VILLAGE HARBOR, MICHIGAN SEDIMENT REMOVAL AND RESIDUALS COVER PROJECT SUMMARY

Eric J. Hritsuk PE1, Michael J. Erickson PE2, Daniel O’Neill3, Matthew Bowman4, and Stephen D. Garbaciak Jr. PE5

ABSTRACT

Village Harbor is a constructed surface water feature connected to Little Traverse Bay of Lake Michigan. The Harbor is a portion of the Little Traverse Bay Cement Kiln Dust (LTB CKD) Release Site, located along the shoreline of Little Traverse Bay. Between October 2008 and May 2009, ARCADIS completed a series of construction activities designed to mitigate elevated pH levels (greater than 9.0 standard units) in near-bottom surface water in two distinct areas of Village Harbor – the southwest corner and the Sump Area. Prior to construction, water depths in the Harbor generally ranged from 3.05 to 3.7 meters (10 to 12 feet), but extended to more than 6.1 meters (20 feet) in the Sump Area – a deep trough feature located in the central portion of the Harbor. Sediment borings performed in the southwest corner and Sump Area yielded observations of a reactive material. To address this situation, in the southwest corner ARCADIS removed sediment and installed a residuals cover, while in the Sump Area, a residuals cover was installed to raise the bottom elevation to be more uniform with other areas of Village Harbor and eliminate the trough feature. Both residuals covers incorporated a low-permeability geotextile clay liner (GCL) to isolate any remaining reactive material from the surface water. This report details the excavation of material in the southwest corner and construction of residuals covers in the southwest corner and Sump Area.

Keywords: GCL, Village Harbor, SAP, pH, settlement monitoring

INTRODUCTION

Village Harbor (the Harbor), refers to the water body located immediately west of Resort Township’s East Park and immediately east of the Bay Harbor commercial district. The Harbor is a constructed surface water feature connected to Little Traverse Bay of Lake Michigan, and is a portion of the Little Traverse Bay Cement Kiln Dust (LTB CKD) Release Site. The LTB CKD Release Site, which encompasses 5 miles of shoreline on Little Traverse Bay, is approximately 8 kilometers (5 miles) west of the City of Petoskey, and located in Resort Township, Emmet County, Michigan (Township 34N, Range 6W, Sections 2 through 10).

The Harbor is approximately 365.9 meters (1,200 feet) long and 45.7-61.0 meters (150-200 feet) wide. It is elongated in the east-west direction, and a western arm extends in the north-south direction. Maximum water depths along transects spanning the Harbor ranged from 3.7 to more than 6.1 meters (12 to more than 20 feet). The deepest part of the Harbor (the Sump Area) is in the central (east-west oriented) portion. A representative view of the Harbor is shown in Figure 1.

1 Project Civil Engineer, ARCADIS, 30 West Monroe Street, Suite 1710, Chicago, IL 60603, P: 312.332.4937, F: 312.332.4434, eric.hritsuk@arcadis-us.com

2 Vice President, ARCADIS, 10559 Citation Drive, Suite 100, Brighton, MI 48116, P: 810-229-8594, F: 810.229.8837, michael.erickson@arcadis-us.com

3 Vice President, ARCADIS, 10559 Citation Drive, Suite 100, Brighton, MI 48116, P: 810-229-8594, F: 810.229.8837, daniel.o’neill@arcadis-us.com

4 Principal Environmental Engineer, ARCADIS, 251 East Ohio Street, Suite 800, Indianapolis, IN 46204, P: 317-231-6500, F: 317-231.6514, matthew.bowman@arcadis-us.com

5 Vice President, ARCADIS, 30 West Monroe Street, Suite 1710, Chicago, IL 60603, P: 312.332.4937, F: 312.332.4434, steve.garbaciak@arcadis-us.com

242

Figure 1. Site layout.

Prior to construction, elevated pH levels (greater than 9.0 standard units [s.u.]) were observed in a limited area of near-bottom surface water in the southwest corner of the Harbor, as shown in Figure 2. Borings advanced in the southwest corner area yielded observations of reactive material. The uppermost sediment in the southwest corner appeared to be a layer of secondary precipitate/reactive material on top of a layer of cobble-size limestone material.

Figure 2. Pre-construction Site conditions.

The Sump Area is a depression that extends deeper than the typical bottom elevation of Village Harbor. The functional definition of the Sump Area is the portion of Village Harbor where the bottom elevation is 171.3 meters (562 feet) North American Vertical Datum 1988 (ft NAVD88) or lower. Based on this definition, the Sump Area encompasses an area of approximately 2,603 square meters (28,000 square feet), as determined from bathymetric data. This elevation range in Village Harbor is generally associated with an area of sediments and overlying surface water with elevated pH readings (greater than 9.0 s.u.), as shown in Figure 2.

