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Posted on: January 11, 2023

Aquifer Sustainability Assessment

Running Water from faucet

ASSESSMENT OF THE SUSTAINABILITY OF THE GERMANY FLATS AQUIFER

 

Recently, there have been questions by a member of Council and the public citing an 800,000 GDP deficit in one of Sparta’s surface drainage subwatersheds. This deficit was reported by CDM-Smith, a consultant to the New Jersey Highlands Council. CDM-Smith has been developing surplus/deficit estimates for municipal use in developing Water Use and Conservation Management Plans (WUCMPs). It should be noted that the WUCMP is a policy and planning document – not a regulatory directive.

Background

The Highlands Region consists of 52 municipalities in 7 counties. (859,268 Acres – 415,000 (48 %) in the Preservation Area, 444,268 (52 %) in the Planning Area)

About half of Sparta Township (46 %) lies within the Highlands Preservation Area and the balance (54%) lies within the Highlands Planning Area. (Sparta: 24,822 Acres; 11,487 Acres in the Preservation Area, 13,335 in the Planning Area)

NJDEP/Highlands Council has authority to regulate certain development aspects within the Preservation Area, however, that authority does not apply to the Planning Area.

The USGS and NJGS created a system to map watersheds. A watershed is a topographical area that drains to a receiving surface water body. NJDEP adopted the use of HUC 14s (Hydrological Unit Code 14) to designate subwatersheds in the state – it is so named because it has a 14-digit designation. It is a surface water drainage area, not a groundwater unit.

Of the 183 HUC 14 subwatersheds in the Highlands Region, 12 are partially or entirely within Sparta Township.

CDM-Smith Model

According to the Highlands Council, “[t]he analysis of water budgets and availability . . .are highly complex. Models are needed to help address these issues, because no direct methods exist for measuring the impact on aquatic ecosystems of changes in hydrologic conditions due to water uses. Models are simplifications of real world conditions, and as such help to make complex decision making possible.” As such, “[t]he Highlands Council recognizes that models are decision aids, not decision determinants.”

The CDM Smith Highlands consumptive use mathematical model that reported the deficit includes estimates of consumptive use and recharge, but it does not estimate groundwater aquifer capacity, nor does it recognize groundwater flow (i.e., movement of water underground), since it is based on surface watershed units. Since the Highlands Council recognizes that models are decision aids, not decision determinants, the “results from the selected model or models must be applied in conjunction with policies and with the results from other analyses . . . before an ultimate estimate of water availability can be developed.” Any approach for estimating water availability must be capable of using model results in concert with additional policies and decision-making factors.

Since beginning their work, CDM Smith has made adjustments and updates to their model several times – each time refining the model and its accuracy. As a result, some deficits have been reduced and some deficits have turned into surpluses. Notwithstanding these adjustments, the model includes a margin of safety, so as to provide a conservative basis for municipal water use policy.

The current estimate of 800,000 GPD deficit reflects the entire HUC watershed, portions of which being located in Lafayette and Andover. Further, the Highlands Council has recognized that the most significant contributor to the HUC deficit is the water withdrawal at the quarry on Limecrest Road, a withdrawal that was authorized by the NJDEP through a water allocation permit. During the years when the quarry was not operating, the deficit was minimal and even turned into a surplus for 2 years.

Germany Flats Aquifer

The Germany Flats Aquifer is a Sand & Gravel Terminal Moraine Aquifer. That is, it was created during the last ice age during the glacier’s retreat when it was melting. At the terminus of the glacier, sand and gravel, contained within the glacier, was deposited in a valley between the two ridgelines. The sand and gravel filled with water and the Germany Flats Aquifer was born. This aquifer is between 100 and 200 feet deep. It has 3 distinct layers of stratigraphy – a shallow unconfined aquifer, a layer of lesser permeability (i.e., confining layer) and a deeper semi-confined confined aquifer. The sand and gravel aquifer is further underlain by the weathered surface of dolomite bedrock. Based on the highly weathered condition of the bedrock, there is close hydraulic communication between the bedrock and the lower sand and gravel aquifer.

The Germany Flats Aquifer has an enormous quantity of groundwater with water quality characteristics highly favorably for public water supply. It is not a bedrock aquifer on which much of the rest of town relies.

A portion of the Germany Flats Aquifer lies within the HUC 14 Watershed that had the reported 800,000 GPD deficit. Sparta’s Germany Flats Sand & Gravel Aquifer lies beneath about 17% of the overall surface area of the HUC.

As such, the HUC 14 watershed with the deficit is a large surface drainage area that extends from Sparta into Lafayette and Andover. A small portion of this drainage area overlies Sparta’s Germany Flats Aquifer. To emphasize: The HUC 14 watershed is not the Germany Flats Aquifer and the Germany Flats Aquifer is not the HUC 14 watershed.

Sustainability

The Township’s authority to withdraw and use water from the Germany Flats Aquifer was obtained from NJDEP through a Water Allocation Permit. Waters of the State are in held in trust by the State for use by its citizens. The Water Allocation Permit is the vehicle that provides users the right to extract groundwater. This Allocation Permit has the force of law. Sparta’s Water Allocation Permit approval was granted by the NJDEP based on extensive hydrogeologic studies that were conducted by the Township, and numerous hydrogeologic studies developed by the N.J. Geological Survey, which is part of NJDEP.

(Conversely, the WUCMP does not provide information nor methods to assess the sustainably (or increased use potential) of the Germany Flats Aquifer. The Water Allocation Permit review by NJDEP serves those purposes.)

Before issuing the Water Allocation Permit, the hydrogeologic studies were needed to demonstrate the short-term and long-term yield and capacity of the aquifer. When sustained drawdown tests were being conducted on the extraction wells, there was little to no drawdown recorded in the aquifer, except in the immediate vicinity of the extraction well (less than 10 feet drawdown) , which recovered quickly when pumping stopped.

Since becoming operational, Sparta’s water utility staff measures quarterly groundwater levels to monitor the water level elevation. Based on these readings, water levels have been relatively consistent– that is – no sustained reduction in the water table elevation! That means, despite using water from the Germany Flats Aquifer, we are not depleting the reserve (i.e., it’s refilling).

Our current Allocation provides additional surplus capacity to address the elimination of older low yielding wells with groundwater quality concerns, as well as to serve new customers.

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