Acid Drainage Grouting

Norfolk, VA

The Job

A 72″ CMP stream diversion pipe under a coal stockpile at a coal mine in West Virginia was experiencing acidic water infiltration. This was causing bypassed stream water to become acidic, so regulators required all of the stream flow to be pumped to treatment ponds and treated. This was expensive, and the flow volume was greater than the design capacity of the treatment system.

The Challenge

Access was quite challenging; the pipe was either 700LF or 1300LF from the nearest access points to the farthest grouting location. Additionally, the infiltrating water was pH 2.

The Solution

CJGeo recommended a hydrophobic prepolymer chemical grout with an extensive performance history in high acidity environments. CJGeo crews sealed a combination of 20 joint leaks and point infiltration sources using the prepolymer chemical grout.

To address acidic water migrating through the stone dust backfill outside of the pipe, CJGeo crews then grouted an in-situ cutoff wall in the trench just downstream of the lowest leak using permeation grouting. The mine operator installed two dewatering wells immediately upstream of the cutoff wall to intercept and pump out the acidic drainage, to keep it isolated from the stream water.