Taken together, the chapters suggest that although Philadelphia's parcel-based fee system is a good first step toward drawing private investment to green infrastructure, many economic barriers remain. In the current market environment, the discounted payback periods of most green infrastructure retrofits on private parcels stretch beyond ten years, which is longer than most investors would be willing to accept. However, the report indicates that a range of strategic policy interventions that PWD and other local stakeholders could undertake would substantially expand the market for viable private investment in green infrastructure. Finally, the authors find that implementation of the policy interventions explored in this report are likely to be in PWD's and local tax payer's best economic interest, as the cost to PWD to implement these policies are likely to reduce the City's total costs to meet its green acre goals.