A 40-year environmental liability resolved through targeted excavation, regulatory collaboration, and rigorous quality assurance.
PEC was engaged to serve as the lead environmental consultant for the remedial action completion activities at a former bulk petroleum storage and distribution terminal in California — a property with an environmental history spanning more than four decades.
The facility had operated as a major fuel terminal since the early 1940s, storing and distributing regular unleaded gasoline, premium unleaded gasoline, ethanol, low-sulfur diesel, diesel, and fuel additives. Following the terminal's decommissioning and demolition, elevated concentrations of total petroleum hydrocarbons as diesel and motor oil (TPH-d and TPH-mo) were identified in shallow soils within the former tank farm area, exceeding residential environmental screening levels (ESLs) established for future redevelopment.
PEC managed all phases of the project — from regulatory coordination and pre-field planning through excavation oversight, confirmatory sampling, backfill, and final reporting — delivering a successful remedial closure and a risk-based No Further Action Determination from the State Regional Water Quality Control Board.
The subject property was a bulk fuel storage and distribution facility that had been in operation since the early 1940s. At its peak, the terminal comprised approximately 15 to 17 aboveground storage tanks (ASTs) — including 12 fuel ASTs, one vapor AST, and four fuel additive ASTs — as well as a truck loading rack, a railroad tank car loading dock, and a barge facility. Products stored and distributed included regular unleaded gasoline, premium unleaded gasoline, ethanol, low-sulfur diesel, diesel, and various fuel additives.
Environmental investigations at the property began in 1984 following the discovery of a product release near the truck loading rack area. Over the subsequent four decades, the property was subject to extensive investigation, monitoring, and remediation activities, including:
Product release identified near the truck loading rack. A nationwide groundwater monitoring program was implemented, and 30+ monitoring wells were installed. Separate phase hydrocarbons (SPH) were detected in multiple wells, with a maximum SPH thickness of 6.2 feet. Potential source areas identified included the former railroad tank car loading rack, diesel dispensers, vapor recovery system release area, and underground product delivery lines.
Groundwater extraction (GWE) pumps were installed to recover SPH and impacted groundwater. A Soil Vapor Extraction (SVE) system was commissioned using a thermal oxidizer, achieving a TPHg destruction efficiency of 93%. The SVE system operated continuously from 1996 onward, significantly reducing vadose zone petroleum impacts.
Ongoing semi-annual groundwater monitoring demonstrated consistent reduction and stabilization of the dissolved-phase petroleum plume. Benzene concentrations in select wells remained above California MCL (1.0 µg/L). The SVE system was eventually shut down following demonstration of asymptotic conditions. Regulatory oversight continued under the State Regional Water Quality Control Board.
All above-ground infrastructure — including ASTs, associated piping, secondary containment, office and warehouse structures — was demolished and removed. A 10,000-gallon underground storage tank (Slop Tank) was removed under PEC oversight, receiving a No Further Action certificate. PEC conducted a comprehensive 2022 Remedial Investigation (RI), advancing Geoprobe® soil borings, temporary groundwater monitoring wells, shallow and deep soil vapor probes, and CPT probes to characterize subsurface conditions.
PEC completed a comprehensive Additional Remedial Investigation, Feasibility Study, and Remedial Action Plan (RAP), incorporating a Site Conceptual Model (SCM). The State Regional Water Quality Control Board concurred with PEC's recommendation that limited excavation of shallow soils — to a depth of 10 feet below ground surface — was the most appropriate remedial approach to address elevated TPH-d and TPH-mo concentrations in the former tank farm area and reduce future development risks.
PEC managed all pre-field activities, excavation oversight, confirmatory sampling, backfill, compaction, and final reporting. The Remedial Action Completion Report was submitted to the State Regional Water Quality Control Board in August 2024.