Work was completed pursuant to the requirements of the Administrative Order on Consent for Removal Action (AOC or Order) for the LTB CKD Site (U.S. Environmental Protection Agency [USEPA] 2005). The proposed remedy for the southwest corner was described in the Removal Action Work Plan (ARCADIS 2008a), and completion of the work was described in the Removal Action Completion Report (ARCADIS 2009a). The proposed remedy for the Sump Area was described in the Work Plan Under Removal Action AOC (ARCADIS 2008b), and completion of the work was described in the Residuals Cover Completion Report (ARCADIS 2009b).

SUMP AREA SOUTHWEST CORNER AREA

243

SUMMARY OF WORK ACTIVITIES – SOUTHWEST CORNER

Mobilization Activities

A vacant lot (Lot 22) is located adjacent to the southwest corner and was used as a support area for construction activities in both the southwest corner and Sump Area. Minimal clearing and grubbing of vegetation was required to develop this property for use as an access road and a staging area. The property naturally sloped at approximately a 3:1 slope from the west along Village Harbor Drive, to the east adjacent to the Harbor. A U-shaped dock was located at the east end of Lot 22.

Mobilization activities began in September 2008, and included establishing project area access and security, constructing the access road and staging area, conducting pre-construction sampling, completing a baseline bathymetric survey, and installing erosion and sedimentation controls.

Project materials, including work boats, temporary loading dock, work barges, material barges, geotextile fabric, aggregate, construction fencing, temporary trailer, dozer, loader, crane, super absorbent polymer (SAP), and excavator were delivered throughout mobilization activities. The work and material barges were placed into the Harbor and assembled upon delivery. A crane was situated on the temporary loading dock to place barges and work boats in the water, as shown in Figure 3. Work boats were stored on the docks located on the southern side of the Harbor. Other materials were staged in the equipment staging area.

Figure 3. View of the support area.

A dozer was used to grade a portion of the hill on Lot 22 to a more gentle slope to construct an approximately 45.7-meter (150-foot) by 6.1-meter (20-foot) temporary access road that connected Village Harbor Drive to the temporary dock installed at the Harbor. An adjacent 12.2-meter (40-foot) strip of Lot 22 along the shoreline between the access road and northern property boundary was graded to serve as a staging area for project equipment and materials. A temporary loading dock was installed to provide better access to the sediment in the southwest corner within the Harbor and to load materials for transport to the Sump Area. The temporary loading dock was located near the eastern end of the access road, approximately 1.5 meters (5 feet) north of a U-shaped dock that was removed prior to construction.

Southwest Corner Construction Activities

The selected remedy for the southwest corner area – which also included beach and dock areas, as shown on Figure 4 – was a combination of sediment removal and residuals cover that included the following major components:

• Removal of sediment:

244

o removal of approximately 0.91 meters (3 feet) of sediment over an approximately 19.8-meter by 10.7-meter (65-foot by 35-foot) area in the southwest corner of the Harbor along the existing submerged slope (southwest corner area)

o removal of 0.61 meters (2 feet) of sediment in an area of approximately 24.4 meters by 10.7 meters (80 feet by 35 feet) located immediately north of the southwest corner (beach area)

o removal of 0.61 meters (2 feet) of sediment in an area of approximately 18.3 meters by 9.1 meters (60 feet by 30 feet) in the vicinity of the U-shaped dock (dock area)

• Processing of excavated sediments with SAP as the solidification agent to remove free liquids prior to transportation to the offsite disposal facility

• Placement of residuals cover over the excavation area, which restored the lake bottom to its approximate pre-construction elevation. The residuals cover consisted of the following materials, ordered from top to bottom:

o shoreline rip rap o gravel bioturbation layer in the southwest corner and dock area with a minimum 0.31-meter (1-

foot) thick sand layer underlying the gravel cover o 0.61-meter (2-foot thick sand cover in the beach area o GCL installed under the upper 0.61 meters (2 feet) of cover material in all areas o mixed granular fill (e.g., sand) below the GCL in the southwest corner

Figure 4. Southwest corner site layout and turbidity barriers.

Turbidity Barrier Installation

A turbidity barrier was installed around the perimeter of the excavation area. During installation activities, an intake valve and a discharge pipe (intake/discharge pipes) for the Bay Harbor Resort heating and cooling system were observed in the water in the southwest corner. The intake pipe was located in the southwest corner, approximately 20 feet east of the shore. The discharge pipe was located at the shoreline between the beach area and southwest corner area.

The alignment of the turbidity barrier was altered from the original design parameters to enable installation of an auxiliary pump and hoses to temporarily provide fresh water to the Bay Harbor Resort for use in their heating and cooling system. Changing the alignment of the turbidity curtain to avoid blocking the flow of clean water to the

DOCK AREA

BEACH AREA

SW CORNER AREA

TURBIDITY BARRIER AREA 1

TURBIDITY BARRIER AREA 2

TURBIDITY BARRIER AREA 3

245

intake was more feasible than permanently installing a bypass pump to feed fresh water to the Bay Harbor Resort for the duration of construction activities.

The work area was separated into three zones, each of which was enclosed by its own turbidity barrier. This allowed the intake/discharge pipes to receive fresh water except for the specific days when excavation or residuals cover placement was being performed in the area. During that time, a bypass pump was used to provide fresh water to the intake/discharge pipes. The three work zones included, 1) the dock and beach areas, 2) the southwest corner area, and 3) the intake/discharge area, as shown in Figure 4.

