SPCC Containment Stormwater Discharge

[brodgers]

I am reviewing the retrofitting of remote electrical transformer substations for compliance with the SPCC rules and have a couple of questions. First, containment structures for new transformers are easily built during the station construction, but for retrofitting – a complete concrete structure is not practical. I am aware of options presented in 112.7(c), but what seems to be the precedent in the utility industry? Concrete curbing?
Secondly, in the regulations “Section by Section Analysis”, in 112.8(b)(2) – EPA says ”This rule does not preclude innovative devices..” regarding the use of imbiber beads, or assumingly chemical check valves, for discharging accumulated stormwater from containment structures. It is the manufactures opinion that chemical check-valves can be used to passively discharge accumulated stormwater from containment structures, but the rules specially state that “you must inspect and may drain accumulated stormwater” and keep adequate records of that event, which is not feasible using these passive drainage devises. Bottom line, it seems that EPA is saying that you can install the innovative devise, but you must operate it like a manual open/close valve. The valve manufactures say they are selling the valves for SPCC compliance but that seems contrary to what the regs allow, unless, the users are proposing this under the exception portion of the rule. Any thoughts?

 

[wbd]

We have some older substations where the transformers do not have any containment. What we depend on is the gravel inside the station containing the oil by the oil adhering to the gravel and slowing runoff and absorption into soil. Yes, in case of a rupture, there will be a lot of clean up but that is weighed against the risk.

 

[brodgers]

I have spoken to US EPA Region 4's SPCC Program Administer about that. While US EPA will basically accept the approach signed off by the PE, in the event that oil reaches a watercourse, the utility and signing PE can expected to be held accountable during the penalty phase of the response. In the past, the utilities have argued that transformers are not bulk storage tanks, and the EPA recently agreed. But by doing so, they also said that transformers must meet the general containment rule 112.7(c), and that the "gravel retardation media" is NOT an acceptable form of "containment." While I agree that precedent indicates that the gravel beds do a pretty good job of retarding any migration of oil considering the risk that oil poses, it seems that EPA does not.

 

[stevenal]

Both for new installations and for retrofitting we attach a liner to the transformer pad. The liners drain to gravity oil separation tanks.

The requirement for manual valves is waived if water is directed to a wastewater treatment facility. But what other treatment is needed for oil contaminated water other than oil removal. I guess I would suggest that the chemical check valve itself constitutes the treatment facility. Anyone buying?

 

[powerrus]

I have also recently compared the provisions of 40 CFR 112 against existing substation designs.

stevenal, are the oil/water separators adequate to contain oil from the single largest container volume? That would make for an extremely large tank for sites with large transformers. If not, is the maximum expected size of an oil discharge reduced through operational procedures (early notification by SCADA, etc.)?

 

[brodgers]

Secondary containment for electrical transformers is governed by the general containment rule, 40 CFR 112.7, not 112.8 - which deals more or less with bulk storage containers. Therefore, the size of a containment or processing of that containment is not required to be the volume of the largest vessel within the containment structure, rather an "adeqauete" volume determined by the PE. If historical precedent leads the PE to believe that a smaller volume of oil than the container volume should be chosen as the design criteria, they are free to design it that way.

 

[stevenal]

Powerrus,

Yes, we completely contain the volume of the single largest transformer at the site. A big tank isn't needed, a number of smaller ones will do. We series up the number required. I'm not sure you could rely on operational procedures to limit the spill in this regard. You could isolate the radiators, but what if they shoot the main tank? Several times. What flow rate and response time do you design for? Don't forget about vacations.

 

[powerrus]

Thanks, brodgers, I see your point. I initially assumed that 112.7(c) pertained to the largest potential discharge source. Upon closer examination, that is not correct.

What logic is generally used to design retention systems for a volume of oil that is less than the largest transformer? Are oil retention volumes based primarily on historical precedence and utility experience in these cases?

 

[brodgers]

Since 112.7(c) is designed to prevent releases from entering a watercourse and therefore the risk factor, the proximity to a watercourse would probably be the critical factor for the design basis. If the distribution or substation was built adjacent to a watercourse, I think 100% plus freeboard would probably be prudent. The further away you get from a watercourse, you made tradeoff containment or the method of containment based on reduced risk. Would you install a concrete containment structure around a transformer adjacent to a major watercourse? Probably. At the same time, remove the watercourse and you may just locally grade the site to drain into a retention basis. This are some of the issues I am struggling with as we evaluate upgrading a large number of transformer sites for compliance with the August 2006 requirement and a reason for joining this board. I plan on developing a pretty basic risk screening tool to score each site and use that risk score to narrow the options for containment. As I said in an earlier post, interested in what others are doing for retrofitting transformer for containment before we finalize our standard design approaches.