St. Maries Creosote Superfund Site
Significant Project Features
- Mobilization, site set up, installation of access roads and improvements to existing roads and infrastructure
- Construction of soil/sediment storage/processing pads. Construction of an extension to existing dewatering pad
- Construction of sediment offloading dock. Removal of dock at completion of project
- Installation of a dredging enclosure area using combination of steel sheeting and H piles. Removal at completion of project
- In-river debris removal, handling, and offsite disposal
- Mechanical dredging (18,000 CY) and backfilling of nearshore river sediments
- Transportation of dredged sediment to dewatering pad for processing and storage prior to low temperature thermal desorption (separate contract)
- Bank soils excavation and restoration
History & Location Details
The St. Maries Creosote site lies along a stretch of the St. Joe River within the boundary of the Coeur d’Alene Tribe Reservation. The site encompasses 13 acres of undeveloped land and 3 acres of sediments in the adjacent St. Joe River. Site owners used the area from 1939 – 1960 to store and treat logs and poles with creosote. The logs were treated by soaking one end in large, heated, creosote-filled vats to prevent the ends from rotting when placed into the ground as poles. As the treated poles were loaded onto rail cars, creosote dripped onto the soil around the vats and rail cars, contaminating the soil and the nearby river sediment.
Sevenson was awarded the contract to implement remediation in May 2015 based upon a competitive proposal. The project was executed under ARCADIS’ Guaranteed Outcomes Initiative. The project was executed in compliance with the Record of Decision, Consent Decree, and Explanation of Significant Differences documents. The remote project location and tight schedule required careful planning. Upon contract award Sevenson initiated mobilization and site set up. This included erosion control measures; rerouting of existing stormwater pipe and installation of additional pipe; construction of new access roads and improvements to existing roads; and the installation of staging and processing pads.
When mobilization and site set up was completed Sevenson commenced with in-water operations. Steel sheeting and H piles were driven to create a 747 LF enclosure for mechanical dredging operations. The enclosure was constructed using a combination of AZ sheeting between 47 ft and 59 ft lengths and HZ Piles either 72 ft or 79 ft. Shorter lengths were used near the shoreline while longer lengths were used in the main channel. Prior to installation a sealant was applied to interlocks of sheeting and piles. Sevenson utilized a 200 ton crane fitted with an APE 200 vibratory driver, positioned on an 80 ft x 60 ft modular float to install the sheet pile wall.
The sheeting installation was supported by an 80 ft x 20 ft modular float transport barge which shuttled sheets and piles to the driving operation. Two (2) 40 ft x 10 ft modular floats were utilized to fabricate a driving frame to maintain alignment of the wall during installation. A 400 HP Tug was used to shuttle sheets and piles to the work zone and to support operational moves. A 100 ton crane loaded sheets and piles from land to the transport barge.
Prior to installation of the enclosure wall a series of navigational aids were deployed in the St. Joe River which is busy with recreational boaters. SWELLSEAL was applied to prevent leakage through the sheet piling interlocks. Pumps were placed within the enclosure to equalize water levels inside and outside the enclosure during dredging. Installation of a fish exclusion area was maintained around the pump suction due to concerns of a threatened species of bull trout.
Sediment Offloading Area
A temporary sediment offloading area was constructed using steel sheet pile in an identified area adjacent to the river bank. Since the location was contaminated, bank soils were excavated and transferred to the dewatering pad for processing prior to constructing the offloading area. Excavated areas were backfilled with clean material to improve the foundation for the temporary facility as well as raise the elevation. The sheets to construct the offloading area were chosen to support the weight of the equipment used to transfer dredged sediment from the hopper scows to the staging pad. Upon completion of the dredging and backfill operations the structure was removed.
Mechanical dredging operations were performed using a barge mounted excavator (Komatsu PC450) with a long reach stick and boom. The working platform drafted approximately two to three feet when fully loaded. The dredge was fitted with a 2.5 CY Anvil level cut bucket. The bucket rotated 360 degrees for optimal positioning. Sevenson developed a venting system for the bucket to reduce the free water trapped inside the bucket. This maximized the volume of sediment removed. Reduction in the volume of water in each bucket reduced decanting and subsequent treatment of water draining from sediments when brought on land.
