Remediation Construction And Management

CATEGORY OF SERVICE, LOCATION:

Vapor intrusion mitigation including passive sub-slab depressurization (SSDS) piping and epoxy floor coating at a former metal fabrication facility that underwent subsurface electrical resistive heating (ERH) thermal remediation in Santa Cruz, California.

TYPE OF CLIENT:

Commercial property owner

BACKGROUND:

The subject property (Site) is a former metal fabrication facility situated in a mixed commercial and residential neighborhood. The former facility released the chlorinated volatile organic compound (CVOC) tetrachloroethene (PCE) into the environment. The chemicals of potential concern (COPC) at the Site are PCE and its degradation compounds trichloroethene (TCE), dichloroethenedichloroethene (DCE) isomers (cis- and trans-), vinyl chloride, and 1,4-dioxane. The Site is under a Voluntary Cleanup and Abatement Agreement with the Central Coast Regional Water Quality Control Board.

After completion of ERH thermal treatment and soil vapor extraction, Site soil vapor continues to have CPOC concentrations above regulatory-negotiated Site-specific clean-up goals. To achieve regulatory no-further-action status, SSDS system installation and epoxy floor sealing mitigation activities were performed to continue safe tenant occupation of the facility, which currently is used for various commercial rental activities.

Environmental investigation, clean-up, and Site worker exposure mitigation is being performed under a grant from the State Water Resources Control Board’s Site Cleanup Subaccount Program.

CLIENT GOALS FOR PROJECT:

The primary goal for this project phase was to: 1) allow regulatory agency-approved occupation of the former metal fabrication facilities building for commercial retail uses.

Vapor intrusion mitigation activities were performed in accordance with the San Francisco Bay Regional Water Quality Control Board’s June 2022 Vapor Intrusion Mitigation Guidance.

PROJECT APPROACH:

Trinity established regulatory-approved Site-specific clean-up goals for COPCs in soil vapor using radon analysis of sub-slab vapor and indoor air to determine the building slab’s ability to prevent vapors under the building to move indoors (building slab “attenuation factor”).
Trinity installed eighteen, 10-foot long sub-slab depressurization trenches (see photograph) throughout the building interior to depressurized the space beneath the building’s concrete slab so that vapors potentially containing COPC could not enter the building interior. The trenches included perforated piping and conveyance piping to transport sub-slab vapor outside the building using wind turbines (passive SSDS).
Application of a 2-part epoxy floor coating throughout the building concrete slab interior to seal any cracks made during subsurface thermal remediation and further increase the building slab attenuation factor (see photograph). The floor sealing contractor and coating products were regulatory-approved and less expensive than other products currently on the market.

NEXT STEPS:

Trinity was able to allow approved building occupation while previous ERH remediation activities continue to reduce subsurface CVOC concentrations to below the Site-specific clean-up goals.

CATEGORY OF SERVICE, LOCATION:

DIRECT PUSH DRILLING USING TRACK MOUNTED EQUIPMENt

Dry Cleaning Chemical Assessment and Remediation, Monterey, California

TYPE OF CLIENT:

Local Municipality

BACKGROUND:

The site operated as a dry cleaner from 1921 to 2000 when the property was purchased by the local municipality and converted into a park. During excavation for an underground utility, tetrachloroethene (PCE), a dry cleaning solvent, was discovered in soil and groundwater. Elevated PCE concentrations remained in groundwater after soil excavation by others, and the California Regional Water Quality Control Board required remediation.

CLIENT GOALS FOR PROJECT:

The client required assistance to implement requirements of the California Regional Water Quality Control Board to assess the extent of dry cleaning chemicals in the subsurface and to reduce concentration in groundwater to acceptable levels. The client needed a strategy to remove or destroy in place the dry cleaning solvents within a highly used City park, cost-effectively and with minimum disruption to the community.

PROJECT APPROACH:

Conduct subsurface assessment activities utilizing Membrane-Interface Probe and confirmation sampling to determine the three-dimensional extent of PCE in groundwater and test the hydraulic conductivity of soil at various depths and locations.
Prepare a Remedial Action Plan with a feasibility evaluation that supported chemical injections to break down the dry cleaning solvents in place via enhanced reductive dechlorination with bioaugmentation.
Coordination with the local agencies, engineers, and specialized technical consultants during implementation of the selected remedial method: injection of a proprietary blend of chemicals and microbes to promote enhanced reductive dechlorination of dry cleaning-related chemicals.
Provide logistical and technical support during installation of remedial observation wells and chemical injections.
Conduct quarterly post-remediation groundwater monitoring to verify the effectiveness of the remedial effort to the satisfaction of the client and the California Regional Water Quality Control Board.

NEXT STEPS:

Groundwater monitoring data indicates significant source reduction is occurring within the dry cleaning solvent plume.
Continue groundwater monitoring until source area remediation goal is successfully met.
Request environmental case closure from the California Regional Water Quality Control Board.

CATEGORY OF SERVICE, LOCATION:

Remedial Excavation and Facilities Demolition Management and Site Closure, Santa Cruz, California

TYPE OF CLIENT:

Municipality

BACKGROUND:

City of Santa Cruz shooting range was shown to be impacted with hazardous levels of lead in soils. A Remedial Action Workplan called for excavation of 4,200 tons of lead-impacted soils, and disposal at Class I and II landfill facilities. In addition to performing the remedial excavation work, the City wanted to demolish and remove all shooting range structures and convert the land back into City Park natural open space. Trinity was contracted to review and help prepare the City’s excavation bid documents, recommend a contractor, and manage and oversee all aspects of the remediation contractor’s operations, on the City’s behalf.

