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USGS - science for a changing world
Sacramento-San Joaquin Delta

Low Intensity Chemical Dosing (LICD)

Rivers, wetlands, and agricultural operations supply natural organic material to the Sacramento-San Joaquin Delta (Delta) and the San Francisco Estuary. This natural organic matter provides many ecosystem benefits, but it also adversely affects drinking water. This occurs because during drinking water treatment, chlorine added for purposes of pathogen control reacts with dissolved organic carbon (DOC) in the water to form carcinogenic and mutagenic disinfection by-products (DBPs). Concentrations of these compounds in tap water are regulated by the Environmental Protection Agency.

On site coagulation with metal based salts, referred to here as low-intensity chemical-dosing (LICD), is anticipated to remove considerable amounts of DOC and DBP precursors from island drainage water, thereby significantly reducing inputs of these constituents to the Delta. Coagulation may also remove mercury from solution. Accumulation of the flocculated material in constructed wetlands, along with sequestration of wetland plant material, is expected to increase land-surface elevations. The project hypothesis is that the combination of coagulation and biotic wetland processes can improve water quality and reverse subsidence beyond that achievable by either technology alone.


image of a boardwalk running between study cells in the Delta wetlands

Field Study

Construction of a replicated field experiment located on Twitchell Island will allow us to determine the effects of a coagulation treatment-wetland system on water quality.



Water Quality

Determine and quantify the effectiveness of coagulants for improving water quality by removal of DOC, DBP precursors, and other constituents of concern from drainage water.

Water quality samples taken from the outflow of the coagulant system.

Accretion

Assess the stability of organic-metal flocculate formed, the fate of removed constituents, and the effects of floc on soil accretion rates.



Ecosystem

Assess organic carbon, nutrient, and metal dynamics in the constructed wetlands and investigate potential environmental and toxicity effects of LICD treated water and newly formed sediments on soil and water quality.



Feasibility

Determine costs associated with constructing and maintaining a coagulation system.