THE METHODOLGY• An Acoustic Corer (AC) was used to survey the sub-seabed at the proposed wind turbine locations.• The campaign was mobilized from the Josephine K Miller (Miller’s Launch) with ROV/Survey supportfrom Meridian Ocean Services.• The AC generates a 12m diameter “acoustic core” to full penetration depth (inset above).• The “acoustic core” is a 3D acoustic intensity image of the sub-seabed. Boulders appear as discretehigh intensity acoustic reflectors and stratigraphy as high intensity layers.• Visualization software was used to manipulate the volumetric data and to section data in X, Y and Zplanes in order that geoscientists interpreted the data offshore to identify boulders ≥0.38m diameter• Boulder size and X-Y-Z position were reported in an Acoustic Anomaly Map and location comparedto the planned pile location.• A total of 20 surveys, representing each pile location, were carried out. The resulting sub-seabedboulder map was then used to micro site the four legged jacket to avoid encountering boulders.• A statistical analysis of the boulders identified was to be carried out.

DE-RISKING INSTALLATION OF OFFSHORE WIND TURBINE FOUNDATIONS IN COMPLEX GEOLOGY AT THE BLOCK ISLAND WIND FARM

USING AN ACOUSTIC CORERMoya Cahill, P.Eng – President, PanGeo Subsea

Water surface

Seabed

Pile A1 (West)

Pile A2 (South)

Pile B2 (East)

12m diam. acoustic cores over each pile

Wind Turbine Located on 4 Legged Jacket

PROJECT BACKGROUND• Block Island Wind Farm (BIWF) – 5 wind turbines located on 4legged jackets using 1.524m diam. pile foundations• Complex geology – sub-seabed comprising Till and containinghigh concentration of boulders at the seafloor• The campaign was carried out between May and June, 2015.THE RISK• Risk of pile foundation refusal if pile encounters buried boulders≥0.38m diameter.THE OBJECTIVE• Survey each of the proposed pile locations using PanGeoSubsea’s Acoustic Corer to identify sub-surface boulders withdiameters ≥0.38m, at the proposed pile installation locations andthereby de-risk the piling operation by allowing the micro-sittingof piles by Deepwater Winds piling contractor Weeks Marine.

Five wind turbines

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Relative Acoustic Intensity

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BLOCK ISLAND WIND TURBINE• Five wind turbines on 4 legged jackets were to be erected on 1.524m diameter piles in water ranging from 19m-24m

Isolated boulder (0.4m diam. at 1.25m depth)

Boulder,(0.5m diam. at 15.8m depth) in a cobble cluster

Isolated boulder/debris (0.55m diam. at 1.6m depth) Boulder cluster at 5.3m depth)

SUB-BOTTOM SYNTHETIC APERTURE DATA PROVIDES ANOMALY IMAGES• HF chirp sonar acquires 20,000 data points used in synthetic aperture rendering• Acoustic anomalies suggestive of boulders ≥0.38m diam. were identified and reported • Anomaly X-Y-Z position, size, shape and interpretation reported

EVALUATING BOULDER LOCATION AND RISK TO PILE PLACEMENT• It was necessary to deliver an onboard Preliminary Site Report within 24 hours of whether any of the boulders identified with the AC wouldpose a risk to the proposed pile• Boulder positions were plotted on three graphs as shown below and superposed on the planned pile location. The graphs were: Eastingversus Depth section, Northing versus Depth section, and Plan View Easting-Northing section.• By comparing the position of the boulder with the position of the pile at a given depth it was possible to access the risk.• In this particular data set, the analysis shown below indicates that an anomaly, suggestive of a 0.8m diam. boulder located at 14.95m belowseafloor, was positioned within the proposed path of the pile.• The Preliminary Site Report was issued to the onboard Deepwater Wind representative with a PanGeo recommendation to relocate the pile.• Using the boulder positioning information for all 4 jacket legs, Deepwater Wind, in consultation with Weeks Marine (installation contractor),decided to move the jacket position, mirco-siting the pile positions to avoid the boulders.

