E & P Drilling Fluid Disposal Facilities in Texas and Louisiana:

Analogs for Environmental Assessments of Abandoned Sites

By

NANCE, H. S., and DUTTON, ALAN R.

Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, Austin, TX

Some E & P wastes are disposed of in clay-lined, bermed, earthen pits at centralized and commercial drilling-fluid disposal sites (CCDD’s). A developing Texas and Louisiana database includes 150+ active and inactive sites. Most regulated sites accept water-based (<3,500 mg/L chloride) fluids. However, hydrocarbons and brackish-to-saline groundwater are frequently present. Abandoned sites are a state’s responsibility for evaluating and remediating, although these sites are generally less well documented. Better-documented sites provide analogs for abandoned sites. Three Texas and Louisiana Gulf Coastal sites exemplify a range of CCDD contaminant and groundwater-level characteristics.

At the Matagorda County site (Texas), waste constituents in pit sludge include nonuniformly distributed chloride, hydrocarbons, and arsenic. Groundwater chloride distributions reflect sludge chloride distributions and suggest causal links. Chloride distributions in outwash areas provide a model for overflow through breached berms. Site documentation is unusual because constituent levels at specific sample locations are noted. Pre-analysis compositing of samples is typical of other site data, although compositing masks local constituent concentrations.

At the St. Mary’s Parish site (Louisiana), groundwater chloride exceeding 2,000 mg/L is distributed in southeast- and northwest-trending plumes, which maintain their extent while concentration levels vary temporally.

At the Iberia Parish site (Louisiana), plumes locally exceed 600 mg/L and vary temporally between southerly and easterly trends. They are episodically flushed (<50 mg/L) from the site. Groundwater mounds at Waguespack occur centrally at the site, a typical situation at many sites. Water-table mounding suggests that some pits have focused recharge of potentially contaminated water to surficial aquifers.