The turbidity barrier was inspected twice daily throughout the duration of the remediation work. Whenever water elevations changed within the Harbor, the turbidity barrier was adjusted to account for the changing water level. Turbidity and pH readings were collected at four locations outside of the work area(s) to test the effectiveness of the turbidity barrier. No pH or turbidity readings exceeded the established Site-specific monitoring limits at any time during work activities. The turbidity barriers were removed at the conclusion of construction activities.

Sediment Removal Activities

Sediment excavation activities were conducted between October 13, 2008 and October 21, 2008. Main tasks included excavating, processing, and transporting the sediments offsite to a commercial landfill for final disposal.

Excavation

As shown in Figure 5, excavation was performed using a long reach excavator. The long reach excavator was equipped with a Real Time Kinetic Global Positioning System (RTK GPS) system to control underwater excavation depths, provide suitable survey control, and document excavation positional data. A baseline hydrographic survey and control points were used to document the extent of excavation and excavation depths.

Figure 5. Excavation activities in southwest corner.

The display mounted within the cab of the excavator displayed the plot of the maximum depth of penetration of the bucket as compared to the design excavation depth. Excavation proceeded until 0.61 to 0.91 meters (2 to 3 feet) of material was removed and target elevations had been achieved, except in the areas where bedrock was encountered. See the “Presence of Bedrock” section for additional information regarding bedrock. Although bucket elevation data were displayed in real time, the data were not continuously collected since this methodology would have resulted in an overabundance of data. To generate a manageable amount of data, elevation data were recorded at 14 control points as established along the perimeter of the excavation area prior to construction, as shown in Figure 4.

Approximately 649.9 cubic meters (850 cubic yards (cy)) of material were removed from the Harbor. Reactive material was observed in only the top foot of material removed from the southwest corner area. No reactive material was observed in the beach or dock areas or in the bottom 0.61 meters (2 feet) of excavation in the southwest corner.

246

Excavated material primarily consisted of sand and rocks interspersed with sediment. To document completion of excavation, ARCADIS collected a sediment sample from 3 feet below original surface and tested for pH. A pH value of 8.4 s.u. was recorded for this sample. Based on visual observations and field screening, excavation of more than 0.91 meters (3 feet) of material in the southwest corner was not warranted.

Sediment Processing

Excavated sediment was loaded into sealed material barges located inside the turbidity barrier. The SAP was added to process and condition the sediment to make it suitably dry for transportation to the offsite disposal facility. Holding tanks were present in the staging area to collect any decant water from the material barges; however due to the rocky nature of the excavated material and the effectiveness of the SAP, water did not accumulate within the material barges and did not need to be decanted, treated, or discharged.

Sediment Transportation and Disposal

The results of a pre-construction waste characterization sample, collected from the Harbor prior to excavation, were reviewed and approved by an offsite commercial landfill prior to disposal. Approximately 1,179 tonnes (1,300 tons) of stabilized dredged material was transported to the offsite commercial landfill for disposal. Excavated material was transferred by excavator from the material barges to lined, 15.3-meter (20-yard) dump trucks, as shown in Figure 6. Truck tires and rear gates were brushed to remove any material before leaving the project area. Due to the dry nature of the stabilized material and the construction of the access road, pressure washing the truck tires was not necessary. All trucks were inspected prior to leaving the project area to verify that free water was not present within the truck. All sediment disposed offsite was documented using waste manifests and gate receipts for the tonnage received at the landfill.

Figure 6. Truck loading activities.

Residuals Cover Materials and Placement

Following excavation of sediment from the southwest corner area, beach area, and dock area, a cover comprised of a combination low permeability (GCL) and granular material (sand and gravel) was installed to isolate and separate remaining reactive materials from surface water in the Harbor. A cross-section of the residual cover in each work area is shown in Figures 7 through 9.

247

Figure 7. Residuals cover in the southwest corner area.

Figure 8. Residuals cover in the beach area.

Figure 9. Residuals cover in the dock area.

The residuals cover was installed between October 21 and October 29, 2008. Construction activities began in the southwest corner and proceeded north to the beach and dock areas. All layers of the cover were installed in each area before equipment was moved to the subsequent areas. The mixed granular fill, sand, and gravel were installed by releasing the material in thin lifts (approximately 15.2 cm or 6 inches) above the water surface from a thumbed-

GEOSYNTHETIC CLAY LINER (GCL)

18” THICK SAND LAYER

6-12” THICK GRAVEL LAYER

TOP OF SEDIMENT IN HARBOR (EL. VARIES)

6’ SAND LAYER

EXISTING GRADE TOP OF SEDIMENT IN HARBOR (EL.