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Acoustic core perimeter

Planned pile location

0.8m diam. boulder coincident with the pile at 14.95m

Planned pile location

Planned pile location

BoulderPositions

BoulderPositions

Acoustic core limit

Acoustic core limit

RESULTS OF THE ACOUSTIC CORER SURVEY AT BLOCK ISLAND WIND FARM• PanGeo Subsea carried out 20 Acoustic Corer™ surveys at the Block Island Wind Farm (BIWF) , providing sub-seabed information to assist in thede-risking of 5 wind turbine generators installed on 4 legged jackets using pile foundation.• Safety was of overriding importance during the campaign. There were zero “lost time instances” during the campaign.• A Preliminary Site Report for each survey site was issued onboard the vessel within 24 hours. It included: a site summary, AC required andlanded position, velocity profile analysis, stratigraphy interpretation, X-Y-Z position, size, and shape of each of the identified anomalies meetingthe ≥0.38m criteria. All of the anomaly attributes together with the geological setting were considered when providing an interpretation of theanomaly.• The results were reported in various formats including acoustic images, anomaly tables, and anomaly plots.• A total of 88 anomalies meeting the ≥0.38m diameter criteria were identified at BIWF. The breakdown was as follows:33 anomalies at Jacket 1; 14 anomalies at Jacket 2; 12 anomalies at Jacket 3; 14 anomalies at Jacket 4; and 15 anomalies at Jacket 5.

• Of the 88 anomalies, 68 were suggestive of discrete boulders, 6 were suggestive of boulder clusters, 7 were suggestive of a cluster of combinedcobbles and boulders, and 7 anomalies were suggestive of cobble clusters.• At the end of the campaign it was determined that some 80% of anomaly interpretations were made with high confidence. Over 94% of theinterpretations were made with a high or moderate degree of confidence.CONCLUDING REMARKS• The Acoustic Corer survey was considered a success from the perspective of Deepwater Wind. The survey identified buried geohazards andallowed Deepwater Wind to reposition their pile foundations thereby de-risking the installation .• All jackets were installed without pile refusal.• All figures extracted from PanGeo Subsea Report RPT-04777-1 McDermott, I.R, Laidley, R., Guigne, J.Y., 2015, “Final Interpretive Report,Acoustic Corer™ Survey to Identify Buried Boulders and Other Geohazards at Block Island Wind Farm” for Deepwater Wind Block Island, LLC.

STATISTICAL ANALYSIS OF THE SURVEY RESULTS • Total of 88 anomalies meeting the ≥0.38m diameter criteria were identified• The breakdown was as follows: 33 anomalies at Jacket 1; 14 anomalies at Jacket 2;12 anomalies at Jacket 3; 14 anomalies at Jacket 4; and 15 anomalies at Jacket 5.• Of these 88 anomalies, 68 were suggestive of discrete boulders, 6 were suggestiveof boulder clusters, 7 were suggestive of a cluster of combined cobbles andboulders, and 7 anomalies were suggestive of cobble clusters.• Just over 86% of anomalies were less than 1.0m effective diameter.• Anomalies in excess of 1m effective diameter were a result of clusters of bouldersand cobbles.• The largest discrete anomaly imaged was suggestive of a 0.9m diameter boulderlocated at the 1-1-B2 pile location.

Discrete Boulder Size DistributionPercentage of anomalies by effective diameter

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MULTIFOLD TRACE DATA PROVIDES VELOCITY PROFILE AND STRATIGRAPHY • Multifold trace data is acquired using the LF chirp. Used to produce near surface velocity profile and stratigraphy• Velocity profile is used to depth convert the synthetic aperture (SAS) data to provide accurate burial depth of boulders• Acoustic stratigraphy ground truthed with previously acquired borehole data• Combined interpretation of the acoustic stratigraphy and boulder data, obtained from the SAS data, indicated that there were 2 boulderregions:1) The First Boulder Region is associated with the uppermost geological unit 1, which was described as a medium dense sand with gravel and

cobbles in borehole data. Every acoustic core contained anomalies suggestive of cobbles and/or boulders within this uppermost geologicalunit. There was evidence of numerous boulders and cobbles exposed at the seafloor.

2) The Second Boulder Region is associated with the boundary between geological units 4 and 5, consisting of stiff silty clay over dense tovery dense sand. The layer is characterized by a concentration of anomalies ≥0.38m diameter in the HF SAS acoustic cores and as reflector“C” in the profiles. This “second boulder layer” is found between 14m to 18m in the AC data for Jackets 1 and 4. Despite previous sub-bottom profiling and several boreholes in the area, this deeper boulder layer had not been detected by previous site investigations.

Anomaly

Boulder layer associated with boundary Cbetween geological units 4 and 5

Near surface boulder layer 1

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AC Stacked Trace Data Cross-Section

As referenced above, a cross-section from HF SAS rendershowing a complex sub-seabedcomprising:

(a) a “dense moraine” that dipsbetween 7-8m and

(b) a deeper reflector suggestiveof a surface comprising relict bedforms that dips between 9-13m

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Cross-Section of the SAS Data Set

• See also the cross section created in one of the SAS data sets below.

SUB-BOTTOM SYNTHETIC APERTURE DATA PROVIDES STRATIGRAPHY

Acoustic Anomaly Maps

Wind Turbine Site 1