Remediation Design of a Metal-Contaminated Sediment Site: Treatability Testing and Its Evaluation

摘要

Background. A series of geo-technical and treatability tests have been conducted toevaluate effectiveness of various sorbents as cap material and conducted remediation designto provide long-term protection of a metal contaminated sediment site in California.Metals, especially copper and arsenic, present at this site pose risk to benthic invertebratesand higher trophic level receptors. The geology at the site is dominated byPleistocene and Holocene geomorphology and the subsurface zone consists of interfingeringalluvial and estuarine depositional environments. The site lies on the southernmargin of Suisun Bay, includes more than 200 acres of tidal marsh. The hydrology of themarsh is characterized by the complex interplay of tides, currents, surface water runoff,evapotranspiration, and weather. Dredging, excavation and filling necessitate constructionof temporary access roadways and hand clearing of vegetation in the constructionareas―rendering these alternatives extremely difficult to implement and destructive ofthe existing habitat. Other concerns include the possibility that construction disturbanceswould persist over long term. During feasibility study, capping was found to be less invasivethan excavation and would result in less damage to the existing habitat duringimplementation for this site. A series of tests have been conducted to evaluate the physicaland chemical characteristics of five cap materials: (1) Martinez Marina Bay Mudfrom a local borrow source (Bay Mud), (2) aggregate gravel coated with modified clay(AquaGate), (3) macroporous aluminosilicate, a synthesized porous reactive material, (4)mineral Apatite (Rock Phosphate), and (5) fishbone product (Apatite II?). These materialswere analyzed for the following tests:1.Moisture content, specific gravity, grain size, total organic carbon (TOC) and X raydiffraction2.Leachable metals, volatile organic carbons (VOCs) and semivolatile organic compounds(SVOCs) to evaluate the potential for each material to leach metal andorganic contaminants3.Sorption tests to determine the arsenic and copper sorption capacity of each of the potentialcap materials4.Desorption of various metals (aluminum, antimony, arsenic, barium, beryllium, cadmium,chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum,nickel], selenium, silver, thallium, vanadium, and zinc) in the presence of contaminatedsediment to assess the potential release of contaminants by the cap materials5.Settling velocities of selected cap materials in site-specific water.The site-specific sediment and surface water samples were analyzed for physical andchemical characteristics, including temperature, pH, conductivity, oxidation-reductionpotential, dissolved oxygen, turbidity, and other geo-technical properties. Sediment,