Page 6 of the PAERAB's Winter 2009 TAPP Contractor Newsletter

concentration trends did not appear to be unusual prior to the second injection and that technical information was provided to the USEPA and to the NJDEP prior to the injections. Arcadis clarifies that it deems prior detailed knowledge of TOC concentration trends to be essential to the effective implementation of an injection.

Text Box: as designed). This resulted in the injection wells forming an imperfect barrier. Arcadis states that actual site conditions were slightly different from those predicted during the design phase and that adjustments were effected in the field. At the December 4, 2008 technical meeting Arcadis presented its justification for initiating a second injection event on December 15, 2008.

Text Box: At the last RAB meeting Arcadis presented a slide show on the Area B groundwater remedy. The first injection of molasses as part of the bioremedy took place between September 15 and September 19, 2008. A pre-mixed, dilute molasses solution was brought in by tanker trucks and injected into wells comprising three barriers perpendicular to the shallow groundwater flow direction. The actual injection scenario was very different from what had been planned – a much lower volume (about 2/3 less) with a much greater concentration (more than double to almost quadruple) was injected into the soil. Part of the problem was the concentration of the solution that arrived – apparently there is little control of the concentration and only a rough approximation of the specified mixture can be attained. Another contributing factor was the lower permeability of the soil surrounding the wells. As a result the actual radius of influence of the injected material was less than the original design radius (e.g., 7.5 to 9 ft instead of 10 ft

Text Box: That justification was not described in the meeting minutes or the slides for the presentation but it apparently related to rapid dissipation of total organic carbon (TOC) in two of the barriers. Arcadis explains that multiple injections had been planned and that the second injection event occurred as originally scheduled. Arcadis maintains that TOC

NEW PERCHLORATE ADVISORY

The USEPA recently revised its 2006 guidance on perchlorate in groundwater. The new interim health advisory establishes a more restrictive level of 15 parts per billion (ppb) in groundwater than previous guidance

recommending a preliminary remediation goal of 24.5 ppb. Referred to as the USEPA’s Interim Drinking Water Health Advisory level it is based on the recommendations of the National Research Council. The relevant USEPA report is dated

December 2008 and it can be viewed at www.epa.gov/OGWDW/contaminants/unregulated/pdfs/healthadvisory_perchlorate_interim.pdf.

The New Jersey Department of Environmental Protection (NJDEP) provides a “Homeowner’s Guide to

Perchlorate” at

www. state.nj.us/dep/watersupply/perchlorate.htm.

This document, last updated in November 2005, provides background information on the source of perchlorate and its health effects.

PHOTO of Area B Molasses Injection activities courtesy of the US Army