High Level Scoping for Upcoming Monitoring Dave Dilks, Joyce Dunkin SRRTTF Technical Track Work Group June 3,

Outline  Background  High level scoping of unknown groundwater source  Cost estimates for all monitoring options – Groundwater assessment – Revisit/confirm dry weather assessment – Wet weather monitoring  Cost estimates for LimnoTech involvement 2

Background  2015 workshop recommended data collection on the following – Wet weather sources – Sources contributing to the ground water load  High level scoping recommended as first step – Conduct data mining – Assess feasibility of obtaining useful results – Propose monitoring alternatives  Wet weather scoping discussed in May 3

Scoping for Groundwater Loading  Better define the source of “unknown” load  Two tasks 1.Review available data 2.Develop/apply groundwater loading model 1.Groundwater data collected by Kaiser show: – Very high, but very localized concentrations – Background contamination of unknown extent 4

5 x x x x x = Background well x Site Schematic

Groundwater Mass Loading Assessment  Simple mass loading analysis conducted to assess – What fraction of the estimated unknown load is from the localized source? – How widespread would the background concentration need to be to explain the unknown load 6

Groundwater Mass Loading Model*  Calculates PCB loading based upon calculated seepage rate and specified concentration  Model inputs include 7 – Hydraulic conductivity – Horizontal groundwater gradient – Horizontal length of impacted zone – Vertical length of bank seepage face – PCB concentration in groundwater *Model and key assumptions provided on SRRTTF web site

Groundwater Model Results  Loading from concentrated plume calculated using two different input assumptions – Estimated load ranged from mg/day  Loading from background sources at Kaiser – Estimated load of 91 mg/day  Sum of these two components = mg/day 8

Comparison of Model to Mass Balance  Total load to segment from mass balance assessment = mg/day – Estimated load from background sources crossing Kaiser site = 91 mg/day – Estimated load originating on Kaiser site = mg/day – Estimated unaccounted for load in segment = mg/day 9

Monitoring Ramifications  Worthwhile to examine the nature of background contamination entering Kaiser property  Potentially worthwhile to examine the nature of contamination elsewhere in the Barker-Trent segment – These sources contribute 7 to 40% of total load 10

Monitoring Options Up-gradient of Kaiser Property  Two options, both based on installing two permanent shallow wells and sampling quarterly for one year 1.Base well location on review of historical land use information 2.Install and sample from five temporary wells, base permanent well location of results 11

Monitoring Options Remainder of Barker-Trent Segment  Recommended monitoring consists of sampling quarterly for one year at five wells  Total cost will depend upon presence of suitable existing wells – EAP is compiling this data, which should be available shortly 12

Groundwater Monitoring Costs  Up-gradient of Kaiser Property – Base well location on review of historical land use information: $70,000 – Base well location on newly-installed wells: $130,000  Remainder of Barker-Trent Segment – Relevant monitoring wells exist: $55,000 – New wells need to be installed: $130,000 13

“Wet Weather” Options Four monitoring options recommended for further consideration by Task Force 1.Revisit/confirm dry weather assessment for Barker Rd. to Trent segment 2.Revisit/confirm dry weather assessment for Greene St. to Trent gage segment 3.Limited sampling of stormwater outfalls 4.Wet weather sampling of Hangman Creek 14

“Wet Weather” Costs  Update dry weather mass balance – Barker Rd. to Trent only: $40,000 – Greene St. to Spokane gage only: $40,000 – Both segments: $65,000  Additional wet weather monitoring – City of Spokane stormwater: $14,000 – Hangman Creek: $27,000  Retrospective loading analysis: $7,500 15

Monitoring Cost Summary “Wet Weather” Groundwater Update dry weather mass balanceUp-gradient of Kaiser Property - Barker Rd. to Trent only$40,000- Location based on land use$70,000 - Greene St. to Spokane gage only $40,000- Location based on monitoring$130,000 - Both segments$65,000 Remainder of Barker-Trent Additional wet weather monitoring - Suitable wells exist$55,000 - City of Spokane stormwater$14,000- New wells required$130,000 - Hangman Creek$27,000 16

LimnoTech/Assessment Cost Summary Coordination/Project Management Analysis - Develop monitoring scopes $5,000- Update dry weather mass balance $7,500 - Participation in SRRTTF meetings $1200/mo- Assess wet weather loads$5,000 - Project Management$400/mo- Retrospective loading analysis$7,500 - Workshop attendance$5,000- Assess groundwater loads$7,500 - Reporting$5,000 17

Stormwater Loading Assessment Example retrospective analysis Could be used to better put stormwater loads in context 18