Washington Administrative Code › Title 173 - Ecology, Department of (See also Titles 197, 317, 372, and 508) › Chapter 173-340 - Model Toxics Control Act-Cleanup › Part 7 - CLEANUP STANDARDS › Section 173-340-708 - Human health risk assessment procedures

Current through Register Vol. 24-14, July 15, 2024
(1)
Purpose.
This section
				defines the risk assessment framework that shall be used to establish cleanup
				levels, and remediation levels using a quantitative risk assessment, under this
				chapter. As used in this section, cleanup levels and remediation levels means
				the human health risk assessment component of these levels. This chapter
				defines certain default values and methods to be used in calculating cleanup
				levels and remediation levels. This section allows varying from these default
				values and methods under certain circumstances. When deciding whether to
				approve alternate values and methods the department shall ensure that the use
				of alternative values and methods will not significantly delay site
				cleanups.
(2)
Selection of
				indicator hazardous substances.
When defining cleanup requirements at a site that is
				  contaminated with a large number of hazardous substances, the department may
				  eliminate from consideration those hazardous substances that contribute a small
				  percentage of the overall threat to human health and the environment. The
				  remaining hazardous substances shall serve as indicator hazardous substances
				  for purposes of defining site cleanup requirements. See WAC
				  173-340-703 for additional
				  information on establishing indicator hazardous substances.
(3)
Reasonable maximum exposure.
(a) Cleanup levels and remediation levels
				shall be based on estimates of current and future resource uses and reasonable
				maximum exposures expected to occur under both current and potential future
				site use conditions, as specified further in this chapter.
(b) The reasonable maximum exposure is
				defined as the highest exposure that is reasonably expected to occur at a site
				under current and potential future site use. WAC
				173-340-720 through
				173-340-760 define the reasonable
				maximum exposures for groundwater, surface water, soil, and air. These
				reasonable maximum exposures will apply to most sites where individuals or
				groups of individuals are or could be exposed to hazardous substances. For
				example, the reasonable maximum exposure for most groundwater is defined as
				exposure to hazardous substances in drinking water and other domestic
				uses.
(c) Persons performing
				cleanup actions under this chapter may use the evaluation criteria in WAC
				173-340-720 through
				173-340-760, where allowed in
				those sections, to demonstrate that the reasonable maximum exposure scenarios
				specified in those sections are not appropriate for cleanup levels for a
				particular site. For example, the criteria in WAC
				173-340-720(2) could be used to demonstrate that the reasonable maximum exposure for
				groundwater beneath a site does not need to be based on drinking water use. The
				use of an alternate exposure scenario shall be documented by the person
				performing the cleanup action. Documentation for the use of alternate exposure
				scenarios under this provision shall be based on the results of investigations
				performed in accordance with WAC
				173-340-350.
(d) Persons performing cleanup actions under
				this chapter may also use alternate reasonable maximum exposure scenarios to
				help assess the protectiveness to human health of a cleanup action alternative
				that incorporates remediation levels and uses engineered controls and/or
				institutional controls to limit exposure to the contamination remaining on the
				site.
(i) An alternate reasonable maximum
				exposure scenario shall reflect the highest exposure that is reasonably
				expected to occur under current and potential future site conditions
				considering, among other appropriate factors, the potential for institutional
				controls to fail and the extent of the time period of failure under these
				scenarios and the land uses at the site.
(ii) Land uses other than residential and
				industrial, such as agricultural, recreational, and commercial, shall not be
				used as the basis for a reasonable maximum exposure scenario for the purpose of
				establishing a cleanup level. However, these land uses may be used as a basis
				for an alternate reasonable maximum exposure scenario for the purpose of
				assessing the protectiveness of a remedy. For example, if a cap (with
				appropriate institutional controls) is the proposed cleanup action at a
				commercial site, the reasonable maximum exposure scenario for assessing the
				protectiveness of the cap with regard to direct soil contact could be changed
				from a child living on the site to a construction or maintenance worker and
				child trespasser scenario.
(iii)
				The department expects that in evaluating the protectiveness of a remedy with
				regard to the soil direct contact pathway, many types of commercial sites may,
				where appropriate, qualify for alternative exposure scenarios under this
				provision since contaminated soil at these sites is typically characterized by
				a cover of buildings, pavement, and landscaped areas. Examples of these types
				of sites include:
(A) Commercial properties in
				a location removed from single family homes, duplexes or subdivided individual
				lots;
(B) Private and public
				recreational facilities where access to these facilities is physically
				controlled (e.g., a private golf course to which access is restricted by
				fencing);
(C) Urban residential
				sites (e.g., upper-story residential units over ground floor commercial
				businesses);
(D) Offices,
				restaurants, and other facilities primarily devoted to support administrative
				functions of a commercial/industrial nature (e.g., an employee credit union or
				cafeteria in a large office or industrial complex).
(e) A conceptual site model may be
				used to identify when individuals or groups of individuals may be exposed to
				hazardous substances through more than one exposure pathway. For example, a
				person may be exposed to hazardous substances from a site by drinking
				contaminated groundwater, eating contaminated fish, and breathing contaminated
				air. At sites where the same individuals or groups of individuals are or could
				be consistently exposed through more than one pathway, the reasonable maximum
				exposure shall represent the total exposure through all of those pathways. At
				such sites, the cleanup levels and remediation levels derived for individual
				pathways under WAC
				173-340-720 through
				173-340-760 and WAC
				173-340-350 through
				173-340-390 shall be adjusted
				downward to take into account multiple exposure pathways.