Environmental Engineering Reference
In-Depth Information
different policy tenets, many of the water quality criteria derivation techniques used
throughout the world are applicable under US and California policy.
4
Criteria Types and Uses
Three types of water quality criteria are described by the USEPA: numeric, narrative, and
operational (USEPA 1985). This chapter is concerned with derivation of numeric crite-
ria, which can be used in setting water quality standards. This section describes many
different types of numeric criteria that may be derived according to various methodolo-
gies, depending on how the values are to be used and how much data are available.
In the literature, numeric water quality criteria are referred to by many different
terms. For example, they may be called trigger values (TVs; ANZECC and
ARMCANZ 2000), guidelines (CCME 1999), criteria (USEPA 1985; Samsoe-
Petersen and Pedersen 1995; Roux et al. 1996), quality standards, thresholds (Lepper
2002; Zabel and Cole 1999), environmental risk limits (ERLs; RIVM 2001), maximum
tolerable concentrations (MTCs; OECD 1995), predicted no-effect concentrations
(PNECs; ECB 2003), water quality objectives (WQOs; Bro-Rasmussen et al. 1994),
and quality targets (BMU 2001; Irmer 1995). The common thread in all of these is
that the values derived are scientifically based numbers which are intended to pro-
tect aquatic life from adverse effects of pesticides, without consideration of defined
water body uses, societal values, economics, technical feasibility, or other nonscien-
tific considerations. This definition corresponds to what the USEPA calls a numeric
criterion (as per Section 304(a) of the Clean Water Act), and it is the derivation of
this type of number that is the subject of this chapter.
4.1
Numeric Criteria Versus Advisory Concentrations
In the US, numeric criteria are derived for compounds when adequate toxicity,
bioaccumulation, and/or field data are available (USEPA 1986). These criteria may
be used for such things as developing water quality standards or setting effluent
limitations (USEPA 1985). If adequate data are not available for criteria derivation,
advisory concentrations are then derived. Advisory concentrations are used to
interpret ambient water quality data. For example, if the ambient concentration of
a chemical is below the advisory concentration, then there is no further concern; if
the concentration is above the advisory concentration, then more data are collected,
preferably enough to allow calculation of a criterion (USEPA 1986).
The USEPA Great Lakes water quality guidance (USEPA 2003a) provides for
derivation of Tier I and Tier II criteria. Tier I criteria, which are derived from
complete data sets according to the USEPA methodology (1985), may be adopted
as numeric criteria, may be used to adopt water quality standards, or may be used
to implement narrative criteria. Tier II criteria, similar to USEPA advisory concentrations,
Search WWH ::
Custom Search