Effects of Oil Field Brine Wastewater Spills on Soil Hydraulic Conductivity.

Oil field brine is wastewater produced during the oil well drilling process.  Brine spills have occurred in North Dakota, resulting in complete crop production loss on the affected soil. Remediation requires removal of the salt from the soil, which might be accomplished by leaching to subsurface drains.  A laboratory study was conducted to determine the effects of brine on the saturated hydraulic conductivity (K_s) of four soils from western ND. Tempe cells were packed with dried, ground soil. Steady state flow of water was established, followed by either 1 or 3 pore volumes of brine to simulate a spill. Finally, water was reintroduced in an attempt to leach the brine from the soil. While K_s was relatively unaffected during the brine application, subsequent leaching with deionized water caused a dramatic reduction in K_s, an average of 60 times slower than pre-brine K_s. After brine application, total dissolved solids (TDS) concentration in the effluent rose to near original brine levels (0.3 Mg L^-1), but then declined back towards initial pre-brine concentrations with continued leaching.  However, the K_s did not increase with continued leaching. Removal of soluble salts during leaching increased the relative sodium concentrations on the exchange complex (ESP>60), causing dispersion/swelling of clay particles and reduced K_s.  Post-brine application of gypsum at rates equivalent to 2.2 and 11.2 Mg ha^-1 in an attempt to add calcium to the exchange complex did not improve the K_s. This evidence suggests that subsurface drainage may not be effective in removing salts from the crop root zone due to very low permeability caused by sodium induced clay dispersion/swelling.