Atmospheric Deposition Strategy

1. Atmospheric Deposition Strategy Straw Proposal

2. What Pollutants Matter? • Highest priority – known impairment AND air sources: Hg, dioxins • Moderate priority – impairment OR air sources/pathways unknown or minor(?): PCBs, PAHs • Low priority – Impairment AND air sources low or likely minor: Cu, PBDEs, Se, organochlorine pesticides

3. Air Deposition Estimates • Deposition ≠ Load • Pervious surfaces have low yield • 30% impervious average? • Separate lower vs upper watershed • Semi-quantitative scaling • Which contaminants might matter • Using regional direct dep to Bay estimates • local dep may be higher or lower

4. Watershed Loads vs AirDep

5. Local Variation • Unknown for most pollutants • Variation near/far from sources • Castro Valley Cu 4x higher near 580 Hwy • Cupertino Hg ~6x higher near cement plant • Other work in literature e.g. SoCal, TX, etc. • Higher impermeability + higher source density = High leverage locations?

6. How Much Is Local Sources? • BAAQMD emissions inventories • Coastal/inland comparisons (e.g. HgTOT) • Long Marine Lab ~6 ng/L wet, 1.8 ng/m3 dry • Moffett Field ~9-12 ng/L wet, 2.2 ng/m3 dry • Even w/o distinct local pollutant source, other pollutants may affect process (speciation/deposition) – NOx, SOx, TSP…

7. Application to Monitoring • Why not just measure stormwater loads • Highly episodic esp. in small watersheds • Need very high sample frequency / flow weighted integrations through events • One (more) step removed from source • Captures transport process too +/-

8. Application to Modeling • Air dep might account for a large % of some pollutants @ (sub)watershed scale • Need to use some assumptions, e.g. uniform vs max variation sensitivity testing • If it makes a difference, more local data may be needed e.g. Zone 4 Hayward watershed, Hg loads (2007-8) = 25-150 g, airdep using Tsai regional estimate = 100 g

9. Application to Management • Can we manage at <regional scale? • Need data at that scale to evaluate • Larger scale = decreased signal • Do we accept ongoing inputs? • Mopping the floor while faucet(s) run

10. Confirm What Pollutants? • Highest priority – known impairment AND air sources: dioxins, Hg • Moderate (?) priority – impairment OR air sources/pathways unknown or minor(?): PAHs, Se, PCBs, • Low priority – Impairment AND air sources low or likely minor: Cu, PBDEs (move up if impairment), organochlorine pesticides

11. General Approach • Ballpark estimates • Does this affect management choice? • Followup if uncertainty affects assessment • Find more data in the literature • Can we extrapolate to here? • Devise methods to obtain needed data • Studies and/or modeling

12. Near-term Needs • “No regret” data needs? • Redo estimate of dioxin deposition w/ CARB data • Less certain refinement needs • Se seems a pretty high proportion of local loads (still small % of Delta though) • Hg also high (but any plan for smaller local or nonpoint source actions?) • Group suggested (re)allocation of $25k for dioxin estimate to more general airdep review

13. Management Actions / Data Needs • List here … e.g. • Emission control • nearfield effectiveness measurement • Natural attenuation • Model scenarios