6-12’ GRAVEL 6” SAND

6-12” THICK GRAVEL

GEOSYNTHETIC CLAY LINER

TOP OF SEDIMENT IN HARBOR (EL. VARIES)

6” SAND

12” THICK SAND LAYER

EXISTING GRADE

RIP RAP (SHORELINE ELEVS. 576-580)

12” THICK GRAVEL LAYER 12” THICK SAND LAYER

GEOSYNTHETIC CLAY LINER (GCL)

12” THICK MIXED GRANULAR FILL LAYER

TOP OF SEDIMENT IN HARBOR (EL. VARIES)

248

excavator bucket. Interim surface elevations were periodically monitored by probing rods and by the RTK GPS system to verify that the desired slope and material thickness was achieved.

Approximately one foot of mixed granular fill consisting of sand and gravel was installed below the GCL to bring the Harbor-bottom elevation to approximately two feet below original grade. Approximately 145 tonnes (160 tons) of mixed granular fill were placed in the southwest corner, beach, and dock areas.

GCL

The GCL consisted of a sodium bentonite clay layer sandwiched between two nonwoven geotextile layers of propylene, needle-punched through the clay to provide increased internal shear strength. The GCL was deployed by pre-cutting the rolls into smaller panels and placing them individually. The necessary panel length was determined, and the panel was cut on land. Ropes were tied to each end of the GCL so that workers could maneuver the GCL from land, docks, or work boats. The excavator moved the GCL into position, and lowered it to water level where crews could use the ropes to align and lower the GCL into place. ARCADIS verified that adjacent panels overlapped by a minimum of 0.31 meters (1 foot) through visual observation and the use of a probing rod. The panels were lowered slowly to avoid disturbing the underlying material. Once hydrated, the GCL was heavy enough to remain in place without the use of temporary anchorages. Approximately 229 linear meters (750 linear feet) of GCL was installed.

Sand and Gravel Layers

The sand and gravel layers provided separation between any remaining reactive material and surface water in the Harbor, and served as ballast for the GCL. The gravel also functions as a bioturbation layer and protection against erosive forces from waves and boat propeller action. Large gravel (e.g., D50 greater than 1.9–centimeter or ¾-inch) was used to provide protection against propeller action from small recreational watercraft in all areas where the Harbor is at least 3.05 meters (10 feet) deep and boat traffic is anticipated.

According to the design, a 0.31-meter (1-foot) thick sand layer was to be placed between the GCL and the gravel layer in the dock area, and a 0.61-meter (2-foot) thick layer of sand was to be placed above the GCL in the beach area. After excavating 0.61 meters (2 feet) of sediment, rock, and lake bottom materials from the beach and dock areas, a rocky slope (rocks with a median diameter of approximately 15.2 cm or 6 inches) remained between the shoreline and the flat bedrock harbor bottom. The presence of sharp, pointed edges on the rocks had the potential to compromise the integrity of the GCL, which was to be placed directly on the slope.

To mitigate potential damage to the GCL, approximately 15.2 centimeters (6 inches) of sand were placed on top of the slope before installing the GCL. The GCL was then covered with an additional 45.7 centimeters (18 inches) of sand in the beach area, and 15.2 centimeters (6 inches) of sand followed by 6 to 12 inches of gravel in the dock area. This modification protects the GCL from the rocky slope, provides enough weight on top of the GCL to maintain stability, and did not alter the final elevation of the Harbor bottom.

Approximately 281.2 tonnes (310 tons) of sand was installed in the southwest corner, beach, and dock areas. A view of the post-construction beach area is shown in Figure 10. A maximum gravel thickness of 0.31 meters (1 foot) was installed above the sand throughout the southwest corner and dock areas and at the base of the beach area. Approximately 150 tonnes (165 tons) of gravel was installed in the southwest corner and dock areas.

249

Figure 10. Restored beach area.

Shoreline Rip Rap

Approximately 68 tonnes (75 tons) of shoreline rip rap were installed over the gravel layer in the southwest corner area to provide additional protection from wave action. The rip rap consisted of stone with a diameter between 10.2 and 30.5 centimeters (4 and 12 inches), selected and placed to match the rip rap used in the rest of the Harbor to the extent practicable, as shown in Figure 11.

Figure 11. Restored southwest corner area.

Presence of Bedrock

A bedrock shelf was encountered near the southern edge of the southwest corner excavation area, and a flat, hard bedrock floor was encountered along the eastern side of the excavation area. Due to the bedrock, the planned excavation depths of 0.61 to 0.91 meters (2 to 3 feet) below original elevation could not be achieved. Although planned excavation depths were not achieved, the uniformity of the bedrock floor demonstrated that all potentially reactive material in these areas had been removed, and excavation was determined to be complete.

In the areas where bedrock was encountered, the residuals cover design was modified so that those excavation areas would be restored to approximately pre-construction elevations after placement of the cover. Along the eastern side of the excavation area, the thickness of the gravel bioturbation layer was decreased from 30.5 centimeters (12 inches) as necessary, but the thickness of the sand layer was not modified. It was determined that this residuals cover configuration sufficiently covered the GCL and provided protection against erosive forces from wave and propeller action.

