Bannock County Groundwater

Proposed Administrative Protection Measures

In January 2011, the Bannock County Citizen’s Advisory Committee and the Groundwater Technical Advisory Committee on Groundwater Protection recommended protection area boundaries and administrative measures to the county and cities of Pocatello and Chubbuck to prevent further degradation of groundwater in the Lower Portneuf Valley Aquifer.

Click here to see the full report.

Proposed Groundwater Protection Area

Overall Groundwater Protection Area

The Overall Groundwater Protection Area boundary is largely defined by the watershed boundaries for the valley. The northern end of the area is defined by the Fort Hall Reservation and the Area of City Impact (ACI) boundaries.

Overall Protection Area Recommendations

  1. Nitrates & Septic Systems
    • Bannock County will adopt new land division and development measures for the Pocatello ACI, similar to the land division and development measures that the County adopted for the Chubbuck ACI.
    • Pocatello will update its sanitary sewer collection system master plan (facility plan) to include un-sewered areas, and work to sewer critical areas. The number one priority is to sewer the Johnny Creek area followed by Black Cliffs.
    • Pocatello and Chubbuck will adopt ordinance requirements that new lots with septic systems shall be a minimum of 5 acres.
    • County will amend zoning ordinance to require that new development on the west benches must connect to sewer or require use of an enhanced treatment septic system that reduces effluent nitrate by at least 50%.
    • Pocatello and Chubbuck will adopt ordinance requirements such that new development in city limits must connect to sewer for three or more new building lots.
    • Cities and County will conduct education and outreach on nitrate impacts.
  2. Hazardous Materials
    • In cooperation with the Idaho Department of Water Resources, Bannock County and the cities of Pocatello and Chubbuck will develop local regulations/recommendations to improve quality of well sealing to prevent vertical migration of contaminants within the aquifer;
    • Pocatello, Bannock County, and Chubbuck will develop ordinances for inspection and tracking of businesses for the presence, use, and management of hazardous materials through the implementation of a uniform business licensing program.
    • Cities and County will conduct outreach and education for hazardous materials use and management.
  3. Stormwater
    • Chubbuck and Bannock County will prepare and adopt a similar manual to satisfy a requirement of the NPDES MS4 permit with the EPA.

Special Management Subareas

Special Management Subareas

Within the overall protection area, there are special management subareas defined by various geologic, hydrologic, and known contaminant constraints.

  • Area 1: Principal recharge area for the aquifer. Also contains dense septic development. The Mink Creek drainage is a designated Nitrate Priority Area.
  • Area 2: Tributary aquifer to the main aquifer. Known area of extremely high nitrate concentrations in groundwater and is a Nitrate Priority Area. Subsurface material is fine silt rather than the gravel and sand found in the valley floor, therefore water movement through the subsurface is extremely slow. Septic development and older wastewater disposal systems have caused significant and harmful levels of nitrate contamination in groundwater. Groundwater from this area feeds into the main valley aquifer.
  • Area 3: Area of the valley floor from the Portneuf Gap to Red Hill (a hydrologic barrier). Comprises the southeastern extent of the aquifer. Groundwater is extremely shallow and overlain by a thin soil cover that provides little protection against spills, leaks, and other releases of hazardous chemicals.
  • Area 4: North Pocatello and Chubbuck area to the reservation boundary. Contains the North Pocatello Nitrate Priority area, the perchloroethylene (PCE) solvent plume and some ethylene dibromide contamination in private wells in the very northwest corner of the area. Depth to groundwater is deeper and clay layers in the subsurface provide a hydrologic barrier for downward movement of contaminated water. However, well construction in this area has provided a vertical pathway for contaminants to migrate from shallow water bodies to the deeper part of the aquifer.
  • Area 5: Areas outside city limits but containing some Areas of City Impact. Recharge areas but not significant inputs. Areas of future development.

Special Management Subarea Recommendations

  1. General (all subareas)
    • Cooperative education program with Health District.
    • New septic tank permits require owners to connect to sewer when the existing sewer line is within 300’ of the property
    • New private and municipal wells shall be constructed with sealing standards that prevent the vertical migration of contamination to the aquifer.
    • Landowner education regarding well locations in designated Nitrate Priority Areas (NPA).
    • Mining (primarily gravel) and restoration should be regulated to protect aquifer.
    • Cities and County adopt ordinances for inspecting all businesses for hazardous materials for presence and proper management of hazardous materials through implementation of a uniform business licensing mechanism.
    • Critical Materials Education and Outreach to businesses and residents.
    • Adopt Water Quality standards for stormwater infiltration.
  2. Area 1: Mink Creek to City Creek
    • New development must connect to sewer or alternative approved treatment system that effectively reduces effluent nitrate by at least 50% as determined by the Health District for three or more new building lots.
  3. Area 2: South 5th Street / Eastern Aquifer AND AREA 3: South Valley Floor
    • New development must connect to sewer. (Excludes existing “grandfathered” lots).
  4. Area 4: North Valley Floor AND Area 5: – Other upland areas within the Watershed
    • New development must connect to sewer for three or more new building lots.
    • Maintain existing county minimum new lot size requirement for septic system in Area of City Impact.
  5. Pocatello & Chubbuck
    • Update the facilities plan for sewering five sub-watersheds: Johnny Creek, Gibson Jack, South Valley, Mink Creek, Pocatello Creek
    • Cities should adopt new requirement that new lots with septic systems should be minimum of 5 acres.
    • Sewer problem areas: Johnny Creek, Bannock Highway, Black Cliffs, Tech Farm Road, Kraft Road, Dell Road.

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