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Natalia Subbotnikova [EH] From: Taj Bahadori <tbahadori@sjgov.org> Sent: Thursday,January 22, 2015 9:53 AM To: 'DelFrate,Todd @Waterboards' Cc: Robert McClellon [EH]; Natalia Subbotnikova [EH]; Michael Kith [EH];Joyesh Chandra; Michael Carroll; 'Isham,Julian'; 'Hold, Howard@Waterboards' Subject: Foothill Landfill - Compliance Well MW-6 Attachments: FSL GW Decline.xlsx; MW-6 Well Design Fig l.pdf Hello Todd, The County has received your letter response to our revised workplan for Well MW-6.Thank you for a quick turn-around on this,the County appreciates the CVRWQCB efforts to meet our schedule. I have discussed your response with our consultant CB&I and we have the following concerns: • It appears that the Water Board's prediction of annual water level decline is based on an average over an extended time period, as much as 17 years(1997 to 2014)for some wells. The concern for the review of that extended period of time, is the fact that the greatest annual degree of decline has occurred within the most recent period of time. This is due to the pronounced drought that has occurred in the Central Valley,which in some locations have caused recent annual water declines of over 10 feet. Attached is a spread sheet that calculates the annual water level decline between 2013 and 2014. During that period of time the annual rate of decline varied from about 2 to 2 %2 feet. The County has proposed the multi-screen well design to take into account this ominous recent water level decline. The County's concern for future water level decline at their Foothill Landfill is not that much different from the concerns that the State Resource Control Board appears to be taking in making water allocations within the Central Valley. • The prediction of well longevity could be significantly reduced below the Water Board's prediction. It is very difficult to predict the future climate patterns for California. The County's proposed well design is based on a more conservative approach than that taken by staff of the Central Valley Water Board. • The Water Board's prediction of well longevity may also be based on the installation of the well during an average seasonal groundwater depth. If the well is installed in February, during wet season when the water level is highest,the longevity of the well will be less than if the well is installed in August when the water level will be the lowest. If the County could wait until the seasonal low time of the year to install the well,this would help in this prediction of well longevity. However,the NOV has required the County to collect a years'worth of data prior the placement of waste in its newest module. If the Water Board could relax the length of the monitoring period between well installation and the placement of waste,the longevity of the well could be extended by drilling later during seasonal low water. The County understands the Water Board staff's concerns regarding the double-screened well design.Thus we would like to propose a compromise design of using a single screen length of 30-feet(see attached design). We believe a 30- feet screened well drilled in February would be equivalent to a 25-feet screened well drilled in August, accounting for seasonal fluctuations. I have spoken to Robert McClellon (LEA)and he stated he could approve a 30-feet screened well permit. Please let us know if the 30-feet screened well is acceptable,we will amend our existing permit and simply revise Figure 1 (attached),the workplan will remain unchanged. This will allow us to proceed on schedule. Currently,we are scheduled to drill well MW-6 in the first week of February 2015 (The driller requires a 2-month advance notice). If we delay this any further we would not be able to provide a year's worth of monitoring data as required by the NOV.