250

The bedrock on the southern side of the excavation area was located on the rocky, sloped shore above the median water line. Since less than 0.61 meters (2 feet) of material was removed from this area, the use of mixed granular fill was not necessary to restore the area to its approximate pre-construction elevation. The GCL was placed directly on the flat bedrock shelf. A 0.31-meter (1-foot) thick layer of sand and a 15.2-centimeter (6-inch) thick layer of gravel were installed on top of the GCL. Although the thickness of these layers resulted in a final elevation that exceeded the pre-construction elevation by approximately 0.31 meters (1 foot), reducing the cover thickness any further to restore the area to its original elevation would not have provided enough weight above the GCL to provide stability and would have resulted in an unstable slope. This area is not in navigable waters, so the final elevation should not affect recreational boating. Rip rap was installed above the GCL to complete the residuals cover.

Post-Construction Survey

A post-construction bathymetric survey was performed on November 4, 2008 to document the final residuals cover elevations. The post-construction survey was performed in the same manner as the baseline survey.

SUMMARY OF WORK ACTIVITIES – SUMP AREA

Work activities in the Sump Area were carried out directly after completion of construction in the southwest corner area, so no separate mobilization was necessary. Lot 22 was used as a support area, and equipment from the southwest corner area efforts were used in the Sump Area. Construction in Sump Area began in November 2008, and after a break for winter weather, concluded in May 2009.

Sump Area Construction Activities

The residuals cover remedy selected for the Sump Area included the following major components:

• Pre-construction bathymetric survey • Installation of a turbidity barrier • Placement of a residuals cover to isolate the sediment containing reactive material and raise the bottom

elevation of the Sump Area to an approximate elevation of 565 feet (ft) NAVD88. The residuals cover consisted of the following materials, ordered from top to bottom:

o 0.31-meter (1-foot) thick gravel armor layer (elevation 565 ft NAVD88) o 0.61-meter (2-foot) thick sand layer (elevation 564 ft NAVD88) o Low-permeability geosynthetic clay liner (GCL) layer o Mixed granular fill layer (elevation 562 ft NAVD88) o Geotextile layer

• Post-construction bathymetric survey

The residuals cover was installed between November 3, 2008 and May 8, 2009. Installation of the residuals cover was performed in two phases separated by a settlement monitoring period/winter shut down. See the “Settlement Monitoring” section for additional information regarding the phased approach.

Baseline Bathymetric Survey

A pre-construction bathymetric survey was completed in November 2008. These baseline survey data were used to determine fill volumes and the footprint of the residuals cover.

Turbidity Barrier Installation

Two turbidity barriers were installed outside of the Sump Area, one to the east and one to the west. A vertical gate was installed in the western barrier to allow work equipment in and out of the Sump Area while maintaining the isolation of the work zone.

251

The turbidity barrier was installed around the perimeter of the Sump Area prior to Phase 1 construction activities, and was removed in December 2008 at the completion of Phase 1 construction activities to protect the curtain from ice damage during the time the project was shut down for the winter. Installation of the GCL – the first layer of the residuals cover to be installed as a part of Phase 2 construction activities – was scheduled to begin during the week of April 6, 2009. At that time, there was significant ice present within Village Harbor. Installation of the turbidity barriers would have been impractical under such conditions. As a result, installation of the GCL was postponed for one week to allow for the ice blockage to subside. However, after that week significant ice was still present in the Harbor. To avoid further delays to the schedule, the GCL was installed without a turbidity barrier around the perimeter of the work area. This modification was discussed with and approved by the USEPA.

USEPA and ARCADIS determined that there would be minimal potential for any adverse environmental impacts – any reactive material present in the underlying sediments was covered by 1.2 to 1.5 meters (4 to 5 feet) of mixed granular fill during Phase 1, and was unlikely to be disturbed by GCL placement. Turbidity was monitored outside of the work area on a daily basis during GCL installation. The turbidity barriers were installed on April 24, 2009 before installation of the sand layer began.

The turbidity barriers were inspected twice daily throughout the duration of the work activities. Whenever water elevations significantly changed within the Harbor, the turbidity barriers were adjusted as necessary. The effectiveness of the turbidity barrier was monitored by collecting field measurements of the surface water pH and turbidity at three locations outside the turbidity barriers. No pH or turbidity readings exceeded the established monitoring limits at any time during work activities.

Residuals Cover Materials and Placement

The residuals cover was installed for two primary reasons: 1) to provide a barrier between the sediment present in the Sump Area and surface water in the Harbor, and 2) to eliminate the trough by raising the bottom elevation of the Sump Area. The isolation and elevation was achieved through the installation of a combination low permeability GCL and granular material.

Installation of the residuals cover began at the east end of the Sump Area and proceeded west for each material lift of each layer. One layer of the cover was completely installed before installation of the subsequent layer began. Interim bathymetric surveys were performed immediately following placement of each lift of each layer to verify that target elevations were being achieved. A cross-section of the Sump Area residuals cover is shown in Figure 12.

Figure 12. Sump Area residuals cover.

