Modified Closure Plan Approval and Closure Report Certification for Northrop Grumman Systems Corporation, East Complex Facility


SCH Number
Public Agency
Department of Toxic Substances Control
Document Title
Modified Closure Plan Approval and Closure Report Certification for Northrop Grumman Systems Corporation, East Complex Facility
Document Type
NOE - Notice of Exemption

Document Description
When the 1995 closure performance standard could not be achieved, Northrop implemented modified closure activities such as soil, soil gas, and groundwater investigation/remediation using human health/ecological risk levels as the closure performance standard. The modified closure activities included soil boring, soil vapor extraction, confirmation sampling, human health risk assessment (HRA), and ecological screening assessment. Soil investigation was performed for the G Tanks as part of a larger sitewide subsurface investigation. Satellite 7 exhibited insignificant levels of Volatile Organic Compounds (VOCs) during the confirmation sampling of the 1995 closure. Soil gas investigation, and soil vapor extraction were performed at 65 bgs. Final modified closure activities were conducted at the G and H Tanks areas to collect additional data suitable for risk assessment purposes. All of the available residual results at the Tanks and Satellite 7 were used to perform a human health risk evaluation. After performing the modified closure activities, Northrop formally submitted a draft Modified Closure Plan which was revised per DTSC's request and deemed to be technically complete. The human health/ecological risk based closure performance standard used in the modified closure activities were a deviation from the 1995 approved Closure Plan. The change in closure performance standard and additional investigation and remediation are the basis of the proposed approval of the Modified Closure Plan for the RCRA units. Northrop submitted a Closure Certification Report for the RCRA units, which reflects the results of implementing the modified closure activities. The results demonstrated that the low residual contamination left in the RCRA units do not impact the contaminated groundwater underlying the Facility. For risk based clean closure of the RCRA units, a performance target was established relative to unrestricted residential land uses. For each receptor scenario, the performance target for the cumulative multi-media, multi-pathway cancer risk level is less than 1 x 10^-6, and the cumulative non-cancer hazard index is less than 1.0. The outdoor/indoor air cumulative excess cancer risk for all evaluated receptor scenarios for the RCRA units do not exceed these performance targets. For short-term worker exposures (1 to 8 hours), health risk management criteria applied by the U.S. Occupational Safety and Human Administration (U.S. OSHA) and California OSHA (CalOSHA) also are applicable. Based on the modeled short-term exposure to volatile emissions, none of the detected contaminants exceeded their respective acute/sub-chronic toxicity threshold criteria. No surface water or native ecological habitat receptors were identified at the Facility. The results of leaching analysis indicated that future migration of residual soil matrix to groundwater will not be significant relative to groundwater beneficial use for municipal drinking water supply. The on-site soil, and groundwater contamination at the Facility are unrelated to the RCRA units and will be addressed in the current corrective action at the Facility. Summarily, there is no evidence of additional contamination or risk to the site from the proposed closure.

Contact Information
Marie Fabilla
Department of Toxic Substances Control
Lead/Public Agency
1011 North Grandview Avenue
Glendale, CA 91201

Phone : (818) 551-2918


Los Angeles

Notice of Exemption

Exempt Status
Type, Section or Code
General Rule, Section 15061
Reasons for Exemption
The physical closure operations described were minimal and consistent with the parameters of section 15061(b)(3). The MCP, as implemented, will not result in significant effects to human health and the environment because: 1) The modified closure performance target values for unrestricted residential land uses were met; 2) The sampling methodology used was the new U.S. EPA Method 8260 Update III coupled with Method 5035, known as the closed-system purge-and-trap methodology. The use of the new method prevented the loss of VOCs during sampling, thus giving an accurate reading during analysis; 3) According to the California Department of Fish and Game, California Natural Diversity Database, there are no currently known threatened or endangered species on or near the Facility. Neither the modified closure activities nor the residual soil contaminant levels poses any ecological risk; 4) The modified closure activities utilized DTSC's current methods of risk assessment which conservatively evaluated the potential risk for outdoor soil, and indoor air under future residential exposure scenario; 5) No significant effect on off-site uses will unlikely occur from the investigation and remediation activities since the nearest residence from the RCRA units resides more than 1/4 mile; and 6) The site is in the Hazardous Waste and Substances Site List pursuant to the Government Code Section 65962.5. The RCRA units are not in the above list, however, other Underground Storage Tanks (USTs) in the Facility that were formerly under the oversight of the Los Angeles Regional Water Quality Control Board (LARWQCB), are listed. Neither of the USTs' releases will impact the RCRA units to be closed.

Disclaimer: The document was originally posted before CEQAnet had the capability to host attachments for the public. To obtain the original attachments for this document, please contact the lead agency at the contact information listed above. You may also contact the OPR via email at or via phone at (916) 445-0613.

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