6. TRANSPORT AND FATE OF CHEMICAL PARAMETERS OF INTEREST "Transport and fate" refers to the movement of contaminants in the environment, their alteration during movement, and their ultimate destination. In line with federal ~dance, this chapter describes the transport and fate of the main chemical parameters of interest (CPOIs) based on the contaminants and stressors of concern identified in the Onondaga Lake Baseline Ecological Risk Assessment and Hwnan Health Risk Assessment (TAMS, 2002a,b) summarized in Chapters 7 and 8 of this Onondaga Lake Remedial Investigation (RI) report. These CPOIs have been grouped for the purposes of this discussion of1ransport and fate based on similar spatial distributions within the lake and on similar geochemical, properties. This yielded the following eight groups: . Mercury and methylmercury. Othermetals. Benzene,toluene, ethylbenzene, and xylene (BTEX) compounds. Chlorinated benzenes. Polycyclic aromatic hydrocarbons (P AHs). Polychlorinated biphenyls (PCBs). Polychlorinated dibenzo-p-dioxins and furans (pCDD/PCDFs). Calcite. Mercury and calcite are discussed separately from the other CPOIs in this chapter because of their relatively tmique geochemistriesand historical importance to lake contamination. Reflecting this importance, extensive analyses of their transport and fate (including development of mass balance models) were performed by Honeywell and its consultants and were later revised by NYSDECrr AMS during the RI. Mass balance models were considered for other CPOIs, as required in the RIfFS Work Plan (PTI, 1991 c). To this end, estimates were made to quantify the sources and sinks of other CPO Is (see Section 6.2). This chapter is organized into five sections, with the fIrst three describing, respectively, the transport and fate of mercury and methylmercury, non-mercury CPOIs, and calcite in Onondaga Lake. The fourth section presents the estimated inventories (masses) of select CPOIs in lake sediments. The last sectionsumm arizes the transport and fate of CPOIs in Onondaga Lake. 6.1 Transport and Fate of Mercury and Methylmercury in Onondaga Lake The purpose of this section is to describe the transport and fate of mercury and methylmercury in Onondaga Lake, describing in detail the process used to derive each estimate of mercury load into the lake and its environs. Mercury and methylmercury are discussed together here, as their chemistries are inherently related. Wherever relevant, this section is consistent with NYSD EC' s Revision of the Onondaga Lake Mercury Modeling Report (NYSDECrr AMS, 1998b). NYSDECrr AMS Onondaga Lake RI 6-1 December 2002 The discussionof mercury loadsis focusedon the 1992period of stratification,May 25 throughSeptember 21, 1992 (NYSDECfT AMS, 1998b).This stratification period was selectedbecause extensive data on water column concentrations,tributary loading, andwater column processesare available. In addition, this stratification period is also a period of relatively constanthydrologic discharges(steady stream flow), and so representsa distinct phasein the hydrodynamic regime of the lake. This period presentsa logical time frame for mass balance estimation. Inputs, which are discussedbelow in Section6.1.1, include precipitation, tributary flow, groundwaterand porewateradvection, diffusive flux from porewater,and methylmercury production in the water column. Previous attemptsby Honeywell to calculateannual inputs were determinedto be unsupportablewith the available data, since those data did not cover an entire year and, in particular, did not cover the spring turnover/high tributary flow period of the lake (NYSDECfTAMS, 1998b). Section 6.1.2 addressesthe transport and fate of mercury in the water column of OnondagaLake during stratification and during fall turnover. Mass balanceestimates of total mercury andmethylmercury were developed for the stratified period. Section 6.1.3 discussesreleases from the Honeywell in-lake waste deposit, as introduced in Chapter 4, Section 4.5. Section 6.1.4 discussesthe deposition of mercury and other metals to lake sediments based on high resolution sediment cores. Prior to discussing mercury fate and transport, it is useful to briefly describe the lake's limnological conditions,as these conditions strongly influence mercurytrnnsport. Thning summer stmtification,the lake's thermocline strongly resistsvertical mixing in the lake. Ignoring internal seiches,the typical depth of the thermocline is about 9 m. This impediment to transport commonly results in two distinct chemical environmentsand provides a logical boundaryfor segmentingthe lake. Wind-driven horizontal mixing in the epilimnion is adequateto keep the epilimnion vertically well mixed. On the other hand,there are no strong forces (e.g., wind) that