Trumble told the planning commission he needed the extension because another legal firm representing the developers is still negotiating the issues with the EPA.
After that, developers plan to submit their final plans and drawings for the proposed development.
Planning commission members expressed concern about granting another six-month extension for the development, which has already had three similar extensions.
Planning Commission member Mark Schiavone said it is unwise to give that many extensions to a development because many factors like school student populations and traffic conditions in a given area can change in that amount of time.
"We have to set a standard here. This is a very bad precedent," Schiavone said.
Planning Commission member David Hammer proposed giving Murphy's Landing developers a six-month extension, but it would be the "last and final time."
The motion failed.
Murphy's Landing has generated controversy because some believe it would mar the historical landscape of Harpers Ferry, W.Va.
The foundation of John Brown's fort is located on the property and in 1906, W.E.B. Du Bois and civil rights leaders of the Niagara Movement, an early civil rights organization, made a barefoot pilgrimage across the property in honor of the abolitionist.
The meeting led to the formation of the NAACP.
In April, Donald Campbell, the superintendent of Harpers Ferry National Historical Park, said park officials were close to reaching a deal to purchase the land.
Campbell said he believed the park and the developers had agreed on a price but other details had to be worked out.
Trumble said he was not aware of any negotiations to sell the land.
Campbell could not be reached for comment Tuesday.