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A Hach Model 2100A Turbidimeter was used to estimate turbidity. The measured
turbidity of a distilled water sample was used as a blank for sample analysis. Turbidity
readings were obtained from the appropriate primary and secondary scales. Values are
reported in nephelometric turbidity units (NTU's). Duplicate analyses were conducted for
every tenth sample. The average value was reported for duplicate analyses.
Dilution was used for highly turbid samples to bring the sample into the
instrument range. The measured turbidity was multiplied by the dilution factor to obtain
corrected turbidity values for the original sample.
Suspended Particle Size Classification
Particle size influences the primary functional mechanisms for control. Therefore,
some insight regarding particle size of the suspended solids is required to successfully
evaluate the performance of the system.
A method for approximating the percentage of silt and clay particles and the
percentage of particles larger than silts was developed. Each sample was evaluated for
TSS as collected or as composited according to the procedure described previously.
Subsequently, the sample was reanalyzed for TSS after passing the sample through a U.S.
Standard number 230 sieve with nominal openings of 63 mm. The formula for
percentage of silts and clays:
TSS B - TSS A
% = 100 - ( x 100)
TSS B
where: TSS B = TSS before #230 sieving (mg/L) and
TSS A = TSS after #230 sieving (mg/L).
In reality, this estimate is conservative. AASHTO classifies silts and clays as those
particles smaller than 75 mm. Wet sieving results in some particle adherence to the
screen.
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