The Board of Appeals, after considering the land and soil type characteristics, including the ability of the soil to absorb expected quantities of sewage disposal effluent, the degree of filtration of effluent before entering bedrock fissures or other groundwater supply, and the characteristics of the soil with respect to surface water runoff, specifically finds that the conversion, including the parking area and septic system, will not result in substantial increase in surface water runoff to neighboring properties or streets, or substantial danger of pollution or contamination of groundwater supply, a groundwater absorption area, a well, pond, stream, watercourse, W District, or inland wetland, and specifically finds and requires that the increased surface water runoff that results from the development shall be retained within the lot in which it originates or shall be discharged into existing identifiable watercourses without material impact on abutting properties;