Groundwater Protection - Big Sioux Aquifer - Eastern SD

 The main project objective was to protect water supplies and shallow groundwater resources. A secondary objective was to reduce potential groundwater contamination from groundwater/surface water interchange and non-point pollution sources. Protection was provided mainly by restricting land use through local zoning ordinances. Education, land use conversion and supplemental projects also helped protect groundwater resources.  

The project covered eleven counties in Eastern South Dakota: Brookings, Clark, Codington, Deuel, Grant, Hamlin, Kingsbury, Lake, Miner, Minnehaha, and Moody. Approximately one-third of South Dakota's population lived in this area. The project covered approximately 7,500 square miles. 

The main water source in the project area is the Big Sioux Aquifer. The Big Sioux Aquifer is a shallow, unconfined aquifer covering approximately 1,000 square miles in the Big Sioux River basin. This glacial outwash aquifer ranges in thickness from a few feet to over 100 feet, but averages 20 feet thick.

Several other unconfined aquifers and isolated outwash deposits, similar to the Big Sioux Aquifer, occur within the project area. These lesser groundwater sources tend to be located either east or west of the Big Sioux Aquifer. 

The main project accomplishment was raising public awareness about groundwater resources, protection and problems. Additional education is needed but more people are aware of potential groundwater problems today than before the project began. People were educated through groundwater protection ordinances, highway signs, presentations at service clubs, etc.

A task force was organized consisting of representatives from US Environmental Protection Agency (EPA), SD Department of Environmental and Natural Resources (DENR), SD Department of Agriculture (DoA), SD Cooperative Extension Service, SD Water Resources Institute, local conservation districts, and agriculture groups such as Farm Bureau, Farmers Union, Pork Producers, South Dakota Irrigation Association and Dakota Rural Action. The task force provided input on methods, procedures, issues, and policies.

Data was gathered for every public water supply well in the project area. The main information source was the SD Public Water Supply Vulnerability Study. A separate report was prepared entitled "Public Water Supply Well Data" to present the information. The report contains 1:24,000 scale topographic maps displaying municipal and rural water system wells. It also contains data about each well including location, depth, aquifer, water right permit number, geology and nitrate-nitrogen concentration. 

Shallow aquifer boundaries were drawn on 1:24,000 scale topographic maps by Jay Gilbertson at South Dakota Geologic Survey. They show areas where sand and gravel deposits are found near the surface (no confining layer between surface sand and gravel). Boundaries are shown as solid and dashed lines. Solid lines are used where position shown on map is generally within 0.1 km (300ft) of the true position. Dashed lines are used where position shown on the map is generally between 0.1 and 0.5 km (300 to 1600 ft) from true position. The topographic maps are available at the EDWDD office for all counties except Minnehaha. Minnehaha County Planning and Zoning office has 1:24,000 scale shallow aquifer maps. The shallow aquifer boundaries have been transferred to 1/2 inch to the mile county highway maps. County zoning offices, First District Association of Local Governments and EDWDD all have copies of these county highway maps. Minnehaha County and the City of Sioux Falls are using a geographic information system (GIS). Shallow aquifer boundaries are part of the system. EDWDD has a county map showing the aquifer boundaries in Minnehaha County. A supplemental GIS in Brookings, Codington, Deuel, Hamlin, Minnehaha and Moody counties was initiated with South Dakota DoA funding. This GIS includes a base layer (roads, streams, lakes, etc.) and shallow aquifer boundaries plus the soils over the shallow aquifer. Area vulnerable to contamination from the surface have been defined based on the soil hydrologic group.

EDWDD developed a procedure for defining wellhead protection areas (WHPAs) in the project area. Generally, the methods accounts for hydrologic boundaries when calculating WHPA boundaries. Most calculated WHPAs in the project area extend beyond aquifer or surface water boundaries. The defined WHPA is adjusted to meet these boundaries. The delineation method used by EDWDD is included in South Dakota's Wellhead Protection Program which was approved by the EPA in 1992. The delineation method was also approved by the project task force. Wellhead protection areas were defined for all shallow municipal and rural water system wells or well fields in every county in the project area except for Brookings and Minnehaha. Brookings County developed an aquifer protection ordinance and defined WHPAs before EDWDD's project began. Minnehaha County defined the entire shallow aquifer as the water source protection so individual WHPAs were not defined. Separate reports describing WHPA delineations were written for each county where WHPAs were delineated. A report was not prepared for Miner County because no shallow municipal or rural water systems are located in the county.

