Atmospheric Deposition Strategy Straw Proposal

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

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

Watershed Loads vs AirDep LoadADminADmaxAvg% Copper74, % Dioxins % Mercury % PAH % PBDE % PCB % Selenium %

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?

How Much Is Local Sources? BAAQMD emissions inventories Coastal/inland comparisons (e.g. Hg TOT ) –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…

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 +/-

Application to Modeling Air dep might account for a large % of some (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) = g, airdep using Tsai regional estimate = 100 g

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

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

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

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

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