0.405 0’ – 5.5’ SP Suitable SDG 100-2 0.000 99.399 0.601 0.503 5.5’ – 14’ SP Suitable Page 52

3.9 Site SS-2

Site SS-2 is located offshore of Imperial Beach, approximately 4.5 miles north of the US-Mexico Border. The site measures 3,000' x 7,000' and covers 21 million square feet (482 acres). This site is located within the Silver Strand Littoral Cell. Historical data available for the region surrounding Site SS-2 includes 50 vibracores and surficial sediment samples that found silty-sand or sandy-silt as the predominant sediment just inshore of Site SS-2 (USACE, 1998). An earlier study found mostly marginally-suitable fine-grained material and occasional areas of suitable material in this region (Osbourne, et al., 1983)

A geophysical survey of Site SS-2 was conducted in January 1999 along tracklines spaced at nominal 500' intervals in a north-south direction and nominal 1,000' intervals in an east-west direction (Appendix A). Site SS-2 has a nearly flat bottom, with depths ranging between 50 to 60 feet deep. The side scan sonar records showed a flat, uniform seafloor except for coarse grained sediment or exposed bedrock in the southeast corner of the site. The majority of the site appeared in the side-scan records to be covered with fine- to medium-grained sediment (Figure 36). The seismic reflection records show an upper layer that is 2'-15' thick underlain by an angular unconformity. Erosional channels or basins eroded into the bedrock surface can be seen on the seismic records towards the north end of the site (Figure 37). The seismic data suggests that the bedrock strata is dipping to the east.

FIGURE 37: Typical Cross-Sectional Profile of Subbottom Features in Site SS-2

After reviewing the geophysical data, ten (10) vibracore locations were selected at the intersection of the north-south and east-west geophysical survey lines (Appendix A). The length of sediment core recovered from these 10 vibracores ranged from 7.5'-16.5'. The core logs indicate that the central and northern portions of the site contain 7' to 16' of moderately well-sorted, very fine- to fine-grained gray sand. The southwest corner contains 5' to 8' of very fine dark-gray sand over very coarse sand to very coarse/pebbly brown sand. A lens of pebbles was also observed in 2 of the vibracores collected near the southern portion of Site SS-2. In general, the vibracore logs show a 2'-8' layer of fine-grained silty sand that overlies a layer of medium-grained sand within the central region of SS-2. The results of the grain-size analyses (Table 11) indicate that 7 out of the 10 vibracores contained some suitable beach replenishment material. In all cases the suitable material was found under 3.5'-8' of unsuitable silty sand. FIGURE 36: Seafloor Features Map of Site SS-2.

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Based upon the interpreted seismic reflection records and the vibracore logs, a layer of 4'-11' of suitable beach replenishment sand is located in the central region of Site SS-2, but this layer of suitable sand is covered by up to 12' of unsuitable silty sand. The suitable sand layer thins to 4' towards the west and uniformly increases in thickness towards the eastern (nearshore) boundary of the site (Figure 38). The layer of suitable sand may extend closer to shore beyond the eastern boundary of the site, but additional surveying will be required to document the nearshore extent of the sand layer. The surficial layer of overlying silt is thickest in the middle of the site, and thins out radially to 4' in thickness towards the site boundaries (Figure 39).

The estimated volume of suitable beach replenishment material in Site SS-2 is 0.7 million cubic yards. An estimated 1.0 million cubic yards of unsuitable material overlies the suitable material within the site. Vibracores taken near the northern and western boundaries of the site did not contain any suitable beach sand, and these areas were excluded from the volume computations. The southeast corner of the site was also excluded from the volume computations because the geophysical survey data suggests that this area is bedrock.

Since the amount of suitable sand in Site SS-2 is less than the unsuitable material overlying it, dredging costs may be prohibitive at this site. It is recommended that additional geophysical lines be surveyed inshore of the present site in order to document the eastward extent of the buried layer of suitable beach sand.

TABLE 11: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SS-2.