CLIENT GOALS FOR PROJECT:

Provide supervision of remediation contractor, to validate costs incurred and seek cost-savings where possible, and to ensure compliance with State and Federal rules and regulations, the approved Remedial Action Plan, and Health and Safety Plan.

PROJECT APPROACH:

Trinity managed all aspects of the demolition and remedation project for the City including regulatory liaison, risk management, public interface and notifications, contractor coordination, scheduling and planning, field operations oversight and management; provided contract, unit price and change order oversight and management; and reviewed draft and final reports.
As a cost saving measure, Trinity recommended pre-profiling soils before beginning excavation activities. A pre-profiling plan was developed by Trinity and the contractor and implemented before excavation work progressed.

RESULTS, RESOLUTION, NEXT STEPS:

Pre-profiling data significantly reduced the volume of soils expected for excavation and disposal from 4,200 tons to 2,631 tons. Of this volume, 1,763 tons were disposed as non-RCRA hazardous waste at a Class II rather than Class I landfill.
Pre-profiling significantly reduced the cost of the project which allowed the City to add removal of the upper three feet of soil over the entire foot print of the gun range and perform additional grading, seeding and winterization work.
The project was completed 28% under budget including extras.
Regulatory site closure was received within six months after completion of field work.

CATEGORY OF SERVICE, LOCATION:

Soil Vapor Extraction System Operation and Maintenance, Monterey, California

TYPE OF CLIENT:

Underground Storage Tank (UST) Fund

BACKGROUND:

The site was formerly operated as a dry cleaner, with four USTs beneath the site from 1940s until 1963, when the property was purchased by our client. Based on former employee indications, the dry cleaning facility contained equipment commonly used with Stoddard solvent cleaning processes, and chlorinated solvents such as tetrachloroethene (PCE) were not used during the time of operation. The USTs were removed in 2000, a series of soil and groundwater investigations were conducted between 2000 and 2003 and a soil vapor extraction system was installed in 2004 under an approved Corrective Action Plan.

CLIENT GOALS FOR PROJECT:

Provide cost effective and responsive remedial system O&M for an occupied residential property.

PROJECT APPROACH:

As a cost savings measure, operate and maintain the SVE system during the low groundwater summer months and shut down the system during the higher groundwater winter months. Collect monthly depth‑to‑groundwater level readings to optimize system operation and shut down periods based on water levels in SVE wells.

RESULTS, RESOLUTION, NEXT STEPS:

SVE mass removal rates are maximized during summer lower groundwater level months. Additional shallow SVE wells installed and connected to the system to increase radius of influence in petroleum hydrocarbon-affected areas. System expansion is planned to include dual‑phase extraction to address impacted groundwater in plume core.
Trinity identified a sewer line leak in the plume area. The leak is a source of shallow groundwater in the affected area, and should be repaired to prevent further shallow groundwater impact.
Annual groundwater monitoring to evaluate system performance.

CATEGORY OF SERVICE, LOCATION:

Active Sub-Slab Vapor Depressurization System (design, construction, O&M), Alameda, CA

TYPE OF CLIENT:

Property Development/Management Company

BACKGROUND:

While reviewing the site for closure, Alameda County requested the collection of sub-slab vapor samples for volatile organic compound (VOC) and Stoddard Solvent analysis to determine if the former dry cleaning operations at the site affected soil beneath the building and resulted in the potential for vapors to migrate into the building. A sampling program was designed and implemented and sub-slab vapor results indicated elevated levels tetrachlorethene, vinyl chloride, carbon tetrachloride and Stoddard solvent were present beneath the building. Mitigation of the vapor intrusion risk to indoor air for the commercial building was warranted. A sub-slab depressurization pilot test was conducted, followed by the design and installation of an active sub-slab depressurization system.

CLIENT GOALS FOR PROJECT:

Mitigate the vapor intrusion risk to indoor air for the commercial building in the most cost-effective manner without significantly disturbing the building tenants or their business operations.

PROJECT APPROACH:

Trinity conducted a sub-slab depressurization pilot test during the weekend after business hours to determine if an active or passive system was needed to mitigate the vapor intrusion concern. Pilot test results indicated that an active sub-slab depressurization system (SSDS) with carbon abatement was needed for the site. The system was designed, permitted, installed and operated and maintained by Trinity.

RESULTS, RESOLUTION, NEXT STEPS:

The SSDS startup and continued operation was successful at mitigating the vapor intrusion pathway beneath the building. The SSDS system influent concentrations reduced significantly enough to cease carbon abatement before discharge to the atmosphere and modify the air permit from monthly to quarterly system monitoring.
The next step is to shut the SSDS down to evaluate rebound effects and determine if sub-slab VOC and Stoddard solvent concentrations are below closure action levels. A component of this phase will be to determine a site-specific attenuation factor to apply to the sub-slab vapor concentrations. Radon gas testing in the sub-slab vapor and inside the building are proposed in order to develop a suitable attenuation factor.