An owner who proposes to alter, or rerate an existing wastewater
treatment facility, or to obtain approval for an existing wastewater
treatment facility after that wastewater treatment facility's permit
has expired, is required to use the wastewater treatment facility's
current operating data for flow and organic loading (biochemical oxygen
demand or carbonaceous biochemical oxygen demand, total suspended
solids, and ammonia nitrogen, as required by the permit) as the design
basis. The compiled data must meet the criteria outlined in paragraphs
(1) and (2) of this section.
(1) Flows.
(A) When an existing wastewater treatment facility
is to be rerated or altered, the wastewater treatment facility's
data for the last five years must be used to determine the annual
average flow, the maximum monthly average flow, the peak flow, the
ratio of maximum monthly average flow to annual average flow, and
the ratio of the peak flow to the annual average flow. All flow data
for these analyses must be collected by a totalizing meter. If the
wastewater treatment facility is less than five years old, all existing
data must be used. All calculations and assumptions must be included
in the engineering report.
(B) An analysis of the peak flow must be based on a
frequency distribution analysis using flow charts for each individual
day.
(C) The projected peak flow must be the result of collection
system monitoring or modeling based on a twoyear, 24hour storm event
for the service area.
(D) For a wastewater treatment facility that will not
be affected by future growth, the design flow for a rerating or alteration
must be calculated using the wastewater treatment facility's average
flow plus one standard deviation.
(E) For a wastewater treatment facility that will be
affected by future growth, the design flow for a rerating or alteration
must be based on future flow, calculated using anticipated changes
from the existing flow. The design analysis may use a linear regression
or other appropriate statistical method for predicting the design
flow when significant data exists.
(2) Organic loadings.
(A) When an existing wastewater treatment facility
is to be rerated or altered, the design organic loading must be calculated
based on the average daily organic loading.
(i) The data used to determine the organic loading
must be from the analyses of at least three composite samples of the
influent wastewater per week, taken during days with representative
flow, for a period of at least one year. If samples are collected
at a frequency of less than three times per week or less than a threepart
composite sample, the executive director may require an owner to collect
and analyze additional samples that are representative of actual conditions
at the wastewater treatment facility. The data must include samples
collected during both wet and dry weather conditions.
(ii) If the samples are not 24hour flowweighted composite
samples, the samples must be representative of the peak loading.
(iii) Sample data must include the following parameters,
at a minimum, unless monitoring of the parameter is not required by
the wastewater permit:
(I) fiveday carbonaceous biochemical oxygen demand
or fiveday biochemical oxygen demand;
(II) total suspended solids; and
(III) ammonianitrogen.
(B) The owner must provide an engineering analysis
for the minimum sampling period in the engineering report, which must
include:
(i) a summary of the monthly data;
(ii) the average monthly load; and
(iii) the standard deviation of the monthly data.
(C) For a wastewater treatment facility that will not
be affected by future growth, the design organic loading for a rerating
or alteration must be calculated using the wastewater treatment facility's
average organic loading plus one standard deviation.
(D) For a wastewater treatment facility that will be
affected by future growth, the design organic loading for a rerating
or alteration must be based on future loading calculated using anticipated
changes from the existing loading. The design analysis may use a linear
regression or other appropriate statistical method for predicting
the design organic load when significant data exists.
(E) The design organic loading must be used to determine
the required size of each treatment unit that provides treatment of
organic waste.
