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SEDC ® R
<br /> SIECOR
<br /> ' newly installed wells contained maximum concentrations of TPHgand MtBE of 72 00
<br /> 0 ,.
<br /> ppb (MW-6) and 750 ppb (MW-6), respectively (IT, 2001).
<br /> Between June 2002 and November 2002, SECOR performed three phases of off-site
<br /> assessment at the site. The initial phase was conducted on June 5, 2002 and consisted
<br /> ' of the advancement of five geoprobe borings (GP-1 through GP-5). Based on the soil
<br /> and groundwater analytical results from GP-1 through GP-5, SECOR performed the
<br /> second phase of offsite assessment on June 21, 2002. The second phase of off-site
<br /> ' assessment consisted of four additional step-out geoprobe borings (GP-6 through GP-
<br /> 9). The final phase of offsite assessment, conducted in November 2002, consisted of A
<br /> ' the installation of six groundwater monitoring wells (MW-10 through MW-15) (SECOR,
<br /> 2003).
<br /> In October 2003, SECOR arranged to sample the Lathrop Grammar School irrigation
<br />' well, located approximately 1,600 feet northeast of the site. This well was the closest of
<br /> three wells identified during a 2000-foot radius receptor survey conducted at the site.
<br /> The well is used to irrigate the grammar school and operates from 7:00 pm to 5:10 am.
<br />' The well was sampled at 4:40 am (under supervision of Manteca Unified School District
<br /> staff), near the end of the well pumping cycle. The water sample was collected from a
<br /> spigot at the well head. The sample was analyzed for total petroleum hydrocarbons
<br /> i calculated as gasoline (TPHg), benzene, toluene, eth (benzene
<br /> Y , xylenes {BTEX
<br /> compounds), and fuel oxygenates MtBE, EtBE, TAME, TBA, DIPE, EDB, 1,2-DCA, and
<br /> ethanol by EPA Method 8260, single run. These constituents were reported as not '
<br />' detected (SECOR, 2003).
<br /> In October 2003, SECOR conducted a study to determine if the Lathrop Grammar
<br />' School irrigation well was affecting groundwater flow or gradient beneath the site.
<br /> Groundwater transducers were placed in site wells and recorded groundwater `T
<br /> elevations for 4 days. Based on data collected from the transducers, it was determined r
<br /> n
<br />' that the Lathrop Grammar School well was not influencing groundwater elevation and
<br /> flow at the site (SECOR, 2003).
<br /> 4.1
<br /> On June 12, 2004, SECOR supervised the advancement of five geoprobe borings (GP-
<br /> 10 through GP-14). The purpose of the work was to delineate the lateral extent of '
<br /> petroleum hydrocarbon impact in soil and groundwater downgradient of the site, and to
<br /> determine the placement of wells to complete delineation of the plume. Soil samples at
<br /> 10 and 15 feet bgs from geoprobe borings GP-10 through GP-14 were collected and
<br /> submitted for laboratory analysis. Soil samples were analyzed for TPHg, BTEX, and
<br /> fuel oxygenates by EPA Method 8260B. TPHg, xylenes, and ethanol were reported in
<br /> soil sample GP-13@10 at concentrations of 1.2 mg/kg, 0.0095 mg/kg, and 0.65 mg/kg,
<br /> respectively. No detectable concentrations of petroleum hydrocarbons were reported in
<br /> the soil samples from borings GP-10, GP-11, GP-12, and GP-14. Groundwater "grab"
<br /> samples collected from each of the geoprobe boring locations were analyzed for TPHg, .
<br /> q.
<br /> BTEX, and fuel oxygenates by EPA Method 8260B. MtBE was reported at a
<br /> 1205 SCMAOC 3
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