• Quarry void for non-hazardous landfill

For some years ESI has been involved in monitoring groundwater at a limestone quarry in the southwest of England.  Discussions over a new proposal to use the quarry void for non-hazardous landfill led to a request to ESI to review the importance of the limestone as an  aquifer. 

An interim report showed that the unit was not used for local private or public water supply and that its hydraulic         conductivity was limited.  However there were outstanding questions about the limestone’s contribution to baseflow in a nearby stream, which is an important environmental resource.  The stream is fed by springs arising on a number of geological units, but the interactions between groundwater in these units and surface watercourses are not well understood. If pollution of the limestone were to arise, it is important to know what consequences (if any) there might be for surface water.

ESI has therefore begun a series of visits to gauge the flows in the stream itself and its     tributaries, as they flow across a series of beds including the limestone in question.  A continuous flow logger has been installed on the stream: this is recording frequent measurements that are downloaded on a monthly basis.  We have also established a number of other monitoring points for periodic flow gauging using an impeller meter (see left). Once data collection is complete, we will carry out a baseflow separation of the       continuous log data (see example in lower figure) in order to judge the proportion of the stream’s flow that is supported by groundwater. The    comparison of flows at the different gauging points will also indicate the relative contributions of the different strata over which the stream    system flows, so that it will be possible to judge the importance of the contribution provided by the quarried limestone unit.