This comment regards the benzene groundwater contamination on the Verizon SDWC property and subsequent properties. There does not seem to be sufficient sampling points located on the properties to the north of N-3 or west of V-MW-9 to accurately estimate the true extent of the plume. Similarly there appears to be insufficient data points to the north east of V-MW-16 on the north part of the Verizon SDWC property to properly determine a contaminant boundary . Was subsequent sampling and monitoring performed alongside I-76 or on the other side of the highway near the Philadelphia Housing Authority building to further delineate offsite impacts? Water level gradients seem to indicate slight a NE flow off of the Verizon SDWC that this report did not consider or investigate. In addition, the pump-and-treat system along Maiden Ln does not look like it changes the gradient of the plume that extends to the Verizon SDWC property and beyond. What is being done to properly delineate and mitigate this off-site benzene issue?

The Verizon SDWC property is a separate remediation site.  A Site Characterization Report indicating closure via a combination of Statewide Health and Site Specific Standards was submitted by the property owners and approved in 2012.   A subsequent SSS Remedial Action Plan was approved in 2012.  A Remedial Action Completion Report was submitted in 2015, in which they requested closure via a combination of Statewide Health, Site Specific, and Background Standards due to impacts at the southern property boundary which is across Maiden Lane from the then refinery.

Groundwater gradient in the area between the Verizon property and the area of the remediation system along Maiden Lane is shallow but we generally observe a groundwater flow pattern that indicates convergence in the vicinity of the AOI 8 boundary with Maiden Lane, near the Mifflin Street Sewer.

The benzene dataset presented in Figure 9-2 of the AOI-8 RIR utilized maximum concentrations from 2014-2016 groundwater sampling, as this was the most comprehensive dataset at the time. It should be noted that benzene concentrations measured in groundwater varied through that time period (as low as 6.2 micrograms per liter (ug/L) in a V-MW-9 groundwater sample on 3/16/16; benzene was not detected in well N-3 groundwater samples on 6/2/14, 3/17/16, and 5/27/16; benzene was not detected in well V-MW-16 groundwater samples on 4/17/14, 6/25/14, 9/5/14, and 3/16/16 (See AOI 8 RIR Table 4-2). An overall decreasing benzene trend in this area was demonstrated in the RIR in Figure 9-5b.

Subsequent gauging and sampling supports the RIR interpretations of groundwater flow patterns in this area and indicates recent N-3 benzene concentrations ranging from non-detect to 6.75 ug/L in groundwater.  The area wells will continue to be monitored and data will be incorporated into future modeling efforts.

A horizontal recovery well was installed in that area for the purpose of LNAPL recovery as well as to mitigate any potential migration of dissolved contaminants away from AOI 8.  The treatment system in that location was started up in January 2021.  Therefore, you would not have seen any changes in the groundwater gradient as a result of pumping in reports submitted prior to that time.