AgdaPkt 2010-02-01 clsd and regular

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7A - ATTACHMENT NO.3 Saltworks Proposal- Water Group Summary Report (22 January 2010) Page 37 elevated aluminum and arsenic concentrations in the sample. The reverse osmosis treatment proposed for onsite groundwater would likely be effective in reducing excessive TOS, chloride, iron, manganese, and arsenic to potable water standards. Recognizing that limited pumping from existing wells could promote lateral, downward, and/or upward migration of poor quality water, an evaluation of detectable saltwater or brine impacts underlying the site was performed using geochemical methods. The evaluation used the available water quality data for major and minor ions for the three samples from near-site wells (Bayport No.1 in 1991 and Pacific Shores Nos. 1 and 2 in 1993; see Table 6). Standard water quality data for seawater and for brine (Hem, 1988) also were obtained for comparison, as was water quality data from two deep monitoring wells in Palo Alto. As a basic data quality control measure, the water quality data were examined for the charge balance of reaction error between the major cations and anions (see Mazor, 1991); this measure revealed that accuracy of the water quality data from the local wells is poor. Nonetheless, the analysis did not indicate the presence of brine or the initiation of saltwater intrusion in existing wells for that time period. 3.5.2 Unresolved Issues Regarding Groundwater as Source of Supply Since site-specific wells and aquifer testing are not available for the Saltworks site, several unresolved issues remain regarding the feasibility of a groundwater supply for the Saltworks project. Issues are related to both the quantity and the quality of the resource and include the ability of onsite production wells to provide sufficient yield, the long-term sustainability of such a groundwater supply, groundwater quality concerns, and the potential for subsidence and/or liquefaction. 3.5.2.1 Groundwater Quantity (Well Yields and Sustainability) OMB's initial proposed reliance on groundwater (as source of potable supply) of up to 700 AFY is equivalent to 1.92 acre feet per day (AF/day) or 434 gallons per minute (gpm) operating 24 hours per day. Recommended pumping cycles would likely be 18 hours per day (0.75 day) resulting in a required well yield of 579 gpm to meet the annual requirement. In addition, daily peak pumping demands can be much higher, up to about 1.5 times greater than the average daily demand, or about 870 gpm. This daily peak demand can be decreased if water storage facilities are planned for the project. Nonetheless, this pumping rate requirement is high compared to what may be capable for the site, as described below. The recommended yield of a production well is a balanced compromise between the available drawdown, operating parameters, well and aquifer characteristics, and groundwater recharge. The available drawdown is the vertical distance between the SWL and the top of the well screen. The recommended drawdown is two-thirds (2/3) the available drawdown or 100 feet whichever is less. The 1/3 safety factor allows for unanticipated or unknown fluctuations in water level elevations due to tidal influences, seasonal fluctuations, interference from other wells, well aging and deterioration, and barrier boundaries. The 100-foot limitation prevents over-pumping from the aquifer, reduces near-well pressure changes that affect geochemical reactions and, generally, increases the longevity of the well. The recommended drawdown in feet is then multiplied by the SC24 to provide an estimate of well yield. These calculations indicate that the recommended yields from the wells summarized in Table 5 range from 20 gpm (Maggiora test Well 3) to 240 gpm (Maggiora Well 2). The average is about 120 gpm, while the median is 110 gpm. Collectively, these data indicate that more than one well 30