Update on storm water and ground water assessmentPosted on 23 November, 2015
Despite the wet weather conditions, most of the groundwater and surface water measurement equipment has been installed and is functioning at Hiawatha Golf Course. Minneapolis Park and Recreation Board (MPRB) staff and consultants are reviewing options to expedite the installation of the remaining measurement equipment.
Water levels at Lake Hiawatha, the ponds on the golf course, and Minnehaha Creek are high due to nearly four inches of rain in the last week. The pump station discharge lines are submerged in the lake. As a result of high water conditions, the installation of flow meters in the pump discharge pipes has been delayed. Depending on weather, the flow meters at the pump discharge pipes will be installed the week of Nov. 23.
Barr Engineering, the MPRB consultant on this project, installed three hand-driven piezometers southwest of Pond F and the instrumentation (a pressure transducer and data logger) has been installed. Piezometers are temporary vertical pipes driven about 5 feet into the ground and are used to monitor the groundwater level at that point. They are being used to monitor how groundwater levels fluctuate at the golf course in response to changes in pumping rates and changes in lake and pond levels. Data from the piezometers is being recorded but has not yet been collected.
Barr installed staff gauges and stilling wells in Lake Hiawatha, Pond D, and Pond F. Staff gauges are like vertical rulers that allow visual measurement of the water levels. Stilling wells are temporary vertical pipes installed in the water near the staff gauges. Electronic instrumentation is installed inside the stilling well to continuously record the water level and are intended to supplement manual measurements. Inside the stilling wells, waves are eliminated and the water surface is still, allowing for more accurate water surface elevation readings. The combination of the these two installations provide information on how Lake Hiawatha levels and golf course pond levels are related to groundwater levels and how changes in lake/pond levels affect groundwater levels and pumping rates.
Four monitoring wells have also been installed in various locations on the golf course to allow for measurement of ground water elevations. These are similar to the piezometers but they are deeper and are intended to be in-place for long periods of time. They are also constructed to allow taking of ground water samples from the wells. Instrumentation has been installed and water levels are being recorded. Water level data and water samples have not yet been collected.
The MPRB originally intended to measure stormwater flows into the golf course from the large storm pipe that drains into Pond A. These stormwater flows drain through the other golf course ponds and are then pumped into Lake Hiawatha. Barr’s work discovered the large storm sewer pipe contained significant accumulations of sediment, and efforts are underway with the City of Minneapolis to remove the sediments so flow meters can be installed. Measurement of the stormwater inflow to the golf course helps to understand how much of the water pumped to Lake Hiawatha is groundwater and how much is stormwater. If sediments cannot be removed and the flow meter cannot be installed, Barr will perform calculations using the pump meter data to estimate the amount of stormwater pumped versus groundwater.
The MPRB is engaging Dr. Otto D.L. Strack as a peer review consultant to review Barr Engineering’s work once data is available for analysis. Dr. Strack is a professor of Civil and Geological Engineering at the University of Minnesota’s Civil Engineering Department and is an expert on ground water analysis and modeling of ground water flows. Dr. Strack’s review of investigations and conclusions is important to the MPRB because of the potential impacts to the golf course and surrounding private properties should pumping conditions change.
In October, the MPRB applied for a ground water appropriation permit from the Minnesota Department of Natural Resources (MnDNR). Communications with the MnDNR are continuing to ensure all necessary information supporting the permit application is provided. When the MnDNR considers the permit application complete, the MPRB will be invoiced for the permit. However, the DNR has indicated it will wait for the results of the Barr work to fully review the permit application.