The remedial challenge at this site was multifaceted. Decades of petroleum storage and distribution had resulted in a complex subsurface environment with multiple overlapping source areas, a large dissolved-phase groundwater plume, and heterogeneous soil conditions that made field screening difficult. Key challenges included:
PEC was engaged as lead environmental consultant beginning in 2021, taking over a complex, decades-long remediation program and guiding it through to successful regulatory closure. The following summarizes PEC's complete scope of work across all project phases.
PEC supervised the removal of a 10,000-gallon double-walled fiberglass underground storage tank (the "Slop Tank") and associated below-grade conveyances and piping infrastructure. Following removal, PEC prepared and submitted the Underground Storage Tank Removal Report to the County Environmental Health Division (EHD) and successfully obtained a No Further Action (NFA) Certificate for the former Slop Tank — February 16, 2022.
PEC conducted a comprehensive inventory of all onsite and offsite groundwater monitoring wells, locating and assessing the viability of each of the 30+ wells associated with the property. PEC identified three wells that were buried or damaged during demolition activities. Working with a licensed surveyor, PEC located and uncovered two buried wells, repaired one well casing, and coordinated the abandonment and replacement of a well damaged beyond repair — ensuring the integrity of the full monitoring network.
PEC prepared and submitted a Groundwater Monitoring Well Abandonment & Installation Workplan to the State RWQCB, received regulatory approval within one week, and oversaw the abandonment of the damaged well by over-drilling to 40 feet and grouting. A new replacement well was advanced, completed, and surveyed. PEC prepared the Well Abandonment and Installation Report and submitted it to the RWQCB under separate cover.
PEC prepared and submitted both the First Quarter and Second Half 2022 Groundwater Monitoring and Sampling Program (GWMSP) reports to the RWQCB. PEC managed field contractor coordination, data review, and regulatory reporting for 31–32 monitoring wells, tracking dissolved-phase TPHd, TPHg, BTEX, MTBE, TBA, and separate phase hydrocarbon (SPH) conditions across the full monitoring network.
PEC prepared the Remedial Investigation Work Plan (RIWP), received RWQCB approval, and oversaw the completion of the full field program between August and September 2022. The 2022 RI included:
PEC directed the preparation of a three-dimensional subsurface model of the property using Earth Volumetric Studio™ (EVS) software. Using kriging — a stochastic spatial interpolation technique — the model mapped 3D analytical data onto volumetric grids to depict:
The 3D model was a critical tool in delineating the soil excavation limits and demonstrating that the groundwater plume was contained onsite.
PEC developed and updated the Site Conceptual Model (SCM) for the property, integrating all historical and current investigation data to characterize:
PEC's SCM and RI reports incorporated a comprehensive fate and transport analysis of the dissolved-phase petroleum hydrocarbon plume, evaluating:
In response to RWQCB data gap requests, PEC conducted a second comprehensive RI in June 2023, including:
Based on the 2023 RI data and updated SCM, PEC determined that no significant changes were warranted to the Feasibility Study or Draft RAP. The final 2023 RI report was submitted to the RWQCB on August 24, 2023.
PEC conducted a fourth-quarter soil vapor sampling program in November 2023 to address RWQCB comments regarding PCE and its degradation compounds. PEC supervised the purging and sampling of 14 vapor wells, evaluated results against commercial and residential ESLs, and concluded:
PEC prepared the Draft RAP and final RAP/RAW, which was approved by the RWQCB in March 2024. The RAP/RAW defined the remedial objectives, excavation limits, waste disposal strategy, and backfill specifications. PEC and the project team then tendered and selected an excavation contractor and laboratory to execute the remedial work.
PEC managed all pre-field activities, including Health and Safety Plan (HASP) preparation, Sampling and Analysis Plan (SAP) development, laboratory supply coordination, grading and excavation permit applications, fire hydrant use permits, 72-hour regulatory notifications to the RWQCB and Air Quality District, Dig Alert / 811 utility clearance, and Ground Penetrating Radar (GPR) clearance for active utilities.
