An increased content of sodium (Na) in water wells in the eastern part of the Black River Basin, that is within the Essex Valley, is a cause of concern for the usability of good quality ground water for domestic uses.
The contamination results from leaky industrial waste ponds, known as mud lakes, which were created as recipients of waste waters from the bauxite- to-alumina processing. The lakes are "sitting" at an elevation of about 140 m (AMSL) over very permeable, fractured and karstified limestone rocks. Many wells were drilled specifically to monitor the Na content around mud lakes which are located west of Nain.
The location map of monitoring wells and Na content in 1999 show the following:
Sodium is here utilized as a tracer to indicate the contamination or the spread of the Na-enriched plume coming down from the waste ponds. Some of monitoring wells point at the time when the plume reached their respective sites.
The well ALPART 3 is one of ALPART's "scavenger" wells. Its role is to divert the flow of the contaminated ground water from its northerly course toward the bauxite plant at the east. It creates a cone of depression by extensive pumping and intends to capture most of Na from the waste pond that may have reached the aquifer. Note extremely high pH values (close to 12). It is partly successful considering that the Na content increased from 794 ppm in 1984 to 1320 ppm in 1999.
The relative success of the scavenging operation is displayed at the site of the well BR-079 (ALPART 9 or Alpart's Pepper 5), which is some 4 km to the north of the northern waste pond. In early 1970's, the Na content was less than 10 ppm, which pointed at uncontaminated ground water. From 1981 there is a steady increase in the Na content with the value of about 60 ppm in 1999.
The success of pumping at the ALPART's plant at Nain is demonstrated at the site of the well BR-083 (Alpart 14A), then the well BR-090 (Alpart 21) which is just north of the northern pond. In this well, the pH value from the 10+ range became reduced to slightly over 7.0, which is "normal" for a limestone aquifer.
The National Water Commission wells at Pepper-Goshen, see the well BR-094 at Phantillands, do not show yet any sign of contamination by Na. This is due to the fact that ALPART's wells at Pepper intercept the contaminant and divert it to their cone of depression.
However, the contamination has spread also to the south of the waste ponds. The well at New Forrest,BR-031, which is some 7.5 km south-east from the southern tip of the south pond, displays an increase in Na almost immediately after the ponds became operational. The same is with the well at at Duffhouse Junction in Bull Savannah.
By monitoring the content of Na in ground water in the Essex Valley, one monitors the extension of the contaminant plume, in space and time. Sodium itself is not a hazardous ingredient. People can drink water with up to 250 ppm of sodium, and in some thermo-mineral waters even more. Yet, the problem of contamination remains since the waste ponds may leak some heavy metals such as Cd, Zn, Pb, etc. which are discharged as impurities from bauxite.
The Mandeville water supply which gets the water from N.W.C. wells at Pepper-Goshen, needs to be protected from Na-contaminated water reaching the wells. The following map shows relative location of Mandeville with respect to pumping sites within the Essex Valley and bauxite plant. A sketch shows the directions of pumping and use of ground water from the Essex Valley.
