Water Resources Professional Project Reports


Miriam Wamsley

Document Type

Technical Report

Publication Date



The Department of Family and Community Medicine (DFCM) at the University of New Mexico is initiating phase III of a three-phase study examining the gastrointestinal health effects in residents who use a private well in an area with on-site wastewater treatment and disposal system (septic tanks). These residents show an increased exposure to detectable Cryptosporidium relative to a control (unexposed) population of residents who use municipal water as their source of water. This exposure was found in three different communities with significantly different hydrogeologic conditions. One community was located in the inner valley of the Rio Grande where depth to ground water averages less than 50 ft., while the other two communities were located in areas where the average depth to groundwater is greater than 400 ft. In the first phase of the study, 30% of the domestic wells exhibited contamination as evidenced by detection of coliform bacteria. In the second phase of the study, 72% of the domestic wells exhibited evidence of year round or seasonal bacterial contamination. On-site wastewater disposal systems are the suspected source of this contamination. Coliform bacterial pathogens found during testing of tap water are unable to survive for long outside of a hosts body, indicating that these samples have a continual source of contaminants. Thus, it appears there is unexpected connection between the wells and the waste or septic tank disposal systems. This paper describes a tracer study that used a fluorescent dye (uranine), a chemical analysis of the well water, and a mapping of the soil suitability for on-site wastewater treatment and disposal. These steps were taken to determine if there is a link between coliform bacteria in domestic wells and on-site wastewater treatment and a connection with septic waste disposal systems. Ten residences served by wells that tested positive for a microbial constituent in Phase II of the study were enrolled in this study. Dye was administered through the toilets in December and January. The tap water was tested weekly for a month and then once a month until the first week of April. The samples were analyzed for the presence of dye by UV fluorometry. One well's analysis strongly suggested dye retrieval. Chemical results indicate that reducing conditions were present in underlying ground water, which may be due to on-site wastewater disposal systems. All ten wells had measurable nitrate concentrations, which are above background levels. Two of these wells had nitrite concentrations above the EPA Maximum Contaminant Level (MCL). Evidence from this study suggests that the Cryptosporidium infections identified previously are thus linked to ground water contamination from septic tank effluent. Mapping of the previous results has been completed and compared to soil maps to ascertain if soil type makes any measurable change in prevalence of wells testing positive for microbial constituents.

Language (ISO)



Sewage disposal, Rural--Environmental aspects., Drinking water--Contamination., Groundwater--Pollution., Cryptosporidium.


A Professional Project report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.