2012 NGWA Ground Water Summit: Innovate and Integrate

Evaluation of Nitrate Contamination in Two Utah Unconsolidated Aquifers—Do Best Management Practices Make a Difference?

Tuesday, May 8, 2012: 8:20 a.m.
Terrace Room D-F (Hyatt Regency Orange County)
Janae Wallace, M.S., Utah Geological Survey;
Mike Lowe, M.S., Utah Geological Survey;

Rural areas in Utah follow the global trend of increasing population coupled with maintaining agriculture as a major land-use practice using irrigation from groundwater.  We compare two agricultural areas, Sanpete Valley and the Bothwell Pocket, undergoing residential development and having nitrate (NO3) contamination in groundwater. 

In Sanpete Valley, animal feed-lot operations (AFOs) are common.  Septic-tank effluent, agricultural fertilizer, and feed-lot waste are potential sources of NO3.  Average NO3 is 3.3 mg/L, based on 443 samples.  Most wells have NO3 <5 mg/L; 3.5% exceeded 10 mg/L.  We examined the relationships between NO3, well depth, and proximity to alfalfa fields, irrigated lands, and AFOs.  No correlation exists between NO3 and well depth or land-use practice, except for wells within 0.25 mile of AFOs.  Multiple sources contribute NO3 to groundwater in Sanpete Valley. 

In the Bothwell Pocket, some vegetable farming has been replaced with sod farms.  We analyzed NO3 from 31 sites.  Average NO3 is 6.5 mg/L.  Forty-two percent yielded values >5 mg/L, and 23% exceeded 10 mg/L. Ten samples with NO3 >5 mg/L were analyzed for δN15 and δO18 isotopes.  Possible sources of NO3 include fertilizer, feed lots, septic tanks, and natural sources.  Most N and O isotope data have values characterized as septic tank/manure and soil, but some ammonia-fertilizer/rain signatures occur near sod farms. 

Educating land owners through Best Management Practices (BMP) (such as placing turkey manure piles on cement pads and away from well heads) may contribute to Sanpete Valley’s low average NO3 of 3.3 mg/L.  In contrast, the higher average of 6.5 mg/L in the Bothwell Pocket may reflect replacement of vegetable farms by more heavily fertilized sod farms.  Better BMPs, such as reducing N-rich fertilizer loadings, may lower NO3 in the Bothwell Pocket.  Comparing the health of these aquifers shows education is the key to improve water resources.