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Quarterly Monitoring Report 1 October-December 1992 Smith's Canal Pump Plant Page 2 a kriging program, depicts a northwesterly gradient of approximately 0.06 feet per feet (approximately 317 feet per mile). Free floating product observed in well MW4 was removed using a disposable hand bailer during each monitoring episode. Free product thickness is measured using an oil/water interface probe capable of measuring to an accuracy of 0.01 feet. Since May 25, 1992, approximately 3.5 liters of free product have been removed from MW4. Table 2 summarizes the product thickness measurements and volume of product removed. All bailed product has been contained in a DOT approved double containment drum pending appropriate disposal. Groundwater samples were collected on December 9, 1992, from wells MW1, MW2, and MW3. Prior to sample collection, each sampled well was purged of a minimum of three well volumes of water to collect representative groundwater samples. Purged water was contained in 55 gallon drums (DOT H), labeled, and stored on site. Floating hydrocarbon product was noted in well MW4 and measured to be approximately 0.50 �r•sr feet in thickness. No groundwater sample was collected from MW4 due to the presence of floating product. Groundwater samples were collected after physical parameters (pH, temperature, and conductivity)were monitored and had stabilized. A dedicated disposable bailer with a bottom-emptying device was used to collect samples from wells MW1, MW2, and MW3. Field purge logs are presented in Attachment 1. LABORATORY ANALYSIS Samples were analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX) and total petroleum hydrocarbons as diesel (TPHD) by state-certified RESNA Environmental Laboratories utilizing EPA methods 8020 and modified 8015, respectively. Analytical results are summarized in Table 3. Laboratory data sheets and chain-of-custody documentation are included in Attachment 2. i Laboratory results indicate dissolved hydrocarbon constituents are not present at or above laboratory detection limits in wells MW1 and MW2. MW3 contained only TPHD at 66 parts per billion, which is marginally above the method detection limit of 50 ppb. Due to consistent nondetectable (ND) concentrations of petroleum hydrocarbons in wells MWl, MW2, and ND concentrations of BTEX in well MW3, RESNA, on behalf of the City of <:> Stockton, proposes a reduction of sampling and analysis frequency from quarterly to annually QRTERLY%4QMR 1992.DRF k