WAC 173-245-040
CSO reduction plan. (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.]