diff --git a/app/js/DockerRunner.js b/app/js/DockerRunner.js
index 5ac234b..393ce3d 100644
--- a/app/js/DockerRunner.js
+++ b/app/js/DockerRunner.js
@@ -35,6 +35,9 @@ const usingSiblingContainers = () =>
     x => x.sandboxedCompilesHostDir
   ) != null
 
+let containerMonitorTimeout
+let containerMonitorInterval
+
 module.exports = DockerRunner = {
   ERR_NOT_DIRECTORY: new Error('not a directory'),
   ERR_TERMINATED: new Error('terminated'),
@@ -646,17 +649,29 @@ module.exports = DockerRunner = {
       { maxAge: DockerRunner.MAX_CONTAINER_AGE },
       'starting container expiry'
     )
+
+    // guarantee only one monitor is running
+    DockerRunner.stopContainerMonitor()
+
     // randomise the start time
     const randomDelay = Math.floor(Math.random() * 5 * 60 * 1000)
-    return setTimeout(
-      () =>
-        setInterval(
-          () => DockerRunner.destroyOldContainers(),
-          (oneHour = 60 * 60 * 1000)
-        ),
+    containerMonitorTimeout = setTimeout(() => {
+      containerMonitorInterval = setInterval(
+        () => DockerRunner.destroyOldContainers(),
+        (oneHour = 60 * 60 * 1000)
+      )
+    }, randomDelay)
+  },
 
-      randomDelay
-    )
+  stopContainerMonitor() {
+    if (containerMonitorTimeout) {
+      clearTimeout(containerMonitorTimeout)
+      containerMonitorTimeout = undefined
+    }
+    if (containerMonitorInterval) {
+      clearInterval(containerMonitorTimeout)
+      containerMonitorTimeout = undefined
+    }
   }
 }
 
diff --git a/npm-shrinkwrap.json b/npm-shrinkwrap.json
index 40fed3c..05e00cd 100644
--- a/npm-shrinkwrap.json
+++ b/npm-shrinkwrap.json
@@ -1536,12 +1536,6 @@
       "resolved": "https://registry.npmjs.org/coffee-script/-/coffee-script-1.6.0.tgz",
       "integrity": "sha1-gIs5bhEPU9AhoZpO8fZb4OjjX6M="
     },
-    "coffeescript": {
-      "version": "1.6.0",
-      "resolved": "https://registry.npmjs.org/coffeescript/-/coffeescript-1.6.0.tgz",
-      "integrity": "sha1-bdTeHrYveE2MjYCWdVLLpUf/2d4=",
-      "dev": true
-    },
     "color-convert": {
       "version": "1.9.3",
       "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.3.tgz",
diff --git a/package.json b/package.json
index c38621a..87403ca 100644
--- a/package.json
+++ b/package.json
@@ -44,7 +44,6 @@
     "babel-eslint": "^10.0.3",
     "bunyan": "^0.22.1",
     "chai": "~1.8.1",
-    "coffeescript": "1.6.0",
     "eslint": "^6.6.0",
     "eslint-config-prettier": "^6.10.0",
     "eslint-config-standard": "^14.1.0",
diff --git a/test/unit/js/DockerLockManagerTests.js b/test/unit/js/DockerLockManagerTests.js
index 177d7a2..bc13c5a 100644
--- a/test/unit/js/DockerLockManagerTests.js
+++ b/test/unit/js/DockerLockManagerTests.js
@@ -12,7 +12,6 @@
 const SandboxedModule = require('sandboxed-module')
 const sinon = require('sinon')
 require('chai').should()
-require('coffee-script')
 const modulePath = require('path').join(
   __dirname,
   '../../../app/js/DockerLockManager'
diff --git a/test/unit/js/DockerRunnerTests.js b/test/unit/js/DockerRunnerTests.js
index 597c5d3..d17d906 100644
--- a/test/unit/js/DockerRunnerTests.js
+++ b/test/unit/js/DockerRunnerTests.js
@@ -17,7 +17,6 @@ const SandboxedModule = require('sandboxed-module')
 const sinon = require('sinon')
 require('chai').should()
 const { expect } = require('chai')
-require('coffee-script')
 const modulePath = require('path').join(
   __dirname,
   '../../../app/js/DockerRunner'
@@ -89,6 +88,10 @@ describe('DockerRunner', function() {
     return (this.Settings.clsi.docker.env = { PATH: 'mock-path' })
   })
 
+  afterEach(function() {
+    this.DockerRunner.stopContainerMonitor()
+  })
+
   describe('run', function() {
     beforeEach(function(done) {
       this.DockerRunner._getContainerOptions = sinon