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�ssARBa Quarterly Report and Closure Request,Site Code 1203 Stockton Regional Wastewater Treatment Facility 2500 W Navy Drive,Stockton,CA Project No W0366 01 Page 3 On behalf of the City of Stockton, RESNA requested closure for the subject site in correspondence to the PHS/EHD dated October 6, 1992 The request was based upon the limited areal extent of residual diesel hydrocarbons in relatively tight soils, the low level of impaction, and the absence of contaminants in groundwater In correspondence dated November 19, 1992, PHS/EHD determined that insufficient groundwater monitoring data was available to warrant closure The PHS/EHD requested a minimum of one additional round of confirmation groundwater sampling to ensure groundwater has not been impacted by petroleum hydrocarbons and monthly measurements of static groundwater levels (to confirm that the gradient direction is consistently northeast). GROUNDWATER MONITORING AND SAMPLING Pursuant to December 24, 1992 PITS/EHD correspondence, RESNA personnel conducted monthly groundwater monitoring during November and December, 1992 Sampling of all site monitoring wells was conducted on December 28, 1992 Field work consisted of measuring the . depth to water in wells MW1, MW2, MW3, and MW4, using an electronic water level probe, purging and sampling each well, and subjectively analyzing collected water samples for the presence of petroleum hydrocarbon constituents Static groundwater was measured in each monitoring well on November 30 and December 28, 1992 Groundwater gradient maps are presented as Figures 3 and 4, respectively Groundwater monitoring data is summarized in Table 3 Figure 3 depicts a northeasterly groundwater gradient of 0 012 ft/ft or approximately 63 ft/mile Figure 4 depicts a northeasterly gradient of 0 0090 ft/ft, or approximately 48 ft/mile Fluid level measurements indicate the groundwater gradient beneath the site is consistently to the northeast Groundwater samples were collected from monitoring wells MW1, MW2, MW3, and MW4 on December 28, 1992 Samples were collected after stabilization of pH, electrical conductivity (EC), and temperature Monitoring wells were purged and sampled according to RESNA's Quality Assurance/Quality Control Plan on file with the PHS/EHD A minimum of 12 casing volumes were purged from each monitoring well Purge water was contained in labeled DOT approved 55 gallon drums and stored on site pending laboratory analyses A dedicated disposable bailer was used to collect each water sample Well purge logs are included as Attachment 1 4QR-1992 FNL