Water Well Journal
Issue link: http://read.dmtmag.com/i/451364
The actual final well depth was found to be 335 feet (con- firmed using three separate measurements), rather than 242 or 265 feet as indicated on other past well records. The video did not reveal any caving, raveling, or unstable areas existing within the open borehole, but it was apparent the airline had separated from the pump at some time and was lodged in the open well beginning at a depth of 162 feet. The profile (or side) view of the well verified the exclusive presence of basalt rock extended throughout the depth of the well, starting from the termination of the well casing down to the final observed depth of 335 feet without any changes to other formation types. The rock exhibited the familiar honey- comb nature and appearance along with the extensive fractur- ing and fissures common to basalt formations. There were no apparent severe occlusions or projections of any formation material into the borehole evident that would create a severe impediment to a pump installation, although the borehole did display several irregularly shaped and large cavernous openings at various intervals, common to broken rock formations. Due to the obstructed view caused by the well casing, it was not possible to identify the presence or extent of a sanitary seal. Determination of the Well's Physical Characteristics Following the video inspection and fishing and removal of the airline piping, an alignment test was conducted to verify the alignment of the open wellbore. An alignment and plumb- ness evaluation was felt to be a mandatory requirement as the concept design assumed the presence of two submersible well pumps would be needed in parallel orientation within the existing water supply well for redundancy and flexibility in operation. The alignment test was performed using an 11.5-inch OD × 12-foot long tool. The alignment test indicated a straight borehole with minimal deviations in any plane. A dummy test was then conducted to check for any dog- legs or severe kinks in the well's alignment and verify the clear passage of a comparably sized pump bowl. This test was performed using a 10.75-inch OD × 21-foot length of pipe to a depth of 185 feet without any accompanying binding or obstructions. The final physical examination of the well consisted of a flow test using the existing pumping equipment. During re- moval, it was discovered the existing well pump was worn and severely plugged with iron oxide. This was corrected be- fore reinstallation of the pump and subsequent well testing. The flow test indicated a yield of 215 gpm from a stabi- lized pumping level of 91 feet after 2.5 hours of pumping, starting with a static water level of 41 feet. Due to flooding of the immediate site, a prolonged well test was not possible. This equated to a specific capacity of 4.30 gpm per foot of drawdown which, if uniformly extrapolated to 140 feet of drawdown, equaled a flow rate as high as 600 gpm at a 180 feet +/- pumping level. However, given the typical relation- ship of declining specific capacity in basalt rock wells with increasing drawdown, the projected maximum yield at 180 feet was most likely believed to be limited to around 350-400 gpm. Aquifer Analysis Even though the existing well delivered sufficient water throughout the flow test, the issue of the aquifer's long-term reliability and stability remained in question. The aquifer ge- ology was determined to be based in basaltic rock, consisting of Miocene basalt flows within the Columbia River basalt group. This formation underlies a significant portion of the South Salem Hills and had been extensively used in past years as a productive aquifer for water supply and irrigation uses. In re- cent years, however, the aquifer had demonstrated a decline in production accompanied by a sustained and noticeable drop in the static water level in various wells throughout the region. This had led to state-mandated restrictions or even complete prohibitions of use in some areas. Given the history and access to the past Fairview pumping and well records obtained over more than a 40-year period, it was determined the aquifer in this specific area had been and was reasonably stable in production capability and the static and pumping water levels had not appreciably changed over that same period. Since the shutdown of the Fairview Training Center, two of the three existing wells on the grounds had been mothballed. This, combined with the test results and the fact most of the water extracted for heating and cooling purposes would be reinjected into the aquifer with only a small percentage used for consumptive use through grounds irrigation, resulted in the conclusion the aquifer was capable of supporting all uses. Water Quality Testing Another element of the investigation and determination of suitability for use included a comprehensive examination of water quality. Although the potability of the local groundwater supply had never been questioned while used for the Fairview Training Center, the reduction of available wells from three down to one raised the question of which well had previously operated as the primary water supply well. Water quality testing was conducted on sample water ex- tracted during the well testing, including tests for coliform bacteria; EPA tests for regulated synthetic and volatile organic contaminants, radionuclides, and inorganic contaminants; sec- ondary contaminants including scaling minerals such as iron, manganese, and calcium carbonate; corrosive factors such as pH, alkalinity, dissolved gases, and corrosion indices; and physical tests for sand and silica. All the water quality tests were indicative of the typical quality associated with local groundwater from a basalt aquifer. There were no physical impediments to using the water and the chemical tests indicated there were no regulated contaminants above the associated maximum contaminant level and no extreme potential toward scaling of interior pipe walls or heat pump coils from precipitation of iron or man- ganese. The water's pH balance was slightly on the alkaline side, which demonstrated the typical corrosive tendencies were low. All in all, there were no apparent prohibitions in the application of the groundwater for the intended uses. ENGINEERING from page 37 38 February 2015 WWJ waterwelljournal.com