The Reynolds Group recently completed a Vapor Intrusion Mitigation (VIM) Feasibility Test. The objective of the test was to see if we could prevent the intrusion of PCE, a chlorinated solvent, into an occupied building by depressurizing the limited space between the building’s concrete slab on grade and the soil immediately beneath it. Typically, the source of chemical vapors that intrude into indoor environments is contaminated soil or contaminated groundwater. VIM is not considered a means of remediating the source of soil or groundwater contamination. The following is meant to provide information on Vapor Intrusion Mitigation.
DTSC and VIM
The DTSC developed a Vapor Intrusion Mitigation Advisory (VIMA, April 2009) to assist with selecting, designing, and implementing appropriate response actions for sites where a potential vapor intrusion risk has been identified for occupants of existing or future buildings. Responsible parties may use the VIMA when 1) risk according to vapor intrusion is estimated by modeling or indoor air sampling; and 2) mitigation is proposed as part of a response action. According to the DTSC 2005 and 2009 guidance documents, the responsible party may propose vapor intrusion mitigation as a pre-emptive solution for a perceived rather than actual threat.
VIM Methods for Existing Buildings
According to the DTSC 2009 VIMA, sub-slab depressurization systems (SSD) are most applicable for existing slab-on-grade building construction. This guidance is also contained in the Interstate Technology and Regulatory Counsel (ITRC) Technical and Regulatory Guidance document dated January 2007. A SSD system is designed to function by continuously creating a lower pressure directly underneath a building floor relative to the pressure within a building. The resulting sub-slab negative pressure inhibits soil gases from flowing into the building, thus reducing VOC entry into the building. VOCs caught in this negative pressure field are collected and piped to an ambient air discharge point. The vacuum or depressurization under the slab is typically accomplished with a motorized blower. The blower draws air from the soil beneath a building and discharges it to the atmosphere though a series of collection and discharge pipes. Other remedies in addition to, or as alternatives to, SSD systems are available to address site specific conditions including sealing cracks and openings in the building foundation/floor and adjusting the building HVAC systems or installing a new system to maintain positive pressure indoors relative to the sub-slab area.
VIM Feasibility Testing
The vacuum readings taken at the monitoring points showed that a small blower could be piped to two or three extraction points to create a vacuum under the entire building slab. Laboratory analyses of the extracted vapor stream showed the system was in fact recovering PCE. The PCE was captured by the carbon filters.
The results of the feasibility test showed that a small mitigation system could be installed and operated for a minimal cost to protect the building occupants from risks associated with vapor intrusion.
TRG assisted a property management company in the wrap up of a tenant lease in Beverly Hills. The former occupant operated a metal plating business in the leased space. As part of the wind down of the lease, the tenant was required to return the property to its original condition. The property manager had been working with another environmental consultant who had identified metals in the soil beneath the former plating operation. However, the property manager retained TRG to perform the cleanup of the property and obtain case closure from the Los Angeles County Fire Department HAZMAT Division.
Concentrations of contaminants such as chromium, copper, lead, nickel and zinc in the soil exceeded allowable limits and necessitated the physical excavation of the soils in order to clean up the site. Unfortunately, the impacted soils were beneath the building and below a shallow basement. Approximately 50 cubic yards of soil needed to be dug up, manifested and properly disposed of. TRG was able to mobilized specialized equipment to the site in order to excavate the contamination from the basement level and load it into bins for transport to an appropriate disposal facility. Confirmation sampling showed pockets of contamination still in place after the initial excavation, and additional spot excavation was performed. TRG reported on the excavation activities which confirmed the metals at the site are now below concentrations negotiated with the County Fire Department. Case closure is eminent.
As you may already be aware, The California UST Cleanup Fund is in the midst of changing its business model in order to manage its cash flow based on projected revenues for fiscal year 2011/12 which begins July 1st. The Fund now requires each claimant to provide a budget for the upcoming year’s assessment or cleanup/remediation activities. If budgets have not been submitted to the Fund, those sites will not receive reimbursements in the coming fiscal year. It is not clear at this point if the Fund will reimburse moneys spent equal to the submitted budgets.
The Fund is anticipating a dramatic decrease in revenues when AB1188 expires at the end of this calendar year. When AB1188 expires, the per gallon fee charged to UST operators will decrease from 2.0 cents per gallon to 1.4 cents per gallon. This 30% decrease coupled with dropping fuel sales as the price of gasoline remains above $4.00 per gallon will leave the Fund with a $126 million shortfall in FY 2011/12. The budgeting process the Fund is initiating is meant to address this shortfall.
Fund management has stated they expect to reveal the details of the new business model in May of this year. It is likely the improved cash management at the Fund will not alleviate the shortfall. It is also likely that assessments and cleanups will suffer delays due to lack of funding. As claimants fall behind on regulatory requirements to investigate and remediate soil and groundwater contamination, they risk falling out of compliance with regulatory agencies’ requirements.
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