The Bathing Water Regulations 2013

Methodology U.K.

2.—(1) In this Schedule, “percentile value” is based on a percentile evaluation of the log₁₀ normal probability density function of microbiological data used for the assessment under regulation 10.

(2) The appropriate agency must derive a percentile value as follows—

(a) take the log₁₀ value of all bacterial concentrations in the data sequence to be evaluated or, if a zero value is obtained, take the log₁₀ value of the minimum detection limit of the analytical method used;

(b) calculate the arithmetic mean (“�”) of the log₁₀ values taken under paragraph (a);

(c) calculate the standard deviation (“�?”) of the log₁₀ values taken under paragraph (a);

(d) derive the upper 90-percentile point of the data probability density function from the following equation: upper 90-percentile = antilog (� + 1.282 �?); and

(e) derive the upper 95-percentile point of the data probability density function from the following equation: upper 95-percentile = antilog (� + 1.65 �?).