Illinois Administrative Code › Title 35 - ENVIRONMENTAL PROTECTION › Part 302 - WATER QUALITY STANDARDS › Subpart E - LAKE MICHIGAN BASIN WATER QUALITY STANDARDS › Section 302.560 - Determining the Tier I Lake Michigan Basin Acute Aquatic Life Toxicity Criterion (LMAATC): Dependent on Water Chemistry

Current through Register Vol. 48, No. 28, July 12, 2024
If data are available to show that a relationship exists
				  between a water quality characteristic (WQC) and acute toxicity to two or more
				  species, a Tier I LMAATC must be calculated using procedures in this Section.
				  Although the relationship between hardness and acute toxicity is typically
				  non-linear, it can be linearized by a logarithmic transformation (i.e., for any
				  variable, K, f(K) = logarithm of K) of the variables and plotting the logarithm
				  of hardness against the logarithm of acute toxicity. Similarly, relationships
				  between acute toxicity and other water quality characteristics, such as pH or
				  temperature, may require a transformation, including no transformation (i.e.,
				  for any variable, K, f(K) = K), for one or both variables to obtain a least
				  squares linear regression of the transformed acute toxicity values on the
				  transformed values of the water quality characteristic. An LMAATC is calculated
				  using the following procedures.
a) For
				each species for which acute toxicity values are available at two or more
				different values of the water quality characteristic, a least squares linear
				regression of the transformed acute toxicity (TAT) values on the transformed
				water quality characteristic (TWQC) values is performed to obtain the slope of
				the line describing the relationship.
b) Each of the slopes determined under
				subsection (a) is evaluated as to whether it is statistically valid,
				considering the range and number of tested values of the water quality
				characteristic and the degree of agreement within and between species. If
				slopes are not available for at least one fish and one invertebrate species,
				the available slopes are too dissimilar, or too few data are available to
				define the relationship between acute toxicity and the water quality
				characteristic, then the LMAATC must be calculated using the procedures in
				Section 302.555.
c) Normalize the TAT values for each species,
				by subtracting W, the arithmetic mean of the TAT values of a species, from each
				of the TAT values used in the determination of the mean, such that the
				arithmetic mean of the normalized TAT values for each species individually or
				for any combination of species is zero (0.0).
d) Normalize the TWQC values for each species
				using X, the arithmetic mean of the TWQC values of a species, in the same
				manner as in subsection (c).
e)
				Group all the normalized data by treating them as if they were from a single
				species and perform a least squares linear regression of all the normalized TAT
				values on the corresponding normalized TWQC values to obtain the pooled acute
				slope, V.
f) For each species, the
				graphical intercept representing the species TAT intercept, f(Y), at a specific
				selected value, Z, of the WQC is calculated using the equation:
f(Y) = W - V(X - g(Z))
Where:
f()
is the transformation used to convert acute toxicity
							 values to TAT values
Y
is the species acute toxicity intercept or species
							 acute intercept
W
is the arithmetic mean of the TAT values as specified
							 in subsection (c)
V
is the pooled acute slope as specified in subsection
							 (e)
X
is the arithmetic mean of the TWQC values as
							 specified in subsection (c)
g()
is the transformation used to convert the WQC values
							 to TWQC values
Z
is a selected value of the WQC
g)
				For each species, determine the species acute intercept, Y, by carrying out an
				inverse transformation of the species TAT value, f(Y). For example, in the case
				of a logarithmic transformation, Y = antilogarithm of (f(Y)); or in the case
				where no transformation is used, Y = f(Y).
h) The Final Acute Intercept (FAI) is derived
				by using the species acute intercepts, obtained from subsection (f), in
				compliance with the procedures described in Section
				302.555(b) through
				(g), with the word "value" replaced by the
				word "intercept". Note that in this procedure, geometric means and natural
				logarithms are always used.
i) The
				Aquatic Acute Intercept (AAI) is obtained by dividing the FAI by two. If, for a
				commercially or recreationally important species, the geometric mean of the
				acute values at Z is lower than the FAV at Z, then the geometric mean of that
				species must be used as the FAV.
j)
				The LMAATC at any value of the WQC, denoted by WQCx, is calculated using the
				terms defined in subsection (f) and the equation:
LMAATC = exp[V(g(WQCx) - g(Z)) + f(AAI)]