Identifier

etd-04252011-233326

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Miscible displacement column studies were conducted on unfractured cores of Topopah Spring Tuff to quantify transport characteristics of bromide&44; pentafluorobenzoic acid &40;PFBA&41;&44; trichloroethylene &40;TCE&41;&44; and naphthalene. Three 5 cm diameter by 2 cm long cores were flushed with pulses of simulated groundwater containing these tracers&44; followed by tracer&45;free solution. Effective porosities were gravimetrically measured as 11&37;&44; 10.6&37;&44; and 9.5&37;. The tracers achieved full breakthrough in an order correlating to their hydrophobicities. Bromide and PFBA sorbed least&44; achieving full breakthrough in fewer than 10 pore volumes. As water analogues&44; both exhibited no quantifiable sorption. Delay to full breakthrough was contributed to rate&45;limited diffusion into lower permeable regions. Their transport was found to be conservative&44; with their retardation factors computed as 1. TCE reached full breakthrough within 40 to 50 pore volumes and naphthalene at 90 to 100 pore volumes. The tracers desorbed from each core in the same order as the arriving front. Bromide and PFBA fully exited the cores within 10 to 20 pore volumes. TCE and naphthalene exhibited significant tailing during desorption&44; never achieving levels below quantifiable detection due to experimental time constraints. Mass balance calculated recoveries of 95 to 100&37; for bromide&37;PFBA&44; 70 to 90&37; for TCE&44; and 80 to 90&37; for naphthalene. The 1&45;dimensional contaminant transport program CXTFIT determined bromide dispersion between 0.032 to 34.0 cm&178;&37;day. TCE sorption matched the one&45;site sorption model with dispersion values 0.01 to 0.41 cm&178;&37;day. Naphthalene sorption matched a two&45;site model with dispersion values 0.075 to 1.96 cm&178;&37;day. Saturated hydraulic conductivities were measured over the range 8.64E&45;4 to 1.73E&45;2 mm&37;day. Petrographic analysis related core structure to fluid flow. The tuff was welded&44; with 1 mm to 2 cm pumice&44; quartz&44; and feldspars clasts in a fine&45;grained quartz and glass matrix. X&45;ray diffractometry reported major mineralogy &40;excluding 70&37; amorphous glass by volume&41; as quartz 11±5&37;&44; albite 41±5&37;&44; and orthoclase 48±5&37;. The pumices were observed as the primary porosity and likely major flow paths. The disconnectedness of the pumices revealed that the cores would have zones of highly variable permeability&44; moving quickly in the porous pumices and slowly through the tight matrix.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hanor, Jeffrey

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