Significant Project Features
- Design-build residential remediation required excavation, characterization, T+D of top 4 feet of soils from 300 properties
- Regularly scheduled project planning sessions prior to initiating remediation activities among a responsible party, its design engineer and Sevenson improved the final design document, identified opportunities for cost savings, and addressed potential remediation and restoration issues prior to mobilization to the field. Project planning activities were ongoing over a two (2) year period
- Neighborhood broken down into 18 blocks of homes. This minimized disruption to homeowners during remediation
- Extensive restoration of affected properties included concrete work, asphalt paving, deck and patio replacement, and landscaping
- Multi-media sampling conducted on soils and air for duration of project
- Detailed community relations plan focused on “open door” policy with residents and local stakeholders
- Newhall Street neighborhood remediation was the largest residential remediation project in Connecticut history
History & Location Details
The Newhall Street neighborhood is located in Hamden, Connecticut. The neighborhood comprises an area that historically consisted of wetlands and low-lying areas. Waste materials were used to fill these areas from the late 1800s to the mid-1900s. Subsequently, homes, public buildings, and parks were built on and next to the historic fill areas. The fill material contained contaminants consisting primarily of metals, PAHs and PCBs.
Sevenson was awarded the remedial action contract based upon a competitive bid proposal.
A consent order was developed between the state of Connecticut and the responsible party. It included an 18-block area consisting of approximately of 300 residential properties. The remedy for the residential properties required excavation of the top 4 feet of fill for characterization and offsite T+D to an approved disposal facility. Removal of underground storage tanks at some properties was required. Restoration of all properties to pre-existing conditions was a significant component of the scope of work. This included landscaping, patios, decks, fencing, driveways, porches, sidewalks, etc.
Once Sevenson initiated remedial action the primary project requirement was maintaining safe access and a safe environment for all residents during construction. Excavation was done with a backhoe using methods to minimize dust generation. Dust control techniques were implemented and consisted primarily of use of a water truck and misting. An air monitoring system was operational during all work activities. Additional measures were implemented during dry and windy conditions.Access to excavation areas was established to provide efficient transfer and delivery of equipment and construction materials as well as facilitate decontamination of equipment and vehicles prior to exiting the site. Access was constructed with geotextile fabric and stone using a track dozer and compacted with a drum roller. Decontamination pads were established in close proximity to loading operations. Pads consisted of a pressure washer, small trash pump with hosing, small tools and a wastewater storage tank to collect all water generated during decon activities. Plastic sheeting was utilized during loading operations to prevent contaminated material from contacting the truck tires. Soil erosion control measures were maintained during excavation operations. Traffic barriers, signage and detour routes were installed adjacent to active work areas to minimize congestion. Traffic control during the day was provided by the Hamden Police Department. Clearing and grubbing of trees and shrubs was required prior to excavation.Permanent structures remained in place during remediation. This included homes, garages, storage buildings with concrete slabs and foundations. Paved streets also remained in place. All other residential features were removed. This included fencing, driveways, sidewalks, decks, patio and landscape. Some residents were relocated during remediation. For those that did remain Sevenson closely coordinated remediation and restoration activities so there was always safe access to their homes. The contents of several structures scheduled for demolition required temporary storage at an offsite facility. Sevenson coordinated this.Hand excavation next to buildings, structures, slab on grades and utilities was done to prevent any damage to the structures. During the documentation of existing conditions of individual properties, structures with integrity issues were identified, documented and consideration to protect or support these structures was detailed prior to excavation.
Temporary stockpiles were covered with poly-sheeting and secured with sandbags to prevent precipitation from entering the stockpile and minimize the potential for dust. Sevenson also installed temporary construction fencing at the perimeter of open excavations to secure open excavations.
Fill material was excavated to a depth of up to 4 feet from the existing ground surface. Excavated materials were direct loaded for transportation and offsite disposal at an approved disposal facility. Also asphalt, concrete materials, and masonry was direct loaded into truck and disposed of at a recycling facility.
Replacement of utilities was performed during backfilling operations. Prior to initiating backfilling, coordination with local utility companies was done to establish protocols, materials, installation procedures, field testing and inspection required for each utility. Backfilling of excavation areas began upon acceptance by Olin’s representative that material removal was completed. This was based on verification sampling and a topographic survey of the excavation limits. Sevenson utilized a local licensed surveyor to establish the necessary controls to re-establish pre-existing features to restore areas to pre-remediation conditions. Backfill materials were delivered to the site, placed and graded utilizing track dozers and/or loaders in loose lifts to the proposed subgraded elevations. Compaction was performed utilizing a steel drum roller, plate tampers, walk behind roller, or tracking with the dozers. As backfilling operations progressed, Sevenson initiated restoration activities at each property. Each property was restored to existing conditions. Individual property sketches were developed and selection of specific restoration items (i.e. fencing, specific planting garden borders, walls, sheds, unit pavers, concrete/asphalt driveways, etc.) for each property were finalized in the agreements with the property owners. This included concrete, asphalt, masonry, carpentry, fencing and landscaping.