Volatile Organic Compounds’ Impact to Groundwater

Posted on September 9th, 2013

In June 2008 when the NJDEP released the new Soil Remediation Standards (SRS) (7:26D), it released revised residential direct contact (RDC) and nonresidential direct contact (NRDC) SRS.  At the same time, the NJDEP also released default Impact to Groundwater Soil Screening Levels (IGW SSLs).  While the NJDEP default IGW SSLs were not specifically promulgated, 7:26D did propose these levels, and accepted that site-specific IGW SRS could be developed.  Several methods were provided to complete this task, including Soil-Water Partition Equation (SWPE), Synthetic Precipitation Leaching Procedure (SPLP), vadose zone model and Dilution Attenuation Factor (SESOIL/DAF), and groundwater transport models (SESOIL/AT123D or SESOIL/MODFLOW-MT3D).  NJDEP also provided the Immobile Contaminants guidance document for the constituents that are highly adsorbed.  The NJDEP provided guidance for these methods, and they were used with some success. However, when none of these methods were successful, the NJDEP default IGW SSL was to be used.  Because the IGW pathway could not be addressed through a deed notice or other institutional or engineering control, and because the NJDEP default IGW SSLs are so low, the IGW pathway began to drive many remediations. 

Since the introduction of the 2008 RDC/NRDC SRS and IGW SSLs, the NJDEP has introduced additional methods (i.e., compliance attainment) and expanded existing methods (i.e., SPLP for VOCs) for complying with these requirements.  However, addressing the IGW pathway does significantly affect the way field sampling plans are prepared.  In order to have success with the NJDEP data analyses approaches, the investigator should carefully plan the investigation so that necessary data to address the impact to groundwater pathway is collected. For instance information, such as: depth to groundwater; vadose zone horizontal and vertical soil contamination delineation; total organic carbon; sieve analyses with distinct percentages for sand, silt and clay fractions; and slug/pump tests may be necessary and should be collected.  With the right data available, there is great flexibility with regards to addressing the IGW pathway and reducing site remediation costs.   

In general, the NJDEP appears to be relaxing its position with respect to addressing the IGW pathway, particularly in cases where the threat to the environment and human health is truly not unacceptable. However, the IGW standards remain the driving factor for remediation at many sites and as environmental professionals, we are obligated to work within the current regulatory framework.

At JMS we are experiencing success with the various available methods to close sites for which extensive, expensive or impracticable remedial actions would otherwise be required.  For an example of how JMS is working within the framework of the NJDEP regulations and guidance to develop effective solutions for its clients, click this link to read a recent project case study. 


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