(a) monitoring of emissions for toxic air contaminants or surrogates thereof where appropriate to determine permit compliance at least twice during the first year of operation and after any detection of permit violations, and at least annually thereafter; such monitoring to include provisions for use of statistically valid sampling procedures in all monitoring; and
(b) sampling and testing of ash and dust residues at least semi-annually, pursuant to a method assuring statistical validity, to determine appropriate disposition or disposal based on relative toxicity.