Brief Outline... | CWCWC Comments... | Preliminary Biodiversity Assessment...
Putnam County Coalition to Preserve Open Space comments... | Jim Bacon comments...

CWCWC comments on Hillcrest Commons

August 5, 2005
Town of Carmel Planning Board
60 McAlpin Avenue
Mahopac, NY 10541

Re: Hillcrest Commons

Honorable Members of the Planning Board,

The Croton Watershed Clean Water Coalition, Inc., (CWCWC) thanks you for this opportunity to submit comments regarding the above-captioned development.

These brief comments are in addition to the analyses being submitted on behalf of CWCWC and Putnam County Coalition to Preserve  Open Space (PCCPOS) by Erik Kiviat, Ph.D. of Hudsonia Ltd. regarding the site’s Biodiversity Assessment; by Eugene J. Boesch, Ph.D., R.P.A. on the site’s cultural and archaeological resources; and comments by James B. Bacon, Esq., regarding legal and stormwater concerns.

CWCWC’s goal is to protect the Croton watershed and its reservoirs from further pollution, whether from stormwater runoff, sewage treatment plants; septics and other causes. The Croton system is a vital component of the larger New York City supply system that provides 9 million people, over half of New York State, with high quality, still unfiltered drinking water.

Regarding the Hillcrest Commons proposal, CWCWC is of the opinion that the estimates for reduction in phosphorus and other stormwater pollutants subsequent to development, are seriously under-estimated

As your Board is aware, pollution from development at Hillcrest Commons would be discharged, in part, into the Croton Falls Reservoir via Michael Brook. According to the joint NYS DEC and NYC DEP study (Nonpoint Source Implementation of the Phase II TMDLs, April 2001), the Croton Falls reservoir needs a reduction in phosphorus loading of 1947 lbs/year in order to come into compliance with the required phosphorus concentration of 15 micrograms/liter. The Croton Falls reservoir is a source reservoir whose waters, when needed in times of drought, are fed directly into the Delaware aqueduct, the major source of still unfiltered water for the NYC greater metropolitan area. It is a critically important reservoir. Unfortunately, the Town of Carmel is its major polluter. The Town contributes 85% of the phosphorus load that needs reducing, or 1659 lbs/year.

Clearly, any development within the Town of Carmel should be carefully designed so as to not increase the phosphorus load to the Croton Falls reservoir.

However, the results from the applicant’s submission are, at the very least, ambiguous. For example, the pre-development phosphorus load (P-load) from the site is given as 4.10 lbs/year. Summing up the post-development P-loads from the various sub-basins (1.0S; 1.1S; 1.2S; 3S; 2.0S; 2.1S; 2.2S; 2.3S), the applicant calculates the total phosphorus (TP) load as having a maximum of 5.00 lbs/year, and a minimum of 2.13 lbs/year. The final P-load could be anywhere within this large gap and be greater or less than the initial value.

 After reviewing the figures on pollutant loads presented by the applicant, it is CWCWC’s opinion that Hillcrest Commons is likely to increase the phosphorus load to the reservoir for the following reasons.

(a) As pointed out by CWCWC attorney, James B. Bacon (and confirmed by David Clouser, P.E., in his comments on the Gateway/Fairways project) the more recent figures for the pre-development phosphorus loading rates (lbs/acre/year) are about half of those used by the applicant, that have now been superseded. Therefore, the applicant’s estimate of the phosphorus emanating from the undeveloped land is too high, and the reduction needed will be too low.

(b) The applicant assumes that Best Management Practices (BMPs) placed sequentially (as is the case for various of the sub-basins) will each, in turn, remove pollutants to the same degree as if they were stand-alone devices. This is an incorrect assumption. The reasons are clearly explained in Watershed Management for Potable Water Supply: Assessing the New York City Strategy, 2000 – The National Academy Press, pp 350-351 – see Attachment A) “Removal efficiencies vary with the changing composition of the stormwater as it passes through the multiple BMPs. For example, the first BMP may accomplish 50 percent removal of sediment and sediment-associated particles. But because larger particles are more efficiently removed, subsequent BMPs will be treating water enriched with finer particles, and removal efficiency will drop below 50 percent. At some point, the incremental removal is negligible, and the pollutant concentration from the  final BMP reaches an irreducible concentration...”

It is customary, in an important watershed such as the Croton, to err on the side of caution and use the lowest pollutant removal value for any particular BMP. This procedure is further justified here because the applicant ignores the fact that the pollutant removal efficiencies of the BMPs diminishes, as explained in the preceding paragraph. If the lower removal values are used, the resulting P-load after development will exceed the pre-development load.

CWCWC concludes that it is doubtful whether the final P-load is indeed below the original load, and recommends that the applicant be required to perform more accurate calculations. The same remark also applies to the results for Biological Oxygen Demand (BOD) and Total Nitrogen (TN).

(c) The 12-acre 1.0S basin is largely, if not entirely, in the Michael Brook watershed. Ten acres out of the twelve are destined to be either commercial or townhouses. The result will be 83% imperviousness. According to Watershed Management for Potable Water Supply: Assessing the New York City Strategy, 2000 – The National Academy Press, Figure 9-3, page 419 (see Attachment B), beyond 45% imperviousness no combination of BMPs is capable of reducing the level of phosphorus below its initial level. Figure 9-3 shows that even the most efficient (BMP-Hi curve) BMPs are incapable of reducing the P-load in stormwater runoff below its pre-development levels. With 83% imperviousness, CWCWC questions the applicant’s conclusion that the P-load will be reduced. Again, we urge that the calculations be reformulated.

As the operator of a small, regulated MS4 (Municipal Separate Storm Sewer System), the Town of Carmel must comply with the six MS4 “minimum control measures” (EPA Storm Water Phase II Final Rule, Fact Sheet 2.), in particular

Measure #4 – Construction Site Stormwater Runoff Control that applies to construction activities that result in land disturbance of one acre or more, and Measure #5 – Post-Construction Stormwater Management.

Measure #4 stipulates: “An MS4 must, at a minimum, develop, implement and enforce a program to reduce pollutants in any stormwater runoff to the small MS4 from construction activities that result in a land disturbance larger or equal to one acre.”

Measure #5 stipulates: “An MS4 must, at a minimum, develop. Implement and enforce a program to address stormwater runoff from new development and redevelopment projects that disturb one acre or more.”

Given these regulations, the Town of Carmel has the power and the duty to protect the watershed and its reservoirs that fall within its jurisdiction.

Respectfully submitted,
Marian H. Rose, Ph.D.
President, CWCWC