SAMPLE PER CENT D 50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 101-1 6.439 69.093 24.468 0.130 0’ – 5.7’ SM Unsuitable SDG 101-2 0.000 74.543 25.457 0.143 5.7’ – 7.5’ SM Unsuitable SDG 102-1 1.110 62.738 36.152 0.085 0’ – 6’ SM Unsuitable SDG 102-2 0.012 99.145 0.842 0.176 6’ – 9’ SW Suitable SDG 103-1 0.000 98.846 1.154 0.214 0’ – 10.6’ SP Suitable SDG 104-1 0.000 98.127 1.873 0.148 0’ – 15.8’ SW Suitable SDG 105-1 0.406 72.716 26.878 0.140 0’ – 7.5’ SM Unsuitable SDG 105-2 0.000 99.669 0.331 0.245 7.5’ – 12’ SP Suitable SDG 106-1 34.871 62.803 2.326 0’ – 5.5’ SP Unsuitable SDG 106-2 1.753 64.800 33.447 0.091 5.5’ – 10’ SM Unsuitable SDG 106-3 15.329 83.175 1.496 0.579 10’ – 16.5’ SP Marginal SDG 107-1 15.285 72.933 11.782 0.379 0’ – 3.5’ SP Unsuitable SDG 107-2 0.000 99.438 0.562 0.176 3.5’ – 11’ SP Suitable SDG 108-1 0.212 60.226 39.562 0.086 0’ – 8.6’ SM Unsuitable SDG 109-1 0.000 69.268 30.732 0.089 0’ – 7.5’ SM Unsuitable SDG 109-2 2.007 95.601 2.392 0.543 7.5’ – 11.5’ SP Suitable SDG 110-1 0.223 79.609 20.168 0.107 0’ – 5’ SM Unsuitable SDG 110-2 5.945 91.089 2.967 0.607 5’ – 10.3’ SP Suitable

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FIGURE 38: Isopach Chart Showing FIGURE 39: Isopach Chart Showing Thickness of Suitable Sand Layer in Site SS-2. Thickness of Silt Overburden In Site SS-2. Page 56

FIGURE 39A: Isopach Chart Showing Thickness of Suitable Sand Layer (hatched) and Thickness of Silt Overburden (contours) in Site SS-2.

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3.10 Site SS-1

Site SS-1 is located offshore of Imperial Beach near the Mexican Border in 40' to 70' of water. The site measures 5,000' x 5,500' and covers 27.5 million square feet (631 acres). Site SS-1 is located within the Silver Strand Littoral Cell. The area surrounding Site SS-1 has been extensively studied in the past. Fifty vibracores that collected just inshore of Site SS-1 found silty sand as the predominant sediment type (USACE, 1998). An earlier vibracore study found mostly marginally-suitable fine-grained material and occasional areas of suitable material near Site SS-1 (Osbourne, 1983). Valuable information is also available from a geophysical and vibracoring survey conducted near Site SS-1 for the South Bay Tunnel Outfall Project (Woodward-Clyde, 1994).

Per SANDAG's specifications, no marine geophysical surveys were conducted in Site SS-1. Fifteen vibracore samples were located in an evenly-spaced pattern to maximize the area of data collection (Figure 40). The vibracorer recovered sediment cores of 6.5’-17.1’ length within the site, and all core samples contained some suitable beach replenishment material (Table 12). The sand identified as suitable for beach replenishment is medium- to coarse-grained and brownish- gray to light-gray in color. This beach-quality sand is exposed on the seafloor in the northeast corner of Site SS-1 and in an area extending from the center of the site to the southeast corner; however, most of the suitable beach replenishment sand within the site is buried under a 2'-6' layer of silty sand that is not suitable for beach replenishment (Figure 41).

Due to the lack of shallow geophysical survey data, the volume of available beach sand was calculated using only the vibracore logs, and the results were extrapolated to the boundaries of the site. Figure 42 is an isopach map showing the thickness of the silt overburden and Figure 43 is an isopach map showing the thickness of the underlying suitable beach sand. It is estimated that at least 7.6 million cubic yards of suitable sand is available within Site SS-1, and the total may be considerably higher if the layer of suitable material extends deeper that the vibracores penetrated. The estimated volume of suitable sand would require excavations ranging from 5 to 22 feet below the seafloor.

Most of the suitable beach replenishment material available at Site SS-1 is covered by 2'-6' of silty sand that is not suitable for beach replenishment. Approximately 3.4 million cubic yards of this silty sand must be removed from the site prior to dredging the beach-quality material below.

