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Work Plan for Additional Subsurface Investigation
<br /> Former Helena Chemical Facility
<br /> July 13,2020
<br /> Page 2
<br /> advanced within the stormwater detection basin to assess and confirm that 1,2,3-TCP has not migrated
<br /> to groundwater and created a 1,2,3-TCP Plume in this portion of the Site.
<br /> 4. 1,2,3-TCP is used as a solvent but has also been associated with the use of agricultural chemicals—soil
<br /> fumigants (pesticides and nematicides). Contaminants likely to co-occur with 1,2,3-TCP in the
<br /> environment due to historic use or storage/distribution of fumigants include, 1,2-dibromo-3-
<br /> chloropropane(DBCP), 1,2-dichloropropane(1,2-DCP), and 1,3-dichloropropene(1,3-DCP), because
<br /> fumigants contained mixtures of these compounds. Groundwater at the Site has been analyzed for
<br /> 1,2,3-TCP and DBCP, but no 1,2-DCP or 1,3-DCP. To address this data gap, soil and groundwater at
<br /> the Site needs to be analyzed for 1,2-DCP and 1,3-DCP, at a minimum, in the area where the highest
<br /> 1,2,3-TCP has been detected.
<br /> 5. Staff concur with the Report's recommendation to install shallow groundwater monitoring wells to the
<br /> north and northeast of the Site.However, because nitrate and 1,2,3-TCP were detected at concentrations
<br /> above water quality objectives at the 30 foot maximum depth of investigation, monitoring wells may also
<br /> need to be installed at deeper depths to provide a complete verticalprofile of the extent of contamination
<br /> and to monitor concentrations of nitrate and 1,2,3-TCP over time.
<br /> Condor presents the rationale for addressing each of these data gaps in Section 4 of this report.
<br /> 2.0 SITE SETTING
<br /> The Site is located in the Great Valley Geomorphic Province in the northern San Joaquin Valley. The San
<br /> Joaquin Valley is a northwest-trending,structural depression,filled with up to six vertical miles of lithified
<br /> non-marine and marine sediments and unlithified non-marine sediments. Regionally, the lithology of the
<br /> upper 3,000 feet of sediments is indicative of uplift and erosion of the Sierra Nevada to the east and, to
<br /> lesser degree,the Coast Range Mountains to the west.The Sierra Nevada Province is an asymmetric range,
<br /> with a steep fault-bounded eastern front and gentle western slope that dips under the sediments of the Great
<br /> Valley to the west. The bedrock complex of the Sierra Nevada Mountains generally consists of
<br /> metamorphosed sedimentary and volcanic rocks of Paleozoic and Mesozoic age (150 to 300 million years
<br /> old) and plutonic rocks(chiefly granitic types)of Mesozoic age(80 to 150 million years old).
<br /> Surface soils are identified as Yellowlark gravelly loam with Class C hydrologic group by the United States
<br /> Department of Agriculture,Natural Resource Conservation Service (MRCS). The NRCS describes Group
<br /> C soils as having a slow infiltration rate when thoroughly wet, that consist chiefly of soils having a layer
<br /> that impedes the downward movement of water,and that have a slow rate of water transmission.
<br /> Shallow groundwater was encountered onsite during drilling at a depth of between 12 and 23 feet below
<br /> ground surface (bgs) but subsequently rose in the boreholes to approximately 5 feet bgs. Groundwater in
<br /> the region generally flows toward the east. The Site-specific groundwater flow direction, based upon the
<br /> surveyed monitoring well casing elevations and measured depth to groundwater, is generally toward the
<br /> south, but has also been measured toward the north-northwest. Shallow groundwater at the OXYCHEM
<br /> Site located across Charter Way to the south generally flows toward the east.
<br /> 3.0 PROJECT BACKGROUND
<br /> The facility has historically been occupied by various tenants for commercial and light industrial uses,
<br /> including a beverage distribution facility, agricultural supplies (chemicals, fertilizers, and pesticides)
<br /> storage and distribution facility,tractor repair facility,battery sales/recycling facility,and various contractor
<br /> storage facilities. Liquid fertilizers were reported to have been stored in three above-ground storage tanks
<br /> (ASTs)formerly located in the northwest corner of the Site.
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<br /> %10 CONDOR
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