Remediation System Operations And Maintenance

 
 

CATEGORY OF SERVICE, LOCATION:

Groundwater Extraction and Treatment System Operation and Maintenance, Hollister, California

TYPE OF CLIENT:

Former Ordnance Manufacturer

BACKGROUND:

A groundwater extraction and treatment system (GETS) was installed at the site to remove trichloroethene, perchlorate and hexavalent chromium from groundwater in the center of the contaminant plume near the property boundary.  Treated water is re-injected into a deeper groundwater zone through an on‑site re-injection well under permit with the Central Coast Regional Water Quality Control Board (CCRWQCB).  Bi-weekly operation and maintenance (O&M) and treatment system performance sampling are required to document the treatment system performance.

CLIENT GOALS FOR PROJECT:

To cost effectively perform bi-weekly O&M and system performance sampling to keep the GETS running with minimal down.  (I didn’t think that discharge limits existed.)

PROJECT APPROACH:

Assign one senior O&M technician and one senior professional to the project to allocate responsibility for achieving client goals, build and maintain consistency and minimize redundancy.  Consistently conduct weekly conference call meetings to update client on system performance and bi-weekly staff meetings to problem solve, communicate upcoming system needs and to determine ways to avoid system performance deficiencies or failures.

RESULTS, RESOLUTION, NEXT STEPS:

  • GETS system performance per CCRWQCB permit requirements have consistently been achieved; Trinity’s cost savings to client of $20,000 annually based on yearly budgets from other firms for previous years.

 
 

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.

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.