FIGURE 41: Typical Cross-Sectional Profile of Subbottom Features in Site SS-1.

FIGURE 40: Seafloor Features Map of Site SS-1.

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TABLE 12: Results from Grain-Size Analyses (percent gravel/sand/silt-clay) for Site SS-1.

SAMPLE PER CENT D50 CORE SOIL ID NO. GRAVEL SAND SILT/CLAY (mm) SEGMENT CLASSIFICATION SDG 111-1 0.210 57.166 42.625 0.096 0’ – 5’ SM Unsuitable SDG 111-2 0.037 97.452 2.511 0.192 5’ – 13.8’ SW Suitable SDG 112-1 0.000 99.430 0.570 0.283 0’ – 6.5’ SP Suitable SDG 113-1 4.097 74.305 21.598 0.197 0’ – 3.8’ SM Unsuitable SDG 113-2 0.000 98.669 1.331 0.335 3.8’ – 7.2’ SP Suitable SDG 114-1 0.134 71.232 28.634 0.109 0’ – 5’ SM Unsuitable SDG 114-2 0.040 99.194 0.766 0.340 5’ – 14.5’ SP Suitable SDG 115-1 0.090 82.235 17.675 0.144 0’ – 5’ SM Unsuitable SDG 115-2 0.000 96.222 3.778 0.226 5’ – 8’ SP Suitable SDG 115-3 0.000 99.063 0.937 0.282 8’ – 17.1’ SP Suitable SDG 116-1 0.000 98.457 1.543 0.266 0’ – 4’ SW Suitable SDG 117-1 0.105 96.465 3.430 0.206 0’ – 6’ SP Suitable SDG 117-2 2.192 94.543 3.265 0.371 6’ – 6.6’ SP Suitable SDG 118-1 0.000 79.459 20.541 0.129 0’ – 5’ SM Unsuitable SDG 118-2 0.118 97.704 2.177 0.311 5’ – 11’ SP Suitable SDG 118-3 1.018 96.927 2.055 0.322 11’ – 14.7’ SP Suitable SDG 119-1 0.855 64.650 34.495 0.095 0’ – 4.5’ SM Unsuitable SDG 119-2 0.000 98.458 1.542 0.250 4.5’ – 6’ SP Suitable SDG 119-3 0.000 50.530 49.470 0.084 6’ – 11.5’ SM Unsuitable SDG 120-1 0.000 90.261 9.739 0.159 0’ – 6’ SP Suitable SDG 120-2 0.000 36.802 63.198 6’ – 12’ ML Unsuitable SDG 121-1 0.000 99.269 0.731 0.293 0’ – 8’ SP Suitable SDG 122-1 0.000 79.000 21.000 0.118 0’ – 5’ SM Unsuitable SDG 122-2 0.013 97.594 2.393 0.236 5’ – 16.8’ SP Suitable SDG 123-1 0.687 96.558 2.755 0.268 0’ – 3.5’ SP Suitable SDG 123-2 0.000 98.148 1.852 0.195 3.5’ – 6.8’ SP Suitable SDG 124-1 2.472 84.946 12.582 0.177 0’ – 4’ SP Marginal SDG 124-2 0.143 98.487 1.371 0.278 4’ – 7.5’ SP Suitable SDG 124-3 0.303 97.377 2.320 0.276 7.5’ – 12.7’ SP Suitable SDG 125-1 0.260 63.160 36.580 0.092 0’ – 4’ SM Unsuitable SDG 125-2 0.000 96.649 3.351 0.155 4’ – 6.5’ SW Suitable SDG 125-3 0.000 95.494 4.506 0.248 6.5’ – 10.7’ SW Suitable

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FIGURE 42: Isopach Chart Showing Thickness of Silt Overburden in Site SS-1.

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FIGURE 43: Isopach Chart Showing Thickness of Suitable Sand Layer in Site SS-1.

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FIGURE 43A: Isopach Chart Showing Thickness of Suitable Sand Layer (hatched) and Thickness of Silt Overburden (contours) in Site SS-1.

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SECTION 4

BIBLIOGRAPHY

CFR. 1994. Guidelines Establishing Test Procedures for the Analysis of Pollutants. Title 40, Part 136, Appendix B. Office of the Federal Register, national Archives and Records Administration, U.S. Government Printing Office, Washington, D.C.

