About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Utah Geological Association

Abstract


Central Utah: Diverse Geology of a Dynamic Landscape, 2007
Pages 361-382

Science-Based Land-Use Planning Tools to Help Protect Ground-Previous HitWaterNext Hit Previous HitQualityNext Hit, Sanpete Valley, Sanpete County, Utah

Janae Wallace, Mike Lowe, Charles E. Bishop

Abstract

Sanpete Valley, Utah, is experiencing increases in residential development on unconsolidated deposits of the valley-fill aquifer, the principal source of drinking Previous HitwaterNext Hit in the valley. In response to state and local governments’ desire to protect the high Previous HitqualityNext Hit of this drinking Previous HitwaterNext Hit source, we provided three tools for land-use planning: a ground-Previous HitwaterNext Hit Previous HitqualityNext Hit classification map, a ground-Previous HitwaterNext Hit recharge-area map, and a septic-tank density map.

Ground-Previous HitwaterNext Hit Previous HitqualityNext Hit classification maps are tools local governments can use for managing potential ground-Previous HitwaterNext Hit contamination sources and protecting ground-Previous HitwaterNext Hit Previous HitqualityNext Hit. Classifying the Previous HitwaterNext Hit Previous HitqualityNext Hit of aquifers is a way to formally identify and document the beneficial use of ground-Previous HitwaterNext Hit resources. Based on data from 408 wells analyzed for general chemistry (118 for total dissolved solids [TDS] and 290 for converted specific-conductance data), 84.9% of the valley-fill aquifer is Class IA (Pristine), 14.9% is Class II (Drinking Previous HitWaterNext Hit Previous HitQualityNext Hit), and 0.2% is Class III (Limited Use). Previous HitWaterNext Hit having lower TDS values deserves higher protection levels.

Ground-Previous HitwaterNext Hit recharge-area maps identify the relative vulnerability of ground Previous HitwaterNext Hit to surface sources of pollution by identifying (using well logs) the presence or absence of clay confining layers overlying aquifers, and the direction of the vertical ground-Previous HitwaterNext Hit gradient. The mountains surrounding Sanpete Valley and the upper parts of alluvial fans along the valley margins are the primary recharge areas. Most of the discharge areas are in the central part of the valley. Secondary recharge areas are present mostly east of the San Pitch River, between the primary recharge areas and discharge areas.

Septic tank soil-absorption systems are the primary means of wastewater disposal in many areas of Sanpete Valley. Based on ground-Previous HitwaterNext Hit flow, background nitrate levels, and projected nitrate loading from new septic tanks, we performed mass-balance calculations to map recommended septic-system density/lot size. We used nitrate data from 340 wells as a ground-Previous HitwaterNext Hit Previous HitqualityNext Hit indicator. The background nitrate concentration (nitrate as nitrogen) in the principal valley-fill aquifer is 3.3 mg/L. We used a regional, three-dimensional, steady-state MODFLOW model to estimate ground-Previous HitwaterNext Hit flow available for mixing in the principal valley-fill aquifer. Ground-Previous HitwaterNext Hit flow available for mixing is the major control on projected aquifer nitrate concentration in the mass-balance approach. Areas having lower ground-Previous HitwaterNext Hit flow rates require larger lot sizes. Our ground-Previous HitwaterNext Hit flow analysis using a mass-balance approach indicates that low and high flow rates in different parts of the valley necessitate two categories of recommended maximum septic-system densities for developments that use septic tank soil-absorption systems for wastewater disposal: 5 acres per system and 10 acres per system (2 and 4 hm2/system). We base our recommended maximum septic-system densities on hydrogeologic parameters incorporated in a ground-Previous HitwaterNext Hit flow simulation that geographically divided the study area into three ground-Previous HitwaterTop flow domains on the basis of flow-volume similarities.


Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24