Cost Estimates for Dam Stabilization versus Dam Removal   

This analysis considers the possible costs of both alternatives using best and worst case scenarios. These are as the tile implies, 'estimates'.  
(Details on what these estimates encompass can be found under Financial Considerations. See assumptions below)

Assumptions for Above Analysis

We are not suggesting that dam removal will cost over $13M. What we are suggesting is that it is realistic to anticipate best and worst case scenarios to aid in the decision making process. It would appear neither the Consultants or our Town Leaders did this simplistic analysis. One assumption that we believe is reasonable to conclude is that there is the potential for more unknown costs with dam removal. This is because they are simply more assumptions that have to be made with costs under a removal scenario. If you listen to the Consultants at Town Council meetings, they never commit to exact costs or definitive estimates. So, what is the probability the high cost for Dam Stabilization will be $1.5M at most, probably close to 100%. And, what is the probability the low cost for Dam Removal will cost as low as $950k?   Given all the unknown costs, probably close to 0%. If the Town considers the Total Cost of Ownership, there is a higher probability that the  cost to stabilize will be  less than the cost to remove the dam  

Under-Estimated and Ignored Costs of Dam Removal

The Town and the Consultants have only estimated at this point the cost to physically remove the dam and reshape the channel at the dam site.   It is a safe assumption that there are many more unknown costs with dam removal than with dam stabilization, given the extent of the impact on the existing ecosystem and physical landscape of this area. 

The following are costs the town has not considered:

The Town Council Chair stated the following in a 9/17/2021 Fosters Daily Democrat article:  “Council Chair Kitty Marple said the dam has been in a state of disrepair for nearly a decade. Marple said some argued the $1.5 million price to shore up the dam and leaving the pond would be comparable to the $1.9 million to remove it. Marple said the removal cost figure doesn't include the grants the town expects it can get to bring the price tag down.”

First, grants are not a given.  We understand that Exeter only received a portion of the grants it anticipated in its 1.8M dam removal.  Additionally, in the Town of Durham’s budget forecast, they estimated only 30%-50% of the cost of removal being potentially covered by grants.  In addition, when the dam in Greenland NH was removed on the Winnicut River in 2009, the original cost was estimated at approximately $1M.  The actual cost has approached $2M.  In addition, this is a quote from, “Winnicut Dam and fishway were removed in 2009. Unfortunately, a fish ladder installed beneath the Route 33 bridge to help ensure passage was poorly designed and has created a velocity barrier for migrating fish. Efforts are currently under way to modify the structure to restore fish passage into the Winnicut River.” 

In addition, there are now ample grants available to perform dam repairs.   US News reported the following on November 16, 2021:  “Infrastructure Bill Unleashes Funding to Address Risky Dams - States will soon be flooded with federal money they can use to repair, improve or remove thousands of aging dams across the U.S. The funding is included in the $1 trillion infrastructure bill signed by President Joe Biden.  Reclamation will get an additional $100 million for repairs at certain old dams. An additional $118 million will fund repairs at dams through the Natural Resources Conservation Service. And $75 million will flow through the U.S. Army Corps of Engineers for a loan program to make dam repairs.”

1 - Impacts to valuation and taxes to waterfront properties

There are approximately 25 homes located on the impoundment that will be negatively impacted by the elimination of the impoundment and reducing this area to a low flow/narrow stream.

J. Hiller  reviewed past TC meetings, and the below was noted as an unresolved item from the 3/4/2019 meeting:  “He (Todd Selig) said the study should specifically highlight tax impacts. He said the study should address to what extent abutting landowners had water rights. He said it should also include an analysis on invasives, and how remediation of the impoundment would be addressed to prevent this. He said the study should include a section on legal liabilities with the different options. He noted that there had been a lot of threats from abutters about suing the Town, and said a question was to what extent they had a legal claim. Councilor Lawson suggested that the analysis of legal liabilities and other legal questions should be done separately from the feasibility study, with appropriate counsel.”  

This has never been addressed by the TC, the consultants, or the Town Administration.

Response from Selig on 10-19-2021:  “Thank you, Jeffrey.  This is something our Assessing Office did evaluate over the last few years and the conclusion after speaking with other communities where dam removal has taken place and the general nature of Durham properties along the impoundment/backwater is that there would be a negligible impact upon value.  In this case under a dam removal scenario, some properties would gain tidal access to the Great Bay and their values might benefit from such access.  And even with dam removal, a significant water feature remains, though certainly altered from the present state.  There is simply not the impact you hope to see to bolster a dam retention argument.”  

