#08 - Irrigation Alternatives for Oak Land Middle School

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Nathan Fuerst, City Administrator, City of Lake Elmo Oak-Land Middle School 3 of 6 The difficulty with this type of system at this school site is the feasibly of collecting and storing enough water for irrigation use. Roof water is typically the best location to collect re-use water from since this source would not have significant amounts of salts, sediments, grass clipping, etc. But much of the existing roof water at this site discharges on to the ground and various locations around the building and is difficult to centralize and collect. With the current building project, much of the new run-off and roof water is collected and will be infiltrated into the ground in accordance with Valley Branch Watershed District (VBWD) storm water treatment requirements. Incorporating a water re-use system would require additional catch basin structures and piping to direct water to the underground storage tank rather than to the current treatment system. To provide one inch of water over the athletic field areas would require a tank of about 32,000 cubic feet or approximately 239,000 gallons. A typical 2-year rain event would provide about 19,000 cubic feet (142,000 gallons) of water. Significant rain events would be required to fill the storage tank and the irrigation system would likely need to be supplemented with another source of water, such as municipal water. Historical data indicates that the average weekly rainfall would produce about 0.88 inches per week or 85,000 gallons per week for the drainage area to the tank. See attached Appendix A for a summary of the costs for this water re-use system. Irrigation Using Water from Rose Lake The third alternative reviewed is using water from Rose Lake for irrigation of the athletic fields. Drawing water from Rose Lake would require permitting through the DNR, VBWD, and may not be allowed. Assuming water can be taken from Rose Lake, the approach would be very similar to that described above using underground storage tanks but using the water “stored” in Rose Lake instead of underground storage tanks. The primary differences in this situation are additional piping, pumps, and filtering to get water from Lake Rose to the treatment/re-use system, but the underground tanks would not be needed. All of the treatment components would be the same. However, runoff to Rose Lake could introduce salts and other contaminants not anticipated in roof water. Rose Lake has the potential for PFAS contamination such that there are potential health concerns with this source of water, and the potential for contamination of the soil from the irrigation water. See attached Appendix B for a summary of the costs for this water re-use system. No Irrigation Another option being considered by the School District is to remove all irrigation from the school site. Much of the site is currently not irrigated. Obviously, irrigation helps keep natural grass fields more playable and resilient, and therefore more usable for school and community use. Summary While there are several options for how the fields at Oak-Land Middle School could be irrigated, the current plan is to leave the existing irrigation system connected to the building water system. With the connection of municipal water, the irrigation would then be supplied by the municipal water. This has been the plan for the entire planning process with City. At the request of the City, the School District has studied other options and their additional costs for implementation. 1. Irrigate with City water (additional project cost $0) 2. Irrigate with a new well system (additional project cost $205,000) 3. Irrigate with captured rainwater (additional project cost $313,400) 4. Irrigate with water from Rose Lake (additional project cost $212,8500) 5. Discontinue irrigation (additional project cost $0)