|
S E C 0 R
<br />The difference between the estimated hydrocarbon mass and amount removed is most likely
<br />attributable to isolated areas within the assessment area that contain higher contaminant
<br />concentrations than previously identified. Also, the radius of influence captured by the SVE well
<br />network was larger than originally estimated. These two factors were evaluated for updated
<br />calculations; however, the updated calculations still showed greater than 200% mass removal
<br />and are not included in this report. Thus, hydrocarbons were likely extracted from soil beyond
<br />the boundaries of the original mass estimate calculations included in SECOR's June 5, 2001
<br />Problem Assessment Report/Final Remediation Plan Addendum.
<br />4.3 Petroleum Hydrocarbons Dissolved in Groundwater
<br />In A -Zone monitoring wells, MtBE was detected during the October 21, 2005 sampling event in
<br />three of 13 wells sampled, including MW -13 at 0.6 gg/l, EX -1 at 160 µg/I, and EX -3 at 8 µg/1.
<br />MtBE has been reported at concentrations of 1 µgAl or less for samples collected from MW -13
<br />during six quarterly monitoring events since sampling began in July 2000. Concentrations of
<br />MtBE at wells EX -1 and EX -3 have dropped significantly since sampling began in March 2000
<br />and January 2001, respectively. Analytical results from groundwater samples collected October -
<br />21, 2005 indicate TPHg and benzene concentrations are below laboratory reporting Iimit (Table
<br />3). The lateral extent of MtBE in the A -Zone is defined by wells MW -1, MW -2, MW -3, MW -4,
<br />MW -5A, MW -6, and MW -20A. Figure 8 illustrates the lateral extent of the plume in the A -Zone.
<br />Figures 9 and 10 illustrate the declining trend of TPHg, benzene, and MtBE in wells EX -1 and
<br />EX -2. Figure 11 illustrates the declining trend of TPHg and MtBE in well EX -3.
<br />` In B -Zone monitoring wells, the maximum concentration of MtBE reported during the October
<br />a
<br />21, 2005 sampling event was found to be 2 pg/l, in well MW -513. Currently, TPHg and benzene
<br />concentrations are below laboratory reporting limit in the B -Zone. The lateral extent of MtBE in
<br />the B -Zone is defined by wells MW -713, MW -9B, MW -11 B, and MW -1213.
<br />In C -Zone monitoring wells MW -10C and MW -19C, there are no constituents reported at or
<br />above the laboratory reporting limit.
<br />The S -Zone monitoring well (MW -8S) has not had any petroleum hydrocarbon constituents
<br />detected above the laboratory reporting limits in the quarterly groundwater samples collected
<br />from the monitoring well since May 2001,
<br />95775 NFAR REPORT Final.doc 9
<br />SECOR lntemational Incorporated
<br />ESTIMATED
<br />MEVEDQ
<br />SSREMAINING7777
<br />tsC"1S CITI]ENT
<br />HYDROCARBQN
<br />€
<br />THROUGH 3R" IN SOIL (lbs) 3
<br />PERCENTAGE
<br />NIAs lbs
<br />:
<br />' 4
<br />QUARTER 2003 " f"a REMOV
<br />QUARTER 20,3 ED
<br />Gasoline
<br />1,4501
<br />... ribs)
<br />Hydrocarbons
<br />4,132
<br />-2,682
<br />284
<br />Benzene
<br />370
<br />85.9
<br />284.1
<br />23
<br />MtBE
<br />67
<br />443.8
<br />-376.8
<br />662
<br />The difference between the estimated hydrocarbon mass and amount removed is most likely
<br />attributable to isolated areas within the assessment area that contain higher contaminant
<br />concentrations than previously identified. Also, the radius of influence captured by the SVE well
<br />network was larger than originally estimated. These two factors were evaluated for updated
<br />calculations; however, the updated calculations still showed greater than 200% mass removal
<br />and are not included in this report. Thus, hydrocarbons were likely extracted from soil beyond
<br />the boundaries of the original mass estimate calculations included in SECOR's June 5, 2001
<br />Problem Assessment Report/Final Remediation Plan Addendum.
<br />4.3 Petroleum Hydrocarbons Dissolved in Groundwater
<br />In A -Zone monitoring wells, MtBE was detected during the October 21, 2005 sampling event in
<br />three of 13 wells sampled, including MW -13 at 0.6 gg/l, EX -1 at 160 µg/I, and EX -3 at 8 µg/1.
<br />MtBE has been reported at concentrations of 1 µgAl or less for samples collected from MW -13
<br />during six quarterly monitoring events since sampling began in July 2000. Concentrations of
<br />MtBE at wells EX -1 and EX -3 have dropped significantly since sampling began in March 2000
<br />and January 2001, respectively. Analytical results from groundwater samples collected October -
<br />21, 2005 indicate TPHg and benzene concentrations are below laboratory reporting Iimit (Table
<br />3). The lateral extent of MtBE in the A -Zone is defined by wells MW -1, MW -2, MW -3, MW -4,
<br />MW -5A, MW -6, and MW -20A. Figure 8 illustrates the lateral extent of the plume in the A -Zone.
<br />Figures 9 and 10 illustrate the declining trend of TPHg, benzene, and MtBE in wells EX -1 and
<br />EX -2. Figure 11 illustrates the declining trend of TPHg and MtBE in well EX -3.
<br />` In B -Zone monitoring wells, the maximum concentration of MtBE reported during the October
<br />a
<br />21, 2005 sampling event was found to be 2 pg/l, in well MW -513. Currently, TPHg and benzene
<br />concentrations are below laboratory reporting limit in the B -Zone. The lateral extent of MtBE in
<br />the B -Zone is defined by wells MW -713, MW -9B, MW -11 B, and MW -1213.
<br />In C -Zone monitoring wells MW -10C and MW -19C, there are no constituents reported at or
<br />above the laboratory reporting limit.
<br />The S -Zone monitoring well (MW -8S) has not had any petroleum hydrocarbon constituents
<br />detected above the laboratory reporting limits in the quarterly groundwater samples collected
<br />from the monitoring well since May 2001,
<br />95775 NFAR REPORT Final.doc 9
<br />SECOR lntemational Incorporated
<br />
|