Report Number: 108
Year: 2005

Mobilization of Aqueous Contaminants Leached From Ordot Landfill in Surface and Subsurface Flows

In 2001, two single leachate samples taken from the perimeter of Ordot Landfill, in central Guam, were screened for fecal indicator bacteria and 175 chemical contaminants including most of those listed as priority pollutants under Section 307(a) of the Clean Water Act. Identified contaminants of concern included the fecal indicator bacteria, Enterococci and E. coli, inorganic N and P, and several heavy metals. Al, Bo and Fe were the most abundant elements identified, while Cd, Hg and Ag (high concentrations previously reported by other investigators) were undetected. Al was almost exclusively present in the particulate form. Low concentrations of eight common industrial solvents were identified including tetrahydrofuran, a highly polar ether used in paints, building materials and furnishings, and 1,2-dichlorethane, used extensively in the manufacture of PVC. Both of these compounds are not readily degradable in the environment. No PCBs or PAHs were detected and the only pesticide identified out of 20 tested for, was p-dichlorobenzene, a moderately degradable compound used extensively in home and industry to control moths, mould and mildew. Despite the presence of several dioxins and furans in one of the leachate samples, the highly toxic members of both classes of contaminants were not detected.

Surface and subsurface waters downgradient of the landfill were monitored periodically over one year (Oct '02-'03) for total coliforms, Enterococci and E. coli, inorganic N and P, and heavy metals. Fecal indicator bacteria MPN counts in receiving surface waters dropped sharply within a few hundred meters downstream of the leachate stream impaction point. However, values often exceeded the US EPA recreational water quality standards all the way to the coast. Enterococci and E coli were significantly correlated with one another only at counts of ~200 or more. Inorganic N was dominated by NH3-N in the leachate stream and NOx-N in the river. Occasional exceedences of the US EPA surface water quality standard for nitrate (as NOx) were observed at all downstream sites. Inorganic P was mostly undetectable in all receiving surface waters despite relatively high levels in the leachate stream. Likewise, the majority of heavy metal contaminants that were enriched in the leachate stream were close to or below the limits of analytical detection in the river. The formation of Fe and Mn oxyhydroxides at redox boundaries within the leachate stream were suspected of scavenging inorganic P and heavy metals from the water column and dumping them in bed sediments. Soil pore waters collected at various depths (0.61-1.83 m) ~100-250 m downgradient of the landfill were comparatively free of fecal indicator bacteria. Inorganic N levels, though enriched, were appreciably lower than those in the leachate stream. Net losses were thought to reflect microbial assimilation, denitrification, and sorption onto positively charged clay particles. Average P levels were also low suggesting removal by oxidic iron in surface layers coupled with soil sorption processes. Neither inorganic N nor P concentrations varied significantly with depth. In contrast, mean pore water concentrations of Al, Cd, Fe and Zn were generally more concentrated at the shallowest level.

Inorganic N enrichment, and its effect on plant and algae growth in the lower reaches of the Lonfit River, was considered to be the most significant ecological impact of the landfill on the watershed. The transmission of human pathogens from the landfill into the river, in leachate streams and surface runoff, and the incorporation of potentially toxic metals into food chains ultimately leading to man, are likely the most important issues from a human health perspective.

Gary R. W. Denton
Mohammed H. Golabi
Clancy Iyekar
Rick H. Wood
Yuming Wen