PEC advanced six hand-augured borings and analyzed samples using a calibrated PetroFlag® Analyzer (Response Setting 5 — Diesel Fuel) and a California ELAP-certified laboratory. This established field screening benchmarks to guide real-time excavation decisions. Waste characterization samples were submitted to and approved by the disposal facility prior to excavation commencement, including California Title 22 metals analysis and STLC testing for an anomalous lead result.
PEC oversaw all active field operations, including excavation of approximately 1,240 cubic yards of impacted soil, continuous PID air monitoring, and collection of 32 confirmatory soil samples from excavation sidewalls and bottom. Three bottom locations that initially exceeded ESLs were addressed through targeted additional removal. All final confirmation samples met residential ESLs.
PEC oversaw the export of 1,284.69 tons of impacted soil in 56 truckloads to a licensed Class III landfill, and the import and compaction of 1,114.47 tons of virgin quarry fill. Compaction was verified to 90% per ASTM D1557 by a licensed geotechnical firm. The site was rough-graded and resurfaced with bark mulch.
In February 2024, PEC prepared and submitted a proposed Monitoring and Reporting Program (MRP) for Monitored Natural Attenuation (MNA) to the RWQCB, recommending transition of the property to long-term passive monitoring. PEC proposed the abandonment of 13 redundant monitoring wells and outlined a streamlined annual monitoring program. The RWQCB concurred with PEC's recommendation that passive remediation through MNA is appropriate for the groundwater plume.
PEC prepared and submitted the comprehensive Remedial Action Completion Report to the State Regional Water Quality Control Board, documenting all field activities, analytical results, quality assurance data, and closure recommendations — including proposed property deed restrictions and a Soils Management Plan for future redevelopment.
Following the successful completion of active remediation and submission of the Remedial Action Completion Report, PEC worked with the State Regional Water Quality Control Board to achieve the project's ultimate regulatory objective: a risk-based No Further Action (NFA) Determination for the subject property.
The State Regional Water Quality Control Board issued a risk-based No Further Action Determination for the subject property, acknowledging that concentrations of contaminants of environmental concern (COECs) remaining in soil and groundwater beneath the property do not pose a direct threat to human health or the environment under the approved land use conditions. This determination formally closed the active remediation phase of the project and transitioned the site to long-term monitored natural attenuation.
The NFA Determination was conditioned upon the following property deed restrictions and covenants, which PEC recommended and successfully negotiated with the regulatory agency:
The deed restriction expressly prohibits the installation of drinking water production wells on the subject property. This restriction protects future occupants and the public from potential exposure to residual dissolved-phase petroleum hydrocarbons remaining in groundwater beneath the property, which continue to undergo natural attenuation.
The property is subject to an ongoing annual groundwater monitoring program under a Monitored Natural Attenuation (MNA) framework, as approved by the RWQCB. PEC's proposed MRP for MNA — submitted in February 2024 — established a streamlined annual monitoring schedule to track the continued decline of dissolved-phase COECs and confirm the absence of offsite migration above regulatory thresholds.
Future redevelopment of the property is restricted to commercial or mixed-use development, with the requirement that the ground floor (first floor) be dedicated to commercial use. This restriction ensures that the most sensitive land use receptors — residential occupants — are not placed at ground level where residual soil vapor concentrations could present a potential exposure pathway, and is consistent with the risk-based ESLs used to evaluate the site.
Prior to and during any future redevelopment activities, the property owner is required to:
Over three years of engagement, PEC delivered exceptional value to the project team and property owner through:
PEC's turnkey site characterization and remediation capabilities — from initial investigation through regulatory closure — were central to this project's success. Learn More →
PEC's UAS and GPS capabilities provided real-time aerial oversight of excavation and remediation activities, supporting field decision-making and documentation throughout the project. Learn More →
This project exemplifies PEC's collaborative model — working alongside a national environmental consulting firm to deliver seamless, client-focused service. Learn More →