What is a QAPP? When I first heard the acronym a few years ago it sounded like something you may step in while mowing your yard if you have a dog, but it is not!
The South Carolina Department of Health and Environment Control (SCDHEC) revised their Quality Assurance Project Plan (QAPP) back in April of 2013 (first written in 2011) in which SCDHEC defines the QAPP as:
“A formal document describing in comprehensive detail the necessary quality assurance (QA), quality control (QC), and other technical activities that must be implemented to ensure that the results of the work performed will satisfy the stated performance criteria. The QAPP components are divided into four classes: 1) Project Management, 2) Measurement/Data Acquisition, 3) Assessment/Oversight, and 4) Data Validation and Usability.”
This 197 page document is the quality assurance bible for doing environmental work in South Carolina and similar documents exist in other states and at the Environmental Protection Agency (EPA).
But today I am going to focus on just one revision in the April 2013 document that relates to off gas controls being required while performing aggressive fluid vapor recovery (AFVR) events. The revision to the document includes the following text on page 84, #9:
- “If the air emissions are anticipated to have an adverse impact in the vicinity of the AFVR, the Agency may require off-gas treatment. The off-gas treatment must have a minimum 80% reduction rate.”
If you are recovering pure gasoline from the ground and blowing it into the air, there is going to be adverse impact to something or someone in the vicinity of the AFVR. The impact would be much less if you were recovering fuel oil or hydraulic oil, both of which are less volatile.
Ok that said, what is my point? There are only two good ways to treat this vapor. One, with granular activated carbon (GAC) or two, with a thermal or catalytic oxidizer. Both of these methods will reduce the emissions by 80% or more. The problems are in the logistics, as well as the cost to make this happen.
Treatment with Granular Activated Carbon (GAC)
The last rate document I saw listed $35/hour as the payment for adding treatment to an AFVR. GAC drums usually come in 55 gallon or 85 gallon sizes containing 200 pounds and 300 pounds of GAC respectively. The 85 gallons drums are what we typically see for this application because the 55 gallon drums are not rated for more than 200 cubic feet per minute (CFM) of air flow. The carbon with the drum typically cost about $2.50 per pound of carbon. Under ideal circumstances, GAC would be a good choice for treating off gas, but the AFVR systems used are less than ideal. Most remediation contractors use either a vacuum truck or a trailer mounted, oil sealed, liquid ring pump to achieve the required 250 CFM at 25 inches of mercury vacuum. These pumps typically have exhaust temperatures that range from 180°F to 400°F, which are way too hot for good carbon efficiency. Liquid ring pumps can produce an oil mist that will foul the GAC if the formation produces high flow resulting in lower vacuum pressures. And lastly, the reason the AFVR event is performed is due to the presence of light non-aqueous phase liquid (LNAPL), so the off gas typically contains very high concentrations of volatile hydrocarbons resulting in massive quantities of carbon(far more than $35/hour will buy) being used during a 96 hour event.
So to sum it up, the carbon usage could be very high due to heat or oil fouling drastically lowering efficiency. Even without either of these conditions, the high concentrations of volatile hydrocarbons will require large quantities of GAC to treat.
Treatment with Thermal and\or Catalytic Oxidizers
Thermal and\or catalytic oxidizers present a different set of problems. I am going to focus on thermal oxidizers because catalytic oxidizers can only handle 25% LEL typically, oil from LRP’s will damage the very expensive catalyst making the cost to operate even higher due to the power requirements of electric catalytic oxidizers. However, if you use an electric catalytic oxidizer with a lower horsepower claw pump which does not emit oil mist you would have a workable solution except for the LEL issue.
My thoughts relative to using thermal oxidizers are as follows:
- The rental\operation cost is way more than $35\hour. You typically have another trailer to mobilize, you need a propane or natural gas source and you need power to run it.
- The oil mist is less of an issue because the unit operates at 1400°F versus 600°F with the catalytic unit.
- Thermal oxidizers can typically handle up to 50% LEL of volatile hydrocarbons.
- Oxidizers in general take some adjusting to various situations and require an operator with more than average mechanical\electrical ability.
I do agree with SCDHEC that these vapors need to be treated having been at sites where the vapors were so strong you could see them in the air like a heat mirage on the road ahead of you in the summer. For decades these vapors have been put into the atmosphere in South Carolina, not to mention the health concerns of the equipment operators who have to be around them. I just believe the cost of treating these vapors need to be revisited and updated as well.
Brian E Chew Sr. P.G.