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Report Second Phase Subsurface tnvenipLion <br /> City of Stockton, Banner!stand, Stockton, CA <br /> May 20, 1992 <br /> W06MAD <br /> i <br /> 7.0 CONCLUSIONS <br /> Based on the results of this assessment and previous work performed at the site, RESNA <br /> concludes that: <br /> • Groundwater in the Stockton arca is of poor quality, exceeding drinking water standards <br /> for a number of analytes including chloride, iron, manganese, TDS, arsenic, barium, <br /> chromium, and selenium. <br /> • The shallow groundwater has been impacted by intrusion of poor quality waters from <br /> deltaic sediments, deep connate water from marine sediments, leakage from improperly <br /> abandoned gas wells and infiltration from the deep'water channel and other surface <br /> waters. <br /> • Laboratory analyses of the shallow subsurface soils reported levels of metals well below <br /> maximum total and soluble threshold limit concentrations. <br /> • Shallow groundwater flow at the Banner Island property is controlled by influx from the <br /> tidally influenced deep water channel. Influx of this water through dredge spoils adjacent <br /> to the channel may also contribute to poor water quality. <br /> • Sampling of the nine wells on the Banner Island site has shown water chemistry <br /> consistent with that throughout the south-central Stockton area. The laboratory analyses <br /> on the two wells across the deep water channel detected the same four metals that exceed <br /> their MCL's at similar concentrations as found at Banner Island. This shaves that th! <br /> V=Wwatrer in the downtown Stockton am his poor water quality and past practices on ' <br /> Banner Island has not degraded water quality: <br /> R040192.iAY 12 <br />