Materials were delivered to the project site and stockpiled at the eastern end of the access road. An excavator, situated on the temporary loading dock, loaded the materials into material barges. The material barges were pushed

252

to the Sump Area using a work boat, where they were tied to the work barge. The RTK GPS-equipped thumbed excavator was located on the work barge and was used to place the materials in the Sump Area. Empty material barges were returned to the temporary loading dock by the work boat.

Phase 1 Construction Activities

Phase 1 construction activities included a pre-construction bathymetric survey followed by placement of geotextile fabric and mixed granular fill to an approximate elevation of 562 ft NAVD88. Phase 1 activities were performed between November 3, 2008 and December 5, 2008.

Geotextile Fabric

On November 7, 2008 approximately 150 tonnes (165 tons) of mixed granular fill were placed in the Sump Area before the geotextile fabric was installed to cover large rocks identified during the pre-construction bathymetric survey. The geotextile layer was to be placed on the floor of the Sump Area prior to placing any mixed granular fill material. Based on the pre-construction bathymetric survey data, large rocks with median diameters between 6 and 30.5 centimeters (12 inches) were identified in the center of the Sump Area between the first and second docks (from west to east) on the northern side of the Harbor. The presence of sharp, pointed edges on the rocks had the potential to compromise the integrity of the geotextile, which was to be placed directly on the floor of the Sump Area.

To mitigate potential damage to the geotextile without significantly altering the design and construction of the cover, approximately 150 tonnes (165 tons) of mixed granular fill were placed on top of the rocks, and the geotextile was placed on this mixed granular fill base. The other layers of the residuals cover were installed as planned.

Approximately 4,276 square meters (46,000 square feet) of 12-ounce-per-square-foot non-woven geotextile fabric was installed between November 8, 2008 and November 17, 2008. Geotextile was installed to provide separation, prevent migration of fine sediment into the mixed granular fill layer, and provide improved strength for bridging over the sediment.

The rolls were cut into panels of varying lengths based on the pre-construction survey data. Centerlines were established and marked every 3.7 meters (12 feet) on the southern shore of the Sump Area to guide placement of the fabric such that there would be a minimum overlap of 0.91 meters (3 feet) between adjacent 4.6-meter (15-foot) wide geotextile panels. These centerlines were also shown on the survey data, which was loaded into the RTK GPS in the long reach excavator. A representative view of geotextile fabric installation is shown in Figure 13.

Figure 13. Geotextile fabric installation in the Sump Area.

On November 14, 2008 an underwater camera was used to inspect the geotextile fabric placement. Review of the video identified one area with insufficient overlap and/or geotextile fabric coverage. The large rocks identified

253

during the pre-construction survey and covered with mixed granular fill prior to installation of the geotextile fabric were still visible between adjacent geotextile fabric panels. Additional fabric was placed in this area on November 17, 2008 to cover the rocks, and fabric installation was determined to be completed.

Mixed Granular Fill

Approximately 4,491 tonnes (4,950 tons) of mixed granular fill were installed in the Sump Area between November 8, 2008 and December 5, 2008. The mixed granular fill was installed by releasing it above the water surface from a RTK GPS-equipped thumbed excavator bucket.

The fill was installed in a total of 9 thin lifts of approximately 15.2 centimeters (6 inches) each to raise the elevation of the Sump Area bottom approximately 1.2 to 1.5 meters (4 to 5 feet), depending on the original bottom elevation, to a final elevation of approximately 562 ft NAVD88. Thin lifts were used to avoid overloading the underlying sediment. Interim bathymetric surveys were performed after each lift to verify that the desired material thickness was achieved. These data were loaded into the RTK GPS system to direct material placement locations and thickness.

Settlement Monitoring

The placement of the residuals cover was originally described as a continuous installation effort, with each layer of the cover placed immediately following the completion of the previous layer. However, based upon detailed review of geotechnical data, ARCADIS recommended that the residuals cover be installed in two phases due to the potential for up to 35.6 centimeters (14 inches) of differential settlement of the soft sediments within the Sump Area. If the differential settlement were to occur over short distances, the integrity of the residuals cover could be compromised. This approach is summarized in the Proposed Construction Method, Sump Area, Village Harbor Emmet County, Michigan Memorandum (ARCADIS 2008c).

To address the potential for differential settlement, construction of the cover was separated into two phases and a settlement monitoring program was implemented. Phase 1 of construction activities was performed between November 3, 2008 and December 5, 2008 and included installation of geotextile fabric and mixed granular fill to an approximate elevation of 562 ft NAVD88. Survey data were collected prior to geotextile installation, between the fourth and fifth mixed granular fill lifts, and at the conclusion of Phase 1 activities to monitor settlement of the underlying sediments.

Settlement survey data were collected from the baseline survey track line prior to commencement of Phase 2 cover construction. These data were compared to the survey data collected at the conclusion of Phase 1 cover construction activities.

The underlying sediments were allowed to settle under the weight of the mixed granular fill from December 11, 2008 to March 30, 2009. A baseline bathymetric survey track was aligned southwest to northeast across the Sump Area to monitor the settlement of the underlying sediments. The track alignment, which is shown in Figure 14, was selected for the following reasons:

• The track was straight and could be maintained fairly accurately with a survey boat. • The track had good markers at both ends for the boat to track. • The track ran over the deepest section of the Sump Area, making it the most representative of locations

subject to potential settling.

