Samples of soil and sediments from Gelang Patah, as well as a few soil samples from a new commercial aquaculture facility in Malaysia and a government aquaculture research station in Thailand, were shipped to Lamont-Doherty Geological Observatory after the consultants' field work was completed. They ground these samples to a fine powder with a mortar and pestle and added known amounts of pyrite powder (prepared from a large single crystal of FeS2) to subsamples of each large sample. Reaction of hydrogen peroxide (H2O2) with these samples resulted in pH values ranging from 1.5 to 3.8 (Table 8). Titration of the acid solutions back to pH 7 with NaOH was used to measure the total acidity yield from each oxidized sample. In general, samples with the lowest pH values had the highest acidity (Fig. 4), as would be expected. The consultants used several oxidation procedures, varying the proportions of sample and peroxide and the time for reaction to occur. The most practical and reproducible sample weight and peroxide volume for their experiments were 0.5 g (dry weight) and 20 ml (Table 9), although there was substantial variation in replicates analysed by all of their procedures. The total acidity for a dike soil sample near Pond 29 was 10 meq/100 g (M-2a, b, c), while sediment from Pond 29 was 20 meq/100 g (M-3a, b, c), and dike soil from a new area of commercial ponds was 100–150 meq/100 g (M-4, 4'). Dike soil from Thailand (T-1 and T-2), with the exception of one sample which cannot be explained at present, was <0.4 meq/100 g. Yields of acidity from addition of known amounts of pyrite powder to these samples ranged from about 30 to 100 percent, assuming 4 equivalents of H+ are produced from 1 mole of FeS2 (Table 10).
Potential acidity measurements on Gelang Patah dike soil and pond sediments by Mr Rosly ben Hassan in November 1981 ranged from 65 to 150 meq/100 g, using a titration end point pH of 8.5. If these values were decreased in proportion to titration values measured here for pH 7 (Table 11) they would still be substantially higher than the consultants observed. Thus the large samples of soil and sediment they collected from Pond 29 appear to have lower acidity potential than is typical of much of the Gelang Patah pond area.
