SITE INFORMATION AND CORRESPONDENCE_FILE 2

Home Browse Search

A S S O C I A T E S I N C its stated requirements. It is ATC's opinion that Criterion 4 has been satisfied as it is presented. • Criterion 5: Pollutants remaining in groundwater do not create or threaten to create risk to human health and safety, or to future beneficial use(s) of groundwater. Patterns of existing and future demands for usable water resources in the area must be considered in determining what period of time is reasonable to reach non-detectable (or background) concentrations. The EHD states that they do not believe the models presented allow evaluation of the first portion of this criterion and a health risk assessment, based on an accepted site model, was not performed. As stated in ATC's Closure Report "ATC contacted Cal Water, the entity that supplies drinking water and operates the municipal supply wells for the area of the site. Mr. Eric Mar, Field Supervisor, said that the water quality in the area of the site is very poor, due to inorganic pollutants from the Stockton Deep Water Channel (nitrates, sulfates, salinity, etc.), and that no future supply wells are planned for that area at this time. Because the overall water quality of the basin is poor and no beneficial future use of the basin is planned by the local water provider." It is apparent that there are no future beneficial uses for the impacted aquifer. Additionally, field data and flow and transport model data indicate that the plume has stabilized and that there is a trend of-decreasing hydrocarbon concentrations. • Criterion 6: The plume is stable and sufficiently limited in lateral and vertical extent and contaminant concentrations detected in groundwater show a decreasing trend with time. One hydrologic cycle (four quarters) of monitoring after active remediation measures have ceased is usually considered to be the minimum necessary to determine site groundwater and plume conditions. The EHD questions the validity of data obtained from the groundwater flow and transport model since the model is based on natural attenuation while the site is currently under active remediation. However, Run 2 of the model is based on a start date in 1995 and initial data utilized in the model is from laboratory analytical data from 1995, before active remediation was initiated at the site. We trust that this additional information clarifies the issues and concerns mentioned by EHD and ATC respectfully requests that EHD reconsider this site for no further action. env ironmenta1\27142Veponse.doc 4