HYDROGEN SULFIDE AND ARSENIC-RICH WATERS ORIGINATING FROM BURIED WOOD WASTE ALONG THE COMMENCEMENT BAY WATERFRONT, TACOMA, WASHINGTON

Thick accumulations of wood waste occur along the Commencement Bay waterfront at the sites of former sawmills. Recent studies have established that H₂S-rich water emanating from this wood waste inhibits the growth of eel-grass, an aquatic plant that provides vital habitat for juvenile salmon and other marine organisms. Efforts to restore the near-shore habitat of Commencement Bay must therefore include mitigation of these sulfide-rich waters. To better understand the origins of these waters we have analyzed D.O., pH, major ions and trace metals in a suite of samples collected from an ~100 year old sawdust pile located in the intertidal zone at N.45th St. and Ruston Way in Tacoma. These samples include pore water from within the pile (PW), fresh water from springs that may discharge into the pile (FW), and water from the bay itself (BW). Average concentrations of major cations in PW (Mg = 828 ppm, K = 306 ppm, and Cl =1150 ppm) are intermediate between those of FW (Mg = 14 ppm, K = 3 ppm, and Cl =39 ppm) and BW (Mg = 857, K = 333 ppm, and Cl = 1160 ppm), suggesting that PW represents a mixture between fresh water (5-15 %) and sea water (85-95%). Hydrogen sulfide levels in PW (avg. 2800 ppm) are dramatically higher than in FW (below detection) and BW (avg. 7 ppm), although total S is higher in BW (781 ppm) than PW (avg. 682 ppm). Trace metal contents of PW (avg. As = 72 ppb; avg. Mo = 35 ppb) are elevated relative to FW (avg. As = 15 ppb; Mo = 18 ppb) and BW (avg. As = 27 ppb, Mo = 23 ppb). We conclude that the permeable wood waste pile acts as an anoxic chamber in which BW SO₄^2- is reduced to S^2-. The pile also appears to be a source of As and Mo but future research is needed to determine whether these and other heavy metals originate from the wood waste itself or from an external water source that we have not yet sampled.