Action to Date by the Durham Town Council and VHB

Town Council's 2013 promise to preserve the dam is being broken

On July 1st, 2013, the Durham Town Council adopted Resolution 2013-20, and “hereby concurs that the Mill Pond Dam adds immeasurably to the rich fabric of the community and that the Town shall take steps needed to preserve it for the duration of its useful life.”

Inaction to Date

Nothing since that time has been done to preserve the dam. Despite this, the dam has once again proven its usefulness to the Town of Durham, perhaps providing its greatest value in the 370+ years of dams existing on this site. The dam is telling us, in no uncertain terms, that we have an enormous issue in our community, and we have an equally enormous moral obligation to address this issue now.  That issue is the pollution we have all collectively caused in the Oyster River watershed. In fact, the dam is providing another invaluable use, acting as a retention pond to hold back contaminants from flowing unabated into the Great Bay.

Since 2008, the Town has paid collectively $525,000 for 8 studies to allegedly to study this issue.   All the studies related to the environment identify the elephant in the room, namely the flow of contaminants into the Mill Pond impoundment, yet the town has not taken steps to resolve the root cause. Two of the largest  current contaminates are nitrogen and phosphorus, and the most impaired contributor is College Brook that flows through UNH and past the Plaza parking lot.

Removing the dam does nothing to address the sources of this pollution. 

Removing the dam will in fact forestall any meaningful remediation, as it will appear that we have magically resolved the issue just by letting the problem flow downstream, into the Great Bay.

Let us focus our collaborative efforts on the real issue. Let us celebrate the dam for the message it sends about continued environmental damage. Rather than shoot the messenger (remove the dam), let us rather hear the message and act.
Spending since 2008

Town Council’s Study versus  Action Mentality

Since 2008, the Town has spent $523,251 on 8 studies of the dam and Mill Pond.  During that same period, only $3,300 has been invested in any sort of maintenance, when repairs were made in 2011 to the right embankment of the dam.  A mere fraction of 1% of the total dollars spent was actually spent doing something to physically improve the situation; the remaining 99+% was supposedly spent studying the issue.

In 2014, the 4th study stated the following:  “TP (total Phosphorus)  concentrations in College Brook were three to four times higher than those observed upstream.  Although flows are lower in College Brook than the Oyster River, reductions in phosphorus inputs to College Brook will be critical in the long term to reducing phosphorus concentrations in Mill Pond.”   

Imagine if a majority of the funds invested in studying the issue had actually been invested in addressing the problem with a solution?   We would have spent $401,000 less on studies, as the 4 studies from 2008 through 2014 cost only a combined $124,000.

Key Findings from the 8 Studies:

2008 Stephens Associate Study
Cost of Study - $52,663 

 “We estimate about $1.4M to rehabilitate, operate and maintain the Dam and impoundment “
Cost of Study $35,850

“With respect to the other compounds analyzed, several heavy metals including arsenic, cadmium, chromium, lead, and mercury were also detected in various sediment samples above the reported Ecological Screening Level Criteria.”    

“The freshwater vegetation species that are likely to become established in the areas of the drawn down pond will involve a mix of woody and herbaceous species. Much of the existing pond area that has bottom elevations above 8.0 feet (+/ -) are anticipated to have no standing water but are likely to have saturated soils for a much of the growing season given the close proximity to the underlying groundwater and the fine-grained nature of the soils. These areas are likely to primarily support various wetland shrub species with a mix of herbaceous plants in the wetter areas that may develop in small depressions. The types of native shrub species that would likely become established include speckled alder, silky dogwood, and northern arrowwood. Invasive species such as glossy buckthorn, oriental bittersweet and Japanese barberry could also become established as these plants are currently present and provide seed sources. Therefore, ongoing monitoring for these and other invasive species is recommended as noted above”.

Cost of Study - $22,250

“The physical test properties of the Durham Falls Dam show the compressive strengths to be very high with an average strength of approximately 5,780 psi.” 

“It is difficult to make a viable recommendation for the future use of the Oyster River Durham Falls Dam due to lack of knowledge of the remaining ASR potential expansion in the existing concrete. It is recommended that this be determined prior to deciding the future fate of the Dam.”

Note - that recommendation was not acted upon.
Cost of Study - $13,568

“TP (total Phosphorus)  concentrations in College Brook were three to four times higher than those observed upstream.”

“Although flows are lower in College Brook than the Oyster River, reductions in phosphorus inputs to College Brook will be critical in the long term to reducing phosphorus concentrations in Mill Pond.”  

