MAC refutes MnDOT's suggestion that they are responsible for the diminished flow at Camp Coldwater Spring.

This response is developed and submitted on behalf of the Metropolitan Airports Commission (MAC) to reply to the suggestion that construction dewatering at the Minneapolis-St. Paul International Airport (MSP) has affected the observed flow at Camp Coldwater Spring. We conclude that there is no basis to suggest that the dewatering at MAC is contributing to the observed reduction in the flow at the spring. The basis for this conclusion is summarized below.

* The MAC has developed Monitoring and Mitigation Plans to regularly monitor the effects of construction dewatering occurring at the MSP. The Plans include weekly monitoring of water levels in 15 wells across the area and routine monitoring of lake-levels near MSP. This information is posted on a weekly basis on the MAC web site, a weekly progress report is submitted via e-mail, and a detailed assessment of the effects of the construction dewatering is developed every other month. The monitoring well network includes wells near the MAC project sites as well as perimeter monitoring wells between MSP and the off-site resources adjacent to MSP. Specifically, the network includes monitoring wells situated between the MAC construction sites and Camp Coldwater Spring.

The groundwater-level monitoring indicates that the MAC construction dewatering has not resulted in drawdown near Camp Coldwater Spring; the reduction in flow at the spring is unrelated to construction dewatering at the MSP. This conclusion is based on comparison of the regional water level changes in three shallow water table wells near Lake Calhoun to the water level changes in the wells that MAC monitors. Those comparisons have shown water level decline in select monitoring wells nearer to the MAC projects that are greater than the regional trends and thus, are attributable to construction dewatering at MSP. Water level changes at the perimeter wells are similar to those observed in the Lake Calhoun background wells, indicating there is no drawdown from MAC construction dewatering noted at the outlying wells. This observation includes those wells that lie between the MAC projects and Camp Coldwater Spring.

* The MnDOT report notes that there were two time periods in 2001 when
pumping rates exceeded 5000 gpm for short periods of time. The high rates were related to the short-term dewatering at the W-Y and Y-3 vehicular tunnel excavations. The W-Y tunnel excavation is located approximately 2-miles from the spring, with the Y-3 tunnel excavation even further distant. Each of these projects included high-rate dewatering for a period of approximately 45-days, at which point the high-rate dewatering was discontinued. While the schedule of this dewatering happened to coincide with the observed reduction in flow at the spring, there is no basis to suggest that the MAC construction dewatering had any affect on water levels, and hence spring flow, in the spring area.

* All of the dewatering projects at MSP are located in an area where groundwater flow has been documented to be in an east-southeasterly direction. The interchange and Camp Coldwater Spring area is to the east-northeast of the MSP dewatering. Based on this groundwater flow direction, which has been observed and presented in numerous reports over the years, the areas at MSP requiring dewatering are not upgradient of the interchange/spring area. Routine water level monitoring - as discussed above - indicate that MSP dewatering does not intercept water migrating toward the spring.

* One final observation is that the water level elevation in the perimeter wells that MAC is monitoring are actually higher in elevation in 2001 than were observed in 2000. This suggests that even the theoretical effect of dewatering at MSP on area resources is lower in 2001 than in 2000.

In conclusion, the lower spring flow noted at Camp Coldwater Spring is not related to construction dewatering at MSP.

MAC refutes MnDOT's suggestion that they are responsible for the deminished flow at Camp Coldwater Spring.