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The Impact to Groundwater Pathway and What It Means For Your Site

Posted on May 15th, 2011

Evaluating environmental soil data has recently become more complex in the state of New Jersey, due to new regulations and guidance aimed at addressing soil contamination’s potential to impact groundwater contamination and quality. Addressing this impact to groundwater pathway is now an integral part of determining if additional investigation

Evaluating environmental soil data has recently become more complex in the state of New Jersey, due to new regulations and guidance aimed at addressing soil contamination’s potential to impact groundwater contamination and quality. Addressing this impact to groundwater pathway is now an integral part of determining if additional investigation is required at a contaminated site. New Jersey Department of Environmental Protection (NJDEP) has established default Impact to Groundwater Initial Screening Levels (IGWISL) for most groundwater contaminants, which are available from the state’s website: http://www.nj.gov/dep/srp/guidance/rs/partition_equation.pdf

These default values provide a base number to compare your initial sampling results to. If no exceedances are identified, no additional evaluation is required for the impact to groundwater pathway. However these numbers are conservative, and are not appropriate for every site in New Jersey. So what do you do when exceedances are identified? Numerous questions and problems have arisen surrounding these regulations; the NJDEP recently posted responses to frequently asked questions regarding impact to groundwater here: http://www.nj.gov/dep/srp/guidance/rs/igw_faq.pdf

Generally speaking, if you have IGWISL exceedances, the next step is to establish a site specific Impact to Groundwater Soil Remediation Standard (IGWSRS). It is important to note that clean groundwater sampling results do not exempt you from this requirement, as the concern is that these soil concentrations could impact groundwater quality in the future, leading to potential groundwater contamination. The NJDEP has approved four options for establishing a site specific IGWSRS. These options are SPLP, Soil-Partitioning Equation, SESOIL, or combined SESOIL/AT123-D. Guidance documents for each of these methods, and how to determine which are appropriate for your site are available from NJDEP here: http://www.nj.gov/dep/srp/guidance/rs/igw_intro.htm

Each of these methods has its benefits and limitations, and it may require more than one method to achieve compliance. However, the use of any of these methods will likely require additional site specific data. It is important to take this into consideration when planning investigation activities, so that adequate number and volume of samples can be collected to provide as many options as possible to determine compliance, and minimize additional site mobilizations.

If all else fails, and sample results still exceed your calculated site specific IGWSRS, remediation will likely be required. As indicated in the department’s FAQ document, capping is generally not an acceptable engineering control to address IGWSRS exceedances. However, the NJDEP’s policies regarding these rules are constantly changing. So as always stay tuned to the NJDEP’s website above, and www.jmsorge.com for the most up to date information.

Thomas Burke
Project Manager, JM Sorge, Inc.


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