“Dredging the existing soft sediment in portions of the Durham Ponds should benefit some uses of the ponds by creating additional open water areas free of aquatic plants for recreation and fishing. Dredging is a very effective way to remove nutrient rich sediment as well as reserves of seeds, spores and other resting stages of plants.”

Note in 2014, VHB recommended selective dredging, and the high  cost for the Mill Pond dam area was only $183,938 - see table below.
Cost of Study - $25,000

“Observed concentrations in College Brook (0.041 to 0.198 mg/l) are substantially higher than those observed in the Oyster River upstream of Mill Pond (0.029-0.054 mg/l) particularly after rain.” 

“The total study area encompasses 1,208 acres, 21% of which is impervious cover. This area contributes an estimated 4,733 lbs of nitrogen annually. Table 1 details land use and pollutant load for subwatersheds 1 and 2.”

More than one third of the nitrogen load is coming from identified “Commercial” sources.

 “The results show that the spillway is stable against flood conditions and the spillway and right abutment (gated outlet structure) are stable against normal flow conditions.” 

Cost of Study - $349,823

“Dam removal is expected to increase the sediment load to the tidal reach beyond NH 108 by more than 155,000 ft3 in five years and by more than 262,000 ft3 in 50 years. The sediment transport simulations suggest that sediment may be deposited in a relatively short reach, roughly located between the Three Chimneys Inn and Durham Landing.” “In 2013, the Durham Pond Limnological Study found that total phosphorus (TP) concentrations in Mill Pond generally ranged between 0.40 and 0.60 mg/L which is two to three times higher than a generally accepted threshold of 0.20 mg/L”
“College Brook had even higher TP levels - much higher than those observed in the Oyster River upstream, suggesting that inputs from College Brook likely have a major influence on the downstream TP levels.” 

“Using predictive modeling, the study found that the elevated TP levels were mostly attributable to stormwater runoff from developed land areas in the upstream watershed.”

“The lowest nitrate levels were usually observed within the impoundment or at the dam compared to the upstream stations. The highest nitrate concentrations were typically observed at the upstream station in College Brook and nitrate levels in Hamel Brook were somewhere in between.”
Table 3.3-3 Summary of Findings - Ecological Screening Assessment of Sediment Sample Analytical Results on page 60 of VHB’s original November 2020 study. “Of the 18 sediment samples taken from the Mill Pond and Upstream, 11 showed high risk of adverse effects to ecological receptors for PAHs (Polynuclear Aromatic Hydrocarbons).  17 of 18 samples showed high risk of adverse effects to ecological receptors for Metals (arsenic, cadmium, chromium, lead, and mercury).
Cost of Study - $43,920)

“The team consulted with NH Department of Fish and Game (NHF&G) personnel who are responsible for operation of the existing fish ladder to develop a concept plan for a downstream fish passage notch. The additional cost of the notch would be approximately $65,000.”

“One key question posed to the team was whether the water quality impairments within the impoundment can be addressed through watershed management strategies if the Town selects Alternative 3 (Dam Stabilization).  The Mill Pond Nutrient Control Study (Roseen, Sahl, and Provost, 2018) described a set of 12 stormwater best management practices (BMPs) within the College Brook and Mill Pond Road portions of the Oyster River watershed. Construction of this program was estimated to cost nearly $1.8 million (2018 dollars). While the focus of this program was to reduce nitrogen loading, the BMPs would also treat phosphorus, the limiting nutrient in Mill Pond. The Supplemental Analysis estimated that this program would reduce the estimated total average annual phosphorus load from the targeted portions of the College Brook and Mill Pond sub-watersheds by approximately 52%.”

 Why are we only discussing the removal of this 1 dam?

According to NH State Dam Bureau, there are 837 state regulated dams in this state. Other state regulated dams in Durham that are not under consideration for removal and in fact have had major repairs performed in the recent past, or plans to repair:  

Wiswall Dam - This dam, constructed in 1912, provides the impoundment for the Town's drinking water supply. Dam abutments were rehabilitated in 2011; however, spillway rehabilitation was not part of this scope and remains necessary. Design funding was previously approved in 2014 and construction improvements are planned for 2023.  

Durham Reservoir Dam on Beards Creek- first built in 1935, rebuilt in 2010. 

Oyster River Reservoir DAM (aka UNH dam) - Less than 1 mile upstream of the Mill Pond Dam.  It contains no fish ladder and is never going to be removed since it is a major source of drinking water for UNH and Durham.