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Ms. Kathleen Minahan 0 - 3 - • 31 January 2007
<br /> removed in 1998 (30 October 1998, Tri-Delta Fertilizers, Progress Report & Amended
<br /> Work Plan for Closing the West Pond by Dellavalle Laboratory). A soil sample
<br /> obtained by Regional Water Board staff from the excavation base in October 1998
<br /> contained 980 mg/kg ammonium, and groundwater beneath the excavation contained
<br /> 410 mg/I ammonium and 370 mg/I nitrate-nitrogen. Therefore, Regional Water Board
<br /> staff believe that the ammonium concentrations observed in groundwater from borings
<br /> SB-11, SB-12, and SB-13 are evidence of ammonium pollution relating to the former
<br /> West Pond. Sulfate was not analyzed for in the 1997 soil or groundwater samples, but
<br /> since ammonium sulfate was also handled in bulk at this facility, it is likely that sulfate in
<br /> groundwater in the vicinity of the former West Pond is also attributable to site activities.
<br /> A review of Regional Water Board correspondence with Tri-Delta Fertilizers show that
<br /> the lined drainage pond to the north replaced a previously unlined drainage pond. In
<br /> 1997, soil samples obtained between two and four feet below the base of the former
<br /> unlined pond contained up to 3,000 mg/kg ammonium. This suggests that there could
<br /> have been migration of ammonium to groundwater before the pond was excavated and
<br /> lined with clay. The 2006 grab groundwater sample from SB-15 contained 1,200 mg/I
<br /> ammonium, and 2,700 mg/I sulfate, which could indicate migration from either the
<br /> unlined or the lined pond.
<br /> Beyond the influence of the former West Pond, it is difficult to ascertain the origin of the
<br /> groundwater pollutants of nitrate, ammonium, sulfate, and petroleum identified beneath
<br /> the Lesco site. The assignment of responsibility for groundwater pollutants is
<br /> complicated by the presence of similar groundwater pollutants from neighboring
<br /> facilities. As presented in the Investigation Report, adjacent properties are also bulk
<br /> product handling facilities, and review of records at the Regional Water Board office
<br /> show that these adjacent facilities have documented releases of products to
<br /> groundwater. For example, on the east side of Lesco, Metropolitan Stevedore
<br /> Company leases land to Martin Operating Partnership, which stores sulfur outside, and
<br /> has groundwater containing 1,700 mg/I sulfate beneath it. On the north side of Lesco,
<br /> Rice Terminals (identified as Unocal AST's in Figures 2 and 3), stores bulk ammonium
<br /> nitrate and has groundwater containing 2,000 and 24,000 mg/I ammonium beneath its
<br /> facility. To the south, petroleum tank farms operated by BP (Arco), under the
<br /> investigative umbrella of Stockton Terminals Technical Committee, have documented
<br /> 64,000 ug/I total petroleum hydrocarbons quantified as diesel in groundwater at West .
<br /> Washington Boulevard.
<br /> In addition, due to the influence of the adjacent Stockton Deep Water Ship Channel,
<br /> the San Joaquin River, and tidal influences, groundwater gradients at these adjacent
<br /> facilities are shallow and inconsistent between monitoring events and inconsistent
<br /> between adjacent sites.
<br /> Monitoring Wells
<br /> To assist in separating on-site sources of pollutants from off-site sources and to identify
<br /> trends in groundwater movement, Lesco has proposed to install four monitoring wells
<br /> and monitor them for at least two months. The wells are generally proposed to be east,
<br /> west, and south of the lined drainage pond, and to be sampled for total petroleum
<br /> hydrocarbons as diesel, dissolved metals, ammonium, chloride, nitrate, sulfate,
<br /> alkalinity, and pH.
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