Phase 2 Technical Activities Report to Ecologys PCB Source Assessment Dave Dilks SRRTTF June 24 2015 1 ID: 168929
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Slide1
Comparability of “Phase 2 Technical Activities Report” to Ecology’s “PCB Source Assessment”
Dave DilksSRRTTFJune 24, 2015
1Slide2
Comments on Draft ReportWhy are results different between current study and Ecology’s 2011 source assessment?
What’s going on with Hangman Creek?2Slide3
Why are Certain Loads So Different between Reports? Different objectives and environmental conditions
3
Ecology (2011)
SRRTTF (2015)
Objective
Define load contribution from different sources
Assess where “unknown” source may be coming from
Time
frame
Annual average
Summer
low flow
Key findings
Stormwater
is a large source
Un-accounted source contributing
to river load
Significant dry weather load entering between Barker Rd.
and Trent Ave.Slide4
Comparability of ResultsComparing oranges to
tangerinesMany loading sources vary by seasonAnnual average loads can’t be directly compared to summer low flow loadsUpstream boundary : 740 cfs vs. 1840 cfs at Post Falls
Stormwater
: “Dry” weather vs. annual average
4Slide5
Annual Stormwater Loading Estimates Have ChangedCity of Spokane has collected extensive wet weather monitoring data subsequent to completion of Ecology report
Current estimate of annual stormwater load is much lower than previous estimate5Slide6
What’s Going on with Hangman Creek?
High concentration measured after rainfallMight this be an important source?
Some increase in flow, but timing is odd
PCB spike not reflected in composite sample (95
pg
/l)
We can’t say for sure
6