254

Figure 14. Sump Area monitoring track layout and pre-fill area.

Monitoring data was collected and analyzed from the bathymetric survey track five times:

• Pre-Construction: November 4, 2008 • After the fourth lift of mixed granular fill: November 22, 2008 • Before the fifth lift of mixed granular fill: December 1, 2008 • At the conclusion of Phase 1 construction activities: December 5, 2008 • Prior to the beginning of Phase 2 construction activities: April 1, 2009

The baseline survey track was run six times during each of the five survey events and the track that showed the least amount of lateral deviation from the baseline alignment was used for analysis. Any portion of a track that showed greater than 0.61 meters (2 feet) of lateral deviation from the baseline track alignment was excluded from a point 7.6 meters (25 feet) before and after the point where the deviation exceeded 0.61 meters (2 feet) to create a best-fit line. The surveyor was able to collect data with less than 0.61 meters (2 feet) of lateral deviation on at least one of the six passes over the baseline survey track during each surveying event. Overall, minimal settlement of the underlying sediments (less than 15.2 centimeters or 6 inches) was observed in the Sump Area, and the residuals cover did not need to be modified.

Phase 2 Construction Activities

Phase 2 construction activities were performed between April 13, 2009 and May 8, 2009 and included placement of the GCL, a 0.61-meter (2-foot) sand layer, and a 0.31-meter (1-foot) gravel layer.

GCL

GCL placement began on April 13, 2008 and was completed on April 24, 2009. The same 12-foot centerlines established for the geotextile placement were used for the GCL placement. This ensured an approximately 2.5-foot overlap between GCL panels. In addition, the planned GCL alignment was loaded into the excavator so the RTK GPS system could be used to verify the GCL was placed in the proper location. The GCL was deployed using two methods, depending on the length of the GCL required.

Shorter GCL panels (less than 12.2 meters or 40 feet) were installed using the same method as described for the southwest corner GCL installation and as shown in Figure 15.

255

Figure 15. GCL installation in the Sump Area.

Longer GCL panels (greater than 12.2 meters or 40 feet) were placed using a more mechanical method, which included a spool for the GCL, ropes, a steel A-frame, and a loader. The GCL was attached to the A-frame, which was attached to the loader, which pulled the GCL from the spool. When the required length of GCL had been pulled from the spool, the GCL was cut from the spool. Hand held ropes were used to guide this end of the GCL into place. After the GCL was placed, the ropes and steel A-frame were disconnected from the GCL.

The panels were lowered slowly to avoid disturbing the underlying material. Temporary anchorages were not required because the GCL was placed on a flat surface and was too heavy to be moved by currents in the Harbor.

Approximately 2,789 square meters (30,000 square feet) of GCL was installed in the Sump Area at an approximate elevation of 562 ft NAVD88. Overlap was confirmed using a combination of the RTK GPS system, probing rods, and visual observations. An underwater camera was used to inspect the GCL placement for sufficient coverage and overlap on April 23, 2009. Two areas were identified on the video where GCL overlap was less than the minimum 1 foot overlap. Additional GCL panels were placed in each of these areas to provide sufficient overlap. An aerial view of the Sump Area during GCL installation is included in Figure 16.

Figure 16: Aerial View of the Sump Area during GCL installation. Extent of GCL footprint represented by dark tint in water.

Sand and Gravel Layers

The sand and gravel layers provided separation between remaining reactive material and surface water in the Harbor and provided ballast for the GCL. A 0.61-meter (2-foot) thick layer of sand was installed to an approximate

256

elevation of 564 ft NAVD88, and the 0.31-meter (1-foot) thick gravel layer raised the final residuals cover elevation to approximately 565 ft NAVD88.

The gravel layer provided a bioturbation layer and protection against erosive forces from waves and boat propeller action. Based on the analysis for design of the armoring system, large gravel (e.g., D50 greater than 1.9 centimeters or ¾-inch) was used to provide protection against propeller action from small recreational watercraft in all areas where the Harbor is at least 3.1 meters (10 feet) deep and boat traffic is anticipated.

The sand and gravel layers were installed from east to west. A RTK GPS-equipped thumbed-excavator bucket released the material at the water surface and evenly spread the sand and gravel across the required areas, as shown in Figure 17. Material was placed from the center (in a north-south direction) to the perimeter of the Sump Area and with a maximum lift thickness of 0.31 meters (1 foot) to provide continued loading and gradual consolidation of underlying materials.

Figure 17. Sand placement in the sump area.