Two model groundwater protection ordinances were developed by First District Association of Local Governments and EDWDD for this project. The ordinances can be included in local zoning ordinances to restrict certain development near shallow water supply wells or over the shallow aquifer. The model county ordinance covers unincorporated areas while the model community ordinance covers the incorporated areas. The model county ordinance was based on the ordinance adopted by the Brookings County Commission in 1989. The ordinance has provisions for two areas: Zone A and Zone B. The county ordinance prohibits most new facilities or land uses in Zone A that have the potential to contaminate groundwater. In Zone B, most facilities are allowed to build as long as performance standards are met such as secondary containment for all storage tanks. The model community ordinance was written very basic because community zoning ordinances vary significantly. The ordinance essentially contains many conditional uses. In other words, most new facilities are allowed to build or expand provided they meet conditions set by the city commission or town council. The model ordinances were used to initiate discussion when counties and communities began formulating aquifer protection ordinances. The model ordinances, especially county ordinances, were modified to meet specific conditions in the area. As counties developed their own ordinances, the model ordinance was revised to reflect these changes.

Alternative wellhead protection measures were formulated for deep wells because recharge does not usually occur near these wells. Since recharge may occur many miles away, wellhead protection areas were not defined for deep public water supply wells. Instead deep water systems were checked to determine if surface water could possibly reach the well and contaminate the system. At first, well fields were surveyed to establish local topography. After surveying 12 well fields and finding no potential contamination sources up-slope from the wells, the remaining wells were field checked before surveying. Field checks showed that deep wells typically located near the highest point in town and surface drainage are usually away from the wells. Most wells were in good physical condition and located in a well maintained area. Potential contamination sources were not found near any deep public water supply. 

Technical assistance has been provided to every county in the project area except Miner since Miner county does not have any shallow public water systems. Technical assistance was also provided to five communities. EDWDD and First District Association of Local Governments cooperated on this task. Work concentrated on county aquifer protection ordinances because these ordinances cover a much larger area than the community ordinances. Furthermore, most wellhead protection areas are located in unincorporated areas. The following seven counties have adopted aquifer protection ordinances: Brookings, Clark, Deuel, Kingsbury, Lake, Minnehaha , and Moody. The ordinances in every county except Minnehaha have two zones. Minnehaha County chose to include the entire aquifer in their water source protection zone because essentially the entire aquifer contributes groundwater to water supply wells in Minnehaha County. Four counties (Clark, Deuel, Grant, and Lake) revised their entire zoning ordinance with assistance from First District Association of Local Governments. At the same time, an aquifer protection district was added to the county ordinance. The process of revising a county zoning ordinance took approximately one year. All county aquifer protection ordinances were modeled after Brookings County except for Minnehaha County. Minnehaha County developed a unique ordinance to fit their specific conditions, especially larger population, and higher water use. Essentially all groundwater in the entire Big Sioux Aquifer in Minnehaha County contributes groundwater to water supply wells so separate protection zones were not defined. The ordinance was also written to correspond with other county zoning regulations.

Observation wells were installed for two reasons: WHPA delineation and early contaminant detection. WHPA delineation wells were installed in Summer 1991 to better define groundwater flow direction and gradient near several public water supply well fields. Early contaminant detection wells were installed in Fall 1992. These wells were installed so a water system could monitor water quality of the groundwater moving toward production wells. WHPA delineation wells were installed around twenty municipal and rural water systems. Forty-nine test holes were drilled and thirty were completed as wells. The test holes also helped define the aquifer near the water systems. Four municipal systems and four rural water systems wanted early contaminate detection wells. A total of forty-nine wells were installed at twenty-eight sites. Thirty-two of these wells were installed at sixteen sites around the Sioux Falls airport well field.

Highway signs were installed to call attention to areas where major roads cross aquifer protection areas. The signs state "Attention, Groundwater Protection Area". Signed have been installed in Brookings, Deuel, and Minnehaha Counties, counties with aquifer protection ordinances. South Dakota Department of Transportation fabricated the signs and installed them along state and federal highways. County highway departments installed the signs along county highways. Clark and Kingsbury Counties are also interested in groundwater protection signs. 

There is a need to continue modifying zoning ordinances as conditions warrant. Water systems need assistance with contingency planning. We need to continue GIS, make information available to water systems, local governments and utilities so they can add layers to the system. We need to help water systems identify locations for new wells and possibly produce maps showing "good" spots for new wells. We need to develop a comprehensive model for water use and management in the Big Sioux basin, consider groundwater and surface water as components of the system, not separate systems. As population increases in the basin, this will become more important. A model is needed to consider what effect groundwater use upstream has on downstream flows in the river (i.e., if Brookings and Watertown triple groundwater use, will Sioux Falls be able to pump surface water from the river). We need to continue developing and supporting non-point source projects in the Big Sioux basin, protecting and improving surface water because it affects groundwater. Since most work is concentrated on municipal and rural water system wells, an effort should be made to check other public water systems such a s suburban housing developments, trailer courts, and on-community housing systems.