|
Southwest Pond Assessment Work Plan
<br /> Lathrop Facility,San Joaquin County,California
<br /> history of operation and construction, cemented fluorosilicate materials, similar to those underlying the
<br /> West Pond, likely underlie the Southwest Pond.
<br /> A sample of the cemented material excavated from the LCRS trench for the West Pond was analyzed for
<br /> total concentrations of the following metals and general minerals: aluminum, antimony, arsenic, barium,
<br /> beryllium, boron, cadmium, total chromium, hexavalent chromium, cobalt, copper, lead, manganese,
<br /> mercury, molybdenum, nickel, selenium, thallium, vanadium, zinc, calcium, magnesium, sodium,
<br /> potassium, iron, bicarbonate, carbonate, nitrate, chloride, sulfate, total alkalinity, fluoride, phosphorus,
<br /> and pH.The total concentrations of the metals and fluoride did not exceed the Total Threshold Limit
<br /> Concentrations or 10 times their Soluble Threshold Limit Concentrations as defined by CCR, Title 22.
<br /> In addition, soluble concentrations of metals and general minerals were evaluated by the Toxic
<br /> Concentration Leaching Procedure using deionized water for extraction.The only constituents to leach
<br /> to an appreciable degree were sodium and fluoride (Geomatrix, 1996).
<br /> The Southwest Pond is located immediately north of agricultural land owned by Simplot and operated as
<br /> cropland by a farmer who is not a direct Simplot employee.As such, it is anticipated that background
<br /> conditions for the area around the pond include some level of residual fertilizer constituent due to
<br /> farming. Several of the parcels in the area surrounding the Lathrop facility either are now or were
<br /> previously used as cropland.As described in the Closure Plan, an assessment of background conditions
<br /> from surrounding farmland will be needed for comparison with conditions in the Southwest Pond.
<br /> The area around the Lathrop facility is subject to frequent windy conditions and a layer of windblown soil
<br /> and sand has accumulated in the Southwest Pond above the asphalt liner in some locations. This soil is
<br /> likely not connected with former pond operations. As described in the Closure Plan, an assessment of this
<br /> soil will be needed to complete the characterization of the pond and materials that may need to be
<br /> removed prior to closure.
<br /> During operation, the base of the Southwest Pond was likely submerged a significant proportion of the
<br /> time while much of the sidewalls would have only been submerged when the pond was relatively full.
<br /> Consequently, the base of the pond is expected to have been exposed to process water for a longer
<br /> cumulative period than the sidewalls. Assuming the pond was operated as described above, soil affected
<br /> by constituents resulting from any leakage that may have occurred through the asphalt liner is expected
<br /> to be concentrated beneath the asphalt liner in the base of the pond. The depth to groundwater beneath
<br /> the pond is estimated to be about 10 feet below ground surface outside the pond. Given the depth of the
<br /> pond base (approximately 5 to 6 feet below surrounding ground surface) and the relatively shallow depth
<br /> to groundwater, affected soil located beneath the base of the pond appears to be in relatively close
<br /> proximity to groundwater. Based on the factors described above, the scope of work described herein
<br /> emphasizes assessment beneath the asphalt liner in the base of the pond.
<br /> 3.0 Soil Assessment Field Activities
<br /> Soil borings will be drilled at the base of the Southwest Pond to collect subsurface soil samples beneath
<br /> the asphalt liner. Soil borings will also be drilled on the sidewalls of the Southwest Pond to collect
<br /> subsurface soil samples. Surface soil samples will be collected from the sediment deposited above the
<br /> asphalt liner;this soil is believed to be windblown sediment and not related to former operations of the
<br /> pond. Additionally, one surface soil sample representative of background data will be collected from
<br /> farmland in the vicinity of the Southwest Pond.
<br /> • wood.
<br />
|