- Remediation & Closure - Hayward
Burns & McDonnell successfully obtained site closure after years of site investigations, remediation and environmental compliance at a freight facility in Hayward, California.
Following a release of diesel at the site, seven underground storage tanks (UST) were removed. At that time, up to five feet of light non-aqueous phase liquids (LNAPL) was observed in the subsurface. After UST removal, a soil vapor extraction (SVE) system was installed. SVE proved useful, but not effective enough for full remediation. In October 2007, the client expressed a desire to move forward with full remediation at the site.
Burns & McDonnell investigated potential remedial options to address the soil and groundwater contamination at the site originating from releases of total petroleum hydrocarbons (TPH) from leaking USTs. Burns & McDonnell chose dual-phase vacuum extraction (DPVE) as the remedial method, and in 2008 conducted a pilot test to assess its suitability as a full-scale remedial application after concurrence of the Alameda County Water District (ACWD).
- Regulatory agency negotiation
- Environmental compliance
- Remedial design
- Dual-phase vacuum extraction (DPVE)
- Groundwater recovery and soil remediation
- Remediation system design and construction
- Remediation system operation and maintenance
- Barry Keene Underground Storage Tank Cleanup Fund Act
During the pilot test, DPVE was applied to wells screened from approximately 5 to 20 feet below ground surface (bgs). The wells were terminated in silty sands and were anticipated to produce moderate amounts of water. The wells produced relatively high amounts of groundwater during the pilot test. The results of the pilot test indicated that DPVE was an effective means of contaminant reduction within the former UST source area of the site.
The ACWD granted approval of a DPVE remedial system for the site in September 2008. The design of the full-scale DPVE system was to treat a source area encompassing about 128,000 square feet, including a total of 10 extraction wells. Installation of seven new DPVE wells to complement the three pilot test wells occurred in early 2009. Because of the City of Hayward Sanitary District groundwater discharge limitation of 10,000 gallons per day and the relatively high extraction well groundwater recovery rates observed during the pilot test, the full-scale DPVE system was designed to continuously apply DPVE to approximately three wells, with the system equipped with automated cycling capability to alternate DPVE efforts among multiple groups of wells. A "cycling" approach allowed for the application of DPVE to all 10 full-scale extraction wells without exceeding the maximum allowable daily discharge volume. This approach was designed to increase the efficiency of free product hydrocarbon (FPH) recovery and soil vapor recovery from zones of reduced permeability, as wells are allowed to remain idle and accumulate FPH and concentrated vapors. Extraction well grouping, cycle timing, stinger depths, and applied vacuum levels were designed to be monitored and adjusted during system startup and continued operation to optimize performance and ensure that groundwater recovery from individual extraction wells did not cause an exceedance of the allowable discharge volume.
In May 2013, the state of California agreed to close the site using the Low-Threat UST Case Closure Policy initiated by the state in 2012. In September 2013, Burns & McDonnell and the client obtained no-further-action concurrence from the state and formally abandoned the monitoring wells in February 2014. Burns & McDonnell also aided this client in obtaining reimbursements from the state of California UST fund for services related to this release.
The design of the trailer unit included a DPVE intake manifold system, a dual-tank vapor/liquid separation (VLS) system, two vacuum pumps, an air compressor, a ventilation system, and associated control valves and electrical controls. Discharge water and emissions treatment equipment were planned to be staged outside of the equipment trailer. The system included a supervisory control and data acquisition (SCADA) system allowing personnel to remotely monitor system performance, control system operation and download operational data, along with a programmable logic controller (PLC) for system operation. The equipment trailer was designed to contain all mechanical and electrical controls necessary to operate and monitor the remediation system locally and remotely.