|
I
<br /> PROBLEM ASSESSMENT R@ORf
<br /> INCLUDING gUARn RLY MOW—DONO rIEPOK
<br /> 1794 East Yosemite Avenue.Manteca.Caltlornia
<br /> 4.0 PROBLEM ASSESSMENT
<br /> FA 4. Petroleum Ff Pdroparbons in Soil
<br /> Analytical results indicate that the soil beneath the site contains BTEX and gasoline. To date,
<br /> a total of twenty soil samples from soil and monitoring well bcrings drilled by ETS, Delta, NGA,
<br /> d and analyzed for BTEX and TPH, as gasoline. Historically,
<br /> and Aegis have been submitte
<br /> depths of 15 and 20 feet. ThP
<br /> the highest concentration of hydrocarbons has occurred at dep
<br /> sit
<br /> maximum I©vels of benzene, toluene, found
<br /> 40,000
<br /> in
<br /> at asmaxi�mumilc nt ehe ntrationeof
<br /> ! 20, 110, 170, and 95 ppm, respectively, TPH was
<br /> 40,000 ppm. The Leaking Underground Fuel Tank (L1JFf) Manual (California Department of
<br /> Water Resources, 1989) maximum allowable level, based on site-specific characteristics
<br /> (depth-to-groundwater, annual rainfall, presence of wells in vicinity) for benzene and toluene
<br /> is 0.3 ppm, for ethylbenzene and xylenes is 1.0 ppm, and for TPH, as gasoline, is 100 pprn•
<br /> 4 Figures 7 and 8 show inferred zero lines for the lateral extent of hydrocarbons in the soil at
<br /> ' ce, respectively. The crass-section
<br /> depths of 15 and 20 feet below surfaan Figure 4 shows
<br /> the inferred vertical extent of hydrocarbons in soil.
<br /> E 4.2 Petroleum Hydrocarbons in Groundwater
<br /> %
<br /> i Elevated concentrations of petroleum hydrocarbons have been detected in all groundwater
<br /> samples collected from MW-1B (formerly MW-1A). MW-1 (abandoned in 1990) showed
<br /> 1 .*ti bove detection limits at the time the well was
<br /> concentrations of xylenes, TPH, and EDC a
<br /> i installed. in August 1988. Concentrations above the detection limits of benzene,
<br /> e#hylbenzene,xylenes,TPH,as gat3oline, and EDC were observed in groundwater from MW-2
<br /> e.hen the well was first installed in April 1989. Groundwater in MW-2 showed benzene,
<br /> is
<br /> toluene, xylenes, and TPH, as gasoline, from the sample collected on July 22, 1991
<br /> Benzene, ethylbenzene, rylencs,and EGC were found above the detection limits in MW-3 at
<br /> e the time of installation in April 1989. EDC was detected in the groundwater sample from MW-
<br /> ' 3, collected February 1, 1991.
<br /> r'a
<br /> l Analytical results from water samples collected from MW-1B (formerly MW-1B) indicate that
<br /> the
<br /> concentrations of benzene, toluene, xylenes, TPH,
<br /> ECB, and EDC have increased. The
<br /> e. and
<br /> July 22, 1991, groundwater sample contained 370.0 ppb benzene,Tge 22 California Code
<br /> 11,000.0 ppb xylenes. The Maximum Contaminant Levels (MCLs)
<br /> of Regulations, Division 4,Chapter 15,Section 64444.5)for benzene and xylenes are 1.0 ppb
<br /> and 1,750.0 ppb, respectively. No California MCL currently exists for toluene.
<br /> 1.4 Concentra+ions of petroleum
<br /> hydrocarbons in groundwater f hydrocarbons rbonsrwe a foune above d above
<br /> limits in April 1989. With the exception of petroleum
<br /> ! ' m MW-2 after this time until the July 22, 1991,
<br /> detection limits in groundwater samples fro
<br /> sampling event.
<br /> not been found on the groundwater at the site. Figure 9 shows
<br /> Floating hydrocarbons have
<br /> -_ -- an zero line forthe extent of dissolved hydrocarbons in groundwater,
<br /> 3
<br />
|