Fischer, P.J., P.A. Kreutzer, L.R. Morrison, J.H. Rudat, E.J. Ticken, J.F. Webb, and M.W. Woods, 1983. Study of Quaternary Shelf Deposits (Sand and Gravel) of Southern California. Prepared for State of California, Department of Boating and Waterways, Sacramento, CA.

Kinnetic Laboratories. 1992. San Diego River Offshore Geophysical, ROV, and Archaeological Survey. KLI-R-92-8. Santa Cruz, CA.

Long, E.R., D.D. MacDonald, S.L. Smith, and F.D. Calder. 1995. Incidence of Adverse Biological Effects Within Ranges of Chemical Concentrations in Marine and Estuarine Sediments. Environmental Management 19:81-97.

McDonald, D.G., R.S. Carr, F.D. Calder, E.R. Long, C.G. Ingersoll. 1996. Development and Evaluation of Sediment Quality Guidelines for Florida Coastal Waters. Ecotoxicology, 5:253- 278.

Moffatt & Nichol Engineers, 1999. Personal Communication with Mr. Chris Webb. Long Beach, CA.

Ogden Environment and Energy, Inc. 1995. Sediment Characterization Report for Nimitz Class Aircraft Carrier Homeporting Facilities, Naval Station North Island California, Volume 1- Sediment Analysis Results. U.S. Department of Navy, Naval Air Station, North Island, California.

Osbourne, R.H., N.J. Darigo, and R.C. Scheidemann, Jr., 1983. Report of Potential Offshore Sand and Gravel Resources of the Inner Continental Shelf of Southern California. Prepared for the State of California, Department of Boating and Waterways, Sacramento, CA.

Plumb, R.H., Jr. 1981. Procedures for Handling and Chemical Analysis of Sediment and Water Samples. Tech. Rep. EPA/CE-81-1, prepared by Great Lakes Laboratory, State University College at Buffalo, Buffalo, NY for the USEPA/Corps of Engineers Technical Committee on Criteria for Dredged and Fill Material. Published by U.S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss. 450pp.

SANDAG. 1998. Regional Beach Monitoring Program, Fall Survey. Prepared for San Diego Association of Governments. Prepared by Coastal Frontiers Corporation, Chatsworth, CA.

U.S. Army Corps of Engineers. 1993. Final Report, Beach Nourishment Sources Along the Carlsbad/Oceanside Coast in Sand Diego County, California. Los Angeles District, CA. Page 64

U.S. Army Corps of Engineers, 1994. Hydrographic Surveying Manual. Engineering and Design Manual No. EM-1110-2-1003. Washington, D.C.

U.S. Army Corps of Engineers. 1998. Vibratory Coring and Surficial Sediment Sampling Near Imperial Beach, California and Vicinity. Field Activities Report. Los Angles District, CA.

U.S. Environmental Protection Agency. 1986 and updates. Test Methods for Evaluating Solid Waste. SW-846, 3rd Edition. Office of Solid Wast and Emergency Response, Washington, D.C.

U.S. Environmental Protection Agency/U.S. Army Corps of Engineers. 1991. Evaluation of Dredged Material Proposed for Ocean Disposal - Testing Manual. EPA-503/8-91/001. February 1991. USEPA, Office of Water/Department of the Army, USACE.

U.S. Navy. 1965. Research and Development Report on the U.S. Navy Electronics Laboratory's Oceanographic Research Tower. NEL Report #1342. Pacific Support Group, U.S. Naval Oceanographic Group, San Diego, CA.

Woodward-Clyde Consultants, 1994. South Bay Tunnel Outfall, Phase 1 - Marine Geophysical Data Report. San Diego, CA.

Woodward-Gizienski and Associates, 1974. Soil Investigation of the Encina Power Plant Offshore Pipeline. Prepared for Bechtel Power Corporation, Norwalk, CA.

APPENDICES

APPENDIX A: Survey Trackline Charts

APPENDIX B: Sediment Chemistry and Grain Size Results

APPENDIX C: Sediment Grain Size Distribution Curve

APPENDIX D: Vibracore Logs

APPENDIX E: Photographs of Vibracore Samples