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Twelve constructed detention ponds collect surface water runoff from the Site. All runoff from the Site Industrial Area (IA) is captured in the ponds prior to being released offsite in a controlled manner. The ponds. shown in Figure I, are grouped together in series based on the drainage in which they are located: . A-Series: 4 ponds (ponds A-I. A-2, A-3. and A-4) in North Walnut Creek, . B-Series: 5 ponds (Ponds B-1, B-2, B-3, B-4 and B-5) in South Walnut Creek, . C-Series: 2 ponds (ponds C-l, C-2) in Woman Creek. and . Landfill Pond: 1 pond located immediately east of the Site sanitary landfill. This paper focuses on stormwater control processes in the South Walnut Creek I Pond B-5 system. Stormwater from the Industrial Area that flows into the B-Series ponds goes directly to Pond B-4, bypassing Ponds B-1, B-2, and B-3. Ponds B-1 and B-2 are isolated ponds not linked to the rest of the series. Pond B-3 receives treated water from the Site wastewater treatment plant and flows to Pond B-4, where it mixes with stormwater flowing directly from the Industrial Area Once in Pond B-4, water flows into Pond B-5 before being released offsite via Walnut Creek. Stormwater quality data for the B-Series inflow are from gaging stations SW023 and GSI0: Both stations are co-located just upstream of Pond B-1 on South Walnut Creek. Data from these stations, when compared with data collected downstream, indicate no consistent improvement in water quality, in terms ofTSS or Pu activity, in samples collected upstream and downstream of Pond B-4. This is likely a result of the small surface area and shallow depth of Pond B-4. Therefore. the controlled detention attenuation model discussed in this paper is based on the settling characteristics of Pond B-5 only. Figure 2. Conceptual Controlled Detention Model/or South Walnut Creek o __GSlO~-G A) Plan View a.. = Q"" B) Cross section InftowfromGS10~-~ :s;.. ~ ~ / "'Com ""'"' lNolU,o... " Pu.,.,'4.0IllCK.