Texas Natural Resource Conservation Commission Interoffice Memorandum Office of Air Quality, New Source Review Program Mechanical Section Memorandum Date: October 18, 1995 Policy No.: 19 From: David Lusk Approved by: Gary Wallin, P.E., Section Manager Subject: Approving Asphalt Concrete Plant Additives Under S.E. 106 Policy: Standard Exemption 106 may be used to authorize use of additives to asphalt concrete mixes provided the emissions meet the requirements of the exemption. Additives are limited to anti-strip chemicals, styrene butyl rubber (SBR-latex), styrene butadiene styrene (SBS), other equivalents, and recycled asphalt products (RAP) when introduced into the drum. Modified recycled tire rubber (crumb rubber) is specifically excluded because the emission rates associated with this material would limit production rates to an impractical level. Background: Asphalt concrete plants and the use of additives are authorized by Standard Exemption 99. Since no standard exemption specifically authorizes changes to the mix formulas for existing facilities, S.E. 106 can be applied. S.E. 106 was created to exempt minor modifications to existing facilities. Crushing operations associated with the Asphalt Concrete Plant would be subjected to permit or exemption under S.E. 73 for rock crushers. Manufacturers' lab analysis for anti-strip additives resulted in a very small percentage of the anti-strip product in emissions. In one anti-strip manufacturer's lab analysis, approximately 0.4% anti-strip by weight became volatile and was emitted. Results, in some cases, were not ever quantifiable because of water gain in the sample. For a typical operation, anti-strip additives are about 1% by weight of the liquid asphalt. Based on the lab analysis and if 0.4% were to be most severe contributor of emissions, then an asphalt concrete plant with these characteristics would conservatively be allowed a maximum production rate of 250 tons per year. Based on the Mechanical Section engineering experience and judgement, most asphalt concrete plants, although producing more per hour, have fewer emissions and can be authorized for anti-strip additives under S.E. 106(d) for compounds with no L value listed. See sample calculations below: Assumptions: 5% of total mix is liquid asphalt 1% of liquid asphalt is anti-strip 0.4% of anti-strip is volatilized (conservative fraction) Emissions = 0.05 x 0.01 x 0.004 x 250 tons/hour x 2000 #/ton = 1 #/hr Manufacturers' lab analysis for other common additives ( SBS, SBR, Gilsonite, EVA, etc.) resulted in no significant, measurable emissions. These additives are typically 6 to 10% of the liquid asphalt which constitute about 5% of the total mix. Quantifying emissions from additives like these is difficult, if not impossible, for several reasons: 1) According to MSDS information, these compounds are stable at storage and mixing temperatures, 2) Manufacturers have shown that the character of emissions from these compounds is undistinguishable from unmodified asphalt, and 3) Laboratory analysis has demonstrated that emissions from these materials were below detectable levels with the equipment and operating temperatures of ACP. Based on this information, S.E. 106 (d) for compounds with no L value would be used. Stack sampling results while using RAP into the asphalt concrete mixes are not statistically different than that of virgin aggregate provided the material is introduced into the drum section and shielded from the flame. Since RAP displaces aggregate on a one to one basis, no new emissions are expected from handling the RAP. Crushing of material is not allowed under this exemption and must be qualified under the appropriate exemption (#73). Note: Some facilities disconglomerate or break up recycled asphalt material with a reclaimer. A "reclaimer", by definition, is not a crusher. If the applicant can justify the function of such equipment and quantify emissions, this equipment can be qualified for S.E. 106 when emissions are less than 6#/hr of the listed pollutant, i.e. limestone. Necessary Action(s): Obtain documentation from the company establishing that additives will not create emissions greater than one pound per hour. This can be accomplished through calculations or a statement to this effect. Some anti-strip amine based additives have offensive odors and may contribute to nuisance conditions. The applicant must use a low or no odor material if nuisance conditions exist. In the event the facility applies for a permit or is subject to a permit renewal, the operations authorized under S.E. 106 shall be incorporated into the permit per the requirements of 116.211, (d), with no changes to the maximum allowable emissions rates table (MAERT). Cold mix and rubber modified (crumb rubber) mixes production at asphalt concrete plants cannot be authorized under this standard exemption due to higher than allowed emission rates. The facility would have to produce less than 1 ton of mix per hour to qualify. These mix types may be authorized under S.E. 99. cc: All Mechanical Section