Current through Register Vol. 24-06, March 15, 2024
(1)
The CSO reduction plan must be sufficiently complete so that plans and
specifications can be developed from it for projects that may proceed into
design within two years of plan submittal. Sufficient detail of any remaining
projects must be provided so that detailed engineering reports can be prepared
in the future.
(2) CSO reduction
plans shall include the following information together with any other relevant
data as requested by the department.
(a)
Documentation of CSO activity. Municipalities shall complete a field assessment
and mathematical modeling study to establish each CSO's location, baseline
annual frequency, and baseline annual volume; to characterize each discharge;
and to estimate historical impact by:
(i)
Flow monitoring and sampling CSOs. Monitoring and sampling at one or more CSO
sites in a group that are in close proximity to one another is sufficient if
the municipality can establish a consistent hydraulic and pollutant correlation
between or among the group of CSO sites. Sampling may not be required for CSO
sites that serve residential basins; and
(ii) Developing a rainfall/stormwater
runoff/CSO model to simulate each CSO site's activity; and
(iii) Verifying the model's accuracy with
data collected under (a)(i) of this subsection; and
(iv) In circumstances where an historical
impact may be discernible, observing and sampling the receiving water sediments
adjacent to each CSO site or group of sites to establish the presence and
extent of any bottom deposits; and
(v) If the sewer service area upstream of a
CSO site includes sanitary sewer sources other than domestic sewage, samples of
the sediment deposits shall receive heavy metal analysis and organic pollutant
screening. Pending review of results of these analyses, the department may
require additional pollutant analyses. If two or more CSO sites serve the same
industrial/commercial sources, sediment sampling adjacent to one representative
CSO site may suffice.
(b) To achieve the greatest reasonable
reduction at each CSO site, control/treatment alternatives that shall receive
consideration include, but are not limited to:
(i) Use of best management practices, sewer
use ordinances, pretreatment programs, and sewer maintenance programs to reduce
pollutants, reduce infiltration, and delay and reduce inflow; and
(ii) In-line and off-line storage with at
least primary treatment and disinfection at the secondary sewage treatment
facility that is served by the combined sewer; or
(iii) Increased sewer capacity to the
secondary sewage treatment facility that shall provide at least primary
treatment and disinfection; or
(iv)
At-site treatment equal to at least primary treatment, and adequately offshore
submerged discharge. At-site treatment may include a disinfection requirement
at CSO sites that are near or impact water supply intakes, potentially
harvestable shellfish areas, and primary contact recreation areas; or
(v) Storm sewer/sanitary sewer
separation.
(c) Analysis
of selected treatment/control projects. Municipalities shall conduct an
assessment of the treatment/control project or combination of projects proposed
for each CSO site. The assessment shall include:
(i) An estimation of the water quality and
sediment impacts of any proposed treated discharge using existing background
receiving water quality data, and estimated discharge quality and quantity. The
department may require a similar analysis for proposed storm sewer outfalls for
basins that drain industrial and/or commercial areas; and
(ii) An estimation of the selected projects'
impacts on the quality of effluent from and operation of a municipality's
secondary sewage treatment facility. During wet weather flow conditions, a
municipality shall maximize the rate and volume of flows transported to its
secondary sewage treatment facility for treatment. However, those flows must
not cause the treatment facility to exceed the pollutant concentration limits
in its NPDES permit; and
(iii) The
estimated construction and operation and maintenance costs of the selected
projects; and
(iv) The general
locations, descriptions, basic design data, sizing calculations, and schematic
drawings of the selected projects and descriptions of operation to demonstrate
technical feasibility; and
(v) An
evaluation of the practicality and benefits of phased implementation;
and
(vi) A statement regarding
compliance with the State Environmental Policy Act (SEPA).
(d) Priority ranking. Each municipality shall
propose a ranking of its selected treatment/control projects. The rankings must
be developed considering the following criteria:
(i) Highest priority must be given to
reduction of CSOs that discharge near water supply intakes, public primary
contact recreation areas, and potentially harvestable shellfish
areas;
(ii) A cost-effectiveness
analysis of the proposed projects. This can include a determination of the
monetary cost per annual mass pollutant reduction, per annual volume reduction,
and/or per annual frequency reduction achieved by each project;
(iii) Documented, probable, and potential
environmental impacts of the existing CSO discharges.
(e) Municipalities shall propose a schedule
for achieving "the greatest reasonable reduction of combined sewer overflows at
the earliest possible date." (RCW 90.48.480.) If
the agreed upon schedule exceeds five years, municipalities shall propose an
initial five-year program of progress towards achieving the greatest reasonable
reduction. Factors that municipalities and the department shall use to
determine compliance schedules shall include but not be limited to:
(i) Total cost of compliance;
(ii) Economic capability of the
municipality;
(iii) Other recent
and concurrent expenditures for improving water quality; and
(iv) The severity of existing and potential
environmental and beneficial use impacts.
Statutory Authority:
RCW
90.48.110. 00-15-019 (Order 00-07), §
173-245-040, filed 7/11/00, effective 8/11/00. Statutory Authority:
RCW
90.48.035. 87-04-020 (Order DE 86-34), §
173-245-040, filed 1/27/87.