A 0.31-meter (1-foot) lift of sand was initially placed on top of the GCL, followed by two 6-inch lifts. The gravel layer was primarily installed in two 15.2-centimeter (6-inch) lifts. The 15.2-centimeter (6-inch) lift thickness allowed greater control and accuracy to slowly raise the cover elevation. Interim bathymetric surveys were performed after each lift to verify that the desired material thickness was achieved. These data were loaded into the RTK GPS system to direct material placement locations and thickness. After the second 6-inch lift of gravel was surveyed, a partial third lift was installed to fill any depressions in the residuals cover and bring the final cover elevation to approximately 565 ft NAVD88. Approximately 3,447 tonnes (3,800 tons) of sand and 2359 tonnes (2,600 tons) of gravel were installed above the GCL in the Sump Area between April 27, 2009 and May 8, 2009.

Post-Construction Survey

A post-construction bathymetric survey was performed on May 8, 2008 to document the final residuals cover elevation. The post-construction survey was performed in the same manner as the baseline survey. Bathymetric survey data generally showed a consistent elevation across the residuals cover.

257

Post-Construction Monitoring

Post-construction monitoring is scheduled to be performed quarterly following the completion of the residuals cover in each area for a period of 1 year. Twenty locations across and around the edges of the southwest corner residuals cover and twenty-one locations sited across and around the edges of the Sump Area residuals cover have been identified for pH monitoring, as shown in Figure 18. During each event, water samples will be collected from the lowest 0.31 meters (1 foot) of the water column and the middle of the water column at each monitoring location. If results of the field monitoring indicate any pH measurements greater than 9.0 s.u., step-out monitoring will be performed to define the limits of pH greater than 9.0 s.u. Samples will be field-measured for pH using a YSI 650 Multi-Probe System (MPS) probe.

Figure 18. Post-construction monitoring locations.

ARCADIS completed two monitoring events in the southwest corner (November 4, 2008 and April 9, 2009) and one monitoring event in the Sump Area (May 14, 2009). No pH measurements greater than 9.0 s.u. were recorded during any of the three monitoring events. After the May 2009 event, the client assumed responsibility for continued post-construction monitoring. The client has verbally stated that no pH results greater than 9.0 s.u. have been recorded in subsequent monitoring events.

Demobilization and Site Restoration

Demobilization and Site restoration activities were performed between May 11, 2009 and May 15, 2009. Project materials, including work boats, work barges, material barges, geotextile fabric, aggregate, GCL, construction fencing, turbidity barriers, temporary trailer, dozer, loader, crane, and excavators were removed from the Site. The work and material barges were disassembled in the water and removed using a crane that was situated on the temporary loading dock. After all equipment had been removed from the water, the temporary loading dock was removed from the Harbor and hauled offsite.

The U-shaped dock was replaced; the temporary access road, including geotextile fabric and aggregate material, was removed, and Lot 22 was regraded to its original slope. Approximately 65 tons of non-hazardous waste material was transported to an offsite landfill for disposal.

Approximately 72.6 tonnes (80 tons) of topsoil was imported to the Site. A thin layer (approximately 7.6 centimeters or 3 inches) of topsoil was spread across the areas to be re-vegetated. Landscaping activities were performed between May 26, 2009 and May 29, 2009 and included repairing the sprinkler system and replacing sod; seeding the

258

area around the southwest corner of the Harbor; and seeding, laying straw, and watering the western portions of the disturbed areas to restore the areas to their pre-construction condition.

CONCLUSIONS

Construction activities were performed in Village Harbor in the Fall of 2008 and Spring of 2009 and were designed to mitigate elevated pH levels (greater than 9.0 s.u.) in near-bottom surface water. The selected remedies included:

• Removal of reactive material from the southwest corner • Construction of a residuals cover in the southwest corner • Construction of a residuals cover in the Sump Area

Approximately 1,179 tonnes (1,300 tons) of material were excavated from the southwest corner, processed, and disposed of at an offsite commercial landfill. A residuals cover was installed to isolate remaining reactive material from the surface water and restore the Harbor bottom to its original elevation. The residuals cover installed in the Sump Area served to both isolate reactive material and raise the bottom elevation of the Sump Area to eliminate the trough feature. The elevation of the Sump Area is now more uniform with other areas of Village Harbor. GCL was incorporated in both residuals covers to isolate remaining reactive material from the surface water and address the elevated pH levels observed prior to construction.

Both residuals covers were installed approximately as designed. Preliminary post-construction monitoring did not yield any surface water concentrations with pH values exceeding 9.0 s.u.

REFERENCES

ARCADIS. 2008a. Removal Action Work Plan – Village Harbor Southwest Corner. ARCADIS. ARCADIS. 2008b. Work Plan Under Removal Action AOC. ARCADIS. ARCADIS. 2008c. Proposed Construction Method, Sump Area, Village Harbor Emmet County, Michigan

Memorandum. ARCADIS. ARCADIS. 2009a. Removal Action Completion Report, Village Harbor Southwest Corner. ARCADIS. ARCADIS. 2009b. Residuals Cover Completion Report, Village Harbor Sump Area. ARCADIS. USEPA. 2005. Administrative Order on Consent for Removal Action (AOC or Order) for the Little Traverse Bay

(LTB) Cement Kiln Dust (CKD) Release Site (Site) (Docket No. VW-05-C-810). USEPA.

259