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. Quarterly Groundwater
<br /> Monitoring Report
<br /> Frontier Transportation
<br /> ' 0399-085
<br /> April 5, 1999
<br /> Laboratory analytical results identified no detectable dissolved concentrations of TPH-g
<br /> above 50 pg/L from groundwater samples collected from MW-1, MW-2, MW-4, MW-5, MW-6,
<br /> and MW-7 using EPA method 8015 modified. Monitoring wells MW-1, MW-2, and MW-4
<br /> identified decreases in TPH-g concentrations from 130 µg/L, 180,ug/L, and 110,ug/L,
<br /> respectively, during the previous monitoring episode performed in December 1998. TPH-g
<br /> concentrations attenuated significantly in MW-3 from 26,000 µg/L in September 1998 to 4,300
<br /> gg/L in December 1998 to 2,500µg/L in February 1999. Please see Figure 6, for recent TPH-g
<br /> isoconcentration map.
<br /> Low level concentrations of BTEXr
<br /> we e identified in groundwater samples collected from
<br /> ' MW-1, MW-2, MW-4, MW-5, MW-6, and MW-7 using EPA method 8020. Groundwater
<br /> analyzed from wells MW-2, MW-5,MW-6, and MW-7 identified exclusively toluene at 0.6 j,4g/L,
<br /> 0.6 ,ug/L, 0.5 ug/L, and 0.5 gg/L, respectively. BTEX concentrations from monitoring well
<br /> MW-4 identified a decrease from<8.3 ug/L in December 1998 to <3.0 gg/L in February 1999.
<br /> Monitoring well MW-1 observed a decrease in BTEX from <17.5 µg/L in December 1998 to
<br /> <4.4 pg/L in February 1999, MW-3 identified a maximum BTEX concentration of 588 /.zg/L in
<br /> ' February 1999, an attenuation of 71% from 2,036 µg/L as identified in December 1998. See
<br /> Figure 7 for Benzene Isoconcentration Map.
<br /> ' MTBE was identified in groundwater from two monitoring wells only. Groundwater
<br /> samples collected from monitoring wells MW-1 and MW-3 identified a decrease in MTBE
<br /> concentrations from 379 Wg/L to 14 gg/L and from 3,700 µg/L to 1,100 µg/L, respectively, since
<br /> 1 the previous monitoring episode (December 1998) using EPA method 8260. No detectable
<br /> concentrations of the remaining EPA method 8260 analytes were identified from groundwater
<br /> sample analysis with the exception of 200 gg/L as 1,2,4-Trimethylbenzene in MW-3 (See Table
<br /> 2)
<br /> 5.0) CONCLUSIONS AND RECOMMENDATIONS
<br /> Based on groundwater sample analysis results the dissolved petroleum hydrocarbons
<br /> appeared to be localized near the former UST location and monitoring well MW-3 in shallow
<br /> groundwater. Groundwater collected from monitoring wells MW-1, MW-2, MW-4, MW-5,
<br /> MW-6, and MW-7 identified low level to no detectable concentrations of petroleum dissolved
<br /> hydrocarbons (TPH-d, TPH-g, BTEX, and MTBE). Concentrations support that the dissolved
<br /> phase plume is confined to the site and is defined to the east, west, north and south of the former —_
<br /> UST area. Groundwater collected from monitoring well MW-3 identified an attenuation in
<br />' dissolved petroleum hydrocarbon concentrations since the previous monitoring episode.
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