Planner says soil conditions are big factor
By:John Tredrea
Nearly two-thirds of 58-square-mile Hopewell Township has “severe limitations” for the on-site treatment of sewage effluent, township planner Michael Bolan said in a May 8 report to the Planning Board.
Commissioned by the board, Mr. Bolan’s report is part of a Geographic Information System (GIS) on which he is still at work and which is an element of the complete rewriting of the township Master Plan.
The Township Committee appropriated $200,000 last year for the Master Plan work by Mr. Bolan and his firm, Banisch Associates of Sergeantsville. Joining him in the task is Van Cleef Engineering of Robbinsville, the township’s longtime engineering consultant.
A small fraction of township land is served by public sewers, with the rest relying on on-site septic systems. Areas served by sewers include the 1,300-unit Brandon Farms development, located in the southeastern tip of the township and served by the Ewing-Lawrence Sewerage Authority (ELSA) and the 122-house Princeton Farms development, in the east-central township and served by the Stony Brook Regional Sewerage Authority (SBRSA). ELSA also has contracted to provide treatment to Merrill Lynch’s 3.5-million-square-foot Scotch Road Office Park, under construction just north of I-95.
“Approximately 62 percent of the township is identified as having severe limitations for the on-site disposal of sewage effluent, and approximately 95 percent is identified as having severe or moderate to severe limitations,” Mr. Bolan wrote in his eight-page memo discussed by the Planning Board at a recent work session.
“We’ve known all along that Hopewell Township is environmentally sensitive and a natural treasure,” said Mayor Marylou Ferrara, also a member of the Planning Board, in a written statement. She said Mr. Bolan’s “compelling presentation hits us over the head with it. Hopewell Township is characterized by natural scenic beauty, important agricultural soils and severe soil and rock constraints to development.”
Mr. Bolan wrote that the only areas of the township not exhibiting soil conditions with severe to moderate limitations for treatment of on-site treatment of sewage effluent “are along the Delaware River, on Baldpate and Pennington mountains, in the Sourlands, and along the diabase intrusion on Crusher Road.” He added that his findings are based on “factors relating to soils, geology and hydrology.”
Baldpate already has been permanently preserved as open space, having become part of the county park system several years ago. Pennington Mountain, located just west of state Route 31 near the county Route 654 junction, is the site of quarry operated for decades by Trap Rock Industries. Like the Sourland Mountains, located in the north-central township, Pennington Mountain is characterized by steep slopes. Development on sloping land already is strictly regulated by the state Municipal Land Use Law (MLUL). About a mile long, Crusher Road connects Route 654 and Carter Road, about a mile east of Hopewell Borough in the east-central township.
“A picture is worth a thousand words. When residents see the extent of the critical environmental constraints existing in the township in front of them on a map, it’s a real eye-opener,” said Township Committeewoman Kathy Bird-Maurice, a Planning Board member.
Land that cannot be developed with on-site septic systems can only be developed with public sewering. There seems scant chance sewering will be made available to much of the township anytime soon. The mayor, Deputy Mayor Jon Edwards, Ms. Bird-Maurice and Committeeman Robert Higgins have all emphasized many times they favor limiting township development as much as possible.
Development applications are strictly regulated by a welter of local, county, state and federal laws that pertain to a wide variety of factors, including soil conditions. A required component of any development application for land without sewers is proof that the soil percolates well enough to sustain an on-site septic system adequate to handle the development proposal.
Factors Mr. Bolan used in determining the suitability of township soils for on-site disposal of sewage effluent are depth of bedrock, depth of the water table, frequency of stream overflow, soil permeability, stoniness of soil and steepness of slopes.
On its own, the depth of bedrock factor serves to curtail substantially the development potential of almost all the land — 92 percent of it — in the township, Mr. Bolan wrote in his memo.
He said about 15 percent of township land has bedrock within two and a half feet of the surface of the ground, meaning those areas, with their “very shallow soils, which may have rock outcroppings … have severe limitations for development.” He said the largest concentrations of land with these characteristics “occur in the Jacob’s Creek and Fiddlers Creek watersheds, with additional concentrations along Bedens Brook south of Hopewell Borough and along Moore’s Creek north of Baldpate Mountain.” He added that, though “less limiting” for development, areas in which the bedrock is between 2.5 and 6 feet below the surface “restrict the location of foundations, basements and septic systems; this category accounts for approximately 77 percent of the land area,” he said.
Similar constraints on development with no access to sewers are provided in the township by the depth of the seasonal high water table, Mr. Bolan said in his memo. The depth to the seasonal high water table is defined as the distance from the surface of the soil that groundwater, and is referred to as seasonal because the groundwater generally reaches its highest level in the soil between December and April.
“The depth to the seasonal high water table is an important determinant of the limitation and opportunities for development,” Mr. Bolan said. “On the one hand, shallow depths to the water table severely limit the location of buildings and septic systems and are associated with wetlands (strongly protected by the state MLUL), but on the other hand these same areas often support more diverse vegetation and wildlife opportunities. Thus, their protection benefits the environment by both preserving areas of high resource value. . .”
Areas in which the seasonal high water table is within 2.5 feet of the surface of the soil place severe restrictions on development, Mr. Bolan said. He said 41 percent of the land in the township falls into this category. Another 30 percent has a seasonal high water table between 2.5 and 6 feet deep. Mr. Bolan said that, in Hopewell Township, land with a table of this depth is “generally found where impervious layers (of soil) impede drainage and along the Delaware River and other stream terraces.” Depending on exactly how deep the table is in these areas, the “soils can be very constraining or relatively unconstrained” in their development potential,” he added.
About 27 percent of the township has a seasonal high water table 6 or more feet below the surface, Mr. Bolan concluded. This land is in the central part of the township, on the ridge tops of Baldpate and Pennington mountains, and in small areas in the northeast and southwest portions of the township.
“The GIS is a work in progress, but we thought it would be valuable for the (planning) board to see and understand the type of information that is being developed,” Mr. Bolan said.