GeoInsighter Spring 2000 Newsletter
Volume 5 Number 1

MCP Alert !

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In the last issue of the GeoInsighter, Mike Dacey summarized the Massachusetts Department of Environmental Protection's (MADEP) efforts to delineate Zone IIs for all public water supply wells with 100,000 gallon per day capacities or greater by June 2000. These delineations are ongoing, and the MADEP is making adjustments to their GIS database to reflect newly delineated Zone IIs.

As discussed in the Fall 1999 GeoInsighter edition, Zone II is defined as the entire extent of aquifer deposits which could fall within, and upgradient from, a water supply production well's capture zone based upon predicted drawdown after 180-day drought conditions at the approved pumping rate. Due to the nature of local geology, Zone IIs typically have a very irregular shape and tend to follow areas characterized by the presence of permeable soil. In the past, MADEP applied an arbitrary 0.5-mile radius around a supply well as an Interim Wellhead Protection Area (IWPA) for locations where a Zone II delineation had not been conducted, regardless of the type of soil present.

The Massachusetts Contingency Plan (MCP) Tier Classification process (310 CMR 40.0500) includes several conditions that result in a site being categorically classified as Tier I, regardless of the Numerical Ranking Spreadsheet score. One of these inclusion criteria includes sites that are located within a Zone II and where ground water impacts are above MCP Method GW-1 risk standards.

Therefore, tier classified sites near public water supply wells that are scheduled for Zone II delineation should be evaluated with regard to the newly delineated Zone IIs to determine whether the adjusted boundaries impact the site's location with regard to the Zone II area. Tier II sites that were formerly outside the Zone II but are now within the Zone II area and have ground water impacts above GW-1 standards will be required to submit a Major Permit Modification to be reclassified as a Tier I site. Because of their location within a Zone II area, more stringent cleanup standards will be applied to these sites. Conversely, sites previously located within IWPAs but now outside delineated Zone IIs may elect to reclassify and possibly achieve Tier II status. These sites may have the opportunity to meet less stringent cleanup standards.

The possible location of a site with respect to the newly delineated Zone IIs may have a significant impact on the MCP requirements for these sites. We suggest that existing sites be re-evaluated with regard to possible impacts associated with MADEP's Zone II delineation efforts. For sites that may be impacted, we suggest that a strategy be developed to outline how compliance activities will be conducted until the Zone II delineation is finalized.

Michael J. Webster
mjwebster@geoinc.com

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