Read previous stories about Friends of the Well and Montezuma Well National Monument.
Geologist Ed DeWitt and hydrogeologist Ray Johnson gave public presentations on April 14th, 15th and 16th as a culmination of their five year study on the geochemistry, groundwater source and groundwater flow model of Montezuma Well and its vicinity.
This study was commissioned by the National Park Service in a response to the ever increasing pressure on the aquifer by surrounding development. To date, Montezuma Well seems to continue flowing at a rate of 1.1 - 1.5 million gallons a day. But the Park's domestic well and many nearby private wells have been loosing water at a rapid rate. Understanding where the water comes from and its underground flow will be key to protecting the Well in the future.
Ed and Ray gave FOTW members a special 1.5 hour field trip on the 14th ahead of the general public. They presented maps and cross-sections of the geology from the Mongollon Rim, (the Well's water source) to the Well and surrounding areas, and used an ingenious prop they called the MOWEnator to demonstrate the flow and what could effect it.
Then we moved onto an area that does not usually have public access, although it can be seen from the parking lot. A large protruding rock to the northwest of the parking lot is actually an old travertine pour throat where a spring much like those at the bottom of Montezuma Well once poured out water building this huge deposit of travertine. Actually the rock that surrounds the current Well is not the same as the surrounding Verde Formation limestone, but a huge travertine mound that was built up by an even older spring somewhere in the vicinity of the top of the hill across the road from the Monument.
We finished up at the contact station where Ed and Ray showed a few more cross-sections of the ground water flow.
Observation of the geochemistry of the water shows the source of the water is from rainfall on the Mongollon Rim. From there is travels down through the Quaternary Basalt, Permian Sandstones and then into the Redwall Limestone. The Redwall Limestone is a very porous layer that moves water rapidly down gradient. At Montezuma Well they believe a less permeable basalt dike intrudes upward through the permeable layers of the aquifer thus forcing the water upward through two vents located at the bottom of the Well. This explains the relatively constant supply of water the Well enjoys, and perhaps the lack of water in the aquifer immediately down gradient of the Well. But Ed and Ray stressed the system isn't that simplistic. Although future deep, up gradient wells that may penetrate the Redwall Limestone would be the biggest threat to flow of Montezuma Well, excessive water withdrawals down gradient could change the overhaul hydraulic head of the system and may have an effect too. Their report has four flow models with and without the basalt dike, and with the basalt dike at different depths and distances from the well. The purpose of their Open-File Report (OFR) is to release the groundwater chemistry, rock data, geologic cross sections, and groundwater flow modeling related to the research objectives. Ed and Ray will provide detailed interpretations of this information in subsequent peer-reviewed journal articles.
USGS Open-File Report 2011-1063: Water and Rock Geochemistry, Geologic Cross Sections, Geochemical Modeling, and Groundwater Flow Modeling for Identifying the Source of Groundwater to Montezuma Well, a Natural Spring in Central Arizona
Bugle Article by Steve Ayers.
Friends of the Well
P.O. Box 864
Rimrock, AZ 86335-0864
info@friends-of-the-well.org
