Environ. Sci. Technol. 1982, 16, 363-367
NOTES A Survey of Discharges from a Natural Gas Drilling Operation in Lake Erie Jon I. Parker* and John 0. Ferrantet
Environmental Impact Studies Division, Argonne National Laboratory, Argonne, Illinois 60439
w We mapped turbid discharge plumes from a Canadian gas drilling rig by continuous-flow nephelometry and measured the concentrations of selected inorganic and organic constituents in the plumes. The buoyant surface plumes were from -600 to 1500 m long, with a maximum width of -250 m and areas less than 25 ha. Maximum total suspended solids in the discharge plumes were usually less than 5.0 mg/L and were rapidly dispersed when discharging ceased. Sodium, magnesium, sulfate, and chloride were diluted to ambient lake-water levels within 50 m of the drilling rig. Volatile hydrocarbons were 25 m (Table I). These constituents apparently dispersed quite rapidly after discharge, since their concentrations at distances >25 m were approximately equal to the concentrations measured at the reference stations. Mg concentrations at 25 m from the drilling rig were significantly higher than at other locations in the 31 May discharge plume and the reference stations. However, Mg rapidly declined to ambient lakewater levels throughout the remainder of the plume, suggesting that the area exposed to elevated Mg levels was small (less than 1 ha).
+
Q 8
I
Lo
v) k-
I4
005
01 2 015
020
025K
RELATIVE LIGHT SCATTERING
Figure 1. Light scattering/dry weight relationship for three different reference suspensions (upper) and the light scattering/TSS relationship for water samples (lower) collected in the discharge plume and at reference stations.
supplied to the nephelometer by a towed submersible pump. The vertical distribution of TSS was periodically sampled by lowering the submersible pump through the water column to within 1 m of the bottom. Triplicate samples of drilling mud and undiluted drilling-rig discharge were analyzed by emission spectrometry for an extensive suite of elements to evaluate their potential for increased concentrations in the discharge plumes. Although drilling mud was not discharged, it was included in these analyses to aid its identification in the event of an accidental spill. The elements included Ag, Al, B, Ba, Be, Bi, Ca, Co, Cr, Cu, Fe, K, Li, Rb, Cd, Mg, Mn, Mo, Na, Ni, Pb, Sb, Si, Sn, Sr, Ti, V, Zn, Zr, La, and Y. Details of these analyses are presented by Ferrante et al. (I). From this suite, Mg and Na were setected for determination in the plume samples. These elements occur at high concentrations in the discharge samples, and they serve as indicators of the behavior of chemical species associated with the particulate and dissolved fractions, respectively, of discharged materials. Sulfate and chloride were also determined because they occurred at high concentration in the drilling-rig discharge. The plume chemistry survey was conducted on 31 May when drill cuttings were being discharged to the Lake. After completion of a nephelometric survey to determine the plume dimensions and heading, triplicate water samples for chemical analysis were collected at 6 locations along the longitudinal axis of the plume and at the reference stations (Figure IC). These samples were analyzed for Mg, Na, chloride, sulfate, volatile hydrocarbons, and carbon tetrachloride extractable hydrocarbons (CTEH). Mg and Na were measured by atomic absorption analysis (I, 3). Sulfate and chloride were measured with a Dionex Model 14 ion chromatograph and checked gravimetrically (1, 3). The volatile hydrocarbons methane, ethane, and propane were determined by gas chromotography ( 4 , 5 ) . Carbon tetrachloride extractable hydrocarbons were measured on Beckman Model 4260 and Digilab FTS2O infrared spectrometers (1).
Results The least-squares regression relationship between the dry weight of TSS (Y) in lake water samples and the 364
Envlron. Sci. Technol., Vol. 16, No. 6, 1982
Table I. Concentrations of Sodium, Magnesium, Sulfate, and Chloride at Midpoint of Transect across Plume C on 31 May, in the Drilling Discharge Fluid, and at the Reference Reference Stations on 31 May sample designation
dist from discharge, m
Mgb SQ,'-"C1272.0 618.0 265.0 605.0 MN 14c Plume Transects 8.8 21.6 18.9 l a (2 m) 25 7.5 l b (2 m ) 25 7.5 8.9 2a (2 m ) 100 9.9 8.7 22.3 18.6 2b (2 m) 100 10.1 8.3 3a (2 m) 200 10.0 8.4 22.5 19.0 3b (2 m) 200 10.0 8.4 4a (2 m) 330 9.9 8.3 22.0 19.0 4b (2 m ) 330 10.0 8.4 5a (2 m) 140 10.1 8.5 22.3 19.0 5b (2 m) 140 10.2 8.3 6a (2 m) 160 10.2 8.1 22.3 19.1 6b (2 m ) 160 10.0 8.2 Reference Stations R, ( 2 m ) 10.0 8.3 22.7 19.6 8.3 22.9 19.5 R2 (2 m) 9.8 R, ( 1 4 m ) 10.2 8.3 .ad na Rz ( 1 4 m ) 9.9 8.3 na na drilling mud 28.4 x 104 a Filtered. Unfiltered. Undiluted drilling discharge fluid from the Guelph Formation, The Na value for the unfiltered sample was 282.0; the Mg value for the filtered na = not available. sample was 49.3.
concn, kg/L methane
ethane
Plume Transects
