SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

,Sent, BY; PWQCB SACRAMENTO; 916 255 3015; Feb-24-99 14.10, Page 6/6 1665 Pacific Avenue -5- 16 February 1499 Petition Summary and Conclusions Regional Board Response (PAgcs 12- 14 10). Detectable concentrations of TPHg in shallow I agree that TPHg contamination in groundwater groundwater in contact with the limited residual below the site and offsite does and will violate the petroleum hydrocarbons adsorbed to soil particles Basin Plan objectives. I also agree that will likely remain above 5 ppb(the commonly contaminant levels will continue to violate these accepted odor threshold for drinking water)and objective for a substantial time period. However, thus violate the Basin Plan's narrative odor as with the above response to No. 9,the objective in a very localized,small volume of contaminated subsurface volume is not small and surrounding groundwater for anywhere from concentrations are not near detection limits. decades to hundreds of years. Contamination is confirmed vertically to at least 54 feet below ground surface and laterally at least 150 feet offsite. TPHg concentrations of 83,000µglL were reported for the 8131198 sampling event. 11). The determination as to what constitutes a The determination of a reasonable time period to reasonable period to attain water quality objectives attain water quality objectives must consider the must be based on evaluation of all relevant factors, residual contaminant mass and contaminated including but not limited to the extent and gravity subsurface volume. An estimated contaminant of any threat to public health and the environment mals has not been provided and the contaminated during the period required to meet Basin Plan subsurface volume is laterally and vertically objectives. Although the time required to attain extensive(laterally,approximately 150 feet offsite, objectives in this case is lengthy, it is a reasonable and vertically to at least 54 feet bgs). Recent period considering the facts of this particular case, vertical characterization activities have not been including that there are no drinking water wells submitted for regulatory review and must be within goo feet of the site and that affected water is evaluated to determine the contaminated of inferior quality and will likely be excluded from subsurface volume and residual contaminant mass. any well which may be constructed in the future. It is highly unlikely that petroleum constituents The nearest municipal drinking water well is detected in the immediate area of the discharge located 800 feet north-northeast of the site will migrate substantially beyond the current (approximately downgradient),and three others are limited spatial extent.and it is highly unlikely that within 3000 feet. The well completion details for this particular very limited pocket of shallow the four nearby production wells do not preclude groundwater will be used directly as a source of vertical contaminant migration as sanitary seals do drinking water in the foreseeable future. not extend below 70 to 96 feet bgs. These production wells.are capable of sustaining pumping rates between 450 and 900 gallons per minute. Also,nothing prevents Cal-Water or any other water purveyor from placing a new well near the contaminated site.