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>. <br />~ III IIIIIIIIIIIII III ~ <br />~t~~~~. <br />UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br />a <br />~ ~ REGION 8 <br />~`~jL Q 99918'" STREET -SUITE 500 <br />DENVER, CO 80202-2466 <br />http://www.epa.gov/reg ion08 <br />Ref: 8EPR-EP <br />January 18, 2000 <br />Ms. Kathleen Reilly ~0~0 <br />Outreach and Assistance Unit JAtJ ~~ ~~~owyY <br />Water Quality Control Division v`5`onptM~oe~ah <br />Colorado Department of Public Health and Environment <br />4300 South Cherry Creek Drive <br />Denver, Colorado 80246-1530 <br />RE: Recommendations for Grotmd-Water <br />Monitoring in the San Luis Are:f <br />Dear Ms. Reilly: <br />As per your request, I have looked into the ground-water flow system in the vicinity of <br />the Town of San Luis with regazd to the potential for impacts to the town's public w.iter supply <br />wells from potential contaminant sources as prioritized by the locals. In addition [o she <br />information that you forwazded to me I was able to locate a few reports on the San Luis Valley <br />that included discussions on the hydrogeology of this azea and was able to track down the records <br />of permitted wells in this azea. <br />I will provide a discussion of my findings on the hydrogeology and ground-water usage in <br />the area and recommendations to the San Luis Water and Sanitation District (SLWSI~) for <br />monitoring the Town of San Luis' source water for the protection of human health. <br />HYDROGEOLOGY AND LOCAL GROUND-WATER USAGE <br />The Town of San Luis lies within the Culebra Re-Entrant section of the San ]~uis Valley. <br />Within the upper 1000 feet below land surface in this azea of the Culebra Re-Entrant the land is <br />underlain in descending order by recent alluvial deposits, the Alamosa Formation, the Servilleta <br />Formation, and the Santa Fe Formation. The primary source of ground water in this azea is the <br />shallow Alamosa Formation, an unconsolidated unit comprised of sands and gravels with clays. <br />In areas at depth within this formation relatively continuous clay units are present th;it provide for <br />confined aquifer conditions. Based on the information acquired, it is believed that tte two wells <br />Printed on Recycled Paper <br />