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FMS #24 Site Investigation Report
<br />California Army National Guard
<br />• EXECUTIVE SUMMARY
<br />ES.1 This site investigation report was prepared for the California Army National Guard
<br />(CA ARNG) under contract to the U.S. Army Corps of Engineers, Sacramento District, following
<br />United States Environmental Protection Agency (EPA) Comprehensive Environmental Response,
<br />Compensation, and Liability Act (CERCLA) guidance (EPA, 1988) and the California Code of
<br />Regulations, Title 23 (Barclays Law Publishers, 2000). The boreholes were drilled to collect soil, soil
<br />gas, and groundwater samples at the former underground storage tank (UST) location at the
<br />CA ARNG Stockton Field Maintenance Shop (FMS) #24 to evaluate the presence of fuels, volatile
<br />organic compounds (VOCs), and metals contamination. The fieldwork was conducted in accordance
<br />with the work plan, Final Field Sampling Plan, Stockton FMS #24 UST Site, California Army
<br />National Guard Site Investigations (URS Group, Inc. [URS], 2006), and the Field Sampling Plan
<br />Addendum (URS, 2007).
<br />ES.2 The Stockton FMS #24 is located at 8010 South Airport Way, Stockton, California, 95206
<br />(Figure ES -1) and includes a former refueling area with dispenser island and USTs (removed),
<br />vehicle inspection rack, one active and one inactive oil/water separator (also identified as clarifiers
<br />by the CA ARNG), vehicle maintenance facility, and hazardous waste storage sheds.
<br />ES.3 This report documents the activities conducted at the former UST location at FMS #24.
<br />FMS #24 previously contained a fuel island with two associated dispensers and fuel lines and USTs
<br />for fueling privately owned and installation vehicles. The contamination source that was investigated
<br />at this site is the former location of two USTs (one 5,000 -gallon diesel and one 10,000 -gallon
<br />gasoline) and associated piping. The USTs were removed in April 1996. During removal and
<br />excavation of the USTs and associated piping, soil samples were collected, and based on soil sample
<br />• analyses, releases of diesel fuel and gasoline had occurred from the two USTs (Versar, Inc., 2004). It
<br />is unknown whether soil removed from the excavation was placed back into the UST excavation pit
<br />or if the remaining space was filled with clean fill material.
<br />•
<br />ESA The site investigation conducted by URS in May 2007 included the collection of soil, soil gas,
<br />and groundwater samples for analysis from five hollow -stem auger (HSA) borings at the site.
<br />Samples were taken from the five boring locations and analyzed for total petroleum hydrocarbons
<br />(TPH) (diesel and gasoline) by EPA Method SW8015; VOCs (including methyl tert butyl ether
<br />[MtBE]/benzene, toluene, ethylbenzene, and xylenes [BTEX]/oxygenates) by EPA Method
<br />SW8260B; and metals by EPA Method SW6010B. Soil and groundwater samples showed concen-
<br />trations of TPH as diesel (TPHD), TPH as gasoline (TPHG), and BTEX compounds in all samples. A
<br />detailed presentation of investigation results is included in Section 3.3. Based on the results of the
<br />May 2007 investigation, sampling and analysis of additional soil borings was recommended to
<br />further evaluate the extent of contamination. In October of 2007, URS conducted a second phase of
<br />soil and groundwater sampling from six step -out boring locations to help define the lateral extent of
<br />soil and groundwater contamination at the former UST site. (Four shallow soil gas locations were
<br />also drilled, and soil gas samples collected, to evaluate potential health risks to workers in site
<br />buildings.) In summary, results from step -out borings (initial step -outs were located approximately
<br />300 feet north, east, south, and west of Phase 1 borings) showed no concentrations of contaminants
<br />of concern in soil samples. Groundwater samples in two of the six Phase 2 borings contained BTEX
<br />and TPHD/TPHG compounds. The lateral extent of soil and groundwater contamination has been
<br />determined by the URS investigations.
<br />December 2007
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