ARCHIVED REPORTS XR0001624 - Laserfiche WebLink

Home Browse Search

• 8 March 1993 (GeaAudit MDC Ukiah-1. 2) Page 2 of 3 PROCEDURES On 3 February 1993 , the water level in each well was measured relative to the top of the casing. The relative piezometric levels and hydraulic gradient were determined from these data (Table 1 and Figure 3) . After water levels were measured, a purge pump was used to surge and purge each well, and approximately 8 gallons of water were removed from all wells to stabilize temperature, pH and conductivity (see Table 2) . The water was stored in 55-gallon drums on-site. Water samples were collected using a disposable plastic bailer. The samples were collected in 40 ml EPA vials and transported in a chilled container to Alpha Analytical Laboratories in Ukiah. The samples were analyzed for total petroleum hydrocarbons (TPH as gasoline) and volatile aromatics (BTE&X) in accordance with EPA methods 8015/LUFT and 602 , respectively. FINDINGS The groundwater gradient direction ranges from northeast to east. The groundwater elevation data and gradient direction are shown graphically in Figure 3 (Lines of Equal Groundwater Elevation) . TPH as gasoline was detected in the sample from MW-1 at 2 , 600 gg/L (ppb) . Benzene, ethylbenzene and xylenes were detected in the sample from MW-1 at levels of 3 ppb, 103 ppb and 170 ppb, respectively. Toluene was detected in samples from MW-2 and MW-3 at levels of 0.93 ppb and 0.4 ppb, respectively. No TPH or BTE&X were detected in any other samples. The water sample analysis is summarized in Table 3 . The laboratory report and chain of custody are attached in Appendix A. CONCLUSIONS Based upon field observations and the analytical results of water samples, groundwater beneath the northeast corner of the site (MW- 1) remains contaminated with moderate levels of petroleum hydrocarbons. However, a comparison of the groundwater sample analytical results from this sampling and from September 1992 (Table 4) indicates a significant decrease in hydrocarbon concentrations in MW-1. The decrease in concentrations suggests that removal of the source, biodegradation or other factors have • reduced the concentrations of hydrocarbons -in groundwater. GeoAudit recommends that the wells be monitored on a quarterly basis for a period of one year. An evaluation of the data can then be completed and, if the current trend is continued, a closure may be requested at that time.