function to mix the hypolimnion. The hypolimnion is rather stagnantand quiescent,which allows particles to permanently settle and concentration gradientsto form in the water column. Wagner et al. (2002) documentedthat sustainedwind eventscan result in the transport ofhypolimnetic waters to the surfacewaters of OnondagaLake during the stratified period. A wind along the long axis of the lake builds up epilimnetic waters in the far end of the lake (a seiche),and to maintain a water balance in the lake, the hypolimnetic water upwells to the surfaceat the windward end of the lake. On September 11, 2002, over a period of 11 hours, Wagner et al. (2002) monitored a wind event with averagespeed of about 10 m/s alongthe main (long) axis of the lake.This wind eventresulted in an upwelling event.Wagner et al. (2002) reported that the hypolimnion lost one-third of its methaneinventory to the surfacewaters. Dissolved oxygen (DO) concentrationsof lessthan 1 mg/L were documentedin the surfacewaters at the windward end of the lake. Basedon reviews of historic weather,lake stratification, andwater quality data, Wagner et al. (2002) noted that at least eight such upwelling events have occurred between2000 and 2002. NYSDECfT AMS OnondagaLake RI 6-2 December2002 A mass balance approach was used to quantify the transport and fate of mercury in both the epilimnion and hypolimnion. The epilimnion is bounded by the air-water interface at the top, the thermocline and shallow sediments at the bottom, and tributaries and the lake outlet at the sides. The hypolimnion is bounded by the thermocline at the top and deep sediments at the bottom. Thning stratification, the hypolimnion is essentially isolated from all external water flows (i.e., tributary flows). In addition to the period of stratification in 1992, data were also obtained to describe lake turnover conditions in fall 1992 and fall 1999. fu early fall, cooler air temperatures and generally higher wind speed serve to cool and deepen the epilimnion. fu response, the depth of the thermocline begins to drop lower in the lake. As the thermocline drops, formerly hypolimnetic water is incorporated into the epilimnion until the temperature difference between the epilimnion and hypolimnion is eliminated. At this point, the lake is isothermal and essentially completely mixed from top to bottom. This is referred to as fall turnover. 6.1.1 Inputs of Total Mercury and Methylmercury to Onondaga Lake fu this section, mercury inputs to the water column from external sources(i.e., across "system boundaries") are discussed and quantified. This discussion focuses on the period of stratification from May 25 through September 21, 1992; however, fall turnover data from 1992 and 1999 are also discussed. For the water column mass balance, boundaries at three surfaces are defined: the air-water interface, the sediment-water interface, and the water-water interface at the mouths of tributaries. The initial Onondaga Lake RI/FS Work Plan (pT!, 1991c) identified several potential sources of mercury to Onondaga Lake, including the tributaries, the Metropolitan Syracuse Sewage Treatment Plant (Metro), groundwater advection, pore water diffusion, porewater advection, and precipitation. The work plan detailed investigations intended to describe the mercury loads from these sources based on concepts and mechanisms documented in other aquatic systems. These sources of mercury to Onondaga Lake are described in this RI as those "sources identified in the RI/FS Work Plan." However, in the course of the investigation additional sourceswere identified, including resuspension and potential advection of materials (i.e., sediments and waste) from the Honeywell in-lake waste deposit and the enhanced release from the profunda! These sources are referred to in this RI as "sources in addition to those identified in the RI/FS Work Plan" or "additional sources." fuputs of total mercury and methylmercury to Onondaga Lake were quantified based on data obtained during this RI, as follows: . Direct precipitation to the lake surface. Tributary flow and discharges from Metro. Groundwater advection. Porewater diffusive flux from sediments. Dissolved-phase release from sediments. NYSDECrrAMS Onondaga Lake RI 6-3 December 2002 . Hypolimnetic accumulation. Net methylmercury production in the water column. 6.1.1.1 Direct Precipitation to the Lake Surface The input of total mercuryand methylmercury to OnondagaLake via directprecipitation to the lake surface was estimatedfrom rainfall rates(National Oceanicand Atmospheric Administration [NOAA], 1992),the surface area of the lake, and an assumed concentration for total mercury and methylmercury in precipitation. A total volume of 5.5 x 106m3 of precipitation was estimatedfrom the NOAA datafor the