|
-
<br /> r
<br /> y f
<br /> r 4
<br /> 2. SITE HISTORY AND PREVIOUS INVEsTIGA'1'I0NS
<br /> 2.1 TANK PULL AND SOIL EXCAVATION
<br /> On 24 July 1986,American Environmental Management Corporation (AEMC)removed and
<br /> disposed of three underground fuel storage tanks and one underground used oil tank. Two of the
<br /> four closure samples collected and analyzed from below the fuel tanks at a depth of 12 feet
<br /> contained concentrations of volatile hydrocarbons. These samples were also analyzed for total
<br /> l,;ad and 1,2-dibromomethane (EDB). No EDB was detected in any of the samples,and normal
<br /> background levels of lead were reported for all samples,indicating no release of leaded gasoline
<br /> (described in I-larding Lawson Associates [HLA} 1986; data not available). LILA was subse-
<br /> quently commissioned to investigate the presence of hydrocarbons in the soil and groundwater,
<br /> and they 4eepened the excavation of the tank field to approximately 20 feet below ground sur-
<br /> face. HLA collected seven soil samples (EX-1-EX-7,Table I) and one groundwater sample
<br /> (GW1,Table 2)from the bottom of the excavation. Three of the soil samples contained levels of
<br /> total petroleum hydrocarbons (TPII)up to 6,900 mg/kg. The, groundwater sample contained
<br /> 130,000 pg/L TPH. Cumulatively, approximately 300 cubic yards of soil were excavated by
<br /> AECM and HLA (represented by samples SP1 [1-121, SP2 [1-12], SP1-4, SP5-8, SP9-12,
<br /> RSP1-4,RSP5-8,and RSP9-12,Table 1). The soils were aerated onsite in accordance with San
<br /> Joaquin Local Health Department(SJLHD)guidelines. After aeration (samples AS-1 and SP3-1,
<br /> Table 1),the soil was used to backfill the excavation,with the permission of SJLHD.
<br /> On 11 December 1986,AEMC removed the piping at the site. Under the direction of D. Moe of
<br /> the San Joaquin Local Health District,six soil samples were,collected at a depth of two feet at
<br /> four locations, ESI-ES4, and analyzed for the aromatics (BTEX)and for organic lead. No
<br /> concentrations of organic lead greater than 0.05 mg/kg were detected in the six samples(ES 1 and
<br /> ES2 were collected in duplicate),and except for sample ES3 (at the southwest corner of the tank
<br /> field, near one of the pump islands), no concentrations of benzene, toluene, ethylbenzene,or
<br /> xylenes (BTEX) greater than 0.001 mg/kg were measured in the soil samples. Concentrations of
<br /> toluene and ethylbenzene,0.076 mg/kg and 1.2 mg/kg,respectively,were detected in ES3; the
<br /> concentrations of benzene and xylenes in this sample,however,were less than 0.001 mgfkp.
<br /> 2.2 GROUNDWATER MONITORING WELLS-IILA
<br /> On 26 and 27 January 1987,NLA installed three groundwater monitoring wells (MW1-MW3,
<br /> Figure 3). During well installation,soil samples were obtained for analysis for total petroleum
<br /> hydrocarbons (TPIi) using EPA Methods 5030 and 8015 (see Table 1). TPH Was rior detected
<br /> in one soil sample,collected at 16 feet in boring MW2, at a level of 60 ntg/kg-
<br /> opment,no liquid-phase petroleum hydrocarbon (LPPI-i) was found in the wells. The direction
<br /> of groundwater flow was determined to be northeast(N50E), at a gradient of 0.001 (HLA 1987).
<br /> After the wells were developed,water samples were collected and analyzed for TPI-1 (as gaso-
<br /> line)and for benzene, toluene,and xylenes. The analytical results (Table 2) suggested that the
<br /> 2
<br /> �err»94vj.,91M
<br /> v-,
<br />
|