Hydrogeology of the Governor Hill Fish Hatchery, Augusta

The State's freshwater recreational fishing industry means tens of millions of dollars per year for Maine's tourism economy. This industry depends strongly on an aggressive fish stocking program run by Maine's Department of Inland Fisheries and Wildlife, which in turn depends on a network of State operated fish hatcheries.

Fish hatcheries, in turn, depend on an ample supply of water.... clean water, lots of it, and at the right temperature. Ground water is especially well suited for rearing fish because in general it contains fewer potentially harmful pathogens than surface water and remains at a reasonably constant temperature throughout the year.

As a result, a number of the State's fish hatcheries are located in geologic settings where they can take advantage of ground water discharging from natural springs. Ground water from springs has the additional advantage that it can be gravity fed into the hatchery raceways, eliminating the cost of pumping the water from the ground.

Figure 1

This website describes the hydrogeologic setting of the Governor Hill Fish Hatchery, just outside of Augusta (Figure 1). The site provides an excellent example of surface water features associated with a glacial delta/esker complex. And, it provides an example of efficiently using what nature provides in the form of natural springs.

The hatchery is located at the toe of a glacial delta (part of the Summerhaven delta complex) composed of thick beds of stratified sand and gravel deposits. The delta was fed with sediment by a series of sub-glacial streams, now evident as a series of glacial eskers found at the north end of the delta (Figure 1).

Figure 2

Spring Brook originates below the delta front, and derives its name from numerous springs at the base of the delta. These springs are depression springs, so called because they occur where the natural variation in the topography creates a depression where the land surface intersects the water table (Figure 2).

In this case, the scarp at the front of the delta intersects the water table generated by recharge on the top of the delta complex. Many of the springs originate at about the 250 foot contour. Figure 3 and Figure 4 are examples of springs on the hatchery grounds.

medium-sized spring at the Governor Hill Fish Hatchery

Figure 3

One of the larger springs above the hatchery

Figure 4

Figure 5

The water from the springs is collected in an upper and lower reservoirs (Figure 5) and piped into the raceways. Levels in the reservoirs can be adjusted by controlling the amount of water withdrawn from the upper reservoir.

Figure 6

The springs were investigated in the early 1900's as a possible source of water for the growing city of Augusta. The flow in Spring Brook alone was insufficient to meet the needs of the city, and it was thought that water pumped from the ponds could be used as an auxiliary supply. Work by the U.S. Geological Survey geologist George Otis Smith (Figure 6) demonstrated the relationship between the springs and the series of ponds in the esker system to the north.

The following quotations from Smith (1905) summarize his conclusions regarding the source of the springs:

The table brings out several noteworthy facts. In the first place, with the exception of Penney Pond, in both chains of ponds the elevations of the water surface decrease southward. This indicates a southward slope of the water table......
......The southern slope of the water table over the greater part of this area indicates the direction of underground flow. This in turn at once explains the source of the springs at the head of Spring Brook. (G.O. Smith, 1905, pages 159-160.)

And:

From the foregoing discussion of conditions controlling the system of ground water in the Silver Lake area, it will be readily seen that such a procedure [using pond water as an auxiliary supply to Spring Brook] would be highly inexpedient. The flow of the springs is directly dependent upon the ground water of the plateau, and as it seems probable that there is little flow outward from this basin either to the east or west by reason of the bounding masses of till and rock, it follows that the annual discharge of the springs at the south end of the plateau approximately equals the amount contributed to the basin by the rainfall. The water of the thirteen ponds is merely the visible portion of the supply of ground water in this basin, and to pump from Silver Lake or Tyler Pond would be simply to draw from the same supply as that from which the springs derive their water. (G.O. Smith, 1905, page 160.)

In the late 1980's, IFW personnel noted a reduction in discharge in the springs. Work by the consulting firm of Caswell, Eichler, and Hill, Inc. produced some further insight into the origin of the springs:

As we walked around the hatchery grounds, we found numerous springs issuing from minor valleys cut into the steep delta face.......The ground water seeps out where the water table intersects the delta face somewhere around elevation 255 feet. The highest yielding springs appear to be associated with gravel and cobble beds, and to occur at two different elevations.
.....You can see [from the cross section (Figure 7)] that the water table slopes gently down towards the hatchery from Tyler Pond. The gravel layers are my interpretation based on observation of the springs. The suggestion is that wherever a gravel layer intersects the ground surface, there is noticeable spring discharge.....
The lack of numerous, high-yielding springs outside of the hatchery grounds suggests that any gravel layers present within the fine sand do not extend very far to the northeast and southwest along the face of the delta. If this obervation is true, then the hatchery springs may be associated with a former stream channel that crossed the delta. (Letter report from Caswell, Eicher, and Hill, Inc. to David O. Locke, dated May 2, 1989.)

