The U.S. Navy's Hunters Point Shipyard (HPS) is a 493-acre federal Superfund site comprised of a 70-acre bedrock upland (Parcel A) and a 423-acre artificial fill lowland (Parcels B-E) adjacent to San Francisco Bay's South Bay. As part of the Superfund remedial investigation/feasibility process under the Navy's Comprehensive Long-Term Environmental Action Navy program, we estimated current and future projected, annual ground water flow and mass metal loading rates from A-aquifer ground water to the Bay to help set priorities and make decisions for ground water remediation.
This paper summarizes and discusses these estimates. To account for the variability in flow and loading mechanisms, annual groundwater flow rates and mass loading rates are given as low, average, and high estimates for current and future conditions. Flow rates and metal loading rates are estimated from: (1) indirect ground water discharge from inland groundwater to leaky storm drains located below the water table because HPS storm drains discharge directly to the bay, and (2) direct groundwater discharge from nearshore ground water to the shoreline of the bay.
Our estimated loading rates account for: (1) flow through storm drains and artificial fill (as well as shoreline concrete walls at dry docks, wooden and rock seawalls, and iron sheetpiles), and (2) shoreline hydraulic gradients which are influenced by leaky sanitary sewer lines located below the water table to act as ground water sinks. We estimated potential bay dilution factors (BDF) for a mean tide in the South Bay as suggested by the National Oceanic and Atmospheric Administration. We compared our estimated metal loading rates to loading rates from HPS ground water background or ambient levels (HGAL), U.S. EPA National Ambient Water Quality Criteria (NAWQC) for chronic saltwater aquatic life, publicly owned treatment plants (POTW) and other bay-area discharge sources as suggested by the California Regional Water Quality Control Board.
Current average ground water flow rates from storm drain and shoreline ground water from HPS to the bay are about 105 and 42.6 acre-feet per year (ac-ft/yr), respectively, for a total of about 148 ac-ft/yr. Under future conditions, it is assumed that leaky sanitary sewers and storm drains will be repaired or replaced, so that the future projected average flow rate from shoreline ground water is about 65.2 ac-ft/yr; there is no future projected storm drain ground water flow. Current and future projected metal loading rates from HPS ground water flow to the bay are: (1) very small compared to potential BDFs which range from several million to over a billion, (2) several orders of magnitude lower than bay discharges from POTWs and other bay-area sources, and (3) well below both NAWQC and HGAL loading rates on a facility-wide basis and on a parcel basis, except for copper, mercury, nickel, and silver.
Copper, mercury, nickel, and silver loading rates are generally slightly higher than NAWQC loading rates but lower than HGAL loading rates; one exception is the nickel loading rate in both storm drains and shoreline groundwater flows from Parcel B under current conditions. At Parcel B, average nickel loading rates exceed the NAWQC loading rate by about 19 times and the HGAL loading rate by about 1.6 times from storm drain ground water flow under current conditions, and exceed the NAWQC loading rate by about 29 times and the HGAL loading rate by about 2.4 times from shoreline ground water flow under both current and future conditions. On a facility-wide basis, most of the current, estimated metal loading rates for copper, mercury, nickel, and silver are contributed by storm drain ground water flow, where Parcel B contributes most of the nickel, Parcel D contributes most of the mercury, and Parcel E contributes most of the copper and silver.
On a facility-wide basis and on a parcel basis, future projected metal loading rates are well below both NAWQC and HGAL loading rates, except for copper, mercury and nickel. On a facility-wide basis, copper and mercury loading rates are slightly higher than NAWQC loading rates and lower than HGAL loading rates; nickel loading rates are higher than NAWQC loading rates and slightly lower than HGAL loading rates. On a parcel basis, Parcel E shoreline groundwater contributes most of the copper, mercury, and nickel under future projected conditions.
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