This was the 10-19-2021 response from our assessor, Jim Rice:  “Dear Mr. Hiller, The preliminary data that I have been compiling regarding this topic is not ready to be shared with the public, as I have not completed my analysis.  Once I have, it will be made available.”

The Durham Tax rate is $.02791 per $1,000 of assessed valuation.   This means for each $100,000 in assessed value, the annual taxes are $2,791.00.  If 25 homes are impacted for assessment purposes by a $100,000 reduction in assessed value, that is $69,775 (25 x 2,791) less each year in tax revenue, or $697,750 in 10 years.   This reduction in property values is going to be shifted to the other property owners in Durham.

In addition, the Town will be liable for the reduction in Market Value to these properties as well.   We know that the assessed value is a percentage of the actual Market value.  Assuming that this percentage is 50% (which seems reasonable given existing assessed values versus market values), that is potentially a $5,000,000 liability the town is liable for, if sued by these homeowners (200,000 reduction for each property x 25 properties).  This does not include the legal fees the Town will need to expend to defend such a lawsuit, as well as the very likely scenario of having to reimburse the property owners for their legal fees as well.

2 - Potential costs for wells impacted by dam removal

Properties on the west side of the impoundment on Mill Rd/Faculty neighborhood are all on city water.   East side of impoundment, Laurel Ln/Newmarket Rd are private wells.  Of the approximately 30 properties on the east side of the impoundment, and on the west side of Newmarket Rd/108,  VHB only included the data for 3 wells.  It appears these 3 wells are the Lund’s  property on 98 Newmarket Rd, the Burns/Bodo property on 20/22 Newmarket Rd, and the Ware property at 10 Laurel Ln.   This is most likely because the NHDES Well Water Inventory available on-line only goes back to 1984.  VHB did no further analysis.   Most of the 17 wells included in their ‘analysis’ are in the neighborhood of York Drive, off Durham Point Rd.
The Lund well is 523 ft, the Burns/Bodo well is 465 ft, the Ware well is only 112 ft.  VHB listed the 10 Laurel Ln well as being on the 6 Laurel Ln property, so they got 1 out of the 3 incorrect.

This analysis is far from adequate given the low percentage of wells actually studied that are most likely to be impacted by dam removal.  One could easily conclude the town runs the risk of being liable for drilling many new wells and/or extending the public water supply at a cost that likely exceeds the cost of dam removal. In addition, residents would not be receptive to having to now pay for town water, especially after paying costs to maintain existing wells.

3 - Management of invasive plant species

Management of invasive plant species will make the former Mill Pond and Hamel Brook impoundments unusable without significant management expense.  The Town Administrator has already stated as recently as the 11/1/2021 TC meeting that the Town does not have the funds to maintain existing vegetation management.

4 - The cost to dredge the Town Landing

What is the cost to dredge the Town Landing area as soon as that becomes un-navigable due to the increase in sediment flow.  The VHB study states the following on page 54 of their November 2020 report, “In total, dam removal is expected to cause increase the sediment load to the tidal reach beyond NH 108 by more than 155,000 ft 3 in five years and by more than 262,000 ft3 in 50 years.”  A tri-axle 28 foot dump truck holds 18 cubic yards.  There are 27 cubic feet in 1 yard, therefore each load holds 486 cubic feet (27 x 18).   155,000 cubic feet is therefore 320 dump truck loads full of sediment. That is the amount that will flow from the existing pond impoundment into the tidal portion of the Oyster River in 5 years.  In 50 years, that figure is 540 dump truck loads of sediment.  For another analogy, 262,000 cubic feet of sediment equates to 50 miles of sediment 1 foot high by 1 foot wide by 1 foot deep  (262,000 cubic ft / 5,280 feet per mile).  

Removing the dam does not remove the sediment issue, it simply transports it from existing problem area 1 to new problem area 2.

5 - The cost to properly remediate contaminated sediments

The cost to properly remediate contaminated sediments is not addressed in the cost.  (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).

6 - The cost to perform a Section 106 - Review of Historical Significance

In a conversation Janet Mackie had with Lindsey Lefebvre (US Army Corps of Engineers), she stated US Army Corp gets involved with federal permits, after local and state review dealing with discharges to waters.  In addition,  in accordance with Section 106 Review of Historical Significance, a study has to be performed to go forward with dam removal.  An estimate of these costs should be included in the total amount for the removal option.