Dredged sediments were loaded into three (3) custom-built 100 CY hopper scows. Each scow was supported by two (2) connected modular floats. Scows were staged in locations to support dredge production rates. As one scow was loaded the other two were positioned at the unloading structure ready to be moved. At the unloading area, scows were decanted using a diesel pump and unloaded using an excavator (Komatsu PC400) fitted with a similar 2. 5 CY bucket that transferred sediment to off road trucks for delivery to the dewatering pad. The dredge barge and hopper scows were supported within the enclosure with tender and flat bottom work boats.
Sevenson utilized a dredge positioning system developed by Hypack (Dredgepack) to minimize over dredging. The system used a combination of inclinometers, software and duel RTK GPS antennas for dredge bucket location.
Sevenson implemented best management practices to reduce turbidity and resuspension within the work area. BMP’s included:
- Use of water-tight barges and inspected to confirm water-tightness prior to dredging and dredged material transport.
- Sediment was dredged from within the dredge prism without excavating beyond the dredge limit.
- An experienced environmental dredging operator was assigned familiar with RTK GPS with Hypack Software. This maximized production.
- Minimized the overfilling of dredge bucket.
- Overlapped dredge cuts to avoid leaving ridges or windrows of contaminated sediment between adjacent cuts.
A total of 20,000 CY of river sediment was removed. Upon completion of mechanical dredging (verified by ARCADIS) and cleaning of the scows and excavators, Sevenson utilized the same equipment for transport and placement of backfill material. An excavator positioned in close proximity to the shoreline loaded hopper scows from land from a backfill stockpile. The backfill stockpile was fed from a material staging area using a loader and off road trucks. Backfill was placed at a rate of 500 CY/day.
During the unloading process, if dredged material was sandy and dewatered to acceptable levels in the hoppers, material was transferred to an off-road truck for placement on the dewatering pad. There Sevenson used a long stick excavator to stack and allow it to free drain and dewater naturally. Once material achieved acceptable moisture level sediment was consolidated and covered for additional dewatering and storage for later treatment.
If dredged material did not dewater to acceptable levels in the hoppers material was unloaded to an off-road truck and transferred to mixing bins for amendment with quicklime. Mixing bins were constructed of interlocking concrete bin blocks. Bins were sized to accommodate approximately a ½ days production. When necessary Sevenson worked material with a loader and long stick excavator to promote drainage. Water was routed to sumps and transferred to the onsite WWTP operated by ARCADIS. Bins and stockpiles were covered with poly during rain events to minimize introduction of additional moisture. Dewatered stockpiled materials were securely covered at the end of the project using heavy tarps and a grid system of UV resistant ropes and sandbags.
The St. Joe River is busy with recreational boat traffic throughout the summer months. Sevenson provided temporary private aids to navigation and markers. All aids to navigation were inspected on a daily basis to ensure proper operation. These lighted buoys, markers, and signs were stationed along the wall and in the St. Joe River to clearly mark the work zone and warn watercraft for the duration of the project. Sevenson monitored navigation activities with the St. Joe’s River.
Debris encountered during dredging and sheet pile installation consisted mostly of logs and wire rope from historic logging activities. Full logs were encountered not only on the surface of the river but also embedded in the sediment. During dredging logs were removed, placed on the deck of the hopper scows then unloaded and staged on the dewatering pad. After a large stockpile of logs was collected they were sawn into smaller sections for removal and disposal. Other debris encountered was removed by bucket, grapple, or a rake. Debris was loaded into the 100 CY scows and pushed to the offloading platform for unloading, staging and offsite disposal.
Restoration was completed as outlined in project specifications. Bank restoration work included placement of a CETCO reactive core mat, sand backfill, 8 oz. non-woven geotextile, riprap, topsoil, erosion control mats, and seeding was performed from the shoreline. Restoration was carried to the areas beyond the work site to match grades and look of undisturbed areas.