Why do some of the Navy sample results have high total organic carbon (TOC) results but total petroleum hydrocarbons (TPH) were not detected?

The TOC detections most likely reflect the sample preservative rather than petroleum impacts in the samples. For the Extended Drinking Water Monitoring (EDWM) program, the Navy used ascorbic acid (Vitamin C) as a dechlorinating preservative for EPA Methods 524.2, 525.2/3, and 8260D (PIANO) analyses. As a result, the ascorbic acid was detected in the TOC analysis.