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This story appears in the Nov. 16 print edition of Transport Topics.

The U.S. Environmental Protection Agency last week formally approved selective catalytic reduction to meet its 2010 emissions standard.

While SCR advocates said the EPA’s move effectively ends Navistar Inc.’s legal challenge to EPA’s guidance on using SCR, a spokes-man for the truck maker said it actually bolstered Navistar’s case.

Navistar has asked a federal court to review EPA’s guidance on SCR, saying that the technology — which its major competitors all plan to use in 2010 — would improperly allow trucks to exceed the emissions standard, because SCR works only if truck drivers maintain diesel ex-haust fluid in their truck tanks.

EPA announced in the Nov. 9 Federal Register that it approved “critical emission-related maintenance” for trucks using SCR, which re-moves nitrogen oxides from engine exhaust by injecting a urea/water fluid that interacts with a catalyst to remove NOx. Navistar is the only truck maker using exhaust gas recirculation instead of SCR to comply with EPA’s 2010 NOx emissions requirement.

Patrick Raher, a Washington attorney representing the SCR engine manufacturers, told Transport Topics the approval will strengthen the EPA and manufacturers’ legal arguments in Navistar’s federal lawsuit challenging EPA’s 2009 guidance on SCR technology.

“The decision drives a stake right in the heart of Navistar’s allegation that EPA does not believe SCR engine technology is adequate,” Raher said. “It also means that EPA has made an official determination under existing regulations SCR maintenance is similar to oil changes, spark plug changes and particulate matter trap maintenance.”

But Navistar spokesman Roy Wiley claimed EPA’s decision supports Navistar’s legal allegations.

“Basically, the item in the Federal Register confirms that urea-based SCR must depend upon the operator to comply with emissions regulations, because the urea tank is small,” Wiley said. “It acknowledges that SCR replenishment is considered a critical emissions-related maintenance.”

Wiley said that the EPA decision, which follows SCR guidance allowing the operation of the vehicle without urea for up to 1,000 miles or 20 hours, “if anything, seems to support the premise of our filing with the U.S. Court of Appeals.”

“We never argued that SCR-based technology using urea doesn’t work,” Wiley added. “We always said, ‘Wait a minute, you’ve got to have a full tank of urea.’ ”

In its lawsuit filed earlier this year, Navistar alleged that the SCR technologies are flawed because they require a driver to refill the diesel exhaust fluid tank. Without DEF, the SCR system cannot meet the 2010 standard, Navistar said.

Navistar also claimed in its lawsuit that EPA had reversed its position on SCR technologies and did not follow proper rulemaking procedures in setting out the SCR requirements outlined in a February guidance document.

John Walsh, a spokesman for Mack Trucks, said the company is “pleased the agency has approved the industry’s responsible and comprehensive approach to this issue.”

“We are pleased EPA recognized the value of our common-sense approach to implementing this important environmental standard,” said Jim McNamara, a spokesman for Volvo Trucks North America.

EPA declined to comment.

The EPA approval was in re-sponse to requests from the Engine Manufacturers Association and two SCR engine makers, Cummins Inc. and Volvo Powertrain. EPA said EMA’s June petition for approval was on behalf of all its members, which include all the manufacturers now planning to use the SCR technologies.

To gain EPA approval, the SCR engine makers were required to demonstrate a “reasonable likelihood” the required maintenance would be performed.

EPA limited its approval of SCR technology to engine model years 2009-11, saying it would “revisit” the issue after 2011. “The agency has limited this approval to model years 2009 to 2011 due to the expectation that SCR-related technologies and the urea infrastructure will continue to develop and mature,” EPA said in its decision document.

The approval was required be-cause EPA has considered “diesel exhaust fluid refills a new type of maintenance uniquely associated with SCR systems.”

EPA noted that it had confidence in the SCR technologies because they include a “constantly viewable DEF level indicator gauge or other mechanism on the dashboard that will notify the driver of the DEF fill level.”

To make sure a driver won’t continue to run the truck after the DEF tank has been empty for a certain number of miles, “Vehicle performance will simultaneously deteriorate to a point unacceptable for typical driving,” EPA said.

In its request for approval, EMA conceded that the frequency of filling DEF tanks, which, on most trucks, would be required at intervals equal to two or three times the distance the truck can travel on a tank of diesel fuel, was limited, because “longer intervals would require larger and heavier trucks.”

“Because of the inherent space and weight constraints in the configuration and efficient operation of heavy-duty on-highway vehicles, there are inherent limits of the size of the DEF tanks that can be installed as components of SCR-based systems,” Jed Mandel, president of EMA, said in the petition letter.