Minutes & Attachments - Marine Corps Base Camp Pendleton

II. Extent of Contamination –Recent Additional DelineationFour new monitoring wells installed and sampled in 2012:• 1115-MW9– Purpose: Define deep aquifer VOC conditions on west side of Site 1115.– Results were below Maximum Contaminant Levels (MCLs). Trichloroethene(TCE) and chloroform were above Project Screening Limits (PSLs).• 1115-MW10 and 1115-MW11– Purpose: Shallow aquifer VOC delineationsoutheast of Site 5/8/9/17– Results were below PSLs• 1115-MW12– Purpose: Refine limit of VOC contamination innortheast portion of Site 1115– Results were below MCLs; Above PSLs forbenzene, TCE, napthalene9 NAS North Island Operable Unit 20January 17, 2013II. Conceptual Target Treatment Zones(TTZs)• Purpose: TTZs are designated to promoteoptimal selection of response actions andremedial alternatives.• TTZs represent distinct chemical and/orhydrogeological conditions.• Delineation of boundaries of dilute plume (nonsourcearea) TTZs will be based on thedominant contaminants present in each area.• “Source zone” TTZs will be defined based onestimated contaminant concentrationthresholds.10 NAS North Island Operable Unit 20 January 17, 2013