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Central Valley Regional Water Quality Control Board To: Stewart W. Black, P.G. Site Cleanup Program Manager From: Will Zimmerman, G.I.T. Gerald Djuth, PE, CEG Date: 16 April 2020 RATIONALE FOR CONSIDERING NO FURTHER ACTION AT FORMER PILKINGTON NORTH AMERICA, 500 EAST LOUISE AVENUE, LATHROP, SAN JOAQUIN COUNTY Setting The former Pilkington North America diesel spill site is located on what was formerly a 117-acre parcel in Lathrop, San Joaquin County, Assessor’s Parcel Number (APN) 198- 120-080 (Attachment 1). The site is located south of East Louise Avenue, and consisted of a glass factory, which has recently been demolished, and an adjoining warehouse to the west of the glass factory. The spill location was immediately south of the former glass factory and directly east of the warehouse. Remaining open space is being developed into an industrial park with multiple warehouses and paved parking areas with minimal landscaping. Residential housing exists across Louise Avenue to the north, and the Occidental Chemical Company cleanup site is located about 900 feet east of the spill location. First encountered groundwater is likely a perched zone at about 10 to 15 feet below ground surface (bgs). Data from the adjacent Occidental Chemical Agricultural Products Co. site defines groundwater in three separate, loosely divided water bearing zones including a Shallow zone from 31 and 83 feet bgs, an Intermediate zone from 84 and 150 feet bgs, and a Deep zone from 151 and 218 feet bgs. Shallow groundwater flow direction at the spill location was generally measured to be east to northeast. Shallow groundwater quality is poor with high total dissolved solids (TDS) and is not used in the site area. Regional groundwater use for irrigation is usually pumped from the Deep zone. Municipal water is provided by the City of Lathrop public water system.