My Aquifer > Groundwater in the LPRV > What threats does our water supply face if nothing is done?


The biggest water problems the lower Portneuf Valley faces in the future are from:

1) Insufficient capacity to meet demand.

Best available information indicates that the aquifer is already supplying 80% of its maximum capacity in normal water years, and may be overpumped during drought periods. Because the municipal aquifer is relatively narrow (Figure 8), it does not contain a lot of water in storage. Therefore, only slight overpumping can lower the water table significantly. For example, during the 2000 water year, the combination of additional withdrawal by Pocatello's newest supply well, #44, and below normal recharge from the Bannock Range, the water table in the southern valley dropped to its lowest level in 30 years; most of this decline can be attributed to the demand which Well 44 placed on the aquifer. Clearly, future management of this water supply will have to be closely tied to future development planning.

2) Degradation of water quality.

The land-use activities that have been identified to be of greatest concern and that have had identifiable impacts on the lower Portneuf Valley's ground water are from: 1) septic sewage and 2) storm water and road runoff.

A third area of potential risk to water quality is the handling and storage of hazardous materials, including fuels. This map shows the locations of identified leaking underground storage tanks (LUSTs) in the valley (pink dots). In the southern valley, a survey of all underground fuel storage tanks (USTs) is also shown (similar information for the northern valley is not available). Based on the rate of occurrence of LUSTs in the southern valley, fully 30% of UST sites have problems. Note that because steel tanks corrode with time, it is not a question of whether USTs will leak, but when and how badly. Although many of these LUST sites were commercial fuel stations and did not affect local ground water when they leaked, some were major releases from large storage facilities which have directly affected ground water (e.g. Union Pacific rail yard diesel tank releases).

A class of activity related to both hazardous materials and drain wells is also worthy of consideration: The practice of constructing floor drains to accept waste water in commercial facilities such as machine shops and service stations currently is neither effectively regulated or inspected / enforced. By analogy with storm water drain wells, the handling of non-domestic wastewater in such facilities may need to be regulated more effectively to minimize the potential for ground water contamination.

To date, threats posed by other activities such as gravel mining have been dealt with on a case-by-case basis, and have been resolved through the open exchange of information and cooperative development of management plans (minutes of Highway Pond Working Group meeting, June, 1999). It is hoped that special cases can be dealt with in future using the Highway Pond consensus approach as a template.

The threats which these classes of activities pose to lower Portneuf Valley ground water are of two types:

a) the sudden appearance of contamination originating from a drain well, gravel pit or other 'point' source, which can shut down public supply wells on short notice; and

b) a gradual deterioration of water quality, eventually making expensive water treatment measures necessary.

In either case, the result is costly remediation of the problem, to provide safe drinking water. The costs of addressing such problems in the past decade have been exceedingly high, and the familiar adage that "it is always cheaper to prevent ground water pollution than to clean it up" has real relevance in this valley. An informal compilation, constructed with the assistance of Pocatello, Chubbuck, and EPA officials, documents the major costs incurred in remediating groundwater and soil contamination in the lower Portneuf Valley over the decade 1990-00. In comparison, costs associated with developing an understanding of aquifer dynamics, assembling existing information for planning purposes, and identifying possible future approaches to ground water protection are very small.