No abstract

No abstract

Two septic tank test sites, one in sand and one in limestone, in Broward County, Florida, were analyzed for effluent migration. Ground water from shallow wells, both in background areas and hydraulically downgradient of the septic tank system, was sampled during a 16-month period from April 1983 through August 1984. Water-quality indicators were used to determine the effluent affected zone near the septic tank systems. Specific conductance levels and concentrations of chloride, sulfate, ammonium, and nitrate indicated effluent movement primarily in a vertical direction with abrupt dilution as it moved downgradient. Effluent was detected in the sand to a depth more than 20 feet below the septic tank outlet, but was diluted to near background conditions 50 feet downgradient from the tank. Effluent in the limestone was detected in all three observation wells to depths exceeding 25 feet below the septic tank outlet and was diluted, but still detectable, 40 feet downgradient. The primary controls on effluent movement from septic tank systems in Broward County are the lithology and layering of the geologic materials, hydraulic gradients, and the volume and type of use the system receives.

Thick-Depth, feet ness below land (feet) surface Limestone, yellowish-gray (5 Y 7/2); sandy, sparse biomicrite, planktonic foraminifers and raollusks; neoraorphic and cavityfilling calcite are present; about 20 to 25 percent quartz, very fine grained, subangular to subrounded; about 3 to 5 percent phosphorite and heavy minerals, very fine grained, subangular to subrounded; well cemented. Limestone, yellowish-gray (5 Y 7/2) to grayish-orange (10 YR 7/4); sandy, intraclastic, poorly washed biosparite, raollusks, bryozoans, and planktonic foraminifers; about 20 percent quartz, medium to very fine grained, moderately sorted (very fine), subangular to rounded; well cemented. Limestone, dark-yellowish-brown (10 YR 4/2); sandy, unsorted biosparite, mollusks; about 30 to 35 percent quartz, medium to very fine grained, well sorted (fine), subangular to rounded; about 10 percent phosphorite and heavy minerals, fine to very fine grained, well sorted (fine), subangular to well rounded; well cemented. Limestone, dark-yellowish-brown (10 YR 4/2) and medium-darkgray (N 4); sandy, unsorted intrasparite, mollusks; about 20 to 25 percent quartz, coarse to very fine grained, moderately sorted (fine), subangular to subrounded; about 5 to 10 percent phosphorite and heavy minerals, very coarse to very fine grained, moderately sorted (very fine), subangular to rounded; well cemented; interbedded with about 20 percent sandy, intraclastic, unsorted biosparite; about 30 percent quartz, very coarse to fine grained, moderately sorted (medium), subrounded to rounded; about 5 percent phosphorite and heavy minerals, very coarse to very fine grained, moderately sorted (fine), subrounded to well rounded; well cemented. Limemud, light-olive-gray (5 Y 6/1); sandy micrite; about 25 percent quartz, medium to very fine grained, well sorted (fine), subangular to rounded; about 15 percent detrital carbonate, medium grained, subrounded to rounded; about 10 percent phosphorite and heavy minerals, fine grained, rounded to well rounded; about 5 to 10 percent shell fragments at 78.5 to 82 feet. Sand, light-olive-gray (5 Y 6/1); quartzose, coarse to medium grained, well sorted (coarse), subrounded to rounded; about 25 to 30 percent shell fragments, mollusks, bryozoans, and claw; about 3 percent RF from a calcareous sandstone to a sandy micrite; about 5 percent phosphorite, coarse grained, rounded; interbedded with about 5 to 10 percent limestone, sandy, fossiliferous micrite; about 25 percent quartz and about 3 to 5 percent phosphorite as above; about 1 percent hematite; moderately cemented.

No abstract