Comparability of “Phase 2 Technical Activities Report” to Ecology’s “PCB Source Assessment” Dave Dilks SRRTTF June 24,

Comments on Draft Report  Why are results different between current study and Ecology’s 2011 source assessment?  What’s going on with Hangman Creek? 2

Why are Certain Loads So Different between Reports? Different objectives and environmental conditions 3 Ecology (2011)SRRTTF (2015) ObjectiveDefine load contribution from different sources Assess where “unknown” source may be coming from Time frameAnnual averageSummer 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.

Comparability of Results  Comparing oranges to tangerines  Many loading sources vary by season – Annual average loads can’t be directly compared to summer low flow loads Upstream boundary : 740 cfs vs cfs at Post Falls Stormwater: “Dry” weather vs. annual average 4

Annual Stormwater Loading Estimates Have Changed City 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 estimate 5

What’s Going on with Hangman Creek?  High concentration measured after rainfall  Might 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