Figure 7

Interestingly, Smith was answering a question that was also posed to the Maine Geological Survey (MGS) by the Maine Department of Inland Fisheries and Wildlife (IFW) in 1999: could IFW's flow at the fish hatchery be significantly supplemented by drilling one or more wells in the toe of the delta and pumping water to add to the spring flow. We used a different line of evidence to reach the same conclusion as Smith: namely, no....

We used a mass-balance argument - a comparison of the present flow through the fish hatchery raceways plus spring flow not presently captured by the hatchery (estimated to about 800 GPM by IFW personnel) with the estimated ground-water recharge to the basins enclosing the ponds in the esker system to the north (Figure 1). Using the basin in Figure 1, a recharge rate of 1.7 ft/year would be required to provide the estimated 800 GPM discharge in the springs. This recharge rate is at the high end of accepted recharge rates over sand and gravel deposits, which range from 1.0 to 2.0 ft/year (Gerber and Hebson , 1996). So, from a mass balance argument, the fish hatchery was already catching essentially all of the recharge falling over the basin feeding the springs. The mass balance argument essentially allowed us to quantify Smith's original argument.

Figure 8

To examine the geometry of the water table in the esker/delta complex, we constructed a north-south cross-section through the ponds and the area around the fish hatchery and plotted all the data on the elevation of the water table (Figure 8). This included pond elevations, depth-to-water data from Maine Geological Survey significant gravel aquifer maps, and spring elevations. The resulting cross-section shows what Smith concluded solely on the basis of the pond elevations and Caswell, Eichler and Hill, Inc. suggested in their reconnaissance - the north-south gradient on the water table in the delta complex is more than adequate to explain the occurrence of the springs that feed the fish hatchery raceways at the toe of the delta.

Figure 9

IFW's question to us in 1999 was prompted by the results of a pump test conducted on several large diameter gravel wells that had been drilled the preceding year just above the fish hatchery at the base of the delta scarp (Figure 9). The results of the pump test showed that shortly after the pump test started (top graph), the water elevations in the reservoirs fed by the springs began to drop (bottom graph). If allowed to continue, this would have severely reduced the natural flow through the fish hatchery raceways. As the pumping rate was reduced (at 600 and 800 minutes after pumping began), the drop in the reservoirs levels slowed or stopped. Interpreting data for a pump test where the pumping rate has been reduced is difficult, so it was not possible to determine from the data if there was some sustainable yield that would not adversely impact the natural flow through the raceways.

However, based on all the data we did have, we concluded that there was not much, if any, "new" water to be captured by the wells, and the maximum rate at which both wells could be pumped without adversely impacting springs/reservoirs was likely less than 200 gallons-per-minute (GPM) per well. We also cautioned that running a prolonged pump test at these lower pumping rates would be necessary to verify this.

IFW has benefited from their investment in the wells, however. While they did not realize the significant new water they were hoping for to expand the hatchery, they have used the wells to better manage the water they do have. Starting in late September/early October and continuing through the winter, they use warmer ground water (at about 48 degrees Farenheit) to supply water to the rearings tanks. The ground water is oxygen depleted, so addition of oxygen is required, but the warmer water greatly speeds the development of the fish fry. In addition, the ground water contains fewer potentially harmful pathogens, so incidents of disease are reduced in the fry population. One of the two wells is artesian (water flows over the top the well without pumping), providing about 100 GPM of water without the need to run the pumps. Water is routinely pumped only from well number 1 (the "upper" well); pumping from well number 2 produces an immediate drop in the water level of the lower reservoir. The total ground water that can be pumped from well number 1 turned out to be about 200 GPM with only a minimal loss of flow from the springs.

Figure 10

Spring-fed raceways for rearing larger fish

Figure 11

Acknowledgements:

Many thanks to Steve Wilson, Hatcheries Director for IFW, for providing access to the well logs, pump test data and other records of geologic investigations of the hatchery, and to Tom McLaughlin, Fish Culture Supervisor at the Governor Hill Fish Hatchery, for taking the time to walk the site and discuss hatchery operations.

References:

Fetter, C.W. (1994), Applied Hydrogeology, 3rd edition, Macmillan, 691 pp.

Smith, G.O. (1905), Water supply from glacial gravels near Augusta, Maine, in Fuller (1905), Contributions to the Hydrology of the Eastern United States, U.S. Geological Survey Water Supply and Irrigation Paper 145, p. 156-160.

Caswell, Eichler and Hill, Inc. (1989), Letter to David Locke dated May 2, 1989.

Originally published on the web as the June 2003 Site of the Month.

Last updated on October 6, 2005