Technical Activities Report: Synoptic Survey and Mass Balance

1. Technical Activities Report:Synoptic Survey and Mass Balance Spokane River Regional Toxics Task Force Technical Track Work Group February 5, 2019

2. Study Objectives • Fill gaps in understanding from 2014 and 2015 mass balance assessments • Are there significant groundwater PCB loads entering: • Upstream of Mirabeau Point? • Between Trent Ave. (Plante’s Ferry) and Greene St.? • Between the Spokane USGS gage and Nine Mile? Draft 2018 Technical Activities Report

3. Sampling Locations Draft 2018 Technical Activities Report

4. Sampling Details • Five day survey duration • August 4 – 8, 2018 • Dry weather, summer low flows • 236 cfs (Barker Rd.) to 1480 cfs (Nine Mile) • ~20% higher than previous synoptic surveys Draft 2018 Technical Activities Report

5. Observed Concentrations • Concentrations ~25% lower than prior synoptic surveys • Higher river flows provide more dilution Draft 2018 Technical Activities Report

6. Mass Balance: Barker Road to Mirabeau Point • Negligible groundwater loading observed in 2018 • In contrast to 2015, which showed possible loading Draft 2018 Technical Activities Report

7. Mass Balance: Mirabeau Point to Trent Avenue • Study plan did not include this reach • Original study area was downstream of Trent Ave. • Barker to Mirabeau reach added later in response to up-gradient groundwater work group Draft 2018 Technical Activities Report

8. Mass Balance: Mirabeau Point to Trent Avenue • Mass balance could have been conducted for this reach by adding samples from Kaiser • They were not • Assumed that groundwater load was already well characterized by previous synoptic surveys Draft 2018 Technical Activities Report

9. Mass Balance: Mirabeau Point to Trent Avenue • Mass balance conducted in response to comments • Using routine Kaiser effluent monitoring data for August • Groundwater load very similar to prior years Draft 2018 Technical Activities Report

10. Mass Balance: Trent Avenue to Greene St. • This river segment was divided into two parts for 2018 • 2014 and 2015 surveys treated this as one large segment • Loss of lower chlorinated homologs between Trent and Upriver Draft 2018 Technical Activities Report

11. Mass Balance: Trent Avenue to Greene St. 2018: Divided into Two Reaches Comparison to Previous Years Draft 2018 Technical Activities Report

12. Mass Balance: Trent Avenue to Greene St. 2018: Divided into Two Reaches Comparison to Previous Years • Similar phenomena observed across years • Loss of di- through tetra- homologs • Gain of penta- through hepta- Draft 2018 Technical Activities Report

13. Mass Balance: Greene St. -> USGS Gage • Gain of penta-chloro homolog seen • Consistent with previous years • Inconclusive regarding other homologs 2018 Comparison to Previous Years Draft 2018 Technical Activities Report

14. Mass Balance: USGS Gage -> Nine Mile • Some gain in several homologs observed below Spokane gage Draft 2018 Technical Activities Report

15. Summary • Groundwater load upstream of Mirabeau Point appears to be negligible during survey • Interesting results between Trent and Greene • Loss of some homologs, gain of others • Consistent with 2014 and 2015 results • Some PCB gain observed for Greene->USGS and USGS->Nine Mile segments Draft 2018 Technical Activities Report

16. Observations/Questions • Results don’t conclusively eliminate the possibility of a load upstream of Mirabeau (at other times) • Load, if it exists here, appears to be sporadic • Results support conclusion that it is infrequent • What is going on downstream of Trent Ave.? • Phenomenon too consistent to be noise • Are estimated loads downstream of Greene St. outside of the noise? Draft 2018 Technical Activities Report

17. Potential Next Steps • Deeper dive into what is happening below Trent Ave. • Uncertainty assessment on homolog-specific mass balance • Are estimated loads above the noise? • Additional monitoring, contingent on above findings Draft 2018 Technical Activities Report

18. Shallow Dive below Trent • Three theories have been proposed • Differential partitioning to solids across homolog groups • Differential volatilization across homolog groups • Groundwater interaction more complicated that currently assumed Draft 2018 Technical Activities Report

19. Shallow Dive below TrentDifferential Partitioning across Homologs • Less-chlorinated homologs are more likely to be dissolved than higher-chlorinated homologs • Preferential loss to groundwater in losing reach? Draft 2018 Technical Activities Report

20. Shallow Dive below TrentDifferential Partitioning across Homologs When considering instream conditions all homologs are primarily in dissolved form Draft 2018 Technical Activities Report

21. Shallow Dive below TrentDifferential Volatilization across Homologs • Less-chlorinated homologs are more likely to volatilize than higher-chlorinated homologs • But only a 10% difference between loss rates for di-chloro and penta-chloro homologs Draft 2018 Technical Activities Report

22. Shallow Dive below TrentDifferential Volatilization across Homologs • Less-chlorinated homologs are more likely to volatilize than higher-chlorinated homologs • Increased volatilization will increase load across homologs Draft 2018 Technical Activities Report

23. Shallow Dive below TrentComplex Groundwater Flows Downstream Flow Upstream Flow Loss to Groundwater Mass balance approach currently assumes that a losing reach is purely losing Draft 2018 Technical Activities Report

24. Shallow Dive below TrentComplex Groundwater Flows Downstream Flow Upstream Flow Loss to Groundwater Gain from Groundwater • No affect on mass balance, if composition of groundwater is similar to river water • What if flow patterns are more complex? • Losing reach is a combination of some gain with more loss Draft 2018 Technical Activities Report

25. Shallow Dive below TrentComplex Groundwater Flows • If representative of broader conditions, could explain the apparent loss of lower chlorinated homologs Groundwater seep data collected by Ecology near Upriver Dam show different composition from river Draft 2018 Technical Activities Report

26. Discussion