Groundwater Professional Bulletin Board

CLARIFICATION ON BEDROCK AND INSTALLATION
OF A MONITORING WELL AT THE SOURCE

The following is a clarification of the guidance provided on page 47 of Tier 2 Guidance concerning the installation of source monitoring wells at nongranular bedrock sites.

During installation of monitoring wells for Tier 2, if soil contamination is less than the detection limit using lab analysis, a monitoring well must be put at the suspected source. (The detection limit must be less than the Tier 1 level for soil leaching to groundwater ingestion.) However, if lab analysis has not been completed for source samples, and there is no need to remobilize before the Tier 2 submittal, either of the two options for after soil removal/remediation may be used (as described below).

Options after soil removal/remediation, to get no action required (NAR) classification for nongranular bedrock:

1. If there are no monitoring wells at the source, monitor until concentrations in all monitoring wells are less than applicable Tier 1 levels for three years. (Applicable Tier 1 levels will be for either actual or potential groundwater ingestion.)
   
   OR
   
   
2. Install a monitoring well at the source, monitor until concentrations in all monitoring wells are less than applicable Tier 1 levels once.